The Application of Fuzzy Mathematics in the Optimization of the Recipe of Filling Paste for Coal Mine Backfill

Backfill is a very important technology that can be used to reduce the environmental footprints resulting from coal mining. The selection of proper filling materials is of great significance to the operation cost and the stability of the goaf. This paper investigated the feasibility of using the coal gangue as the main component of the filling paste so as to reuse the byproducts in coal mining to the maximum extent. The filling pastes were composed of coal gangue as the aggregates, cement or gypsum as cementitious materials, and some additives. In order to determine the optimal recipe, the performances of filling pastes were first comprehensively evaluated according to their fluidity, mechanical properties, shrinkage, and permeability. The results showed that cement content was the most influential factor, while the fly ash addition was the weakest factor for the performance of filling pastes. Moreover, the appropriate use of a water reducer and expansion agent improved the working performance of the paste. Based on the performances of filling pastes, the fuzzy mathematics evaluation method was then used to establish the weight vector and index vector. The principle of maximum membership degree and the principle of maximum closeness were used to identify the identified objects and find the best recipe for the filling paste. The results showed that this evaluation method could fully reflect the influence of various factors and provide accurate evaluation results.