Effect of Sodium Chloride on Hydration of Calcium Aluminate Cement at Different Temperatures

Effects of NaCl on the hydration of calcium aluminate cement (CAC) at 5℃, 20℃ and 40℃ were analyzed by X-ray diffraction, scanning electron microscopy, mercury intrusion porosimetry and calorimetry. Results show that lower amount of NaCl accelerates the early hydration of CAC, while excessive NaCl delays the early hydration of CAC. Effects of NaCl on the hydration products of CAC are highly dependent on the curing temperature. At 5℃ and 20℃, the incorporation of NaCl greatly contributes to the formation of CAH10, thus the pore structure is optimized and compressive strength is enhanced significantly. At 40℃, the addition of NaCl accelerates the transition from metastable hydration products (CAH10, C2AH8) to C3AH6, leading to a significant increasing in the amounts of harmful pores in hardened cement paste and an obvious decrease in strength. Although the amount of bounded chloride ions increases with the increase of NaCl content, the trend of increasing gradually slows down. With the proceeding of hydration, the amount of bounded chloride ion increases at 5℃ and 20℃, while it decreases with age at 40℃. © 2019, Materials Review Magazine. All right reserved.