Comparison of different methods for enhancing reactivity of pozzolans

This paper compares three methods for the activation of pozzolanic reactivi ty of a natural pozzolan: (1) prolonged grinding of natural pozzolans (mech anical method), (2) elevated temperature curing of cement pastes containing a pozzolan (thermal method), and (3) use of chemical activators such as Na 2SO4 and CaCl2 (chemical method). The pozzolanic reactivity of natural pozz olans was evaluated using a mixture of 80% natural pozzolan and 20% hydrate d lime. Several parameters such as Ca(OH)(2) consumption rate, strength dev elopment, ultimate compressive strength and cost were compared. All three a ctivation methods accelerated both the pozzolanic reaction and strength dev elopment rates of the lime-pozzolan pastes. However, mechanical activation did not show a significant effect on the ultimate strength, while thermal a ctivation decreased the ultimate strength and chemical activation (addition of 4% Na2SO4 or CaCl2. 2H(2)O based on the mass of lime-pozzolan blends) i ncreased the ultimate strength of lime-pozzolan mixtures significantly. The application of mechanical or thermal activation techniques needs extra equ ipment and energy, and thus increases materials costs significantly. Chemic al activators can be added during the grinding of the natural pozzolan or d uring the mixing of concrete containing a pozzolan, so the requirement of e xtra equipment is minimal. Although the addition of chemical activator(s) i ncreases the total material costs, the cost per unit strength development d ecreases. Based on current test results, chemical activation is the most ef ficient and feasible method for the activation of natural pozzolans. (C) 20 01 Elsevier Science Ltd. All rights reserved.