Investigation of crack self-healing behaviour and its impact on strength and permeability recovery in cemented paste tailings

Abstract

Cemented paste backfill (an engineered mixture of tailings, binder, and water), as one of the sustainable technological innovations for mining waste management, is used extensively around the world as a cementitious construction material in underground mines. The induced cracks within the CPB material tend to severely weaken the integrity and mechanical strength of the CPB structures as well as increase their permeability properties, undermining their safety, serviceability, durability, and environmental performance. However, no studies have been conducted to investigate the autogenous self-healing capability and behaviour of CPB. Therefore, this paper presents the results of an experimental study on the autogenous healing behaviour in CPB material to understand the self-healing mechanism and evaluate the self-healing efficiency through the recovery of mechanical and permeation properties. To this end, the CPB specimens were pre-damaged at different initial curing periods (i.e., 3, 7, and 28 days) and at different pre-damage levels (i.e., 30 %, 50 %, 75 %, 90 %, or 100 % of ultimate compressive strength in the pre-peak phase); then cured with self-healing periods of 1, 7, 28 or 90 days. Mechanical and hydraulic conductivity tests were performed on the pre-damaged specimens to monitor the self-healing changes. The results demonstrate that a significant self-healing capability does exist in the CPB materials due to the formed self-healing products from continuous cement hydration interior of the CPB matrix and carbonation of calcium hydroxide. The mechanical strength and hydraulic conductivity of pre-damaged specimens can be restored to similar values of the control specimens after 7 days and 28 days of self-healing periods, respectively. Furthermore, the study also reveals that the CPB specimens with high pre-damage levels (i.e., 75 %, 90 %, or 100 %) can even achieve up to 42 % higher mechanical strengths than the control specimens after 90 days of the self-healing period, indicating that the initiated cracks within the CPB matrix can ameliorate the hydration reactions favoring the self-healing performance. The results presented in the paper would have significant impacts and practical implications with respect to CPB structure design, mechanical stability, and durability.