Polymer-modified magnesium oxychloride cement: investigating the effects of epoxy and polyurethane on water submergence performance

Building material technologies have recently shown interest in alternative and low CO₂-binders that require reduced energy consumption. Magnesium oxychloride (MOC) cement is an attractive alternative binder due to properties like low density, fire resistance, and thermal insulation. However, MOC cement has poor water resistance, which limits its durability. This study investigated enhancing the water submergence performance of MOC using organic polymer modifications. MOC cement samples were prepared with polyurethane (PU) or epoxy (EX) added directly during mixing (M) or as a surface coating (P). Compressive-strength was measured after 28 days of air curing and after 7, 28, and 60 days of water submergence. The 28-day strength of control MOC decreased by 26.1% and 32.6% with M-PU and M-EX mixing, likely due to reduced workability and hydration. However, P-PU and P-EX coating had no adverse strength effects. After 60 days of submergence, the compressive-strength of control MOC declined by 90.4%, while M-PU and M-EX had reduced losses of 52.9% and 67.7%, respectively. P-PU and P-EX displayed the greatest durability with strength losses of only 25.8% and 22.4% after 60 days. The polymer modifications provided a hydrophobic barrier limiting water ingress into the MOC. Overall, the EX-polymer modification led to better water resistance compared to PU, attributed to superior hardness, adhesion, and chemical resistance. The results demonstrate that polymer modification with PU or EX can effectively improve the water submergence durability of MOC cement.