Separation of calcined coal gangue and its influence on the performance of cement-based materials

Coal gangue (CG) is a kind of solid waste which discharged from the process of coal mining and washing. It has complex and volatile composites is not conducive to control its quality. If the high content minerals in CG could be separated relatively and applied properly according to its characteristics, the utilization of CG resources could be much more efficient. In this paper, granular CG was calcined and activated. According to the difference of color and texture, calcined coal gangue (CCG) was divided into yellow-white CCG (YW-C), red-brown CCG (RB-C) and light-red CCG (LR-S). The composition and properties of separated CCG were studied, and the feasibility of separating granular CCG based on its color, apparent density and composition difference was analyzed. The difference in reactivity of separated CCG and its causes were analyzed based on ²⁹Si and ²⁷Al NMR. The influences of separated CCG on the properties of cement-based materials were investigated. Results showed that, the three kinds of separated CCG all contained quartz, among those CCGs, LR-S has the highest content of quartz. YW-C contained a large amount of metakaolin, and its apparent density was only 2550 kg/m³. RB-C contained more colored iron phase, while LR-S contained a small amount of feldspar. The apparent density of RB-C and LR-S were significantly higher than that of YW-C. The reactivity of separated CCG was quite different. The relative contents of Q³(-101.86 ppm) structure and Al [5] in YW-C were 81.31% and 81.19% respectively, which were much higher than those in LR-S. Comparing with LR-S, YW-C with higher pozzlanic reactivity was mixed into cementitious materials could react with cement hydration products to produce C-(A)-S-H gel which will enhance the interface bonding between CCG particles and matrix, refine the pore size of matrix. The addition of YW-C is more conducive in improving the mechanical properties of cement-base materials.