Q & Ans - What common tests are conducted on cement? Name the various admixtures for use with concrete.

Q - What common tests are conducted on cement? Name the various admixtures for use with concrete.

Ans - Common tests are conducted on cement –

Field Test –

1. Colour of the cement should be uniform and grey.

2. Cement should feel smooth when touched or rubbed in between fingers like flour. If hand is inserted in a bag it should feel cool. If a small quantity of cement is thrown in a bucket of water it should sink and should not float on the surface.

3. Cement should be free from any hard lumps.

Laboratory Tests -

1. Fineness Test – It should be done by sieve analysis / Air Permeability apparatus. Cement Particles size should be less than 90µ ( 0.09 mm )

2. Soundness Test – The expansion of cement is measured in laboratory by Lechatelier Mould which is an indication of free lime present in cement.

3. Setting time ( Initial & Final ) test - Tested by Vicat apparatus, Initial setting time 30 minutes and final setting time 10 hours.

4. Compressive Strength Test – Checked by making mortar cubes in 1 : 3 by weight and testing the cubes in compressive testing machine. It should be after 3 days – 160 Kg / cm2, after 7 days – 220 Kg / cm2 and after 28 days – 330 Kg / cm2.

5. Consistency of standard cement paste - Tested by Vicat apparatus.

Various admixtures -

( 1 ) Chemical Admixtures - Admixtures may be any one of the following classes for use in concrete :-

( a ) Water reducing or plasticizing Admixtures – lingo - sulphonate or poly hydroxy compounds.

( b ) Retarding Admixtures - Starches, Cellulose products, Sugars and hydroxyl - carboxylic acids and their salts.

( C ) Accelerating Admixtures - Calcium chloride, flouro silicates and Triethanolamine.

( d ) Water reducing and retarding Admixtures.

( e ) Water reducing and accelerating Admixtures

( f ) Permeability reducing (water proofing) Admixtures

( 2 ) Liquid admixtures :- Admixtures introduced into the concrete as liquids generally fall into the following categories -

( a ) Air entraining Admixtures - Animal and vegetable oils and fats; natural wood resins and their sodium salts; and alkali salts of sulphated and sulphonated organic compounds.

( b ) Water reducing.

( c ) Water reducing retarders.

( d ) Retarders.

( e ) Water reducing accelerators/

( f ) Accelerators.

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