Study on Thermal Activation of Coal-bearing Kaolinite and Its Influence on Long-term Strength of Cement Paste

Abstract

Purposes The high-value utilization of coal gangue has attracted attention, and the activation and action of coal-bearing kaolin have great significance value for utilization of coal gangue. Methods The thermal activation parameters of kaolinite in coal gangue were optimized by orthogonal test, and the compressive strength and microstructure of paste consisting of cement and metakaolin formed under the optimal activation conditions were studied. Findings The experimental results show that the optimum thermal activation conditions of metakaolin are calcination temperature 800 ℃, holding time 2 h, and grinding fineness of 2.82 μm. Calcination temperature has the greatest influence on the activity of metakaolin, followed by grinding fineness and holding time. By using metakaolin instead of 20% (mass fraction) cement, the compressive strength of cement paste at all curing ages, especially in the early age, can be improved effectively. XRD and SEM test results show that the pozzolanic reaction of metakaolin consumes a lot of calcium hydroxide, and forms calcium silicate hydrate with lower calcium-silicon ratio and denses structure.

Keywords

• coal-bearing kaolinite
• orthogonal test
• cement paste
• compressive strength
• coal gangue