Effect of grain size on hydration and rheological behavior of calcium aluminate cements containing spinel

Abstract

AbstractIn this paper, using industrial alumina, calcined magnesite, ground calcium carbonate as raw materials, spinel-containing calcium aluminate cements (CMA) were prepared at 1500 °C with different calcine holding times (3 h and 6 h). The mineral composition and microstructural characteristics of prepared cement samples were studied using X-ray diffraction and scanning electron microscopy, and their hydration and rheological behavior were also investigated. The results indicated that increasing holding time can promote growth of CaAl2O4 grains and reduce setting time. The hydration mechanism of CMA follows the nucleation and crystal growth–diffusion (NG–D) process, and the hydration rate of CMA–3 h in the acceleratory period is higher than that of CMA–6 h, but there is no significant distinction in deceleration and stabilization periods. The slowdown of hydration rate directly affects the rheological behavior of CMA slurry, leading to decrease in yield stress, and thixotropic character. Also, the storage modulus (G') growth rate of CMA–3 h slurry is significantly higher than for CMA–6 h slurry, indicating the CMA synthesized at 1500 °C for 6 h possesses lower hydration activity.