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.