Hydration Kinetics and Performance of MgO-Activated Slag Binder with Available Carbonate and Silicate

The combination of magnesium oxide (MgO) with various reactive aluminosilicates has recently been studied as an alternative binder, which bridges the chemistry of alkali-activated materials containing reactive MgO and hydrated magnesium silicate (M-S-H) binders containing reactive aluminates. This study is devoted to investigating the hydration kinetics and hydration products of the MgO-activated slag binder with available carbonate and silicate. The compressive strength results are used to assess the effect of the mechanism performance of the MgO-activated slag binder. A thorough investigation involving X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric-differential thermal analysis (TG-DTG), and Si29 MAS-nuclear magnetic resonance (Si29 MAS-NMR) was performed to investigate the evolution of carbonates and silicates. The precipitation of part of Mg2+ and Ca2+ from the solution as carbonate is beneficial to promote the hydration process, and it can reduce the Ca/Si ratio and Mg/Si ratio in C-(A-)S-H and M-S-H gel. The filling effect and nucleation effect of silicate formed by silica fume (SF) reduces the content of interlayer water, bound water, hydrotalcite, and the generation of exposed fibrous crystalline, which forms a dense microstructure. The improved hydration kinetics via the use of available carbonate and silicate led to samples with increased hydration and enhanced performance (51.6 versus 21.9 MPa at 28 days) when compared to the control sample.