Many waste clay bricks have been produced when brick concrete buildings are demolished; at the same time, grouting treatment in goaf ground needs lots of cement. Waste‐clay‐brick‐powder (WCBP) is proposed to replace a large part of the cement to prepare environmentally friendly slurry suitable for ground grouting in mine goaf. Laboratory tests of replacing 50–90% of cement with WCBP are carried out. Bentonite and water‐reducing agent are used to optimize the slurry based on the performance indexes of water‐separation ratio, stone rate, viscosity, setting time, and compressive strength. Scanning electron microscopy (SEM) tests are also conducted to investigate the microscopic mechanism of some WCBP‐cement samples. Test results show that the slurry made of 20% cement, 70% WCBP, 10% bentonite, and 0.15% water‐reducing agent can meet the needs of ground grouting in mine goaf, and its stone rate is 12% higher than that of pure cement slurry. SEM results show that the WCBP in the early stage mainly exerts the microaggregate effect, and the pozzolanic activity in the later stage plays a role in supplementing the strength.

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