Effect of wetting-drying cycle on hydraulic and mechanical properties of cemented paste backfill of the recycled solid wastes

Cemented paste backfill (CPB) technology is beneficial to the recycling of solid wastes and sustainable development in mines. However, the wetting-drying cycle caused by water intrusion and goaf drainage has a great influence on the waterproof and support performance of CPB. In this study, the hydraulic and mechanical properties of CPB samples under wetting-drying cycles were studied by permeability tests, nuclear magnetic resonance (NMR) tests and uniaxial compression tests. The results show that with the increasing number of wetting-drying cycles, the porosity and permeability of CPB samples increase; the porosity and permeability of CPB samples with small particle size distribution and cementing strength are more sensitive to the increasing number of wetting-drying cycles. During the wetting-drying cycles, the uniaxial compressive strength and elastic modulus of CPB samples gradually deteriorate. This effect is more significant for CPB samples with the smaller particle size distribution and cementing strength. According to the periodic destruction of CPB cemented structures caused by wetting-drying cycles, the deterioration process of mechanical properties of CPB samples can be divided into two stages: initial deterioration stage and re-deterioration stage. The microstructure analysis of CPB samples was used to verify the periodic destruction of the cemented structures. Finally, protective measures of CPB were proposed to ensure the stability of CPB. The CPB with large particle size distribution and cementing strength should be adopted. Besides, the filling rate and the monitoring condition of the goaf can be strengthend to reduce and even avoid wetting-drying cycles.