5 materials of cement concrete

8/10/2019 5 Materials of Cement Concrete

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Subject: Building Material

UNIT 5

Materials For Cement

Concrete.


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INTRODUCTION

The cement concrete is a mixture of cement,sand,pebbles or crushed rock and water, which, when

placed in the skeleton of forms and allowed to cure,

become hard like stone.

The cement concrete has attained the status of major

building materials because of following reasons.

1. Its set quickly as compared to lime.

2. It has good compressive strength.

3. It can be readily moulded into desire size and

shape.4. It binds rapidly with steel and as it is weak in

tension, the steel reinforcement is placed in cement

concrete to resists tensile stresses. This is termed as

R.C.C(reinforced cement concrete).


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Different Types Of Cement.

1.Acid-resistant

cement.

2.Blast furnace

cement.3.Coloured cement.

4.Expanding cement.

5.Quick settingcement.

6.Hydrophobic cement.

7.Low heat cement.

8.Pozzolana cement.

9.Extra rapid hardening

cement10.Sulphate resistingcement

11.White cement

12.Air entraining

13. High alumina

14. Water proof cement


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Details of different cement with their uses

1.Acid-resistant cement:-It is composed of the

following.

Acid-resistant aggregates such as

quartz,quartzites,etc Additive such as sodium fluosilicate Na2SiF6 and

Solution of sodium silicate or soluble glass.

By adding 0.5% of linseed oil it resistant to water

is increased and it is known as acid and water

resistant cement.

USES:-In chemical industry its used as heat

resistant & acid resistant coating.


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2. Blast furnace:-For this cement, the slag as obtained from

blast furnace is used. Slag is a waste product in the

manufacturing process of pig iron.Uses:- Construction in cold regions like marine and under

ground works.

3.Coloured cement:-Cement of desired colour may be

obtained by mixing pigments with ordinary cement.Uses:- Widely used for floor finishing, stair treads,artifical

marble, window sill slab etc.

4.Expanding cement:-Contain sulpho aluminate stabilizing

agent, expands on setting.Use:-It is used for construction of water retaining

structures and also for repairing the damaged concrete.


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5.Quick setting cement:-This cement is produced by

adding small % of aluminum sulphate and finely grinding

the cement. And less % of gypsum is added. The setting

action setting starts within five minutes and becomes hardin 30 min.

Uses:-It is used in under water construction & running

water.

6.Hydrophobic cement:-This type of cement containadmixtures which decrease the wetting ability of cement

grains.

Uses:-Can be stored for long periods. Thus frost

resistance and water resistance is increased.7.Low heat cement:-It contains less C3S and C3A

percentage, and higher percentage of C2S.this cement

posses less compressive strength.

Uses:-It is mainly used for mass concrete work.


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8.Pozzolana cement:-It contains volcanic ash, pozzolana. Heatof hydration is low. And high tensile strength.

USE:-Hydraulic structures i.e. dam, Sewage works.

9.ExtraRapid hardening setting cement:-This cement is

obtained by adding calcium chloride with rapid hardening

portland cement. This type of cement should be

transported,placed,compacted and finished within 20 minutes

after mixing.10.Sulphate resisting cement:-The sulphate resistant cement

is made with low C3A content is found to be effective. Such

cement with low C3A and comparatively low C4AF content

is known as sulphate resisting cement. This cement has a

high silicate content. The specification generally limits the

C3A content to 5 percent.

Uses:-In foundations where soil contain sulphate.

In marine construction.


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11.White cement:-It is prepared from pure limestones, free from iron oxides.

USES:-swimming pools, decorative works etc.

12. High alumina:-Its contain alumina, lime,bauxite. Compressive strength is more.

Use:-Cold region, frosts area, sea water etc.


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Grade o f cement

Grade refers to the strength of cement at 28

days, when tested as per IS: 4031-1988.

If the 28 days strength is less than 33 N/mm2, it

is called 33 Grade Cement.

If the 28 days strength is lies between 33 to 43

N/mm2, it is called 43 Grade Cement.

If the 28 days strength is lies between 43 to 53N/mm2, it is called 53 Grade Cement.


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Field tes t o f cement.

The colour of cement should beuniform. Its colour should be gray orgreen.

Cement should sink and should notfloat when thrown in water.

It should be in the form of fine powder.There should be no lumps in bag.

The cement should feel smooth whentouched or rubbed in between fingers.

No cracks should be observed on

paste after setting.


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Laboratory Test

Laboratory test are

Compressivestrength

Chemical composition

Fineness

Tensilestrength

Consistency

Settingtime

Soundness


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Chemical composition

The following are the chemical requirements ofordinary portland cement as per IS-269-1998.

i. Ratio of % of alumina to that of iron oxide should beless than 0.66.

ii. Ratio of percentage of alumina,silica,iron oxide shouldbe between 0.66 and 1.22,when calculated by followingformula:

CaO 0.7SO3

2.82 + 1.223 + 0.6523

i. Loss on ignition should not be greater than 4%ii. Sulphur content should be greater than 2.75%

iii. Weight of insoluble residue should not me greater than1.50%

iv. Weight of magnesia should not exceed 5%


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SoundnessSoundness of cement is determined by Le-Chatelier method as per IS: 4031 (Part 3)

1988.

Volumetric changes after setting of cement are

responsible for causing cracks, distortion and

disintegration of concrete.

Le chaterlier apparatus


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Procedure to determine so undness of cement :

i) Place the mould on a glass sheet and fill it with the cement paste formed

by gauging cement with 0.78 times the water required to give a paste of

standard consistency.

ii) Cover the mould with another piece of glass sheet, place a small weight

on this covering glass sheet and immediately submerge the whole

assembly in water at a temperature of 27 2oC and keep it there for 24hrs.

iii) Measure the distance separating the indicator points to the nearest 0.5mm

(say d1).

iv) Submerge the mould again in water at the temperature prescribed above.

Bring the water to boiling point in 25 to 30 minutes and keep it boiling for

3hrs.

v) Remove the mould from the water, allow it to cool and measure the

distance between the indicator points (say d2).

vi) (d2d1) represents the expansion of cement.


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Dimension of Le-Chatelier Apparatus.


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CONSISTENCY TEST

The basic aim is to find out the water contentrequired to produce a cement paste of standardconsistency as specified by the IS: 4031 (Part 4)1988.

The principle is that standard consistency of

cement is that consistency at which the Vicatplunger penetrates to a point 5-7mm from thebottom of Vicat mould.

Apparatus Vicat apparatus conforming to IS:5513 1976, Balance, whose permissiblevariation at a load of 1000g should be +1.0g,Gauging trowel conforming to IS: 10086 1982.


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Procedure to determine cons is tency of cementi) Weigh approximately 400g of cement and mix it with aweighed quantity of water. The time of gauging shouldbe between 3 to 5 minutes.ii) Fill the Vicat mould with paste and level it with atrowel.

iii) Lower the plunger gently till it touches the cementsurface.iv) Release the plunger allowing it to sink into the paste.v) Note the reading on the gauge.vi) Repeat the above procedure taking fresh samples ofcement and different quantities of water until the

reading on the gauge is 5 to 7mm. Reporting of Results

Express the amount of water as a percentage of theweight of dry cement to the first place of decimal.


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INITIAL AND FINAL SETTING TIMEWe need to calculate the initial and final setting time as perIS: 4031 (Part 5) 1988. To do so we need Vicat apparatusconforming to IS: 5513 1976, Balance, whose permissiblevariation at a load of 1000g should be +1.0g, Gauging trowelconforming to IS: 10086 1982.

Procedure to determ ine ini t ial and final sett ing t im e ofcementi) Prepare a cement paste by gauging the cement with 0.85times the water required to give a paste of standardconsistency.ii) Start a stop-watch, the moment water is added to thecement.

iii) Fill the Vicat mould completely with the cement pastegauged as above, the mould resting on a non-porous plateand smooth off the surface of the paste making it level withthe top of the mould. The cement block thus prepared in themould is the test block.


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A)INITIAL SETTING TIMEPlace the test block under the rod bearing theneedle. Lower the needle gently in order tomake contact with the surface of the cementpaste and release quickly, allowing it to

penetrate the test block. Repeat theprocedure till the needle fails to pierce thetest block to a point 5.0 0.5mm measuredfrom the bottom of the mould.The time periodelapsing between the time, water is added tothe cement and the time, the needle fails topierce the test block by 5.0 0.5mmmeasured from the bottom of the mould, isthe initial setting time.


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B) FINAL SETTING TIMEReplace the above needle by the onewith an annular attachment. The cementshould be considered as finally set when,

upon applying the needle gently to thesurface of the test block, the needlemakes an impression therein, while theattachment fails to do so. The periodelapsing between the time, water isadded to the cement and the time, theneedle makes an impression on thesurface of the test block, while theattachment fails to do so, is the final

setting time.


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Some places get plenty of rainfall in therainy season and have high humidity inother seasons.The transportation andstorage of cement in such places cause

deterioration in the quality of cement. Insuch far off places with poorcommunication system, cement perforcerequires to be stored for long time.Ordinary cement gets deteriorated andloses some if its strength, whereas thehydrophobic cement which does not losestrength is an answer for such situations.


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Portland pozzolana cement producesless heat of hydration and offersgreater resistance to the attack ofaggressive waters than ordinaryPortland cement. Moreover, it reducesthe leaching of calcium hydroxidewhen used in hydraulic structures. It is

particularly useful in marine andhydraulic construction and other massconcrete constructions.Uses:


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Sulphate attack is greatly accelerated if accompanied byalternate wetting and drying which normally takes place in

marine structures in the zone of tidal variations. Sulphates

react both with the free calcium hydroxide in set cement to

form calcium sulphate

Extra rapid hardening cement accelerates

the setting and hardening process.

A large quantity of heat is evolved in a very

short time after placing.

The acceleration of setting, hardening and

evolution of this large quantity of heat in

the early period of hydration makes the

cement very suitable for concreting in cold

weather.


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Storage Of Cement.The cement should be stored carefully. Otherwise it may absorb

moisture from the atmosphere and may become useless forstructural work. Following precautions are to be taken for thestorage of cement.

Place of storage should be dry.

Floor walls and roof should be water proof.

Storage place should be at higher level. Fitting of shutter of doors,windows,ventilators should be

proper.

Cement bags should be protected from rain and winds.

Bags should be stacked in piles.number of bags should not be

more than 10 to 12 in pile. A distance of about 300 mm should be kept between the pile of

cement bags and exterior.

Period of storage should not be more than 3 months undernomal circumstances.

While removing bags from piles, steps should be formed bytaking two or three bags.


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ADDIMTURES

Properties of cement or concrete can be improved by mixingadmixtures.

Acceleratorsspeed up the hydration (hardening) of the concrete.Typical materials used are CaCl2, Ca(NO3)2and NaNO3. However, use of chlorides may causecorrosion in steel reinforcing and is prohibited in some countries, sothat nitrates may be favored.

Retardersslow the hydration of concrete and are used in large ordifficult pours where partial setting before the pour is complete isundesirable

Air entrainmentsadd and entrain tiny air bubbles in the concrete, whichreduces damage during freeze-thawcycles, increasing durability.However, entrained air entails a trade off with strength, as each 1% ofair may decrease compressive strength 5%.

Plasticizersincrease the workability of plastic or "fresh" concrete,allowing it be placed more easily, with less consolidating effort. A typicalplasticizer is lignosulfonate. Plasticizers can be used to reduce thewater content of a concrete while maintaining workability and aresometimes called water-reducersdue to this use. Such treatmentimproves its strength and durability characteristics
http://en.wikipedia.org/wiki/Acceleranthttp://en.wikipedia.org/wiki/Calcium_chloridehttp://en.wikipedia.org/wiki/Calcium_chloridehttp://en.wikipedia.org/wiki/Calcium_nitratehttp://en.wikipedia.org/wiki/Calcium_nitratehttp://en.wikipedia.org/wiki/Calcium_nitratehttp://en.wikipedia.org/wiki/Calcium_nitratehttp://en.wikipedia.org/wiki/Sodium_nitratehttp://en.wikipedia.org/wiki/Sodium_nitratehttp://en.wikipedia.org/wiki/Retarder_(chemistry)http://en.wikipedia.org/wiki/Air_entrainmenthttp://en.wikipedia.org/wiki/Weatheringhttp://en.wikipedia.org/wiki/Plasticizerhttp://en.wikipedia.org/wiki/Plasticizerhttp://en.wikipedia.org/wiki/Weatheringhttp://en.wikipedia.org/wiki/Weatheringhttp://en.wikipedia.org/wiki/Weatheringhttp://en.wikipedia.org/wiki/Air_entrainmenthttp://en.wikipedia.org/wiki/Retarder_(chemistry)http://en.wikipedia.org/wiki/Sodium_nitratehttp://en.wikipedia.org/wiki/Sodium_nitratehttp://en.wikipedia.org/wiki/Calcium_nitratehttp://en.wikipedia.org/wiki/Calcium_nitratehttp://en.wikipedia.org/wiki/Calcium_nitratehttp://en.wikipedia.org/wiki/Calcium_nitratehttp://en.wikipedia.org/wiki/Calcium_nitratehttp://en.wikipedia.org/wiki/Calcium_chloridehttp://en.wikipedia.org/wiki/Calcium_chloridehttp://en.wikipedia.org/wiki/Calcium_chloridehttp://en.wikipedia.org/wiki/Accelerant

5 materials of cement concrete

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