Influence of the fineness of pozzolan on the strength of lime natural-pozzolan cement pastes

The fineness of a cement is an important factor affecting the rate of strength development. This paper examines the importance of the fineness of natural pozzolans to the strength development of lime-pozzolan cements (LPCs). A natural pozzolan from Bolivia, which is typical of natural pozzolans found in South and Central America, was ground to various finenesses, blended with lime with a mass ratio of 80:20, and the resulting LPC was used to make hardened cement paste cylinders. In some pastes 4% sodium sulphate or 4% sodium chloride activator was used to enhance strength development. Strength of the cylinders were measured at ages from 3 to 90 days during continuous moist curing at 50°C. The experimental results show that there is a good linear correlation between the Blaine fineness of the natural pozzolan and compressive strength at all ages and for all pastes. The fineness of the natural pozzolan has its most significant effect on early strength gain. The addition of chemical activator increases both the rate of strength gain and the sensitivity of strength gain to fineness.