Binding Mechanism of CSA Cement on Premixed Cl− and Its Governing Parameters

Abstract

Calcium sulfoaluminate (CSA) cement showed a good binding capacity on the external Cl− transported into concretes from its surrounding environment. However, it is unclear whether the same binding mechanism can still apply if the Cl− ions were introduced during a concrete mixing stage when marine resources, without being properly processed, are used as fine aggregates. Experimental work on CSA mixes, with different water/powder, gypsum content, and existences of premixed Cl−, has been conducted and showed that the highest binding capacity on premixed Cl− was obtained in the mixes with a higher water/powder and without gypsum. Mineralogy and Cl− binding results of the tested CSA mixes proved that except for the calcium monosulfoaluminate hydrate (Ms), which has been well established with a good Cl− binding capacity, the CAH10 produced should also contribute to the binding on premixed Cl−. The premixed Cl− in the CSA cement led to a conversion of Ms and CAH10 to Friedel’s salt and, meanwhile, shortened the setting time, altered the heat release process, prohibited the generation of microcracks, and resulted in a more densified microstructure.