Hydration characteristics of low carbon cementitious materials with multiple solid wastes

Abstract

Coal gangue and carbide slag accumulate annually and cause significant pollution, due to the lack of practical and efficient uses for these waste materials. In this series of studies, coal gangue, calcium carbide slag, steel slag, dihydrate gypsum, and calcium carbonate were used synergistically to prepare low-carbon cementitious material (LCCM) clinker. This method increases the utilisation rate of carbide slag and coal gangue, which was able to reach 80%. The mechanical properties of the LCCM were tested. The compressive strength of LCCM after hydration for 3 days achieved the same compressive strength as 42.5 Portland cement (PC42.5) that had been hydrated for 28 days. In addition, the hydration characteristics of the LCCM were analysed by measuring heat of hydration and chemically bound water, X-ray diffraction, thermogravimetric analysis, infrared spectroscopy, and scanning electron microscopy. Results showed that the hydration rate of the LCCM was faster in the early stage and was mainly concentrated in the first 3 days, yet it maintained continuous hydration in the later stage. In addition, the life cycle assessment method was used to evaluate the advantages of LCCM in terms of CO2 emissions and energy consumption. LCCM had greater advantages in the context of CO2 emissions and energy consumption compared with traditional cement. Specifically, CO2 emissions reduction could reach 55%. This study demonstrates the efficient resource utilisation of carbide slag and coal gangue, which can reduce their pollution to the natural environment.