Regulating hydration and microstructure development of reactive MgO cement by citric acids

Reactive MgO cement (RMC) is a novel binder formed through the hydration and carbonation of MgO, but its low reactivity hinders its wider application. Preliminary research has suggested that citric acids can form compounds with Mg²⁺ that regulate these processes, but the mechanism is yet to be understood well. This study investigated the effects of citric acids on the fresh and hardened properties of RMC. Results showed that the shear yield stress and plastic viscosity of the RMC pastes decreased with the addition of citric acids. Under standard curing, 4 wt% and 8 wt% citric acids increased the compressive strength of RMC by ∼100 % at 14 days. The adsorption of citrate on MgO inhibited the formation of brucite, forming an amorphous network-like microstructure crystallised after 14 days. Under CO₂ curing, the compressive strength of RMC with 8 wt% citric acids increased by 12 % at 14 days, which could be ascribed to the porous microstructure formed that promotes the uptake of CO₂ and the densification of the microstructure.