Experimental study on mechanical properties of superfine sand and coal gangue concrete

In order to realize the efficient use of coal gangue, making coal gangue concrete that can be directly used on the ground of mine roadways, the horizontal orthogonal design method was used to conduct experimental research on the mechanical properties of coal gangue concrete with three strengths of C20, C30 and C40, and to explore the influence mechanism of various factors on the mechanical properties of coal gangue concrete cube test specimens. The results show that the coal gangue replacement rate has the greatest impact on the compressive strength of the concrete cubes. For coal gangue concrete of C20, C30 and C40 strength grades, the compressive strength of the 28 d concrete cube with a replacement rate of 80% is 64.1%, 63.4%, and 62.2% when the replacement rate is 0, and the compressive strength of the 28 d concrete cube with a replacement rate of 100% is 53.0%, 56.8%, 61.5% respectively when the substitution rate is 0. Compared with those of natural aggregate concrete, coal gangue aggregate concrete has poor mechanical properties, and overall strength is low. Regression analysis was carried out on the cubic compressive strength and axial compressive strength of coal gangue concrete with replacement rates of 80% and 100% at 7 d and 28 d. The results obtained are similar to the requirements for ordinary concrete in the current national standards, indicating that the axial compressive strength of coal gangue concrete with replacement rates of 80% and 100% can meet the requirements. The performance is poor, so that the splitting strength of coal gangue concrete cannot meet the requirements of the specification, the elastic modulus is significantly lower than that of ordinary concrete, the Poisson’s ratio test value has a large dispersion, and the change rule is not obvious. Based on the test results, it is determined that the optimal ratio of C20 grade strength coal gangue concrete in roadway floor of Ningtiaota Coal Mine of Shanbei Mining Company is determined as follows: coal gangue replacement rate is 100%, water-binder ratio is 0.45, and no water reducing agent is added, that is, the mass ratio of cement, water, yellow sand and coal gangue is 1∶0.45∶1.31∶2.67.