Flow ability of cemented paste backfill with chloride-free antifreeze additives in sub-zero environments

Abstract

Currently, the addition of antifreeze additives or admixtures to cemented paste backfill (CPB) during its preparation is an inexpensive technology to address the risk of CPB freezing during its transportation in sub-zero environments. However, the effects of chloride-free antifreeze additives on the flow ability of CPB under sub-zero conditions are not well understood. No studies have been performed on the rheological propertiefs of CPB with chloride-free antifreeze additives in sub-zero environments. Hence, the objective of this study was to assess and gain a deeper insight into the effects of chloride-free antifreeze additives on the rheological properties of CPB with different binder types (Portland cement, ground blast furnace slag) and contents in sub-zero conditions. CPB specimens with different types of chloride-free antifreeze (calcium nitrite (Ca(NO2)2), calcium nitrate (Ca(NO3)2), and urea (CO(NH2)2)) and concentrations (5, 15, and 35 g/L) were prepared and cured under sub-zero conditions (−6, −12, and −20 °C). The rheological properties (yield stress and viscosity) of CPB were determined at curing times of 0 min, 15 min, 1 h, and 2 h. In addition, microstructural analyses, investigation of electrochemical properties, and a series of monitoring experiments were conducted. It was found that the addition of chloride-free antifreeze reduced yield stress and increased viscosity. Meanwhile, the significant effect on the rheological properties of CPB also depends on the curing time, antifreeze concentration, cement content, sub-zero temperature, and cement to slag ratio. The findings of this study can advance the development of chloride-free antifreeze CPB technology and provide important guidance for successful pipeline transportation of CPB in sub-zero environments.