Coupled thermo-hydro-mechanical–chemical behaviour of cemented paste backfill in column experiments. Part I: Physical, hydraulic and thermal processes and characteristics

Cemented paste backfill (CPB) technology has been widely used to fill underground mine voids for underground mine support and/or tailings disposal. Once placed, the CPB structure is subjected to strong coupled thermal (T), hydraulic (H), mechanical (M) and chemical (C) processes. In this paper, an experiment with insulated-undrained high columns has been carried out to understand these THMC processes. A CPB mixture is loaded into two columns and instrumented with various sensors to monitor the evolution of temperature, pore water pressure and suction for a period of 150 days. In addition, four other CPB columns are cured at 7, 28, 90 and 150 days, and then extensive laboratory testing is carried out on the CPB samples with regards to their thermal conductivity, saturated hydraulic conductivity, water retention properties, and mechanical and physical properties. Also, the rate of evaporation is monitored in a cylindrical CPB sample for the entire period of study. The results obtained show that a higher temperature can result in faster microstructural refinement and hence lower fluid transport ability. Reduction in the degree of saturation decreases thermal conductivity. The hydraulic properties are strongly coupled to chemical and mechanical factors. Mechanical deterioration following surface shrinkage and cracks can increase the saturated hydraulic conductivity. Also, changes in pore fluid chemistry affect microstructural evolution and can influence physical properties, such as void ratio and degree of saturation. Moreover, the obtained results support that the THMC properties of CPB are strongly coupled due to several internal mechanisms, such as heat of hydration, self-desiccation, suction development and cement hydration. The findings can contribute to a better understanding on the behaviour of CPB and thus towards the designing of more cost-effective and durable CPB structures. The results of the evolution of the mechanical, chemical and microstructural processes are discussed in a companion paper (see Part II, this issue).