Observations of chloride ingress and calcium oxychloride formation in laboratory concrete and mortar at 5 °C

The combination of chloride deicer exposure and temperatures near the freezing point of water makes for an aggressive environment for many concrete pavements and bridge decks. In laboratory-simulated conditions, the formation of calcium oxychloride hydrate (3CaOCaCl215H2O or 3CaOCaCl212H2O) phases has been associated with the expansion and deterioration of concrete and mortar, but calcium oxychloride phases have yet to be observed in the field. A decomposition path from calcium oxychloride hydrate to CaCl2Ca(OH)22H2O to calcite CaCO3 is proposed here, and offered as an explanation for the lack to date of convincing field evidence for a calcium oxychloride hydrate deterioration mechanism.