Microwave pre-curing of Portland cement-steel slag powder composite for its hydration properties

A comparative study was carried out between normal curing, 40 °C steam curing for 10 h, 80 °C steam curing for 4 h and microwave pre-curing for 45 min to investigate the effect of microwave pre-curing on the hydration of Portland cement-steel slag powder composite. The compressive strength of mortar prepared with composite binder was tested. The hydration and microstructure of the composite were also studied by XRD, TG-DSC, MIP, Water absorption and SEM-EDS methods. The results show that although the hydration degree of composite binder microwave treated is lower than that cured with steam, the porosity, especially the pores larger than 50 nm, is reduced significantly by microwave pre-curing. Therefore, a small amount of hydrated products can connect each phase into a whole to improve the compressive strength of mortar treated with microwave when compared with other three regimes. In addition, as for the inert RO or Fe2O3 in the steel slag, it does not have an adverse effect on the microstructure as it can be tightly connected with the hydrated gel. But microwave pre-curing cannot accelerate the hydration of C2F, which is different from 80 °C steam curing.