Optimisation of early hydration, microstructure, and elevated-temperature resistance of calcium aluminate cement using steel-making slag

Abstract

The strong elevated-temperature resistance of calcium aluminate cement (CAC) allows it to withstand the ultrahigh temperatures required for the in situ combustion of heavy oil; however, the high early hydration heat and strength retrogression of this cement restrict its application in the cementing engineering of heavy oil wells. Therefore, in this study, we investigated the effects of various slags on the hydration heat and temperature, compressive strength, and elevated-temperature resistance of CAC pastes. X-ray diffraction (XRD), thermogravimetry, and scanning electron microscopy (SEM) were used to evaluate the influence of slag on the hydration products and microstructure of the CAC pastes at 30, 60, and 800 °C. The results revealed that adding slag reduced the hydration heat and temperature of the CAC pastes; specifically, the maximum hydration temperature of the CAC paste containing 100% 600-mesh slag (CM6-5) decreased by 33.4%. Additionally, the slag changed the hydration products of the CAC paste from metastable products (CAH10 and C2AH8) to stable products (C2ASH8) with no conversion process, leading to the dense microstructure of CM6-5. The compressive strengths of CM6-5 cured for 14 d at 30 and 60 °C increased by 60.98% and 215.35%, respectively, compared with those of the pure CAC paste. In addition, CM6-5 exhibited excellent elevated-temperature resistance. The XRD results indicated that an elevated temperature of 800 °C changed the crystal phases of CM6-5; however, when cured for 14 d at 800 °C, CM6-5 maintained a dense microstructure, and its compressive strength upon curing at 800 °C did not result in strength retrogression.