Loading-rate dependant fracture behavior of cemented paste backfill under curing pressure

Abstract

This study investigates the loading-rate-dependent fracture behavior of cemented paste backfill (CPB) under varying curing pressures. CPB is widely used in underground mining to fill voids, and its mechanical performance is critical to ground stability and operational safety. While most laboratory testing is conducted under atmospheric conditions, CPB in the field cures under confining pressure, which can significantly affect its mechanical properties. To simulate real-world conditions, CPB samples were prepared and cured at pressures of 0, 29, and 58 psi, representing different backfill heights. Samples were tested at 7-, 28-, and 90-days using fracture mechanics-based tests under three different loading rates (0.1, 1, and 10 mm/min) across Mode I, II, and III fracture modes. Key parameters examined included material stiffness, fracture toughness, energy of crack initiation, and total energy of fracture. The results demonstrated that both higher curing pressure and increased loading rate generally enhance the mechanical performance of CPB, with the most significant gains observed between 0.1 and 1 mm/min. Notably, stiffness and fracture toughness improved with curing time, while energy absorption was primarily governed by crack initiation. Auxiliary testing confirmed that increased curing pressure led to denser microstructure, slightly lower void ratios, and higher degrees of saturation. These physical changes likely contributed to the enhanced fracture behavior. The findings underscore the importance of considering both curing conditions and loading rate in the design and testing of CPB to ensure accurate predictions of field performance.