Improved chloride binding stability for hydration products of calcium aluminates by phosphorus modification

Abstract Improved chloride binding stability for calcium aluminate cements is proposed by the doping of phosphorus. Phosphorus‐modified aluminates clinker has an improved chloride binding stability compared to pristine aluminates, ordinary Portland cement and sulfur‐modified calcium aluminates, as verified by experimental observation. The existence of the newly found phosphorus‐modified Friedel's salt (PFS) accounts for the excellent chloride binding stability, which was understood by density functional theory calculations. Local density of states of the valence band minimum is predominantly localized around P atoms in the PFS, but evenly distributed in the Friedel's salt (FS). The frontier band energy of the partial density of states on Cl and O elements in the PFS is lower than that in the FS by 0.21 and 0.05 eV, respectively. This makes the PFS more stable than the FS salt to ionic attack.