Evaluation of calcined coal slime in binary and ternary ordinary portland cement composites: The role of calcination temperature

Coal slime is a by-product of coal washing plants, which accounts for around 8.3% of total coal production. China generates about 200 million tons of coal slime annually, and most of which can not be utilized efficiently. As a result, the disposal of coal slime leads to serious environmental problems and high costs. To provide a green utilization of coal slime, this study investigated the preparation of binary and ternary cement binder systems by using various calcined coal slime particles. The effects of calcination temperatures (600 °C, 700 °C, 800 °C, and 900 °C) on the evolution of mineral phases, microstructure and morphology of coal slime were addressed and discussed. The feasibility of calcined coal slime in blended cement preparation was tested and evaluated in comparison with calcined coal gangue. The results indicated that kaolinite in coal slime can be effectively transformed into metakaolin at 600 °C. The increase of calcination temperature after 600 °C reduced the reactivity, porosity and water demand of calcined coal slime. 600 °C Calcined coal slime effectively promoted the formation of monosulfate and the monocarboaluminate in binary and ternary cement, respectively, as well as the hydration process. The highest compressive strength of the calcined coal slime blended sample achieved 48.04 MPa, which presented a higher performance than the calcined coal gangue. The organic components in coal slime could be the key to reaching a high reactivity at a low (600 °C) calcination temperature. The calcined coal slime has the potential to be a reactive additive in cement-based materials.