Effects of accelerated carbonation on the microstructure of Portland cement pastes containing reactive MgO

Reactive MgO is produced at a lower kiln temperature compared to ordinary Portland cement (OPC) and gains its physical properties mainly as a result of carbonation processes. Use of reactive MgO as cement replacement has recently gained attention in context with precast concrete products subjected to carbonation curing. This study investigates pastes containing 0–40% reactive MgO and the effect of accelerated carbonation curing on the: formation of new carbonate phases, microstructural development, and microhardness. Outcomes from this study revealed that the primary Ca and Mg-bearing carbonates formed are calcite, aragonite, magnesium calcite, and nesquehonite. The combined effect of carbonation and reactive MgO resulted in: a reduction in pore size and total pore volume, increase in apparent density, and greater microhardness compared to OPC paste. The chemical processes, and physical properties revealed that the dense inter-connected network structure consisting of Ca and Mg carbonates is a significant factor that influences the microhardness.