Pozzolanic reaction in the presence of chemical activators - Part I. Reaction kinetics

This study has examined the effect of activators (Na2SO4 and CaCl2) on pozz olanic reaction kinetics in a lime-pozzolan blend, which consists of 80% gr ound volcanic ash and 20% hydrated lime, at 23, 35, 50, and 65 degrees C. T he addition of 4% Na2SO4 increased both the early and later strengths of li me-pozzolan pastes from 23 to 65 degrees C. The presence of 4% CaCl2. 2H(2) O decreased the early strength but increased the later strength at 23 degre es C, and increased both the early and later strengths of the paste from 35 to 65 degrees C. Measurement of free Ca(OH)(2) in hardened pastes indicate d that the presence of Na2SO4 and CaCl2 accelerated the consumption of Ca(O H)(2). A fair linear correlation could be established between measurable co mpressive strength and the degree of reaction of Ca(OH)(2) regardless of ac tivators. Kinetic analyses using modified Jander's equation suggest that th e pozzolanic reaction process in the lime-pozzolan pastes could be divided into three phases: Phase I, controlled by the pozzolanic reaction rate; Pha se II, controlled by the diffusion of reactants through a layer of porous h ydration products; and Phase III; controlled by the diffusion of reactants through a layer of dense hydration products (C) 2000 Elsevier Science Ltd. All rights reserved.