Effect of temperature on phase composition and microstructure of artificial pozzolana-cement pastes containing burnt kaolinite clay

The influence of high temperature on the phase composition and microstructure of cement paste is vital for fire-resistance studies. Pozzolana tends to improve the microstructure of cement paste, due to its reaction with hydrated products. This study aimed to investigate experimentally the change occurring in the phase composition and microstructure of burnt kaolinite cement pastes after being exposed to high temperatures. The kaolinite clays were thermally activated by firing at 850 degrees C for 2 h. The ordinary Portland cement (OPC) was partially substituted for by 0, 10, 20, and 30% of activated kaolinite clay by weight. The treatment temperature varied from 100 to 600 degrees C by increment of 100 degrees C a period of 3 h. The phase composition and microstructure measures were performed by means of differential thermal analysis and scanning electron microscopy. The results of this investigation show recrystallization and carbonation of Ca(OH)(2); they also show a deformation of C-S-H and C(4)AH(13) phases. (C) 1998 Elsevier Science Ltd