Experimental Study on the Effect of Rubber Fibre Content on the Mechanical Properties and Failure Mode of Grouting Materials

To promote waste tyre resource utilisation and reduce environmental pressure, this study prepared five stone sample groups using waste tyre rubber fibre (RF) as a modifier, combined with blast furnace slag, fly ash, carbide slag, and calcium chloride, with RF contents of 0%, 6%, 10%, 14%, and 18%. Working performance was analysed via density, fluidity, and water separation rate tests, while mechanical properties and failure mechanisms were explored through uniaxial compression tests, acoustic emission (AE) monitoring, and SEM microstructure observations. Results showed that as RF content increased, slurry density and fluidity decreased nonlinearly, water separation rate first rose then fell, and uniaxial compressive strength dropped significantly (64.97% lower at 18% RF than 0%). Failure mode shifted from shear to tensile–shear mixed failure, AE signal activity weakened, energy release gentled, and crack propagation was delayed. Microstructurally, 6–10% RF ensured uniform fibre dispersion, blocking microcracks and optimising interfacial zones, while 14–18% RF caused agglomeration and pore defects. The optimal grouting material ratio was determined as 10% RF, blast furnace slag: fly ash = 4:1, 40% carbide slag, 1% calcium chloride, and a 0.7 water–cement ratio (total solid component 100%).