The fineness of cement is a measure of the size of particles of cement and is expressed in terms of the specific surface area of cement. The fineness of cement is measured as the % weight retained on a 90µm IS sieve over the total weight of the sample. In the laboratory, the fineness of cement is tested by sieving and by the determination of a specific surface. For ordinary cement, the weight of residue left on the sieve shall not exceed 10%. The fineness of cement is the significant factor affecting the rate of hydration, rate of gain of strength, setting time, and rate of evolution of heat. The rate of strength development increases with fineness. Since the specific surface area is inversely proportional to the size of the particle, the surface area is more for finer cement than for a coarser cement. Therefore, the finer the cement, the higher the surface area for hydration and hence faster the development of strength.
Smaller cement particles react much quicker than the larger particles. A cement particle with a diameter of 1 µm will react entirely in 1 day, whereas the particle with a diameter of 10µm takes about 1 month. It is found that the particle size fraction below 3 microns affects one day’s strength and 3 to 25-micron fraction influence the 28 days’ strength. Setting time decreases with an increase in the fineness of the cement. Too much smaller particles in cement results in quick setting, thereby leaving no time for mixing, handling, and placing. Also, such cement is susceptible to air set and early deterioration. To increase the setting time of cement, it must be manufactured in a different range of particle sizes.
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