Insights on chemical and physical chloride binding in blended cement pastes

• Published in: Cement and concrete research 2022-06, Vol.156, p.106747, Article 106747
• Main Authors: Wilson, William, Gonthier, Julien Nicolas, Georget, Fabien, Scrivener, Karen L.
• Format: Article
• Language: English
• Subjects: Binders (materials); Binding; Blended cement pastes; Calcium alumina silicate hydrate (C-A-S-H); Cement paste; Chloride binding; Chlorides; EDX image analysis; Ettringite; Friedel's salt solid solution; Hydrates; Image analysis; Magnesium; Solid solutions
• ISSN: 0008-8846; 1873-3948
• DOI: 10.1016/j.cemconres.2022.106747

This study investigates chloride binding in blended cement pastes exposed to 0.5 M NaCl solutions (with and without pH adjustment) using X-ray diffraction and energy-dispersive X-ray spectroscopy image analysis (edxia). The aim is to better understand the effects of the binder type, the water-to-binder ratio and the pH on the chemical binding in AFm phases and the physical binding on C-A-S-H. Results show that the binding cannot be predicted from AFm and C-A-S-H contents alone because competing ions in the system affect both the Friedel's salt solid solution chemistry and the C-A-S-H binding capacity. Notably, the high content of aluminous hydrates in LC3 systems leads to a high chemical binding even if Friedel's salt solid solutions have relatively low chloride contents (particularly at a higher pH). On the contrary, the CEMIII/A paste showed low binding because of relatively high sulfate and magnesium contents which compete for incorporation/adsorption in aluminous hydrates (AFm, ettringite and hydrotalcite).