portland cement concrete

7/21/2019 Portland Cement Concrete

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BASICS OF CONCRETEPORTLAND CEMENT CONCRETE



TERMS

Curing is protecting concrete after placing so that proper hydrationoccurs

Water-Cement Ratio is the ratio by weight between water andcement used to make paste

The water-cement ratio should be the lowest value required to meetthe design considerations

Hydration is the chemical reaction that takes place when Portlandcement and water are mixed together

The hydration reaction is considered complete at 28 days

False set is the stiffening of a concrete mixture with little evidence ofsignificant heat generation



terms

Workability is the term used to describe the ease with whichconcrete can be placed and consolidated

Placeability encompasses traits loosely accumulated in the terms“workability” and “consistency.”

Consistency is the relative mobility of the concrete mixture. It ismeasured in terms of slump – the higher the slump the more mobilethe mixture – and it affects the ease with which the concrete willflow during placement.

Slump is a measure of consistency of concrete, defining the ability of

fresh concrete to flow

Bleeding is the rising of excess water tot he surface of the concreteshortly after it has been poured



WATERPORTLAND CEMENT CONCRETE



CONCEPTS

Used to wash aggregates, as mixing water , during the curing processand to wash out mixers

Water used in making concrete should be clear and free of sulfates,acids, alkalis and humus

Potable water from municipal water systems or wells provides watersuitable for use

Water from lakes, ponds, or rivers should be carefully checked forsuitability before use



AGGREGATESPORTLAND CEMENT CONCRETE



CONCEPTS

Approximately 60 to 80 percent of concrete is made up of aggregates

The cost of concrete and its properties are directly related to theaggregates used

Aggregates selected should be clean, hard, strong and durableparticles, free of chemicals, coatings of clay, or other materials thatwill affect the bond of the cement paste

The commonly used aggregates such as sand, gravel and crushedstone produce normal-weight concrete weighing 135 to 160 lb percu.ft

Aggregates must possess certain characteristics to produce aworkable, strong, durable and economical concrete



CHARACTERISTICS OF AGGREGATES

Resistance to Abrasion and Skidding

Resistance to Freezing and Thawing

Compressive Strength

Shape and textures of particlesSpecific Gravity

Absorption and Surface Moisture

Chemical Stability

Harmful Materials



Resistance to abrasion and skidding

Abrasion resistance is important when the aggregate is to be used inan area that is subject to heavy abrasive use, such as factory floor

Aggregate for abrasion resistance is tested following ASTM C131standards

To give skid resistance, the siliceous particle content of the fineaggregate should be 25 percent or more



Resistance to freezing and thawing

The freeze-thaw properties of an aggregate are important inconcrete that will be exposed to a wide range of temperatures.Significant considerations are the porosity, absorption, permeabilityand pore structure of the aggregate

Suitable aggregates may be chosen from those used in the past thathave given good results. Unknown materials should be evaluatedusing ASTM tests.



Compressive strength

The strength of aggregates under compression is an important factorto consider when choosing materials.

This is tested by standard compression tests on hardened concretesamples



Shape and texture of particles

The shape and texture of aggregate particles influence theproperties of fresh concrete more than the cured concrete

Rough-textured, angular, elongated particles require more waterthan to smooth , rounded aggregates

Angular particles require more cement to maintain the requiredwater-cement ratio

Cements tends to bond better to angular particles than to smoothparticles

This must be considered when flexural strength or high compressivestrength is specified



Specific gravity

The measure of the relative density of an aggregate

The ratio of an aggregate’s weight to the weight of an equal volumeof water

Used to determine the absolute volume occupied by the aggregate

Most natural aggregates have specific gravities between 2.4 and 2.9



Absorption and surface moisture

These are tested in order to control the net water content of theconcrete and determine suitable batch weights

Moisture conditions are designated in four categories

Oven dry

Air dry

Saturated surface dry

Damp

Surface moisture can increase the bulk(volume) of average and fine sands morethan coarse sands



Chemical stability

Chemically stable aggregates do not react chemically with cement,which could cause harmful reactions

Some aggregates contain minerals that do react with alkalies incement, causing abnormal expansion and cracking in the concrete



Harmful materials

Silt, organic materials, coal, sand soft rock particles may be presentin aggregate materials

Series of ASTM tests is used to identify these harmful materials inaggregate samples and aggregate specifications limit the amount of

these materials that may be present



ADMIXTURESPORTLAND CEMENT CONCRETE



CONCEPTS

Are ingredients added to concrete other than Portland cement,aggregates and water

They may be added before or during mixing

Admixtures change the properties of concrete

Perform more than one function

Advisable to make trial mixes before using admixtures

Trial mixes or small sample batches duplicate job conditions as accurately aspossible so that the admixture dosages and results will be close to jobexpectations

Trial mixes also allow study of the admixtures’ compatibility if more than oneadmixture is to be used in the concrete



Reasons for using admixtures

To improve workability of the fresh concrete

To reduce water content, thereby increasing strength for a givenwater-cement ratio

To increase durability of the hardened cement

To retard setting time or increase it

To impart color to concrete

To maintain volume stability by reducing or offsetting shrinkageduring curing

To increase concrete resistance to freezing and thawing



Types of admixtures

Air-entraining Agents

Retarders

Water Reducers

Accelerators

Pozzolans

Workability Agents

Superplasticizers

Permeability-Reducing and Damp Proofing Agents

Bonding Agents

Coloring Agents

Hardeners

Grouting Agents

Gas-Forming Agents



AIR-ENTRAINING AGENTS

Used to entrain microscopic air bubbles in concrete

Entrainment can be produced by using air-entrained Portland cement or byadding an air-entraining admixture to concrete as it is being mixed

It can be added before or during the mixing process

Some ingredients used air-entraining admixtures include polyethylene

oxide, polymers, fats and oils, sulfonated compounds and detergentsEntrained air bubbles improve the durability of concrete which increases

resistance to damage due to freeze-thaw cycles and de-icers, which cancause scaling

Air-entraining gives improved workability during placement and superiorwater-tightness

Improves resistance to sulfate attack from soil water and seawaterAir-entrained concrete is used in cold climates where concrete, such as

paving and architectural concrete, is exposed to the freeze-thaw cycle

Effective for concrete exposed to soil and water where sulfate attack ispossible



retarders

Slow the setting time of cement paste in concrete

Often employed in hot weather, where hydration is accelerated byexcessive heat

More water is required to achieve the desired slump, whichproduces lower strength concrete

Retarders tend to reduce the water required , resulting in a betterwater-cement ratio and ultimately increased concrete strength

Helps when it is necessary to pour large amounts of concrete orwhere placement is difficult

Reduce increased temperatures caused by the heat of hydration inlarge concrete masses



Water reducers

Reduce the amount of water needed to produce concrete of a givenconsistency

Can be used to increase the amount of slump without requiringadditional water

Makes for a lower water-cement ratio resulting in greater concretestrength

Lignin solfonic acids and mettalic salts are common water-reducingagents



accelerators

Speeds up the strength development of concrete

Strength development can also be accelerated by using Type III (Highearly strength portland cement) by increasing the amount of cementto lower the water-cement ratio or by curing at higher temperatures

Used in cold weather to develop strength faster in order to offsetfreeze damage

Frequently used accelerator is Calcium Chloride which should beadded to the concrete mix in solution rather than in dry form



pozzolan

Siliceous and aluminous material that when finely ground in thepresence of moisture, chemically reacts with calcium hydroxide atordinary temperatures to form compounds possessing cementitiousproperties

Sometimes added to concrete to help reduce internal temperaturesPozzolans can replace 10 to 35 percent of the cement



Workability agents

Workability is the term used todescribe the ease with whichconcrete can be placed andconsolidated

Improved workability may be

needed if the concrete requirespumping or placing in formscontaining considerable reinforcing



superplasticizers

Small clumps while mixing water and cement can reduce workability andinhibits hydration

Coat the cement particles, causing them to break away from the lumps anddisperse in water

Gives each cement particle a negative charge causing them to repel eachother, thus, providing more thorough dispersement

Superplasticizers can be used to:Reduce water and cement at a constant water-cement ratio, giving a concrete the

same strength as a normal mix but reducing the amount of cement used

Produce normal concrete at normal water-cement ratios that is so workable it canbe placed with little or no vibration or compaction and not have excessive

bleedingProduce a concrete of higher strength by reducing the water content required

while maintaining the normal cement content

The effectiveness of superplasticizers has a short duration (30 to 60minutes) before the concrete has a rapid loss in workability



Permeability-reducing and damp proofing

agents

Permeability is a measure of the amount of water that passesthrough channels running between the outer faces of the concrete

The permeability-reducing agent reduces the flow of water throughthese channels

They should not be used in well-proportioned mixes because theyincrease the amount of mixing water required, thus, increasing ratherthan decreasing permeability

Damp proofing admixtures are used to reduce moisture that istransferred by capillary action



Bonding agents

Can be added to Portland cement mixtures or applied to the surfaceof old concrete to increase bond strength

Usually water emulsions of certain organic materials, such as a liquidacrylic polymer, which may be added to the Portland cement with or

without mixing waterAccomplished by exposing the surface of the aggregate in the

hardened concrete, applying a cement paste slurry to the hardenedsurface and immediately pouring the new layer of concrete over it



Coloring agents

Concrete can be colored by mixing pure, finely ground mineraloxides with dry Portland cement

Thorough mixing is necessary to produce uniform color

Oxides added to normal Portland cement are usually limited to

earthly colors and pastels because of the cost and graying effect ofthe cement

Concrete can also be colored by exposing the aggregate

Color can be placed on the surface of concrete before it sets

Can use synthetic oxides mixed with fine silica sand



hardeners

Used when a concrete is subject to heavy wear, such as that of thefactory or warehouse floor

One form of chemical hardener is a colorless, nontoxic,nonflammable liquid containing magnesium and zinc fluosilicates

with a wetting agentThe wetting agent reduces the surface tension of the liquid

hardener, which makes it easier for it to enter the pores of theconcrete

Concrete surfaces can also be hardened using dry powder hardeners



Grouting agents

Portland cement grouts are widely used for stabilizing foundations,filling cracks in concrete walls, filling joints, grouting tendons oranchor bolts and in other applications

Grout properties can be altered using various admixtures



Gas-forming agents

Added to concrete or grout to cause a slight expansion in it before ithardens

This helps eliminate voids caused by settlement of the concrete orgrout



Proportioning of concrete

ingredientsPORTLAND CEMENT CONCRETE



concepts

Concrete strength is inversely proportional to the water-cement(W/C) ratio

A reduction in water while maintaining cement content will give anincrease in strength

Rule of thumb for good concrete is 0.45 to 0.58 W/C ratio says thateach 0.01 reduction in W/C ratio will increase the 28-day strength by100 psi.



concepts

The determination of the relative amounts of materials required toproduce a concrete that will be economical and workable in theplastic state and that will have the required properties in thehardened state is called mixed design or proportioning

Proportioning may vary from the simple 1:2:3 formula (ACI 211.1 mixdesign procedure)



Proportioning of concrete

Factors to be considered in proportioning concrete are as follows:

Mixing apparatus

Concrete handling

Concrete transportation

FinishingCuring

Strength requirements



SAMPLE PROBLEM

Concrete is required for a portion of a structure that will be belowground level in a location where it will not be exposed to severeweathering or sulfate attack. Required average strength will be 24Mpa with slump of 75 to 100mm. The coarse aggregate has a

nominal maximum size of 37.5mm and dry rodded mass of1600kg/cu.m. The properties of ingredients are cement type I withspecific gravity of 3.15, coarse aggregate whose bulk specific gravityis 2.68 and absorption of 0.5%, fine aggregate with bulk specificgravity of 2.64 and absorption of 0.7%, and fineness modulus of 2.8.Calculate the quantities of cement, coarse aggregate, fine aggregate

and water based on a) weight and b) volume



CONCRETE ESTIMATINGPORTLAND CEMENT CONCRETE



CONCEPTS

Determination of concrete quantities through volume calculations

Concrete is purchased by cubic yard or cubic meter

Typical waste factors for concrete construction range from 3 to 8percent, with lower values used for formed placements and higher

values for slab on grade projects

Waste factors may also include spillage and pump losses due toconcrete that will remain in the pump lines and hopper



CONCRETE

MANUFACTURINGPORTLAND CEMENT CONCRETE



CONCEPTS

Concrete can be mixed by hands in small portable mixers, in transitmix trucks and in large stationary mixers

To produce quality concrete, the batching and measuring ofingredients must be done accurately

Materials should be weighed and combined rather than combine byvolume

Water is the one ingredient that is usually measured out either byweight or by volume



concepts

Weighing materials allows for adjustments in moisture conditionsespecially in fine aggregates where bulking occur due to moisture

All weighing equipment should be checked periodically andadjustments made when required.

Admixture equipment should be checked daily since overdoses canbe very detrimental to quality concrete production



Concrete mixing

The actual mixing of concrete is performed for the most part bymixing equipment

The mixing equipment is usually rated for two functions:

Actual mixing of the ingredients to produce concrete

The actual mixing of concrete is performed for the most part by mixingequipment

The agitating capacity is higher than the mixing capacity

Mixing equipment can be stationary, mounted on wheels andtowable, mounted on a truck for transit mix or mounted on crawlers

for paving operations



Concrete mixing

The required mixing time of a stationary mixer may vary butgenerally one minute is required for the first cubic yard and 15seconds for each additional cubic yard

The mixing time is measured from the time all of the solid

ingredients are in the drum, provided that all of the water has beenadded before one-fourth of the mixing time has elapsed

ASTM C94 specifies mixing time based on drum revolutions.Generally, 70 to 100 revolutions at a rotation rate designated by themanufacturer of the mixer is required to produce uniform concrete

No more than 100 revolutions at mixing speed can be made. Allrevolutions over 100 must be made at agitating speed



Concrete mixing

ASTM C94 specifies that discharge of the concrete shall becompleted within 1 ½ hours or before the drum has revolved 300revolutions – whichever comes first – after the introduction of themixing water to the cement and aggregates, or after the introductionof cement to the aggregates



Concrete mixing methods

Stationary or central mixers are also used by some ready-mixproducers

Paving mixers are mixers mounted on crawler treads. The materialsare fed into the mixers from dry-batch trucks and the machine travels

along the finish grade and deposits fresh concrete behind itself to bescreeded and finished by the rest of the paving train



Concrete mixing methods

Shotcrete is a non-proprietary term used to describe mortar orconcrete that is placed by high-velocity compressed air and adheresto the surface on which it is projected

Concrete mixing equipment loads should not exceed rated capacities



CONCRETE TESTSPORTLAND CEMENT CONCRETE



TESTS WITH FRESH CONCRETE

STRENGTH SPECIMENS

Specimens of freshly poured concrete may be field-molded or laboratory-molded.

The molding of test cylinders should be started within fifteen minutes afterthe specimens are obtained

Field-molded specimens should be made and cured as specified by ASTMC31 or AASHTO T23

Laboratory-molded specimens should bemade and cured as specified by ASTM C192 or AASHTO T126

The size of the test cylinder depends upon the aggregate size.



Test with fresh concrete

Slump Test

Unit Weight Test

Air-Content Test

Cement Content Test



Slump test

Each load of transit-mixed concrete has a certificate listing itsingredients and their proportions

An on-site slump test is made to see if the required consistency hasbeen achieved

A mix with a high slump may be too wet and one with low slumpmay be too stiff

The slump test is made following ASTM C143 specifications



Slump test

A standard slump cone is 8in (200mm) in diameter at the bottomand 12in (305mm) high.

The cone is placed on a flat surface and held still by standing on thefoot support

It is filled full and rodded 25 times with a 5/8 inch (16mm)diameter, 24 in(600mm) long rod with rounded tip



Slump test

Another method for slump test is the Ball Penetration Test asspecified by ASTM C360. The depth to which a 30lb (13.6 kg),6in(150mm) diameter hemisphere will sink into fresh concrete ismeasured



Slump test



Unit weight test

Involves weighing a properly consolidated specimen in a calibratedcontainer following ASTM C138 standards

It can be determined the quantity of concrete produced per batchand give indications of air content.



Unit weight test



Air content test

Methods for measuring air content include the pressure method(ASTM C231), the volumetric method (ASTM C173) and thegravimetric method (ASTM C138).

The pressure method requires the sample be placed in a pressure air

meter and subjected to an applied pressureThe volumetric method measures air content by agitating a known

volume of concrete in an excess of water

Volumetric method is suitable for concrete containing ll types ofaggregates



Air content test

The gravimetric method uses the same test used for the unit weighttest of concrete. The actual unit weight of the sample is subtractedfrom the theoretical unit weight, as determined from the absolutevolumes of the ingredients, assuming no air is present.

Gravimetric method requires laboratory control and thus, is notsuitable for on-site use



Air content test

Pressure Method

Volumetric Method Test



Cement content test

This is used to determine the water and cement content of freshconcrete

The water – cement ratio has a major influence on strength,therefore, this test gives an estimate of the strength potential

without waiting for samples to harden and cure, which usually takesseven to twenty eight days



Cement content test



Tests with hardened concrete

Specimens for strength tests of hardened concrete are made andcured according to ASTM C31 (in the field) and ASTM C192 (in thelaboratory)



Tests with hardened concrete

Compressive Strength Test

Flexural Strength Test

Abrasion Test

Freeze-Thaw Test

Accelerated Curing Test



Compressive strength test

After the test cylinder has cured asrequired it is ready for thecompression strength test

Made according to ASTMspecifications and is one of the most

frequently required test



Flexural strength test

Used to determine the flexural orbending strength of concrete

Concrete sample is formed in a moldin the shape of a beam

The span of the test beam should be

three times the depth of the beamplus two additional inches



Abrasion test

Used to ascertain the resistance to wear ofhardened concrete samples

A hardening admixture or surface coating isused with the sample concrete mix

The specimen is weighed before and after

the test. The loss in weight determines theability to resist abrasion



Freeze-thaw test

Cured concrete specimens are placedin a freeze-thaw tester, which is acabinet much like a freezer

It is run through a series of freeze-thaw cycles

The loss between the original weightand final weight of the specimen isused to determine which sampleswithstand the freeze-thaw cycle best



Accelerated curing test

Used when it is desirable todetermine acceptance of structuralconcrete without the usual 28-daycuring period

ASTM C684 has three methods for

making accelerated strength test



Non-destructive tests

Used to evaluate the strength and durability of hardened concrete

Commonly used tests are rebound, penetration, pull-out anddynamic or vibration tests




Rebound TestMade with Scmidt rebound hammer, it

measures the distance a spring-loadedplunger rebounds after striking theconcrete surface. The reading is relatedto the compressive strength




Penetration TestUses a Windsor probe, which is a

power-activated gun that drives ahardened alloy probe into concrete.The exposed length of the probe ismeasured and related by calibration

table to the compressive strength ofthe concrete




Pull-Out TestRequires that a steel rod with an

enlarged end be cast in the concrete. Adevice used to pull the rod form theconcrete measures the force required.This gives the shear strength of the

concrete, but, it has a disadvantage ofdamaging the surface of the concrete




Dynamic or Vibration Test

Also called as Ultrasonic Test

Uses the principle that the velocity of sound in a solid can be measured byeither recording the time it takes short impulses of vibrations to pass througha sample or determining the resonant frequency of a specimen.

High velocities indicate a very good concrete while very low velocitiesindicate a poor concrete



PREPARING AND PLACING

OF CONCRETEPORTLAND CEMENT CONCRETE



STEPS INVOLVED IN CONCRETING

Batching

Mixing

Transporting and Placing

Compacting



batching

Batching is the measurement of materials for making concrete isknown as batching.

The following two methods of batching is practiced:

Volume batching

Weight batching.



Volume batching

In this method cement, sand and concrete are batched by volume.

A gauge box is made with wooden plates, its volume being equal to thatof one bag of cement. One bag of cement has volume of 35 litres.



Volume batching

The required amount of sand and coarse aggregate is added bymeasuring on to the gauge box. The quantity of water required for makingconcrete is found after deciding water cement ratio.

For example, if water cement ratio is 0.5, for one bag of cement (50 kg),

water required is 0.5 × 50 = 25 kg, which is equal to 25 litres. Suitablemeasure is used to select required quantity of water.



Volume batching



Weight batching

This is the recommended method of batching. A weighing platform isused in the field to pick up correct proportion of sand and coarseaggregates. Large weigh batching plants have automatic weighingequipments.



Weight batching



mixing

Mixing: To produce uniform and good concrete, it is necessary tomix cement, sand and coarse aggregate, first in dry condition andthen in wet condition after adding water.

The following methods are practiced: Hand Mixing

Machine Mixing.



Hand mixing

Required amount of coarse aggregate for a batch is weighed and isspread on an impervious platform. Then the sand required for thebatch is spread over coarse aggregate.

They are mixed in dry condition by overturning the mix with shovels.Then the cement required for the batch is spread over the dry mixand mixed by shovels.



Hand mixing

After uniform texture is observed water is added gradually andmixing is continued. Full amount of water is added and mixing iscompleted when uniform colour and consistency is observed.

The process of mixing is completed in 6 –8 minutes of adding water.This method of mixing is not very good but for small works it iscommonly adopted.



Hand mixing



Machine mixing

In large and important works machine mixing is preferred (typicalconcrete mixer).

Required quantities if sand and coarse aggregates are placed in the

drum of the mixer. 4 to 5 rotations are made for dry mixing and thenrequired quantity of cement is added and dry mixing is made withanother 4 to 5 rotations.



Machine mixing

Water is gradually added and drumis rotated for 2 to 3 minutes duringwhich period it makes about 50rotations. At this stage uniform andhomogeneous mix is obtained.



Machine mixing



Transporting & placing of concrete

After mixing concrete should be transported to the final position. In smallworks it is transported in iron pans from hand to hand of a set of workers.Wheel barrow and hand carts also may be employed.




In large scale concreting chutes and belt conveyors or pipes withpumps are employed. In transporting care should be taken to seethat segregation of aggregate from matrix of cement do not takeplace.

Concrete is placed on form works. The form works should be cleanedand properly oiled. If concrete is to be placed for foundation, the soilbed should be compacted well and is made free from loose soil.




Concrete should be dropped on its final position as closely aspossible. If it is dropped from a height, the coarse aggregates fallearly and then mortar matrix. This segregation results into weakerconcrete.



Compaction of concrete

In the process of placing concrete, air is entrapped. The entrappedair reduces the strength of concrete up to 30%. Hence it is necessaryto remove this entrapped air.

This is achieved by compacting the concrete after placing it in itsfinal position. Compaction can be carried out either by hand or withthe help of vibrators.



Hand compaction

In this method concrete iscompacted by ramming, tamping,spading or by slicing with tools. Inintricate portions a pointed steel rodof 16 mm diameter and about ametre long is used for poking the

concrete.



Compaction by vibrators

Concrete can be compacted by using high frequency vibrators.Vibration reduces the friction between the particles and set themotion of particles. As a result entrapped air is removed and theconcrete is compacted. The use of vibrators reduces the compactiontime.




When vibrators are used for compaction, water cement ratio can beless, which also help in improving the strength of concrete. Vibrationshould be stopped as soon as cement paste is seen on the surface ofconcrete. Over vibration is not good for the concrete.



Curing of concrete

Curing may be defined as the process of maintaining satisfactorymoisture and temperature conditions for freshly placed concrete forsome specified time for proper hardening of concrete.

Curing in the early ages of concrete is more important. Curing for 14days is very important. Better to continue it for 7 to 14 days more. If curing is not done properly, the strength of concrete reduces. Cracksdevelop due shrinkage. The durability of concrete structure reduces.



Curing of concrete

The following curing methods are employed:

Spraying of water

Covering the surface with wet gunny bags,

straw etc. Ponding

Steam curing and

Application of curing compounds.



Curing of concrete

Spraying of water : Walls, columns,plastered surfaces are cured bysprinkling water.

Wet covering the surface: Columns

and other vertical surfaces may becured by covering the surfaces withwet gunny bags or straw.

f



Curing of concrete

Ponding: The horizontal surfaces likeslab and floors are cured bystagnating the water to a height of 25to 50 mm by providing temporarysmall hunds with mortar.

f



Curing of concrete

Steam curing: In the manufacture of pre-fabricated concrete units steamis passed over the units kept inclosed chambers. It acceleratescuring process, resulting into thereduction of curing period.

C i f



Curing of concrete

Application of curing compounds:Compounds like calcium chloridemay be applied on the curing surface.The compound shows affinity to themoisture and retains it on thesurface. It keeps the concrete surface

wet for a long time.



PRECAST CONCRETE

PRODUCTSPORTLAND CEMENT CONCRETE

CONCEPTS



CONCEPTS

These are concrete products are construction items usuallymanufactured off site and delivered to the construction site ready forinstallation into the structure

During the manufacturing process the same quality controlmeasures applied to site-cast concrete are used to ensure the use ofquality materials in the production of precast items

t



concepts

Precast structural elements such asbeams, columns and highway medianbarriers are produced in casting bedsof varying shapes and lengths



PORTLAND CEMENT

CONCRETE

Concrete is the world’s widely used constructionmaterial

Concrete is 60 – 80 percent aggregates which areconsidered as inert ingredients and 20 – 4opercent paste which are considered activematerial

is composed principally of aggregates, a portlandor blended cement, and water, and may containother cementitious materials and/or chemicaladmixtures.

INTRODUCTION:



Requires raw materials which contain lime, silica, alumina

Plain concrete, commonly known as concrete, is an intimate

mixture of binding material, fine aggregate, coarse aggregate

and water.

This can be easily moulded to desired shape and size before

it looses plasticity and hardens. Plain concrete is strong in

compression but very weak in tension.

A small quantity of admixtures like air entraining agents,

water proofing agents, workability agents etc. may also be

added to impart special properties to the plain concrete

mixture.

In proportioning of concrete it is kept in mind that voids incoarse aggregates are filled with sand and the voids in sand

are filled with cement paste

INTRODUCTION:



Major Ingredients are

Binding materials (cement, lime, polymer)

Fine aggregates (sand)

Coarse aggregates (crushed stone)

Water

FUNCTIONS OF VARIOUS INGREDIENTS:



Cement

The binding material

After addition of water it hydrates and binds aggregates and the

surrounding surfaces like stone and bricks. Generally richer mix

(with more cement) gives more strength.

Setting time starts after 30 minutes and ends after 6 hours.

Hence concrete should be laid in its mould before 30 minutes of

mixing of water and should not be subjected to any external

forces till final setting takes place.

Fine Aggregates

Consists of river sand. It prevents shrinkage of cement.

When surrounded by cement it gains mobility enters the voids

in coarse aggregates and binding of ingredients takes place. It

adds density to concrete, since it fills the voids. Denser theconcrete higher is its strength

.

FUNCTIONS OF VARIOUS INGREDIENTS:



Coarse Aggregates

Consists of crushed stones.

It should be well graded and the stones should be of igneous

origin. They should be clean, sharp, angular and hard. They give

mass to the concrete and prevent shrinkage of cement.

Water

Water used for making concrete should be clean.

It activates the hydration of cement and forms plastic mass. As it

sets completely concrete becomes hard mass.

Water gives workability to concrete which means water makes it

possible to mix the concrete with ease and place it in final

position. The more water the better is the workability. However

excess water reduces the strength of concrete.

To achieve required workability and at the same time goodstrength a water cement ratio of 0.4 to 0.45 is used, in case of

machine mixing and water cement ratio of 0.5 to 0.6 is used for

hand mixing.

CEMENT:



Cement is a commonly used binding material in the construction.

The cement is obtained by burning a mixture of calcarious (calcium)

and argillaceous (clay) material at a very high temperature and then

grinding the clinker so produced to a fine powder.

It was first produced by a mason Joseph Aspedin in England in 1924.

He patented it as portland cement.

Any material that can be made plastic and that gradually hardens to

form an artificial stonelike substance is called a cementitious material.

Hydraulic cements, namely portland and natural, along with limes, fly

ash, and silica fume, are currently the principal cementing materials

used in structures.

CEMENT:



They become plastic by the addition of water; the mix then sets and

hardens.

The other principal type of cementing agents are asphalts, which are

made plastic either by heating, emulsifying, or by the addition of a

cutback agent. Asphalt concretes are vastly different from hydraulic

concretes. The hardening process of the latter requires a hydration

mechanism.

HISTORY OFCEMENT:



The earliest cement known was puzzalon cement, which was first used

by the Romans over 2000 years ago. There are examples of puzzalonic

cement structures still in existence and in good condition.

Those cements were produced by mixing lime with volcanic ash, called

pozzolana, which is found near the town of Pozzuola, Italy.

Assyrians and Babylonians were perhaps the first to use clay as

cementing material.

In ancient monuments, e.g. forts, places of worship and defence

structures, stones have been invariably used as a construction material

with lime as the binder. Records show that Egyptians have used lime

and gypsum as cementing materials in the famous pyramids.

HISTORY OFCEMENT :



Natural cements in more recent years were produced by burning a

limestone high in clay minerals and magnesia to drive off the carbonic

acid and then grinding the resultant clinker into a fine powder.

In comparison to Portland cement, natural cement possesses lower

tensile strength, gains strength more slowly, and its properties are less

uniform.

Vitruvius, a Roman scientist, is believed to be the first to have the

know how about the chemistry of the cementitious lime. One of the

most notable examples of Roman work is the Pantheon. It consists of a

concrete dome 43.43m in span.

The calcareous cements used by the Romans were either composed of

suitable limestones burned in kilns or were mixtures of lime andpuzzolanic materials (volcanic ash, tuff) combining into a hard

concrete.

HISTORY OFCEMENT :



Joseph Aspedin of Yorkshire (U.K.) was the first to introduce Portland

cement in 1824 formed by heating a mixture of limestone and finely

divided clay in a furnace to a temperature high enough to drive off the

carbonic acid gas.

In 1845, Issac C. Johnson invented the cement by increasing the

temperature at which the mixture of limestone and clay were burned

to form clinker.

This cement was the prototype of the modern Portland cement.

Cements used in construction industry may be classified as hydraulic

and non hydraulic.

The latter does not set and harden in water such as non-hydraulic limeor which are unstable in water, e g. Plaster of Paris.

HISTORY OFCEMENT :



The hydraulic cement set and harden in water and give a product

which is stable. Portland cement is one such.

MANUFACTURE OF PORTLAND CEMENT:



Cement can be manufactured either from natural cement stones or

artificially by using calcareous and argillaceous materials. The

examples of natural cements are Roman cement, Puzzolana cement

and Medina cement and those of artificial cement are Portland

cement and special cements.

Requires raw materials which contain lime, silica, alumina and iron

MANUFACTURE OF PORTLAND CEMENT

WET PROCESS:




WET PROCESS:




DRY PROCESS:



CHEMICAL COMPOSITION OF PORTLAND CEMENT:

The three constituents of hydraulic cements are lime silica



The three constituents of hydraulic cements are lime, silica

and alumina. In addition, most cements contain small

proportions of iron oxide, magnesia, sulphur trioxide and

alkalis.

CHEMICAL COMPOSITION OF PORTLAND CEMENT:

The three constituents of hydraulic cements are lime silica and



The three constituents of hydraulic cements are lime, silica and

alumina. In addition, most cements contain small proportions of iron

oxide, magnesia, sulphur trioxide and alkalis.

There may be small quantities of impurities present such as calcium

oxide (CaO) and magnesium oxide (MgO).

When water is added to cement, C3A is the first to react and cause

initial set. It generates great amount of heat. C3S hydrates early and

develops strength in the first 28 days. It also generates heat.

C2S is the next to hydrate. It hydrates slowly and is responsible for

increase in ultimate strength. C4AF is comparatively inactive

compound.

PHYSICAL PROPERTIES OF PORTLAND CEMENT:

The following properties should be checked before selecting Portland



The following properties should be checked before selecting Portland

cement for the civil engineering works. IS 269-1967 specifies the

method of testing and prescribes the limits

FinenessSetting Time

Soundness

Crushing Strength


Fineness



Fineness

It is measured in terms of percentage of weight retained after

sieving the cement through 90 micron sieve or by surface areaof cement in square centimeters per gramme of cement.

According to IS code specification weight retained on the

sieve should not be more than 10 per cent. In terms of

specific surface should not be less than 2250 cm2/gm.

Setting Time

A period of 30 minutes as minimum setting time for initial

setting and a maximum period of 600 minutes as maximum

setting time is specified by IS code


Soundness



Soundness

Once the concrete has hardened it is necessary to ensure that

no volumetric changes takes place. The cement is said to beunsound, if it exhibits volumetric instability after hardening.

Crushing Strength

For this mortar cubes are made with standard sand and tested

in compression testing machine as per the specification of IS

code. The minimum strength specified is 16 N/mm2 after 3

days and 22 N/mm2 after 7 days of curing.

PHYSICAL TESTS ON CEMENT:

Fineness Test



Fineness Test

One factor which affects the hydration of cement, regardless

of its chemical composition, is its fineness. The finer a cement is ground, the higher the heat of hydration

and resulting accelerated strength gain. The strength gain due

to fineness is evident during the first 7 days


Setting Time Test



Setting Time Test

Initial setting time and final setting time are the two

important physical properties of cement. Initial setting time isthe time taken by the cement from adding of water to the

starting of losing its plasticity.

Final setting time is the time lapsed from adding of the water

to complete loss of plasticity. Vicat apparatus is used for

finding the setting times

Vicat apparatus consists of a movable rod to which any one of

the three needles shown in figure can be attached. An

indicator is attached to the movable rod. A vicat mould is

associated with this apparatus which is in the form of split

cylinder.


Setting Time Test



Setting Time Test


Soundness Test



Soundness Test

It is conducted by sieve analysis. 100 gms of cement is taken

and sieved through IS sieve No. 9 for fifteen minutes. Residueon the sieve is weighed. This should not exceed 10 per cent by

weight of sample taken.

This test is conducted to find free lime in cement, which is not

desirable. Le Chatelier apparatus.

Soundness is the ability of a cement to maintain a stable

volume after setting. An unsound cement will exhibit

cracking, disruption, and eventual disintegration of the

material mass.

The current test for soundness in cement is the ASTM

Autoclave test.

TYPES OF PORTLAND CEMENT (ASTM C150):

ASTM Type I (Normal)



ASTM Type I (Normal)

ASTM Type II (Moderate Heat or Modified)

ASTM Type III (High Early Strength)

ASTM Type IV Low Heat) ASTM Type V Sulfate Resisting)

Air Entraining Portland Cement

White Portland Cement

Portland Blast Furnace Slag Cement

Portland-Pozzolan Cements

Masonry Cement

Special Portland Cement

Oil Well Cement

Waterproofed Portland Cement

TYPES OF CEMENT:

In addition to ordinary Portland cement there are many varieties of



In addition to ordinary Portland cement there are many varieties of

cement. Important varieties are briefly explained below:

White CementColoured Cement

Quick Setting Cement

Rapid Hardening Cement

Low Heat Cement

Pozzulana Cement

Blast Furnace Cement

Acid Resistant Cement

Sulphate Resistant Cement

Fly Ash Blended Cement

TYPES OF CEMENT:

White Cement



The cement when made free from colouring oxides of iron,

maganese and chlorium results into white cement. In the

manufacture of this cement, the oil fuel is used instead of coal forburning.

White cement is used for the floor finishes, plastering,

ornamental works etc. In swimming pools white cement is used

to replace glazed tiles.

Coloured Cement

The cements of desired colours are produced by intimately mixing

pigments with ordinary cement. The chlorium oxide gives green

colour. Cobalt produce blue colour. Iron oxide with different

proportion produce brown, red or yellow colour.

TYPES OF CEMENT:

Quick Setting Cement



Q g

Quick setting cement is produced by reducing the percentage of

gypsum and adding a small amount of aluminium sulphate during

the manufacture of cement. Finer grinding also adds to quick setting property. This cement

starts setting within 5 minutes after adding water and becomes

hard mass within 30 minutes. This cement is used to lay concrete

under static or slowly running water.

Rapid Hardening Cement

This cement can be produced by increasing lime content and

burning at high temperature while manufacturing cement.

Grinding to very fine is also necessary.

This property helps in earlier removal of form works and speed in

construction activity.

TYPES OF CEMENT:

Low Heat Cement



In mass concrete works like construction of dams, heat produced

due to hydration of cement will not get dispersed easily.

This may give rise to cracks. Hence in such constructions it ispreferable to use low heat cement. This cement contains low

percentage (5%) of tricalcium aluminate (C3A) and higher

percentage (46%) of dicalcium silicate (C2S).

Pozzulana Cement

Pozzulana is a volcanic power found in Italy. It can be processed

from shales and certain types of clay also. In this cement

pozzulana material is 10 to 30 per cent. It can resist action of

sulphate. It releases less heat during setting. It imparts higher

degree of water tightness.

TYPES OF CEMENT:

Blast Furnace Cement



In the manufacture of pig iron, slag comes out as a waste product.

By grinding clinkers of cement with about 60 to 65 per cent of

slag, this cement is produced. The properties of this cement aremore or less same as ordinary cement, but it is cheap, since it

utilise waste product.

Acid Resistant Cement

This cement is produced by adding acid resistant aggregated such

as quartz, quartzite, sodium silicate or soluble glass. This cement

has good resistance to action of acid and water. It is commonly

used in the construction of chemical factories.

TYPES OF CEMENT:

Sulphate Resistant Cement



By keeping the percentage of tricalcium aluminate C3A below five

per cent in ordinary cement this cement is produced. It is used in

the construction of structures which are likely to be damaged byalkaline conditions. Examples of such structures are canals,

culverts etc.

Fly Ash Blended Cement

Fly ash is a byproduct in thermal stations. The particles of fly ash

are very minute and they fly in the air, creating air pollutionproblems.

Thermal power stations have to spend lot of money to arrest fly

ash and dispose safely. It is found that one of the best way to

dispose fly ash is to mix it with cement in controlled condition

and derive some of the beneficiary effects on cement.

portland cement concrete

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