Abstract
Despite offering higher early strength and faster hydration rates, low-carbon sulphoaluminate cement (SAC) remains vulnerable to adverse cold weather conditions during winter construction. This study proposes the utilization of sodium nitrite (SN) as an antifreeze admixture to enhance the mechanical properties of SAC paste under sub-zero temperatures (−5 °C and −10 °C). The influences of SN on the hydration kinetics, phase assemblage, freezing point, microstructural evolutions and mechanical properties of SAC paste under sub-zero temperature are comprehensively investigated. It turns out that the mechanical properties of SAC paste at low temperatures (−5 °C and −10 °C) can be significantly improved by incorporating SN. Low-temperature differential scanning calorimetry (LT-DSC) results showed that the freezing point of SAC paste is sharply decreased from −1.1 °C to −11.6 °C owing to the elevated effect of SN on the ion concentration within pore solution. Moreover, X-ray diffraction (XRD) and thermogravimetric (TG) analysis are conducted to confirm the increase in the hydration degree of SAC paste with SN under sub-zero temperatures. Furthermore, mercury intrusion porosimetry (MIP) results demonstrate the role of SN on the refining pore of SAC paste. In conclusion, this work proposes a new way and optimal control of dosage for enhancing the mechanical properties of SAC cement at low temperatures.
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