Effect of Activated Coal Gangue in North China on the Compressive Strength and Hydration Process of Cement

Abstract

For comprehensive utilization of the coal gangue from different locations, coal gangues were calcined at temperatures of 800°C, 900°C, and 1,000°C for 2 h, respectively, and then blended in cement with a replacement level of 10%, 20%, 30%, and 40% by weight to fabricate the blended cement mortars. By means of Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscope (SEM), and an ion solubility test, the thermal-activation mechanism and pozzolanic activity evaluation for coal gangue was investigated, and the effect of coal gangue on mechanical properties and the hydration process of cement mixture was also studied. Results show that the optimum thermal-activation temperature of coal gangue is 800°C: the coal gangues in Yangquan, Huozhou, and Xinzhi, China, had higher activity and the replacement level of coal gangue in the cement can reach 40% by weight, but the coal gangues in Yanzhou, Zhengzhou, and Qitaihe, China, showed lower activity. The replacement level of coal gangue in the cement should not exceed 20% by weight. The active SiO2 and Al2O3 in the thermal-activated coal gangue are able to react with the Ca(OH)2, which was produced by cement hydration, and form hydrated calcium silicate and hydrated calcium aluminate gel to enhance the compressive strength of cement.