Stability of the hydrate phase assemblage in Portland composite cements containing dolomite and metakaolin after leaching, carbonation, and chloride exposure

To reduce CO2 emissions during the production of cement and to cope with increasing demands for concrete, and thereby cement, the cement industry needs to identify new supplementary cementitious materials. These new composite cements should provide, among others, a similar or improved durability of the concrete structures. This study investigated the hydrate phase assemblage in Portland cement pastes containing dolomite or a combination of dolomite and metakaolin after leaching, carbonation, and chloride exposure. The phase assemblage and phase compositions of the exposed samples and the unexposed reference samples were investigated using TGA, XRD, and SEM-EDS. The reaction of dolomite in the cement paste resulted in the formation of hydrotalcite. It was found that, unlike most other hydration phases, hydrotalcite can withstand high degrees of leaching and carbonation. When the samples were exposed to a chloride solution, the formation of a chloride-containing hydrotalcite was observed.