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Fast track concrete technology

Prof. A.R.Santhakumar Emeritus Professor of Civil Engineering

IIT (Madras),600 036 India Email: santhaar@gmail.com.

Abstract

Construction is the ultimate objective of design and machines make accomplishment of that task possible. The efforts of the engineer who designs a project , and the constructor, who builds the project are directed towards the same goal: creation of some infrastructure that will improve the quality of life for mankind and serve the purpose for which it is built in a satisfactory manner. Construction is the ultimate objective and machines and methods make accomplishment of that objective possible. The constructor must select the proper equipment to process materials and build the structure economically. Whereas most manufacturing companies have a permanent factory a construction company carries its factory with it from site to site depending on job requirement. 1. INTRODUCTION

In order to supply the required land for accommodating the huge population, and to provide ample infrastructure and community facilities to substantiate an acceptable standard of living, commercial operations and other necessary developments, many critical locations which may be unsuitable for development to most international yardsticks, are built with very large sized and high-rise buildings. The following situations are some of these examples.

FIBER REINFORCED CONCRETE FOR RETROFITTING

Dr. C.Antony Jeyasehar R.Balamuralikrishnan Professor and Head, Sr.Lecturer E-mail: auhdse@sify.com E-mail:bmk_gaya@rediffmail.com

Dept. of Civil and Structural Engineering Annamalai University, Annamalainagar- 608 002

Tamilnadu, India Telephone No: 91-4144-239732

Fax No: 91-4144-239732 1. Introduction The use of randomly oriented, short fibers to improve the physical properties of a matrix is

an age – old concept. For example, fibers made of straw or horsehair have been used to

improve the properties of bricks for thousand of years. In modern times, fiber – reinforced

composites are being used for a large variety of applications. The composite could be a clay

brick reinforced with natural fibers or a high – strength, fiber – reinforced ceramic

component used in space shuttle. The fiber reinforced composites made with the primarily

Portland cement – based matrices. The matrices can consist of any of the following:

1. Plain Portland cement

2. Cement with additives such as fly ash or condensed silica fume

3. Cement mortar containing cement and fine aggregate

4. Concrete containing cement, fine and coarse aggregates.

The presence of micro cracks at the mortar-aggregate interface is responsible for the inherent

weakness of plain concrete. The weakness can be removed by inclusion of fibers in the

matrix. The fibers help to transfer loads at internal micro cracks. Such a concrete is called

fiber reinforced concrete. Thus the fiber-reinforced concrete is a composite material

essentially consisting of conventional concrete or mortar reinforced by fine fibers.

The fibers can be broadly classified as

1. Metallic fibers

2. Polymeric fibers

3. Mineral fibers

4. Naturally occurring fibers

Metallic fibers are made of either steel or stainless steel. The polymeric fibers in use include

acrylic, carbon, nylon, polyester, polyethylene and polypropylene fibers. Glass fiber is the

predominantly used mineral fiber. Various types of organic and inorganic naturally occurring

fibers such as cellulose are being used to reinforce the cement matrix.

Fiber reinforced concrete (FRC) has been used since the 1960’s (ACI 544.1, 1996), although

use was generally limited to warehouse floor or pavement overlays. Steel, glass, carbon and

Polymer Modified Concrete for Retrofitting Dr. C.Antony Jeyasehar R.Balamuralikrishnan Professor and Head, Sr.Lecturer E-mail: auhdse@sify.com E-mail:bmk_gaya@rediffmail.com

Dept. of Civil and Structural Engineering Annamalai University, Annamalainagar- 608 002

Tamilnadu, Tel. No: 91-4144-239732, Fax No: 91-4144-239732

1. Introduction

In virtually all cases of concrete deterioration, the problem is associated with corrosion of

steel reinforcement. It is well established that steel reinforcement well embedded in good

quality concrete is protected from corrosion by the passivating nature of the highly alkaline

cement matrix. Therefore, whenever, possible, it is desirable from both technical and

economic considerations deteriorated reinforced concrete should be repaired with

impermeable highly alkaline cement based materials closely matched in properties to the

parent concrete. However there are many instances where repair composition containing

polymers, either as admixtures for cementation systems or as high strength binders (for

adhesive mortars and grouts) are the most appropriate. Over the past twenty years, many

different polymers have been used in a range of applications in the repair and maintenance of

building and other structures. With out the unique properties of some of the polymer systems,

many of the repairs undertaken would, with out doubt, have been much more costly and have

taken much longer to carry out.

To realistically appraise the position of concrete repair technology and the complex fabric of

problems it faces today, we must pause periodically to review where we are and where we

might be going. The majority of the faults and problems are caused by lack of attention to

design details, specifications and poor in-site workmanship. Material, although important, is

less of an evil. Material, per se, does not problem; the end product made from a material - the

repaired structure - performance. The concern should not be solely with repair, material

themselves, but with the uses to which they are being put, with the gray area of overlap

between material properties, and the end engineering product - the repaired structure.

Experience world-wide now confirms that even when specific national code requirements of

durability in terms of concrete cover and concrete quality are achieved in practice, there is an

unacceptable high risk of premature deterioration of concrete structures exposed to

aggressive conditions. Deterioration of concrete and corrosion of reinforcement have thus

become the major causes of loss of serviceability and safety of reinforced and prestessed

LIGHTWEIGHT CONCRETE: MATERIALS, PRODUCTION CHARACTERISTICS,

PROPERTIES AND APPLICATIONS

Kunhanandan Nambiar E K1

ABSTRACT: In concrete construction, self-weight usually represents a large proportion of the total load in the structure and hence, any attempt to reduce the self-weight of the structure is undoubtedly considered as an advantage. In addition to reducing stresses through the life time of the structure, the total weight of material to be handled during construction is also reduced, which consequently increases the productivity. Further more, lightweight concrete offers better thermal insulation, seismic resistance and fire protection than ordinary concrete.

INTRODUCTION

Practical range of densities of lightweight concrete (LWC) varies between 300kg/m3 and 1850 kg/m3. Basically there is only one way of making concrete lighter – the inclusion of air in its composition. However this air-entrainment can be achieved by three different ways viz. ; (i) by replacing the ordinary aggregate with a hollow cellular or porous aggregate that includes voids within its body, this is termed ‘lightweight aggregate concrete’; (ii) by omitting finer sizes from the aggregate grading thereby creating ‘no fines concrete’; (iii) by introducing gas/air bubbles in the plastic mix of cement/ cement-filler slurry (aerated concrete) or by introducing pores due to excessive water proportion in the mortar (microporites), both after setting leaves a cellular structure, termed as ‘cellular concrete’ (Shrivastava, 1977). A general classification of lightweight concrete is presented in Fig. 1.1. Out of these, lightweight aggregate concrete and aerated concrete are the most popular classes.

Fig. 1 Classification of lightweight concrete

Lightweight concrete can also be classified according to the purpose for which it is to be used: we distinguish between structural lightweight concrete (ASTM C 330-89) and concrete used in non-load bearing walls (concrete used in masonry units, ASTM C 331-89) , for insulation purposes (ASTM C 332-87), and the like. The strength and density ranges of these concretes are given in Table 1. The essential feature of insulating concrete is its coefficient of thermal conductivity which should be below about 0.3 J/m2s oC/m (Neville, 1995)

. Table 1 Classification based on use

Type of LWC Insulating Masonry Structural

Density range, kg/m3 <800 500-800 1400-

1800

Strength range, MPa 0.7-7 7-14 ≥17

Also, classification based on strength is given in Table 2.

Table 2 Classification based on strength

Type of LWC

Insulating concrete

Moderate strength concrete

Structural concrete

Strength range, MPa

0.7-7 7-17 17- 41

Density range, kg/m3

250-800 800-1350 1350-1850

Lightweight concrete

Lightweight aggregate concrete

Cellular concrete

No-fines concrete

Aerated concrete

Microporites

Foam concreteGas concrete

1Assistant Professor, N S S College of Engineering, Palakkad, 678 008

CHEMICAL ADMIXTURES FOR CONCRETE G B Vamadev* FOSROC Introduction Concrete is the most widely used construction material in the world. Its consumption is around 20 billion tonnes annually which comes to around two tonnes per every living person. The reasons for such widespread use of concrete are its adaptability, durability, strength, availability and economy. Concrete is the only material which can be used everywhere; literally, from pavements to roofs. But the most sought after properties of concrete, viz., workability in the fresh state and strength and durability in the hardened state, cannot always be realised with its regular constituents. In such cases, chemical admixtures become essential requirements for concrete. Admixture An admixture is defined as 'the material added during the mixing process of concrete in a quantity not exceeding 5% by mass of the cement content of the concrete to modify the properties of the mix in the fresh and/or hardened state'. Both chemical and mineral admixtures are widely used. Silica fume and fly ash are the most widely used mineral admixtures. Chemical Admixtures As mentioned above, the purpose of using chemical admixtures is to modify certain properties of concrete. The ACI committee has listed the properties mentioned below. In the fresh state, admixtures perform the following functions : 1. Increase workability 2. Accelerate or retard the setting time of concrete 3. Reduce or prevent settlement or to create slight expansion 4. Modify the rate and/or capacity for bleeding 5. Reduce segregation 6. Improve pumpability 7. Reduce slump loss * G B Vamadev – Business Manager –Concrete Industries, Fosroc Chemicals (India) Pvt. Limited, Bangalore

BEHAVIOUR OF CONCRETE EXPOSED TO FIRE

Dr. George Mathew, Reader School of Engineering

Cochin University of Science and Technology, Kochi-22

The behaviour of various physical properties of concrete that has influence on the overallbehaviour of concrete when exposed to fire has been discussed in this paper. The possibledamage to reinforced concrete structural members when exposed to fire and the methodof reinstatement of fire damaged RCC members are also discussed in this paper. Concrete is the most widely used material in construction. In general, the use of concrete in construction can be grouped in to two, viz. 1. Used as structural concrete- Used

to construct structural members such as Reinforced Cement Concrete ( RCC) and Pre-Stressed Concrete (PSC) members and

2. Used as a protection material to structural steel against fire – Primarily Plain Cement Concrete ( PCC)

The structural behaviour of a building subjected to fire depends primarily on the variations developed in the properties of individual materials which are exposed to fire. The material properties which are of importance when a structure is exposed to fire are: 1. Thermal Expansion 2. Thermal Diffusivity 3. Modulus of Elasticity 4. Poisson’s Ratio 5. Stress-Strain Relationship

6. Creep Deformation and 7. Strength As concrete is made of differentmaterials, its behaviour with temperaturedepends on several factors and as such ageneral remark can only be made withrespect to the various properties. Thermal Expansion of Concrete Thermal expansion of materials is one ofthe important properties as far as firesafety is concerned. In structures,members restrained from expansion bythe surrounding elements or thedevelopment of differential expansion ofdifferent materials leads to the failure ofmembers in a structure, which mayultimately lead to even itscollapse.Thermal expansion of concreteis influenced by different parameterssuch as the type of cement - type of aggregate - water content at the time of

temperature change and - age of concrete

QUALITY CONTROL OF CONCRETE George Mathew

Reader, Cochin University One of the most important requirements in good concrete construction is that the quality of concrete used in the structure should conform to that specified in the design. There are several tests that can be made with both plastic and hardened concrete, but the strength test is widely used in specifying, controlling, and evaluating concrete quality. Quality concrete must be able to 1)carry loads imposed upon it; 2) resist deterioration; and 3) be dimensionally stable. Although the strength test is not a direct measure of concrete durability or dimensional stability, it provides an indication of the water-cement ratio of the concrete. The water-cement ratio, in turn, directly influences the strength; durability; wear resistance; dimensional stability; and other desirable properties of concrete. The strength test is also used to measure the variability of concrete.

VARIABILITY OF CONCRETE Concrete is subject to numerous factors that affect its strength and other properties. These may include variations in the manufacturer of cement; preparation of aggregates; batching, mixing, and curing of concrete; and finally in the preparation, handling, and testing of the sample specimens. The major sources of variation in the strength test results are listed in Table 1.

Table 1 – Principal sources of variations in strength test results

Variations in properties of concrete Discrepancies in testing methods Changes in water-cement ratio Poor control of water Excessive variation of moisture in aggregate

Improper sampling procedures

Variations in water requirement Aggregate grading, absorption, particle shape. Cement and admixture properties Air Content Delivery time and temperature

Variations due to fabrication techniques Molding of specimen Poor quality molds Handling and curing of newly made specimen

Variations in characteristics and proportions of ingredients Aggregates Cement Admixtures

Changes in curing Temperature variation Variable moisture Delays in bringing specimens to the laboratory

Variations in batching, mixing, transporting, placing and compaction Variations in temperature and curing

Poor testing procedures Care of specimen, transportation Improper placement in testing machine Testing machine platens out of specifications. Incorrect speed of testing.

Cement

• Trends in India• Special Concrete• Cement Manufacturing Procedure • Types of Cement• Major Compounds in Cement• Physical Quality Parameters• Chemical Quality Parameters• Cement Plants & Products• Packaging

CEMENT M.A. Joseph Aditya Birla

• Trends in India • Manufacturing Procedure • Special Types of Concrete • Types of Cement • Major Compounds in Cement • Physical Quality Parameters • Chemical Quality Parameters • Cement Plants & Products • Packaging

Effect of Supplementary Cementing Materials on Chemical Durability of Concrete.

Nazeer M Faculty in Civil Engineering TKM College of Engineering

Kollam – 691 005. Kerala.

ABSTRACT Increasingly greater attention has been paid in recent years to the problem of structural durability of plain and reinforced concrete structures. The extensive application of these building materials and their limited life in various media has necessitated a growing volume of repair and restoration of reinforced concrete structures. Considering the difficulties of such repairs, it is imperative to provide an adequate and guaranteed service life of reinforced concrete right at the time of designing and erecting the building or structure. Recently, High Performance Concretes incorporating various mineral admixtures are used to combat the adverse effects of chemically aggressive environment. The supplementary cementing materials used for improving the performance of concrete are silicafume, flyash, ground granulated blast furnace slag, and metakaolin. These materials are either added as admixtures (mineral admixtures) or as a partial replacement of cement. A concrete with these materials, prepared from lower w/c ratio and with chemical admixtures, shows reduced permeability and enhanced strength. This report discusses the effects of supplementary cementing materials against the chemical deterioration of concrete. INTRODUCTION Durability of hydraulic-cement concrete is defined as its ability to resist weathering action,chemical attack, abrasion, or any other process of deterioration. Durable concrete will retain itsoriginal form, quality, and serviceability when exposed to its environment. Major causes ofconcrete deterioration are freezing and thawing, aggressive chemical exposure, abrasion,corrosion of metals, and chemical reactions of aggregates. Freezing and Thawing When water begins to freeze in a capillary cavity, the increase in volume accompanying thefreezing of water requires a dilation of the cavity equal to 9% of the amount of excess water outthrough the boundaries of the specimen or some of both effects. During this process, hydraulicpressure is generated and the magnitude of that pressure depends on the distance to an escapeboundary, the permeability of the intervening material and the rate at which ice is formed.Experience shows that disruptive pressures will be developed in an saturated specimen of pasteunless every capillary cavity in the paste is not farther than three or four thousandths of an inchfrom the nearest escape boundary. Air entrainment has proved to be an effective means ofreducing the risk of damage to concrete freezing and thawing. Causes of deterioration of the hardened concrete by freeze-thaw action can be related to thecomplex microstructure of the material, and also the specific environmental conditions.

1

Fracture Mechanics ofConcrete Structures

Palivela Subba Rao

Associate ProfessorDepartment of Civil Engineering

JNTU College of EngineeringKakinada

1

RUDIMENTS OF FRACTURE MECHANICS

Palivela Subba Rao,

Associate ProfessorDepartment of Civil engineering

JNTU College of engineeringKakinada, (AP)

Rudiments of Fracture Mechanics1

1.1 Introduction In general, material/ structural component fails either due to any of the following or

their combinations. i) Yielding ii) Buckling iii) Fatigue iv) Impact v) Fracture etc. Thereforea component is designed so as to avoid the yielding of the maximum loaded point. This isconsidered as the basic requirement of design and is taught in all courses on strength ofmaterials at under graduate level.

Over the ages, man has been under an impression that strength of material is materialproperty and strength is the criterion for failure of material / structural components under aninfluence of external loads. Contrary to this, the incidents that occurred in the past during theSecond World War times taught man lesions: There is some other criterion for failure ofmaterial, beyond strength criterion. Failure of Liberty ships during the world war-II has givena way to think in a different way from conventional way of understanding of material failure.

Crack occurrence in a structural component either during its construction/manufacturing or during its life time is inevitable. Performance of a cracked structuralcomponent under mechanical loading is very much different from that of the samecomponent without crack. The study of performance of a cracked body under the externalloading is called as ‘Fracture Mechanics”. Therefore “Fracture mechanics” is based on theimplicit assumption that there exists a crack in the structural component. The crack may beman made such as a hole, a notch, a slot, etc.

For a long time man had some idea about the role of a crack or notch. While cutting atree, he would make a notch with an axe at its trunk and then pull it down with a rope. Whilebreaking a stick he would make a small notch with a knife before bending. Leonardo daVinci (1452-1519) was the first person to make a set up to measure the strength of a wire. Hefound that strength of a wire depends on its length. It was his argument that longer wire waslikely to have more number of cracks.

1.2 Strength of materials Approach (Strength criterion) The basic assumption in strength of materials approach is that stress is uniform through

out the net cross-sectional area, if there is a hole or crack in structural component. Suppose arectangular plate is under a uniform tension as shown in fig.1 If the strength of the plateis yσ , its width, B and thickness, t ; then the failure load, yy BtP σ= . This is based on theassumption that stress is uniform through out the width. For example, if the same plate has anelliptical hole as shown in fig.1, then its failure load, ( ) yy taBP σ2−= , according to strengthof materials criterion. But the actual failure load, from experiments, has been found to beentirely different from the calculated load, ( ) yy taBP σ2−= , which is much lessthan ( ) yy taBP σ2−= . The plate with an elliptical hole under uniform tension is analyzed

Mr. P.Subba Rao, Associate Professor, Department of Civil Engineering , JNTU College of Engineering, Kakinada, (AP).

Repair and Rehabilitation of Concrete Structures Using Special Materials

Dr. Prasad Varma Thampan C.K.* Introduction: Reinforced concrete (RC) is the most extensively used material for construction of

different types of structures such as bridges, tanks, chimneys, dams, buildings, harbors

etc. Maintenance and repair of such structures is presently one of the most significant

challenges facing the concrete building industry. The distress to concrete can be caused

from various sources. The required degree of high standard is not always achieved during

original construction in the case of materials and required degree of quality control is not

achieved in practice and as a result of this the structure is seriously affected which in turn

requires early repair and renovation work. It is reported that the expenses incurred in

Russia on repair and restoration of industrial structure over a normal period of four to five

years reach the total cost of the structure. In USA, the total annual loss due to concrete

deterioration is reported to be 3% of the annual construction expenditure. Even in India,

where the per capita consumption of cement/concrete is much less than global average,

the annual loss due to deterioration of steel and concrete structure is estimated to be of the

order of Rs 300-500 crores. The circumstances leading to inadequate quality control are

worse in our country, where concrete is still a material ‘made at site’ rather than in ready

mix-plants in most of the constructions. In addition to faulty construction and natural

aging, man made explosions as well as natural hazards like earthquake, cyclone, etc. also

can cause serious distress to structures.

The distress in concrete can be observed in the form of cracks. Cracks in concrete are the

manifestation of some disorder; structural, physical, chemical or even biological disorders

in the body of concrete, which shows up as cracks, which further aggravate the

deterioration process of concrete with time. Hence timely analysis of the causes of

distress, correct selection of repair materials and implementation of most suitable repair

methodology are required for an effective, economical and early rehabilitation of the

affected structure.

Assessment of damages in concrete structures: The distress and damages in concrete shall be examined in detail and be assessed to

determine (1) the cause of damage (2) the type and extent of damage. Table 1 shows the

symptoms of damage as cracks, spalling, discoloration etc and the probable cause of such * Assistant Professor of Civil Engineering, N.S.S. College of Engineering, Palakkad-8.

constructive solutions

Dr. V. SYAM PRAKASHProfessor

College of Engineering Trivandrum

Dr. V. SYAM PRAKASHProfessor

College of Engineering Trivandrum

READY MIXED CONCRETE FOR QUALITY CONSTRUCTION

Dr. V. SYAM PRAKASH

Professor

College of Engineering

Trivandrum