Answer by Sumanth Reddy:
Ordinary Portland Cement (OPC) and Portland Pozzolana cement (PPC) differ primarily in their composition ultimately affecting its applicability.
PPC commonly has pozzolan material added to cement (either before clinkering or added to ground clinker). Pozzolan commonly used is fly as and is put upto 15%.
Pozzolans have an effect in reacting with the Calcium hydroxide formed after hydration of alite and belite phases in cement. Their composition is primarily Silica and alumina, though they are essential for formation of alite and belite in cement clinker, this external addition is an attempt to control the free calcium hydroxide presence in the paste.
In terms of utility, long term strength of such cements are strength gaining with the hydration period extending quite longer than OPC. On the downside, the early strength properties are going to be affected. The fresh properties are going to be slightly better because of action of fly ash as filler.