Delaying Effect of NaCl on The Conversion of Hydrates of Calcium Aluminate Cement

Abstract

The effect of NaCl on the conversion of hydration products of calcium aluminate cement(CAC) was determined by means of MIP, XRD, DSC-TG and SEM. Results show that the addition of NaCl promotes the formation of CAH10 at early hydration stage. The total porosity and proportion of harmful pore in hardened CAC paste with NaCl are lower and the 7d-strength is 40% higher than that of the control. The later curing at 40°C accelerates the conversion from metastable C2AH8, CAH10 to C3AH6, and the strength decreases with the increasing of curing age. After 90 days, there is no metastable hydrate detected in CAC paste. However, the addition of Niacin CAC paste can prominently delay the conversion of C-A-H. Massive CAH10 still exists in the paste with NaCl, resulting in a slower retraction of late strength.