Enhancing carbonation of magnesium oxide (MgO) cement (RMC)-based composites with calcined limestone

Increasing pore solution pH in a concrete matrix will enhance CO₂ dissolution. In this study, calcined limestone was used as a replacement of reactive magnesium oxide (MgO) cement (RMC) at 5 and 10 wt.% to increase its carbonation rate and content. Its influence on strength development, chemical evolution, and microstructure was also investigated. The calcined limestone was found to increase the pore solution pH and consequentially reduce the hydration of RMC. Aggravated by a smaller particle size of the formed brucite, the composite strength under air curing was significantly reduced. Yet, the high pH environment, smaller hydration products and microporosity enhanced carbonation and retained strength development. The carbonation products were characterized by a mixture of hydrated magnesium carbonates (HMCs), calcite, and amorphous phases. The outcome of the study opens up a possibility for using less pure sources of magnesite and calcium oxide as a brine precipitation agent to produce RMC for construction applications.