The system CaO-Al2O3-CaCl2-H2O at 23±2°C and the mechanisms of chloride binding in concrete

The stable quaternary diagram for the system CaO-Al2O3-CaCl2-H2O at 23 +/- 4 degreesC has been constructed. Among the phases in this system are the calcium oxychlorides Ca(OH)(2).CaCl2.H2O and 3Ca(OH)(2).CaCl2.12H(2)O, The formation of Friedel's salt (FS) and calcium oxychlorides provides a mechanism for chloride binding in Portland cement concrete. The compatibility relationships involving these compounds, FS and Ca(OH)(2), were established empirically, and 3Ca(OH)(2).CaCl2.12H(2)O was found not to coexist in equilibrium with FS. The solubility behaviors of these compounds may play a role in affecting temperature-dependent corrosion rates. Additionally, the formation of oxychlorides from solutions containing elevated concentrations of NaCl may provide a mechanism by which ASR is facilitated. (C) 2004 Elsevier Ltd. All rights reserved.