Petrographic evidence of calcium oxychloride formation in mortars exposed to magnesium chloride solution

Many researchers have reported chemical interactions between CaCl2 and MgCl2 solutions and hardened Portland cement paste. One potentially destructive phase reported in the literature is calcium oxychloride (3CaO·CaCl2·15H2O). In the past, limited numbers of researchers have reported identification of this phase by X-ray diffraction. In this work, petrographic evidence of oxychloride formation is presented based on optical microscopy, scanning electron microscopy and microanalysis. This evidence indicates that calcium oxychloride does form in mortars exposed to MgCl2 solutions.