The interaction between monosulfoaluminate and calcium chloride aqueous solution

Scanning transmission X-ray microscopy (STXM) and calcium L_2,3-edge near-edge X-ray absorption fine structure (Nexafs) spectra were used to investigate the morphology and chemical information of cement-based materials. The interaction between calcium chloride (CaCl₂) and monosulfoaluminate (Ms) was investigated and the intermediate phases were identified. With an increase in the concentration of the calcium chloride solution, calcium Ms was converted into ettringite, Kuzel's salt (Ks) and Friedel's salt (Fs) to varying degrees, while SO₄²⁻ ions in the ettringite and Ks were continuously replaced by Cl⁻ ions in the solution, eventually forming Fs and gypsum. Based on the calcium L_2,3-edge Nexafs absorption spectra, ettringite, Ms, Ks and Ms were greatly distinguished by the number and shape of the leading peaks in the spectra due to the difference in SO₄²⁻ content among the interlayer structures of Ms, Ks and Fs. The present work is based on the references for the STXM study of the calcium (sulfo)aluminates, for demonstrating a more complete understanding of the phase evolution under chloride environments.