Microstructure and mechanical behaviors of coal gangue - Coal slime water backfill cementitious materials

Coal gangue and slime water are difficult to dispose and utilize on a large scale, which could cause environmental pollution and waste of resources. Therefore, the co-treatment of coal gangue and slime water can serve as an environmentally friendly and novel way for the collaborative resource of solid wastes. Based on this, a method for preparation of slime water-based cementitious material (SWCM) was developed, and the enhanced mechanical property of a coal gangue pile modified by SWCM (CGSWCM) was investigated. For the preparation of SWCM, 6 types of additives were selected, and solidification was achieved with a liquid to solid ratio of 3:1. A compressive strength of 0.45 MPa was acquired with raw SWCM, and the value decreased to 0.38 MPa, then increased to 0.44 MPa when the mass of the kaolin increased from 2 to 10 g. X-ray diffraction and scanning electron microscopy results showed that the pore size of the coal gangue pile decreased and the rod-like ettringite transferred to a linear shape when mass of kaolin increased. The analysis of thermogravimetry proved that the increased mass of kaolin improved the thermal stability, thus decreasing the mass loss. Therefore, it was proposed that the mechanical properties of CGSWCM was affected by evolved hydration product, gap between coal gangue particles and ettringite (AFT) morphology.