Cementitious and hardening properties of magnesia (MgO) under ambient curing conditions

Abstract

This study investigated the cementitious and hardening properties of MgO under different ambient curing conditions. The strength development of MgO paste and mortar specimens cured in air, water, wet-dry cycles and sealed conditions were measured. The phase assemblage of MgO-(CO2)-H2O system was predicted by thermodynamic calculations and then hydrating and hardening mechanism were identified by multiple microstructural analytical techniques. The results showed that hydration of MgO under air condition yielded low strength pastes due to limited formation of hydrate and carbonate phases, while sealed samples hydrated to form noncementitious crystalline Mg(OH)2 alone. Water curing or wet-dry cycles enhanced hydration of MgO and subsequent carbonation at atmospheric CO2 concentration. The amorphous carbonate phase was confirmed by combining phenolphthalein spray test, TGA and FTIR results, which was speculated as the cause of significant strength gain. Moreover, reduction in water-to-cement ratio enabled MgO mortar to set more quickly and show higher strength up to 40 MPa.