A Comprehensive Review of Magnesium Oxychloride Cement (MOC) and Alternative Cementitious Binders: Properties, Performance and Applications
Abstract
Magnesium oxychloride cement (MOC) has become increasingly popular as an environmentally friendly substitute for ordinary Portland cement (OPC), which has properties such as fast setting time, high strength at early age, low thermal conductivity, low processing energy and low carbon footprint when compared to other binders. However, due to its poor resistance to moisture, dimensional instability in wet conditions and risk of chloride attacks on reinforcing steel, wider structural applications of MOC have not yet been realized. The present paper reviews MOC hydration process, phase composition, microstructure formation with a special emphasis on the stabilization of Phase 5 (5Mg(OH)₂·MgCl₂·8H₂O) and Phase 3 (3Mg(OH)₂·MgCl₂·8H₂O), the two most important crystal phases affecting mechanical and physical properties of MOC paste. Several modification methods of MOC are reviewed, which include addition of phosphates, pozzolanic materials, fibers, polymers and carbonation assisted curing in terms of softening coefficient improvement and retaining of strength at wet state. The scope is further widened to encompass other binders, which are alternative and complementary to MOC, such as magnesium phosphate, geopolymers, calcium sulfoaluminate, and other new generation low carbon binders in terms of their energy efficiency, mechanical behavior, and environmental impacts compared with MOC. Applications for these binders are considered, ranging from traditional construction purposes, fire protection, artificial stone, waste immobilization, 3D printing elements, light weight non-structural materials, and industrial floors. The paper concludes with highlighting existing research gaps concerning the long-term durability of these binders under environmental exposure, the lack of standardized test methods, limited information on life cycle assessments, and problems with scaling of modification techniques.