Improving the hydration activity and volume stability of the RO phases in steel slag by combining alkali and wet carbonation treatments

Poor volume stability of steel slag (SS) is due to the existence of free-CaO, free-MgO, and RO phases. Combined treatments of alkali and wet carbonation (AWC) were conducted on the RO phases to stimulate hydration activity. The hydration degree of AWC_RO phases with MgO molar ratios of 0.84 increased from 10.6 % to 57.6 %. The effects of FeO-MgO-MnO proportions on the hydration activity of RO phases were investigated electronically based on the density functional theory. Results showed that Fe imparted higher inhibition effects on MgO hydration than Mn. The compressive strength of mortar with added AWC_SS was 34.4 % higher than with added untreated SS at 28 days, with an expansion rate decreased from 0.0447 % to 0.0298 %. The main products of AWC_RO phases were Mg(OH)2 and Mg5(CO3)4(OH)2·4H2O, which exhibited seed crystal effects, accelerating the early hydration of cement. This method provides guidance towards a meaningful solution to poor SS volume stability.