Hydration activity and expansibility of different divalent metal oxide solution compositions in steel slag

Steel slag (SS) accounts for 15–20% of steelmaking output; its application in cement concrete has been limited because of poor stability. In this study, the divalent metal oxide solid solution (RO phase) in SS was analogue synthesised to study its hydration activity and expansibility. The results showed that the hydration activity and expansibility of magnesium oxide (MgO) in the analogue-RO phase is affected by the content of ferrous oxide (FeO); with the increase of molar ratio (x) of iron oxide to magnesium oxide in the analogue-RO phase, the autoclave expansion rate and hydration activity of the cement paste decreased. When x ≤ 0.5, the RO phase had high hydration activity and could cause poor soundness of SS. When x = 1, the RO phase had low hydration activity and could cause slight expansion of SS. When x ≥ 2, the RO phase had no hydration activity and could not cause any expansion of SS. The control of different analogue-RO phase compositions induced different hydration and expansibility, which provided a theoretical basis for the influence of the RO phase on the soundness of SS and enabled measures to be proposed to reduce the expansion of SS, thereby promoting high-volume utilisation of SS in cement and concrete.