Fineness, or particle size of portland cement affects hydration rate and thus the rate of strength gain. The smaller the particle size, the greater the surface area-to-volume ratio, and thus, the more area available for water-cement interaction per unit volume. As per IS code limits it should not be less than 225 sqm/kg but to get * higher earlier strength * now a days cement fineness is increased to 300 sqm/kg or even more than this. Effect of increased fineness is on strength and hydration process so if *we check technical data sheet of any cement company initial setting time is increased to more than 150 min and final setting time is reduce to 300 min or even less * As IS code limit is not less than 30 min for initial setting and not more than 600 min for final setting. So all parameters are within limit of IS standard but * increased initial setting and decreased final setting is reducing time of hydration process resulting into higher heat of hydration in short time* So in my opinion now use of blended cement which can reduce hydration process is very important and this can achieve by using fly ash , GGBS or other mineral additives to cement. *Cracking of slab or concrete is result of higher fineness and reduced final setting * Early and higher curing during first 72 hrs is requirement for minimising this issues.
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