Chloride binding in cement paste with calcined Mg-Al-CO_3 LDH (CLDH) under different conditions

摘要

The chloride binding capacity of cement paste with Mg-Al CLDH, obtained through calcining a commercial LDH, is investigated under different chloride concentration, environmental temperature, and concrete pore solution alkalinity conditions. The transformation mechanism of Mg-Al CLDH to Mg-Al-Cl LDH is mainly explored by means of X-ray diffraction (XRD) , Fourier-transform infrared spectroscopy (FT-IR) and Differential thermogravimetric analysis (DTG). There appears to be a threshold chloride concentration of 1.0 mol/L for Mg-Al CLDH (6% incorporation) effectively enhancing the chloride binding capacity of cement paste. Both lowering and raising (38 degrees C) the environmental temperature is disadvantage to the transformation of Mg-Al CLDH to Mg-Al-Cl LDH in cement paste, and the amount of bound chloride at different curing temperatures follows as 38 degrees C 50 degrees C approximate to 20 degrees C 3 degrees C. Higher pore solution alkalinity is also adverse to both of the formation of Friedel's salt and the rehydration of CLDH. With increasing pH from 12.5 to 13.5, the improvement of Mg-Al CLDH on the chloride binding capacity of cement paste became weaker. Mg-Al CLDH improves the chloride binding capacity of cement paste is not only related to the excellent anions exchanging ability of it , but also related to the promotion of Friedel's salt formation of it. (C) 2020 Elsevier Ltd. All rights reserved.