Experimental Research on Application of Waste Concrete Powder–Waste Brick Powder–Cement Grout for Foundation Reinforcement in Mining Goaf

Combined with a strategic policy for the recycling of construction waste, this paper puts forward a programme for treating a goaf foundation with waste concrete powder, waste brick powder, and cement grout (BCP cement grout). The BCP cement grout is prepared by replacing part of the waste concrete powder with waste brick powder, and the changeable rule of the setting time, water separation rate, stone rate, and viscosity of the grout with different rates for replacement are studied. X-ray diffraction (XRD) and scanning electron microscopy (SEM) are carried out. The mineral composition is analyzed and the microscopic mechanism is studied. The results show that the ratio of BCP cement grout developed by the experiment is reasonable; the unit cost is less than 160 yuan/t, which is 40% lower than that of pure cement grout; and both a good economic effect and good environmental effect are obtained. It has the advantages of low water separation rate, high stone rate, and low viscosity. When the ratio of cement powder: waste concrete powder: waste brick powder is 3:5:2 or 3:6:1, the 28 d compressive strength of the stone body is more than 2 MPa, meeting the filling requirements for a goaf foundation. It is not only technically feasible but also economically reasonable to apply construction waste powder to fill the goaf foundation. Recycling and utilizing construction waste can also achieve the ecological restoration of mined-out areas, highlighting the ecological benefits.