Study of performances and microstructures of mortar with calcined low-grade clay

Abstract

This paper studied the effect of calcination temperatures (600–900 °C) on physical characteristics and microstructure changes of low-grade clay containing 14.6% kaolinite and 17.8% 2:1 clay mineral. The pozzolanic activity of calcined low-grade clay as a supplementary cementitious material was evaluated using strength activity index and relative strength index. The results show that the kaolinite transformed from crystalline phase to amorphous metakaolin phase at 600 °C, while the particle size of clay first increases and then decreases. The optimal calcination temperature is found between 700 and 800 °C, whereas the optimal cement replacement level is 10–20 wt%.