Effects of Curing Methods on Hydration-Hardening Performance of Reactive MgO Cement.

Reactive MgO cement (RMC), which undergoes hardening through the reaction of MgO with water and CO₂, is a novel cementitious material that has gained significant attention in recent years. The hydration and carbonation processes of RMC samples are significantly affected by the curing method and water content. This work compared the effects of standard curing ((20 ± 1) °C, 95% relative humidity), water curing ((20 ± 1) °C, and carbonation curing ((20 ± 3) °C, 70% relative humidity, 20% (volume fraction) CO₂) on the properties of RMC with water-cement ratio (w/c) of 0.5, 0. 6, and 0.7, respectively. The types and content of the phases of the hydration and carbonation reaction products as well as their micro-morphological characteristics were investigated. The results show that the residual content of MgO in samples is 10% ~ 15% (mass fraction) at 3 d and disappears at 14 d under standard curing and water curing. When w/c is 0.6, the compressive strength of paste reaches 7.7 and 3.2 MPa at 14 d under standard curing and water curing, respectively. The strength of paste under carbonation curing is superior to that under standard curing and water curing (3 d compressive strength, 16.19, 0.42, and 0.43 MPa, 14 d compressive strength, 22.34, 7.46 and 7.23 MPa). The quantitative analysis results show that the carbonation product is mainly MgCO₃ ⋅ 3H₂O. When w/c is 0.6, the content of MgCO₃ ⋅ 3H₂O is 12.12% and 11.29% higher than that of samples with w/c = 0.5 and 0.7. The main reason for the optimal compressive strength could lies in that these needle-rod MgCO₃ ⋅ 3H₂O are bonded to each other form a dense microstructure. [ABSTRACT FROM AUTHOR]