Friedel’s salt, Ca2Al(OH)6(Cl,OH)·2H2O: its solid solutions and their role in chloride binding

Abstract Solubility relationships between Friedel’s salt and hydroxy AF m suggest an essentially complete solid solution with only minor discontinuities. Solid–aqueous partitions were determined by equilibration of 11 compositions at 10 mol % intervals at ∼20 °C in experiments of 6–17 months’ duration. Aqueous chloride concentrations >2mM, approximately, are required to incorporate significant Cl in hydroxy AF m ; the process is complete, giving essentially pure Friedel’s salt, at a chloride content of ∼14 mM. The self-generated pH of the solid solutions are high: pH >12 for all compositions. The implications for diffusion of chloride ions through cement paste are discussed.