Durability of MgO-based binders: a critical review from RILEM TC 311-MBC

The urgent need to decarbonise the cement industry has motivated global research on MgO-based cements, including magnesium oxychloride (MOC), oxysulfate (MOS), carbonate (MC), and silicate (MS) cements. While this new class of cements may offer material advantages over Portland cement, questions surrounding their long-term durability continue to limit their broader implementation. This critical review, prepared for RILEM TC 311-MBC, evaluates the durability literature on these four types of MgO-based binders. Findings show that while MOC and MOS cements exhibit attractive early-age strength, they suffer rapid strength loss under sustained exposure to moisture because their main hydrates are highly soluble. Field test data is critically needed. MC binders, dominated by hydrous carbonate-bearing brucite, exhibit good resistance to chloride and sulfate environments; however, their strength decreases with increasing humidity, and accelerated carbonation can trigger expansion or micro-cracking, depending on the availability of pore spaces. Contrastingly, MS cements develop dense M-S-H matrices with permeability and frost performance on par with, or better than, PC-based concretes. This promising class of cements resists natural carbonation but remains sensitive to micro-crack formation when nesquehonite precipitates in high CO₂ environments. Across all MgO-based binders, reinforcement corrosion is driven by moisture transport rather than by differences in passivation due to the near-neutral pH of their pore solutions. The research community is encouraged to close these gaps so to advance the formulation of durable and environmentally sustainable MgO-based cements.