Mechanical and Microstructural Properties of Cemented Paste Backfill with Chloride-Free Antifreeze Additives in Subzero Environments

Abstract

Cement paste backfill (CPB) is an innovative technology of recycling mine waste (tailings) into construction materials to increase mine safety and productivity and promote sustainable mining. However, the application of CPB technology in mines located in cold or permafrost areas has been difficult due to freezing temperatures. These subzero temperatures can cause fresh CPB to freeze while being transported through the pipelines, which has significant financial implications for the mine. To overcome these problems, antifreeze additives are added to the CPB during its mixing or preparation to enhance the rheological properties of fresh CPB. The addition of antifreeze additives in CPB is an inexpensive and easy-to-operate method currently known to ensure its smooth delivery in subzero environments. But the mechanical and microstructural characteristics of CPB with chloride-free antifreeze additives in subzero conditions are not well understood. Therefore, this study experimentally examined the mechanical (strength, deformation behavior) and microstructural properties of CPB containing chloride-free antifreeze additives and cured under subzero conditions. Three kinds of chloride-free antifreeze (calcium nitrate, calcium nitrite, and urea) with different concentrations (0, 5, 15, and 35 g/L) were separately added to the CPB samples curing at different subzero environments (−1°C, −6°C, and −12°C) for different ages (7, 28, 60, and 90 days). The uniaxial compressive strength (UCS) tests, a series of microstructural (XRD, MIP, DT/DTG, SEM) analyses and monitoring (suction, volumetric water content) experiments of CPB were performed. The obtained results showed that the addition of antifreeze weakened the mechanical properties of CPB. Furthermore, the UCS of CPB was significantly affected by the antifreeze type, antifreeze concentration and subzero curing temperature. The findings in this research will support the successful application of antifreeze cemented backfill technology in cold regions.