Effects of mineral admixture on properties of cement-based foam material developed for preventing coal spontaneous combustion

This study investigated the cement-based foam material (CBFM) used in mine fire-extinguishing materials by using a self-made compound foaming agent, water, cement, mineral admixture included fly ash (FA), blast furnace slag (BFS) and silica fume (SF), etc. The effects of mineral admixture type, dosage, foam content and water-binder ratio on the properties of CBFM were analyzed using the orthogonal tests, further determining the optimal ratio of CBFM. Moreover, the influence of mineral admixture type on the performance of the CBFM was analyzed by comparing the scanning electronic microscope and X-ray diffraction test. As a result, when the BFS content was 20%, the foam content was 2 times that of the cementitious slurry, and the water-binder ratio is 0.5, the overall performance of CBFM could be optimized. The surface morphology and mineral component inves-tigation exhibited that CBFM with BFS as a mineral admixture had the more uniform closed-cell structure than FA and SF. Moreover, the novel material had the inhibitory effect on the transformation of calcium aluminate hydrate and hydrated calcium sulfoaluminate, which in turn could maintain the strength of the composite. The experimental results showed that the fire extinguishing and cooling effect of CBFM was better than that of traditional fly ash foam, and it could quickly cool down the temperature burning coal pile within 30 min. In addition, the solidification products of CBFM would form a wrapping layer on the surface of the loose coal pile, inhibiting the contact between coal and air, further preventing coal spontaneous combustion effectively.