Improving the Carbonation of Reactive MgO Cement Concrete via the Use of NaHCO₃ and NaCl

The performance of reactive MgO cement (RMC)-based concrete formulations is determined by the carbonation process, which is hindered by the inadequate CO₂
dissolution in the pore solution. This study addresses the improvement of carbonation and associated performance of carbonated RMC-based concrete samples via the introduction of sodium bicarbonate (SBC) and sodium chloride (SC). The use of these additives increases the initial pH, which accelerates the dissolution of CO₂ within the pore solution. The influence of SBC and SC on the progress of hydration is evaluated by isothermal calorimetry and pH measurements. Mechanical performance results are supported by X-ray diffraction (XRD), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM), which identify the formation and morphology of final phases. The presence of SBC and SC enhances the dissolution of CO₂ and improves the content and morphology of carbonate phases, leading to the formation of a strong carbonate network that increases sample performance by >100% at 28 days.