Disclosure to Promote the Right To Information

Whereas the Parliament of India has set out to provide a practical regime of right to information for citizens to secure access to information under the control of public authorities, in order to promote transparency and accountability in the working of every public authority, and whereas the attached publication of the Bureau of Indian Standards is of particular interest to the public, particularly disadvantaged communities and those engaged in the pursuit of education and knowledge, the attached public safety standard is made available to promote the timely dissemination of this information in an accurate manner to the public.

इंटरनेट मानक

“!ान $ एक न' भारत का +नम-ण”Satyanarayan Gangaram Pitroda

“Invent a New India Using Knowledge”

“प0रा1 को छोड न' 5 तरफ”Jawaharlal Nehru

“Step Out From the Old to the New”

“जान1 का अ+धकार, जी1 का अ+धकार”Mazdoor Kisan Shakti Sangathan

“The Right to Information, The Right to Live”

“!ान एक ऐसा खजाना > जो कभी च0राया नहB जा सकता है”Bhartṛhari—Nītiśatakam

“Knowledge is such a treasure which cannot be stolen”

“Invent a New India Using Knowledge”

है”ह”ह

SP 23 (1982): Handbook on Concrete Mixes [CED 2: Cement andConcrete]

HANDBOOK

ON

CONCRETE MIXES

(BASED ON INDIAN STANDARDS)

HANDBOOKON

CONCRETE MIXES(BASED ON INDIAN STANDARDS)

BUREAlJ OF INDIAN STANDARDS

MANAK BRAVAN, 9 BAHADUR SHAH ZAFAR MARGNEW DELHI 110002

SP 23 : 1982

FIRST PUBLISHED MARCH 1983

FIRST REPRINT JULY 1988

SECOND REPRINT DECEMBER 1990

THIRD REPRINT JANUARY 1994

FOURTH REPRINT MAY 1997

FIFTH REPRINT MARCH 1999

SIXTH REPRINT NOVEMBER 200 I

(Incorporating Amendment No. I)

co BUREAU OF INDIAN STANDARDS 1990

UDC 666.97.033 (021)

ISBN 81-7061-012-5

PRICE Rs. 700.00

PRINTED IN INDIAAT VISA PRESS PVT. LTD., 122. DSIDC SHEDS, OKHLA INDL. AREA, PHASE-I, NEW DELHI 110020AND PlJBLISI~ED BYBUREAU OF INDIAN STANDARDS, NEW DELHI 110002

SPECIAL COMMITTEE FOR IMPLEMENTATION OF SCIENCE ANDTECHNOLOGY PROJECTS (SCIP)

Chairman

MAJ GEN HAItKIRAT SlNQH

W-15 Greater Karlash I. New Deihl J10048

A/embers Representmg

Shn A K Banerjee

Prof Dinesh Mohan

Dr S Maudgal

Dr M Rarnaiah

Shn A SankaranShn A Chakraborty (Alt~rnQt~)

Shn T K Saran

Dr H. C Yrsvesveraya

Shn G Raman (Member ~c.!tIQry)

Metallurllcal and Engmeermg Consultants (Indra)Lirmted, R.n~hl

Central Budding Research Institute. Roorkee

Department of Science and Technology, New Deihl

Structural Engmeering Research Centre. \1adra\

Central Pubhc Works Department, New Deihl

Bureau of Pubhc Eo nterpnses, New Delhi

Cement Research Instnute of India, New Delhi

Indian Standards Institution, New Delhi

FOREWORD

Users of various civil engineering codes have been feeling the need forexplanatory handbooks and other compilations based on Indian Standards. Theneed has been further emphasized in view of the publication of the NationalBuilding Code of India 1970 and its implementation. In 1972, the Department ofScience and Technology set up an Expert Group on Housing and ConstructionTechnology under the chairmanship of Maj-Gen Harkirat Singh. This group carriedout in-depth studies in various areas of civil engineering and construction practices.During the preparation of the Fifth Five Year Plan in 1975, the Group was assignedthe task of producing a Science and Technology plan for research, development andextension work in the sector of housing and construction technology. One of theitems of this plan was the production of design handbooks, explanatory handbook sand design aids based on the National Building Code and various Indian Standardsand other activities in the promotion of National Building Code. The Expert Groupgave high priority to this item and on the recommendation of the Department ofScience and Technology the Planning Commission approved the following twoprojects which were assigned to the Indian Standards Institution:

a) Development programme on Code implementation for building and civilengineering construction, and

b) Typification for industrial buildings.

A Special Committee for Implementation of Science and Technology Projects(SCIP) consisting of experts connected with different aspects (see page v) was set upin 1974 to advise the lSI Directorate General for identifying and guiding thedevelopment of the work under the chairmanship of Maj-Gen Harkirat Singh,Retired Engineer-in-Chief, Army Headquarters and formerly Adviser(Construction), Planning Commission, Government of India. The Committee hasso far identified subjects for several explanatory handbooks/compilations coveringappropriate Indian Standards/Codes/Specifications which include the following:

Functional Requirements of BuildingsFunctional Requirements of Industrial BuildingsSummaries of Indian Standards for Building Materials"Building Construction PracticesFoundation of BuildingsExplanatory Handbook on Codes for Earthquake Engineering

(IS: 1893-1975 and IS : 4326-1976)tDesign Aids for Reinforced Concrete to IS : 456... 1978tExplanatory Handbook on Mansonry CodejExplanatory Handbook on Indian Standard Code for Plain and Reinforced

Concrete (IS: 456-1978)·Handbook on Concrete Mixest

·Under print.tPrinted.

Concrete Reinforcement DetailingFornl WorkTimber EngineeringSteel Code (IS: 800)Causes and Prevention of Cracks in Buildings"Plumbing ServicesLoading CodeFire SafetyPrefabricationTall BuildingsDesign of Industrial Steel StructuresInspection of Different Items of Building WorkBulk Storage Structures in SteelLiquid Retaining Structures

This handbook which has been formulated under this project providesinformation on the factors that influence concrete mix design and discusses them indetail. Basic features of concrete mix design systems, classification and gradedesignation have been highlighted. Relevant Indian Standards on materials forconcrete and their methods of testing, and other special literatures available on thesubject have been taken into consideration in preparing this handbook. Thehandbook will be useful to designers of concrete structures, field engineers, qualitycontrol engineers and laboratories engaged in design, research and testing ofconcrete mixes,

Some of the important points to be kept in view in the use of this handbook areas Follows:

a) This handbook is intended to provide general guidance on the design ofconcrete mixes. Problems of mix design of special and peculiar nature shallbe dealt with on the merits of each case.

b) The mix design is in accordance with the strength requirements andacceptance criteria specified in 'IS: 456-1978 Code of practice for plain andreinforced concrete (third revision)'.

c) Wherever there is any dispute about the interpretation or opinion expressedin this handbook, the provisions of the relevant Indian Standards referred toand discussed shall apply. The provisions in this handbook particularly thoserelating to other literature should be considered as only supplementary andinformative.

This handbook is based on the first draft prepared by the Cement ResearchInstitute of India, New Delhi. The draft handbook was circulated for review toAndhra Pradesh Engineering Research Laboratories, Hyderabad; Central ResearchStation, ACC Research and Development Division, Thane; Central Road ResearchInstitute, New Delhi; Irrigation and Power Research Institute, Amritsar; HindustanConstruction Company Limited, Bombay; Tarapore and Company, Madras;Gammon India Limited, Bombay; and the views received have been taken intoconsideration while finalizing the Handbook.

viii

CONTENTS

SECTION 1

I. INTRODUC'110NI. I Concrete Mix as a System1.2 Classification of Concrete Mixes

1.2.1 Grades of Concrete

SECTION 2

2. C'ONC~RErrE MAKIN(j MATERIALS2.0 General2.1 Cements

2.1.1 }Iydration of Cements2.1.2 Portland Pozzolana and Slag Cements2.1.3 Tests on Cements

2.2 Aggregate-2.2.1 Classification of Aggregates

2.2.1.1 (Jenera)2.2.1.2 Geological Classification of Natural Aggregates

2.2.2 Properties of Natural Aggregates2.2.2.1 Mechanical Properties2.2.2.2 Particle Shape and Texture2.2.2.3 Porosity and Absorption2.2.2.4 Deleterious Constituents2.2.2.5 Soundness of Aggregates2.2.2.6 Alkali-Aggregate Reaction

2.2.3 Lightweight Aggregates2.3 Water

2.3.1 Miscellaneous Inorganic Impurities2.3.2 Silt or Suspended Clay Particles2.3.3 Oil Contamination2.3.4 Sea Water2.3.5 Curing Water

2.4 Admixtures2.4.1 Accelerating Admixtures2.4.2 Retarding Admixtures2.4.3 Water-Reducing Admixtures2.4-.4 Air-Entraining Admixtures2.4.5 Information on Admixtures

Page

3334

7

999

111112131313131414151616202123242626262626262728282929

Page

SECTION 3 S3

3. PROPERTIES OF FRESH AND HARDENED CONCRETE 553.0 Introduction 553.1 Workability S5

3.1.1 Different Measures of Workability 5S3.1.2 Factors Affecting Workability 56

3.1.2.) Influence of Materials and Mix Proportions 563.1.2.2 Effects of Time and Temperature on Workability 57

3.1.3 Requirement of Workability 583.2 Compressive Strength 58

3.2. J Influence of Mix Proportions 583.2.2 Effect of Placing, Compaction and Curing 60

3.2.2.1 Steam Curing of Concrete 603.2.3 Relation with Tensile Strength 61

3.3 Durability of Concrete 62

SECTION 4 83

4. VARIABILITY OF CONCRETE STRENGTH-Sl'ATIS1~ICAL 85ASPECTS4.1 Measures of Variabilities of Concrete Strength 85

4.1. ) Factors Contributing to Variability 854.1.2 The Distribution of Results 854.1.3 Characteristic Strength 864. J.4 Target Mean Strength 86

4.2 Statistical Concepts in Concrete Mix Design 864.3 Acceptance Criteria 86

SECTION 5 93

5. PRINCIPLES OF CONCRETE MIX DESIGN 955.1 Basic Considerations 955.2 Factors in the Choice of Mix Design 955.3 Outline of Mix Design Procedure 96

SECTION 6 101

6. METHODS OF CONCRETE MIX DESIGN 1036.0 Introduction 1036.1 The ACI Mix Design Practice 1046.2 The USBR Mix Design Practice 1056.3 The British Mix Design Method (DOE Method) 1056.4 Mix Design in Accordance with Indian Standard Recommended 106

Guidelines for Concrete Mix Design

SECTION 7 123

7. EXTREME WEATHER CONCRETING 12S7.1 Hot Weather Concreting 12S

7. J.1 Effects of Hot Weather on Concrete 12S7.1.2 Recommended Practices and Precautions 126

7.1.2.1 Temperature Control of Concrete Ingredients 126

x

7.1.2.2 Proportioning of Concrete Mix Materials and MixDesign

7.1.2.3 Production and Delivery7.1.2.4 Placement, Protection and Curing

7.2 Cold Weather Concreting7.2.1 Effects of Cold Weather on Concreting7.2.2 Recommended Practice

7.2.2.1 Temperature Control of Concrete Aggregates7.2.2.2 Use of Insulating Formwork7.2.2.3 Proportioning of Concrete Ingredients7.2.2.4 Placement, Protection and Curing7.2.2.5 Delayed Removal of Formwork

SECTION 8

8. TESTING OF CONCRETE MIXES8.1 Sampling and Testing of Concrete8.2 Frequency of Sampling8.3 Workability Tests of Fresh Concrete8.4 Analysis of Fresh Concrete8.5 Measurement of Air Content8.6 Setting Time of Concrete8.7 Tests for Strength8.8 Analysis of Hardened Concrete

xi

Page

127

127128128128129129129130130130

137

139139139139140140140141142

Page

21

4

567

R9

10) 1

)11314J 516

171819

202122

23

24

25

262728

(J radcs 0 f ConcreteCompound Composition of Ordinary Portland Cernent-,Heat Evolut ion of Different Compounds of Portland Cement

(at 21°C)Physical and Chemical Requirements of Indian Standard

Specification- for Different CementsPropcrticv of Concrete Influenced by Aggregate PropertiesLivt of Rock- Placed Under the Appropriate GroupsExpected Relationship Between Variou-, Tests for Different Rock

GroupsParticle Shape of Aggregate'>Surface Character ivtics of Aggregate,Porosity of Some (:011101011 RocksTypical Ranges of Values of Absorption of Different Type- of

RocksLimits of Deleterious Materials in Aggregates (Percentage)Propenie- of Sands in Their Natural ConditionsReactive MineralsReact ivc Rock"Concentration of Some lmpuriucs in Mixing Water Which can be

Considered 3) TolerablePermissible Limit for SolidsPhysical Requirements for Concrete AdmixturesOptimum Air Content-, of Concretes of Different Maximum Si,C'"

of AggregateComparison of Consistency Measurements by Various MethodsRelation Between Slump and Relative Water ContentSuggested Ranges of Values of Workability of Concrete for

Different Placing ConditionsMinirnum Cement Content Required in Cement Conerete to Ensure

Durability Under Specified Conditions of ExposureRequirements for Plain and Reinforced Concrete Exposed toSulphate AttackMinimum Cement Content Required in Cement Concrete to Ensure

Durability Under Specified Conditions of Exposure forPrestressed Concrete

Requirements for Prestressed Concrete Exposed to Sulphate AttackLimit for Chloride Ion in Concrete Prior to Exposure in ServiceBreakdown of Standard Deviation for Compressive Strength for

Different Standards of Control

xii

42930

30-31

323333

34343434

3535353536

3tl36~~7

37

646464

65

66

67

686988

TABLES Page

29 Assumed Standard Deviation 8930 Values of k 8931 Relationship Between Water-Cement Ratio and Compressive 110

Strength of Concrete32 Approximate Mixing Water (kg/rn! of Concrete) Requirements for 110

Different Slumps and Maximum Sizes of Aggregates33 Volume of Dry-Rodded Coarse Aggregate per Unit Volume of III

Concrete34 Probable Minimum Average Compressive Strength of Concrete for ) 11

Various Water-Cement Ratios35 Approximate Air and Water Contents per Cubic Metre of Concrete III

and the Proportions of Fine and Coarse Aggregate36 Adjustment of Values of Water Content, Percent Sand and Percent 112

of Dry-Rodded Coarse Aggregate37 Approximate Compressive Strengths of Concrete Mixes Made with J 12

Water-Cement Ratio of 0.538 Approximate Water Contents (kg/rn') Required to Give Various 112

Levels of Workability39 Suggested Values of Standard Deviation 11340 Degree of Quality Control Expected Under Different Site 113

Conditions41 Approximate Entrapped Air Content 11342 Approximate Sand and Water Contents per Cubic Metre of 113

Concrete43 Approximate Sand and Water Contents per Cubic Metre of 114

Concrete44 Adjustment of Values in Water Content and Sand Percentage for 114

Other Conditions

xiii

FIGURES Page

I Rate of Hydration of Pure Compounds 382 Development of Strength of Pure Compounds 393 Relationship Between Strength of Concrete at Different Ages and Fineness 39

of Cement4 Calculated Temperature Rise of Different Cements Under Adiabatic 40

Conditions5 Strength-Age Relationship for 1:2:4 Concrete by Weight Made with 40

Different Cements6 Relationship Between Compressive Strength and Hydrate-Space Ratio 417 Strength Development of Concretes Made with Portland Blast-Furnace 41

Cement (Water-Cement Ratio =0.6)8 Strength Development of MIS Concrete Made with Portland- 42

Pozzolana Cement (Water-Cement Ratio == 0.55)9 Effect of Prolonged Mixing on Fineness Modulus of Sand and Gravel 43

Sizes10 Influence of Void Content of Sand in a Loose Condition on the Mixing 44

Water Requirement of Concrete11 Influence of Amount of Clay Fraction on 28-Day Compressive Strength 45)2 Illustration of Division Between Innocuous and Deleterious Aggregates 46

on Basis of Reduction in Alkalinity Test13 Creep of Concrete of Nominal 210 kgf'/cm! Strength Made with Different 47

Lightweight Aggregates, Loaded at the ~ge of 7 Days to42 kgf'/cm!

14 Compressive Strength of Normal and Rapid Hardening Cement with 472 Percent Calcium Chloride Addition

IS Effect of Retarding Admixtures on Retention of Workability 4816 Effect of Water Reducing Admixture on the Workability of Concrete 4917 Effect of Air-Entrainment on Freeze-Thaw Durability of Concrete 5018 Slump: True, Shear and Collapse 7019 Relationship Between Slump, Compacting Factor and Vee-Bee Time for 70

Concrete of Different Aggregate-Cement Ratios20 Relationship Between Workability and Water Content of Concrete for 71

Different Maximum Sizes of Aggregate21 Change in Compacting Factor with Time 7222 Effect of Concrete Temperature on Slump and on Water Required to 72

Change Slump23 Typical Relation Between Compressive Strength of Concrete and 73

Aggregate-Cement Ratio for Various Compacting Factors24 Effect of Cement Content on the Compressive Strength of Concrete 73

xiv

FIGURES Page

25 Design Curve for Cerncnt Concrete Mixes in Relation to 7-Day 74Compressive Strength of Cement

26 Effect of Compaction on Compressive Strength of Concrete 7427 Relationship Between Percentage of Voids and Compressive Strength of 75

Concrete28 Influence of Curing Conditions on Strength of Test Cylinders 7529 Curing and Strength Relationship for Portland Cement Concrete 7630 Typical Steam Curing Cycle 7631 Effect of Curing Regime on 28-Day Strength of Concrete 7732 Comparison of Relationship Between Compressive and Flexural 78

Strengths of Concrete33 Relationship Between Split Tensile Strength and Compressive Strength of 79

Concrete34 Relationship Between Compressive and flexural Strengths of Concrete 7935 Relationship Between Split Tensile Strength and Flexural Strength of 80

Concrete36 Interrelationships of Water-Cement Ratio and Cement Content on 80

Workability and Permeability of Fresh Concrete37 Cement Paste Volume Required in Concrete of Various Water-Cement 81

Ratios for Marine Durability38 Normal Distribution of Concrete Strengths 9139 Typical Normal frequency Curves for Different Control Ratings 9140 Influence of MaximUITI Size of Aggregate on Cement Requirement of 9R

Concrete Mix41 Maximum Size Aggregate for Strength Efficiency Envelope 9942 Procedure of Concrete Mix Design 11543 Relationship Between Compressive Strength and Water-Cement Ratio 11644 Estimated Wet Density of Fully Compacted Concrete 11745 Recommended Proportions of Fine Aggregate for Grading Zones 1,2,3 118

and 446 Generalized Relationship Between Free Water-Cement Ratio and 119

Comprewive Strength of Concrete47 Relationship Between Free Water-Cement Ratio and Concrete Strength 120

for Different Cement Strengths48 Relationship Between Free Water-Cement Ratio and Compressive 12]

Strength of Concrete for Different Cement Strengths Determinedon Reference Concrete Mixes (Accelerated Te~t- Boiling WaterMethod)

49 Effect of Temperature on Compressive Strength of Concrete Made \\ ith 131Ordinary Portland Cement

50 Effect of Temperature of Cement on Concrete Strength 13251 Effect of Low Temperature on Compressive Strength of Concrete 13352 Effect of Cycles of Freezing and Thawing of Fresh Concrete During 133

Pre-hardening on Compressive Strength53 Required Temperature of Mixing Water to Produce Heated Concrete 1J..J54 Form Protection - 90 em Concrete Cube, Thermocouple at Centre of 135

Face (Next to Form)

xv

SECTION 1

INTRODUCTION

SECTION 1

J.J Concrete Mix as a System - Concreteis by far the most widely-used man-madeconstruction material and studies indicatethat it will continue to be so in the years anddecades to come'. Such versatility of con­crete is due to the fact that from the commoningredients, namely, cement, aggregate andwater (and sometimes admixtures), it ispossible to tailor the properties of concreteso as to meet the demands of any particularsituation. The advances in concretetechnology has paved the way to make thebest use of locally available materials byjudicious mix proportioning and properworkmanship, so as to result in a concretesatisfying the performance requirements.While the properties of the constituentmaterials are important, the users are nowinterested in the concrete itself havingdesired properties. In the true sense, con­crete is thus the real building material ratherthan the ingredients like cement and ag­gregates, which are only intermediate pro­ducts. This concept of treating concrete asan entity is symbolized with the progress ofready-mixed concrete industry, where theconsumer can specify the concrete of hisneeds without bothering about the ingre­dients; and further in pre-cast concrete in­dustry where the consumer obtains thefinished structural component-s satisfying the

.performance requirements.

This Handbook, therefore, treats concretein its entity as a building material. Thevarious aspects covered are the materials,mix proportioning, elements of workman­ship (for example placing, compaction andcuring), methods of testing and relevantstatistical approach to quality control andspecial precautions needed in extreme­weather concreting. The discussion on theseaspects centres around the appropriate pro­visions in the various Indian Standardswhich are relevant. However, certain otherproperties of hardened concrete, namely,elasticity. creep and shrinkage are notcovered in this Handbook.

While considering the concrete mixes as amaterial in itself, note has to be taken of theactions and interactions of its constituentson the characteristics of the end product.which may often give rise to conflicting

INTRODUCTION

demands. For example, the requirements ofworkability demand that water content inthe mix should be more, whereas the re­quirements of compressive strength dependupon lower water-cement ratio and,therefore, the water content be kept as lowas practicable. In this context a concrete mixforms a 'system'. Concrete mixes are alsocharacterised by the fact that, unlike theother common structural materials like steel,these are mostly manufactured at site; the in­herent variability of their properties andneed for proper quality control, therefore,become important considerations.

1.2 Classification of Concrete Mixes­Concrete mixes are classified in a number ofways, often depending upon the type ofspecifications, which are broadly of twotypes; the 'prescriptive' specifications wherethe proportions of the ingredients and theircharacteristics (namely, type of cement,maximum size of aggregate, etc) arespecified, with the hope that adherence tosuch prescriptive specification will result insatisfactory performance. Alternately, a'performance' oriented specification can beused wherein the requirements of thedesirable properties of concrete are specified(example - strength, workability or anyother property). Concrete is accepted on thebasis of these requirements being satisfied,and the choice of materials and mix proper­tions is with the producer.

Based on the above considerations, con­crete can be classified either as 'nominalmix' concrete or 'designed mix' concrete ashas been specified in IS : 456-19782• Britishpractices go a step further to specify 'stan­dard' mixes] or 'prescribed' mixes"which ateelaboration of 'nominal' mixes, to cater fordifferent ranges of workability and differentaggregate characteristics, for the desiredcompressive strength.

IS : 4565 had earlier classifled concreteinto 'controlled' concrete and 'ordinary' con­crete, depending upon the levels of controlexercised in the works and the method ofproportioning concrete mixes. According tothis. where the mix proportions were fixedby designing the concrete mixes withpreliminary t~sts were called 'controlled

3

SP : 23-1982

NOTE 4 - Grades of concrete lower than M 30 shallnot be used in prestressed concrete.

TARt.: I (iRADt:S OF CONCRET[

(Clause 1.2.1)

Grades of concrete lower than M 15 are notto be used in reinforced concrete works andgrades of concrete lower than M 30 are notto be used for pre-stressed concrete works.Similar grading of concrete on the basis of28 days characteristic strength has also beenadopted by IS07 and most of the other codesof practices.

NOTE I - In the designation of a concrete mix,letter M refers to the mix and the number to thespecified characteristic compressive strength of IS-emcube at 28 days, expressed in Nzmrn'.

NOTE 2 - M 5 and M 7.5 grades of concrete may beused for lean concrete bases and simple foundations formasonry walls. These mixes need not be designed.

NOTt. 3 - Grades of concrete lower than MIS shallnot be used in reinforced concrete.

SPECIFIED CHARACTJ:RISfiC

COMPRESSIVE: STRENGTH AT

28 DAVS (N/mm2)

5

7.S

10

15

20

25

30

35

40

45

SO55

60

M5

M 7.5

M 10

M 15

M 20

M 25

M 30

M 35

M40

M 45

M 50

M 55

M60

GRADf Dt::SIGN.a.TION

/.2./ GRADES OF CONCRETE - Among themany properties of concrete, its compressivestrength is considered to be the most impor­tant and has been held as an index of itsoverall quality. Many other engineering pro­perties of concrete appear to be generallyrelated to its compressive strength. Concreteis, therefore, mostly graded according to itscompressive strength. The various grades ofconcrete as stipulated in IS : 456-19782 andIS : 1343-198()6 are extracted in Table 1. Outof these, two grades, namely, M 5 andM 7.S, are to be used for lean concrete basesand simple foundations for masonry walls,

concrete'; whereas 'ordinary concrete' wasone where 'nominal' concrete mixes wereadopted. This might have inadvertently ledto a feeling that no quality control wasnecessary in case of nominal mixes.Howevert realizing that mix proportioning isonly one aspect of quality control of con­crete and that quality control really encom­passes many other aspects like choice of ap­propriate concrete materials after propertests, proper workmanship in batching, mix­ing, transportation, placing, compactionand curing, coupled with necessary checksand tests for quality acceptance and qualitycontrol, the present concrete codeIS : 456.19782 makes a significant departure,in that there is nothing like 'uncontrolled'concrete; only the degree of control varies,from 'very good' to 'poor' or no control.

Concrete can be classified in many otherways in special situations; by its density (forexample, light weight, normal weight orheavy weight concrete), workability (forexample, flowing or pumpable concretes) orits durability in specific environments (forexample, sulphate-resisting concrete -or itsresistance to fire).

REFERENCES

BURKS (5 D) Will concrete be the leading buildingmatenal of the future? Pr J Amer Caner Inst 68, 5,1971, j21-26

2 IS 456-1978 C.ode of practice tor plain and reinforced concrete (third revisions

3 CP 116 Part 2 1969 Code of practice for thestructural use of precast concrete Bnnsh StandardsInstuunon

SP : 23-1982

4 (,P 110 Part I 1972 Code of pract«,e tor thestructural use of concrete Bnuvh StandardsInsntuuonI~ 456 1964 (. ode of practice for plain and runforced concrete (S("( ond revtstom

6 I~ 1143 1980 (ode of practu e tor prevtrcvscdconcrete (/1'\1 revisionv

7 ISO l893 1977 (. oncrete da~\lt icauon by comprcsstve strength Inter national Orgaruzauon forStandardizanon

SECTION 2

CONCRETE MAKING MATERIALS

SECTION 2 CONCRETE MAKING MATERIALS

NoTE - It may f however t be noted that the maxi­mum permissible [mit of MgO content in ordinaryPortland cement is ( percent (see Table 4).

The compounds of these oxides present inthe raw materials, however, interact witheach other and form a series of more com­plex products during clinkering. The stage ofchemical equilibrium reached during clinker­ing in the kiln may be disturbed somewhatduring cooling. Assuming that cement hasthe same equilibrium as existing at theclinkering temperature, the basic compoundcomposition of Portland cement along withtheir ranges may be as-shown in Table 2.

The role of each of these compounds inthe properties of cement has been studied in

to the respective Indian Standards mention­ed above. In case of Portland slag cement,·the slag content should not be more than 50percent.

Among the various types, ordinaryPortland cement conforming toIS : 269-19762 is perhaps the most common.

.Further discussions relating to compositionand hydration of cements in this clause andin 2. J.J generally pertain to ordinaryPortland cement conforming toIS : 269-19762• Ordinary Portland cement isobtained by intimately mixing together acalcarious material such as limestone orchalk, and an argillaceous material (that is,silica, alumina and iron oxide bearingmaterial), for example, clay or shale, burn­ing them at a clinkering temperature of1 400 to 1 450°C and grinding the resultingclinker with gypsum. Since the raw materialsconsist mainly of lime, silica, alumina andiron oxide, these form the major elements incement also. Depending upon the wide varie­ty of raw materials used in manufacture ofcements, the typical ranges of these elementsin ordinary Portland cement may be express­ed as below:

2.0 General - The common ingredients ofconcrete are cement, coarse and fine ag­gregates and water. A fourth ingredient call­ed 'admixtures' is used to modify certainspecific properties of the concrete mix infresh and hardened states. By judicious useof available materials for concrete makingand their proportioning, concrete mixes areproduced to have the desired properties inthe fresh and hardened states, as the situa­tion demands. In this section the physicaland chemical properties of the concrete mak­ing materials which influence the propertiesand performance of concrete mixes arediscussed.

2.1 Cements - Cement is by far the mostimportant constituent of concrete, in that itforms the binding medium for the discreteingredients. Made out of naturally occurringraw materials and sometimes blended or in­terground with industrial wastes, cementscome in various types and chemical composi­tions. For general concrete constructions,IS : 456-1978 1 permits the use of the follow­ing types of cement, subject to the approvalof the engineer-in-charge:

a) Ordinary or low heat Portland cementconforming to IS : 269-19762•

b) Rapid hardening Portland cement con­forming to IS : 8041-19783•

c) Portland slag cement conforming toIS : 455-1976 4

•

d) Portland pozzolana cement conform­ing to IS : 1489-1976\

e) High strength ordinary Portlandcement conforming to IS : 8112-1976',and

f) Hydrophobic cement conforming toIS : 8043-19787•

In addition to these, high aluminacement conforming to IS : 6452-19728 andsupersulphated cement conforming toIS : 6909-19739 can be used under special cir­cumstances with necessary precautions.

For prestressed concrete construction,IS : 1343.198010 permits the use of ordinaryPortland cement, rapid hardening Portlandcement, high strength ordinary Portland ce­ment and Portland slag cement conforming

9

Si02

A120 J

Fe20 )

CaOMgO

Percent19 - 24

3 - 61 - 4

59 - 64

0.5 - 4

SP : 23·1982

length. As indicated in Table 2, their relativeproportions in the cement may vary and in­deed, the differences in the various types ofordinary Portland cement are really due to-the differences in the proportions of thesemajor compounds and fineness. The twosilicates, (elS and C2S) which" together con­stitute about 70 to 75 percent of the cement,are more important from the considerationsof strength giving properties. Upon hydra­tion, that is, reaction with water, both ClSand C2S perhaps result in the same pro­duct - called calcium silicate hydrate hav­ing approximate composition C)S2HJ andcalcium hydroxide ". Because of the similari­ty of their structures with that of a naturallyoccurring mineral, the hydrates are called'tobermorite'. From approximatestoichiometric calculations, C3S and C2Sneed approximately 24 and 21 percent waterby weight, respectively, for chemical reac­tion but CJS liberates nearly three timescalcium hydroxide compared to hydration ofC2S.

The reaction of C)A with water is veryquick and may lead to immediate stiffeningof the paste - a phenomenon known as'flash set'. The role of gypsum added in themanufacture of cement is to prevent suchfast reaction. The reaction of gypsum andC]A with water first gives rise to an insolublecompound called calcium sulphoaluminate(ettringite). But eventually the final productof hydration is possibly cubic crystal oftricalcium aluminate hydrate (C]AHj. Ap­proximate stoichiometric calculation showsthat C)A reacts with 40 percent of water byweight, which is more than that required forsilicates; however, since the amount of C)Ain cement is comparatively small, the netwater,required for the hydration of cement isnot substantially affected. The products ofhydration of C.AF phase is not so wellknown. Neville!' states 'C.AF is believed tohydrate into tricalcium aluminate hydrateand an amorphous phase, probablyCaO.Fe20 ) aqueous. It is possible also thatsome Fe20 ) is present in solid solution in thetricalcium aluminate hydrate' .

The role of these four major compoundson the properties of cement can be sum­marised by the kinetics of reaction, develop­ment of strength and evolution of heat ofhydration of these individual compounds.The state of art can be summarised by Fig.III and 211, and Table 311• From these it will

10

be clear that C]A and C4AF are the earliestto hydrate but their direct individual con­tribution to overall strength development ofthe cement is perhaps lesssignificant than thesilicates. In addition, C)A phase is responsi­ble for the highest heat evolution both dur­ing the initial period as well as in the longrun. Among the silicates, ,C)S has faster rateof reaction accompanied by greater heatevolution and larger contribution to theinitial strength than C2S phase; however, itis likely that both C3S and C~ phases con­tribute equally to the long term strength ofcement.

Apart from the chemical composition,fineness of cement contributes to the kineticsof reaction and initial rate of gain ofstrength. Generally greater the fineness,greater is the rate of development of strengthduring the Initial period (see Fig. 31l) andlarger is the heat evolution. This is possiblebecause greater fineness enables a larger sur­face of cement to come in contact with waterduring the initial period, although the longterm effect may not be different. In addi­tion, the particle sizes also influence thehydration and strength at various ages. Par­ticles below S micron hydrate within 1 to 2days and the hydration of 10-25 micronsizes may commence after 7 days.

THe different 'types' of cement are madeby the adjustment in the relative proportionof chemical compounds and the fineness tosuit the particular requirement. A summaryof the requirements for physicalcharacteristics and chemical composition ofdifferent Indian cements" is reproduced inTable 4. It will' be seen that whenever ahigher rate of initial strength gain is re­quired, this is achieved by grinding the ce­ment to greater fineness and the cementcomposition perhaps being richer in C3S andC3A phases, but it may give rise to more heatof hydration. Contrary to this, the low heatcements would be required to be ground to alower fineness and would have lower percen­tage of C)A and greater percentage of C2S.The characteristics of different types of ce­ment may be summarised as in Fig. 41~ andSU which are qualitatively applicable toIndian conditions. From Fig. S it is apparentthat irrespective of differences in the initialstrength, concretes made ,with differentcements tend to have the same long termstrength.

2././ HYDRATION OF CEMENTS - Thephysical properties of concrete depend to alarge extent on the extent of hydration ofcement and the resultant microstructure ofhydrated cement. While the hydration pro­ducts of individual compounds were describ­ed above, it must be realized that the hydra­tion of cement is the collective hydration ofeach of the compounds present therein andthere is no selective hydration of any of thecompounds. Nevertheless, the microstruc­ture of hydrated cement is more or lesssimilar to those of the silicate phases. Uponcontact with water, the hydration of cementproceeds both inward and outward in thesense that hydration products get depositedon the outer periphery and the nucleus ofunhydrated cement inside gets graduallydiminished in volume": At any stage ofhydration the cement paste (that is,cement + water) consists of the product ofhydration (which is called 'gel', because ofthe large surface area), the remnant ofunreacted cement, Ca(OH)2 and water,besides some other minor compounds .. Hex­agonal prismatic crystals of ettringite areformed first on the tricalcium aluminatephases. Crystals of calcium hydroxide formabout four hours after mixing. Thin acicularparticles of calcium silicate hydrate startprotruding from the surface' of cementgrains after two hours". In matured pastes,particles of calcium silicate hydrate form aninterlocking network and owing to thesimilarity with the naturally occurringmineral, tobermorite is called 'tobermoritegel'. This gel -is poorly crystalline, almostamorphous and appears as randomlyoriented layers of thin sheets or buckled rib­bon". The thickness of primary 'gel' par­ticles is estimated to be 3.0 x 10-9 to4.0x IO-9m'9.

The products of hydration as describedabove form a random three dimensional net­work gradually filling the space originallyoccupied by water. Accordingly, the harden­ed cement paste has a porous structure, thepore sizes varying from very small(4 x lO-'Om) to much larger, and are called'gel' pores and 'capillary' pores-". The waterpresent in these pores are held with differentdegrees of affinity and the pore system insidethe hardened cement paste mayor may notbe continuous. As hydration proceeds, thedeposit of hydration products on the originalcementgrain makes the diffusion of water to

11

SP : 23-1982

the unhydrated nucleus more and moredifficult, so the rate of hydration decreaseswith time.

Each gram of cement of average composi­tion needs about 0.253 g of water forchemical reaction". In addition, acharacteristic amount of water is needed tofill the gel pores. The total amount of waterthus needed for chemical reactions and to fillthe gel pores is about 42 percent II. Sincehydration can proceed only when the gelpores are saturated, it has often beenmistakenly held that water-cement ratio lessthan 0.40 or so should not be permitted inconcretes. However, it must be emphasisedthat even in presence of excess water, com­plete hydration of cement never takes placebecause of the decreasing porosity of thehydration products, nor is it necessary thatcement should be fully hydrated". In fact,water-cement ratio Jess than 0.40 is quitecommon in structural concretes, more so inhigh strength concretes.

In concretes, the hardened cement paste isthus a porous ensemble; the concentration ofsolid products of hydration in the total spaceavailable (that is original water + hydratedcement) is an index of porosity. Like anyother porous solid, the compressive strengthof cement pastes (or concretes) is related tothe parameter gel-space ratio" or hydrate­space ratio" (see Fig. 6). The water-cementratio, which is held as the most importantparameter governing compressive strength(see 3.2), is really an expression of the con­centration of hydration products in the totalvolume at a particular age for the resultantdegree of hydration".

2./.1 PORTLAND POZZOLANA AND SLAG

CEMENTS - Among cements of differenttypes. mention may be made of Port­land pozzolana cement conforming toIS : 1489-1976~ and Portland slag cementconforming to IS : 455-19764 because of in­creased production of these cements in thecountry mainly to offset the shortage of or­dinary Portland cement.

Portland slag cement is manufactured byintergrinding ordinary Portland cementclinker with granulated slags obtained as aby-product from the manufacture of steel.The slags have more or less the same consti­tuents as in ordinary Portland cement invarying proportions, depending upon the

SP : 23·1982

processes involved. Typical oxide composi­tions of Indian slags suitable for themanufacture of Portland slag cement are asfollows':

PercentSi02 27-32

AI203 17-3'FeO 0-1CaO 30-40MgO 0-17

The slag should, however, be in glassyform. IS : 455-19764 permits the proportionof slag to be in the range of 25 to 65 percent.The products of hydration of such Portlandslag cement are believed to be similar to thatof ordinary Portland cement; Ca(OH)2liberated by the hydration of ordinaryPortland cement acts as an activator for thereaction of slag", Since the hydration of slagcomponent depends initially upon liberationof Ca(OH)2' the rate of development of earlystrength may be somewhat slower (seeFig. 'II). However, for all engineering pur­poses, Portland slag cement may be held tobe similar to ordinary Portland cement andthe requirements of physical characteristicsare also identical in both cases. Portland slagcements give lower heat of hydration andbetter sulphate resistance".

Portland pozzolana cement (seeIS : 1489-1976.5) is made by blending or in­tergrinding reactive pozzolana (for example,flyash, burnt clay, diatomaceous earth, etc)in proportions of 10 to 2S percent with or­dinary Portland cement. Pozzolanas as suchdo not possess cementitious property inthemselves but in combination with Ca(OH)2liberated from the hydration of ordinaryPortland cement, give rise to cementitiousproducts at room ambient temperature andthe ultimate products of hydration in bothcases are believed to be identical", The re­quirements of 7-day strength of Portlandpozzolana cement (see IS : 1489-19765) arethe same as that of ordinary Portland ce­ment (21.~N/mm2). The use of Portlandpozzolana cement is recommended inIS : 456-1978 1 as substitute for ordinaryPortland cement for plain and reinforcedconcrete work in general building construc­tion. In addition to 7·day compressivestrength, IS: 1489.19765 specifies theminimum 28-day compressive strength ofPortland pozzolana cement. However, for

12

the reasons cited, the rate of development ofearly strength may be somewhat lower (seeFig. 824) and concrete made with Portlandpozzolana cement may need somewhatlonger curing period under field conditions,delayed removal of forrnwork, etc. Portlandpozzolana cement also has the advantage: oflower heat of hydration and better sulphateresistance; in fact these properties led to itswide application in USA2'.

2.1.3 TESTS ON CEMENTS - The usual testsmade,on cement are: fineness, setting time,soundness, heat of hydration, compressivestrength and chemical composition. Allphysical and chemical composition tests arecarried out in accordance with the pro­cedures described in IS: 4031... 196826 -..ndIS : 4032-196827•

The Blainesair permeability method is us­ed for determining the fineness of cement.The method is based on the permeability toflow of air through a bed of the cement. Thefineness is expressed as specific surface areaper gram of cement.

The setting times are measured by Vicatapparatus, with different penetratingattachments. The term setting is used todescribe the stiffening of the cement paste,and the terms 'initial set" and 'final set' areused to describe arbitrary chosen stages ofsetting.

The soundness of cement is determined inan accelerated manner by Le-Chatelier ap­paratus. This test detects unsoundness due tofree lime only. Unsoundness due tomagnesia present in the raw materials fromwhich cement is manufactured can be deter­mined by autoclave test. This test is sensitiveto both free magnesia and free lime!'. In thistest high pressure steam accelerates thehydration of both magnesia and lime. Theresults of the autoclave test are affected by,in addition to the compounds causing expan­sion, the CJA content. The test gives thus nomore than a broad indication of the long­term expansion expected in service.

The heat of hydration is the amount ofheat in calories per gram of unhydrated ce­ment, evolved upon complete hydration at aliven temperature. The method of determin­ina the heat of hydration is by measuring theheats of solution _of unhydrated andhydrated cement in a mixture of nitric andhydrofluoric acids: the difference between

the two values gives the heat of hydration.The heat of hydration thus measured con­sists of the chemical heat of the reactions ofhydration and the heat of absorption ofwater on the surface of the gel formed by theprocesses of hydration. The heat of hydra­tion is required to be determined for lowheat Portland cement, as specified inIS : 269-19762•

The compressive strength of cement isdetermined on 1:3 cement-sand mortar cubespecimens with standard graded sand, castand cured under controlled conditions oftemperature and humidity. The water con-

lent is determined as (I! + 3) percent by4

weight of cement and sand, where P ispercentage of water required for standardconsistency. In most of the cases, it cor­responds to a water-cement ratio of 0.37 to0.42.

The chemical analysis i~ carried out todetermine the oxide composition of cement.The percentages of main compound in ce­ment (that is, CJS, ('2S, CJA and C4AF) canbe calculated (rom oxide composition usingBogue's equations", which is applicable toordinary Portland cement only. In additionto the rnaln compounds, two of the minorcompounds are of interest. They arealkalis - Na 20 and K20. The insolubleresidue determined by treating withhydrochloric acid, is a measure of impuritiesin ordinary Portland cement; largely arisingfrom impurities in gypsum. The loss on igni­tion shows the extent of carbonation of freelime and hydration due to the exposure ofcement to the atmosphere.

2.2 Aggregates - Aggregates which occupynearly 70 to 7S percent volume of concreteare sometimes viewed as inert ingre­dients in more than one sense. However. it isnow well recognised that physical, chemicaland thermal properties of aggregatessubstantially influence the properties andperformance of concrete. A list of propertiesof concrete which are influenced by the pro­perties and characteristics of aggregates isgiven in Table 528• Proper selection and useof aggregates are important considerations,both economically as well as technically. Ag­gregates are generally cheaper than cementand imparting greater volume stability anddurability to concrete.

13

SP : 23-1982

2.2. I C: A'i~1I I( AliON OJ A( ,(,RI-c;ATL "

2.2. J.J GENERAl - General classificationof aggregates can be on the basis of theirsizes, geological origin, soundness in par­ticular environments, unit weight or onmany other similar considerations as thesituation demands, In so far as the sizes areconcerned, aggregates range from a few cen­timetres or more, down to a few rnicrons.The maximum size of aggregate used in con­crete may vary, but in each case the ag­gregate i~ to be so graded that particles ofdifferent size-fractions are incorporated inthe mix in appropriate proportions. As perIS : 383-1970~tJ fine aggregates are those,most of which pass through 4.75 mm ISsieve; aggregates, most of which are retainedon 4.75 mm IS sieve are termed as 'coarse'aggregates, Sand is, generally considered tohave a lower size limit of about 0.07 mm.Materials between 0.06 mm and 0.002 rnrnare classified as silt, and still smaller par­ticlev are called clay. Sometimes combinedaggregates are available in nature comprisingdifferent si ze-Iract io ns of the aboveclassification, which are known as 'ali-in­aggregates'. In such cases they need not beseparated into fine and coarse fractions butadjustments often become necessary to sup­plement the grading by the addition ofrespective ~ilC fractions which may be defi­cient in the total mass. Such 'all-in­aggregates' are generally not found suitablefor making concrete of high quality. Ag­gregates comprising particles falling essen­tially within a narrow limit of size fractionsare called 'single-size' aggregates.

2.2. J.2 (if-Ol OGI(I\I (L"~,,)I"I< AllON OJ

NATURAl AGGRl:(lATES - Aggregates for con­crete are generally derived from naturalsources which may have been naturallyreduced to size (for example, gravel orshingle) or may be required to be crushed.As long as they conform to the requirement'of IS = 383-197Q29 and concrete of satisfac­tory quality can be produced at aneconomical cost using them, bothgravel/shingle or crushed natural aggregatecan be used for general concrete construc­tion. Aggregates can be manufactured fromindustrial products also, which areused for special purposes, for example, lightweight concretes, concretes requiring betterthermal insulating properties, etc. From thepetrological stand-point. the natural ag­gregates, whether crushed or naturally

SP : 23·1981

reduced in size, can be divided into severalgroups of rocks having commoncharacter ist ics . Natural rocks can beclassified according to their mode of forma­tion (for example ignious, sedimentary ormetamorphic origin) and under each classthey may be further sub-divided into groupshaving certain petrological characteristics incommon. Such a classification adopted inIS : 383-19702'1 is reproduced in Table 6.Depending upon the minerals found in ag­gregates the mineralogical classificat ion canalso be rnade. However, such classificationsare not very helpful in predicting the perfor­mance of the aggregates in concrete. This i~

so, because each rock will probably have anumber of minerals present and even amongthe most abundant minerals in a particularaggregate it i~ difficult to classify one beinguniversally desirable or otherwise.

2.2.2 PROPl:.RTIES OJ- NATURAL AG­(JRL< ,A Il·~ - As pointed out earlier, the pro­perties and performance of concrete aredependent to a large extent on thecharacteristics and -properties of aggregatesthemselves, and knowledge of the propertiesof aggregates is thus important. In the casesof marginal aggregates the record of perfor­rnance of concretes made with them may bethe best guide. However, tests in thelaboratory as well as petrographic exarnina­tions are used in most general cases.

2.2.2. J t\1F< HANICAL PROPERTll ~ - Thesignificance of the various tests formechanical properties are discussed below:

a) Tests on strength of aggregate - Thestrength of aggregates in the conven­tional sense may appear to be not acriterion in so far as aggregates arcgenerally of an order of magnitudestronger than the concretes made withthem ~nd a notional feeling thatstronger aggregates are better may besufficient. However. the localizedstresses in an element of concrete maybe much higher than the overallstrength of concrete due to stress con­centrations and in case of high strengthconcrete the mechanical strength of ag­gregates may itself become critical.Moreover, the mechanical strength ofaggregates is important from the pointof view of quarrying, stability in themixer, better resistance to abrasion or

14

attrition during subsequent service lifeof concrete. Quite often among ag­gregates of similar geologicalclassifications one having highermechanical strength has been found tobe sounder in chemical environments.IS : 2386 (Part IV)-196330 prescribesthe following three tests for testing thestrength of aggregates:

1) Crushing strength,

2) Crushing value, and

3) Ten percent fines value.

The tests on crushing strength do notgive very reproducible results butessentially measure the quality of theparent rock rather than those of the ag­gregates derived from it. This test maybe useful for assessments of newsources of aggregates without provenrecords.

Among these three, crushing valuetest, which is performed on bulk ag­gregates is more popular and resultsare rep rod uc ibIe, 1S : 383- 1970 2~

specifies limits of crushing value as 45percent for aggregates used for con­crete other than for wearing surfacesand 30 percent for concrete for wearingsurfaces, such as runway, pavementand roads. For weaker aggregates witha crushing value of over 25 to 30 per­cent, crushing value, test is not soreliable in the sense that materialcrushed before the full load havingbeen applied tends to get compac.. tedthereby inhibiting crushing at a laterstage and the intrinsic value may not bemeasured in such cases. For such situa­tions 'ten percent fines value' test maybe more reliable which measures theload required to produce 10 percentfines from 12.5 to 10 mm particles.There is not much data available cor­relating the 10 percent fines value withthe crushing value as given inIS : 383-197()29 which does not specifyany limit for this test. BS : 882:196531

prescribes a minimum value of 10tonnes for aggregates to be used inwearing surfaces and 5 tonnes whenused in other concretes.

Another related aspect is thetoughness of aggregates which is ameasure of the resistance of the

material to failure by impact. IS : 2386(Part IV)-196330 prescribes a methodfor determining the impact value whichis sometimes taken as an alternative tocrushing value test. The results also ingeneral correspond to each other andthe requirements of IS : 383·197()29 aresimilar to those for crushing value test.This is a convenient test which can becarried out in the site laboratory.

b) Hardness and abrasion resistance­In addition to crushing strength andtoughness resistance, abrasionresistance is an important considera­tion specially for concretes exposed towearing actions. Concretes made withaggregates having good abrasionresistance are necessary for makingconcrete which will be subjected toabrasion and attrition during service.More than that, the abrasion and attri­tion resistance of aggregates are alsoimportant to assess the likelihood ofbreakage during handling and stock­piling as wellas during mixing in a mix­er. Recent tests conducted· byNRMCA32 have reported certain fineaggregates degrading due to attritionduring mixing, more so in prolongedmixing in case of ready-mix concrete,with consequent increase in the propor­tion of fines in the combined ag­gregates thereby lowering theworkability. In these tests, the sandsamples were considered otherwise'satisfactory'. Some typical results asto the effect of prolonged mixing onfineness modulus of sand and gravelare reproduced in Fig. 9.

IS : 2386 (Part IV)-1963JO recom­mends Los-Angeles test for the hard­ness and abrasion resistance ofaggregates in addition to scratch testessentially for the detection of soft par­ticles. The Los-Angeles attrition testcombines test for attrition and abra­sion and is .quite popular. This test isfound to be more representative of theactual performance expected of theaggregates and results can also be cor­related with other mechanical proper­ties of aggregates. IS: 383-197029

requires that a satisfactory aggregateshould have Los-Angeles abrasionvalue of not more than 30 percent foraggregates used for wearing surfaces

IS

SP : 23-1982

and 50 percent for aggregates used fornon-wearing surfaces. Table 7'0 in­dicates the type of relationship that canbe expected between various tests fordifferent rock groups.

2.2.2.2 PARTICLE SHAPE AND TEXTURE - Theexternal characteristics of mineral aggregatesin terms of physical shape, texture and sur­face conditions significantly influence themobility of the fresh concrete and the bondof aggregates with the mortar phase. Tworelatively independent properties, sphericityand roundness define the particle shape.Sphericity is defined as a function of theratio of the surface area of the particle to itsvolume whereas roundness measures therelative sharpness or angularity of the edgesand corners of a particle. To avoid lengthydescriptions of the aggregate shape,IS : 383-19702' lists four groups of aggre­gates in terms of particle shape (seeTable 8).Well rounded particles require less water andless paste volume for a given workability;nevertheless, crushed or uncrushed roundedgravels generally tend to .have a strongeraggregate-mortar bond and result insubstantially the same compressive strengthfor a given cement content. The unit watercontent could be reduced by S to 10 percentand sand content by 3 to 5 percent by the useof rounded gravel. Use of crushed ag­gregates, on the other hand, may result in 10to 20 percent higher compressive strength.For water-cement ratios below 0.4, the useof crushed rock aggregate has resulted instrengths up to 38 percent higher than whengravel is usedII. Elongated and flaky par­ticles, having a high ratio of surface area tovolume, lower the workabilijy of the mixand can also affect adversely the durabilityof concrete since they tend to be oriented inone plane with water and air voidsunderneath. A flakiness index not greaterthan 25 percent is' suggested for coarseaggregates.

Surface texture is the measure of polish ordullness, smoothness or roughness and thetype of roughness of the aggregates.IS : 383-197029 classifies surface charac­teristics of the aggregate into five headingsor groups (see Table 9). The grouping isbroad and it does not purport to be a precisepetrographical classification, but is basedupon a visual examination of hand speci­mens. Rough porous texture is preferred to a

SP : 13·1982

smooth surface; the former can increasebond of cement paste by 1.7 times and leadsto 20 percent more flexural and compressivestrength in concrete.

The shape and texture of fine aggregatesignificantly affect the water requirement ofthe mix. As a typical example, Fig. 1011shows the influence of void content (indirectexpression of shape and texture of fine ag..gregate) of sand in a loose condition on themixing water requirement of concrete.

2.2.2.3 POROSITY AND ABSORPTION­

Porosity, permeability and absorption ofaggregate influence the bond between ag­gregate and cement paste, the durability. ofconcrete with regard to the aggressrve

. chemical agencies, resistance to abrasion ofconcrete, and freezing and thawing; out ofthese, resistance to freezing and thawing isnot an important consideration in the condi­tions prevailing in India, unlike the colderclimates of western countries. The po­rosity of some common rocks is given inTable 1011.

The water absorption properties of ag­gregates are important in the sense thatdepending upon the condition in which theaggregates are used that is, saturated, sur­face dry, dry or bone dry. Porous maybecome reservoir of free moisture inside theaggregates. Afterwards this moisture may beavailable for hydration or may actually ex­tract some water used for mixing and the en­tire water may not be available for perfectworkability and subsequent hydration ofcement. The absorption of water by ag­gregate is determined by measuring the in­crease in weight of an oven-dried sampleafter immersion for 24 hours. However, theabsorption of water from the mix by dry ag­gregates is somewhat proved as the paste ormortar paste surrounds the surface and in­deed the absorption may not proceed to thefull and may come to an end within firsr 10or 20 minutes. Under such circumstances thewater absorption of aaresates in the first 10or 20minutes is sometimes more meaningfulthan the full absorption capacity determinedin 24 hours. Some typi~1 ranges of values ofdifferent rocks are givenin Table l~JJ. Sincethe outer layer of the gravel particles can bemore porous and absorbent due to weather­ing, gravel generally absorbs more w~ter

than crushed rock of the same petrolollcalcharacter.

16

2.2.2.4 DELETERIOUS CONSTITUENTS - Anumber of materials may be consideredundesirable as constituents in aggregatesbecause of their intrinsic weakness, softness,fineness and other physical characteristics,the presence of which may affect thestrength, workability and long-term perfor­mance of concrete. By way of their actions,these can be classified as falling into anyoneof the following categories:

a) Which are present as coating aroundthe aggregates and may interfere withthe bond characteristics.

b) Which are essentially fine particles andincrease the total specific surface areaof the aggregate thereby affecting theworkabililty.

c) Which are themselves soft and friable,and can be considered as a weak inclu­sion in the composite, being potentialside of stress concentration.

d) Which can affect the chemical reac­tions of hydration of cement.

IS : 383 ..197029 identifies iron pyrites,coal, mica, shale or similar laminatedmaterial, clay, alkali, soft fragments, seashells, organic impurities, etc, as suchundesirable ingredients in aggregates. It hasto be remembered that each of these willhave actions falling in one or more-of theabove categories; for example clay can bepresent as coating around the aggregatethereby reducing the bond. They can be pre­sent as fine particles which increase the waterdemand for a particular workability andthey themselves are soft enclosures. It is dif­ficult to precisely tell what proportion ofeach will definitely pose adverse effects onthe properties of concrete as it depends uponthe particle size and shape, the size of theconcrete members. the distribution of suchimpurities in the aggregate and above all theexposure conditions. Nevertheless manycodes of practices including IS : 383-197()29have set limits about the presence ofdeleterious constituents and have prescribedrelevant methods of tests to 4etermine theamount thereof. The related Table fromIS : 383-197()21 as to the limit of deleteriousmaterials in aggregates is reproduced inTable 12. The salient points about'deleterious materials are discussed below:

a) Clay lumps, clay and silt - Claylumps could beof two types:1) those which will get broken during

the mixing operations; and2) those which survive mixing opera­

tion and will be present in the con­crete.

The amount of clay lumps which canbe handpicked is required to be limitedto one percent of the clay. The propor­tion of clay which is likely to be brokendown in mixing is included in the testfor 'material passing 75 microns ISsieve' which also include the other finesin the aggregate like silt and fine dust.Another test prescribed in IS: 2386(Part 11)-196334 to determine specifical­ly the proportion of clay, silt and finedust is by sedimentation method.While IS : 383-197Q29 prescribes a limitof 3 percent for fine aggregates and incrushed coarse aggregates or naturalcoarse aggregates and, one percent forcrushed rocks for the material passing7S micron IS sieve, there is no cor­responding limitation in the deleteriousconstituents detected by the sedimenta­tion test. The deleterious constituentsdetermined by these two test methodsmayor may not be the same. However,the British practice limits the propor­tion of clay silt and fine dust content inaggregates (as determined by thesedimentation method) to 3 percentby weight in sand and one percentby weight of crushed coarse aggre­gates.

The effect of such fine particles onthe workability and strength of con­crete may be appreciated by ftte factthat for everyone percent clay in thefine aggregate, the compressivestrength of concrete can decrease by 5percent (see Fig. 11 H).

b) Lightweight and soft fragments ­IS : 383-197Q29 sets different limits forlightweight pieces and soft fragmentsin the aggregates (see Table 12) andgives two different test methods todetermine the same; however. in prac­tice a deleterious constituent may in­deed be falling under both categories.Lightweight pieces are essentially coaland lignite and the method of deter­mination is by gravity separation in aliquid of specific gravity 2.0. Coal andlignite may cause localised pitting andstaining in concrete surfaces. In addi-

17

SP ; 23-1982

tion, some particles specially of softervariety may swell when come in con­tact with moisture and thereby weakenthe concrete. Because of the stainingwhere the appearance of the finishedsurface is a criterion, the permissibleamount of coal and lignite is limited to0.5 percent. It may be noted that all theparticles having specific gravity lessthan 2.0 may not be coal and lignitealone, and may include other type ofparticles which may not have suchdeleterious effects on surface ap­pearance. That is why some specifica­tions (for example, ASTM C33 36 andIS : 2386 (Part 11)-196334] imply thatparticles having specific gravity lessthan 2.0 and of black and brownish­black colour are considered as coal andlignite.

The test (scratch-hardness) for softfragments as prescribed in IS: 2386(Part I1)-1963~ is essentially to detectmaterials which are so poorly bondedthat the separate particles in the pieceare easily detached from the mass. Softinclusions, such as clay lumps, shale,wood and coal are included in the testfor lightweight pieces if the specificgravity is lower than 2.0. Such softsmall fragments when present in largerquantities (2 to S percent) may lowerthe compressive strength of concrete bybeing a weak spot in the composite andgiving rise to stress concentration asdiscussed earlier. IS: 383-197029

specifies that soft fragments shall notbe more than 3 percent in naturalcoarse aggregates whereas the shalecontent in natural fine aggregates islimited to one percent.

c) Organic impurities - Organic im­purities like those resulting from pro­ducts of decay of vegetable matter in­terfere with the chemical reactions ofhydration of cement. Such organic im­purities are more likely to be present infine aggregates; those in coarse ag­gregates can be removed duringwashing. Not all the organic matterpresent in aggregates may be harmfuland in.most cases it is desirable to testthe strength properties made with suchaggregates (mostly fine aggregates) andcompare with those made with ag­gregates known to be free from organic

SP : 23·1982

impurities. This test is, however,resorted to only when the organic im­purities are detected by a colorimetrictest as prescribed in IS : 2386(Part 11)­196334• In this test the change in thecolour of a 3 percent sodium hydroxidesolution, in contact with the sample for24 hours indicates the presence oforganic matter; darker the colour,more the organic content. The colourof the solution is compared with a stan­dard solution. This test is mainly anegative test which means that if there·is no colour change, ITOorganic matteris present but if the colour changes, thepresence of organic matter is indicated.Another test prescribed in IS: 2386(Part VI)-1963l 7 for mortar makingproperties of fine aggregates is com­parative test on the basis of strengthsof mortar made with suspected sandand good sand as enumerated earlier.

d) Mica in aggregates - Mica which isoften considered to be harmful forconcrete may be present in almost allriver sands although the proportionmay vary from negligible to substantialamount. The mica being flaky andlaminated in structure affects thestrength and workability of concretethe way other flaky and laminated par­ticles do. The effect on durability willmostly result from the unsatisfactoryworkability of the fresh concrete andleads to increased permeability; inaddition Neville has contemplated thatin the presence of active chemicalagents produced during the hydrationof cement, alteration of mica to otherforms may result. Mica is generallyfound in two varieties : Muscovite,KAl2 (Si]Al) 0'0 (OHz), is potassiumaluminium silicate which is colourlessor has a silvery or pearly lustre. The se­cond variety of mica biotite which isblack brown or dark green in colour, isa complex silicate of potassium,magnesium, iron and aluminiumKJ<MgFe)ll - (SiAl). 0 20 (OHJ. Ofthese two, the muscovite variety is nowbelieved to be more harmful for con­crete. To give. an idea of their relatedinfluence if 1 to 2 percent muscovitemica brings down the strength of con­crete-by IS percent the same reductionmay be expected in the presence of 10

18

to IS percent of biotite type mica inconcrete sand. In most situations boththe varieties are present together and ifthe muscovite variety is' more promi­nent it poses more problems.

The amount of mica present in someof the Indian river sands is given inTable 13)1,39. It may be seen that inmany cases the mica content could beas high as 12 percent and the problemis often aggravated by the fact that thesand is of finer variety, the finenessmodulus being as low as 0.6 or so in thecase of sand from river Ganges.

IS : 383-197029 does not specifyupper limit of mica in fine aggregates;however, a cautionary note is addedstating that the presence of mica in thefine aggregate has been found toreduce considerably the compressivestrength of concrete and further in­vestigations are underway to determinethe extent of the deleterious effect ofmica. It is advisable, therefore, to in­vestigate the mica content of fine ag­gregate and make suitable allowancesfor the possible reduction in thestrength of concrete or mortar.IS : 383-197029 , . however, specifiestolerable limits 'of mica in terms ofdeleterious contents of alkali mica andcoated grains taken together and thesesubstances are limited to 2 percent byweight in sand. In the investigationsdone so far on the extent of deleteriouseffect of mica it has been found thatunder such situation mica content aslow as even one percent has resulted inadverse effects on the properties ofconcrete and mortar, specially ofmuscovite variety. It has generally beenseen that the workability.a·41 is adverse­ly affected when the mica content is ofthe order of S percent or more; above 8percent the mortar mixes may indeedbecome unworkable or the water con­tent may become too high. The effecton workability and strength is general­ly more the leaner the mix; in one casewith 2 percent mica content the com­pressive strel18th has been reported to10 down by 11 to 19 percent at the aleof 7 days and. 24 to 30 percent at 28days. With 12 percent mica content,the respective reductions were reportedto be 40 to 50 percent at 7 days and 47

to SS percent at 28 days. The tests ondurability have been on the basis ofabrasion resistance, percentage loss ofweight of mortar specimens exposed to10 alternate cycles of wetting in con­centrated sodium sulphate solution anddrying. and tests on coefficient ofpermeability. The results indeed are ofrelative nature. Nevertheless it can beconcluded that mica content in excessof 6 percent may be considered to bedeleterious for good abrasion resistingconcrete. The coefficients ofpermeability for typical concrete mixeswere found to increase about 10 to 20times as the mica content increasedfrom 2.S percent to 8.7 percent.

From the foregoing discussionswhile it will be very ·difficult to set alimit for the mica content in sand inmost of the cases, it would be necessaryto carry out trial mixes with such sandand adjust the mix proportions so as toresult in satisfactory compressivestrength, adequate workability andpermeability of concrete as the situa­tion will demand. The beneficiation ofsand involving removal or reduction inthe mica content in sand by floatation,density separation or wind blowing orany other method may be considered iffound to be more economical thanadjustments in mix proportions or pro..curernent of good sand from anothersource.

In so far as determination of micacontent in the fine aggregate is con­cerned, there is no specifie test inIndian Standards. However, two com­monly adopted methods are based onthe consideration that mica particles ofthe muscovite and biotite varieties dif­fer from other deleterious constituentsof sand, such as clay and silt, withrespect to their specific gravity whichranges from 2.8 to 3.0. Mica particlesalso differ from the siliceous particlesin sand in that they are more angularand flaky. These differences inphysical properties can betaken advan­tage of, to separate out mica fromsand, by adopting the followingprocedures".

1) Floatatton or density separationmethod - In this method, an inert

19

SP : 23-1982

liquid medium consisting of a solu­tion of potassium iodide in mercuriciodide having density within therange of 2.8 to 3.0 is used. Whensand is immersed in this solution,the relatively lighter siliceous par­ticles float and mica particles havingcomparatively higher density, settleat the bottom of the solution. Thefloating sand particles are removedand washed free of chemicals. Theliquid medium is usable again.

2) Wind-blowing method - In thismethod, air is blown against a thincolumn of sand from a funnel intoan improvized channel. This resultsin flaky mica particles being carriedto a greater distance than the sandparticles of corresponding size, andthus resulting in the separation ofmica particles from sand. The actualdistance to which the particles areblown depends upon the velocity ofair. For finer fraction, a velocity of19 km/hour and for coarser frac­tion, a velocity of 26 km/hour arerecommended.

The floatation method for deter­mination of mica content in sand ismore accurate than the wind-blowingmethod, although it involvesa costly li­quid medium. The efficiency of wind­blowing method depends on the textureand shape of the mica grains being dif..ferent from those of the siliceousgrains composing sand.

e) Salt contamination in sea dredged ag­gregates - Aggregates dredged fromsea are also used for making concrete,though to a very limited extent. Pro ..perties peculiar to sea-dredged ag­gregates are that the salt primarilysodium chloride-(NaC 1) and sea shellare present more frequently. Sea­dredged aggregates may also containorganic impurities due to sea-weed,dead fish, coal. oil and disposal at sea.

The salt content in the sea-dredgedaureptes is directly proportional tothe moisture content at the time ofdredaina but the final salt contentdepends upon the amount of washingand the type of water used for washing.Approval for the use of sea-dredged

SP : 13·1981

aggregates is not normally granted inthe following situations":

1) Where calcium chloride is also used;

2) Where the cement to be used is otherthan ordinary Portland cement orrapid-hardening Portland cement orsulphate resisting Portland cement;and

3) Where the concrete is to beprestressed or steam cured.

Where such approval is granted, thesodium chloride content of the fine andcoarse aggregate shall not exceed,respectively, 0.10 percent and 0.03 per­cent by weight of dry aggregate. Ifeither aggregate exceeds the limits, thetotal sodium chloride concentrationfrom the aggregate shall not exceed0.32 percent? by weight of the cementin the mix. In any case, the totalamount of chloride and sulphate ionsfrom all sources that is, aggregates,cement, water and admixtures, shouldnot exceed the value specified inIS : 4S6-I~781 and IS : 1343-1980 1°.

Shell, that is calcium carbonate, insands has no harmful effect and quitegood concrete can be produced if theshell is present in quantities up to 20percent. But the hollow or large flatshells have detrimental effect asregards to durability of concrete asthey adversely affect the quality andpermeability of the concrete. The shellcontent of the aggregates shall notexceed 2, S, IS percent, respectively,for 40, 20, 10 mm nominal sizes ofcoarse aggregate and 30 percent forfine aggregate42•

2.2.2.5 SOUNDNESS OF AGGREGATES - As'"gregate is said to be unsound when it pro­duces excessive volume changes resulting intile deterieration of concrete under certainphysical conditions, such as freezing andthawing, thermal changes at temperaturesabove freezing and alternate wetting anddrying. Frost damage to concrete is distinctfrom the expansion -.s a result of chemicalreactions between the aggregate particle andthe alkalis in cement. Certain 811regatessuch as porous cherts. shales, somelimestones particularly laminated limestonesand some sandstones, are known to besusc~ptible to this frost damage. High ab-

20

sorption is a common characteristics of theserocks with a poor service-record, thoughmany durable rocks may also exhibit highabsorption. Thus, critical conditions forfrost damage are water content and lack ofdrainage. These characteristics of high ab­sorption and lack of drainage depend uponthe pore characteristics of aggregate. It hasbeen reported in the case of some aggregatesthat porosities in the region of + 8 micron(as determined by mercury-intrusion porosi­ty test) appear to separate the high from thelow durability aggregates.

IS : 2386 (Part V)-1963'-J specifies a testfor determining soundness of aggregates.This test popularly known as 'sulphate test'consists of subjecting a graded and weighedsample of aggregate to alternatively immer­sion in saturated solution of sodium sulphateor magnesium sulphate and oven drying andthus determining the weight loss afterspecified cycles of immersion and drying.The overall mechanism of this sulphate testis yet not fully understood but probably thistest involves a combination of actions thatis, pressure of crystal growth, effects ofheating and cooling, wetting and drying andpressure development due to migration ofsolution through pores but this test in noway is considered to simulate exposure ofconcrete to freezing and thawing due to com­plexity of field exposure and does not pro­vide a reliable indication of field perfor­mance. Consideration should always begiven to the service record of the aggregateand this sulphate test serves only as a guideto the selection of aggregate. In a generalsense, most aggregates with high soundnesslosses tend to have poor durability but thereare numerous exceptions. It has beenreported that few high soundness loss ag­gregates had excellent durability and sound­ness test failed to detect several a"regates oflow durability". Thus reliance should alwaysbe based on the actual performance from theservice-record. Dolar-Mantuani" is of theopinion that the test does indicateweaknesses in auregates. If the specificationlimits are used carefully together with soundengineering judgemen&. the test is certainlyuseful because of the relatively short timeneeded to perform it. IS: 383-197Q29 as ageneral luide restricts the averale loss ofweight after .s cycles to 12 percent whentested with sodium sulphate and 18 percentwhen tested witb malnesium sulphate.

2.2.2.6 ALKALI-AGGREGATE REACTION - Thisreaction takes place between the alkalis inthe cement and the active siliceous consti­tuents or carbonates of aggregates. Undermost conditions, this reaction causes ex­cessive expansion and cracking of concrete.These deleterious reactions have been en­countered in many parts of the World and inall climatic zones. The reactions are:

a) Alkali-silica reaction, and

b) Alkali-carbonate reaction.

A typical example of the effects of alkali­silica reaction has been provided by the con­crete of a military jetty in Cyprus", con­structed in 1966. By 1972, widespread crack­ing and spalling of concrete were noticed andparts of the surface concrete crumbled andbecame friable, in some places to a depth upto 15 ern, Damage due to alkali-silica reac­tion had also been noticed in TuscaloosaLock and Dam, USA in 195247

• Dry dock insouth Carolina also showed alkali-silicareaction cracking with quartz gravel ag­gregate in 1969. The reactive material wasmetamorphic quartz or metamorphic andhighly weathered quartz. In the year1965-66, Lachswehr Bridge of northern Ger­many had severe damage due to this reac­tion. The area of major concern in Germanyis in two classes of reactive constituent inaggregates, opaline sandstone and reactiveflint.

Certain dolomitic aggregates fromBahrairr" have been found to reactdeleteriously with cement paste. The reac­tion has been noticed to be promoted by thepresence of gypsum and excess hydroxyl inthe .mixture and by the marked porosity oftheaggregate.

In 1956-S7, expansive reactivity of con­crete was noticed at Kingston", Ontario. Aclose look at culverts and bridges con..structed only a few months earlier showedpattern of man cracking. Observations in­dicated that dolomitic limestone aggregate"from local quarries was an essential ingre-dient of the affected concrete. By priorgeological exploration of existing and poten­tial quarry sites and subsequently testing thedifferent rocks for alkali - carbonate reac­tivity, it is possible to select non-reactive ag­gregates. For constructing a major concretehighway, this procedure appeared to berealistic and economical considering the ex-

21

SP : 23·1982

tra cost of using low alkali cement or bring­ing aggregates from outside.

Newlon and Sherwood'? suggested thefollowing measures to reduce expansion ofconcrete where it is essential to use alkalireactive carbonate aggregates, for economy:

a) If the aggregate is of a high degree ofreactivity, dilution of reactive ag­gregates with a non-reactive one,reduction of cement alkalis or both,are necessary to eliminate cracking andreduce expansion significantly.

b) The limit of 0.60 percent alkali for low­alkali cement does not appear to be lowenough to reduce the reaction with thehighly reactive carbonate aggregates,even with aggregate dilution of 50 per­cent. To reduce the reaction to an ac­ceptable level, the reduction of alkalisto 0.40 percent may be necessary. rrreduction of alkalis to this limit is notpossible, then corresponding greaterdilution of aggregate is required.

The reactive forms of silica are opal(amorphous), chalcedony (crypto crystallinefibrous) and tridymite (crystalline). Thechemical composition, physical characterand · the reactive minerals" are given inTable 14. The reaction minerals occurringin the reactive rocks are given in Table 153J •

Rocks' containing opal, chalcedony, chert,volcanic glass, crystobalite , tridyrnite orfused silica have shown to be reactive inmany instances. As little as 0.5 percent of adefective aggregate is sufficient to cause con­siderable damage in concrete. The maximumexpansion is produced when reactiveaggregates make up about 4 percent of thetotal aggregates and this disadvantageousconcentration is often referred to as thepessimum".

The actual reaction occurs betweensiliceous minerals in aggregates and thealkaline hydroxides derived from the alkalis(Na20 and K20) in the cement. The result ofreaction is alkali-silicate gel of 'unlimitedswelling' type, and because the gel is confin­ed by the surrounding cement paste, internalpressure causes cracking and disruption.

The carbonate in aggregates is generallyargillaceous dolomitic limestone. A widerange of carbonate rocks havebeen reportedas being potentially reactive, ranging frompure limestone to pure dolomite. The

SP : 23 ..1982

presence of clay minerals incorporated in theaggregate and the crystalline texture of thecarbonate rocks influence the reaction. Thereactive carbonate materials are confined tospecific ranges of rock composition betweencalcitic dolomites and magnesiumlimestones. Dolomites and limestones con­taining excess Mg or Ca ions in their crystalstructure over the ideal proportions are morelikely to be reactive". The dolomitic rockconsists of substantial amounts of dolomiteand calcite in the carbonate portion, withsignificant amounts of acid insoluble residueconsisting largely of clay, Dolomitizationreaction" is believed to be the alkali - car­bonate reaction producing harmful expan­sion of concrete. Magnesium hydroxide,brucite [Mg(OH)2] is formed by this reac­tion.

One method of determining the potentialalkali-aggregate reactivity is by 'mortar bar'test as given in IS: 2386 (Part VII)­196351_ The method of test covers the deter­mination of reactivity by measuring theexpansion developed by the cement­aggregate combination in mortar bars duringstorage under prescribed conditions of test.The test is more conclusive but has the disad...vantage of requiring several months and alsorequiring that coarse aggregate be crushedrather than tested in its normal state. Withlarger specimens, however, uncrushed ag­gregate may be tested".

The second method of determining thepotential reactivity of aggregates is the'chemical method' as prescribed by IS : 2386(Part VII)-1963". This method of test deter­mines the reactivity as indicated by theamount of reaction of the aggregate with a 1N sodium hydroxide solution under controll­ed test conditions. The method has the ad­vantage that it can be performed in 3 days,but for many aggregates the results are notconclusive", However, the illustration ofdivision between innocuous and deleteriousaggregates (based on Mielenz and Witte'swork II) is reproduced from IS: 2386(Part VII) - 1963'· in Fig- 12.

Both the test methods mentioned above donot always detect the alkali-carbonatereactivity but this may be detected byanother test. in which concrete prisms madewith questionable agregates and a hiahalkali cement are exposed to an environmentof 23°C and with 100 percent relative

22

humidity and noting the amount of expan­sion. Expansion of prisms made of ques­tionable aggregate are then compared withthose obtained on companion prisms ofknown sound limestone",

The problem of alkali-aggregate reactioncan be overcome by use of low-alkali cement(that is, containing less than 0.6 percentalkali calculated as Na20) or by addition ofsuitable finely ground pozzolana to the con­crete mix _ The pozzolana reacts chemicallywith the alkalis before they attack the reac­tive aggregates".

Air entrainment is also believed to beuseful in counter acting alkali-aggregatereaction. Use of reactive aggregate itself infinely divided form is also known to inhibitdestructive effects of alkali-aggregate reac­tion.

Detailed petrographic examination andX-ray identification are being used toexamine suspect aggregates. But the conclu­sions are unreliable and all available pastevidence must be taken into account whenevaluating a new aggregate.

Detailed petrographic, mineralogical andchemical data compared with similar dataalready available for reactive aggregates mayprovide the most satisfactory means of iden­tifying potentially reactive aggregates".

The problem of alkali-aggregate reactionis not generally encountered with natural ag­gregates used in this country. Limited dataare available on alkali reactivity of naturalcoarse aggregates in India'4.". Gogte"evaluated some common Indian aggregateswith emphasis on their susceptibility toalkali-aggregate reactions from a study of anumber of samples of rock aggregatesbelonging to different Indian geological for­mations, more or less representing thoseused for concrete constructions all over thecountry, trle following conclusions weredrawn based on their petrographiccharacters and mortar-bar expansion tests:

a) Indian rocks vary widely in theirsusceptibility to alkali-aggregate reac­tions. Even rock aggregates havingidentical characteristics were found todiffer considerably regarding theirbehaviour with hiah-alkali cements.

b) The potential alkali reactivity ofcrystalline rocks. for example granites.

granodiorites, gneisses, charnockites,quartzites and schists, is related to thepercentage straining effects in quartz.Rock aggregates containing 40 percentor more strongly undulatory, fracturedor highly granulated quartz are highlyreactive and with 30-35 percent strain..ed quartz are moderately reactive.Rock aggregates belonging to theabove groups containing predominant­ly unstrained or recrystallised quartzshow negligible mortar expansions andthus are innocuous.

c) The basaltic rocks with S percent ormore chalcedony or opal or about 15percent palagonite show deleteriousreactions with high alkali cements.Sedimentary and metasedimentaryrocks, for example, sandstones andquartzites containing 5 percent or moreof chert also show deleterious reactivi­ty with cement alkalies. These reac­tions could be attributed to the microto crypto-crystalline texture andfibrous extinction of these mineralswhich is also an indication of thepresence of dislocated silica zones.

d) The problem of alkali-aggregate reac­tion needs to be viewed from newangles. The arbitrary classification ofsilica minerals into alkali reactive andnon-reactive, produces many excep­tions. Because of dislocated zones ofsilica in deformed quartz, some seem­ingly innocuous aggregates, for exam­ple, granites, charnockites andquartzites, which do not contain thewell-known alkali-reactive con­stituents, such as opal, chalcedony orvolcanic glass show deleteriouschemical reactivity with cementalkalies.

2.2.3 LIGHTWEIGHT AGGREGATES-­

Lightweight aggregates can be either naturallike diatomite, pumice, scoria, volcaniccinders, etc, or manufactured like bloatedclay, sintered fly ash or foamed blast furnaceslag. Lightweight aggregates are used instructural concrete and masonry blocks forreduction of the self weight of the structure.The other usages of lightweight aggregateare for better thermal insulation and improv­ed fire resistance.

Unlike for normal weight aggregates fromnatural sources, there is no Indian standard

23

SP : 23-1982

specification for lightweight aggregates.However, IS : 9142-1979~6 covers specifica­tion for artificial lightweight aggregates forconcrete masonry units, while IS: 2686­1977~7 covers cinder aggregate for use in limeconcrete for the manufacture of precastblocks. However, IS: 456-1978 1 envisagesthe use of bloated clay and sintered f.ly ashaggregate with proven performance in struc..tural concrete. The use of lightweight ag­gregates in India is not so common; howeverthey have been widely used in USA and otherWestern countries.

The main requirement of lightweight ag­gregates is their low density; some specifica­tions limit the bulk density to 1 200 kg/rn'for fine aggregates and 960 kg/rn' for coarseaggregates for use in concrete. Both coarseand fine aggregates "may be lightweight.Alternatively, lightweight coarse aggregatescan be used with natural sands. Thecharacteristics of lightweight aggregateswhich require consideration for use in struc­tural concrete are as follows:

a) Some lightweight aggregates may con­tain closed pores or voids in thematerial, apart from high waterabsorption of the order of 8 to 12 per­cent. The closed pore system inside theaggregate mass will not be accessible tomixing water but they will displace anequal amount of mixing water or paste'(equal to volume of pore). The waterabsorption aggregates will absorb partof the mixing water the moment theycome in contact with it in a mixer andthat part of the water may not beavailable for reaction with cement.Because of this, the usual concept fordesigning normal weight concretemixes may not be applicable tolightweight aggregates and on larger orimportant works separate relationshipsbetween the relative density, waterabsorption, moisture content of theaggregates on the one hand andworkability, density and compressivestrength on the other may have to beestablished.

b) Being artificially produced by sinteringor pelletizing, most of the synthetic ag­gregates may have a smooth surfaceand rather regular shapes which mayreduce the bond characteristics withthe mortar and thereby result in lowercompressive strength

SP : 23-1982

c) I f, during mixing the lightweightaggregates get crushed, the void struc­ture is broken down resulting in acoarse surface texture which may lowerthe workability.

d) The modulus of elasticity of concretesmade with most of the lightweightaggregates is lower than the normalweight concrete, may be Y2 to ~.

Creep and shrinkage of concrete arealso greater (will vary from equal toabout double) (Fig. 1358) compared tothose of normal weight concrete, hav­ing the same compressive strength".These result in higher deflection of thestructural members.

Because of high absorption, workableconcrete mixes become stiff within a fewminutes of mixing. Therefore, it is necessaryto wet (but not saturate) the aggregatesbefore mixing in the mixer. In the mixingoperation, the required water and aggregateare usually premixed prior to addition ofcement. As a rough guide, the extra waterneeded for lightweight aggregate concrete isabout 6 kg/rn' of concrete to obtain a changein the workability of 2S mm slump. Richmixes containing cement about 350 kg/rn' ormore, are usually required to producesatisfactory strength of concrete. The con­crete cover to reinforcement using lightweight aggregates in concrete should be ade­quate. Usually it is 25 mm more than fornormal concrete. This increased cover isnecessary, because of its increasedpermeability and also because concrete car­bonates rapidly by which the protection tothe steel by the alkaline lime is lost.

Deflection calculations considering lowertensile strength and modulus of elasticity oflightweight concrete, generally result inhigher initial deflection. Tobin'" observed 10percent more deflection for the lightweightslab compared to normal weight concreteslab under the same superimposed loading.Lower tensile strength of lightweight con­crete must be taken into account in designfor the calculation of allowable crackingstress for prestressed members or for deflec­tion calculation based on a cracked sectioninstead of a homogeneous section".

The increased creep of lightweight con­crete does not add to the deflection of struc­tural members. as the ratio of creep strain toelastic strain is the same for both lightweight

24

and normal weight concrete. The effect ofshrinkage on deflection arises from therestraint of shrinkage due to steel reinforce­ment. Tests have shown that for usualamount of reinforcement, the effect ofshrinkage on deflection is quite smallregardless of the type of concrete. Thus thedifference between the shrinkage deflectionof lightweight and normal weight concretemembers of comparable design is quitesmall".

Bloated clay aggregates are spherical inshape, hard, light and porous. The size ofthe particles ranges from 5 to 20 mm. Thefine aggregate is produced by crushing thelarger particles. The water absorption ofbloated clay aggregates is about 8 to 20 per­cent. The physical properties of suchaggregates seem to. vary with the bloatingcharacteristics of the raw material and theprocessing equipment used in manufacturingthe aggregate. The use of this aggregate i~

advocated in places where the cost of crush­ed stone aggregate is high and suitable claysespecially silts from water works are easilyavailable. Concrete produced from this ag­gregate has hulk density of the order of1 900 kg/rn '.

The sintered fly ash aggregate is roundedaggregate with a bulk density of about 1 000kg/rn'. This type of aggregate is suitable formaking masonry units as well as structuralconcrete. Concrete prepared from this ag­gregate has unit weight of 1 200 to 1 400kg/rn'.

Foamed blast furnace slag aggregate isproduced with a bulk density varying bet­ween 300 and I 100 kg/rn', depending on thedetails of the cooling process and to a certaindegree on the particle size and grading. Con­crete made with this aggregate has a densityof 950 to 1 750 kg/rri'.

Vermiculite is another artificial light ..weight aggregate which when heated to atemperature of 650 to 1 oooDe expands to asmany as 30 times its original volume by ex..foliation of its thin plates. Thus the densityof exfoliated vermiculite is only 60 to 130kg/rn' and the concrete made with it is oflow strength and exhibits high shrinkage butis used as an excellent heat insulator.

2.3 Water - Compared to other ingre­dients of concrete. the quality of waterusually receives less attention. However,

unwanted situations leading to distress ofc~n~rete, contributed among others by themlxln~ and cu~ing water being not of the ap­propriate quality has focussed the attentionon quality of water as well.

Potable water is generally consideredsatisfactory for mixing concrete. Should thesuitability of water be in doubt, particularlyIn remote areas or where water is derivedfrom sources not normally utilized fordomestic purposes, such water should betested. The permissible limits for solids andimpurities for mixing and curing water asspecified in various specifications includingIS : 456-1978' are in excess of the re­quirements of potable water. Perhaps, themost comprehensive investigations on waterfor concrete making were carried out byAbrams; these and a few others are sum­marized in Ref 61 and the recommendationsin the various codes of practice includingIS : 456-1978' are largely based on thesetests. Abrams": 62 tested 68 different watersamples including sea, alkali, mine, mineraland bog waters and highly polluted sewerageand industrial wastes on mortar and concretespecimens. The effects were expressed main­ly in terms of differences in the setting timesof Portland cement mixes containing impuremixing waters as compared to clean freshwaters and concrete strengths from 3 days to2 years and 4 months compared with controlspecimens prepared with distilled water. Adifference in 28 days compressive strengthby maximum 15 percent of control test wasconcluded to be the best measure of thequality of mixing water. IS : 456-1978' alsoincorporates a similar provision, except therequirement of compressive strength is to benot less than 90 percent. It was also conclud­ed that the setting time is not a satisfactorytest for measuring suitability of a water formixing concrete and in most of the cases thesetting time was found to be the same.IS : 456.1978 1 prescribes a difference ininitial setting time of ± 30 minutes withinitial setting time not less than 30 minutes,

Based on the minimum strength ratio of85 percent, the following waters were foundto be suitable for concrete-making: bog andmarsh waters; waters with a maximum con­centration of 1 percent SO4; sea water, butnot for reinforced concrete; alkali water witha maximum of 0.15 percent Na2 SO.. or Nacl;pumpage water from coal and gypsummines: and waste water from slaughter

25

SP : 23-1982

house~, breweries, gas plants, paint and soapfactories. The waters found unsuitable forthe purpose were acid water, lime soak waterfrom tannery waste, carbonated mineralwater disch~r~ed from galvanizing plants,water containing over 3 percent of sodiumchloride or 3.5 percent of sulphates andwater containing sugar or similar com­pounds. The lowest content of total dissolv­ed solids in these unacceptable waters wasover 6 000 ppm except for a highly car­bonated mineral water that contained2 140 ppm of total solids.

From the above, the main reason forholding potable water (the exception beingwater containing sugar) as suitable for mak­ing concrete would be obvious. as very fewmunicipal waters would contain more than2 000 ppm of dissolved solids .and specifica­tions of potable water would exclude nearlyall of the above mentioned polluted waters.On the basis of these tests and the work doneby others, the limits of some impurities inwater for mixing and curing concrete thatcan be held to be tolerable arelisted in Table1663• Compared to these, the permissiblelimits in IS : 456-1978 1 reproduced in Table17 are on the conservative side. In addition,there are additional tests to determine thealkalinity (as carbonates and bicarbonates)and the acidity of the water sample inIS : 456-]978 1• The limit of alkalinity isguided by the requirement that to neutralize200 ml sample of water, using methyl-orangeas an indicator, it should not require morethan toml of 0.1 normal sci. This alkalini­ty is equivalent to 265, 420 and 685 ppm ofcarbonates (as Na2CO) , bicarbonates (as~aHCO}) and the sum of the two, respec­tively, and should be seen in the backgroundof Abrams' tests which showed that concen­trations up to 2 000 ppm were in generaltolerable. Regarding acidity, thepH value ofthe water is required to be generally not lessthan 6. However, the pH value may not be asatisfactory general measure of the amountof acid or basic reaction that might occurand the effect of acidity in water is bestgauged on the basis of the total acidity 'asdetermined by titration?". The limit of totalacidity is guided by the requirement that toneutralise 200 ml sample of water. usingphenolphthalein as indicator, it should notrequire more than 2 ml of 0.1 normalNaOH. This acidity is equivalent to 49 ppmof H1S0 4 or 36 ppm of HCl.

SP : 13·1982

2.3.1 MISCELLANEOUS INORGANIC IM­PURITIES - Kuhl" made a broad survey ofthe effects of miscellaneous inorganic salts.The salts chosen constituted a cation seriesand an anion series. For the cation series,chlorides were used except that wheresolubility was low nitrates were used. Theanion series comprised sodium salts. Thesalts of the cation series that caused a mark­ed reduction in strength of concrete werethose of manganese. tin, zinc, copper, andlead (nitrate). The zinc and copper chloridesretarded so much that no strength tests werepossible at 2 and 3 days. The action of leadnitrate was completely destructive,

Out of anion series. sodium iodate,sodium phosphate, sodium arsenate andsodium borate reduced the initial strength ofconcrete to an extraordinary low degree andin certain instances to zero. Another salt thathas been found to have detrimental effect onstrength development is sodium-sulphideand even a sulphide content of 100 ppmwarrants testing (see Table 16).

2.3.2 SILT OR SUSPENDED CLAY PAR.

TICLES - Considerable muddiness or tur­bidity in mix water can be tolerated if it issimply suspended clay or fine rock par..ticles". IS : 456-19781 allows 2 000 mg/I ofsuspended matter (Table 17). Muddy watershould remain in settling basins before use.

Algae - Doe1l6z. ] 3 has shown that thewater containing algae has the effect of en-

, training huge quantities of ail in the concretethus resulting in lower strength. Algae alsoreduces the bond between aggregates and ce­ment paste. The presence of algae to the ex­tent of 0.1 percent by mass of mixing waterentrained 6 to 7 percent of air causing astrength reduction of more than IS percent.

2.3.3 OIL CONTAMINATION - Generally, oilcontamination can be removed by floata­tion. Mineral oils not mixed with anfmal orvegetable oils are probably the least objec­tionable from the standpoint of strengthdevelopment". Davis" carried out tests to in­vestigate the effect of oil contamination.Three different oils were used, namely, amineral oil (SAE 30). a diesel fuel oil and avegetable seed oil (sunflower)."The resultswere summarized as follows: 2 percent bymass of cement of mineral oil resulted insianificant increases in strenath at aU aaes.A4dition of' 4 percent and 8 percent of

26

mineral oil also resulted in strength gain butnot of the order of 2 percent. In case ofdiesel oil 8 percent of oil slightly reduced thestrength, whereas at lower percentagesstrength gains were observed. In case ofsunflower oil 8 percent of oil had a detri­mental effect to the strength of concreteparticularly at later ages.

2.3.4 SEA WATER - Sea water generallycontains 3.5 percent of dissolved solids,about 78 percent (that is, 27 000 ppm) ofwhich is sodium chloride and 15 percent(that is, S 300 ppm) of which is chloride andsulphate of magnesium. Opinions differwhen it comes to categorically classifying seawater as either allowable or not for use formaking concrete. In so far as the re­quirements of strength are concerned, theearly age strength (up to 3 days or so) mayindeed be somewhat higher, possibly becauseof the accelerating effects of the chloridespresent; but long term strengths may besomewhat lower. However, the major con­cern is attributed to the risk of corrosion ofreinforcing steel due to the chloride as wellas other problems of durability of concreteassociated with sulphates, In general, therisk of corrosion of steel is more when thereinforced concrete member is exposed to airthan when continuously submerged underwater. including sea water", Based on thisthe consensus is not to permit the use of seawater for making concrete in reinforced con­crete constructions": 15. Under unavoidablecircumstances, it may be used for plain con­crete61• 6S. 66 when it is constantly submergedin water. IS: 456-1978 1 incorporates asimilar provision but the use of sea water forprestressed concrete is not permitted in anycase.

2.3.5 CURING WATER - IS : 4S6-1978­states that water found satisfactory for mix­ing concrete can also be used for curing cO,n­crete but it should not produce any objec­tionable stain or unsighty deposit on thesurface. Iron and organic matter in thewater are chiefly responsible for staining ordiscolouration and especiafty when concreteis subjected to prolonged wetting. even avery low concentration of these can causestaining. Accordina to IS: 456-1978', thepresence of tannic acid or iron compounds incuring water is objectionable.

2.4 AdmixtJua - Present day concreteoften incorporates a fourth inaredient called

admixtures, in addition to cement, ag­gregates and water. Admixtures are added tothe concrete mix immediately before or dur­ing mixing, to modify one or more of thespecific properties of concrete in the fresh orharderred states. IS : 9103-197967 lays downthe procedures for evaluation of admixturesfor concrete and the changes in the proper­ties of concrete that should be expected whenthe admixtures are used.

The different types of admixtures coveredby the Indian Standard (IS: 9103-197961) areas follows:

a) Accelerating admixtures,

b) Retarding admixtures,

c) Water-reducing admixtures, and

d) Air-entraining admixtures.

In addition, IS : 456-1978 1 permits the useof pozzolana like fly ash conforming toIS: 3812 (Part 11)-198168 or burnt-clay con­forming to IS : 1344-198269 as admixturesfor concrete. They are used mainly to im­prove the workability of concrete andthereby reduce the water demand for a givenworkability. However t because of poz­zolanic reactions taking place, the role ofsuch pozzolana as admixture cannot bestrictly delineated from that of part replace­ment of cement. Moreover, these finelydivided mineral additives are usually addedin much larger dosage than chemical admix­tures listed above.

Before using an admixture in concrete, theperformance of it should be evaluated bycomparing the properties of concrete withthe admixture and concrete without any ad­mixture. Though the admixtures covered inIS : 9103 .. 197967 are intended mainly formodifying a single property in concrete,some of the admixtures available in themarket are often capable of modifying morethan one property of concrete. For example,water-reducing admixtures can also be set­retarders and air-entraining admixturesincrease the workability of the concrete mix,in addition to .providing air-entrainment.

In addition, an admixture can improve thedesirable properties of concrete in more thanone way. For example, water-reducing ad­mixtures can be used: (a) to increase theworkability of concrete with the same waterand cement contents, (b) to increase thecompressive strength of concrete withoutchanging the workability by reduction of the

27

SP : 23·1982

water content in the concrete mix, when thecement content is unaltered, or (c) to effectsaving in cement content by reduction inboth the cement and water contents in themix, while maintaining the same workabilityand compressive strength as in the referenceconcrete.

Although the standard specificationswould define the minimum performance re­quirements of an admixture, in practice, theresultant improvements in the characteristicsof concrete may be required to be more thanthe minimum specified in these specifica­tions. For example, a viable water-reducingadmixture should allow a reduction in thewater content between 5 to 12 percent andconsequently cause an increase in the 28-daycompressive strength of concrete by nearly10 percent?", On the other hand, by modify­ing the concrete mix design -in conjunctionwith the use of a water-reducing admixture,the economy in the use of cement can be ofthe order of 10 percent".

Concretes made with admixtures whencompared with identical concrete madewithout admixtures should manifest improv­ed physical properties as given in Table 1861 •

In case of air-entraining admixtures, areference admixture of approved qualityshould be used in the controlled concrete toentrain identical amount of air.

The performance of an air-entrainingadmixture can be evaluated in accordancewith ASTM C 233-7672• As stipulated inIS : 9103-197967

, the relative durability fac­tor of concrete containing admixture undertest should not be less than 80 for specifiednumber of 300 freeze-thaw cycles, thedurability factor being related to the relativedynamic modulus of elasticity of standardprism specimens.

Some admixtures are likely to containwater soluble chlorides and sulphates.These. if present' in large quantities, maycause damage to the concrete structures dur­ing the course of time. The chlorides maycause corrosion to the steel reinforcementwhereas the sulphates may cause disintegra­tion of concrete by forming sulphoalumi­nates. IS: 9103-197967 for admixtures forconcrete, stipulates that the chloride contentof the admixtures should be declared bv themanufacturers.

2.4.1 ACcElERAnNo ADMIXTURES - Theseare substances which when added to concrete

SP : 23-1982

increase the rate of hydration of cement,shorten the setting time and increase the rateof strength development. The chemicals thataccelerate the hardening of concrete mixesinclude soluble chlorides, carbonates, sili­cates, fluorosilicates and hydroxides andalso some organic compounds, for example,triethanolamine.

The most widely known accelerator iscalcium chloride. The addition of CaCl2 tothe concrete mix increases the rate ofdevelopment of strength. Accelerating ad­mixtures are used when concrete is to beplaced at low temperatures. Indian Standardrecommendations IS : 7861 (Part 11)-1981 73

for cold weather concreting envisages the useof CaC12 up to a maximum of 1.5 percent bymass of cement for plain and reinforced con­crete works, in cold weather conditions.CaCI 2, however, is not permitted to be usedin prestressed concrete because of its poten­tial danger in augmenting stress corrosion.

The increase in the rate of development ofearly strength of concretes containing or­dinary and rapid hardening Portland cementis shown in Fig. 143 3 • At normaltemperatures, addition of 2 percent CaCI 2=

(a) accelerates the rate of strength of con­crete containing ordinary Portland cement atearly ages approximating that of a rapidhardening Portland cement, and (b) in­creases the strength and abrasion resistanceof concrete at all ages up to 1 year".However, addition of calcium chloride ad­mixture may bring about reduction in flex­ural strength of concrete at ages of 28 daysand beyond.

2.4.2 RETARDING ADMIXTURES - A delay inthe setting of concrete is achieved by the useof retarding admixtures. Retarding actionrs exhibited by sugar, carbohydratederivatives, soluble zinc salts, solubleborates, etc. Retarding admixtures are usedin hot weather when normal setting time ofcement gets reduced due to hightemperature. IS: 7861 (Part 1)-197514 en­visages the use of such admixtures to offsetthe accelerating effects of high temperature.The retarding action of a set-retarder to thepenetration resistance of concrete is shownin Fig. 1S7~.

A small quantity of sugar (about o.OS per­cent by mass of cement) delays the settingtime of concrete by about 4 hours".

28

However, the effect of sugar depends greatlyon the chemical composition of cement. Theperformance of such a retarder should bedetermined by trial mixes with the actual ce­ment to be used in construction. A largequantity of sugar (say 0.2 to 1 percent bymass of cement) prevents the setting ofcement",

2.4.3 W·ATI:.R-RfDlJCING AOMIXTURf ~ ­

The water-reducing admixtures are usuallybased on calcium or sodium salts orderivatives of lignosulphonic acids from thewood pulping industry. Modern admixt uresbased on lignosulphonic acid derivatives arcformulated from the purified products, afterremoving the sugar and other impurities.Polycarboxylic acids, their salts, modifica­tions and derivatives also find some applica­tion as water-reducing admixtures;'.

The increase in the workability of concrete(in terms of compacting factor) using a water­reducing admixture 1~ shown in Fig. 1671•

The determination of workability is animportant factor In testing concrete admix­tures. Rapid loss of workability occurs dur­ing the first few minutes after mixing ofconcrete and gradual loss ot workability takesplace over a period from 15 to 60 minutesafter mixing". Thus the relative advantageof water-reducing admixtures decreases withtime after mixing. Therefore, IS: 9103­1979b' stipulates that the workability of freshconcrete containing admixtures should bedetermined not sooner than 15 minutes norlater than 20 minutes after completion ofmixing of concrete.

Water-reducing set-retarders belong to thefollowing two main groups:

a) Lignosulphonic acids and their salts,and

b) Hydroxylated carboxylic acids andtheir salts.

These admixtures increase the setting timeby about 2 to 6 hours during which concretecan be vibrated, revibrated and finished.This is particularly important in hot weatherconditions or where the nature of construe..tion demands a time 6~P between the placingof successive layers of concrete. It is possibleto offset the set-retarding property of thiskind of admixture, if the situation sodemands, bv incorporating an accelerator.for example, CaC12 or trtethanolamine".

2.4.4 AIR ..ENTRAINING ADMIXTURES­

These admixtures cause air to be incor­porated in the form of minute bubbles in theconcrete during mixing, usually to increaseworkability and resistance to freezing andthawing. They control the amount of air infresh concrete and disperse properly sized airbubbles throughout the concrete. Theorigins of air-entraining admixtures are asfollows":

a) Natural wood resins:b) Animal or vegetable fats and oils;

c) Various wetting agents, such as alkalisalts of sulphated and sulphonatedorganic compounds;

d) Water soluble soaps of resin acids andanimal or vegetable fatty acids; and

e) Miscellaneous materials, such assodium salts of petroleum sulphonicacids, hydrogen peroxide. aluminiumpowder, etc.

The resistance of air-entrained concrete interms of dynamic modulus of elasticity andchange in length, against freezing and thaw­ing is shown in Fig. 17'8.

The entrained air bubbles (approximately0.05 to 1.25 rom dia) reduce the capillaryforces (the force causing absorption of waterby concrete) by restricting the effectivelength of each capillary pore in concrete.The capillaries are interrupted by relativelylarge air voids in air-entrained concrete. Thevoids cannot fill with water from thecapillaries because of surface tension effectsand, therefore, under freezing conditions,they behave as 'expansion chambers' to ac­commodate the ice formed. When the icemelts, surface tension effects draw the waterback into the capillary so that the air bubbleacts as a permanent safety valve, giving con-

SP : 23-1982

tinuous protection to concrete against frostdamage". The resistance of air-entrainedconcrete is thus attributed to a combinationof reduced permeability of cement paste, thebreakdown of capillary action and the reliefof pressure in the concrete pores under theconditions of freezing and thawing.

Entrainment of small amount of airresults in concrete of insufficient durability,whereas with large amount of air­entrainment there is an excessive strengthreduction in concrete. Therefore, an op­timum percentage of air giving a balance be­tween compressive strength and durabilitymust be used in practice. Table 1980 gives op­timum air contents for concretes of differentmaximum sizes of aggregate.

2.4.5 INFORMATION ON ADMIXTURES - Tofacilitate approval of an admixture, thefollowing information is needed:

a) The trade name of the admixture, itssource, and the manufacturer's recom­mended method of use;

b) Typical dosage rates and possibledetrimental effects of under and overdosage:

c) .Whether compounds likely to causecorrosion of reinforcement ordeterioration of concrete (such as thosecontaining chloride in any form as anactive ingredient) are present and if so,the chloride ions by mass or expressedas equivalent anhydrous calciumchloride by mass of admixture; and

d) The average expected air content offreshly mixed concrete containing anadmixture which causes air to be en­trained when used at the manu­facturer's recommended rate ofdosage.

TABI~f: 2 COMPOUND ('OMPOSITJON OF ORDINARY PORTLAND CEMENn,

(Clause 2.1)

------ -------------------------

COMPOU~D

Tricalcium silicate

Dicalcium silicate

Tricalcium aluminateTetracalcium

aluminoferrite

FORMULA

3 CaO. Si02

2 CaO. Si023 CaO. Al2014 cso, A120J . Fe10)

ABBREVIATION PERCENTAGE BY MASS IN

CEMENT

30-50

20-4S8-12

6-10

29

SP : 23·1982

(Clause 2.1)

6'/z Years \

117± 7

53 ± ~

328± 25

III ± 24

1 Year

117± 7

54± 4

279 ± 23

90±22

7 Days

53± 11

10± 7

372± 39

118±37

HEAT EVOLUTION (cal/g), -A...-- ~ __

28 Days 90 Days

90± 7 104± S

25 ± 4 42 ± 3

329 1: 23 311 ± 17

l18±22 98± 16

/] Day~

58± 8

12± S

212:t 28

69±27

c]sC2S

CJA

C'4AF

COMPOUND

NOTE - Table 3 i'i from 'The Chemistry of Cement and Concrete (Third Edition J970)' by F. M, lee and Publishedby Mis Edward Arnold Ltd, London.

----- -- ----------. -------~----------

-"....-- ..._----------- ------ ------ ------

TAB".: 4 PHYSI<..'AI. AND ('II~:MI('AL REQUIRt:Mi:NTS OF INDIAN STANDARD SPE<":IFI('ATION~

FOR DI.~.~ER.:NT CEMENTS

(Clause 2.1)

CHARA<.-TfRI~TIC ORDINARY RAPID low HEAT HIGH PORTl AND PORTLAND

PORTLAND }-fARDl-NIN(, PORTl AND STRENGTH POZZOI ANA SLAG CEM[N I

C£:.Mf.NT PORTa AND CEMENT PORTLAND CFMENT (IS : 455(IS : 269- CEM["If (IS : 269- CEMf:Nr (IS : 1484- 1976)

1976) (IS : 8041- 1976) (IS : 8112- . 1976)1976) 1976)

Physicat Requirements

Fineness:

Specific surface (cm2/ g) , 2 250 3 250 3 200 3 SOO 3000 2 250Min

Setung time, vicar:Initial set t ing time 30 30 60 30 30 30

(minutes), Min

Final selling time (hours), 10 10 10 10 10 10Max

Soundness:Le-Chat e li er method, loa, Sb loa: Sb loa, Sb loa, Sb J()4l, Sh loa,Sb

expansion (rnrn), Max

Autoclave expansion" , 0.8 0.8 0.8 0.8 0.8 0.8percent, Max

Heat of hydration (cal/g),Max:

7 days 6528 days 75

Compressive sr reng t h(kgf/cm2) , Min:

1 day 1603 days 160 275 100 230 1607 days 220 160 330 220 220

28 days 3'0 430 310

Dryina shrinkale (percent), O.ISMax (Conlinu~d)

30

SP t 23-1982

TABl.t: 4 PHYSICAl. ANI) CHEMICAL Ri:QlJIREMENTS or INDIAN STANDAR1) SP[Ll."ll·ATIONSFOR DIFFt:RENT CI:Mf:NTS - Contd

CHARACTERI~TI<

Chemical RequirementsMaximum percentage of

M (Magnesia)

S (Total sulphur contentcalculated as sulphuricanhydride. 503)

ORDINARY RAPID Low HEAT HIGH PORTLAND PORTI AND

PORTlAND HARDENING PORTLAND STRf:N(,TH POZZOlANA Sl AG CI:ML Nl

CEMENT PORTLAND CEMENT PORTLAND CEMENT (IS : 455~

(IS : 269- CEMENT (IS : 269- CEMENT (IS : 1484- 1976)1976) (IS: 8041- 1976) (IS : 8112- 1976)

1976) 1976)

6.0 6.0 6.0 6.0 6.0 8.0

2.75. 3.~ 2.75,3.0' 2.75, 3.D'- 2.75, 3.0<: 2.75,3.OC 3.0

Insoluble residue 2.0 2.0 2.0

Loss on ignit ion

Per mit ted additives(other than gypsum)

Sulphide sulphur

Content of slag, percent

Content of pozzolana,percent

l.imc saturation factor!

Ratio of percent ofalumina to that ofiron oxide

5.0 5.0

1.OC 1.ot

0.66 to 1.02 0.66 to 1.02

?:0.66 ~O.66

5.0

1.(1

~O.66

0.66 to 1.02

~O.66

a - Unaerated, b - Ae-rated (required when sample fails in 'a'), C - When CJA > 7 percent,d - Where x is the declared percentage of pozzolana,e - Air-entraimng or other agents which have proved not to be harmful,

f - Lime saturation factor =: ~~~O - o.7~03 • and2.8 Si02 + 1.2 AI20) + '0.65 FC20 1

x -- Declared percentage of pozzolana In the given Portland pozzolana cement.

"The test I~ to be performed If MgO > 3 percent.

31

SP : 13·1911

TABLE 5 PROPERTIES OF CONCRETE INFLUENCED BY AGGREGATE PROPERTIES

(Cia... 2.2.1.2)

CONCRETE PROPERTY

Strength and workability

Shrinkage and creep

Durability

Resistance to wetting and drying

Resistance to heating and cooling

Abrasion resistance

Alkali - aggregate reaction

Resistance to freezing and thawing

Co-efficient of thermal expansion

Thermal conductivity

Specific heat

Unit weiaht

Modulus of elasticity

Slipperiness

Economy

'RELEVANT AOOREGATE PROPERTY

StrenlthSurface textureParticle shape, flakiness and elonlation indicesMaximum size, gradina. deleterious constituents

Modulus of elasticityParticle shapeGradina ·CleanlinessMaximum sizePresence of clay

Pore structureModulus of elasticity

Coefficient of thermal expansion

Hardness

Presence of particular silicious constituents

SoundnessPorosityPore structurePermeabilityDegree of saturationTensile strengthTexture and structurePresence of clayCo-efficient of thermal expansionModulus of elasticity

Thermal conductivity

Speeifie heat

Specific .ravityParticle shapeGradinaMaximum sizeModulus of elasticityPoisson's ratio

Tendency to polish

Particle shapeOradinaMaximum sizeAmount of processing requiredAvailability

NOTE - Table S is from 'Selectlon and Usc of Aurea-tes for Concrete' Reported by ACI Committee 621 (ACIManual of Concrete Practice, Part I. 1979). American Concrete Institute, USA.

32

SP : 23-1982

TAB"''': 6 LIST OF ROCkS PLACED UNDER THE APPROPRIATE GROUPS

tCtause 2.2.1.2)

IGNEOUS ROCKS

Granite GroupGraniteGranophyre

Gabbro GroupGabbroNoriteAnorthosite

Aplite GroupAplitePorphyry

Dolerite GroupDolerite

Rhyolite GroupRhyoliteTrachyte

Basal' GroupAndesite

GranodioriteDionteSyenite

PeridotitePyroxeniteEpidiorite

Quartz reef

Larnprophyre

FelsitePumicite

Basalt

SEDIMENTARY ROCKS

Sandstone GroupSandstoneQuartziuc (silicified)

sandstone

Limestone GroupLimestone

METAMORPHIC ROCKS

QuartZite GroupRecrystallized quartziteGondite

Granulite and Gneiss GroupsGranite gneissComposite gneiss

Schist GroupSlate

Marble GroupMarble

ArkoseGraywackeGnt

Dolomite

AmphiboliteGranulite

PhylliteSchist

CrystallineLirrlestone

~--------------- - -_._-~_.__.--~_.. . -~ ---- - ----- -----

TABLE 7 EXPECTED RELATIONSHIP BETWEEN VARIOUS Tt:STS FOR DI ....'i:R..:NT ROCK GROUPS

(Clouse 2.2.2.1)

ROCK GROUP CRUSHING AOOREGATE ABRASION IMPACT ATTRITION

STRENGTH CRUSHING VALUE VALUE VA1UF

MN/m2 VALUE ~~

Dry Wet

Basalt 200 12 17.6 16 3.3 5.5

Flint 20S 17 19.2 17 3.1 2.5

Gabbro 19S 18.7 19 2.5 3.2

Granite 18S 20 18.7 13 2.9 3.2

Gritstone 220 12 18.1 15 3.0 5.3

Hornfels 340 11 18.8 17 2.7 3.8

Limestone 165 24 16.5 9 4.3 7.8

Porphyry 230 12 19.0 20 2.6 2.6

Quartzite 330 16 18.9 16 2.5 3.0

Schist 245 18.7 13 3.7 4.3

NOTE - Table 7 is from 'Properties of Concrete (Second Edition, 1973)' by A. M. Neville and published byMIs Pitman Publishing Corporation, Sir Isaac Pitman and Sons ltd, london.

-------------- ---.-,..... --

33

SP : 23-1982

TABLE. PARTICLE SHAPE OF AGGREGATES

(Clause 2.2.2.2)

Ct ASSII-ICATION DE:SCRIPTION

Rounded Fully water worn or completely shapedby attrition

Irregular or partly rounded Naturally irregular, or partly shaped byattrition and having rounded edges

Angular Possessing well defined edges formed atthe intersection of roughly planer faces

Flaky Material, usually angular, Of which thethickness is small relative to the widthand/or length

EXAMPLES

River or seashore gravels; desert,seashore and wind blown sands

Pit sands and gravels; land or dugflints; cuboid rock

Crushed rocks of all types; talus; screes

Laminated rocks

TABLE 9 SURFA('E CHARA(:TERISTI("S OFAGGR..:GATES

TABLt: 10 POROSIT·\ 0.' SOMl: ('OMMONRO('KS

(Clause 2.2,2.2) (Clause 2.2.2.3)

----- ----

NOTE - With certain materials, it may be necessary touse a combined description with more than one groupnumber for an adequate description of the surface tex­ture, for example. crushed gravel of Groups 1 and 2,and oolites of Groups 3 and S.

GROUP SURfACE TEXTURf

(Clause 2.2.2.3)

O.O-~8.0

1.9-15.1

0,0-37.6

0.4- 3.8

POMO'll', Pl-Rl1-NT

ABSORPTION, PfRCENT

0.1-0.3

0.1 ~0.7

0.2 -0.4

0.1-0.6

O.2-0.S

0.2-0.6

0.2-0.6

0.2-0.7

O.2-0.S0.2-9.0

0,2-0.4

2.0-5.0

'I'ABl.f: 11 TYPIC-'AI. RAN(~.=S ()F v Al.lJ.~~ OFABSORPTION 0.- DI.·.·.~R~NT T\ Pt-:S OF ROC'KS

ROCK TYPE

Basalt

Diabase and dolerite

Diorite

Gneiss

Granite

Limestone

Marble

Porphyry

Quartzite

Sandstone

Slate

Travertine

Roes, (iROlIP

Grit stone

Quartzite

Limestone

Granite

NOll: - Table I0 is from •Propcrt U~~ of Concrete(Second Edition, 1973)' b) A. ~t: Neville and publishedby Mis Pitman Pubhshrng Corporation, Sir IsaacPitman and Sons Ltd, London.

EXAMPLE

Black flint

Chert; slate; marble;some rhyolite

Sandstone; oolites

FineBasalt; trachyte;

keratophyre

MediumDolerite; granophyre;

granulite;microgranite; somelimestones: manydolomites

CoarseGabbro: gneiss;

granite;granodiorite;

syenite

Scoriae: pumice; trassHoneycombed andporous

Glassy

Smooth

Granular

Crystalline

5

1

2

3

4

NOTE - Table 11 is from 'Concrete Technology (FifthEdition, 1977)' by F. S. Fulton and published by the-Portland Cement Institute, Johannesburg.

34

SP : 23-1982

TABl..E 12 LIMITS 0." DELETERIOUS MATERIAl..S IN AGGREGATES (PERLt:~TAGt:)

(Clause 2.2.2.4)

DELETERIOUS SUBSTANCE FINE AGVREGA11;5

ru~~~ush~--.A - Cr~sh~d--\COARSE AtJGRElJA ll:~

runcrU~hC~~l~h~'Coal and ligniteClay lumpsSoft fragmentsMaterial passing 7S-micron IS SieveShale

1.001.00

3.001.00

1.001.00

15.00

1.001.003.003.00

1.001.00

3.00

--------------_._--~-~------- - ~--- "-- ~---------

TABl.. f: 13 PROPl-:RTII-.:S 0." SANDS IN THEIR NATlJRAL ('ONl)ITIONS

(Clause 2.2.2.4)

SlNo.

1)

2)

3)

4)

SAMPLES FROM

Jamuna RiverSandMica

Kosi RiverSandMicaGanga RiverSandMica

Bisnumati RiverSandMica

MICA CONTENT

(PERCENT)

11.00

10.00

4.60

10-12

FINENESS

MODULUS

1.000.99

1.521.66

0.69O.5k

2.RI

TYPE~ OF MICA PARTIClFS

Mainly biotite with a small pro­portion of muscovite particles

Mainly biotite with a small pro­portion of muscovite particles

Mainly muscovite with a smallproportion of biotite

TABLl-: 14 MEAt"TIV.: MIN.:RAI..S

(Clause 2.2.2.6)

T ABt..E 15 REA<'-"TIVE R()(~KS

(Clauses 2.2.2.6 and 2.2.3)

NOTE - Opal is deliterious in amounts exceeding 0.25percent by mass of aggregate. Chalcedony is deleteriousin amount exceeding 5 percent by mass of aggregate.Chert is composed as a rule of chalcedony. opal andcrypto-crystalline quartz.

REACTIVE

MINERALS

Opal

Chalcedony

Tridymite

Phyllite

Zeolite

Heulandite

Ptilotite

CHEMKAL

COMPOSITION

Si02

(Hydrous silicates)

PHYSICAL

CHARAL~II:.K

Amorphous

Cryptocry stallinefibrous

Crystalline

REACTIVE ROCKS

Siliceous RocksOpaline chertsChalcedonic chertsSiliceous limestones

Volcanic Rocks

Rhyolites and rhyolitetuffs

Decite and decite tuffsAndesite and andesite

tuffs

Metamorphic Rocks

Phyllites

Mise ellaneous

Any rocks containingveins, inclusions orgrains of the reactiverocks or mineralslisted above

REACTIVE COMPONENTS

OpalChalcedonyChalcedony and/or opal

Volcanic glass, devitrifiedglass and t r idyrnit e(deleterious in excess of3 percent by mass ofaggregate)

Hydromica

3S

NOTE - Table IS is from 'Concrete Technology (FifthEdition, 1977)', by F. S. Fulton, and published by ThePortland Cement Institute, Johannesburg.

SP : 13-1981

1·AB1.t: 16 ('()Nl'ENTRATION OF SOM.~ IMPlIRITI.:S IN MIXIN(; ",'ATERwHI~'H <-'AN Bt: CONSII)..:RI':D AS TOLERABLi:

(Clause 2.3)

IMPURITYSlNo.

1) Sodium and potassium carbonates and bicarbonates

2) Sodium chloride

3) Sodium sulphate

4) Calcium and magnesium bicarbonates

5) Calcium chloride

6) Iron salts

7) Sodium iodate, phosphate, arsenate and borate

8) Sodium sulphide

9) Hydrochloric and sulphuric and other commoninorganic acid

10) Sodium hydroxide

11) Silt and suspended particles

MAXIMUM TOlERABLf CONCENTRA nON

I 000 ppm (total). (If this is exceeded, tests for settingtime and 28 days strength should be made)

20000 ppm

10 000 ppm

400 ppm of bicarbonate ion

2 percent by weight of cement in plain concrete

40 000 ppm

SOO ppm

Even 100 ppm warrants testing

10000 ppm

0.5 percent by weight of cement if set not affected

2 000 ppm

---_.~,._--------------

---------- ~ --------------~---_._-~-.-

TABl~E 17 PERMISSIBLf: LIMIT FOR SOLIDS

(Clause 2.3)

SOLIDS

Organic

Inorganic

Sulphates (as SOt>

Chlorides (as CI)

Suspended mat ter

PERMfSSJ8lF LIMIT, Maxmg/I

200

3000

5002 ()()() for plain concrete workI 000 for reinforced concrete work

2000

~----~----~---------------------------TABLE 18 PH"SICAL REQUIREMENTS FOR CONCRt:TE ADMIXTURES

(Clause 2.4)

REQUIREMENTS

(I)

ACCELERATINO

ADMIXTURE

(2)

RETARDING

ADMIXTURE

(3)

WATER REDUCING

ADMIXTURE

(4)

AIR-ENTRAINING

AOMIXTURF.

(S)

Water content, Max, percentof control sample

Time of setting, allowabledeviation from controlsample, hours:Initial

Max

Min

Fino/

MtlXMin

95

-3 +3-1 +1

± 1

-2 +3 ±1

-1

(Continuedt

36

SP : 23-1982

TARLt. 18 Plt\!~I( AI. Rt"QUIR~M.:~TS.10R lO~( HEll'.. ADMIXTlJRFS - Contd

RfQlItRl-MI-NT~

(I)

ACCELERATIN(J

AO\1IXTURE

(2)

RETARDING

ADMIXllfRl-

(3)

W &\l1:R Rl:DUC INt. AIR-[NTJ{AI~I~(,

ADMIXTURE AO\1IXTl RI

(4) (5)

Cornprevstve strength, percentof control samples, Mtn

3 day, 125 90 110 90

7 days 100 90 110 90

28 days 100 90 110 90

6 months 90 90 100 90

I year 90 90 100 90

Flexural vtrength, percent ofcontrol samples, Min

3 days 110 90 100 90

7 days 100 90 100 90

28 days 90 90 100 90

Length change, percent increaseO\Cf control samples. Max

28 days 0.010 0.010 0.010 0010

6 months 0.010 0.010 0.010 oPI0

I year 0.010 0.010 0.010 0010

Bleeding, percent mcrease over 5 S 5 2control samples. Max

~

~- -- ------------

TARt.: 19 OP1'1MUM AIR CONTENTS OF CONCRETES OF DIFFER....NTMAXIMUM SIZES 0.' AGGR...GATE

(Clause 2.4.4)

MAXIMUM SIZE OF AGGREGATE

(rnm)

10

12.5

20

2540

SO

70ISO

OPTIMUM TOTAL AIR CONTl:.NT

(PERCENT)

8.0

7.0

6.0

5.0

4.5

4.0

3.5

3.0

ApPROXIMATE AMOUNT OF AIR

NATURAL LY ENTRAPPED

(PERCENT)

3.0

2.5

2.0

1.5

1.0

0.5

0.3

0.2

Non - Table 19 is from 'Recommended Practice for Selecting Proportions for Normal Weight Concrete' Reportedby ACI Committee 211 (ACI Manual of Concrete Practice. Part I. 1979). American Concrete Insutute, USA.

37

SP : 13-1982

1 .0

0-8 n------

0.2

0_6 +----- ------ .,- ----

CLU.....-4£t:C>:I:

Zo~ 0.4U«et=u,

o10 100 180

TIME (LOG SCALE) J DAYS

Fig. 1 Rate of Hydra/ion of Pure Compounds

NOTE - Figure I is from 'Properties of Concrete (Second Edition, 1973)' by A. M. Neville and published byMis Pitman Publishing Corporation. Sir Isaac Pitman and Sons Ltd. London.

38

SP : 23-1982

80

70

o

3

~-+-----~~------+-----..".e:.- "C 25 ----------4

10

50

60

20

:t: 40.....ozLaJ

~ 30V')

lLJ>V;VlUJQ:o,~ou

z

N

EE

36090 ieoAGE, DAYS

Fig. 2 Development of Strength of Pure Compounds

287

N01E - Figure 2 is from 'Properties of Concrete (Second Edition, 1973)' by A. M. Neville and thepublisher M/~ Pitman Publishing Corporation, Sir Isaac Pitman and 'Sons Ltd, London.

41

~------+

o ~'-DAY~

+ ~ VEAR

o

o

-------+....

N

Ee-z

:x: 3S~

oZUJa-t-V)

lLJ>V\V)

UJ 2.C%Q.:l0u

212SlO 2110

CEMENT FINENESS ( BLAINE) • em 2, 9

Fig. 3 Relationship Between Strength of Concrete at Different Ages and Fineness of Cement

39

9028

AGE, DAYS

Fig. 4 Calculated Temperature RISe of Different Cements Under Adiabatic Conditions

SP : 13-1982

27

24

21

0 18u

L&J 150:::::Jt-<l 12a:~ 9~WJto- 6

3

00 1 2 3 7

NOTE - Figure 4 IS from 'Concrete Technology (Vol I, Fourth Edition. 1979)' by 0 F Orchard and published byApplied SCience Publishers Ltd, London

84

iI

N 70 ­EE

I

1~,

HIGH ALUMINA

~~--~I

--t-----

--~-- - T

902873

O ............-.:.:&.::;1;;;....-----'- -J- .J- ..1

o ", 1/4 1/2 3/4 1

AGE,DAYS

Fig. 5 Strength-Age Relationships for 1:2:4 Concrete by Weight Made With Different Cements

NOTE - Figure S ,~ from 'Concrete Technology (Vol I. Fourth Edmon. 1'79)' by D F Orchard and published by ApphedSc.1ence Publishers Ltd, London

40

SP : 13·1982

60 60 -~ i-_SO I

ILLJ ~'O II-

4,

UJ~30~ 50

U C)Z 00 =20 -U

LL 40 ~15ON -ZJ: E '--~O 0l- EC>z "

30UJ Za:to- ,

5V'l -, u 0.1 0.2 0.3 O~ o.sQ60..7.... 20 --XhlLOG SCALI) ~--eUJ> I 0

ViU1UJ I

Q: 10 -t~ -ct. I

~0U

0 .....--......-------.......------ .....__...........o 0.1 0.2 0.3 0.4 0.5 0.6

HYDRATE-SPACE RATIO (Xh)

Fig. 6 Relationship Between Compressive Strength and Hydrate-Space Ratio

6 0 ~-......------r------------------....

50

PORTLANDN BLAST- FURNACEe~

z 40~

ORDINARy PORTLAND..X...~

30ZLUIX....V')

UJ> 20i1\(/)

UJ~Q.~0 10U

o 7 28 AGE, DAYS "Fig, 7 Strength Development oJ Concretes Made with Portland Blast-Furnace Cement

(Water-Cement Ratio = 0.6)

NOTE - Figure 7 is reproduced from •Properties of Concrete (Second Edition, 1973Y by A. M. Neville and publishedby Mis Pitman Publishing Corporation, Sir Isaac Pitman and Sens Ltd, London.

41

SP : 13·1982

::c....ozw~....U)

zUJU 1~-Ha-~---~~------t--------exUJe,

AGE, DAYS

21

Fig. 8 Strength Development of M 15 Concrete Made with Portland-Pozzolana Cement(Water-Cement Ratio::: 0.55)

42

SP : 13·1981

180

o

......... ---.. x---

GRAVELQUART Z

LIMESTONE

QUARTZ

LIMESTONE

120

•

SAND• QUARTZ

e QUARTZ

x LIMESTONE

o LIMESTONE

60

E 6-8E\Dt")

N•'-'w •~ 6-6

"w~'"cJc(

(/) UJen

:::> ac-' :;)

::> 0c u0:%

~ 0UJZUJZu..

E:L0Ln....•E 2-0E

CDCW).N

CZ~en '·8 0

MIXING TIME, NINUT ES

Fig. 9 Effect of Prolonged Mixing on Fineness Modulus of Sand and Gravel Sizes

43

SP : 23-1982

--- - -- ---+---#-

I--- --1--­

III

I22...-------+---~

23

171--------+-~---+_---__4~---__+_----+_---____t----_4

("'") 21E

C1'~

... 20Zw....Z0u

C% 19 ----UJ.....-:l~

C)Z 18 --- -- -------- ---~ -s~

so46423116 ....----....----.....---.....----.....----....-----~----..

36

'1010 CONTENT t PERCENT

Fig. 10 Influence of Void Content of Sand in a Loose Condition on the Mixing WaterRequirement of Concrete

NOTE - Figure 10 is from 'Properties of Concrete (Second Edition, 1973)' by A. M. Neville and published by PitmanPublishing Corporation, Sir Isaac Pitman and Sons Ltd, London.

44

SP : 23·1981

e-o3·02·0

a--.....•

O'--__J--__.....L-__....I..-__........__--'-__-.....__-..-.Io...-.__......_---'

o

0. SERIES (AVERAGE OF 6 TESTS /POINT) REL f:=100-'-921·/ CLAY)20 6 C SERIES (AVERAGE OF 3 TESTS I POINT) CORRELATION -

o E SERIES (AVERAGE OF 3 TESTS IPOINT) COE;FFICIEN =0·19• B SERIES (AVERAGE OF 6 TESTS /POINT)

10 -

10

'0

120 ------------------.-----...,.-----.---,....-----.

100

t%.....ozwa:....enw~CI)(/)w~Q.

~ou

~C

I•N

AMOUNT OF CLAY (-/. Of TOTAL AGGREGATE BY WEIGHT)

Fig. 11 Influence ofAmount ofClay Fraction on 28-Day Compressive Strength

45

SP : 13-1981

00

rII

Jl

- l

I-~._.~

~-~tit 0 •h--

I ~

J ~

• 4

~,

-- -,---1.. A •~~---. ~ ~- .:~"NOCUOUSAGGRfGAT!S

,. ::.~\&

,,

at!

", .. A.'" DELE fER'OU$t1I _XX XJ~ • AGGREGATE 5_. •• I X X•

••• 0° • :/ ,I •

X ••,

, 2-5 5-0 '0 25 SO '00 2S0 SOO 1000 l~o

'00

700

600

7-5 'IS 750SILICA DISSOlVED. F"OM 300 TO ,~ MICRONS SIZ[ AGGREGATE

MATERIAL (M'L'WOLES ILITAE) BV 1 N MIOH SOLUTiON (QUANTlT't.Se)

Aggregate causing mortar expansion more than 0.1 percent in ayear when used with a cement containing 1.38 percent alkalis

o Aggregate causing mortar expansion 18S8 than 0.1 percent In a yearunder same conditions

x Aggregat•• for which mortar expansion data are not available butwhich are Indicated to be deleterious by petrographic examination

• Aggregat•• for which mortar expansion data are not available butwhich are Indicated to be lnnccuous by petrographic examination

Boundary line between Innocuous and deleterious aggregates

Fig. 12 Illustration of Division Between Innocuous and Deleterious Aggregates on Basis ofReduction In Alkalinity Test

46

SP : 13·1982

1200r--------..,..-------.,.--------~------....

NORMAL WEIGHT

• ... '8... - ---~..... - .. --.- __~ ...---·--3

~ ,- __ 4 - - - _. - -

LIGHT WEIGHT AGGREGATE........A-NO-....l

-~ l,~ ---.- -7

----. 80019

...e,wwexu

400

o 100 200 300 400

TIME UNDER LOAD, DAYS

Fig. 13 Creep of Concrete of Nominal 210 kg//crn2 Strength Made with DifferentLightweight Aggregates, Loaded at the Age of 7 Days to 42 kg//ern2

NOTE - Figure 13 IS taken from 'Creep of concrete Plain, Reinforced and Prestressed' (1970) by A MNeville and published by North-Holland Pubhshmg Company, Amsterdam

10---- RAJID IHARDENING ~ce ME NT

(2 ./. CAl(IUfl4 CHLORtDE.?~ ,;......--- ~

>/~ ",~~... ~ ,

~\~t>,.... ,-

~~ --

RAPID

" ~11HARDENINO V ",V ()~ .,CEMENT

~ ()~~ <:-:. /,NO ADDITIVEJp(" .It.''' V ,.\ .~

~-~

~ ~ ~ - ~

V -, :/V A.../ NOR ~Al

I- - ~ PORTLANO-

/ ~,.... #fJ

"CEMENT

~. (NO ADOIYlver-

V ~~ '" ~

--- ----~

~V ", NORMAL~ PORllANOa ~

~ ,/ CE~E NTf' - ~ - .. ( 1 ./. CA l Cl UN CHLO~ toe ~

" ~ I I 1~ ,. ~ - f---

/' "

70

N60E

E<,Z

50..J:to-o

40Zwa:~

V)

30w>'-'ltJ),UJ 20a:Q.

~0U 10

o6

"'--12 3 4 5 7 10 14 28

--- __~_.--J

HOURS

"'--DAYS~

AGE

Fig. 14 Compressive Strength of Normal and Rapid Hardening Cement with2 Percent Calcium Chloride Addition

NOTE - Figure 14 I~ from 'Concrete Technology (Fifth Edition, 1977)' by F. S Fulton and pubhshed byPortland Cement Insntute, Johannesburg

47

SP : 13·1912

'0,•7

.~~- W/C :O·S'J. NORMAL DOSE

,5432

0.70N

E~ 0.60

Z

UJ 050uZ~.....U'l 0.40~I.&JCt

Z0.30

0t-eltt 0.20I-UJZUJCL 0.10

0.000

TIME HOURS

Fig. /5 Effect of Retarding Admixtures on Retention of Workability

48

0.95

0.90

~ 0 ..... u -ex ~

~

o'C

Z ~ U <l c,

0.85

~ 0 U

Q.8

()

--, ,

"-"-

"

I"" "

"I

'"I

"'"-~

r-----

..,~~

......

--... ....

........

.I--

----

¥IIC

=O

.60

+A

O...

IXT

UR

E~~~

....

....

.I-

---L

-_

__

__

__

__

__

__

__

__

__

__

__-

.

fw

/c

=0

.61

........

.....

315

30

TIM

EA

FT

ER

TH

EC

OM

PL

ET

ION

OF

MIX

ING

,m

in.

60

TJJ~

Fig

.16

Eff

ect

of

Wat

erR

educ

ing

Adm

ixtu

reon

the

Wor

kabi

lity

of

Con

cret

eN ~ . .. ~ Q

ON

SP : 13·1912

J:.... ot 0.15oZUJ...J

1" 0 10~

LU... 0.05C>

ZclJ:

0U

•.....•11 0

100 200 300 400

NUMBER OF FREEZE - THAW CYCLES

Fig. 17 Eflect of Air-Entrainment on Freeze-Thaw Durability oj Concrete

so

REFERENCES

IS 456-1978 Code of practice for plain and reinforced COOl-rete (third revisions

2 IS 269-1976 Speoficanon for ordinary and lowheat Portland cement (third revtsiom

3 I~ 8041 1978 Specifrcanon for rapid hardeningPortland cement (first revtstoni

4 IS 455-1976 Specification for Portland slag vement (third revtstomIS 1489 1976 Specrhcauon for Portland POl

zolana cement (second revtsions6 IS 8112 1976 Speuncauon for high strength or

dmary Portland cement7 IS 8043 1978 Specification for hydrophobic

Portland cement (flr~t revisions8 IS 6452 1972 Specification for high alumina ce

ment for structural use9 IS 6909 1973 Specrfrcauon for supersulphated

cement10 I'S 1343 1980 Code of practice for prestressed

concrete tftrst revu/on)11 NEVILLE (A M) Properties of concrete 1973 Pit

man Pubhshmg12 LEA (F M) The chemistry of cement clod concrete

1970 Edward Arnold (Pubhsners) Ltd13 HIGGINSON (E C) The effect of cement fineness on

concrete ASTM Special Technical Pubhcauon473 1970 American Society for Tesnng andMaterials

14 CRJ Cement Standards of the- World, ~P-1-77

Cement Research lnsutuu of lndra, New Deihl1978

IS ORLHARD (D ~) Concrete Technology Vol 1Thud Edition J973 Applied Science PublishersLimited, I ondon

16 \\'ILlIAM~)N (R B) Sohdifuauon of Portland ce­ment University of Cahforrua Report No U(SE:SM 70 - 21 Berkeley, 1970

17 VI:.RBl:LK (G J) and HELMUTH (R A) Structure andph) su.al properties of cement paste Proceedingsoj the Fifth International Symposium on theChemistry of Cement, Tokyo 1968 Part III, P1-44

18 MILL'> (R H) Collapse of structure and creep Inconcrete Proceedtngs oj the International Conjerence on Structure, Solid Mechanu s andEngineering Design If' CIvil Engtneenng MaterialsSouthampton, P 751 68

19 Powr.as (T () Physical properties of cementpaste Proceedings of the Fourth InternationalSymposium on the Chemistry of Cement,Washington 1960 Nauonal Bureau of Standards,Monograph 43, VII, Sesvion V, P 577 609

20 POW~RS (T C) and BROWNYARD (F Ll Studies ofthe physrcal propcrues of hardened Portlandcement paste PC A Bulletin 22 4947

21 Mill ~ (R H) Factors Influencing cessauon ofhydration In water cured cement pavtes Syrnposium on Structure of Portland Cement Pavteand Concrete Highway Research Boai d SpecialReport 90, 1966, P 406 24

22 VISV['i\ARA' A (H C) and MULLICK (A K) Relationbetween water content in concrete mixes and lornpre s srvc strength ~econd l nrc r nat i o na l(IB/RIL~M ~ympo"lum on MOisture ProblemsIn BUilding The Netherlandv, 1974

23 KOJ.URlI (M) J-I~ Avh and I ly Ash Cement Proce~dlngs of Iht' fifth Internallonal f)vn,poslufn onthl' ( hl'1nlHrv of ("'I.~,nenl ToA} 0 I Q68 Part IV P

51

SP : 23-1982

75-10524 IJT Prehrmnary report on the Investigations con

ducted on factory made pozzolana cement Structural Engmeenng Laboratory, Indian Institute ofTechnology, Madras, 1976

2~ ACI Committee 201 GUide to durable concrete JAmer Concr Ins! 74, 12, 1977, P 573-609

26 IS 4031 1968 Methods of physical tests forhydrauhc cement

27 IS 4032 1968 Method of chermcal analysis ofhydraulu.. cement

28 AC.l Committee 621 Selection and use of aggregates tor concrete ACI Manual of ConcretePractice, Part L 1974

29 IS 383 1970 Specifrcanon for coarse and fine aggregates from natural sources for concrete (secondrevtstom

30 IS 2386 (Part IV) 1963 Methods of test for aggregates for concrete Part IV Mecharnsal propernes

31 as 882 1965 Specrfrcauon for coarse and fine aggregate from natural soun..es Bnush StandardsInstitution

32 NRMC.A Aggregate degradation dunng mixingNRM( A Technical Information Letter No 3411978 National Ready Mixed Concrete ASSOClanon

33 l-LJI TON (f ~) Concrete Technology 1977 ThePortland Cement Insutute, Johannesburg

l4 I~ 2386 (Part 11) 1963 Methods of test for aggregatex for concrete Part II Esumauon ofdeletenous matenal.. and organic impunues

15 BUTH (E), IVEY (D 1 ) and HIRSCH (T J) Dirty aggregares, what difference does It make? Hlgh\\ayRevearch Record No 226 1968 Highw a)Research Board

36 A~TM l 33 78 Speuncauon for concrete aggregates Amencan Societv tor resting andMatenals

l7 I~ 21R6 <Part VI) 1963 Methods of test tor aggregates for concrete Part VI Measuring mortarmaking proper: IC~ of fine aggregate

38 HOON (R C) and SHARMA (K R) The selecnon,procevsmg and specrtrcanon of aggregate for concrete for large dams-e-Effect of employingmicaceous sand a, fine aggregate fracuon on theproperties of cement mortar and concrete Proceedtngs of the Seventh Congress of the Internauonal Commission on Large Dams J96J Rome

19 GOKHAL I- (Y C) Economic aspects of themanufacture of COOl-rete for general constructionIn Kathmandu Valley, Nepal Ind Caner J 36,5,1962, 185-89

40 HOON (R C), SHARMA (K R) and <;;HARMA (5 ~)

'-- ernent mortars and concrete mix design, Effectof mica contained In sand fracuon on the properties of mortar and concrete J National BUildingsOrgantratton 5, 7. 1960, 38-52

41 HOON (R C) and VENKATFSWARlU (V) Benefu ranon of nucaveous sand for use av fine aggregatelnd C oncr J 16 7, 1962 256-63

42 II V.l~ (A F G) Sea dreged aggregate for concreteProceedings of a S) InpOSIU1n held at FulmerGrange, BucAlnghamshtre 1968 Sand and GravelAsvocranon of Great Bntain

41 J~ 2~86 (Part V) 1961 Method, of test for aggregates for concrete Part V Soundnevs

44 AC I 22) R-61 Selecuon and use of aggregate forconcrete A( I Manual of t oncrete Pralth..e, PartL 1979

SP : 13·1982

4S DOLAR - MANTuANI (l) Soundness anddeleterious substances Significance of tests andproperties of concrete and concrete makingmatenals, ASTM STP 1698 American Society forTesnng and Materials 1979 P 744-761

46 FRENCH (W J) and POOLE (A B) Alkah -aggregatereactions and the MIddle East Concrete 10, I,1976, 18-20

47 MATHER (B) New Concern Over Alkali-AggregateReaction NRMCA Pubhcanon No 149 1975National Ready Mixed Concrete Association

48 FRENCH (W J) and POOLE (A B) Deleterious reaclions between dorormtes from bahrain and cementpaste Cern Caner Res 4, 6, 1974, 925-37

49 SMITH (P) Learning to hve with a reactive car­bonate rock Proceedings of the Symposium onAlkali-Carbonate Rock Reacnons HighwayResearch Record No 4.5, 1964 HIghway ResearchBoard

SO NEWLON (H H) and SHERWOOD (W C) Methodsfor reducing expansion of concrete caused byalkali-carbonate rock reaction Proceedtngs of theSymposium on Alkatt..Carbonate Rock ReactionsHIghway Research Record No 4S, J964 HighwayResearch Board

S1 IS 2386 (Part VII)-1963 Methods of test for aggregates for concrete Pan VII Alkah aggregatereactivity

S2 SWENSON (E--G) Reactive aggregates undetected byASTM tests ASTM Bulletin No 226 19S7 P48-51

53 WASHA (G W) Volume change Sllnlflcance oftests and properties of concrete and concrete mak..mg materials ASTM Special Technical Pubhcalion No 169-A 1966 American Society forTesting and Materials

.54 JAOUS (P J) and BAWA (N S) Alkali-aggregatereaction In concrete pa\ ement, Road ResearchBulletin No 3, 1957, Indian Roads Congress, NewDeihl

SS GooTE (8 S) An evaluation of some commonIndian rocks With special reference of alkali­aggregate reacuons Engg Geology 7, 2, 1973,P 13's-153

,56 IS 9142 1979 Specifrcauon for artrfrcralbghtwetght aggregates for concrete masonry units

~7 IS 2686-1977 Specmcauon for CInder aggregatesfor use In lime concrete (first reVISion)

58 NEVILLE. (A M) Creap of concrete plain, reinforced and prestressed 1970, North - HollandPubhshmg Company - Amsterdam

59 ACI Committee 213 GUide for structuralhahtwelght aggregate concrete ACI Manual ofConcrete Practice, Part I, 1974

60 TOBIN (R E), HOLM (T A), RASMUSSEN (P c." andMc MANUS (R N) Changes In the forthcomingrevised ACI bUilding code relative to structurallightweight concrete ACI Pubhcation SP 29Lightweight Concrete 1971 Arnencan ConcreteInstitute

61 STEINDUR (H H) Concrete mix water - How rrn

52

pure can at be') peA Research Department Bulk (I

119, 1960 Portland Cement Association Resear...and Development Laboratories

62 Me COy (W J) MIXing and cunng water for concrete Ssgmfrcance of tests and properties of concrete and concrete making matenals ASTMSpecial Technical Pubhcauon No 169 A 1966American Society for Testing and Materials

63 Requirements of rmxing water for concrete IndConcr J 3,1963,95, 98 and 113

64 SHALON (R) and RAPHAEL (M) Influence of seawater on corrosion of remforcement J A merCaner (Prj SS,6, 1959, 1251-68

65 12-CRC Committee Corrosion of reinforcernentand prestressing tendons, A State-of the ArtReport Mal Struct 9, 51. 1976, 187-206

66 GUTT (W H) and HARRISON (W H) Chemicalresistance of concrete Concrete 11, S, 1977,35-37

67 Ie;; 9103 1979 Specifrcanon for admixtures forconcrete

68 IS 3812 (Part 11)·1981 Specificanon for flyashPart II For use as admixture for concrete (ftrstrevtsiont

69 IS 1344-1982Specificanon for calcined clay POlzolana (second revtstom

70 MIELl'NZ (R C) Chemical and air ..entraining admixtures for concrete National Ready MixedConcrete ASSOCIation Pubhcanon No J32, 1970

71 Rrxov (M R) Wtiler reducing admixtures for concrete Concrete admixtures use and apphcauons1977 The Construction Press LImited, England

72 ASTM C 233 76 Standard method of tesung airentraimng admixtures for concrete ArnencanSociety for Testing and Materials

71 IS 7861 (Part II) 198J Code of pracnce for extreme weather concrenng Part II Recommendedpractice for cold weather concreting

74 IS 7861 (Part I) 1975 Code of practice for extreme weather concreting Part I Recommendedpractice for hot weather concretmg

7S HEWLETT (P C) An mtroducnon to and aclassifrcanon of cement admixtures Concrete admixtures use and apphcauons 1971 The Construcnon Press LImited, England

76 GHOSH (R K), CHATIFRJEE (M R), BHATIA (M l )and BHATNAGAR (R C) lnvestrgauon on sugarmixed concrete for pavements Road ResearchBulleun No 17, Indian Roads Congress, 1973

77 "LETCHER (K E) and R08ERT~ (M H) Test methodsto assess the performance of admixtures In concrete Concrete s.s, 1971, J42 48

78 HUSSEll (D J T) Freeze thaw and seating tests onSIlicone treated concrete Highway ResearchRecord No 18 1963 Hlghwd)' Research Board

79 BENNETT (K) AIr entraining adrruxtures for Loncrete Concrete adrmxtures Use and applicanons1977 The Construcuon Press Limited, England

80 ACI 211 1 71 Recommended prac nee for selecnngproportions for normal weight concrete ArnencanConcrete Institute

SECTION 3

PROPERTIES OF FRESH AND HARDENEDCONCRETE

SECTION 3 PROPERTIES OF FRESH AND HARDENEDCONCRETE

3.0 Introduction - Concrete has to havesatisfactory properties both in the fresh andhardened states. While workability as defin­ed below is the cardinal desirable property offresh concrete, strength and durability arethe most important properties of concrete inthe hardened state. As was brought out inSection I, demand of satisfactory propertiesof concrete in the fresh and hardened statesmay often bring conflicting requirements inthe material and mix proportions; the aim ofthe rational mix design is also to reconcilethese factors.

In this section, these important propertiesof concrete, namely, workability, com­pressive and tensile strengths and durabilityare discussed along with the various factorswhich influence them.

3./ Workability ---From the stage ofmix­ing till it is transported, placed in the form­work and compacted, fresh concrete shouldsatisfy a number of requirements which maybe summarized as follows:

a) The mix should be stable, in that itshould not segregate during transpor­tation and placing. The tendency ofbleeding should be minimized.

b) The mix should be cohesive and mobileenough to be placed in the formaround the reinforcement and shouldbe able to cast into the required shape.

c) The mix should be amenable to properand thorough compaction as possiblein the situation of placing and with thefacilities of compaction.

d) It should be possible to obtain asatisfactory surface finish.

The diverse requirements of stability t

mobility, compactability, placeability andfinishability of fresh concrete mentionedabove are collectively referred to as'workability'. The workability of fresh con­crete is thus a composite property. It is dif­ficult to precisely define all the aspects in asinaJe definition. IS : 6461 (Part VII)-1973 1

defines workability as 'that property offreshly mixed concrete or mortar which

S5

determines the ease and homogeneity withwhich it can be mixed, placed. compactedand finished ........•. It is also clear thatthe optimum workability of concrete variesfrom situation to situation and concretewhich can be termed as workable for pour­ing into large sections with minimum rein­forcement may not be equally workable forpouring in thin sections with heavier concen­tration of reinforcement. A concrete maynot be workable when compacted by handbut may be satisfactory when mechanicalvibration is used.

3. J.l DIFFERENT MEASURES OF WORK­

ABILITY - There are different methods ofmeasuring the workability of fresh con­crete. Each of them measures only a par­ticular aspect of it and there ig. really no uni­que test which measures workability of con­crete in its totality. Although new testmethods are being developed frequently,IS : 1199-19S92 envisages the following threemethods:

a) Slump test,b) Compacting factor test, andc) Vee-Bee consistency test.

Out of these three, the slump test isperhaps the most widely used, primarilybecause of the simplicity of the apparatus re­quired and the test procedure. For such con­cretes where slump test is suitable (seebelow), the concrete after test slumps evenlyall round which may be called 'true slump'.When the mixes are harsh or in case of verylean concrete one half of the cone may slidedown the other which is called a 'shearslump'; or it may even collapse (Fig. 183) .

Apart from some conclusion being drawnregarding the harshness or otherwise of themix, slump test is essentially a measure of'consistency' or the 'wetness' of the mix.The test -is suitable only for concretes ofmedium to high workabilities (that is, slump25 to 12S nun). For very stiff mixes havingzero slump, the slump test does not indicateany difference in concretes of differentworkabilities. It has been pointed out thatdifferent concretes havina the same slumpmay have indeed different workability under

SP : 23·1982

the site conditions. However, when theuniformity among different batches of sup­posedly similar concretes under field condi­tions is to be measured, slump test has beenfound to be useful".

The compactability, that is, the amount ofwork needed to compact a given mass ofconcrete, is an important aspect ofworkability. Strictly speaking, compactingfactor test measures workability in an in­direct manner, that is, the amount of com­paction achieved for a given amount ofwork. This test has been held to be more ac­curate than slump test, specially for concretemixes of 'medium' and 'low' workabilities(that is. compacting factor of 0.9 to 0.8). Itsuse has been more popular in laboratoryconditions. For concrete of very lowworkabilities (that is, compacting factor of0.70 and below which cannot be fully com­pacted for comparison, in the mannerdescribed in the test method) this test is notsuitable.

Vee-Bee test is preferable for stiff concretemixes having 'low' or 'very low' workability.Compared to the other two tests, Vee-Beetest has the advantage that the concrete inthe test receives a similar treatment as itwould be in actual practice. Since the endpoint of the test (when the glass plate ridercompletely covers the concrete) is to beascertained visually, it introduces a source oferror which is more pronounced for concretemixes of high workability and consequentlyrecords low Vee-Bee time. The test istherefore, not suitable for concrete of higherworkability that is, slump of 75 mm orabove.

Experience has shown that mix propor­tions influence the workability of concrete,and more pertinently, different workabilitytests to different extent. Therefore, it isfutile to expect a rilid correlation betweenthe workabilities of concrete as measured bydifferent methods. Table 20' attempts todescribe different workabilities of concretein terms of slump, Vee-Bee time and com­pacting factor. The table Jives the range ofexpected values by different test methods forcomparable concretes may 8iv~ an indicationof the correlation between them. SimilarlyFiS. 19' indicates a general pattern of rela­tions between workability tests for concretemixes hlvins varying _saregate-cementratios. In the absence of definite correlations

56

between the different measures of workabili­ty under different conditions, it is recom­mended that, for a given concrete, the ap­propriate test method be decided beforehandand workability expressed in terms of suchtest only rather than interpreting from theresults of other tests.

3.1.1 FAcrORS AFFECTING WORKABILITY­The workability of fresh concrete dependsprimarily on the materials and mix propor­tions and also on the environmentalconditions. These are discussed in 3.1.2.1and 3.1.2.2.

3.1.2.1 INFLUENCE OF MATERIALS AND MIX

PROPORTIONS - While a number of relationsbetween the various mix parameters andworkability of fresh concrete are available, arational approach to unify the effects of dif­ferent mix variables can be sought in thecement-aggregates-water system. Aggregatesoccupy nearly 70 to 75 percent of the totalvolume of concrete and economy demandsthat the volume of aggregates in the concreteshould be as large as possible. The particleinterference as well as the total specific areaof the aggregate are to be minimized to theextent possible by the proper choice of size,shape and proportion of fine and coarse ag­gregates. Different size fractions are to be sochosen as to minimize the voids content.Such a dry mixture of aggregates havingminimum voids content will not be mobileand will need water for lubricating effects.The water-cement ratio in itself determinesthe intrinsic properties of the cement pasteand the requirements of workability are suchthat there should be enough cement paste tosurround the aggregate particles as well as tofill the voids in the aggregates. On anengineering scale. the water content of themix is the primary factor governing theworkability of the fresh concrete. Theworkability increases with the water contentas shown in Fig. 20',' and displays a relation­ship as follows":

y=cwPwhere

y = specified consistency value(for example, slump);

C = term which depends on thecomposition of the concrete(cement content, air content,aggregate grading, etc) andmethod of measuring con-~istency;

w = water content of fresh con­crete; and

n = depends on the maximum sizeof aggregate.

This relationship implies that the amountof change in the measured value ofworkability (for example, slump or compac­ting factor) due to relative change of watercontent in concrete is independent of thecomposition of concrete within wide limits.As an example, Table 21 10 indicates thechanges in the workability in terms of slumpthat can be expected with relative changes inthe water content in the mix, taking thewater requirement for a 40 mm slump asunity.

Next in importance are the aggregate pro­perties, the effects of which can be sum­marized as follows:

a) For the same volume of aggregates inthe concrete, use of coarse aggregatesof larger size and/or rounded ag­gregates gives higher workabilitybecause of reduction in the totalspecific surface area and particle in­terference. Use of flaky/elongated ag­gregates results in low workabilityprimarily because of increase in parti­cle interference.

b) The use of fine sand with correspond­ing increase in specific surface areaincreases the water demand for thesame workability or conversely for thesame water content, workabilitydecreases. If the sand is very coarse,the net effect on workability is. in­crease in particle interference anddecrease in specific surface area.

c) Because of the greater contribution tothe total specific area, the grading ofthe fine aggregates is more critical thanthe grading of coarse aggregates.Nevertheless, the proportion of fine tocoarse aggregates should be so chosenas neither to increase the total speci fiesurface area (by excess of fine ag­gregate) nor to increase the particle in­terference (due to deficiency in fineaggrega te) .

d) Once the water content in the mix isfixed, there is some relation betweenthe water-cement ratio and the gradingof the aggregates. It is seen in practicethat there would be one optimum com­bination of coarse and fine aggregates

57

SP : 23-1982

resulting in the highest workability fora given water-cement ratio). Generally,mixes with higher water-cement ratiowould require a somewhat fine gradingand for mixes with low water-cementratio (as in the case of high strengthconcrete), coarser grading is pre­ferable.

From the consideration of workability,the mix parameters are expressed in terms ofwater content, water-cement ratio and pro­portion of fine to coarse aggregates; oncethis is done, the aggregate-cement ratio isautomatically fixed. Influence of the factorslike grading and maximum size of aggregatesand aggregates-cement ratio on theworkability is discussed in more detail inSection S.

3.1.2.2 EFFECTS OF TIME AND TEMPERATURE

ON WORKABILITY - Fresh concrete loosesworkability with time mainly because of lossof moisture due to evaporation. Part of mix­ing water is absorbed by aggregates or lostby evaporation in the presence of sun andwind and part of it is consumed in thechemical reaction of hydration of cement.The loss of workability varies with the typeof cement used. the concrete mix propor­tions, the initial workability and thetemperature of the concrete. On an average,a 12 em slump concrete may loose about5 em slump in the first one hour. Theworkability in terms of compacting factordecreases by about 0.10 during a period ofone hour from the time of mixing. Theworkability of concrete mix appears to berelatively stable during the period from 15 to60 minutes after the completion of mixing(see Fig. 21 11) . Although the standardmethods of test for workability imply thattests be carried out soon after mixing, Flet­cher!' suggested that for general purposes,workability of fresh concrete should bedetermined not sooner than 15 minutes norlater than 20 minutes, after the completionof mixing especially where placing of con­crete is likely to take so much time or longer.Such decrease in workability with time aftermixing may be more pronounced in con­cretes with admixtures like plasticizers.Evaluation of workability at a certain timeafter mixing is perhaps more necessary thanin normal concretes without admixture.

The workability of a concrete mix is alsoaffected by the temperature of concrete and,

SP : 23-1982

therefore, by the ambient temperature. On ahot day. it becomes necessary to increase thewater content of the concrete mix in order tomaintain the desired workability unless otherprecautions are taken (see 7.J.2). Theamount of mixing water required to bringabout a certain change in workability alsoincreases with temperature. Fig. 2212 showsthe effect of concrete temperature on theworkability of concrete (in terms of slump)and the percentage change in water re­quirements per 25 mm change in slump, fordifferent concrete temperatures.

3./.3 REQUIREMENT OF WORKABILITY - Inaddition to the desired compressive strength.the concrete should have workability suchthat it can be placed in the formwork andcompacted with the minimum effort,without causing segregation or bleeding Thechoice of workability depends upon the typeof compacting equipment available, the sizeof the section and the concentration of rein­forcement. For heavily reinforced sectionsor when the sections are narrow or containinaccessible parts or when the spacing of rein­forcernent makes placing and compactiondifficult, concrete should be highly work­able for full compaction to be achieved witha reasonable amount of effort. Table 2213

gives range of workabilities required in termsof slump, compacting factor and V-B timefor concretes depending upon the placingconditions at site. It may be noted that thenominal maximum size of aggregates itselfmakes a difference in the degree ofworkability that may be suitable u.ider a par­ticular placing condition. The range ofvalues indicated are considered suitable forconcretes having aggregates of nominal max ...imum size 20 mm. Generally the value ofworkability will increase with the increase inthe size of aggregate and will be somewhatlower for aggregates of smaller size than in­dicated.

Notwithstanding the guidance forworkability given tn Table 22, the situationat hand should be properly assessed to arriveat the desired workability in each case. Theaim should be to have the minimum possibleworkability consistent with satisfactory plac­ing and compaction of the concrete. Itshould be remembered that insufficientworkability resulting in incomplete compac­tion may severely affect the strength,durability and surface finish of concrete and

58

may indeed be uneconomical in the long run.The effectiveness of vibration equipmentavailable for compaction should also betaken into consideration.

3.2 Compressive Strength - The com­pressive strength of hardened concrete isconsidered to be the most important proper­ty. It can be measured easily on standard siz­ed cube or cylindrical specimens and is oftentaken as an index of the, overall 'quality' ofconcrete. Many other desirable properties ofconcrete, for example shear and tensilestrength, modulus of elasticity, bond, im­pact, abrasion resistance and durability etc,are also taken to be related to the com­pressive strength, at least to a general extent.

Among the materials and mix variables,water-cement ratio is the most importantparameter governing compressive strength.Besides water-cement ratio, the followingfactors also effect the compressive strengthof concrete:

a) The characteristics of cement,b) The characteristics and proportions of

aggregates,c) The degree of compaction,d) The efficiency of curing,e) The temperature during the curing

period,f) The age at the time of testing, andg) The conditions of test.

The influence of mix proportions, placing.compaction, curing and age of testing, onthe compressive strength of concrete arediscussed in 3.2./ to 3.2.3.

3.2. J INFLUENCE OF MIX PROPORTIONS

a) Water-cement ratio -- The com­pressive strength of concretes at a givenage and under normal temperature,depends primarily on the water-cementratio; lower the water-cement ratio,greater is the compressive strength andvice-versa. This was first enunciated byAbrams as:

K IS=-~·_­

KWIC

2

where S is the compressive strength andw/c represents the water-cement ratioof a fully compacted concrete mix, andK, and K 2 are empirical constants.

In day to day practice, the constantsXI and K, are not evaluated; insteadthe relationship between compressivestrength and the water-cement ratio areadopted, which are supposed to bevalid for a wide range of conditions.These relationships are discussed inSection 6.

b) Aggregate-cement ratio - The in­fluence of the physical characteristicsof the aggregates on the compressivestrength of concrete was discussedearlier in Section 2. As long as theworkability of concrete is maintainedat a satisfactory level, the compressivestrength of concrete had been found toincrease, with increase in aggregate­cement ratio, the water-cement ratiobeing held constant'. However, inhigh-strength concrete mixes of lowerworkability, or in such situationswhere due to increase in aggregate­cement ratio the workability is reducedto such an extent that concrete cannotbe properly placed and thoroughlycompacted, Ihe above is not true. Inhigh-strength mixes of low workabili­ty, a decrease in aggregate-cement ratiomay result in small increase in com­pressive strength, provided the watercontent in the mix is also reducedproportionately (Fig. 2314) ;

c) Cement content and characteri­stics - The water-cement ratio andthe aggregate-cement ratio togetherdetermine the cement content of theconcrete mix. Generally, the cementcontent itself would not have a directrole on the strength of concrete; if ce­ment content is required to increase theworkability of concrete mix for a givenwater-cement ratio, then the com­pressive strength may increase with therichness of the mix. However, for aparticular water-cement ratio therewould always be an optimum cementcontent resulting in 28-daycompressivestrength being the highest (see Fig.241') . Increasing the cement contentabove the optimum value may not in­crease the strength of concrete speciallyfor mixes with low water-cement ratioand larger maximum size aggregate',

The influence of strength of cementon strength of concrete is not very

S9

SP : 13-1981

precisely known. It has generally beenfound that greater the 7-day strengthof cement (as given by the standard testprocedure), the greater is the com­pressive strength of concrete at 28 day,for identical mix proportions (Fig.2616) . However, there may not be aone-to-one correspondence between7-day strength of cement and 28-daystrength of concrete. Because therelative increase in strength of cementat 28-day is smaller, the greater the7-day strengrh'"; perhaps 28-daystrength of cement would give bettercorrelation. As a guide, it has beenfound that for an increase in 7-daystrength of cement of SO kgf'/cm", theincrease in 28-day strength of concreteis of the order of 40 to SO kgf/cm",

'.

d) Effect of age of testing - Concrete isgenerally tested for its compressivestrength at the age of 28 days. Becauseof continuing hydration, the later agestrength of concrete would generally behigher than at 28 days; however. theexact increase win depend upon thetype of cement, mix composition andthe extent of curing. The influence ofthe type of cement on the later strengthof concrete has been discussed in Sec­tion 2. From Fig. S (Section 2) it maybe seen that although cements ·of dif­ferent types result in different rate ofgain of initial strength, the strengths atlater ages tend to become similar.Therefore, a cement type which resultsin comparatively lower strength at 28days would have proportionatelygreater increase in strength at later agesand vice-versa. The mix proportionsthemselves influence the rate of gain ofstrength, in that concrete with lowerwater-cement ratio tends to attain highinitial strength and, therefore, furthergain in strength at later ages is propor­tionately smaller than with higherwater-cement ratio. This is so becauseconcrete with lower water-cement ratiowould result in a greater gel-space ratioduring the initial period but the hydra­tion product may be laid in a moredisorderly fashion thereby impairingfurther hydration to some extent.

Under general conditions, IS :4S6-1978u allows the strength to be in­creased by 10 percent at 3 months.

SP : 13·1982

1S percent at 6 months and 20 percentat 12 months over and above the28-day strength. It is to be noted thatIS : 456-197813 does not permit anysuch increase of strength with agewhere high alumina cement is used; thereason being that high alumina cementconcretes tend to reach their potentialstrength much more quickly than othercements ~see Fil. 5 of Section 2).

3.2.2 EFFECT OF PLACING, COMPACTION AND

CURING - The concrete should be placed inits final position in the formwork as early aspossible after the completion of mixing, sothat there is no drying out of the mix, andthe mix is workable enough to receive com­paction. Dropping of concrete from greatheights may lead to segregation and entrain­ment of air bubbles, displacement of thereinforcement and damage to the concretealready placed. If segregation takes place, itwill result in concrete of poor quality. If,however, the mix is designed properly andproper precautions are taken to avoidsegregation during placing, pouring of con­crete from a height of 10 to 1S metres is notuncommon.

The necessity for thorough compaction isbasic to successful concrete manufacture,since the concrete mix is designed on thebasis that it may be tltoroughly compactedwith the available compacting equipment.When the fresh concrete is. compacted byvibration, the particles are set in motionreducing inter-particle friction so that con­crete is easily placed. Vibration eliminatesmost air pockets on the surface of theconcrete.

The increase in compressive strenlth bylowering the water-cement ratio may berestricted if the compaction is insufficient, asshown schematically in Fig. 26 J • Thepresence 'of even S percent voids .in thehardened concrete left due to incompletecompaction may result in a decrease in com­pressive strength by about 35 percent(Fig. 271') .

As already point~ out in Section 2, thehydration of cement can take- place onlywhen the capillary pores remain saturated.In addition, additional water available fromoutside is needed to fdl the lei-pores, whichwill otherwise make the capillaries empty.The funetioni of curinl are thus two-fold; to

60

prevent the loss of water in the concretefrom evaporation as well as to supplementwater consumed in hydration of cement. Inconcrete mixes with higher water-cementratio, the hydration can proceed by self­desiccation and prevention of evaporation ofwater (for example, by covering with wetgunny bags, membranes and curing com­pounds) may be sufficient.

For high strength concrete with lowerwater-cement ratio, the mixing water maynot be sufficient for hydration to proceed byself-desiccation and mere prevention ofevaporation of water will not suffice. In suchsituations continuous pending of water willbe needed more than in case of mixes withhigh water-cement ratio (Fig. 28]).

Concrete will continue gaining strengthwith time provided that sufficient moisture isavailable for the hydration of cement whichcan be assured only by proper moistcuring, -(Fig. 292') shqws the effect of dura­tion of moist curinl on compressive strengthof concrete. On an average, the one yearstrength of continuously moist cured con­crete Is SO percent higher than that of 28-daymoist cured concrete, while no moist curingcan lower the strength by about 30 percent.Moist curing for first 7 to 14 days may resultin compressive strength being 8S to 92 per­cent of that of 28 days moist curing".IS : 456-19781] stipulates a minimum of 7days moist curing, while IS : 7861 (Part I)·197512 stipulates a minimum of 10 daysunder hot weather conditions.

3.2.2.1 STEAM CURING OF CONCRETE - Sincethe chemical reactions of hydration of ce­ment can be thermally activated, increasedrate of strength development of concrete isachieved by resorting to steam curing at at­mospheric pressure. The primary object ofsteam curing is to develop high early strengthof concrete, so that concrete products can beremoved from the formwork and handled asearly as possible, and is mainly adopted inprecast concrete works.

A number of considerations govern thechoice of steam curing cycle namely theprecuring period, the rate of increase anddecrease of temperature and the level andtime of constant temperature. An early risein temperature at the time of settina of con­crete may be detrimental to concretebecause, the aieenconcrete may be too weak

to resist the air pressure set up in the poresby the increased temperature. Too high arate of increase or decrease in temperatureintroduces thermal shocks and the ratesshould generally not exceed 10 to 20°C perhour. The higher the water-cement ratio ofthe concrete. the more adverse is the effectof an early rise in temperature. Therefore, inorder to meet the requirement of com­pressive strength of concrete, thetemperature and/or time required for curingcan be reduced by having a lower water­cement ratio. While in an identical timecycle, higher the maximum temperaturegreater is the compressive strength. The ad­vantages of curing above 70°C are negatedby dilational tendencies due to expansion ofconcrete. All the above mentioned factorslead to the conclusion that for concrete of aspecified composition and curing period,there is one curing temperature which will beable to produce maximum compressivestrength at the end of the curing cycle.

A typical steam curing cycle is given in(Fig. 3()22). In the normal steam curing pro­cedure, a presteaming period of 1 to 3 hoursis usual. The rate of initial temperature riseafter the presteaming period is of the orderof 10 to 20°C per hour and the maximumcuring temperature is limited to 8S to 90°C.Temperature higher than this will not pro­duce any increase in the strength of concreteand in fact, as discussed above, atemperature of 70°C may be sufficient. Fora particular product, the maximum desiredtemperature raised at a moderate rate andthen the steam is cut off, and the product isallowed to soak in the residual heat andmoisture of the curing chamber. Due to dif­ferences in the product and the methods ofmanufacture, different curing cycles are tobe adopted based on local conditions. Byadopting proper steam curing cycle, morethan 70 percent of the 28-day compressivestrength of concrete can be obtained inabout 16 to 24 hours>,

Recent findings" suggest that the steamcuring of concrete should be followed bywater curing for at least 7 days (Fig. 31). Inabsence of this supplementary wet curing forat least 7 days, the later-age strength ofsteam-cured concrete may be lower by 20 to40 percent than that of normally-curedconcrete.3.2.3 RELATION WITH TENSILE STRENGTH ­

The tensile strength (both flexural and

61

SP : 23·1981

split tensile) is closely related to compres­sive strength of concrete, but thereis no direct proportionality between them,the ratio of the two strengths being a func­tion of the level of concrete strength. Ascompressive strength increases, the tensilestrength also increases but at a decreasingrate.

IS : 456-1978 13 gives a formula for flex­ural strength in terms of the characteristiccompressive strength of concrete, as in­dicated below:

fer = 0.70Jid Nzmm?

In order to Obtain a quicker idea of thequality of concrete, IS: 456 .. 1978)) alsospecifies optional tests (compressive as wellas flexural strengths at 7 days) for differentgrades of concrete. A comparison of therelationships between compressive strengthsand flexural strengths, at 7 and 28 days ageof concrete is shown in Fig. 32. According toPCAI9, the flexural strength is given by:

Fer = K JJ; Nz'mm?

where Ie is the cube strength of concrete,and K has a value of 0.68. In a large numberof tests carried out, K varied from 0.73 forerushed quartzite aggregate down to 0.48 forrounded river pebbles.

ACI 318-77 2• gives the relationship as:

fer = 0.63.ji; Nz'mm!

where Ic is the specified compressivestrength of concrete.

This relationship is also shown in Fig. 32 forcomparison.

Numerous factors influence the aboverelationship of the strengths. Incompletecompaction has greater effect on com­pressive strengths than on flexural strength.The tensile strength of concrete is moresensitive to inadequate curing than the com­pressive strength possibly because of theserious effects of non-uniform shrinkage (offlexure test beams). Thus air-cured concretehas a low tensile to compressive strengthvalue than concrete cured in water and testedwet 19. The ratio of two strengths is alsoaffected by the grading of the aggregate).This is because of the different magnitude ofthe wall effect in beams and; the- sur­face/volume ratios being different with therequirement of different quantities ofmortar for thorough compaction in compres­sion specimens. The experimental results

SP : 23·1982

obtained by various in~stigators for therelationship between split' tensile strengthand compressive strength of concrete liewithin the zone indicated in Fig. 3325 while arepresentative relationship with flexuralstrength is given in Fig. 3425• In absence ofdetailed test data, it may be held that the in­trinsic tensile strength of concrete is of theorder of IOta 15 percent of compressivestrength. Flexural strength is on an averageSO percent greater than split tensile strength(Fig. 3525).

3.3 Durability of Concrete - Durabilityof concrete can be defined and interpretedto mean its resistance to deteriorating in­fluences which may through inadvertance orignorance reside inside the concrete itself, orwhich are inherent in the environment towhich concrete is exposed". Normally everybatch of concrete is designed to serve auseful life of many years, and under normalcircumstances, concrete is generally durable.Problems arise when concrete contains in­gredients which were not known beforehandto be deleterious or when it is exposed toharmful environments not anticipatedearlier.

The absence of durability may be eithercaused by external agencies like weathering,attack by natural or industrial liquids andgases, bacterial growth, etc, or by internalagencies like harmful alkali-aggregate reac­tions, volume changes due to non­compatibility of thermal and mechanicalproperties of aggregate and cement paste,presence of sulphates and chlorides from in­gredients of concrete, etc. In the case of rein­forced concrete, the ingress of moisture orair will facilitate the corrosion of steel,leading to an increase in the volume of thesteel and cracking and spalling of concretecover.

Recommendations for making durableconcrete in various codes of practices en­visage limits for maximum water-cementratio, minimum cement content, coverthickness, type of cement and amount ofchlorides and sulphate! in concrete, etc. Allthese recommendations taken toaether tendto result in concrete being dense, workable,placeable and having as low a permeabilityas possible under the given situation.Therefore, adherence to one limit withoutconsideril1l others, or uniform applicationof these recommendations with no reprd tothe situation of placina. for example. con-

62

gestion of reinforcement, cover thickness,workability of concrete or-the characteristicsof the aggregates, may not ensure the fulfil­ment of the objectives. These can be explain­ed by means of Fig. 3621 and 3721• Startingwith the water-cement ratio. it is known thatthe permeability of cement paste increasesexponentially with increase in water-cementratios above 0.45 or so; from the considera..tions of permeability, the water-cement ratiois thus usually restricted to 0.45 to O.SS, ex­cept in mild environment. For a given water..cement ratio, a given cement content in theconcrete mix will correspond to a givenworkability, namely high, medium or low(Fig. 36) and an appropriate value has to bechosen keeping in view the placing condi..tion, cover thickness and the concentrationof reinforcement. In addition, the cementcontent is chosen by two other considera­tions. Firstly, it should ensure sufficientalkalinity (pH value of concrete) to providea passive environment against corrosion ofsteel, for example, in concrete in marine en­vironment or in sea water, a minimumcement content of 3S0 kg/m' or more is re­quired for this consideration13,21. Secondly,the cement content and water-cement ratio isso chosen as to result in sufficient volume ofcement paste to overfill the voids in the com­pacted aggregates. Clearly, this will dependupon the type and nominal maximum size ofaggregate employed. For example, crushedrock or rounded river gravels of 20 mm maxi­mum size of aggregate will, in general, haverespectively 27 and 22 percent of aggregatevoids. A cement content of 400 kg/m' andwater-cement ratio of O.4S will result in pastevolume being 30 percent which may besuitable for the former (that is crushed rockof 20mm maximum sizeaggregate). whereascement content of 300 kalm3 and water­cement ratio of 0.50 will result in 2S percentpaste volume (Fig. 37) being sufficient tooverfill the voids in 20 mm rounded gravelaggregates. Increasing cement content willresult in higher workabilities.

IS : 456-1978 u lists the requirements fordurable concretes in terms of minimumcement content. type of cement and maxi­mum water-cement ratio required for rein­forced concrete structuresto ensuredurabili­ty apinat: <a> specified conditions of ex­posure, and (b) different concentration ofsulphates present in soil and ground water.These are reproduced in Tables 23 and 24

respectively. Similar requirements forprestressed concrete structures as perIS : 1343-198()2' are reproduced in Tables 2Sand 26. The purpose of specifying aminimum cement cootent is to ensurereasonable durability as discussed above.The values specified in Tables 23 and 24 arein general for 20 mm nominal maximum sizeof aggregate. The cement content has to bereduced or increased as the nominal maxi­mum size of aggregate increases ordecreases, respectively.

Concrete in sea-water or exposed directlyalong the sea-coast should be at least MISgrade in the case of plain concrete and M 20in the case of reinforced concrete. The use ofPortland slag or Portland pozzolana cementis advantageous under such conditions". Inaddition, IS : 456-1978 1l stipulates that thecover to concrete be modified as follows:

Increased cover thickness may be providedwhen surfaces of concrete members are ex­posed to the action of harmful chemicals (asin the case of concrete in contact with earthcontaminated with such chemicals), acid,vapour, saline atmosphere, sulphuroussmoke (as in the case of steam-operatedrailways), etc, and such increase of cover maybe between 1S mm and SO rom beyond thevalues for normal conditions; however, theactual cover should not exceed 7S mm,

For reinforced concrete members totallyimmersed in sea-water, the cover should be40 mm more than that specified for normalconditions. For reinforced concretemembers, periodically immersed in sea-wateror subject to sea spray, the cover of concreteshould be SO mm more than that specifiedfor normal conditions. For concrete of gradeM 2S and above, the additional thickness ofcover specified above may be reduced tohalf.

The type of cement is also important inorder to resist the sulphate solutions in soiland ground water. The ordinary Portlandcement having C)A content less than S per­cent has got the maximum resistance againstsulphatlc environment. Super sulphatedcement is supposed to provide an acceptablelife for concrete against acidic environment,when the concrete is dense and made with awater-cement ratio of 0.40 or less. ThePortland slag cement and the Portlandpozzolana cement are preferable in marineor sulphuric conditions26,21 although

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SP : 23-1982

IS : 4S6-197813 has treated it at par withordinary Portland cement.

The chances of deterioration of concretefrom harmful chemical salts (chlorides andsulphates) should be minimized. The levelsof such harmful salts in concrete comingfrom the concrete making materials that is,cement, aggregates, water and admixture aswell as by diffusion from environmentshould be limited.

For the corrosion of embedded steel tobegin, there is a threshold value for the'chloride content in concrete dependent uponthe alkalinity present (pH of concrete).Chloride in concrete may be present in thewater (in soluble form) or chemically com­bined with other ingredients. Solublechlorides induce corrosion but chemicallycombined chloride is believed to have littleeffecr", Tests on soluble chloride are time­consuming and difficult. It is easier tomeasure the total (soluble plus combined)chloride and to test for soluble chloride, onlywhen follow up studies are needed", Oxygenand moisture are necessary for electro­chemical corrosion. Table 27 indicates therecommendations of ACI Committee" onlimits for chloride ion in concrete in dif­ferent conditions of exposure. IS:456-1978 13 limits the" total amount ofchloride in concrete to 0.1 S percent by massof cement, on the basis of recommendationscontained in Reference 29. For prestressedconcrete, IS: 1343-198()27 limits the totalamount of chloride ions in concrete to 0.06percent by mass of cement.

The sulphates in concrete may be fromdifferent ingredients of concrete, that iscement, coarse and fine aggregates, waterand admixture. IS: 4S6-197813 limits thetotal sulphate content of the concrete mixfrom all such sources to 4 percent by mass ofcement.

Resistance to alternate freezing and thaw­ing is not so important for the conditions'prevailing in the country. But whereversituations demand, air-entrained concretecould be employed using an air-entrainingadmixture. Air-entrainment lowers the com­pressive strength but increase workability ofconcrete. which may permit certain reduc­tion in the water content of the concrete mixso that the loss in the compressive strengthof concrete can be compensated by loweringthe water-cement ratio.

SP : 23-1982

TABLE 10 COMPARISON OF CONSISTENCYMEASUREMENTS BY VARIOVS METHODS

(Clause 3.1.1)

TABLE 11 RELATION BETWEEN SLUMP ANDRELAnVE WATER CONTENT

(Clause 3.1.2.1)

WORKABILITY SLUMP VEE· BEE COMPACi· SL SLUMP RELATIVE VOLUME OFDESCRIPTION mm TIME INO No. mm WATER IN THE MIX

s FACTOR'

Extremely dry 32-18 1) 2~ 0.962

Very stiff 18-10 0.70 2) 40 1.000

Stiff 0-25 10-~ 0.1S 3) .50 1.012

Sti ff plastic 2S-S0 5-3 O.8~4) 75 1.045

Plastic 7'-100 3-0 0.90 ') 100 1.069

Flowing ISO-175 0.95 6) 125 1.088

7) ISO 1.10SNOTE - Table 20 is from 'Recommended Practice for 8) 175 1.119Selecting Proportions for Normal Weight Concrete'Reported by ACI Committee 211 (ACI Manual of NOTE - Table 21 is from 'The Properties of FreshConcrete Practice, Pan I, 1979). American Concrete Concrete' (1968) by T.e. Powers and published by JohnInstitute, USA. Wiley and Sons. Inc., New York.

TABLE 22 SUGGESTED RANGES OF VALVES OF WORKABILITY OF CONCRETE FOR DIFfERENTPLACING CONDITIONS

(C/QU# 3.1.2.2)

PLACING CONDITIONS

(I)

Concreting of shallow sectionswith vibration

Concreting of lightly reinforcedsections with vibration

Concreting of lightly reinforced'sections without vibration,or heavily reinforced sectionswith vibration

Concreting of heavily reinforcedsections without vibration

DEOREE OFWORKABILITY

(2)

Very low

Low

Medium

Hiah

VALUES OF WORKABILITY

(3)

20-10 seconds, Yee-Bee timeor

0.75-0.80, compacting factor

10-5 seconds, Vee-Bee timeor

0.80-0.85, compacting factor

S-2 seconds, Vee-Bee timeor

0.85-0.92, compacting factoror

25-7' mm, slump for 20 mm· auregate

Above 0.92, compacting factoror

75-12S mm, slump for 20 mm· aureaate• For smaller allreaate the values will be lower.

64

SP : 13-1981

TABLE 13 MINIMUM CEMENT CONTENT REQUIRED IN CEMENT CONCRETE TOENSURE DURABILITY UNDER SPECIFIED CONDITIONS OF F:XPOSURE

(Clause 3.3)

PLAIN CONCRETE REINFORCED CONCRETE

r------~ \'Minimum

A~

Minimum Maximum MaximumCement Water Cement WaterContent Cement Content Cement

Ratio Ratio

(2) (3) (4) (5)

kglml kg/m3

220 0.7 250 0.6S

EXPOSURE

(J)

Mild - For example. completelyprotected against weather, oraggressive conditions, exceptfor a brief period of exposureto normal weather conditionsduring construction

Moderate - For example, shelteredfrom heavy and wind drivenrain and against freezing, whilstsaturated with water; buriedconcrete in soil and concretecontinuously under water

Severe - For example, exposed tosea water, alternate wettingand dryina and to (reezinawhilst wet, subiect to heavycondensation of water or corro­sive fumes

250

310

0.6

O.S

290

360 0.45

NOTE 1 - When the maximum water-cement ratio can be strictly controlled, the cement content may be reduced by10 percent.

NOTE 2 - The minimum cement content is based on 20 mm aggregate. For 40 rom aggregate. it should be reduced byabout 10 percent; for 12.S mm aggregate, it should be increased by about 10 percent.

65

SP : 13-1981

TABt...: 24 REQUIREMENTS FOR Pl.AIN AND REINFORCED CONCRETE EXPOSED TOSULPHATE ArrACK

(Clause 3.3)

(7)

"'\Maximum

Free Water/Cement

Ratio

(6)

REQUIREMENTS t'OK DENSE,

FULLY COMPACTEDCONCRETE MADE WITH

AGGREGATES COMPl.YINO

WITH IS : 383- J970·

MinimumCementContent

,..-- .....A _

(S)

TYPE OF

CEMENT

,

(4)

In GroundWater

(Parts per100000)

(2)

In Soil

CON('EN1RATION OF SULPHATES.

EXPRESSED AS 503,.... -.lA.'- ~

-----"-----\\, Tot;1 S03 503 in 2: 1

(percent) waterextract

gil

(3)(I)

CLASS

ttlan';J

1)

2)

3)

Less than0.2

0.2 to O.S

o.s to 1.0 1.9 to 3.1

Ordinary Portlandcement or Portlandslag cement or Port­land pozzolanacement

30 to 120 Ordinary Portlandcement or Portlandsla&cement or Port­land pozzolanacement

Supersulphatedcement

120 to 250 Sup e r sui p hat e dcement

330

310

330

O.SS

o.so

O.SO

O.M

NOTE 1 - q'his table applies only to concrete made with 20 mm aggrep.tes complying with the requirements ofIS : 383-1970· placed in near-neutral ground waters of pH 6 to 9, containing naturally occuring sulphates but notcontaminants, such as ammonium salts. For 40 mm auregate the value may be reduced by about 1S percent and for12.~ rom aggregate, the value may be increased. by about I~ percent. Concrete prepared from ordinary Portlandcement would not be recommended in acidic conditions (pH 6 or less). Supersulphated cement gives an acceptable lifein mineral acids, down to pH 3.S provided that the concrete is dense and prepared with a water/cement ratio of 0.4 orless.

NOTE 2 - The cement contents given in Class 2 are the minimum recommended. For SOl contents near the upperlimits of Class 2, cement contents above these minimum are advised.

NOTE 3 - Where the total SOl in col 2 exceeds O.S percent, a 2: 1 water extract may result in a lower site classificauonif much of the sulphate is present as low solubility calcium sulphate.

NOTE" - For severe conditions such as thin sections under hydrostatic pressureon one side only and sections partlyimmersed, considerations should be given to a further reduction of water-cement ratio, and if necessary an increase inthe cement content to ensure the dearee of workability needed for full compaction and thus minimum permeability.

NOTE ~ - Portland sl.. cement conformina to IS : 4SS-1976t with sla8 content more than SO percent exhibits bettersulphate resisting properties. '

NOTE 6 - Ordinary Portland cement with the additional requirement that C3A content be not more than ~ percentand ~ C] A +C~F (or its solid solution 4CaO, Al% 0], Fe20] + 2CaO, Fe20J be not more than 20 percent may beused In place ofsupersulpbatedcement.

·Specification for coarse and fine aurclates from natural sources for concrete (.s«ond revision).tSpecification for Portland 51.. cement (third revision).

66

SP : 13-1981

TABLE 15 MINIMUM CEMENT CONTENT REQUIRED IN CEMENT CONCRETE TO ENSUREDURABILITY UNDER SPECIFIED CONDITIONS OF EXPOSURE FOR PRESTRESSED CONCRETE

(Clauw 3.3)

EXPOSURE

(I)

Mild - For example, completely protected against weather or aggressive condi­tions. except for a brief period of exposure to normal weather conditionsduring construction

Moderate - For example, sheltered from heavy and wind driven rain andagainst freezing, whilst saturated with water, buried concrete in soil andconcrete continuously under water

severe - For example, exposed to sea water. alternate wetting and drying andto freezing whilst wet subject to heavy condensation or corrosion fumes

MINIMUM MAXIMUM

CEMENT WATER

CONTENT CEMENT

kg/ml RATIO

(2) (3)

300 0.65

300 O.SS

360 0.45

NOTE - The minimum cement content is based on 20 mm nominal maximum size. For 40 mm aggregate. minimum'cement content should be reduced by about 10 percent under severe exposure condition only, for n.s mm aggregatethe minimum cement content should be increased by about 10 percent under moderate and severe exposure conditionsonly.

67

SP : 13-1981

TABLE 26 REQUIREMENTS FOR PRESTRESSED CONCRETE EXPOSED TOSULPHATE ATrACK

(Clouse 3.3)

CLASS CONCENTRATION OF SULPHATES. TYPE OF REQUIREMENTS FOR DENSE.EXPRESSED AS S03 CEMENT FULLY COMPACTED

, A , CONCRETE MADE WITH

AOOREOATES COMPLYINGIn Soil In Ground WITH IS : 383-1970*

A Water A,Total SO) SO] in 2:1 (Parts per r

Minimum Maximum(percent) water 100 (00) Cement Free Water/

extract Content Cementgil Ratio

(1) (2) (3) (4) ( ~ ) (6) (7)

kglm3

1) Less than Less than Ordinary Portland 280 O.SS0.2 30 cement or Portland

slag cement

2) 0.2 to 0.5 30 to 120 Ordinary Portland 330 O.~O

cement (see Note .5)or Portland slagcement

3) 0.5 to 1.0 1.9 to 3.1 120 to 250 Ordinary Portland 330 0..50cement (see Note .5)

NOTE I - This Table applies only to concrete made with 20 mm auregates complying with the requirements ofIS : 383-1970· placed in near-neutral ground waters of pH 6 to 9, containing naturally occuring sulphates but notcontaminants, such as ammonium salts. For 40 mm auregatc the value may be reduced by about 1S percent and for12.S mm aggregate the value may be increased by about 15 percent. Concrete prepared from ordinary Portlandcement would not be recommended in acidic conditions (pH 6 or less).

NOTE 2 - The cement contents givcq in Class 2 are the minimum recommended. For SO) contents near the upperlimit of Class 2, cement contents above these minimum are advised.

NOTE 3 - Where the total SO) in col 2 exceeds O.S percent, then a 2:1 water extract may result in a lower siteclassification if much of the sulphate is present as low solubility calcium sulphate.

NarE 4 - For severeconditions such as thin sections under hydro-static pressure on one side only and sections partlyimmersed. considerations should be liven to a further reduction of water<ement ratio, and if necessary an increase inthe cement to ensure the dearee of workability needed for full compaction and thus minimum permeability.

NOTE 5 - For Class 3 concrete. ordinary Portland cement with t~e additional requirement that C)A content be notmore than 5 percent and 2C3A +C,AF (or its IOHd solution 4CaO. ~O" Fe20, +2CaO. Fe'l0~ not more than 20percent is recommended. If this cement is UJed for CIua 2 concrete, minimum cement cootent may be reduced to 310kalm3•

·Ss*ir'Catlon for COUIe and rme aurepces from natural IINrca of concrete ($tICOnd ,"Ision).

68

SP : 13..1912

TARLt.. 27 LIMIT FOR (,HLORIDI:..ION IN <"ON<"Rt..Tt.. PRIOR TO IoXP~UK. I~ 'tK"Il.1o

(Clouse 3 3)

SlNo

(I)

I)

2)

3)

4)

TYPE OF CONCRETE OR SERVICE

(2)

Prest ressed concrete

Conventionally reinforced concrete located In a moist environment andexposed to chlonde

Conventionally reinforced concrete located in a moist .environment butnot exposed to chlonde

Above ground buildmg construction where the concrete Will ~tay dry(does not Include locauon where the concrete Will be occasionallywetted. such as kitchens. parking garages and water front structures)

CHLORIDE ION.

PERCENT BV

MASS Of CEMENT

(3)

006

010

o IS

No limn for pro­tection againstcorrosion"

·If calcium chlonde IS used as an admixure, It IS generally recommended that the hmu be set at 2 percent by mass ofcement for reason other than corrosion

69

SP : 13·1981

.1-,__"UPTOJJO125mm , ,, \,

TRUE SHEARSLUMP

COLLAPSE

Fig. 18 Slump: True. Shear and Collapse

5

A

V

\ I

... l.\ '\II!...\ \.. , \

2 ~,

'\ \? \...v

'\'~ '{~ \. -,~fp \6

~ -,"

i\ ~'t'r-, "~•~O2

'"........

~ r----...~

...v ....

~~21 50 75 100 12-

~ 5LUM~ mm

~~O25

~ ~ so

~"

I

\ I....a

100 ::I

\~

tit

12S1

1'01'004 a., 0-. o·t

2

-.wZ;:

COMPACTING 'ACTOR

Fig. /9 Relationship Between Slump, Compocting Factor and Vft-Bft nmeJor Concrete 01Different Aggregate-Cement Rllilos

70

110.

LE

GE

ND

.I

Ir

I~~

1~

~~

IS"~

~I

~~R

OU

ND

ED

A&

GR

EG

AIE

lCO

OK

E)a~,

~~~~I

Ia~

~

150~

AN

GU

LA

RA

GG

RE

GA

nlco

OKIl

~.

II

.--

--J

!7

,

/I

.--

-.A

NG

UL

AR

AG

GR

eG

AT

EI

II

.-I

I.

.I

1201

(Ae

I21

1-1

-76

'I

I.

Ie

//1/

E a....

'0.

I2:

~~

/::» ..

J,Q

~ti

t~

.~

6O.

o_

--

0-

--

-: ./

I/'

I,.

/'I

,~

30

I

160

180

200

220

WAT

ERC

ON

TE

NT

,kg/

m3

rIJ

."

Fig

.20

Rel

atio

nshi

pB

etw

een

Wor

kabi

lity

and

Wat

erC

onte

nto

fCon

cret

efo

rD

iffe

rent

Max

imum

Size

so

fAgg

rega

tet • ... I w

SP : 23·1911

w/e.0-61

-Ie. o.ao. A... ---- __ ~A4'xrUR! 8---'--- .............. ......... -.

Wlc .0-55

wI<:. 0-&0+ ADMIXTURE C----------------------

ADMIXTURE B = WATER-REDUCING ADMIXTURE(NORMAL SETTING GRADE)

C a WATER -REOUCING ADMIXTURE(ACCELERATING GRADE)

ViI/c.O-15-------4I

-----------...

0I5...--....-----......-------~---------------..,

Q(

o~

o

~ oe5rT----'l\~1--O;;;:;;;;===:::::f::==-~~~!..========Jz...u~a.~ oeot--~..-.ilIIII------_+_--------._ ....... ~u

60153C>71t--......-------'--------......----------------..

TIME IN MINUTES AFTER THE COMPLE TIONOF NIXING

Fig.21 Change in Compacting Factor with Time

.50403020

~ !'" N~ a:w 1&1A. Q.. 0 ......"'--_......_-.10__"""'-_.-1..._.--.

5 10

CONCRETE TEMPEAATURE,·C

Fig. 22 Effect ofConcrete Temperlltu,~ on Slump and on Water Required to elulnge Slump

72

SP : 1]·1911

80,----.----.,-----r---.....,..--........__---.

%"-N~ e 60

~ ~ r--r---t-----1~--J~~__-l~Z..W '" 4 Olll&:.::----~-=--_·..-> ....

~~W U~Za.. 0 20 -- - - - .. - ,. - - _.-2: UOIL.UO

3·0 3·5 40 4 5 so 5

AGGREGATE -CEME NT R ArlO BY WEIGHT

Fig. 23 Typical Relation Between Compressive Strength ofConcrete and Aggregate-CementRatio for Various Compacting Factors

NOTE - Figure 23 is from 'Concrete Mix Design (Second Edition, 1966)' by J. D. Mcintosh and published by Cementand Concrete Association. London.

590531472413354295236

49

42

235 254

3S (0-40)

OPTIMUM ICEMENT 254CONTENT (0·41)

28

177

w>(l)N(/) EW E0:::--..o..z~o ..u:I:....~ 21""---""'+---

~ZOW,0:

~ ~ 14t---~-

CEMENT CONTENT, kg/m3

Fig. 24 Effect of Cement Content on the Compressive Strength of Concrete

73

SP : 13-1982'

e 50n-a.-+----+--+----t----1~__,u

.......at

.K

~%...c.!)zW0:...fI)

w~fnUJW~Q.2:ou

>­~o•

CDN

0·' 0-6 Q.8 1·0

WATER-CEMENT RATIO

7·DAY CEMENT STRENGTH440 kg/cm2 •••••• Curve 'A'396 " •• 'B'352 " . . . . . . " 'C'308 .. . . . . . . " '0'264 " . . . . . . ". 'E'220 " . . . . . . " 'F'

HAND COMPACTION

FULLY COMPACTEDCONCRETE

Fig. 25 Design Curve for Cement Concrete Mixes in Relation to 7-Day CompressiveStrength of Cement

VIBRATION%:...C)zw~t-enw~enenwa:G.Zou -------------

WATER-CEMENT RATIO

Fig. 26 Effect of Compaction on Compressive Strength oj Concrete

NOTE - Fi.ure 26 is from 'Properties of Concrete (Second Edition, 1973)' ba A. M. Neville and published by Pitman• Pubtishina Corporation, Sir Isaac Pitman and Sons Ltd, London.

74

SP : 23·1981

z0t-Uc(

~~(/)04C{U

...j

X:-' 100~::><,!)LL

Z ....We( 80~...- ...(/)c(

:t: 60Wt-

~LL(1)0en 4OWwo==<!>Q.~2: .... 20ozuUJ

0Q::w 25 20 15 10 5 0Q.

PERCENTAGE OF VOIDS

Fig. 27 Relationship Between Percentage of Voids and Compressive Strength of Concrete

70

N

E60E 11

ZSO

:I:.....

'"Z 40LUa:.....Vl

30UJ>\i)~

20UJ0:c,~0 10U

00-28 032 036

AGE ATTEST ~

040 044

WATER I CEMENT RATIO

Fig. 28 Influence of Curing Conditions on Strength of Test Cylinders

NOTE - Figure 28 is from 'Properties of Concrete (Second Edition, 1973)' by A. M. Neville and published by PitmanPublishina Corporation, Sir Isaac Pitman and Sons Ltd, London.

75

SP : 23·1911

~ow.~

:'-::)• (,) 160~

t; ~ 140ZolLI Z W120~ ...~ ~:'00w %~ 10> "'0en ~ u 60cnwUJ a: 40IX ...

~ en 20ou ~ 0

CcDN

A. ---,..........~ - - -- l-- I-- .... - ~- -..

t> 0

L ..-t-~---~- _.. -~-

~c;. ----I

10---

+ I

I ~-'~-~---------~i -..- --,-~

-- - ---

2 3 4 5 6 7 8 9 10 11 12

AGE, MONTHS

A - Continuously moist cured8 - Contlnuou81y air curedC - Moist cured 1 month then air

curedD - Moist oured 3 months then air

cured

Fig. 29 ClUing and Strength Relationship for Portland Cement Concrete

NOTE - Fi.ure 29 is from 'Concrete TechnoloaY and Practice (Fourth Edition, 1977)' by W_1\_ Taylor andpublished by Me Oraw-HiU Book Company Australia Pty Limited. Sydney.

CL ,

; -.~O

I

'"I ~

A I

100

U•UJCC 10:J

&&J V\0ex .J

::l U~ Z 604 UJ~

IJJ~Q.

~4UJ

UJ ... 40~ \I)

~:J:t- 20i

02 , • 10 12 14 16 II

riME AFTER PLACING OF CONCRETE ,HOURS

A - Preateamlng period, 3 houla8 - Temperatu....... period, 2¥l houNC - '-loci at mulrnum temperature, ~ houriD - Cooling period, 5 hours

Fi,. 30 Typal Stetlm Curl", Cycle

76

SP : 13-1981

DURATION ,h

---

4.40

-_. - --~

2.45

=~

~==

2.00

-

-

...

--

80

70

60

so

~ &0

~ 50e%

'"~ 100V)

~ 90

~ 80..J

~ 70

..z~ 100cr;t' 90

STANDARD CURING STEAM-CURINGFOLLOWED BYWATER CURING

STEAM - CURINGFOLLOWED BYDRYING AT 20·C 165-'.

Fig. 31 Effect of Curing Regime on 28-1JcIy Strength of Concrete

77

SP : 13·1981

s ....-----......------r--------r------,....------.

2531e-11

14AG (IS: 456 )

I'4

DAYS AGE ( IS: 456 )

41-------.........--------l.....-------+--~---__,1Ir-------t

2 ......-----~_.----~~------+-------+-------.....

31--------+-----~~~ K-----.......------..-------...,

z

N

EE

o 10 20 30 40 50

COMPRESSIVE STRENGTH. N Imm 2

Fig. 32 Comparison of Relationships Between Compressive and Flexural Strengths ofConcrete

78

+-

NEE 70

'""'"'Z

J: 60...(!)z 5w~... 40enW> 30enenw0:a.2:0u

0

I-I

III

I I

--+-----L-+-- ~-I I1- t ~- j~ I I

~ ~ It2 3 4 5 6 7 8 9

SPLIT TENSILE STRENGTH, N/mm2

SP : 13-1911

J;'ip. 33 Relationship Between Split Tensile Strength and Compressive Strength of Concrete

~6

NEE 49

Z

:t: 42...~zUJ 35crt-V)

UJ 28

~VltJ')

21UJ~Q..~ ,I.00

7

14 2.1 2 e 15 42 49 56 6.3 70

FLEXURAL STRENGTH, N/mm2

Fig. 34 Relationship Between Compressive and Flexural Strengths of Concrete

79

SP : 23-1911

N 7EEz

,,

3:5t-

C)ZLIJa: ,...1Il

..J 3<l~:l><LLJ 2..JI.L

o6 7 e 9

SPLITTING STRENGTH, N Imm 2

rIg. 35 Relationship Between Split Tensile Strength andFlexural Strength of Concrete

PERMEABILITY11

( JI 10 mIl)

HIGH WORKABILITY

(100-150mm slump)

o....4a:

o

150 200 alo 300 150 400 450 500 550

MINIMUM CEMENT CONTENT, kg 1m 3

Fig. 36 Interreliltionships 01 Waler-Cement Ratio and Cement Content on Workability andPermetlbi/lty ofFresh Concrete

80

SP : 13-1911

0.' WEDIUM \ ~HIGH WORKABILITY 1100-1S0. mm SLUM")150 -100 ","'I~ 250 \ 300 CENENT CONT!NT\

Ikgl mJ J0 \

:c• ALUMINATE a '·'.1t-z 0.6.,2UJu.....«

0.5IU

~~

2 50=-!)(

iROCK

25 30 35 40

ce ....! NT ftAST I! VOLUME • PERcENl CO~,CRETE

Fig. 37 Cement Paste Volume Required in Concrete of Various Water-Cement Ratios forMarine Durability

81

SP : 13-1982

REFERENCES

1. IS: 6461 (Part VII)-1973 Glossary of termsrelating to cement concrete: Part VII Mixing, lay­ing, compaction, curing and other constructionaspects.

2. IS: J199-1959 Methods of sampling and analysisof concrete.

3. NEVILLE (A M). Properties of concrete. 1972. Pit­man Publishing.

4. BLOEM (0 L), GAYNOR (R D) and WILSON (J R).Testing uniformity of large batches of concrete.NRMCA Publication No. 100. National ReadyMixed Concrete Association. 1961.

5. ACI 2J 1-65 Recommended practice for selectingproportions for no-slump concrete. AmericanConcrete Institute.

6. DEWAR (J D). Relations between variousworkability control tests for ready mixed concrete.Technical Report TRA/37S. Cement and ConcreteAssociation, U.K. 1964.

7. COOKE (A M). A Guide to the design of concretemixes. Technical Report TR 36. Cement and Con­crete Association of Australia. 1974.

8. ACI 211.1-76 Recommended practice for selectingproportions for normal and heavy weight con­crete. American Concrete Institute.

9. POPOVICS (5). Relation between the change ofwater content and the consistence of fresh con­crete. Meg Concr Res. 14,41; 1962; 99-108.

10. POWERS (T C). The Properties of fresh concrete.1968. John Wiley & Sons, Inc.

11. FLETCHER (K· E). and ROBERTS (M H). Testmethods to assess the performance of admixturesin concrete. Concrete. " 5; 1971; 142-48.

12. IS: 7861 (Part 1)-1975 Code of practice for ex..treme weather concreting: Part I Recommendedpractice for hot weather concreting.

)3. IS: 4S6-I978 Code of practice for plain and rein­forced concrete.

14. MCINTOSH (J D). Concrete mix design. 1966. Se­cond Edition. Cement and Concrete Association,london.

IS. MATHER (8). Stronger concrete. Highway

82

Research Record No. 210. Highway ResearchBoard, Washington, 1967.

16. IRe: 44-1976 Tentative guidelines for cementconcrete mix design for road pavements. TheIndian Roads Congress, New Delhi.

17. Fixing the 28-day strength of cement under a co­operative testing programme. Cement ResearchInstitute of India, New Delhi. 1978.

18. DANKE (P S). Role played by the quality of cementin concrete making. Ind. Concr J. 52, 9; 1978;236-40.

19. GLANVILLE (W H), COLLINS (A R) and MATHEWS

(D 0). The Gradina of aureaates and theworkability of concrete. Road Research TechnicalPaper No. S, HMSO. London. 1947.

20. TAYLOR (W H). Concrete technology and practice.1977. Mcgraw - Hill Book Company, Sydney.

21. PATEMAN (J D). Influence of site curing on com­pressive strength of cubes. Concrete. II, 2; 1977;30-31.

22. MADHAVA RAO (A G), PARAMESWARAN (V S) andABOOL KARIM (E). Experimental investigation onprestressed concrete railway sleepers. Proceedingsof the International Symposium on PrestressedConcrete Pipes, Poles, Pressure Vessels andSleepers, Madras. 1972. VI, P 1-30.

23. SoROKA (I), JAEGERMANN (C H) and BENTUR (A).Short-term steam-curing and concrete later-agestrength. Maler Struct. II. 62; 1978; 93-96.

24. ACl 318-77 Building code requirements for rein­forced concrete. American Concrete Institute.

2S. POPOVICS (5). Relation between various strengthsof concrete. Highway Research Record No. 210Highway Research Board, Washington, 1967.

26. ACI COMMITTEE 201. Guide to durable con­crete: J. Amar Coror lnst, 74, 12; 1977; 573-609.

27. IS: 1343-1980 Code of practice for prestressedconcrete ifirst revision).

28. BROWNE (R D) and DoMONE (P L J). The long termperformance of concrete in the marine environ­ment. Proceedings of the Joint Corrosion Con­ference Institute of Marine Engineers, London.1973.

29. Limits on chloride recommended. Concr Constr.23, 3; 1978; ISJ-S4.

SECTION 4

VARIABILITY OF CONCRETE STRENGTHSTATISTICAL ASPECTS

SECTION 4 VARIABILITY OF CONCRETESTRENGTH - STATISTICAL ASPECTS

4.0 In this Section, information ispresented on different methods of measuringthe variability of concrete strength and theapplication of principles of statistics to con­crete mix design. In addition, the acceptancecriteria for concrete as specified inIS : 4S6-19781 have also been discussed.

4.1 Measures of Variabilities of ConcreteStrength

4. J. J FACTORS CONTRIBUTING TO

VARIABILITY - It is found that the strengthof concrete varies from batch to batch over aperiod of time. The sources of variability inthe strength of concrete may be consideredto be due to the following factors:

a) Variation in the quality of constituentmaterials used,

b) Variation in the mix proportions due tobatching process,

c) Variations in the quality of batchingand mixing equipment available,

d) The quality of supervision andworkmanship, and

e) Variation due to sampling and testingof concrete specimens.

The above variations are inevitable duringproduction to varying degrees. For example,cement from different batches may exhibitdifferent strengths and the variability ismore when cement from different sources isinvolved. The grading and shape ofaggregates even from the same source varieswidely and it is not economically feasible toeliminate such variations particularly whenthe aggregates are not factory made. Con­siderable lJriations occur in the mix propor­tions from batch to batch irrespective ofwhether the hatching is by weight or volume.These can be attributed partly to the qualityof plant available and partly due to the effi­ciency of operation.

Some of the variations in tnt test resultsare due to variations in the sampling,making, curing and testlDa the specimeneven when carried out in terms of the rele­VfIll Indian Standard specifications.

The relative influence of some of the

8~

factors .ffedina the variability of concretestrength in terms of standard deviation isgiven in Table 282• These values are based onconditions in UK and may not be directlyapplicable for conditions in India. Forinstance, the variability contributed bycement from one works or from differentworks in India may be higher than thosegiven in Table 28. Similarly, batching ofcement in bulk, servo-operated weighingsystems is not common in India. Hence thevalues quoted should be taken as illustrativeonly. Even though the overall variabilityarising out of the above five factors may bereduced, such a reduction is not humanly/economically feasible beyond certain limits.

4.1.2 THE DISTRIBUTION OF RESULTS­

Having accepted the inevitability of varia­tions, it is necessary to understand thestatistical concepts underlying such varia­tions and provide for suitable safeguards inthe mix design by way of margin.

It is now generally recognized that thevariations in concrete strength follow theNormal or Gaussian distribution. When alarge number of test results are plotted in theform of a histogram, the resultant curve ap­proaches that of a Normal distribution curve(s~ Fig. 38). The area beneath the curverepresents the total number of test results.The proportion of the results less than thespecified value is represented by the areabeneath the curve to the left hand side of avertical Une drawn through the specifiedvalue.

The normal distribution curve is sym­metrical about its mean, has a precisemathematical equation and is completelyspecified by two parameters, namely, meanstrength and standard deviation.

The mean strength is defined as thearithmetic mean of the set of actual testresults.

The standard deviation (5) is a measure ofthe spread of the results and the formula forworking out the standard deviation is givenin IS : 4~~1978J.

Appendix A,give5 a sample calculation ofstandard deviation (S) for samples belonging

SP : 23-1982

to different groups and updating the Svalues. Alternatively. the values of S may bequickly arrived at by using a scientificcalculator having standard deviation pro­gramme.

Figure 39 indicates the shape of thedistribution curves for different degrees ofcontrol for a typical grade of concrete'. Itmay be appreciated that the value of S isminimum for very good control and pro­gressively increases as the level of controldecreases.

The correlation between the characteristicstrength and standard deviation indicatesthat for a given degree of control, the stand­ard deviation increases as the specifiedcharacteristic strength up to about20 N/mm2 and remains constant beyondthis characteristic strength value. However,Table 29 (see IS : 456-19781) gives specificvalues of assumed standard deviation forvarious grades of concrete.

Coefficient of variation is a non-dimen­sional parameter and is equal to the standarddeviation (5) divided by the mean strength,However t its use is not envisaged inIS : 456-19781•

4.1.3 CHARACTERISTIC STRENGTH - As thecube test results follow the Normal distribu­tion, there is always the probability thatsome results may fall below the specifiedstrength. Recognising this factor,IS : 4S6-19781 has brought in the concept ofcharacteristic strength, The term'characteristic strength' means that value ofthe strength of the material below which notmore than 5 percent of the test results areexpected to fall.

4.1.4 TAROETMEANSTRENOTH - Consider­ina the inherent variability of concretestrenath durin, production, it is necessary todesip the mixto have a target mean strengthwhich is areater than the characteristicstrength by a suitable marJin.

fa - Is +K.Swhere

I. - tarla mean strenath.I. = characteristic strqth,I - a constant, dependina on the

definition of characteristicstren,gth and is derived from themathematics of Normal distribu­tion (.sw Table 30), and

S • .tandard deviation.

86

The value of K is equal to 1.6~ (seeIS : 456-19781) where not more than 5 per­cent of the test results are expected to fallbelow the characteristic strength.

I. = felt + 1.65 S

4.2 Statistical Concepts in Concrete MixDesign - The design of the concrete mixshall be so done as to ensure that the targetmean strength is realized during preliminarytrial mix testing stage. The only parameter tobe defined in arriving at the value ofI, is thevalue of standard deviation.

The value of standard deviation for suchuse shall beeither an assumed value depend­ing on the degree of control available or avalue based on past data using the sameplant, materials and standard of supervision.The later value, if available, Is to be pre­ferred.

Where the past data is not available duringinitial stages of preliminary trials, the valuesgiven in Table 291 may be used. As soon asadequate number of test results (Min 30) areavailable, the actual calculated value ofstandard deviation shall be used for revisingthe mix design.

4.J Acceptance Criteria - IS : 456-19781

stipulates that random samples from freshconcrete shall be taken as specified inIS : 1199-19594 and cubes shall bemade, cur­ed and tested as described in IS : Sl6-19S9'.If required for some other purposes•.forexample. to estimate the time when theformwork can be stripped, tests may be con­ducted at early ages also but the acceptanceor otherwise is always on the basis of 28 daysstrength. The average of the strength ofthree specimens is the test strength of anysample. The acceptance criteria as given inIS : 456-19781 is reproduced below:

ns. ACCEPTANCE CRITERIA

I j.l The concrete shall be deemed tocomply with the strength requirements if:

a) every sample has a test strenath notless than the characteristic value; or

b) the strength of one or more samplesthoup less than the characteristicvalue. is in each case not less thanthe sreater of:1) the characteristic strenath minus

1.35 times the standard devia­tion; and

SP : 13-1982

3

n

engineer-in-charge. '

The main statistical features of theAcceptance Criteria are as under:

a) The 'minimum' strength is expressedby 'characteristic strength' belowwhich certain test results are allowed tofall. Such 'low' results, which are in­evitable to occur t are not regarded as'failures' and the concrete in the struc­ture that they represent should not beconsidered automatically for rejection.

b) Notwithstanding such statistical con­cept for minimum strength, the ab­solute value is also specified which istaken as 0.8 times the characteristicstrength.

c) For the purposes of acceptance eachsample is expected to ~equal to or ex­ceed the characteristic strength re­quired.

d) Because of the random nature ofstrength, a sample may have strengthlower than the characteristic strengthalthough expectedly not lower than3 times standard deviation below themean, that is, 1.3S times the standarddeviation below the characteristicstrength but by the same logic, thereshould be other samples whosestrength should have exceeded thecharacteristic strength. The average ofall such samples should then be not less

t~han the c~:~cte]ristiC strength plus

1.65 -J times th~ s~dardn deviation

Note that the standard deviation of1

average of n samples is -- times~

that of individual samples. When n issufficiently large, this approaches the'mean' or 'target' strength, as it shouldbe.The acceptance is thus on the basis ofthe average of all samples tested tillthat time rather than on individual lowresults. Thus a larger set of test data isutilized in decision makins.

e) However, when the average of n suchsamples is less than the characteristicstrength plus

~ 6.. ---~ times the standard· J-J deviation

15.6 Concrete shall be assessed daily forcompliance.

15.7 Concrete is liable to be rejected if itis porous or honey-combed; its placinghas been interrupted without providing aproper construction joint; the reinforce­ment has been displaced beyond thetolerances specified; or constructiontolerances have not been met. However t

the hardened concrete may be acceptedafter carryina out suitable remedialmeasures to the satisfaction of the

2) 0.80 times the characteristicstrength; and the averagestrength of all the samples is notless than the characteristicstrength plus

1.6S

15.5 Concrete of each grade shall beassessed separately.

1.65 - times the stand-J number of ard deviationsamples

Ij.2 The concrete shall be deemed notto comply with the strength requirementsif:

a) the strength of any sample is lessthan the greater of:1) the characteristic strength minus

1.3S times the standard devia­tion; and

2) 0.80 times the characteristicstrength; or

b) the average strength of all thesamples is less than the character­istic strength plus

31.65 - • times the stand-J number of ard deviation

samples

/5.3 Concrete which does not meet thestrength requirements as specified in 15.1but has a strength greater than that re­quired by 15.2 may, at the discretion ofthe designer t be accepted as being struc­turally adequate without further testing.

15.4 If the concrete is deemed not tocomply persuant to J5.2, the structuraladequacy of the parts affected shall be in­vestigated and any consequential action asneeded shall be taken.

87

SP : 13·1912

the concrete is deemed not to havecomplied with the acceptance criteriaand the structural adequacy is to be in­vestigated.

Illustrative Example:In a construction work, concrete of

grade M 20 (20 Nz'mrn') is to be used.The standard deviation for this gradeof concrete has been established to be4 Nz'mm', In the course of testing con­crete cubes, the following results areobtained from a week's production(average strength of 3 specimens testedat 28 days in each case, expressed inNz'mm'):

24.8, 27.0, 28.S, 23.6, 18.0, 21.6,15.0 Nz'mm". Apply-ing the criteria of IS : 456-1978, it maybe noted as follows:a) The first four results are straightway

accepted, the sample strength beinggreater than the characteristic stren­gth (20 Nz'mm') in each case.

b) The Sth result of 18 Nzrnm! is lessthan the characteristic strength(20 N/ptm2) and is compared with:

i) 0.8 x characteristic strengththat is, 16 Nz'mm",

ii) (20.0 - 1.3S x 4.0) that is 14.6Nzmm',Since 18 Nz'mm! is greater than

16 Nz mm-, we check theaverage strength of the samples,which is(24.8 + 27.0+ 28.5 + 23.6 +18.0) + S = 24.4 Nz'mm", and

20.0 + ~. 65 - '"1.;5Jx 4.0

= 23.6 Nz'mm",'Since the average of 5

samples is greater than 23.6Nz'mm? the 5th sample is accep­table.

iii) The 6th result is also acceptable.The 7th one (IS Nzrnm') islower than J6.0 Nzrnm'.The average strength of all theseven samples is,(24.8 + 27.0 +28.S +23.6 +18.0+ 21.6+ 15.0) + 7 = 22.6N/mm2

which is greater than

20.0 + [1.65 J ~ Jx 4.0

=22.1 Nz'mm-,The 7th sample thus does notcomply with the requirement(but cannot be deemed not tohave complied with the require­ment) the acceptance will de­pend upon the discretion of thedesigner.

---------------------- --~----_.

TABLE 28 BRf:AKDOWN OF STANDARD DEVIATION FOR COMPRESSIVE STRl':NGTH FORDI.~.~ERENT STANDARDS OF CONTROL

(Clause 4.1.1)

ITEM OF

CONTROL

STANDARD DEVIATION FOR MEAN STRENGTHS

Of JS N/mm2 OR MORE IN N/mm2

Item PlusTesting

All Items__----A....-~~-----,I Cement Cement

(one works) (many works)

Cement from one works 3.05 3.65

Cement from many works 3.60 4.15

Botching:

i) Cement in bulk, Servo-operated 2.~~ 3.30 4.50 4.85weighing

ii) Cement and aggregates weighed 3.80 4.30 '.25 5.60

iii) Cement weighed. 8urcaates by volume 4:55 4.9S 5.80 6.1S

iv) Cement and aagreaales by volume S.20 S.~O 6.35 6.65

v) Cement and allreaates by volume Gi a 3:0S 3.65 4.7S S.IOcontinuous mixer

Testing 2.0S

NOTE - Table 28 is from 'Concrete Constituents and Mix Proportions' (1974) by B. W. Shacklock and published byEyre an Spottiswoode Publicanons Ltd.• London.

----------------------_._---_.•._---_...~-

88

SP : 13·1911

TABLE 29 ASSUMED STANDAItD DEVIAnoN

(em,.. 4.1.2 11""4.2)

GRADE OF CONCU11J

M 10

M 15

M20M25M 30

M 35

M40

AIIuMED STANDAaDOBVIATION

N/mm2

2.3

3.54.6

5.3

6.0

6.3

6.6

TABLE 30 VALVES Of K

(C/QII.J!I 4. J.4)

PERCENT AGE OF R.!sULTS

BELOW THE CHAaACTERISTICSTRENOTH

50

16

10

S

2.S1.0

O.S

0.0

K

o1.00

1.28

1.6.5

1.96

2.332.SS

Infinity

APPENDIX A(Clause 4.1.2)

SAMPLE CALCULATION OF STANDARD DEVIATION

The results below represent a series of test results for a given grade of concrete.

SAMPLE CONCRETE SAMPLE CONCRETENUMBeR STRENGTH NUMBER STRENOTH

(kgf/cm2) (klf/cm2)

I 290 30 264

2 299 31 301

3 339 32 329

4 353 33 301

S 302 34 3S0

6 323 3S 3027 274 36 3048 292 37 299

9 288 38 2fT!

10 329 39 28S

11 3J6 40 281

12 297 /41 297

13 2.'S 42 271

14 301 43 280

15 316 44 281

16 2S2 4~ 283

17 308 46 344

18 2SS 47 313

19 302 48 316

20 274 49 271

21 294 SO 343

22 308 51 294

23 313 52 273

24 283 53 266

25 304 S4 260

26 260 55 266

27 28' '6 2S3

28 278 57 3'029 311 58 339

(Conlillwd)

89

SP : 13-1981

APPENDIX A - Contd

SAMPLE

NUMBER

S96061

6263

646~

666768697071

72

CONCRETE

STRENGTH(kgf/cm2)

330327308

339

281301

276290288367297276334

292

SAMPlfNUM8~R

7374

7576777879~o

81

8283

84

8586

--- ------~- ---

CON<.:JtETE

STRENGTH(kgf/cm2)

2903132882733223~

313346

357

313332339

351353

Group J (Samples 1 to 30)

n = 30Ex = 8 865Ex2 = 2 637 609

x = 295E(X-X)2 = 17 994.73

J17-994.73

S = = 24.91 kgf'/cm!30-1

This is the standard deviation of the concreteproduced to date.

Group 2 (Samples 31 to 56)n =: 26

I;x = 7 666Ex2 = 2 277 204

i = 294.85E(x - i)2 = 16 913.38

J16 913.38S = = 26.01 kgf'/cm!

26-1

Standard Deviation of Concrete ProducedUp to End of Group 2

n = 30+26 = 56I:x = 8 86S+ 7 666 = 16 '31

Ex2 = 2 637 «I)

+2 277 204 = 4 914 813(n - 1) = 56 - 1 = SS

90

x = Ex = 295.20n

E(x - X)2 = 34 920.84

_ J34920.84S - 55 = 25.20 kgf'/crn!

Gruup 3 (Samples 57 to 86)

n = 30Ex = 9 389

Ex2 = 2 960 011x = 312.97

E(x - X)2 = 21 566.97

S -J ~I 566.97 = 27.27 kgf'/cm!30-1

Pooling of Standard DeviationsNow to obtain the standard deviation of

the concrete class to date, it is necessary topool the standard deviations from differentgroups.

Total sum of squares, that is,~(x - X)2 = 34 '920.84 + 21 566.97

= 56 487.81E(n-l) = SS+29=84

S2 = Total sum of squares/total(0-1)

S = 2S.93 kaf/emJ

SP : 23-1982

xL..e-----I 3 • - --T-- - JtJ --- ---

I9S .4S -t,

'" t---- 2 ti..... I'"UJI Ito-

u, I10

IcrUJ ICD

"~ I c:::JZ ,

~ 1.35 8"

I

-,-..- -- 25 -----~

COMPRE SSIVE STRENG TH OF CONCRETE

Fig. 38 Normal Distribution of Concrete Strengths

41·233.730.9

~--VERY GOOD

(,.. 2." N/mm2)

21.114.1

COMPRESSIVE. STRENGTH, N I mm 2

Fig. 39 Typical Normal Frequency Curves for Different Control Ratings

NOTE - Figure 39 is from 'Recommended Practice for Evaluation of Compression Test Results of Field Concrete'reported by ACI Committee 214 (ACI Manual of Concrete Practice, Part I. J979). American Concrete Institute,USA.

91

SP : 13-1912

REFERENCES

I. IS: 456-1978 Code of practice for plain and rein­forced concrete (third '"WOlf).

2. SCHAKLOCK (B W). Concrete Constituents and MixProportions, 1974. Cement and Concrete Associa­tion, London.

92

3. ACI 214-77 Recommended practice for evaluation ~

of strenath teat results of concrete. American Con­crete Institute.

4. IS: 1199-1959 Methods of samplinaand analysis ofconcrete.

S. IS: 516-1959 Methods of test for strenath of con­crete.

SECTION 5

PRINCIPLES OF CONCRETE MIX DESIGN

SECTION 5 PRINCIPLES OF CONCRETE MIX DESIGN

5. J Basic Considerations - Design ofconcrete mixes involves determination of theproportions of the given constituents, name­ly, cement, water, coarse and fine aggregatesand admixtures, if any, which would pro­duce concrete possessing specified propertiesboth in the fresh and hardened states withthe maximum overall economy. Workabilityis specified as the important property of con­crete in the fresh state; for hardened statecompressive strength and durability areimportant. The mix design is, therefore,generally carried out for a particular com­pressive strength of concrete with adequateworkability so that fresh concrete can beproperly placed and compacted, and toachieve the required durability. In specialsituations, concrete can be designed for flex­ural strength or, for that matter, for anyother specific property of concrete. ,2.

The proportioning of concrete mixes isaccomplished by the .use of certain relation­ships established from experimental data,which afford reasonably accurate guide toselect the best combination of ingredients soas to achieve the desirable properties. Thefollowing basic assumptions are made indesign of plastic concrete mixes of mediumstrength:

a) The compressive strength of concrete isgoverned by its water-cement ratio,and

b) For a given aggregate characteristics,the workability of concrete is governedby its water content.

For high strength concrete mixes of lowworkability, considerable interaction occursbetween these two criteria and validity ofsuch assumptions may become limited.Moreover, there are various other factorswhich affect the properties of concrete, forexample, the quality and quantity of cement,water and aggregates; procedures of batch­ing, mixing, placing, compaction and cur­ing, etc. Therefore, the specific relationshipsthat are used in proportioning concretemixes should be considered only as a basisfor trial mixes. Further modifications arenecessary at thesite based on the situation aswell as specific materials available.

It is noted that a design in the strict sense

95

of the word is not possible in relation to con­crete mix proportioning. Concrete makingmaterials are essentially variable and the twobasic assumptions enumerated above maynot be held to be quantitatively exact underall situations. If more accurate relationshipsbetween the proportions of materials and theproperties of concrete (for example, rela­tionship' between compressive strength andwater-cement ratio or water content andworkability) are available, they should beused. Mix design on the basis of recommend­ed guidelines is really a process of making aninitial guess at the optimum combination ofingredients and final mix proportions isobtained only on the basis of\ further trialmixes.

5.2 Factors in the Choice of MixDesign - Both IS: 456-19783 as well asIS : 1343-198Q4 envisage that design of con­crete mix be based on the following factors:

a) Grade designation,b) Type of cement,c) Maximum nominal size of aggre-

gates,d) Minimum water-cement ratio.e) Workability, andf) Minimum cement content.

Out of these, the grade designation givesthe characteristic strength requirement ofconcrete. Depending upon the level of quali­ty control available at the site, the concretemix has to be designed for a target meanstrength (see 4.1.4) somewhat higher thanthe characteristic strength.

The workability of concrete for satisfac­tory placing and compaction is related to thesize and shape of the section to be concreted.the quantity and spacing of reinforcement,and the methods to be employed fortransportation, placing and compaction ofconcrete. A guide to workability require­ments for different conditions of placing isdescribed in Section 3 (see 3./.3).

The type of cement is important mainlythrough its influence on the rate of develop­ment of compressive strength of concrete aswell as durability under aggressive en­vironments. The different types of cements

SP : 13·1912

that can be used with the approval of theEngineer-in-Charge are discussed in 2.1.From among the different types of cementsavailable, the Engineer-in-Charge is requiredto make his choice dependin. upon the re­quirements of performance at hand. Wherevery high compressive strength is required.for example. in prestressed concrete railwaysleepers, high strenath ordinary Portland ce­ment conformlns to IS : 8112·1976' will befound suitable. Where an early strenathdevelopment is required, rapid hardeninaPortland cement conformin. to IS : 8041­19786 is preferable. On the other hand insituations where heat of hydration has to belimited. for example, in mass concrete con­structions, low heat Portland cement confor­ming to IS: 269-1976' is preferable.Portland pozzolana cement and Portlandslag cement are permitted for use in rein­forced concrete constructions; whilePortland slag cement is also permitted forprestressed concrete constructions. Withsuch blended cements, the rate of develop­ment of early strenath may be somewhatslower. On the other hand. these blendedcements render greater durability to the con..crete in sulphatic environment and seawater. The requirements of durability areachieved by limitations in terms of minimumcement content, the type of cement and themaximum water-cement ratio, as discussedin detail in Section 3.

The maximum nominal.size of auregatesto be used in concrete is governed by thesize of the section and spacing of thereinforcement. Both IS: 456-1978' andIS : 1343-198~. specify that the nominalmaximum size of coarse auregate shouldnot be greater than one-fourth of theminimum thickness of the member. and itshould be restricted to S nun less than theminimum clear distance between the mainbars or. S nun less than the minimum cover tothe reinforcement and S nun less' than thespacioa between the cables, strands orsheathing in case of prestressed concrete.Within these limits, the nominal maximumsize of coarse aureaates may be as large aspossible. In general, it is found that lar,erthe maximum siZe of aure_le, smaller isthe cement requirement for a particularwater-cement ratio (IH Fi,. 40'). ThIsarisesmainly from the fact that workability of con­crete increases with increue in maximumsize of .-repte. However, the maximum

96

size of agaregates also influences the com­pressive strength of concrete in that, for aparticular volume of aggregate. the com­pressive strength tends to increase withdecrease in the size of coarse aggregate. Thisis due to the fact that smaller size agaresatespresent a larger surface area for bondingwith the mortar matrix; it also results fromthe fact that the stress concentration in themortar-aggregate interfaces increase with in­crease in the maximum size of aggregatel •

There is thus an interaction of the maximumsize of auregate as well as the grade of con­crete which determine the 'strength efficien­cy' of the cement and. therefore, the require­ment of cement for a particular compressivestrength is to be specified (Fig. 41'). FromFig. 41' it is seen that for concrete withhigher water-cement ratio, larger maximumsize of aaregates may be beneficial whereasfor high strength concretes 10 or 20 mm sizeof aggregates is preferable. It is because ofsuch reasons that IS: 4S6-1978 3 andIS : 1343-19804, while recommending thatnominal size of coarse aggregates be as largeas possible. also suggest that for reinforcedand prestressed concrete works, aggregateshaving a maximum nominal sizeof 20 mm orsmaller are generally considered satisfactory.

In appropriate circumstances, the maxi­mum limit of cement content in the concretemay also have to be specified. This isbecause concrete mixes having high cementcontent may give rise to shrinkage, crackingand creep of concrete also increases with thecement paste content. In thick concrete sec­tions restrained against movements, highcement content may give rise to excessivecracking caused by differential thermalstresses due to hydration of cement in youngconcretes. For high strength concretes, in­creasing cement content beyond a certainvalue, of the order of SSO kg/rn! or so, maynot increase the compressive strength. Promthese considerations as well as those ofoverall economy, the maximum cement con­tent in the concrete mixes was limited to530 kg/mJ for prestressed concrete struc­tures (see IS : 1343-1980') and for reinforcedconcrete liquid retaining structures [seeIS : 3370 (Part 1)-I96~IOJ.

5.J Outline 01 Mix Design P.ro­cedure - The various factors for determin­in, the concrete mix proportions and' thestep by stlp procedure for concrete mix

design can be schematically represented as inFig. 42. The basic steps involved can be sum­marised as follows:

a) Arrive at the mean target strength fromthe characteristic strength specified andthe level of quality control,

b) Choose the water-cement ratio for meantarget strength and check for require­ments of durability,

c) Arrive at the water content for theworkability required.

d) Calculate cement content and check forrequirements of durability,

97

SP : 23-1982

e) Choose the relative proportion of thefine and coarse aggregates from thecharacteristics of coarse and fine aggre­gates,

t) Arrive at the concrete mix proportionsfor the first trial mix, and

g) Conduct trial mixes with suitable ad­justments till the final mix compositionis arrived at.

Most of the available mix design methodsare essentially based on the above procedure,the details of the same are discussed inSection 6.

SP : 23...1982

700,......-........----.,.--...,..-----.p--_

iWATER-CEMENT

RATIO

t"

500E--CIt......ZW....Z0U

t-Zw2wu

4·15 10 20

MAXIMUM SIZE OFAGGREGATE ,mm

Je 16

Fig. 40 Influence ofMaximum Size ofAggregate 0" Cement Requirement of Concrete Mix

NOTE - Figure 40 is from 'Hardened Concrete: Physical and Mechanical Aspects: ACI Monoaraph No.6' by A. M.Nevilleand published by American Concrete Institute.

98

SP : 23·1982

1.00 r----,----...------....----....... -.. -...

-- ~-~--+-------I

SLUMP:97 TO 147 mf'l'lCURING; 28 DAYS, MOIST

0·" 0 t-+---t--~-+-------+-----~~----+--------t

0.6 0 ...,....~-4___-__.l_....-----~-

0·30

0.50 t---~~r--__

0.10

o·g 0 1-----+-------+

>UZUJ

U[Lt.LUJ

:I:l-

e>ZWD::t­(/)

-­.....zw~wU

at.x

N---­Eu---

02 C' ......---I~--_~ --.L. ..L- .-.. .J

4·75 10 20 75 150

MAXIMUM SIZ E AGGREGATE 1 mm(LOG SCALE)

Fig. 4/ Maximum Size Aggregate for Strength Efficiency Envelope

99

SP : 13·1982

REFERENCES

SHACKLOCK (B W). Concrete constituents and mixproportions. 1974. Cement and Concrete Associa­tion, London.

2. GHOSH (R K), CHATIERJEE (M R) and RAM LAL.Flexural strength of concrete - its variations,relationships with compressive strength and use inconcrete mix design. Road Research BulletinNo. 16. Indian Roads Congress. 197~.

3. IS: 4S6-1978 Code of practice for plain and rein­forced concrete (third revision).

4. IS: 1343-1980 Code of practice for prestressedconcrete (first revisiom.

~. IS: 8112-1976 Specification for high strengthordinary Portland cement.

100

6. IS: 8041..1978 Specification for rapid hardeningPortland cement (first revision).

7. IS: 269·1976 Specification for ordinary and lowheat Portland cement (third revision).

8. NEVILLE (A M). Hardened concrete. Physical andmechanical aspects. 1971. ACI Monograph No.6.American Concrete Institute.

9. BLICK (R l), PETERSEN (C F) and WINTER (M E).Proportioning and controlling high strength con­crete in proportioning concrete mixes. ACt SpecialPublication SP 46. 1974. American ConcreteInstitute.

10. IS: 3370 (Part 1)..1965 Code of practice for con­crete structures for the storage of liquids: Part IGeneral requirements.

SECTION 6

METHODS OF CONCRETE MIX DESIGN

SECTION 6 METHODS OF CQNCRETE MIX DESIGN

6.0 Introduction - The mix designmethods being used in different countries aremostly based on empirical relationships,charts and graphs developed from extensiveexperimental investigations. Most of themfollow the same basic principles enunciatedin Section S and only minor variations existin different mix design methods in the pro­cess of selecting the mix proportions. Someof the common mix design methods formedium and high strength concretes havebeen discussed in this section. They are: (a)The ACI Mix Design Method, (b) The USBRMix Design Practice, (c) The British MixDesign Method and (d) The Mix DesignMethod according to Indian StandardRecommended Guidelines for Concrete MixDesign.

The ACI method I gives mix design fornormal and heavy weight concrete (air­entrained and non-air-entrained) in theworkability range of 25 to 100 mm slump.the maximum 28-day cylinder compressivestrength being 450 kgf/cm", There is aseparate method- for mix design of 'noslump' (slump being zero to 25 mm) concrete(air-entrained and non-air-entrained) havingmaximum 28-day cylinder compressivestrength of 475 kgf/cm-,

The British method) outlines a procedurefor design of normal concrete mixes (super­seding Road Note No. 4 method') having28-day cube compressive strength as high as7S0 kgf'/cm? for non-air-entrained concrete.The workability of concrete is given in termsof slump and Vee-Bee time.

In the USBR method", mix proportioningis done only for air-entrained concrete, themaximum 28-day cylinder compressivestrength being 4SS kgf/emI • when waterreducing and set controlling admixtures areused.

In all the four methods. the water-cementratio is chosen for the target mean strengthfrom empirical strength - w/c ratio rela­tionships and water content is chosen for therequired workability for aggregates insaturated surface dry condition. In so far asthe aaarcaate volume is concerned, themethods differ to some extent. In the ACImethod', the volume of coarse aggregate in

the concrete mix is first determined depend­ing on the maximum size of aggregate andthe grading of fine aggregate, whereas in theBritish method), the proportion of fine ag­gregate is determined first depending on themaximum size of aggregate, the degree ofworkability, the grading of fine aggregateand the water-cement ratio of the concrete

.mix.

In USBR method, the proportion of dry­roJded coarse aggregate is determined cor­responding to the maximum size of ag­gregate, a fixed fineness modulus of sandand a fixed workability in terms of slump.The ACI method also determines the pro­portions of dry-rodded coarse aggregate inthe concrete mix, the rodding being done ac­cording to ASTM C 296 for unit weight ofaggregate. It is based on the concept that indry-rodded void content, the differences inthe amount of mortar required for work­ability with different aggregates due to dif­ferences in particle shape and grading areautomatically compensated for.

The latest British mix design method) doesnot consider the combined aggregate gradingcurves like those used in Reference 4 (formaximum sizes of aggregate of 40 mm and20 mm) and those developed for 10 mm maxi­mum size of aggregate by Mcintosh andEmtroy". This implies admission to the useof aggregates of any grading as long as theyare within the grading limits specified by theappropriate Codes/Specifications.

In the ACI and USBR methods, the aircontent of concrete is considered to arrive atthe absolute volume of the mix ingredients.The batch weight of the materials per unitvolume of concrete is calculated from the ab­solute volumes. In the British method, thequantities of the ingredients are calculateddirectly from the wet density of concretewhich is dependent on specific gravity of thecombined aggregates (on saturated surface­dry condition).

The 'Indian Standard recommendedguidelines for mix design" includes designof normal concrete mixes (non-air­entrained), both for medium and high.strength concrete. In this method of mixdesign, the water content and proportion of

103

SP : 23-1981

fine aggregate corresponding to a maximumsize of aggregate are first determined forreference values of workability. water­cement ratio and grading of fine aggregate.The water content and the proportion of fineaggregate are then adjusted for any dif­ference in workability, water-cement ratioand grading of fine aggregate in any par­ticular case from the reference values. Thebatch weight of materials per unit volume ofconcrete is finally calculated by the absolutevolume method. The specific relationships(Figures and Tables) that are given in thismethod of mix design, have been arrived atby exhaustive tests at the Cement ResearchInstitute of India"!" as well as on the basisof data on concrete being designed and pro­duced in the country".

These guidelines, although based on dataon concrete, majority of which were madewith ope, are also almost equally applicableto concretes made with PPC. The final mixproportions, selected after trial mixes, mayentail some minor changes in each case; suchvariations may also be necessary in case ofcements of one type (either ope or PPC)but from different sources, or aggregatesvarying in quality. In so far as selection ofwater-cement ratio for the target com­pressive strength at 28-day in concerned,Fig. 46 is applicable for both ordinary-portland and portland pozzolana cementswith comparable validity. However, if amore precise estimate is made with the helpof Fig. 47 where cements are classified on thebasis of their 28-day strengths, then use ofope or PPC is not expected to make muchdifference.

Experiences with fly...ash-cement concretesindicate that in such cases, for comparableworkabilities, the water content can bereduced by about 3 to 5 percent and propor­tion of fine aggregates reduced by 2 to 4percentage points. It is doubtful whethersuch generalization can be straightway ex­tended in case of concretes made with PPCalso. .but any difference that would benecessary can be easily established by trialswith the materials at hand.

On the other hand, the British andAmerican methods mentioned earlier t soundas they are in principle, are based on the ex­perience, materials and construction techni­ques prevalent in those countries and theTables and Charts may need some modifica-

104

tions before they become applicable to In­dian conditions. In its approach, the ISmethod is similar to USBR method as well asthe method specified in IRe: 44-1976 12 mixdesign for concrete pavements. In the IRemethod, 7 days compressive strength of ce­ment has been considered as an additionalparameter influencing the relationship bet­ween water-cement ratio and the 28 dayscompressive strength of concrete. Thenecessary curves are shown in Fig. 2S ofSection 3.

6.1 The ACI Mix Design Practice - TheACI 211.1-771 recommends a method of mixdesign in which the water content determinesthe workability of the concrete mix for dif...ferent maximum size of aggregate. The bulkvolume of coarse aggregate per unit volumeof concrete is determined for different maxi­mum sizes of aggregate and for differentfineness moduli of sand. The water-cementratio is determined in the usual procedure tosatisfy both strength and durability re­quirements. The volume of fine aggregate isdetermined for unit volume of concrete,from the difference in volume between theconcrete and other ingredients. Allowancefor air content in concrete is made prior tocalculating the volume of fine aggregate.The procedure adopted for the selection ofmix proportions is as follows:

a) The water-cement ratio is selected fromTable 31 for the target mean 28-daycompressive strength.

b) The water content is selected fromTable 32 for the desired workabilityand maximum size of aggregate.

c) The cement content is calculated fromthe water content and the water-cementratio required for durability orstrength.

d) The coarse aggregate content is esti­mated from Table 33 for the maxi­mum size of aggregate and the fine­ness modulus of sand.

e) The fine aggregate content is determin­ed by subtracting the sum of thevolumes of coarse aggregate, cement,water and air content from the unitvolume of concrete.

For stiffer concrete mixes •J\CI 211-65 2

Recommended practice for selecting propor­tions for no-slump concrete' is to be follow­ed. This-is an extension of the ACI standard

211.1-19771 with two differences: (a) themeasurement of workability is done by com­pacting factor t Vee-Bee consistency or droptable test, instead of slump test, and (b) thecoarse aggregate content is higher for moreworkable mixes. Thus the tables for waterrequirement for different degrees ofworkability and coarse aggregate volurne perunit volume of concrete are changed. Therest of the mix design procedure is unaltered.

6.2 The USBR Mix Design Practice - Inthis method of mix design, the water contentof air-entrained concrete and the propor­tions of fine and coarse aggregates are deter­mined for a fixed workability and grading offine aggregate. The water content andpercentages of sand or coarse aggregate areadjusted for changes in the materials andmix proportions. The water-cement ratio forcompressive strength is determined in theusual procedure. The step-by-step procedureof mix proportioning is as follows:

a) The water-cement ratio for the targetmean 28 day compressive strength ofconcrete is determined from Table 34.This is for either air-entrained concreteor for air-entrained concrete withwater-reducing, set-controlling admix­tures.

b) Approximate air and water contentsand the percentages of sand and coarseaggregate per cubic metre of concreteare determined from Table 35. for con­crete containing natural sand with afineness modulus of 2.7S and havingworkability of 75 to 100 mm slump.

e) Adjustment of values in water contentand percentages of sand or coarse ag­gregate are made as provided in Table36'for changes in the fineness modulusof sand; slump of concrete, air con­tent, water-cement ratio and sand con­tent other than the reference values inTable 35.

d) The cement content is calculated usingthe selected water-cement ratio and thefinal water content of the mix is arrivedafter adjustment.

e) Proportions of aggregates are deter­mined, by estimating the quantity ofcoarse aggregate from Table 3S (dry­rodded unit weight coarse aggregatemethod) or by computing the totalsolid volume of sand and coarse ag­gregate in the concrete mix and

lOS

SP : 23·1982

multiplying the final percentage ofsand after adjustment. Either methodis satisfactory and will produce ap­proximately the same proportionsunder average conditions.

6.3 The British Mix Design Method (DOEMethod) - The latest method) replaces thetraditional British mix design method" ofRoad Note No.4. It discards the use ofspecific grading curves of the combined ag­gregates, uses the relationship betweenwater-cement ratio and compressive strengthof concrete depending on the type of cementand type of aggregates used. It replaces themix design Tables correlating water-cementratio, aggregate-cement ratio, maximum sizeof aggregate, type of aggregate differing inshapes (rounded and irregular), degree ofworkability and overall grading curves of thecombined aggregates in earlier Road NoteNo.4. Instead, water content required togive various levels of workability is deter­mined for two types of aggregates, namely J

crushed and uncrushed.

The degree of workability 'very low','low', 'medium' and 'high' have now beenreferred in terms of specific values of slumpand Vee-Bee time. The method of mix designresults in expressing the mix proportions interms of quantities of materials per unitvolume. of concrete in line with Europeanand American practice. The procedure ofmix proportioning is as follows:

a) The water-cement ratio for target meancompressive strength is determined us­ina Table 37 and Figure 43 and com­pared with the maximum water-cementratio specified for durability and thelower of these two values used.

b) The water content depending upon thetype and maximum size of aggregate togive a concrete of the specified slumpor Vee-Bee time is selected fromTable 38.

c) The cement content is calculated fromthe water-cement ratio and water con­tent of the mix.

d) The total aggregate content (saturatedand surface-dry) is determined by sub­tracting the cement and water contentfrom the wet density of concrete, "thewet density being obtained fromFig. 44 depending upon the water con­tent and the relative density of thecombined aggregate.

SP : 23-1981

e) Finally, the proportions of fine andcoarse aggregates are determined fromFig. 4S depending on the water-cementratio, the maximum size of aggregate,the workability level and the gradingzone of the fine aggregate.

6.4 Mix Design in Accordance with IndianStandard Recommended Guidelines forConcrete Mix DesignS - The followingbasic data are required to be specified fordesign of a concrete mix:

a) Characteristic compressive strength(that is, below which only a specifiedproportion of test results are allowedto fall) at 28 days <l:k);

b) Degree of workability desired (forguidance seeTable 22);

c) Limitations on the water-cement ratioand the minimum cement content toensure adequate durability for the typeof exposure (see Tables 23 to 26);

d) Type and maximum size of aggregateto be used;

e) Standard deviation (S) for compressivestrength of concrete: The standarddeviation has to be calculated from theresults of tests as described in 4. J.2.When the results of sufficient numberof tests under site conditions and forthe grade of concrete are not available,the values of standard deviation fordifferent degree of control as given inTable 39 may be adopted. The degreeof quality control expected dependsupon a number of parameters and it isnecessary that appropriate values fromTable 39 are chosen. Table 40 providesguidance regarding the degree of quali­ty control to be expected, dependingupon the infrastructure and practicesadopted at the construction site. Thiscan be used to characterise the level ofquality control in the particular situa­tion for using Table 39.

The step-by-step procedure of mix propor­tioning is as follows:

a) The target mean strength is first deter­mined as follows:

It=let. + X.S. (1)where It=taraet mean compressive

strenath at 28day••let=characteristic compressive

strenath at 28 day.,S = standard deviation,

106

K = a statistical value dependingupon the accepted proportionof low results and the numberof tests (see Table 30).

NOTE - As per IS : 4S6--197'. the characteristicstrength is defined as that value below which notmore than , percent of the test results are ex­pected to fall. In such case. K = 1.65 in equation(I).

b) The water-cement ratio for the targetmean strength is chosen from Fig. 46.'The water-cement ratio so chosen ischecked against the limiting water­cement ratio for the requirements ofdurability (Tables 23 to 26) and thelower of the two values adopted.Fig. 46 is based on a large number ofresults under Indian conditions, but ona given situation, may need slightmodifications depending upon thecharacteristics of cement available'<As such, it is used more as a guide andactual water-cement ratio is determin­ed by means of trial mixes as describedin Ref 8. A more precise estimate ofthe preliminary water-cement ratio cor­responding to the target averagestrength may be made from the rela­tionships shown in .Fig. 47, using thecurves corresponding to the 28-daycompressive strelllth of cement. It is tobe noted that cements have beencharacterised by its 28-day strength inFig. 47 rather than upon its 7-daystrength (see Fig. 25) because 28-daystrength of concrete is found to be bet­ter related to the 28-day strength of ce­ment rather than at earlier ages, moreso for blended cements. The relation­ship in Fig. 46 is really a mean curvethrough Fia. 47.

However. such trials will need 28days for determining the strengthcharacteristics of cement and atleastanother 28 days for the trial mixes. Inorder to cut down the time required fortrials, an alternative method has beensuuested in Ref 8.

In this method, the acceleratedstrenath (boiling water method in ac­cordance with IS: 9013-197811) of a'reference' concrete mix havin, water­cement ratio 0." and workability of0.80 compactina factor with the ce­ment proposed to be used is determiD­eel on 15 em cube specimens. The

SP : 23·1982

(3)

(2) andx 1000

x 1000

v = [w + ~ + ;. ~:. ]

1

the percentage of sand in the total ag­gregate already determined, the coarseand fine aggregates content per unitvolume of concrete are calculated fromthe following equations:

where,

V = absolute volume of freshconcrete

= gross volume (1 m') minusthe volume of entrappedair,

S, = specific gravity of cement,

W = mass of water (kg) per m' ofconcrete,

C = mass of cement (kg) per mJ

of concrete,p = ratio of fine aggregate to

total aggregate by absolutevolume,

fa' c. = total masses of fine ag­gregate and coarse ag­gregate, (kg) per m l of con­crete respectively, and

Sra. Sea = specific gravities ofsaturated surface dry fineaggregate and coarse ag­gregate respectively.

An illustrative example of mixdesign is reproduced from Reference 8.The actual mix proportions are arrivedat by means of a num!>v of trial mixes.In order to account for the variabilityin results of laboratory trials, it is ad­visable to carry out a number of testswith the final mix proportions arrivedat after such trial mixes. In addition.necessary adjustments in mix propor-·tions should also be carried out depen­ding upon the results obtained underactual constructlons.

nominal maximum size of aggregate ofthe 'reference' concrete should be10 mm and fine aggregate should con­form to Zone II of Table 4 ofIS : 383-197013• Corresponding to thisaccelerated strength, the water-cementratio is determined for the target meanstrength, from Fig. 48. These curves arebased on the relation between 28-daycompressive strength of concrete hav­ing water-cement ratio of 0.35, whichis found to be, on an average, 0.934times that of 28-day strength of cementtested as per IS : 4031-1968 11, and cor­relation of accelerated and normal28-day strength of concrete (seeSection 81t ) .

c) The air content (amount of entrappedair) is estimated from Table 41 for themaximum size of aggregate used.

d) The water content and percentage ofsand in total aggregate by absolutevolume are next selected from Tables42 and 43 for medium and highstrength concretes, respectively, for thefollowing standard reference condi­tions:

i) Crushed (angular) coarse ag­gregate,

ii) Fine aggregate consisting ofnatural sand conforming tograding zone II of Table 4,IS : 383-1970 13, in saturated sur­face dry condition,

iii) Water-cement ratio of 0.60 and0.3S for medium and high strengthconcretes respectively, and

iv) Workability corresponding tocompacting factor of 0.80.

e) For other conditions of workability,water-cement ratio, grading of fine ag­gregate and for rounded aggregates,adjustments in water content andpercentage of sand in total aggregateare made as per Table 44.

f) The cement content is calculated fromthe water-cement ratio and the finalwater content arrived after adjustment.The cement content so calculated ischecked against' the minimum cementcontent from the requirements ofdurability (Tables 23 to 26) and thegreater of the two values adopted.

g) With the quantities of water and ce­. ment per unit volume of concrete and

107

SP : 13-1982

c) Target Mean Stre".,th of Con­crete - For a tolerance factor of 1.65and using Table 39, the target meanstrength for the specified characteristiccube strength is 2O+4.6x 1.6S=27.6N/mm2•

e) Selection of Water and Sand. Con­tent - From Table 42, for 20 mmnominal maximum size aggregate andsand conforming to grading Zone II,water content per cubic meter of con­crete is equal to 186 kg and sand con­tent as percentage of total aggregate byabsolute volume is equal to 3S percent.

For change in values in water-cementratio, compacting factor and sand

d) Selection of Water-Cement Ratio ­From Fig. 46, the water-cement ratiorequired for the target mean strengthof 27.6 Nz'mm! is O.SO. This is lowerthan the maximum value of 0.65prescribed for 'Mild' exposure (seeTable 23).

6) Sieve analysisi) Coarse aggregateIi) Fine Agregate

IS Sieve Fine Aggregate RemarksSi~e (Percent Pass-

ing)

4.75 mm 100 Conformingto grading

2.36 mm 100 Zone III ofTable 4 of

1.18 mm 93 IS: 383.197013

600 micron 60300 micron 12

ISO micron 2

2.60

2.60

o.S per­cent1.0 per­cent

3.1S

Nil (ab­sorbedmoisturealso nil)2.0 per­cent

Good

Mild

20 Nzrnm!•

20mm(angular)

0.90compac­tingfactor

ii) Fine aggregate

ii) Fine aggregate

S) Free (surface) moisturei) Coarse aggregate

4) Degree of qualitycontrol, and

S) Type of exposure

b) Test Data for Materials

1) Cement used-ordinaryPortland cement satis­fying the requirementsof IS : 269... 197617

2) Specific gravity ofcement

3) i) Specific gravity otcoarse aggregates

ii) Specific gravity offine aggregate

4) Water absorptioni) Coarse aggregate

ILLUSTRATIVE EXAMPLE ON CON­CRETE MIX DESIGN (Grade M 10)

a) Design Stipulations

1) Characteristic com­pressive strength re-quired in the field at28-days

2) Maximum size ofaggregate

3) Degree of workability

IS Si~ve Analysis of Coone Percentage of Different RemarksSize AggregateFractions Fractions

(mm) (Percent Passing) .4- " ,, Am I II Combined\I II 60 Percent 40 Percent 100 Percent

20 100 100 60 40 100 Conforming to1.0 0 71.20 0 28.5 28.S Table 2 of4.7S 9.40 3.7 3.7 IS : 383·1970'32.36 0

108

belonging to Zone III, the followingadjustment is required:

SP : 13·1981

f. = 546 kg/m", andC. = 1187 kg/rn!

For decrease in water-cement ratio by (0.60-0.50) that is, 0.1 0 - 2.0For increase in compac-ting factor (0.9-0.8)that is, 0.10 +3 0For sand conforming toZone III of Table 4 ofIS : 383-197013 0 - 1.S

Total +3 - 3.5

Change in Condition(see Table 44)

AdjustmentRequired in

, A ,

Water Percent­content age sandpercent in total

aggregate

The mix proportion then becomes:

Water Cement Fine CoarseAggregate Aggregate

191.6 383 kg S46 kg 1187 kglitres

O.SO: 1 1.42: 3.09

h) Actual Quantities Required/or the Mixper Bag of Cement - The mix is,0.50: I: 1.42:3.09 (by mass). For SO kgof cement, the quantity of materialsare worked out as below:1) Cement = SO kg2) Sand =71.0 kg3) Coarse Aggregate = 154.5 kg

(Fraction I = 92.'( kg,Fraction II = 61.8 kg).

Therefore required sand content aspercentage of total aggregate by ab­solute volume=35-3.S=31.5 per­cent.Required water content =186+5.58=191.6 litres/rn'.

t) Determination of Cement Contentwater..cement ratio = 0.50

water = 191.6 litres191.6

cement = 0.50 = 383 kg/rn!

This cement content is adequate for'mild' exposure condition (seeTable 13).

g) Determination of Coarse and FineAg­gregate Content - From Table 41 t forthe specified maximum size of ag­gregate of 20 mm, the amount ofentrapped air in the wet concrete is2 percent. Taking this into account andapplying equations 2 & 3.

0.98 m3

[383 1 f. ]

= 191.6 + 3.1S + O.3IS . 2.60

1x 1 000

and 0.98m3

[383 1 c. ]

== 191.6 + 3.15 + 0.685 · 2.60

1x 1000

109

4) Water:i) For water-cement ratio of 0.50,

water =25.0 litresii) Extra water to be added for ab­

sorption in case of coarse ag­gregate, at 0.5 percent bymass =(+ ) 0.77 litres

iii) Water to be deducted for freemoisture present in sand, at2 percent by mass = (-) 1.42litres

iv) Actual quantity of water to beadded =2S.0+0.77-1.42=24.3Slitres

5) Actual quantity of sand required afterallowing for mass of freemoisture = 71.0 + 1.42 = 72.42 kg

6) Actual quantity of coarse aggregate re­quired:

i) Fraction I:: 92.7 - 0.46. =92.24 kg

ii) Fraction 11=61.8-0.31=61.49 kg

Therefore, the actual quantities of dif­ferent constituents required for the mixare:

water =24.35 kgcement = 50.00 kgsand ::: 72.42 kg

Coarse awepte:Fraction I - 92.24 kgFraction II = 61.49 kg

SP : 13-1912

TABLE 31 RELATIONSHIP BETWEEN WATER-eEMENT RATIO AND COMPRESSIVESTRENGTH Of CONCRETE

(CIQUM 6.1)

COMPRESSIVE STRENOTH

AT 28 DAYS, kif/em'WATER-CEMENT RATIO, BY WEIGHT

------------',,~---------,, Non-Air-Entrained Air-Entrained Concrete

Concrete

(I)

4S0400

3S0

3002S0200

ISO

(2)

0.380.43

0.48

O.~~

0.62

0.70

0.80

(3)

0.40

0.46

0.'30.61

0.71

NOTE - Table 31 is from tRecommended Practice for Selecting Proportions for Norm" Weight Concrete' Reportedby ACI Committee 211 (ACI Manual of Concrete Practice, Part I, 1979). American Concrete Institute, USA.

TABLE 31 APPROXIMATE MIXING WATER (ka/.3 OF CONCRETE) REQUIREMENTS FORDIFFERENT SLUMPS AND MAXIMUM SIZES or AGGREGATES

(C/Quw 6.1)

SLUMP, em MAxIMUM SIZES OF AOOUOATBS IN mm

I "10 12.5 20 2~ 40 50 70 150

Non-Air-Entrained Concrete

3 to.s 205 200 185 180 160 155 145 1158 to 10 22S 21S 200 195 175 170 160 I~

15 to 18 240 230 210 lOS 18' 180 170

Approximate amount of entrained air in non: 3.0 2.5 2.0 1.5 1.0 0.5 0.3 0.2air..cntrained concrete, percent

3.0

120

13~

135150160

3.5

Air-Entrained Concrete"165 160 14' 140

180 175 160 155

190 185 170 1656.0 5.0 4.5 4.0

175

190205

7.0

3 to'8 to 1015 &0 18

180

200215

Recommended aver_Ie total air content, 8.0percent

NOTE - Table 32 is from 'RecommendedPractice for Selectinl Proportions for Normal Wei.ht Concrete' Reportedby ACI Committee 211 (ACI Manual of Concrete Practice, Part I, 1979). AmericanConcrete Institute. USA.

110

SP : 23-1982

-- ----------

TABLE 33 VOLUME OF DRY-RODDED{~OARS~ AGGREGATE PER UNIT

VOl..UME OF CONl'Ri..TE

tClause 6 I)

TABI..E 34 PROBABLE MINIMUM AVERAGE(,'OMPRJ-:SSIVE STRENGTH 0.' ( ONCRl.TE FOR

vARIOUS W AT.:R·Ci.-Mf:'lT RATIOS

(Clause 6 2)

(I) (2) (3)

0.40 399 4SS

o45 343 392

O.SO 294 336

0.55 252 294

0.60 217 252

o65 182 217

0.70 J54 189NOTf.. - Table 34 IS from 'Concrete Manual' (EighthEdition Revised Repnnt, 1981). Bureau of Reclamation,United States Department of the Interior, USA.

MAXIMUM Fll'.l \jl-')~ MOOLl r OF S"'~()

Size OFr--- - ----A.-.____~

AGGREC,ATE 2.40 260 2.80 300mm( I) (2) (3) (4) (5)

10 0.50 0.48 0.46 044

12.5 0.59 o 57 o 55 0.S3

20 066 064 0.62 060

25 071 069 0.67 0.65

40 0.76 0'74 o 72 0.70

~O o 7R o 76 o 74 0.72

70 o 81 o 79 o 77 o 75

ISO o 87 o 85 0.83 o 81

Nore - Table 33 I~ from •Recommended Pracuce forSelecting Proporuons tor Normal Weight Concrete'Reported by ACI Committee 211 (ACI Manual ofConcrete Pracnce, Part I, 1979) Amerrcan ConcreteInstitute. lJSA

\\' ATfR CEMENT

RATIO BY

WE=.IGtiT

COMPRESSIVE STREN(JTH

Al 28 DAYS (kgf/cm2)r----~-~-~-~,

Au-Entrained Air-EntramedConcrete Concrete Wit h

Water-Reducing.Set-Controlhng

Admixtures

TABLE 35 APPROXIMATf.. AIR AND WATER ('ONTENTS PER ('URIC METt..R Of co-«.RETlAND THE PROPORTIONS OF FINE AND (-'OARSE AGGRt..GATt..

(Clause 6.2)

MAXIMUM RECOMMENDED SAND, PERC I:NT PER<"fNT, DRY A1R-ENTRAIN~D AIR-ENTRAINED

SIZE OF AIR CONTENT, Of TOTAL RODDED UNIT CONCRETL CONCRETE WITH

COAR<iE PERCENT AGGRI-<JATE WEIGHT Of COARSE AVERAGE WATER WATE.R REDUCING,

AG0RI:.<JATE By SOLID AGGRE0ATE PEl CONTl:NT SET -CONTROLlINL

mm VOLUME UNIT VOlU\1E kg/m3 ADMIXTURE,

OF CON( RETE AVERAGE WATER

CONTENTkg/m)

(J) (2) (3) (4) (5) (6)

10 8 60 41 189 177

13 7 50 52 180 168

20 6 42 62 165 156

25 5 37 67 156 147

40 45 34 13 145 136

SO 4 30 76 136 122

7S 3.5 28 81 121 112

ISO 3 24 87 97 91

NOTE I - This table is applicable for concrete containing natural sand with fineness modulus of 2 75 and averagecoarse aggregate and having a slump of 7S to 100 mm at the mixer.

NOTE 2 - Table 35 is from 'Concrete Manual', (EIghth Edition Revised Reprint, 1981). Bureau of Reclamation,United States Department of the Interior, USA.

111

SP : 23-1982

---------------------------------- .._-----TARLt: .16 ADJUSTMENT OF VALUES OF WATER CONTENT. PERCENT SANl) AND Pt:R<:t:NT

OF DRY-RODDED COARSE AGGREGATE

(Clause 6.2)

CHANGES IN MATERIAL

OR MIX PROPORTIONS rz:':Water ContentPercent

ADJUSTMENT REQUIRED IN

----/\.--~-- _. :\Sand Percent. Dry-Rodded

Percent Coarse Aggregate

(I) (2) (3) (4)

± 1.0

±2.0

±I

±O.S

± O.S to 1.0

±3

±3

±J

Each 0.1 increase or decrease in finenessmodulus of sand

Each 2S rom increase or decrease in slump

Each 1 percent increase or decrease in aircontent

Each O.OS increase or decrease in water­cement ratio

Each I percent increase or decrease in sandcontent

NOTE - Table 36 is from 'Concrete Manual'. (Eighth Edition Revised Reprint. 1981). Bureau of Reclamation,United States Department of the Interior, USA.

TABLE 37 APPROXIMATE COMPRESSIVESTRENGTHS OF CONCRETE MIXES MADE

WITH WATER-CEMENT RATIO 0." 0.5

(Clause 6.3)

TABI..E JI APPROXIMATE ~'ATERCONTENTS(kg/m J) REQUIRED TO GIVE VARIOUS LEVELS

OF WORKABILITY

(Clause 6.3)

0-10 10-30 30-60 6O-J80> 12 6-12 3-6 0-3

20

40

SLUMP (rnm) ­VEE- 8ft: (5) -

TYPE OF

AGGREGATE

MAXIMUM

SIZE OFAGGREGATE

(mm)

(1)

10

2/3 W, + 1/3 We

(2) (3) (4) (S) (6)

Uncrushed ISO 180 205 225

Crushed 180 205 230 150Uncrushed 13S 160 180 t9~

Crushed 170 190 210 225

Uncrushed liS 140 160 17S

Crushed ISS 175 190 20S

NOTE I - When coarse and fine aggregates of differenttypes are used. the water content is estimated by theexpression:

whereW,== water content appropriate to type of fine

aggregate, andWe = water content appropriate to type of coarse

aggregate.

NOTE 2 - Table 38 is from 'Design of Normal Con­crete Mixes (197S)' by D. C. Teychenne, R. E. Franklinand H. C. Erntroy. Contributed by courtesy of theDirector, Building Research Establishment andreproduced by the permission of the Controller of HerBritannic Majesty's Stationery Office. Crowncopyright.

ss

S3

60

4840

47

4634

27

33

18

25

30 40

23

(~) (4) (S) (6)(2)

Crushed

Uncrushed

Uncrushed

Crushed

TYPE OF COMPRESSIVE

COARSE STRENGTH (N/mm2)

AGGREGATE , Age(days) - \

3 1 28 91.

(1)

TYPE OF

CEMENT

Ordinary 1PortlandCement

orSulphate

Resisting JPortlandCement

Rapid }HardeningPortlandCement

NOTE - Table 37 is from 'Desian of Normal ConcreteMixes (1975)' by D. C. Teyehenne, R. E. Franklin andH. C. Erntroy. Contributed by courtesy of the Director,Building Research Establishment and reproduced by thepermission of the Controller of Her Britannic Majesty'sStationery Office. Crown copyright.

112

SP : 23-1981

TABLt: 41 APPROXIMATE t__ NTRAPPEDAIR ('()NTf:NT

(Clause 6.4)

NOTl- - Table 41 i4i from 'Hardened Concrete;Mechanical Aspects: ACI Monograph No.6 (1971)' byA. M. Neville with the permission of the AmericanConcrete Institute, USA.

TABtE 42 APPROXIMATE SAND AND WATER(~ONTENTS PI':R ClJBIC METR.: OF CONCRETF:

(Clause 6.4)

W/(' =0.60Workability = 0.80 CF

(Applicable for concrete up to grade ~ 35)

- - ~____ ~ ... r ____... __ .... _

TABLE 39 SUGGESTED VALU es OF STAN I)ARDI)EVIATION

(Clouse 6.4)

GRADE OF S I ANDARD DfVIA liON "OR DIFI'[RE:NT

CONCRETE DElJRl:f 0 .. (~O"'TROI (N/mm2)r---~ ~ - _---A-___

Very Good Good Fair~

(I) (2) (3) (4)

1'.1 10 2.0 2.3 3.1

M IS 2.5 3.5 4.5

M 20 3.6 4.6 5.6

M 25 4.3 S.3 6.3

M 30 5.0 6.0 7.0

M 35 5.3 6.3 7.3

M40 5.6 6.6 7.6

M 45 6.0 7.0 8.0

M 50 6.4 7.4 8.4

M 55 6.7 7.7 8.7

M60 6.8 7.8 8.8

- ~ -----

NO\1INAl MAXIMUM SllE:.

0 .. AGGRf.(,A TE (rnm)

(I)

10

20

40

ENTRAPPl-O AIR, A5

PERCEST OF VOL UMf OF­

CONC"RETE

(2)

3.0

2.0

1.0

·Water content corresponding to saturated surface dryaggregate.

TABl.E 40 DE(~REE OF QUAI.lTY CONTROL.EXPt:CTl-:ll UNDt:H I)I.~.·ER[NT

SITE ('ON iJITIONS

(Clause 6.4)

DEGRE~ 0" CONDI flO"" OF

CONl ROL PRODl ( flON

Very Good Fresh cement from single source andregular tests, weighbatching of allmaterials, aggregates supplied insingle sizes. control of aggregategrading and moisture content, controlof water added, frequent supervrsion,regular workability and strength tests,field laboratory faciliues.

Good Carefully stored cement and periodictests, weighbatchmg of all materials.controlled water, graded aggregatesupplied, occasional grading andmoisture tests, perrodic check ofworkability and strength, mtermutentsupervision, experienced workers.

Fair Proper storage of cement, volumehatching of all aggregates allowingfor bulking of sand, weighbatchmg ofcement, water content controlled byinspection of mix, occasional super­vision and tests.

113

~1AXIMVM

SIZE Of

AG('R~GArE

(mm)

(1)

10

20

40

WATER CONTfNl •PER CUBIC

Mf-1RE OF

CONCRETf

(kg)

(2)

208

186

16S

SAND AS PFRCE~T

OF TOTAl

AGGREGATl- 8Y

ABSOLUTE VOLUME

(3)

40

'\5

30

51» : 23·1982

~---------_._---~._-----.-

·Water content corresponding to saturated surface dryaggregate.

TABLE 43 APPROXIMATE SAND AND WATF:RCONTENTS PI':R CUBI(~ METRE OF CONCRETi:

(Clause 6.4)

W/C ~ 0.35Workability « 0.80 CF

(Applicable for concrete above grade M 35)

MAXIMUM

SIZE OF

AOOREGATE(mm)

(1)

10

20

WATER CONTENT­

PER CUBIC

METRE OF

CONCRETE(kg)

(2)

200180

SAND AS PERCENl

OF TOTAL

AGGREGATE BY

ABSOLUTE VOLUME

(3)

28

25

114

TARt.: 44 ADJUSTMENT ()F \'ALUES INWATER ('ONT.~N'f AND SANI)

pt:aCENTAG.: FOR OTHER t"ONDITIONS

(Clause 6.4)

CHANGE !~ ADJUSTMENT REQUIRED IN

CONDlflONS r: 1\~

STIPULATED Water Percent SanoFOR TABLES Content in Total41 AND 42 Aggregate

(1) (2) (3)

For sand conforming 0 + 1.5 Percentto grading Zone I, for Zone IZone III or Zone IV - 1.5 Percentof Table 4, for Zone IIIIS : 383-1970 - 3.0 Percent

for Zone IVIncrease or decrease 1: 3 Percent 0

in the value of com-pacting factory by 0.1

Each O.OS increase 0 ± I Percentor decrease in water-cement ratio

For rounded - ISkg/mJ -7 Percentaggregate

LIA

BlllT

VT

OC

HE

MIC

AL

AT

TA

CK

OR

SIZ

EO

FC

ON

eR

ET

EM

AS

S

IAG

EAT

WH

ICH

ST

RE

NG

TH

ISR

EQU

IRE

0

SIZ

EO

FS

EC

TIO

NA

ND

SP

AC

ING

OF

RE

INF

OR

CE

ME

NT

RE

QU

IRE

D

WO

RK

AB

ILIT

Y

GR

AD

ING

OF

FIN

EA

GG

RE

GA

TE

r

TYPE

AN

DS

HA

PE

OF

CO

AR

SE

AG

GR

EG

AT

E

T

I I

MA

XIM

UM

SIZ

EO

FA

GG

RE

GA

TE

I

I 11

1

WA

TE

R­

CEM

ENT

RA

TIO

TY

PE

OF

CE

ME

NT

i

CH

AR

AC

TE

RIS

TIC

ST

RE

NG

TH

.... \A

WA

TE

RC

ON

TE

NT

AN

DF

INE

AG

GR

EG

AT

EIN

PE

RC

EN

TO

F

TO

TA

LA

GG

REG

ATE

BYA

BSO

LU

TE

VO

LU

ME

1C

ON

eR

ET

Et-1

IX

PR

OP

OR

TIO

NS

ICA

PA

CIT

YO

F1

CO

NC

RE

TE

,..I

XE

RI

]rI

J~

WE

IGH

TO

FIN

GR

ED

IEN

TS

PE

RB

AT

CH

Fig

.42

Pro

cedu

reo

fC

oncr

ete

Mix

Des

ign

N e.- • .... =w

SP : 13-1982

STARTING LINE USING

DATA FROM TABLE~ _

I

1 0

80

90.----.....~-----.----.......-----.----......---...

70

N

E 60E--z~

J:.-50~

... -~--

zUJCtt-V)

UJ 40>InV)

wa:0-~ 300u

0-90·80·5 0·6 0·7WATER I CEMENT RATIO

Ol..----~---~----.......----------...----..,I0.3

Fig. 43 Relationship Between Compressive Strength and Water-Cement Ratio

NOTE - Figure 43 is reproduced from •Design of Normal Concrete Mixes (197Sr by D. C. Teychenne, R. E. Franklinand H. C. Erntroy. Contributed by courtesy of the Director, Building Research Establishment and reproduced by thepermission of the Controller of Her Britannic Majesty's Stationery Office. Crown Copyright.

116

&P : 23·1982

2700

RELATrVE DENSITOF COMBINED

2600 AGGREGATE (ON('I') SATURATED ANDe SURFACE DRY0- BASIS)~

--.. 2500 ---~~

LtJ 2 9....UICl

2400u~ 2 8uu,0 2 7>-

2300t:V)

2 &zUI0

I.- 2 5w 2200 -t~

2 4

260240140120 160 180 200 220

FREE -WATER CONTENT, kg/m 3

Fig. 44 Estimated Wet Density of Fully Compacted Concrete

2 100~ ~__--I. ""'-__"-"' ..L- ~ ."'--__--...I

100

NOTE - Figure 44 l~ reproduced from 'Design of Normal Concrete MIXe'i (197.5)' by D C Tcychenne, R E franklinand H C Erntroy Contnbuted by courtesy of the Director. BUIlding Research Estabhshment and reproduced by thepermission of the Controller ot Her Bntannu Majesty's Stationery Office. Crown Copynght

117

SP : 13·1981

MAXIMUM AGGREGATE SIZE : 20 mm

SLUMP: 0-10mmv- 8 : >'2 sec

10 -30 mm

6-12s~c

30- 60 mm3 - 6 sere

60-180 mm

0-3s«c

0 .. 8

0.80.6

0·40·8080·6

0.4 0.6 0.8 0.4 0-6 0.8

FREE-WATER/CEMENT RATIO

0·40·8

().&

0·60.4

0·4

70 I--~.---+---~-+-~

10 ~_--r...__....a.-__"","--~

0-2

50 ~---4-----+--- "'-

80 r-----......--.........- .......- ...

50"---+-

60

10 "'-----...---------0·2

60 t------+-----+---t---1

30

MAXIMUM AGGREGATE SIZE,: 40 mm70 r----......--.....,...--...-....

to- 30zUJuct~ 20

Fig. 45 Recommended Proportions of Fine Aggregate for Grading Zones J, 2, 3 and 4

NOTE - Figure 4S is from 'Design of Normal Concrete Mixes (197S)' by D. C. Teychenne, R. E. Franklin and H. C'.Erntroy. Contributed by courtesy of the Director, Building Research Establishment and reproduced by the permissionof the Controller of Her Britannic Majesty's Stationery Office. Crown Copyright.

I J8

SP : 23-1982

60-0

N

EE<,z

... 50·0UJ~

L&J~

UZou '0-0LLo:J:~

C>Z~ 30·0~(J)

LLI>enCI) 20-0LIJ~

0-~ou

~ 10·0o

tcoN

"-.

'<r-,'<,

.. ----

~,"'"<,~~

~ .............. ........ -_.--

o0-30 0·35 0·'0 0·50

WATER-CEMENT RAflO

0-55 0-60 0-65

Fig. 46 Generalized Relationship Between Free Water-Cement Ratio and CompressiveStrength of Concrete

119

SP : 23·1982

70-0,....-----,---..-.or-----r----...,..---"""P-'----....-----.

60·0

F

E50·

N 0EE

---.z C~ '0·0C) 8zUJQ:.... Aen

~ 30-0w0::UZ0U

> 20·0-c(0

I

CDN

10·0

--~~--+-----­

II

-f--- ­I

I

I

--1---

0·650-600·550·500'45o 400·35O....-.__---"'_-_--'--__........-_-.......---....Io----~--~0·30

WATER-CEMENT RATIO

28.Day Strength of Cement, Tested According to IS : 4031-1968

A - 31.9-36.8 N/mm 2 (325-375 kg/cm2)

B - 36.8-41.7 N/mm 2 (375-425 k~/cm2)

C·- 41.7-46.6 N/mm2 (425-475 kg/cml)D - 46.6-51.5 N/mm z (475-525 kg/cm2

)

E - 51.5-56.4 N/mm2 (525-575 kg/cm 2)

F - 56.4-61.3 N/mm 2 (575-625 kg/cm 2)

fig. 47 Relationship Between Free Water-Cement Ratio and Concrete Strength for DifferentCement Strengths

120

SP : 23-1982

10· 0 r-----r----,.....---,.....---or----~---...----

N60·0E

e F'"zW- E~

LcJ50-0~

uz 00uu.. C0

:r: '0-0to- a<-'zl&JQ: A~

(/)

LIJ 30·0>(J)(/')

LIJa:CL

~ 20·0u

>-c{0,GON 10-0 -

0·650·600·550·50O·LS0-35Oa.....----t..----~---'-----"-----~---""----.........0·30

WA1ER-CEMENT RATIO

Accelerated Strength (Tested According to IS : 9013-1978) of Reference Concrete Mixes

A-123-152 N/mm2 (125-155kg/cm 1)

B - 152-18 1 N/mm2 (155-185 kg/cm Z)

C - 18 1-21.1 N/mm J (185-215 kg/cm z)0-21.1-240 N/mm 1 (215-245kg/cm 1

)

E - 24 0-27 0 N/mm 2 (245-275 kg/cm 2)

F - 27.0-299 N/mm2 (275-305 kg/cn1 7)

Fig, 48 Retationsbip Between Free Water-Cement Ratio and Compressive Strength (~I

Concrete for Different Cement Strengths Determined on Reference Concrete .\fl\e\

(Accelerated Test - BOiling Water Me/hod)

121

SP : 23-1982

RrFrRENCE~

At I 211 1 77 Recommended prac u,.. e for velectingproportions for normal and heavy weightconcrete Arner u.an Concrete lnsuture

2 ALI 211 65 Recommended practice tor <elecungproportion for no slump concrete ArneruanConcrete Insuture

3 TE'CH["-NE (D C). FRA"Jkll'" (R L) and ERNTROY

(H C) Design of normal concrete mrxes 1975Department ot the Fnvironment Her "1aJe~t> s4;)tat ionery Office. London

4 ROAD RESfARCti LABOkA TOR' Design of concreterruxes Road Note No 4 1950 Her Majesty'sStationery Offue london

~ U ~ B R Concrete Manual, 1975 Eighth EditionDeparrnent of the Intenor Bureau of Reclamanon, USA

6 A~TM C 29 71 Standard lest method for urutweight of aggregate American Society for Testingand Matenals

7 \1c:INTO~H (J D) and ERNTROY (H C) The\\ orkabiluy of concrete rrnxes with 3/8 In aggregates Cement and Concrete AssocrauonResearch Report No 2, london. June19~5

8 IS 10262 1982 Recommended gurdelmes for concrete mix design

122

9 High strength concrete mixes (unpubhvhedreport), 1978 Cement Resear,.. h tnsunne of India,New Deihl

10 Experimental invcsugauon on medium strengthconcrete (unpublished report) 1978 <. ementResearch lnsutute of India. New Deihl

II VI~\E.~VARAYA(H C) and MULllcK (A K) Relationbetween water content In concrete mixes andcornpressrve strength Second InternationalCIB/RIL [M S)mpOS1Um on Moisture ProblemsIn BUilding Rotterdam. Netherlands, 1974

12 IRC 44-1976 Tentative guidelmes for cementconcrete mix design tor road pavements TheIndian Roads Congress, New Delhi

13 1<; 383 1970 Specifrcauon for coarse and faneaggregates from natural sources for concrete(second revision)

14 MALLICk (A K), IV[R (S R) and BARL (K II)Vanabihty of cements and adjustments In concretemixes by accelerated tests VII ERMCO Congrcsvlondon. 1983

15 I~ 9013 1978 Method of making, currng anddetermining compressive strength of acceleratedL.urcd concrete test specimens

16 IS 4031 1968 Methods of physrcal tests forhydrauhc cement

17 IS 269 1976 Specifrcanon for ordinary and lowheat Portland ~~ment ttturd revision)

SECTION 7

EXTREME WEATHER CONCRETING

SECTION 7 EXTREME WEATHER CONCRETING

7.0 What has been discussed so far inearlier sections refer to properties of con­crete for practice of concreting under 'nor­mal' conditions of temperature and humidi­ty. Nevertheless, there can be situationswhere the temperature of concrete at thetime of placing and the environmentaltemperature during concreting and its subse­quent curing periods may be different fromthose of normal conditions that is, either thetemperature is higher or lower. The situationmay become further aggravated by decreaseof the humidity in the atmosphere, increaseof wind or combinations of these. In suchsituations the properties and performance ofconcrete are likely to be affected unless dueprecautions are taken.

The problems of extreme weather con­creting stem mainly from the fact thatkinetics of hydration of cement, so essentialfor the development of strength and otherintrinsic properties of concrete, are altered.In general, an increase in temperature willaccelerate the rate of hydration and decreasein temperature will decelerate it. Therefore,the initial rate of development of strengthcan be expected to be faster in hot weatherand slower in cold weather. Coupled withthis is the problem of loss of water due toevaporation, which may affect theworkability of fresh concrete and plasticshrinkage that accompany the rapid dryingdue to consequential loss of water from thefresh concrete. Yet another aspect is the typeof microstructure of cement paste that isformed during such accelerated ordecelerated hydration; a higher temperaturemay lead to an accelerated growth ofhydrates which may not be as orderly or ascompact as can be expected, if the reactionswere to proceed at normal rate. In coldweather, although the initial strength may bereduced, the miscrostructure formed isperhaps more orderly and compact.

A comprehensive study on the effects ofmixing and curing temperature on thevarious properties of concrete like com­pressive strength, flexural strength,workability, air entrainment, etc, was car­ried out by the Portland Cement Associa­tion, which has formed the basis of cIS: 7861(Part 1)-1975 Code of practice for extreme

125

weather concreting: Part 1 Recommendedpractice for hot weather concreting' and'IS: 7861 (Part 11)-1981 Code of practice forextreme weather concreting: Part II Recom­mended practice for cold weather con­creting' .

7. J Hot Weather Concreting - Anyoperation of concreting done at atmospherictemperature above 40°C or any operation ofconcreting (other than steam curing) wherethe temperature of concrete at the time of itsplacement is expected to be beyond 40°Cmay be put under hot weather concreting.Concrete is not recommended to be placed ata temperature above 40°C without properprecautions. The climatic factors affectingconcrete in hot weather are high ambienttemperature and reduced relative humidity,the effects of which may be more pronounc­ed with increase in wind velocity. The effectsof hot weather are most critical duringperiods of rising temperature and fallingrelative humidity or both. There are somespecial problems involved in concreting inhot weather, arising both from temperaturerise of the concrete and consequentialincrease in rate of evaporation from thefresh concrete mix. These problems concernthe mixing, placing and curing of the con­crete.

7.1.1 EFFECTS OF HOT Wl-ATHER ON CON

CRETe - In the absence of special precau­tions, the effects of hot weather may bedescribed as follows:

a) Accelerated setting - A highertemperature of the fresh concreteresults in a more rapid hydration andleads to accelerated setting. Thisreduces the handling time of concreteand also lowers the strength of harden­ed concrete. Quick stiffening maynecessitate undesirable retempering byaddition of water. Added waterwithout proper adjustments in mixproportions will adversely affect theultimate quality of concrete in place,and may adversely influence place..ment, consolidation and finishing.With the increase in concretetemperature, the slump (workability)decreases and hence the water demand

SP : 23·1982

increases with increase in temperatureof concrete, for constant consistancy(see Fig. 22). As a typical example, itwas reported that approximately25 mm decrease in slump resulted foreach 11°C increase in the concretetemperature. Another disadvantagefrom accelerated setting of concrete isthe formation of cold joints.

b) Reduction in strength - Concretemixed, placed and cured at elevatedtemperatures normally develops higherearly strengths than concretes produc­ed and cured at normal temperaturesbut at 28 days or later strengths aregenerally lower. Tests have shown thatfor concretes placed and cured up to 28days at various temperatures rangingfrom 49°C to - 4°C at 100 percentrelative humidity, the initial strength(up to an age of 7 days or so) wasgenerally greater, at higher tem­peratures. However, the difference inthe strength at various temperaturetended to be narrower as the age ofconcrete increased, and indeed at anage of nearly one year the lowtemperature concrete developed higherstrength than those at highertemperatures (see Fig. 491) . For the in­fluence of simultaneous reduction inthe relative humidity, it was shown thatspecimens moulded and cured in air at23°C, 60 percent relative humidity andat 38°C, 25 percent relative humidity,produced strength of only 73 and 62percent, respectively, in comparisonwith the specimens moist cured at 23°Cfor 28 days. It was also found that thelarger the delay between casting andplacing, greater is the strength reduc­tion. High temperature results ingreater evaporation loss and hencenecessitates increase of mixing waterconsequently reducing strength.

c) Increased tendency to crack - Rapidevaporation may cause plasticshrinkage and cracking, and subse­quent cooling of the hardened concretewould introduce tensile stresses. It isgenerally believed that plasticshrinkage is likely to occur when therate of evaporation exceeds the rate atwhich bleeding water rises to the sur­face, but it has been recently foundthat cracks also form under a layer of

126

water and merely become apparent ondrying. The most important factorinfluencing plastic shrinkage crackingis the rate of evaporation of waterfrom the surface of the concrete. Thisdepends on the ambient temperature.the relative humidity, the wind speedand the concrete temperature. Resultsfrom a road construction indicatedthat the intensity of cracking wasproportional to the maximum daytemperature during construction.Cracking was almost confined to themorning work which was attributed tothe exposure of concrete to direct sunand higher air temperature for a longertime, than the concrete laid during theafternoon.

d) Rapid evaporation of water during cur­ing period - In order to obtain a goodconcrete the placing of an appropriatemix must be followed by curing in asuitable environment during the earlystages of hardening. The necessity ofcuring arises from the fact that hydra­tion of cement can take place only inwater-filled capillaries. For this reason,a loss of water by evaporation from thecapillaries must be. prevented. Furthermore, water lost- internally by self­desiccation has to be replaced by waterfrom outside. Rapid initial hydrationseems to form products of poorphysical structure, probably moreporous, so that a large proportion ofthe pores will remain unfilled. Thisleads to lower strength.

e) Difficulty in control of air content inair-entrained concrete - It is moredifficult to control air content in air­entrained concrete. This adds to thedifficulty of controlling workability.For a given amount of air-entrainingagent. hot concrete will entrain less airthan concrete at normal temperatures.

7. J.2 RECOMMENDFD PRACTICES ANO

PRECAUTIONS

7.J.2./ TEMPERATURE CONTROL OF CONCRETE

INGREDIENTS - The most direct approach tokeep concrete temperature down is by con­trolling the temperature of the ingredients.The aggregates and mixing water exert themost pronounced effect by virtue of theirquantity and specific heat, respectively.

SP : 23-1982

T =S(W. + We) + WYf + WI+ JYwa

(Ww - W)Tw + Wwa Twa- 79. 6 W.S(Wa + We) + Ww + W,+ W wa

+

a) Cold water as mixing water (withoutice)

S(Ta Wa + T4: W,) + (Tw Ww + Twa Wwa)

S(W.+ We)+ WWWWI

b) With ice added to mixing water

T =

lowest practical levels so that thetemperature of concrete is below 40°C at thetime of placement. The temperature of theconcrete at the tirne of leaving the mixer orbatching plant should be measured withsuitable metal-clad thermometer. In theabsence of such measurement. thetemperature may be calculated from thefollowing formula:

Aggregates may be kept shaded from directsun rays. They may be sprinkled with wateror may be cooled by methods, such as inun­dating them in cold water or by circulatingrefrigerated air through pipes or othersuitable methods. Mixing water has thegreatest effect on lowering the temperatureof concrete, because the specific heat ofwater (1.0) is nearly 5 times that of commonaggregates (0.22). The temperature of wateris easier to control than that of other ingre­dients. The use of cold mixing water willaffect a moderate reduction in concrete plac­ing temperature. Under certain cir­cumstances, reduction in water temperaturemay be most economically accomplished bymechanical refrigerator or mixing withcrushed ice. To take advantage of the latentheat of fusion, the ice shall be incorporateddirectly into the concrete as a part of mixingwater. Conditions shall be such that the ice iscompletely melted by the time mixing is com­pleted.

Investigations were carried out on theeffects of temperature of cement on thestrength of concrete. Cements havingtemperatures of 23°C, 64°C and 80°C wereused in preparing concretes, each at thetemperature at the end of mixing period of24 °C and 40°C, the final concretetemperature being attained by adjusting thetemperature of concrete ingredients (seeFig. SO). Tests showed that so long as thecomparison is made on the basis of equalconcrete temperatures, the temperature ofcement did not exert any significantinfluence on the strength of concrete.

7.1.2.2 PROPORTIONING OF CONCRETE MIX

MATERIALS AND MIX DESIGN - Mix should bedesigned to have minimum cement contentconsistent with other functionalrequirements. As far as possible, cementwith lower heat of hydration shall be prefer­red instead of cements having greaterfineness and heat of hydration.

Use of water-reducing and/or sct­retarding admixtures are beneficial. Suchadmixtures should, however-, be used afterproper evaluation.

7.1.2.3 PRODUCTION AND DEl.IVERY­

.Temperature of the aggregates, waterand cement- shall be maintained at the

where

T temperature of freshly mix­ed concrete (Oe);

Ta, t; T;.Twa = temperature of aggregate,cement, added mixingwater, and free water on ag­gregate, respectively (Oe);

Wa , Wwe'WWW}--fmass 0 aggregate, cement,wa', added mixing water t free

water on aggregate and icerespectively (kg); .and

S = Specific heat of cement andaggregate (Cal/g.X')

Examples for the calculation oftemperature of fresh concrete when coldwater or ice is added in place of mixing waterat higher temperature are reproduced belowfrom IS : 7861 (Part 1)-1975 2:

a) Cold water as mixing water (witnoutice)Consider a concrete mix having thefollowing ingredieras (per m '), and theinitial temperature shown against each:

Cement 336 kg at 35°CWater 170 kg at 30°CAggregates 1 850 kg at 45°CS = 0.22 Cal/g.oC

It is assumed that the aggregates aredry, that isWw.=o

127

SP : 23·1982

T =

T =

Hence, reduction in concretetemperature is:

(39.9- 33.4)OC= 6.5°C

The temperature (in °C) of fresh con­crete as mixed with these ingredientswill be:

0.22(45 x 1 850 + 35 x 336)+ lOx 170

7.2.J EFFECTS OF COLD WEATHER ON CON.

CRETING - In the absence of special precau­tions, effects of cold weather concreting maybe described as follows:

a) Delayed setting - When thetemperature is falling to about SoC orbelow, the development of concrete

7.2 Cold Weather Concreting - As waspointed out before, the production of con­crete in cold weather introduces specialproblems which do not arise while con­creting at normal temperatures. The pro­blems are mainly due to slower developmentof concrete strength. the damage that canhappen if concrete in the plastic state is ex­posed to low temperature which cause icelenses to form and expansion to occur withinthe pore structure, and subsequent damagedue to alternate freezing and thawing whenthe concrete has hardened. From the testscarried out at peA laboratories! referred toearlier it was found that, there is atemperature during the early life of concretewhich could be considered optimum withregard to its satisfactory performance atlater stages. Mainly on the basis of thesetests most of the codes do not advocate con­creting to be done at an atmospherictemperature below SoC. Accordingly, anyconcreting operation done at a temperaturebelow SoC is termed as cold weather con­creting.

(not dripping) gunny bags, hessian. cloth,etc. Once the concrete has attained somedegree of hardening sufficient to withstandsurface damage (approximately 12 hoursafter mixing), moist curing shall commence.The actual duration of curing shall dependupon the mix proportions, size of themember as well as the environmental condi­tions; however, in any case it shall not be lessthan 10 days. Continuous curing is impor­tant, because the volume changes due toalternate wetting and drying promote thedevelopment of surface cracking. On expos­ed unformed concrete surfaces, such aspavement slabs, wind is an important factorin the drying rate of concrete. Hence, windbreakers shall be provided as far as possible.On the hardened concrete and on flat sur­faces in particular, curing water shall not bemuch cooler than the concrete because of thepossibilities of thermal stressess and resul­tant cracking.

0.22(1850+336)+ 170=33.4°C

T

O.22(1 850 + 336) + 170=39.9°C

Suppose, the mixing water is added atSoC, then the temperature of concrete(in °C) as mixed will be:

0.22(45 x I 850 + 35 x 336)+ 5 x 170

b) With ice added to the mixing waterin the example under (a), suppose 50percent of the mixing water (that is,85 kg) is replaced by ice.Then the temperature of fresh concreteas mixed is given by:

0.22(45 x1 850 + 35 x 336)+ (170 - 85) x 30 - 79.6 x 85

0.22(1850+336)+85+85= 25.6°C

Hence, reduction in concrete temp..erature is:(39.9 - 25.6)OC=14.3°C

The period between mixing and deliveryshall be kept to an absolute minimum. At­tention shall be given to coordinate thedelivery of concrete with the rate of place..ment of concrete.

7.1.2.4 PLACEMENT, PROTECTION AND CUR·

ING - Formwork t reinforcement andsubgrade shall be sprinkled with cool waterjust prior to placement of concrete. The areaaround the work shall be kept wet to theextent possible to cool the surrounding airand increase its humidity. Speed of place­ment and finishing helps to minimize pro­blems in hot weather concreting. Sufficientmen and machinery shall be employed tohandle and place the concrete immediatelyon delivery.

Immediately after consolidation and sur­face finish, concrete shall be protected fromevaporation of moisture without lettingingress of external water, by means of wet

128

strength is retarded compared with thestrength development at normaltemperatures. The hardening periodnecessary before removal of formworkis thus increased and the experiencefrom concreting at normal temperaturecannot be used directly. Effects oftemperature of concrete on thestrength development can be expressedas in Fig. 51). Although the initialstrengths of concrete are lower, it hasnow been found that the long-termstrength of concrete will not be severelyaffected provided that the concrete hasbeen prevented from freezing during itsearly life lsee 7.2.1(b) below]. Thecombined effects of time andtemperature as expressed in terms of'maturity' of concrete was discussedearlier (see Section 3). However, suchconcept has not been found to be strict­ly applicable for winter concretingunder actual site conditions", One ofthe reasons may be that the actualtemperatures of concrete, which couldindeed be different from the ambienttemperature; were not taken into ac­count in such comparisons.

b) Freezing of concrete at earlystages - The permanent damage thatcan be expected when the concrete stillin fresh stage is exposed to freezingtemparature can be seen from Fig. 525.

It is generally felt that if concrete isallowed to freeze before a certain 'pre­hardening period' concrete may sufferirrepairable loss in its properties somuch so that even one cycle of freezingand thawing during the pre-hardeningperiod may reduce the compressivestrength to 50 percent of what could beexpected for normal temperature con­crete. Opinions differ as to the lengthof such 'pre-hardening period' whichindeed depends upon the type ofcement and the environmental condi­tions. While some specify it in terms ofthe time required to attain a com­pressive strength of the order of 3S to70 kgf'/crn", others have specified it interms of a period varying from 24hours to even 3 days depending uponthe degree of saturation and water­cement ratio.

c) Stresses due to temperature differen­tials - Large temperature differen-

SP : 23-1982

rials within the concrete member maypromote cracking and has a harmfuleffect on the durability. Such differen­tials are likely to occur in cold weatherat the time of removal of formwork.

7.2.2 RECO~1MENDl-,D PRACflCf-

7.2.2./ TEMPERATURE: (ON fROL or· C()NCRf:l rAGGREGATES - The most direct approach tokeep concrete temperature above the per­missible minimum is by controlling thetemperature of the ingredients. All availablemeans shall be used for maintaining thesematerials at as high a temperature as prac­ticable. Heating of the aggregates shall besuch that frozen lumps, lee and snow areeliminated and at the same time overheatingis avoided. The average temperature of anaggregate for an individual', batch shall notexceed 65°C. The mixing water shall beheated under such a 'control and in sufficientquality as to avoid appreciable fluctuation intemperature from batch to batch. The re­quired temperature of mixing water to pro­duce specified concrete can be obtained fromFig. 531 which are also included in IS : 7861(Part 11)-1981 7• The heated water shall comein direct contact with aggregate first and notin contact with cement. Water havingtemperature up to the boiling point may beused provided the aggregate i~ cold enoughto reduce the temperature.

7. 2 . 2 .2 USE 0 F ll'~ ~ U L A r I N (j f () RM .

WORK - Sufficient amount of heat isgenerated during hydration of cement. Suchheat can be gainfully conserved by having in­sulating formwork covers which may main­tain the concrete temperature above thedesirable limits up to the first 3 days and(may be even up to 7 days), even when theambient temperatures are lower. The form­work covers can be of timber, clean straw,blankets, sacking, tarpaulins, plast icsheeting, etc, in conjunction with air gap asinsulation, efficiency of which depends uponthe thermal conductivity of the medium aswell as on the ambient temperature condi­tions. Tests on 90 em concrete cubes madewith ordinary Portland cement (310 kg/rn ')and insulated either with 50 rnrn lumber or20 mm plywood showed that the concretetemperatures were nearly 30 to 40°C abovethe air temperature (see Fig. 54'). Formoderately cold weather t timber formworksalone are sufficient and are preferable to

129

SP : 23-1982

steel forrnworks. The following comparisonof different insulating materials, taken fromACI 306-19661 indicates how the efficiencyof different combination varies due to theircoefficient of thermal conductivity; theinsulating values are indicated with referenceto 25 rnm commercial blankets as reference:

Insulating Material EquivalentThickness

mm

25 mm commercial blanket 2S2S mm loose-fill insulation of 25

fibrous type

25 mm insulating board 2025 mm saw dust 1525 mm timber 825 mm damp sand 0.6

In addition to insulated formworks, theconcreting operations may sometimes re­quire to be carried out in heated enclosures.The size of the section should be taken intoaccount while using insulated formworksbecause of the thermal gradient that mayresult across the cross-section; usually thetemperature at the centre of such massivesection will be somewhat higher than nearthe formwork and the temperature aroundthe corner are usually the lowest.

7.2.2.3 PROPORTIONING OF CONCRETE INGRE­

DIENTS - Since the quantity of cement in themix affects the rate of increase intemperature, additional quantity of ordinaryPortland cement, rapid hardening Portlandcement or accelerating admixtures used withproper precaution can help in getting the re­quired strength in a shorter period. Air­entraining agents are generally recommend­ed for use in cold weather. Air-entrainmentincreases the resistance of hardened concreteto freezing and thawing and normally at thesame time improves the workability of freshconcrete. In cold weather concrete construc­tions, calcium chloride has been used as anaccelerating admixture. However the matteris a subject of big controversy in so far asincidence of corrosion of reinforcing steel isconsidered. The winter condition as expectedin India may not be as severe as elsewhere,where the successful use of calcium chlorideis cited. In a study to stimulate the strengthdevelopment of concrete under wintry condi­tion as in India, it was found that perhaps airentrained concrete with insulated formworkis sufficient to ensure the minimum concretetemperature as well as to prevent the fresh

concrete from damage during the pre­hardening period'. In any case, calciumchloride shall not be used in prestressedconcrete construction.

7.2.2.4 Pl.ACEMENT. PRorECTION AND CUR·

ING - Before any concrete is placed, all ice,snow and frost shall be completely removed.It should be remembered that no amount ofinsulation can supply heat at below freezingtemperature. Care should be taken to seethat the surface on which the concrete is tobe placed and the steel and all eminent partsare sufficiently warm. It will be wrong to ex­pect that the heat from the fresh concretewill thaw a frozen surface or mould insidethe formwork without damaging the con­crete. Whenever it is proposed to placeconcrete at or below 2°C, it is essential toknow that the time taken for the concretetemperature to fall to freezing point is atleast equal to the minimum prehardeningperiod. For weather conditions below- lOC t the temperature of the concrete asmixed should be IS.SoC and as placed IOoe.During periods of freezing or near-freezingconditions, water curing is not necessary.

7.2.2.5 DEL.AYED REMOVAL OF FORM

WORK - Because of slower rate of gain ofstrength during the cold weather, the form­work and props have to be kept in place forlonger time than in usual concreting prac­tice. The appropriate time for removal offormwork may be ascertained from thestrength of test cubes left at site under thesame conditions of temperature and humidi­ty as the structural element concerned. Thetime of removal of formwork thus arrivedshould not be less than the duration ofnecessary protection afforded by the form­work (see 7.2.2.2). As a general guidance,the minimum time limits for stripping offormwork of members (carrying only its ownweight), and at air temperature about 3°e asgiven in Reference 7 is reproduced below:

With Withope RHC

.pays Days

Beam sides, walls, columns 5 3Slabs (props left under) 7 4Beams soffits (props left 14 8

under)Removal of props to slabs 14 8Removal of props to 28 16

beams

130

SP : 23·1982

200,----,----r------r-------,..---------r------~

36590287

~--- .- - -- .- - - • ------ ---- ------ --.:.I11III-__-_~-

31

13·eIt·C

o ~--- -_4·C23 C - --

~7.......,...-~~-_++-----_32·CJ.O·C49·C

0w.....4~ 1600z

UJC)

~

.....4

:I:

~ 120zwa:~

(J)

UJ

~(/)enLlJQ: 800-~

au.u

0C"")

C't

LA.-oUJ 40C>~.....zUJua:UJQ..

0

AGE OF TEST DAYS (lOG SCALE)

Fig. 49 Effect of Temperature on Compressive Strength of Concrete Made with OrdinaryPortland Cement

131

SP : 23-1982

N

EE-...z

9080

---0

7060

___1--0---

so30

0-

0--

20

1-----0--

CONCRETE TEMPERATURE 2' ·C, CUREDAT 23 ·C, ,0 0 PE RCEN' A H

CONCRETE TE~PERATURE 'O·C CUREO, DAVS AT 40·C ANO 100 J.I(' RCE'NT RH,

~t-MA'NOt-k At 23°t, 100 PERl.fNT WH

III

IIt

II

1

II

I10

,I I--+0---------11-- --~ -~ --- -r' . -

I I

1 I

LEGEND

60,...----..,.....-----r-------,..----r-----..------r-----r-------r-----,

40 - --

so

...J<{Q::::>xw2'--- ..:-- -A.- -....;.. ---a. "'""-- ~ ~ ---"- _

.J 0U.

w>~ 30-wa::n,~N

o E20u E.......z

• 6w....w~

u~ 5 ---- -U

u,o

~ ~C>ZW~t-(/) 3 ---

.w.­W0:UZoU

LLoJ:.....ozw~....(/)

TEMPERATURE OF CEMENT ,oe

Fig. 50 Effect of Temperature of Cement on Concrete Strength

'132

SP : 23.J982

~~~~

a

A ~ 0x-_.-

V - ~

./

Y- -

LEGEND-~---- CEMENT CONTENT

/ OF THE Mrx (kg/m 3)a -- 200

V 0 ----D -- 270

~I/ X -- 340 --

---- - -~ - -

~---

211510-5-10 o 5TEMPERATURE. ·c

Fig. 5/ Effect of Low Temperature on Compressive Strength of Concrete

%

t; .00zLLI

~ 90enQ

~ 80u> 70-'...c 60Z

~ SO

~9 40f:~ 301&1

~ 20....Z&IJ 10u~.

IIIQ.. 0

2S22

------6------- ----

/ /

4 7 10 13 16 19NUMBER OF CYCLES OF FREEZING AND THAWING

Fig. 52 Effect of Cycles of Freezing and Thawing of Fresh Concrete During Prehardentngon Compressive Strength

IIIC)......z~ 1OI-----+-----+-----~~~r....-.,~~--hL-~~----,~+--+---~~-~-...,'-czIIIG.. 0,

:r.110-------------...----------------------~

"~100~--a:~ 90t-------+--- STANDARD MOIST CURED CYLINDER STRENGTH

oI&J~ 80 t-- +-- -+-- -.+---- -+- --+-- -+- --l-__--J

:)U

... 70 .......---+-----+------+------+-----+------+---~ ,---06-----------01

ens~ 601-----+-----.........----t------+----..........----+--~-4- ------I

C~c 50.......-----ot------..-.-....---~QZ~ 40 ....-."--...-.'-~....._"II'__-wl--~~__~-~---~~---~+----.----+-

'"

133

SP : 23-1982

CEMENTCONT ENT: JOO kg/m

~--r· ~i-

" 80-------------;--.........--..--.....-......z)C

i 60lL uo. ~

wa:Q: w40:J~

~~~

w 20Q.2:UJto-

o 5 10 1S 20 25TEMPERATURE OF CONCRETE;C

MOISTURE CONTENT OFAGGREGATE

DAMP (4% IN FINE, 1% IN15 20 2S COARSE)

OF CONCRETE,-C WET (8% IN FINE, 2% INCOARSE)

o

8 Qr-----.,..----.....---...--r-----,........---.

TEMPERATURE OF AGGREGATE AND CONTAINED MOISTURE = 1-C

TEMPERATURE OFCEMENT = SoC

1S 20 25OF CONCRETE,~

o

C) &0 r-----.------.----,~-__-____.z~

Fig 53 Required Temperature of MIxing Water to Produce Healed Concrete

134

SP : 23·1911

20 SOmm Lum Ir--I I

.---.....- ....."..,..~r20mm plywood &-,,(-1- -,~::::::.. ... - -- t~rp~ulin t

II '--'1 rr--:---.J_--

~- ~ ~ -\- - -: - -- ! - - +-'- ~: ~~- -.::.Cement I 3 I 120mm plywood Icontent:310kg/m I I

I I I I__tAi~ t«!"p«~.tu~~. ~_. i,'\, __"_+- __

''-. I ........... --. ,.1'-' ,-""",' '-_.

8 12 16 20 2' 2,8 32 36HOURS SINC! CASTING

Fig. 54 Form Protection - 90 em Concrete Cube, Thermocouple at Centre of Face(Next to Form)

135

SP : 13-1982

RLFl:RFN(:ES

Kl.IEG[k (P). Effect of mixing and curingtemperature on concrete strength. Bulletin 103.Research and Development Laboratories of thePortland Cement Association. Chicago, 1958.

2. IS: 7861 (Part 1)-1975 Code of practice for extremeweather concreting: Part I Recommended practicefor hot weather concreting.

.'. (JR' INWAI n (E). Cold weather concreting with high­early strength cement. Proceedings; RILEM Sympo­viurn: Winter Concreting Session B1• Copenhagen.1956.

4. MALHOTRA (V M) and BERWANGER (C). Effect ofbelow freezing temperatures on strength develop­ment of concrete. ACI Publication SP 39: Behaviourof Concrete Under Temperature Extremes. Paper~r 39-1; 1971. P 37-58.

136

S. MUSTARD (J N). Winter curing of concrete as relatedto the New Canadian standard. ACI Publication SP39: Behaviour of Concrete Under TemperatureExtremes. Paper SP 39-4; 1973. P 59-78.

6. PINK (A). Winter concreting. Cement and ConcreteAssociation, London, 1974. P 1-24.

7. IS: 7861 (Part 11)-1981 Code of practice forextreme weather concreting: Part II Recommendedpractice for cold weather concreting.

8. ACI 306-1966 Recommended practice for coldweather concreting. ACI Manual of Concrete Prac­tice. Part I; 1974. P 306-1-19.

9. V1SVESVARAVA (H C) and MULL1CK (A K).Compressive strength of concrete in winter - Aprobabilistic simulation. 2nd Internationalsymposium in winter concreting, ~lLEM, Moscow,October 1975. Proc Vol 2. P 83-103.

SECTION 8

TESTING OF CONCRETE MIXES

SECTION 8 TESTING OF CONCRETE MIXES

8.0 Concrete is required to be tested inboth fresh and hardened states. Fresh con­crete is tested for workability to determineits capacity for satisfactory placing. Theworkability test also gives information aboutthe consistency of the concrete mix such thatthe concrete can be transported, placed,compacted and finished easily and withoutsegregation. The analysis of fresh concrete isrequired to judge the stability that is toidentify segregation of the concrete mix,uniformity in mixing and to determine theproportions of the ingredients of concreteactually used. Tests on setting time of con­crete are required to determine the time up towhich it can be vibrated and to decide therate of movement of formwork, for exam­ple, in slip form construction.

The testing of hardened concretespecimens is required for checking the quali­ty and compliance with the specifications.Compression test on concrete cubes at theage of 28 days is done for these purposes.Additional tests include those for flexuralstrength, tests by accelerated curing and testson cored samples.

8. / Sampling and Testing of Concrete ­A 'sample' is a statistical term which is usedin the engineering sense to mean a small por­tion of concrete taken to represent thewhole. Compliance with the specifiedcharacteristic strength of concrete (definedin 4. / .3) is judged by compression test onstandard cubes (1.5 x 15 xIS em) preparedfrom such sample of concrete. The methodof sampling fresh concrete for the prepara­tion of cubes is given in IS : 1199-19S91• Inorder to get a relatively quicker idea of thequality of concrete, optional tests, namely,modulus of rupture on beams at 72 ± 2 hoursor at 7 days; or compressive strength test at 7days on cubes may be carried out in additionto 28-days compressive strength test. The re­quirements of these tests arc given in Table 5of IS : 456-1978',

8.2 Frequency of Sampling - Taking intoaccount the theory of probability, samplingfrequency of fresh concrete is based onstatistical principles and is adopted to ensurethat each batch of concrete shall have a

139

reasonable chance of being subjected to test.The sampling should be spread over theentire period of concreting and cover all themixing units. IS : 456-19782 lays down thefrequency of sampling which is related to thequantity of concrete involved and" thespecified frequency is to be applied separate­ly for each grade of concrete. It is necessarythat at least one sample shall be taken fromeach shift of concreting. Higher rates ofsampling may be required in the beginningof the work in order to establish the levels ofquality quickly. Also, in critical elements/portions of the structures, a higher rate ofsampling is desirable. 'Critical elements/portions' are those elements which areregarded · as critical by the designer.However, for relatively small works andunimportant buildings and works in whichquantity of concrete is less than 1S m", thestrength test may be waived by the engineer­in-charge at his discretion"

8.3 Workability Tests of Fresh Con­crete - Workability of concrete should bemeasured at frequent intervals (at least oncefor each shift) during the progress of work inthe field, by means of slump test or compac­ting factor test or Vee-Bee time consistencytest as appropriate (see IS: 1199-1959 1) .

Out of these, in actual site conditions slumptest is more common for medium strengthconcretes and compaction factor test forhigh-strength concretes. The significance ofthese test methods has already been discuss­ed in detail in Section 3. The Kelly ballpenetration test as given in ASTM StandardC 360-1963' may also be used, in addition tothe slump test.

If the proportions of materials are proper­ly followed and the workmanship issatisfactory, the results should not differ bymore than the following tolerances fordifferent workability tests:

Slump: ± 25 mm or ± one-third of the requiredvalue, whichever isless

Ball penetration: ± 12 mmCompacting factor: ± 0.03, where the

required value is 0.90or more;

8.4 Analysis of Fresh Concrete­Analysis of fresh concrete enables the deter­mination of mix proportions of concrete thatis proportions of cement, aggregate andwater content. Although it has potentials ofbecoming useful tools of quality control, atpresent IS : 4634-19681' specifies such a testonly for determining the efficiency of con­crete mixers.

In the method of analysis described inIS : 1199-19S91 (Buoyancy method), theanalysts has to be supplemented by tests ofspecific gravity and water absorption on fineand coarse aggregates. The coarse and fineaggregates are separated by wet sievingthrough sieves of appropriate openings. Thecement content of a sample of concrete isdetermined by difference in weight in waterof the concrete and aggregates so separated.The water content in the mix is determinedby the difference in the weight of concrete inair and the sum of weights of coarse and fineaggregates and cement as determined.Although there are not enough data on theaccuracy of this method, in case of similarbuoyancy methods, it is claimed that thesolid components of fresh concrete can bemeasured to r 1 percent of the total concreteand the water to ± 2 percent of the totalconcrete", The method takes about 2 hoursand requires fairly high degree of experienceand skill.

8.5 Measurement ojAir Content - Air inconcrete is of two types:

a) that purposely entrained to promoteworkability and reduce segregation andbleeding and to increase frost­resistance of concrete, and

b) unwanted air due to imperfect compac­tion or the drying out of excessive mix­ing water.

The air content of non..air-entrained con­crete is the casual air which is automatically

SP : 13-1982

Vee-Bee time:

± 0.04, where the re­quired value is lessthan 0.90 but morethan 0.80;± O.OS. where the re­quired value is 0.80 orless.

±-3 seconds or ± one­fifth of the requiredvalue, whichever isgreater.

140

entrained even though concrete is compactedas thoroughly as possible, the amountdepending on maximum size of aggregateused.

There are three methods of measuring thetotal air content of fresh concrete:

a) ,he gravimetric method,b) the volumetric method, andc) the pressure method.

The pressure method (see IS : 1199-19591)

provides the most dependable and accuratemethod of determining the air content ofconcrete.

The air content of concrete is usuallyrequired to be determined for air-entrainedconcrete. The percentage of air contentdetermined from individual samples taken atthe point of placing the concrete andrepresentative of any given batch of concreteshould be within ± 1.S of the required value.The average percentage air content from anyfour consecutive determinations fromseparate batches should be within± 1.0 of the required value.

8.6 Setting Time of Concrete - The set ..ting time of concrete is determined by thepenetration resistance apparatus (springreaction type). The details of the test methodare given in IS: 8142-19765• The methodmeasures the load necessary for a needle topenetrate a fixed distance into the cementmortar. Because of the interference fromlarge particles of coarse aggregate, themethod is not directly applicable to normalconcrete. For determining the setting time ofconcrete, this method is used indirectly oncement mortar sieved from concrete. Whenthere is a strict correspondence of mixingprocedure, the penetration resistance valuesof cement mortar sieved from concrete havebeen shown to correspond to those obtainedfrom equivalent mortars where the coarseaggregate is absent'.

Experiments' suggest that a penetrationresistance of 3.S Nz'mrn! on the sievedmortar corresponds to the so called 'vibra­tion limit' that is the point during thehardening of the concrete at which the con­crete can no longer again be made plastic byrevibration. The time elapsed after addingwater to reach a penetration resistance valueof 3.S N/mm2 can, therefore, give an ap­proximate guide to the time available foravoiding the formation of cold joints bet-

ween successive layers of concrete. At apenetration resistance value of about 27.6Nzrnrn", the concrete has a compressivestrength of almost 0.7 Nzmm! and is con­sidered to have hardened. Thus the initialand final setting times have been defined byIS : 8142-19765, by respective penetrationresistance value as follows:

Initial setting time - The elapsedtime, after initial contact of cementand water, required for the mortar(sieved from the concrete) to reach apenetration resistance of 3.43 Nzrnrn",

Final setting time - The elapsedtime, after initial contact of cement andwater, required for the mortar (sievedfrom the concrete) to reach a penetra­tion-resistance of 26.97 Nzmm"

8.7 Tests for Strength - Tests for com­pressive strength of concrete should be con­ducted on the samples (cube specimens) ob­tained from the frequency of sampling.Usually, it is necessary to test at 28 days,samples (each sample consisting of three15 em cubes) prepared and cured in accor­dance with IS : 516-19597• Additional testsmay be carried out by accelerated curing ofconcrete as in accordance withIS : 9013-19781 or under normal curing at 7days as specified by IS : 456-19782, in orderto get a quicker idea of the quality, but theacceptance of concrete will be only on thebasis of 28-day compressive strength.

The test strength of the sample shall be theaverage of the strength of three specimens,provided the individual variation is not morethan ± 1.5 percent of the average. Taking

- the test specimen in sets of three from abatch and using the average value, reducesthe testing error considerably, but usuallythe effect of testing error on the standarddeviation value is relatively smaller.

In the field, samples of fresh concrete canbe obtained either from the mixers or at thetime of deposition. Approximately, equalportions of concrete from three differenttimes during its discharge from the mixer orfrom at least five well distributed positionsduring deposition are required to be takenand test specimens prepared from the com­posite sample of fresh concrete. The samplesare required to be demoulded after storagefor 24 ± Y2 hour at temperature within therange of 22 to 32°C, and thereafter stored in

141

SP : 13-1982

clean water at a temperature of 24 to 30°C,until they are transported to the laboratoryfor testing. Since temperature of moist cur­ing influences the compressive strength ofconcrete, storage at temperatures beyondthis range is likely to affect the test results.Specimens, when received in the laboratoryare to be stored in water at a temperature of27 ± 2°C until the time of test. It is necessaryto test the specimens in a saturated condi­tions because concrete specimens tested in adry state are likely' to show an increase instrength'.

Two criticisms can be levelled against theusefulness of the 28-day cube tests. The firstis that the results being available only after28 days, they do not offer scope of qualitycontrol of concrete at the fresh stage andsoon after placing. Consequently, it does notallow a judgement to be made before moreconcrete is subsequently placed on top of itand any remedial or corrective measures, ifrequired, is not possible without affectingthe subsequent placement. Mainly fromthese considerations, accelerated strengthtests are becoming popular in which the con­crete specimens are subjected to moist curingat elevated temperatures (warm watermethod) or curing in water at its boilingpoint (boiling water method) under pre­determined curing regimes. IS : 9013-1978'prescribes two such methods for quality con­trol purposes and it is found that statisticallysignificant correlation exists between com­pressive strength of such accelerated curedconcrete and those cured under normal 28­day curing. Such accelerated test resultsbecome available within about 24 to 28hours after casting. The correlation is likelyto be affected by the materials and mix pro­portions used and it is advisable to establishappropriate correlation curves for thematerials and mix proportions to be used afthe site.

Tests with Indian cements show that therelationship between strength of concretespecimens with accelerated curing andnormal curing for 28 days is not significantlyaffected by variations in the physical proper­ties and chemical composition of ordinaryPortland cement 10.11.12.

Another limitation of the results of testson 28-day cube specimens is that even whencured under controlled conditions oftemperature and humidity, it does not

SP : 13-1982

indicate the actual compressive strength ofconcrete in the structures. This is because ofa number of intrinsic and environmentalparameters which are different in case ofconcrete in the cube specimens and in thestructures. It is held that the most reliablemeasure of the actual strength of concrete inthe structures can be obtained by testingspecimens of hardened concrete obtainedfrom the structure by core drillingl 3• Theprocedure of obtaining cored samples fromhardened concrete is described in

" IS: 1199-19591 and method of their testingin IS : 516-19597• Such core testing is usual­ly resorted to when the 28-day cube resultsdo not meet the specified acceptance criteria,when the cube tests had not been taken orthe results are disputed, or when the designload on the structure is to be enhancedsometimes during its service life to accom­modate some modifications in the usage andoccupancy of the structure than originallyproposed for.

There are a number of factors whichinfluence the measured strength of corespecimens, which have been discussed indetail in Reference 13. Cored samples aregenerally cylinderical in shape. with 1SO mmdiameter; alternatively 100 mm diameter isalso permitted, but the diameter should notbe less than three times the nominalmaximum size of aggregates. The length todiameter (L/D) ratio is required to be 2. Forthe ratio less than 2 but not less than 0.95(this being permitted), the indicated strengthincreases and necessary correction factorsare to be applied to express the indicat­ed strength to that of L/D = 2. Such a setof correction factors -are given inIS : SI6-1959. The influence of the size ofthe specimens having identical L/D ratio onthe compressive strength is not very clear;generally smaller diameter specimens areexpected to indicate higher strength. Theearlier version of the code for plain and rein­forced concrete (IS : 4S6-1964) stated thatcompressive strength of 100 mm cubes wasexpected to be 10 percent higher than thoseof 1SO mm cubes; but in case of corespecimens, no correction due to size of coreis envisaged in IS : .516-19597• Direction ofdrilling. presence of reinforcement and ageof concrete all influence the indicatedstrength but precise estimation of these ef­fects is difficult to make. The core strength isultimately required to be expressed in terms

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of equivalent cube strength for acceptancepurposes. For this purpose. the strength of1SO nun diameter and 300 mm high corespecimens can be taken to be 0.8 times thatof 1SO mm cube specimens.

Apart from those factors intrinsicdifferences in the qualities of concrete in thestructure from which core specimens areobtained and that in the companion cubespecimens, exist because of differences in themanner of placing, compaction and curing.As a result, the strength of hardened con­crete in the structure is expected to be withina range of 55 to 80 percent of the cubestrength13. IS : 456-19782 stipulates that foracceptance purposes, the average equivalentcube strength of three core samples shall beat least 85 percent of the characteristicstrength for the grade of concrete at thecorresponding age.

The above discussion pertains to com­pressive strength of concrete. In someinstances, tensile strength of concrete is alsorequired to be measured. The tensile strengthis determined either by flexure test (seeIS : S16-19597 ) or split cylinder test (seeIS : 5816-197014 ) . Their relationships withcompressive strength. of concrete has beendiscussed earlier in Section 3.

8.8 Analysis of Hardened Concrete­Analysis of cement content in hardenedconcrete is frequently required, wheneverconcrete has either exhibited low strength orany other inadequate performance. Al­though different methods like microscopic,petrographic and even nucleonic areavailable and new methods are beingdeveloped, only chemical methods arerecognized in the national standards of mostcountries, including IS : 1199-19591•

In all methods of analysis of hardenedconcrete, sample selection plays an impor­tant part. Since only a small quantity goes inthe analysis, it should be as representative ofthe concrete in question as possible. For thisreason, several samples of 4-S kg are takenand the representative sample is obtained byrepeated quartering. Samples of cement andaggregate used in the constructions, ifavailable. aid in the analysis and yield moreaccurate results.

The procedure prescribed in IS: 1199­19S91 involves determination of soluble silica(SiOz) in the mortar fraction which is

supposed to be resulting from cement alone.The sample is broken up, crushed and thenreduced to a fineness of IS Sieve of aperturesize 106 micron to 75 micron and solublesilica content determined by treating it withhydrochloric acid and sodium hydroxidesolutions. Assuming that the soluble silicacontent in the cement to be 21.40 percentby mass, the quantity of cement is cal ..culated.

The relevant AST~1 method C8S15 alsopermits determination of soluble lime(calcium oxide) by leaching with acid solu­tions and the cement content being determin­ed on the assumption that cement containslime ro the extent of 63.S percent. In addi­tion, soluble silica basis as above is alsopermitted,

The above methods involve two assump­tions. none of which may be strictly correct.

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SP : 23·1982

First method assumes the relative contents ofsilica and lime in the cement which varyconsiderably between cements: secondly themethods assume that aggregates do not con..tain soluble silica (on silica basis) or solublelime (lime basis). If the samples of cementand aggregates are available, both theseassumptions can be checked and necessarycorrections applied which improve theaccuracy. In the absence of these, theestimated cement content may be in error by10 to 20 percent from the true cement con-tent. These methods are applicable only incase of ordinary Portland cement and arenot applicable to Portland slag cement orPortland pozzolana cement, unless blanksamples of such blended cements actuallyused are available at the time of analysis.This is because slags and some reactivepozzolana can release silica, some other flyashes can release lime.

SP : 13·1982

REFERENCES

J• IS: 1199-19.59 Methods of sampling and analysisof concrete.

2. IS: 4~6-1978Code of practice for plain and rein­forced concrete.

3. ASTM Standard C 360-1963 Ball penetrauon infresh Portland cement concrete. American Societyfor Testing and Materials.

4. KIRKHAM (R H H). The Analysis of fresh concrete.Concr Constr Enqin. 1949; 54.

~. IS: 8142-1976 Method of test for determiningseuin. time of concrete by penetration resistance.

6. FLETCHER (K E) and ROBERTS (M H). TestMethods to Assess the Performance of Admixturesin Concrete. Concrete S, .5; 1971; 142·48.

7. IS: 516-19'9 Methods of tests for strength ofconcrete.

8. IS: 9013-1978 Methods of making, curing anddetermining the compressive strength of ac­celerated cured concrete test specimens

9. MILLS (R H). Slrenath - Maturity Relationshipfor Concrete which is Allowed to Dry. RILEM Int.Symp. on Concrete and Reinforced Concrete in

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\

Hot Countries, Haifa, 19(tO.10. MAltl (5 e), DEVADAS (P G). and MUlllCk (A K).

Correlation of Strengths of Accelerated Cured andNormally Cured Concrete. Research BulletinRB·12·79, November 1979. Cement ResearchInstitute of India, New Delhi.

II. GHOSH (R K), CHA1IERJEE (M R) and RAM LAl.Accelerated strength tests for quality control ofpaving concrete. ACI Publication SP·~6:

Accelerated Strength Testing. 1978. P 169-182.12. REHSI (S S), aARO rs K) and KALItA (P D). Ac­

celerated testing of 28-day strength of concrete,lSI Bulletin, 23, 6; 1971, 273-76.

13. Concrete core testing for strength. Concrete Socie­ty, Technical Report No. 11. London, May 1976.P 44.

14. IS: S816-1970 Method of test for splitting tensilestrength of concrete cylinders. '.

IS. ASTM C 8S-86 Samplina and test methods forcement content of hardened Portland cementconcrete. American Society for Testing andMaterials.

16. IS: 4634-1968 Method for testing performance ofbatch type concrete mixers.