MICROSTRUCTURE AND HYDRATION CHARACTERISTICS OF ARTIFICIAL POZZOLANA-CEMENT PASTES CONTAINING BURNT KAOLINITE CLAY

The reaction of pozzolana with the lime liberated during the hydration process of Portland cement modifies some properties of cement and res ulting concrete. This study aimed to investigate experimentally the ch ange occurring in the phase composition and microstructure of pozzolan ic cement pastes containing activated kaolinite clay. The artificial p ozzolana (burnt kaolinite clay) were thermally activated by firing at 850 degrees C for two hours. The ordinary Portland cement (OPC) was pa rtially replaced by different amounts of activated kaolinite clay by w eight. The changes in the electrical conductivity were reported during setting and hardening processes after gauging with water, The change occurring in the phase composition and microstructure of cement pastes were investigated by differential thermal analysis and scanning elect ron microscopy. The results of this investigation show that, the therm al activated kaolinite clay prolonged the initial and final setting ti mes and reduced the porosity, it also improved the microstructure of t he formed hydrates by recrystallization of hydrated calcium silicates (mainly as CSH-(I)) together with the formation of hexagonal calcium a luminate hydrate (mainly as C(4)AH(13)). (C) 1997 Elsevier Science Ltd .