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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/AccelerantTop Related