Ceramics-Silikáty 50 (4) 193-199 (2006)

Chemical activation and set acceleration of lime-natural pozzolan cement

A. Allahverdi, J. Ghorbani

In order to shorten the setting time and to fasten the strength development of lime pozzolan cements, different methods including calcinations, acid treatment, prolonged grinding, elevated temperature of curing and addition of chemical activators have been tried to improve the pozzolanic reactivity of natural pozzolan. In this work, the effects of some chemical activators and set accelerators on set and strength behaviours of a lime-natural pozzolan cement containing 70% natural pozzolan of the type pumice and 30% hydrated lime (by mass) have been investigated. Results obtained show that addition of alkaline compounds and Portland cement clinker can improve the set and strength behaviours of lime-natural pozzolan cements. Sodium sulfate is the most effective chemical activator for lime-natural pozzolan cements compared to Na₂CO₃, NaOH, CaCl₂ •2H₂O, and ordinary Portland cement-clinker. The most effective set accelerator for the studied lime-natural pozzolan cement however is sodium hydroxide compared to Na₂SO₄, Na₂CO₃, NaCl, CaCl₂•2H₂O and ordinary Portland cement-clinker. Addition of 6 wt.% Na₂SO₄ could noticeably increase 90-day compressive strength and presence of 4% NaOH as a set accelerator could effectively decrease both initial and final setting times.

Keywords: Lime, Natural Pozzolan, Chemical Activation, Set Acceleration