Influence of sodium chloride on the hydration of calcium aluminate cement constantly cured at 5, 20 and 40°C

Abstract

The influence of sodium chloride (NaCl) on the hydration evolution of calcium aluminate cement (CAC) cured at 5°C, 20°C and 40°C was investigated by calorimetry, X-ray diffraction, differential scanning calorimetry–thermogravimetry, scanning electron microscopy and mercury intrusion porosimetry. The chloride binding capacity and compressive strength of the CAC were also determined. The results showed that the chloride binding capacities of all the CAC samples increased with an increasing sodium chloride content, but the trend of growth gradually slowed. The influence of sodium chloride on the hydration of CAC was found to be highly dependent on its dosage and the curing temperature. At 5°C and 20°C, the early hydration of CAC was accelerated by a small amount of sodium chloride, leading to greater amounts of CAH10. Additionally, the pore structure of hardened cement paste was optimised for a higher compressive strength. However, excessive sodium chloride was found to delay the early hydration to some extent. When the curing temperature was increased to 40°C, sodium chloride accelerated the phase conversion, accompanied with an increase of harmful pores and a sharp decrease in compressive strength. The findings indicate a potential application of CAC-based constructions made with sea sand, especially at temperatures below 20°C.