Theory:
Cement is obtained by grinding various raw materials after calcination. The degree to which cement is ground to smaller and smaller particles is called fineness of cement. The fineness of cement has an important role on the rate of hydration and hence on the rate of gain of strength and also on the rate of evolution of heat. Finer cement offers a greater surface area for hydration and hence the faster development of strength although the ultimate strength
is not affected. Fineness also provides more cohesiveness to concrete and avoid separation of water at the top of concrete (called bleeding). However, increase in fineness of cement increases the drying shrinkage and cracking of the concrete.
Fineness of cement is tested either by sieving or by determination of specific surface using air-permeability apparatus. The specific surface is defined as the total surface area of all the particles in cm2 per one gram of cement. Although determination of specific surface is more
accurate to judge fineness of cement, it is rarely used except for specific purpose. In contrast sieving is most commonly used method to determine fineness of cement and is quite good for field works.
Objective:
Determination of fineness of cement by dry sieving.
Reference:
IS 4031 (Part-1):1988.
Apparatus:
IS-90 micron sieve conforming to IS: 460 (Part 1-3)-1985;
Weighing balance;
Gauging trowel;
Brush.
Material:
Ordinary Portland cement
Procedure:
1. Weigh accurately 100 g of cement to the nearest 0.01 g and place it on a
standard 90 micron IS sieve.
2. Break down any air-set lumps in the cement sample with fingers.
3. Agitate the sieve by giving swirling, planetary and linear movements for a
period of 10 minutes or until no more fine material passes through it.
4. Collect the residue left on the sieve, using brush if necessary, and weigh the
residue.
5. Express the residue as a percentage of the quantity first placed on the sieve to
the nearest 0.1 percent.
6. Repeat the whole procedures two more times each using fresh 100 g sample.
Result:
Percentage residue of cement sample by dry sieving is ___________ percentage.
Conclusions:
The given sample of cement contains less than/ more than 10% by weight of material coarser than 90 micron sieve. Therefore it satisfies/ not satisfies the criterion as specified by IS code.
Precautions:
(Discuss about the precautions to be taken while conducting this experiment)
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Questions: (Answer the following questions.)
1. Discuss the effects of fineness on hydration of cement?
2. Enumerate the advantages and disadvantages of using finer cement.
3. What is the correction factor of a sieve? Explain its necessity.
