Expansive soil modified by waste steel slag and its application in subbase layer of highways

Steel slag is a waste by-product of the steel industry. The recycling usage of steel slag is limited due to the mutative chemical compositions it contains and its low cementation. In this investigation, the composition adjustment and activation of steel slag were studied to produce an optimal slag-based composite with improved cementation efficiency. The controlling moduli of cement clinker were introduced to standardise the composite. Subsequently, the composite was used to modify Hefei expansive soil (a kind of engineering waste for swelling properties) in embankment construction. The basic physical properties including free swelling ratio, California bearing ratio, unconfined compressive strength, microstructure, and mineral evolution were evaluated to understand the engineering performance and mechanism of modified expansive soils. The results show that the cementation of the slag was significantly improved after the composition adjustment and activation. Furthermore, the treated soil can satisfy the requirement of the Chinese standard for first-class road/highway when the composite incorporation ratio is more than 5%. The microstructural and mineralogical analysis shows that the component adjustment and activation enrich the cementation of the slag, resulting in the suppression of the swelling potential and improved strength. The above findings improve the reuse efficiency of steel slag, especially in expansive soil modifications.