Effects of curing and stress conditions on hydromechanical, geotechnical and geochemical properties of cemented paste backfill

Cemented paste backfill (CPB) is an emerging mine-backfill technique that allows environmentally hazardous tailings returning back to the underground openings or stopes, thereby maximizing the safety, efficiency and productivity of process/operation. CPB provides efficient ground support for mine structures and permits a fully excavation and extraction of ore bodies. It also decreases surface tailings storage requirements and thus, rehabilitation/reclamation costs after closure. This paper investigates the effects of curing and stress conditions on hydromechanical, geotechnical and geochemical properties of CPB. In this respect, a new laboratory apparatus (CUAPS: curing under applied pressure system) was used to mimic the in-situ CPB conditions to compare the performance of consolidated backfills with unconsolidated conventional moulds (i.e. undrained or drained). The results have shown that for a given backfill recipe, CUAPS-consolidated samples always present better strengths than those obtained from mould-unconsolidated samples i.e. the underestimation of backfill strength. A full evolution of geotechnical and geochemical properties of CPB was compared at three binder contents (3, 4.5 and 7 wt.%) and curing times (7, 14 and 28 days). The application of stress during curing was found to contribute positively to the CPB hardening process and hence, the strength and geotechnical properties as a result of the removal of water and binder hydration. Consequently, CUAPS-consolidated samples can be agreeably used to better assess in situ CPB behavior and to achieve an ideal CPB recipe in terms of safety and economy.