construction material cement

8/11/2019 Construction Material CEMENT

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Construction Material

CEMENT

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THE CEMENT

Cement is most important material in building

construction . The name cement refer to thematerial manufacture from lime stone and clay and

made available in powder form, which mixed with

water can set to hard durable mass even underwater.

FUNCTION OF CEMENT :

to bind the sand and coarse aggregate together to fill

voids in between sand and coarse aggregate particle to

form a compact mass


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OPC:

Ordinary Portland cement

Chemical composition of Portland Cement:

a) C3S: Tricalcium Silicate = 3CaO.SiO2 (50%)

b) C2S :Dicalcium Silicate = 2CaO.SiO2( (25%)

c) C3A :Tricalcium Aluminate = 3CaO.Al2O (10%)d) C4AF :Tetracalcium Aluminoferrite = 4CaO. Al2O3.Fe2O3(10%)

e) Gypsum (5%)


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Hydrates and hardens rapidly and is

largely responsible for initial set and

early strength.

Early strength of cement is higher with

increased percentages of C3S.

C3S: Tricalcium Silicate


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C2S : Dicalcium Silicate

Hydrates and hardens slowly.

Contributes largely to strength increase at

ages beyond one week.

Responsible for long term strength


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Alite (C3S) and Belite (C2S)


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C3A :Tricalcium Aluminate

Liberates a large amount of heat during the firstfew days of hydration and hardening.

Also contributes slightly to early strength

development.

Gypsum added to the cement slows down thehydration rate of C3A.

Cements with low percentages of C3A areespecially resistant to soils and waterscontaining sulfates.


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Hydration of Cement

In the presence of water the cement compoundschemically combined with water (hydrate) to formnew compounds that are the infrastructure of thehardened cement paste in concrete.

Both C3S and C2S hydrate to form calciumhydroxide and calcium silicate hydrate (CSH).Hydrated cement paste contains 15% to 25%Calcium hydroxide and about 50% calcium

silicate hydrate by mass. The strength and otherproperties of hydrated cement are due primarilyto calcium silicate hydrate.


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C3A reacts with water and calcium hydroxideto form tetracalcium aluminate hydrate.

C4AF reacts with water and calciumhydroxide to form calcium aluminoferritehydrate.

Hydration of Cement


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Relative Reactivity of Cement

compounds


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Relative volume of major compounds in

hydrated cement paste


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THE CEMENT MANUFACTURING

PROCESS

1. BLASTING : The raw materials that are used

to manufacture cement (mainlylimestoneand

clay) are blasted from the quarry.

Quarry face

3. CRUSHING AND TRANSPORTATION :The raw materials, after crushing, are transported to the plant by conveyor. The plant stores

the materials before they are homogenized.

2. TRANSPORT : The raw materials are loadedinto a dumper.

crushing

conveyor

dumper

storage at

the plant

loader


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CEMENT - MANUFACTURE


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Portland Pozzolana Cement (PPC)

This type of cement is most common type

available now in market.

This is made by blending 10-25% reactive

pozzolana like flyash or calcined clay withOPC

Addition of pozzolana makes cement

sensitive to curing and it requires longer

curing than OPC.


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SULPHATE RESISTANT

PORTLAND CEMENT

Sulphate-resisting Portland cement (SRPC) is a

special purpose cement used where sulfates are

present in concentrations that would damage

Normal Portland cement concrete or mortar.

Sulfate resistance is achieved by adjustments to

chemical composition to limit the level oftricalcium aluminate (C3A) in the SRPC


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SRPC : PROPERTIES

Applied at place where there is exposure to

sulphate such as used in concrete below

ground

Higher content of Tetracalcium Aluminoferrite& reducing the Tricalcium aluminate to

aluminium

Has darker color than OPC


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SRPC is made by fusing together a preciselycontrolled blend of very finely groundlimestone, shale and iron oxide at hightemperatures to form cement clinker.

A small quantity of gypsum is added to thisclinker before grinding to produce the finalfine powder - Sulfate-resisting Portlandcement.

SRPC is manufactured in a modern dryprocess works at Castlemungret, Co.

Limerick and is supplied either in bulk or in

bags.

SRPC : PROPERTIES


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SRPC : ADVANTAGES

Long Term Strength Development

High Strength Concrete

Heat of Hydration

Pure Water and Acid Attack

Sulphate AttackAlkali Aggregate Reactivity


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Long Term Strength Development

A significant characteristic of SRPC is the

ability to continue significant strength

development beyond the normal 28 day

period. The benefits of this are obvious, considering

that 28 days is a very short period in the life

of most concrete structures


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High Strength Concrete

Studies have shown amazing benefits of the

use of SRPC in high performance concrete.

The lower reactivity of the slag makes it

easier to control slump in the first two hoursthat follow mixing,

as well as to reduce the amount of heat

developed during hydration at higher cement

contents.


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Heat OF Hydration

Sulphate Resistant Portland Cement have a

much lower heat of hydration than other

cements, making them ideal for mass

concrete work. The lower heat of hydration results in smaller

temperature gradients within mass concrete

structures, thereby minimising thermal

cracking.


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Pure Water and Acid Attack

The use of SRPC is recommended in

applications where concrete is exposed to

pure water and/or acidic conditions.

Examples are water pipes and reservoirs, softdrink factories and sewage works.


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Sulphate Attack

SRPC provides higher resistance to sulphate

attack for applications specifically requiring

sulphate resistance.

Applications include sewage works andcoastal environments.


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Alkali Aggregate Reactivity

SRPC has been shown to reduce the risk of

alkali aggregate reaction in concretes

containing reactive aggregates.


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BFSC Portland blast furnaceslag

cement

This type of cement constitutes about 10% of

cement produced in India.

The slag forms 25-60% of the cement.

Every ton of cast iron produce 0.3 tons offurnace slag which can be used in cement

industry.

During its setting the Ca(OH)2liberated byOPC hydration acts as an activator for the

slag.


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BFSC Portland blast furnaceslag

cement

Even though it is equated with OPC it

behaves more like PPC and has lower heat of

hydration and better sulphate resistance.

At present BFSC produced in India is onlyGrade-33 and there are proposals to make

Grade-43 cements with 45-70% slag content.

BFSC with more than 50% slag has good

sulphates resistance


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Hydrophobic cement

In places of high rainfall and humidity normal

cement tends to set when stored, due to

mositure present in the atmosphere.

By grinding the cement clinker with waterrepellent film forming substance like oleic acid,

a water repellent film is formed around cement

particle during manufacturing itself. This

prevent setting of cement during storage.

During mixing with aggregates this film is

broken and cement behave as ordinary

cement


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Blended cement

For economy a mixture of portland cement,

blast furnace slag and flyash is allowed to be

used in some countries. This is known as

blended cement. In India this type of cement is not produced.


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Rapid Hardening Portland cement

(RHPC)

Rapid Hardening Portland cement (RHPC) is

a special purpose cement used in concrete to

ensure a higher rate of early age strength

development than that typically achievedusing Normal Portland cement (NPC).

The improved early age strength performance

of RHPC is principally achieved through

increased product fineness.


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RHPC : ADVANTAGES

More finely grounded than OPC

Allows formwork to be struck earlier

Providing savings either the quantity of

formwork required in time Produce heat earlier than OPC, so it can be

used in cold weather


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RHPC :Qualities

RHPC is produced using carefully selectedraw materials.

Strict quality control throughout each stage ofthe manufacturing process ensures that aconsistent final product is achieved.


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RHPC : Strength

Rapid Hardening Portland cement achieveshigher earlier strengths than OPC because itis more finely ground.

Rapid Hardening Portland cement ischemically similar to OPC and as suchconcrete mixes should be designed with thisin mind.

In particular, optimum ultimate strength ofconcrete using RHPC will depend, like OPC,on careful attention to the water/cement ratio,consistent with ensuring satisfactory placingand compaction.


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FINENESS OF CEMENT

Fineness of cement is a measure of size of

particle of cement. It is expressed as specific

surface of cement (in sq. cm /gm).

FINENESS OF

CEMENT

SIZE OF

PARTICLE

SPECIFIC

SURFACE OF

CEMENT

IS MEASURE OF

IS EXPRESSED AS


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PHYSICAL TESTS OF CEMENTIS 4031 (PART-1 to 11) & I. S. 269 1978.

Test for Fineness

The first requirement is that 90% of cementshould pass IS 90 mircons. Indian standard

also specifies fineness test by blaines airpermeability method as described in IS 4031-1968

95% of cement particles are smaller than 45

micrometer, with the average particle around15 micrometer.

Fineness of cement affects heat released andthe rate of hydration.


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TESTS FOR FINENESS(IS 4031 & I. S. 269 1978. )

The principle is basedon relation betweenthe rate of flow of airthrough a cement bed

and surface area ofparticles comprisingthe cement bed ofgiven porosity

It should be at least 225m2/kg

BLAINE AIR PERMEABILTYAPPARATUS
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TESTS FOR FINENESS(I. S. 269 1978. )

BLAINE AIR

PERMEABILTY

APPARATUS

S S O SS


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TESTS FOR FINENESSSTEP WISE PROCEDURE

1. Calculate the bulk volume of compacted bed of standard cement

V = (WA-WB) / D WhereWA= gms of, mercury required to fill the permeability cell

WB= gms of mercury required to fill the portion of the cell not

occupied by the bed of cement formed by 2.8 gms of standardcement sample .

D= Density of mercury at temperature of test.

2. Determine the weight of the standard sample ( W) required to

produce a bed having porosity

of 0.500 0.005 (e) as follows:

W = 3.15V(1-e)

Where V = Bulk volume of compacted cement powder

And e = Desired porosity of bed of cement (0.500 0.005)

TESTS FOR FINENESS


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TESTS FOR FINENESSSTEP WISE PROCEDURE

3. Determine the time taken by the manometer liquid to fall from

second mark from the top to the third mark on the, manometer

when air is allowed to permeate through the compacted cement

4. Calculate the constant of the apparatus (k) by using the following

formula

Ss = k Ts wherek = Ss/ TsWhere Ss is the fineness of standard portland cement in Sq.

cm/gm.

5. Using the same quantity (w) of the cement sample find the time

(Ts) in seconds required for the manometer liquid fall fromsecond mark to third mark

6. Calculate the specific surface of cement in Sq. cm/gm using the

form

S= k Ts

BIS REQUIREMENT FOR
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BIS REQUIREMENT FOR

FINENESS

1. As per I. S. 269 the residue of cement sampled on the sieve 90 micron

after sieving should not exceed .following % by weight for different

types of cements.

Ordinary Portland cement 10%

Rapid hardening cement 5%Low heat cement 5%

2. As per I. S. 269 the specific surface area of cement sample should not

exceed following for different types of cement.

Ordinary Portland cement 2250 sq. cm per gm

Rapid hardening cement 3050 sq. cm per gm

Low heat cement 3250 sq. cm per gm


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T f N l d d


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Test of Normal or standard

Consistency (IS 4031) Consistency refers to the relative mobility of a freshly

mixed cement paste or mortar or its ability to flow.

Normal / standard consistency

Permit vicatsplunger to penetrate

5 to 7 mm from bottom

Amount of water as % by weight of

dry cement

T t f N l t d d


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Test of Normal or standard

Consistency ( IS 4031)It is the consistency at which

the vicat plunger G of10mm diameter and50mm length will

penetrate 33-35 mmwithin 3 to 5 minutes ofmixing .

The test procedure is to

carry at least three trialexperiment by mixing thecement with distilled watervarying from about 24 to

27 % of weight of cement . VICAT APPARATUS

Test of Normal or standard Cons

istency


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Test of Normal or standard Consistency

STEPWISE PROCEDURE: (as per I.S.4031-1988)

1. Weigh about 400 gm of cement accurately and placed it in

enamel trough .

2. To start with add about 25% of potable water and mix it by

means of spatula. Care should be taken that the gauging time is

not less than three minutes and not more than 5 minutes.

3. Apply thin layer of oil to inner surface of mould. Fill the Vicat's

mould with this paste in the mould resting on non- porous plate.

4. Make the surface of cement paste in level with the top of mouldwith the trowel. The mould should be slightly shaken to the expel

air.

5. Place the mould together with the non-porous plate under the

rod bearing the plunger so that it touches the surface of the test

block.

Test of Normal or standard Cons

istency


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Test of Normal or standard Consistency

STEPWISE PROCEDURE: (as per I.S.4031-1988)

6. Release quickly the plunger allowing it to sink in the cement

paste in the mould. Note down the penetration of the plunger in the

paste ,when the penetration of plunger becomes stable in the

mould.

7. If the penetration of plunger in the paste is less than the 33 to 35

mm from the top of the mould, prepare the trial paste with

increasing percentage of water and repeat the above mentioned

procedure until the plunger penetrate to a depth of 33 to 35 mm

from the top or 5 to 7 mm from the bottom of mould.

8. Expressed this amount of water as a percentage by weight of dry

cement.


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Test for Soundness (IS 4031)

Soundness is the ability of a hardened paste toretain its volume after setting.

The cement is said to be sound when thepercentage of free lime and magnesia is with in

specified limits .A cement is said to be unsound (i.e. having lack

of soundness) if it is subjected to delayeddestructive expansion.

These materials expand in the structure andthus the concrete or mortar also expand,

causing unequal expansion of paste


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Test for Soundness (IS 4031)

The Soundness test is an indication of excess oflime caused by inadequate burning of cement orexcess of magnesia or sulphates .

1. Le chateliersTest2. Autocalve test

Le Chatelier Test


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Le Chatelier TestSTEP WISE PROCEDURE ( AS PER IS : 4031):

1. Prepare a cement paste formed by gauging cement with 0.78 times

water required to give a paste of standard consistency. The

gauging time should not be less than 3 minutes nor greater than 5

minutes.

Le Chatelier Test


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Le Chatelier TestSTEPWISE PROCEDURE ( AS PER IS : 4031):

2. Oil the inner surface of the mould. Place the mould on a glass sheet

and fill it with cement paste, taking care to keep the edges of the

mould gently together. Cover the mould with another piece of glass

sheet and peace a small weight on this covering glass sheet and

immediately submerge the whole assembly in water at atemperature of 27Cand keep it for 24 hours.

3. Take out the assembly from water after 24 hrs. Measure the

distance between the indicator points and record it (D1)

4. Submerge the mould again in water and bring the water to boiling in

25 to 30 minutes and keep it boiling for three hours.5. Remove the mould from the water. Allow it to cool and measure the

distance between the indicator points and record it ( D2 ).

6. Three samples should be tested and average of the results should

be reported.


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Le Chatelier Test

This test shows unsoundness due to lime only.Unaerated cement paste at normal consistencyis first tested for expansion. If the test resultsdoes not satisfy requirement of 10mmexpansion .

Another test shall be made after aeration ofcement by spreading of sample to a depth of75mm at relative humidity of 50% to 80% for 7days the expansion in this aerated cement testshould not be more then 5 mm


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Autoclave Test

Autocalve Test is used for both lime andmagnesia excess indication .

All the cement having a magnesia content morethen 3 % is to be tested for soundness by thistest with unaerated cement .

The test consist of heating bar made of cementpaste with water of normal consistency andmeasuring its expansion


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Test for Setting Time

The Setting Time is also determined by vicatsneedle on cement paste of normal consistency. For this test , we use 1mm square needle ,this time to penetrate 33-35mm is taken as

initial setting time.For final setting time we use special needle (5mm

dia) and time at which this needle will notpenetrate more then 0.5mm is taken as final

set.


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Compressive Strength

This is most important test. The compressivestrength of cement is determine from cube offace 50cm2 in area made of cement mortar withone part cement and three part of standard

sand (conforming to IS 650-1966) by weightand water corresponding to 25% normalconsistency plus three percent of combinedweight of cement and sand .


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Heat of Hydration (IS 4031-1968)

Hydration of cement is chemical reaction and itproduce heat . In very massive construction thiseffect can rise the temperature of concrete asmuch as 50C . In such cases , we should use

low heat cements or adopt cooling method.The test is carried out by calorimeter. Low heat

cement should satisfy following criteria

1. In 7 days, heat generated should not be morethan 65 calories/gm of cement.

2. In 28 days, heat generated should not be morethan 75 calories/gm of cement.


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Cont. on Heat of Hydration

Cements do not

generate heat at

constant rate as

illustrated inFigure for a typical

Portland cement


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Storage of Cement

Cement is moisture-sensitive material; if keptdry it will retain its quality indefinitely.

When exposed to moisture, cement will setmore slowly and will have less strengthcompared to cement that kept dry.

At the time of use cement should be free-flowing and free of lumps.


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Storage of Cement


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