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

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 CAH(10) produced should also contribute to the binding on premixed Cl-. The premixed Cl- in the CSA cement led to a conversion of Ms and CAH(10) 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. (C) 2021 American Society of Civil Engineers.