Mechanical behaviour and microstructure of steel slag-based composite and its application for soft clay stabilisation

Abstract

A new steel slag-based composite material (SSC), containing the steel slag, metakaolin and cement, was proposed to replace the traditional cement for the stabilisation of soft clays in deep mixing projects. The results obtained from unconfined compression tests showed that the metakaolin agent is crucial to the strength growth of the SSC paste. At a preferable mass ratio (Cement:Metakaolin:Steel slag=50:15:85), the SSC paste can achieve a higher strength than that of pure cement.The strength development of SSC stabilised clay is similar to traditional cemented soils, and the updated water/SSC ratio can be employed to assess the strengths based on Abrams’ law. The pore size distributions indicated that the cumulative pore volume and the macro pore size both decreased with the cement proportion increasing. The main components, such as β-C2S, γ-C2S, CSH, CaSO4·2H2O, Aft and CASH, were identified in XRD patterns and SEM images. The mechanisms were summarized as: (1) a large amount of CSH formatted the reticulate and fibrous structures, and became the binder between the unhydrated aggregates; (2) metakaolin promoted the secondary hydration and pozzolanic reaction of cement and steel slag, resulting in the further enhancement of the binders.