Reactive Magnesium Oxide and Magnesium-Based Compounds as Alternatives to Portland Cement

The development of alternative binders to ordinary Portland cement is motivatedby the high thermal energy demand, calcination emissions, and environmentalimpact associated with clinker production. Magnesium-based cementitious systems,particularly reactive magnesium oxide cement, magnesium oxychloride cement,magnesium oxysulfate cement, magnesium phosphate cement, and magnesium silicatehydrate cement, have attracted considerable scientific attention because of theirrelatively low-temperature processing, rapid hardening potential, chemical versatility,and ability to participate in mineral carbonation.This paper presents an advanced analysis of the physicochemical behavior ofmagnesium-based compounds as partial or complete alternatives to Portland cement. The analysis integrates hydration thermodynamics, carbonation chemistry,dissolution–precipitation kinetics, pore-structure evolution, reaction–diffusion theory,fracture mechanics, and thermodynamic phase-equilibrium concepts.The principal reactions include the formation of brucite, hydrated magnesiumcarbonates, magnesium oxychloride phases, magnesium oxysulfate phases, struvite,and magnesium silicate hydrate gel. The principal limitation of magnesium-basedcement is that its performance depends strongly on the calcination route, particle size,water-to-binder ratio, curing humidity, carbon dioxide concentration, and additivechemistry.The most technically promising approach is a tailored hybrid system based onreactive magnesium oxide, silica-rich supplementary materials, controlled carbonation,and chemical or polymeric modification.