© 2023 Elsevier LtdFresh-state properties, compressive strength, and microstructural properties of reactive MgO cement-based (RMC) systems cured under accelerated carbonation or ambient conditions were examined in the paper. RMC, which is an environmentally greener alternative to ordinary Portland cement (OPC), was incorporated in the reference series to contrast its mechanical properties with other cementitious materials. To assess the synergy of RMC with other binders such as micro-silica, slag, and fly ash, as well as to find a way to incorporate more sustainable materials in the mortars, binary systems were designed. Lastly, to evaluate the influence of ultra-fine nano-silica (NS), on the composite binders, tertiary systems were formulated. In the carbonated series, a significant pH decrease, as well as a striking increase in compressive strength were observed. Accelerated carbonation induced the formation of magnesium calcite, which is supported by eclectic microstructural analyses. The highest compressive strength was measured in the carbonated reference series, binary and tertiary series also demonstrated respectable strength which was accompanied by compact microstructure. The addition of NS correlated with a decrease in the number of pores, especially large capillary pores, whereas no perceivable change in reaction products was discovered. In conclusion, this study demonstrated that reactive MgO-based cement could be used as a complete or partial replacement for conventional binders in structural concrete; the promising qualities of carbonated specimens ensure its usage as high-strength concrete.