Thermal activation and structural transformation mechanism of kaolinitic coal gangue from Jungar coalfield, Inner Mongolia, China

The benefits of industrial solid waste as a supplementary cementitious material in the manufacture of eco-efficient cement are evident in the context of sustainable and green development. Coal gangue from the Jungar coalfield, Inner Mongolia, China, was characterized and activated thermally at 500 °C–1000 °C. This study investigated the effects of thermal activation conditions on the phase and structural changes of the minerals in coal gangue. The pozzolanic activity of the thermally activated coal gangue was evaluated using both direct and indirect methods. The experimental results show that the coal gangue had a silicoaluminous nature mainly comprising of kaolinite. The pozzolanic activity of coal gangue depends on the phase and structural transformation of kaolinite during calcination. Highest pozzolanic activity is reached when calcined at 800 °C for 2 h, with lime consumption and strength activity index up to 1039 mg g ⁻¹ and 1.1, respectively. The high pozzolanic activity of metakaolinite was attributed mainly to the formation of a five-coordinated Al sheet and the less polymerized Si sheet after dehydroxylation under calcination.