Phase evolution and microstructural changes induced by accelerated carbonation in MgO-slag binders with Na2CO3 and silica fume

Reactive MgO binders have the potential to provide adequate mechanical properties and to reduce the carbon footprint. However, the reaction products and the microstructure evolution of binder containing Ca and Mg under the influence of accelerated carbonation are unknown. The study aims to characterize the reaction products and the effect on the microstructural evolution of MgO-slag binder with Na2CO3 and silica fume under accelerated carbonation curing conditions. During the accelerated carbonation of MgO-slag binder to sequester CO2, it is observed that the 28d compressive strengths of S0 and S2 were increased by nearly 80 % (20.65 vs. 37.19 MPa) and 16 % (55.92 vs. 64.92 MPa), respectively, and the reaction of MgO and slag degree was also significantly improved. Although partial degradation of C-(A-)S-H and reduction of M-S-H are found during carbonation, the conversion of reactive MgO into hydrated magnesium carbonates (HMCs) during carbonation complemented the pore-filling effect offered by interlocking of crystals, such as hydrotalcite, HMCs, with the binding strength provided by the M-S-H, C-(A-)S-H gels, to form a dense microscopic morphology.