Impact of pre-curing time, water-to-cement ratio, SCMs, and antifreeze on the freezing point of mortars: an electrical testing approach

This study uses alternating current impedance spectroscopy to determine the freezing point and temperature range (FTR) of cement paste and mortar. The effects of pre-curing time, water-to-cement (W/C) ratios, supplementary cementitious materials, and antifreeze on FTR were analyzed. The relationship between relative strength development (f_c) and effective resistivity change (f_r) during curing at −10 °C was explored. Results show that effective conductivity σ_eff can distinguish three stages in the freezing process: temperature control (stage I), phase transition (stage II), and post-temperature control (stage III). Activation energy for ion conduction was determined for stages I and III, while the change in ln(σ_eff) with temperature was analyzed for stage II. FTR decreased with longer pre-curing and lower W/C ratios. Fly ash increased the FTR, while silica fume reduced it. CaCl₂ and Ca(NO₂)₂ not only reduce the FTR but also exhibit a linear relationship between f_c and f_r during curing at −10 °C.