Acceleration of strength gain of lime-pozzolan cements by thermal activation

This paper deals with the effect of curing temperature on: (a) the time for development of appreciable strength, (b) ultimate strength and (c) strength development rate of lime-natural pozzolan cement pastes with and without chemical activator (4% Na 2SO 4 and 4% CaCl 2.2H 2O). The results indicate that the initial hardening time (time for pastes to achieve significant strength) decreases noticeably as the curing temperature rises. The ultimate strength of these cement pastes indirectly shows good linear correlation with the curing temperature; the rate of strength development fits the Arrhenius equation well. The addition of 4% Na 2SO 4 does not change the initial hardening time, but can increase both the strength gain rate and ultimate strength by 50 to 90%. The presence of 4% CaCl 2.2H 2O greatly improves the ultimate strength — by 2 or more times compared to the control pastes; initial hardening time, however, increases. Based on the strength development rate constants and the Arrhenius equation, the apparent activation energies of the control pastes, pastes with 4% Na 2SO 4 and the pastes with 4% CaCl 2.2H 2O are 66, 75 and 99 KJ/mol respectively.