Microscopic Pore and Filling Performance of Coal Gangue Cementitious Paste

To obtain the influence laws of the fine gangue rate on the properties of coal gangue cementitious paste, the slump, divergence, stratification, bleeding, setting time and mechanical strength with the change of fine gangue rate were studied on the basis of keeping the amount of cementing material and slurry concentration unchanged. The porosity and the distribution of pore diameter of the filling specimen for curing 28 d were tested by a mercury injection instrument under different fine gangue rate conditions. It was shown that the slump, divergence, setting time and compressive strength of the paste firstly increased and then decreased with increasing fine gangue rate. The stratification and bleeding rate decreased with increasing fine gangue rate. The smaller the critical pore size of the paste was, the smaller the porosity was, the smaller the average pore size was. When the fine gangue rate was 40%, the maximum critical pore diameter of the paste was 55.79 μm, and the corresponding porosity was 17.54%, and the properties of filling paste were the best. When the fine gangue rate further increased, the aggregate surface area increased, and the reaction product of cementitious materials could not effectively fill the pores. It weakened the agglomeration effect. The particles surface of coal gangue was fragmental and flake deposit with irregular shape and uneven fold morphology. It was easy to be bonded with the surface of other filling material. The hydration products of coal gangue cementitious material were a large number of C-S-H gel with fibrous shape and ettringite（AFt） with compact block structure. The theoretical reference was provided for the preparation of low cost gangue cemented filling materials in coal mines.