Microstructures of magnesium oxychloride Sorel cement

Due to the ever-increasing awareness of the need for environmental protection, research involving magnesium oxychloride (MOC) Sorel cement has been the subject of increasing interest recently. The sporadic and inconsistent evidence of acicular crystals in the MOC phases has, however, puzzled researchers performing microstructural studies of MOC cement. The present investigations showed that the divergence in strength among Sorel cements with different mixture designs can be attributed to the various phase assemblages and the distinct microstructures that result. Comprehensive microscopic observations illustrate that the crystalline phases of MOC cement were, in general, needle-shaped crystals, bundled in different forms, with a granular surface of nano-sized tiny grains. Imprints of bundled needle-shaped crystal were also observed in the massive and dense microstructure of cement paste with a high compressive strength. The different crystalline phases of the microstructures under investigation were further identified by elemental composition analysis. The microstructural identification of Sorel cement provides a sound basis for a detailed study of the different crystalline phases.