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.

Automated summary

Experimental work on calcium sulfoaluminate (CSA) mixes has shown that the binding capacity of CSA cement on external chloride ions is influenced by the water/powder ratio and the presence of gypsum. The study also found that a substance called CAH(10) contributes to the binding of premixed chloride ions. The presence of premixed chloride ions in CSA cement affects the mineralogy and physical properties of the cement, leading to a more densified microstructure.