Performance of cement-based materials containing calcined coal gangue with different calcination regimes

The storage of coal gangue (CG) takes up a lot of lands and pollutes the environment. Calcined CG has the potential to be used as supplementary cementitious material. In this paper, the CG from Yibin, Sichuan province of China were treated with different calcined temperature, holding times and cooling modes, and the microtopography, phase composition and pozzolanic reactivity of calcined CG were studied. Meanwhile, the fluidity, mechanical properties, hydration products, and pore structure of cement paste and mortar with different calcined CG were analyzed. The apparent color of coal gangue under different treatment methods has also been studied to promote its better application for a wider range in cement-based materials. Results showed that there exists an optimal calcination condition of calcined CG at 800 degrees C and holding time of 2 h. Rapid cooling and slow cooling reduced the activity of calcined CG. Calcined CG powder would reduce the fluidity of cement mortar. However, proper calcination temperature and sufficient holding time could eliminate it to some extent. It was also found that calcination temperature has a greater impact on the early age reactivity of CG when compared to different temperature treated CG powder, C8T2 sample has the best early activity. Compared to rapid cooling, slow cooling and water-cooling mode, room temperature cooling would result in higher reactive CG. CG powder after proper thermal treatment could refine the pore structure of the hardened cement paste in the later age (28 days), reduce the harmful pores content (>100 nm), and increase harmless pores content (<100 nm) in hardened cement paste. It was found that the CG powder of calcined at 800 degrees C for 2 h, cooling in water and room temperature might be more suitable as the supplementary cementing material combined the apparent color, pozzolanic reactivity, and preparation process.