Interface microstructure and mechanical properties of concrete with antifreezing admixture at subzero temperatures

The mechanical properties of hardened cement paste, mortar and concrete with different antifreezing admixture and mineral admixture cured at 20°C and -20°C were investigated. The distinct difference on the compressive strength changes of hardened cement paste, mortar and concrete maybe attributed to the bigger difference within the interface transition zone (ITZ). Micro-hardness test, scanning electron microscopy, energy dispersive X-ray analysis and X-ray diffraction were used to analyze the range of the ITZ, element distribution, calcium oxide/silica ratio and orientation of calcium hydroxide. The results show that the anti-freezing admixture can improve the ITZ microstructure in concrete at sub-zero temperatures. Antifreezing admixture combined with mineral admixture can provide an ideal interface microstructure for concrete at sub-zero temperatures.