Effect of electrochemical chloride removal and ground granulated blast furnace slag on the chloride binding of cement paste subjected to NaCl and Na2SO4 attack

This paper aimed to evaluate the effect of electrochemical chloride removal (ECR) on the stability of bound chlorides in ground granulated blast furnace slag (GGBS) blended cement pastes subjected to NaCI and Na2SO4 attack. Two chloride attack conditions (pure chlorides, 5%NaCl + 0%Na2SO4, and the coexistence of chlorides and sulfates, 5%NaCl + 3%Na2SO4) were applied. Four cement paste mixtures were prepared by replacing the cement with 0%, 10%, 20%, and 30% GGBS. The results showed that, under an electric field, the incorporation of GGBS in cement pastes increased the stability of bound chlorides, whereas the presence of sulfate ions decreased the stability of the bound chlorides. Moreover, the content of bound chloride ions increased with increasing GGBS content after ECR treatment. X-ray diffraction (XRD) and thermal gravimetric and differential thermal gravimetric (TG-DTG) analyses demonstrated that the incorporation of GGBS in the paste samples increased the content of Friedel's salts, thereby enhancing the stability of their chemically bound chlorides both before and after ECR treatment. The overall findings revealed that the ECR treatment not only effectively removed the free chlorine ions from the cement pastes but also induced the release of bound chlorides. (C) 2019 Elsevier Ltd. All rights reserved.