Increasing the early strength of high-volume Hwangtoh-cement systems using bassanite

초록

Calcined Hwangtoh (HT) clay is a potentially viable supplementary cementitious material. However, using large amounts of HT significantly reduces the early strength of concrete, and this problem has yet to be addressed. We explored the effectiveness of improving the early strength of cement-HT systems by using bassanite (calcium sulfate hemihydrate, CaSO4 center dot 0.5H(2)O) to activate HT. The effects of different contents (0-4 wt.%) of bassanite on the mechanical properties, hydration reaction, and microstructure of high-volume (45 wt%) HT-cement systems were investigated. The experimental results show that the addition of bassanite to HT-cement systems facilitates the formation of ettringite crystals in the early stage, thereby increasing the early strength. After one day, the compressive strength of the paste with a bassanite addition of 3% increased by 82.3% compared with the paste without bassanite, and no significant effect on the later strength was observed. However, for a bassanite addition of >4%, excessive sulfate causes poor volume stability, leading to substantial reductions in the compressive strength at later stages.

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