Mechanical properties of diatomite modified concrete with different moisture contents after high temperature treatment

Underground coal gasification is a promising and clean technology for coal resources mining and the backfill body for controlling overburden failure will be exposure to high temperature and mine water. Diatomite is effective in increasing the thermal resistivity of cement-based matrices, but the mechanical behavior of diatomite modified concrete with different moisture contents after high temperature treatment remains unexplored. A modified coal-based solid waste backfill material is developed, by incorporating diatomite as supplementary cementitious materials to enhance the high-temperature performance. In the modified composite material, coal gangue constitutes 50% of the coarse aggregate, with an additional 0.5% basalt fiber incorporated. SEM, XRD and EDS were used to reveal compressive strength stabilization mechanism of specimens with different moisture contents after high temperature treatment. Experimental results show that the uniaxial compressive strength of specimens after exposure to 400 °C reaches its maximum, increasing by 17.1% compared with that at room temperature. Additionally, the mechanical properties of modified concrete containing 0%, 5%, 10%, 15% and 20% diatomite under the couple effect of water and high temperature is studied. The strength reduction caused by the degradation of C-S-H due to high-temperature dehydration can be offset by the formation of new, stable C-S-H through pozzolanic reactions after groundwater immersion, which fills pores and microcracks. The moisture content has little effect on uniaxial compressive strength of samples, which is very important for the stability of underground backfill body influenced by groundwater.