Effects of curing temperature and age on the mechanical properties and damage law of coal-based solid waste cemented backfill

Backfilling the underground caved zones with coal-based solid waste allows large-scale disposal of the waste and abates overburden damage. Since the curing temperature and age play an essential role in affecting the strength of the backfill, the uniaxial compression test, acoustic emission damage monitoring, and microscopic scanning electron microscopy were carried out on the standard cube specimens with the curing temperature of 20, 27, 35, 42.5 and 50 °C (accompanied by the curing age of 3, 7, 14 and 28 days, respectively). The microstructure evolution and damage constitutive model of coal-based waste cemented backfill (CWCB) were discussed to reveal how CWCB strength develops. The results demonstrate that: (1) The increase of curing age and temperature would underpin the mechanical properties of CWCB, since the maximum strength reached 5.45 MPa, with the curing temperature of 42.5 °C and the curing age of 28 days. (2) A curing temperature of 50 °C inflicted physical and mechanical damage on the bonding interface of the backfill. As shown by the microscopic morphology comparison (20, 27, 35, and 42.5 °C), more irregular structures inside the specimens were resulted from excessive hydration reaction. This defect triggered a dramatic ascent in the acoustic emission ringing count at 28 days of age, jeopardizing the strength to merely 76% of that at 42.5 °C, while macroscopically, the failure was manifested as an X-shaped conjugate inclined plane shear pattern. (3) The temperature-dependent segmented damage constitutive model established based on the Weibull distribution was in good agreement with the experimental stress-strain curve. The damage-strain curve reflects three phases: slow increase, steep rise, and slow down, which correspond to the plastic deformation, damage failure and residual stages, respectively, in the stress-strain curve.