Investigation on rheological properties of cemented pastefill with chloride-bearing antifreeze additives in sub-zero environments

Abstract

A low-cost method used to prevent cemented pastefill (CPB) from freezing during transport is the addition of chloride-bearing antifreeze additives or admixtures. Currently, many of the effects of these antifreeze additives on the rheological properties of CPB in sub-zero environments are still not sufficiently understood. The objective of this research is to examine and elucidate the effects of chloride-bearing antifreeze additives on the rheological properties of CPB at sub-zero conditions. CPB specimens with two types of chloride-bearing antifreeze (NaCl and CaCl2) at three different concentrations (5, 15, and 35 g/L) are prepared and cured under three different sub-zero curing conditions (−6, −12, and − 20 °C). The yield stress and viscosity of the CPB are measured after specific curing times. Supplementary tests, such as microstructural analyses, pH, zeta potential, and a series of monitoring experiments (for electrical conductivity and volumetric water content), are performed. The addition of antifreeze is observed to decrease yield stress and increase viscosity. Increases in antifreeze concentration and cement content, decreases in sub-zero curing temperature, and addition of slag are all determined to have significant effects on the rheological properties of CPB. Antifreeze additives are also inferred to promote hydration of cement at an early age, lower the freezing point of CPB, and delay freezing of CPB. These findings have high guiding significance for CPB pipeline transportation in sub-zero mining environments.