Friedel's salt, Ca2Al(OH)6(Cl,OH)•2H2O:: Its solid solutions and their role in chloride binding

Solubility relationships between Friedel's salt and hydroxy AF, 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 similar to 20 degrees 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 similar to 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. (C) 1998 Elsevier Science Ltd.