Chloride binding in blended binder systems: Importance of the structures of CSH gel

Application of supplementary cementitious materials (SCMs) as binary or ternary blended binders to substitute Portland cement and eventually decrease the carbon dioxide foot print has been introduced in cement industry through decades. Although years of research have been devoted to the topic of blended binders, there still exists a lack in proper understanding of hydration and durability of these materials. It is the well-known topic of chloride binding, which is well proven to be essential for a better understanding of the durability of concrete in the environments prone to chloride ingress. The binding phenomena includes chemical and physical binding, where the chemical form accounts for new phases such as Friedel’s salt and the physical form depends on the chlorides that are adsorbed to hydration products - mainly CSH gel. However, there exists a major lack of understanding about the changes in the structure of CSH gel in different types of blended systems which in relation make it difficult to account for the actual chloride binding. This is why a better understanding of the chloride binding mechanism in blended binders is the major goal in this study. The work program includes detailed analysis of the changes in structure of CSH gel in different blends and the relation with chloride binding. The changes in the structure of CSH are accounted for using NMR analysis and the effect of these changes on chloride binding is addressed through adsorption tests.