This paper describes the strength and microstructural behaviour of lime–slag-treated clay. The microstructure was investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM), and the strength of the treated clay was measured using the unconfined compressive strength (UCS) test. Untreated clay was prepared in the laboratory by mixing commercially available kaolin and bentonite, while hydrated lime and ground granulated blastfurnace slag (ggbs) were used as binders. XRD analyses of lime–slag-treated clay showed the existence of numerous reaction products such as calcium silicate hydrate (C–S–H), calcium aluminium silicate hydrate (C–A–S–H), and hydrotalcite (HT), which facilitated the strength increment. For a fixed proportion of lime, the relative intensity of pozzolanic reaction products was found to increase with increasing slag content. Slag was found to be very active to promote the pozzolonic reaction with lime, as evidenced from the presence of crystalline reticular (C–S–H) and platy (C–A–S–H) cementitious products in the SEM images. The role of lime in the activation of slag was also seen to have an upper limit whereby excess proportions failed to provide significant additional benefit. The UCS of lime–slag-treated clay was found to be higher in comparison with lime or slag alone with the same replacement ratio. This was due to the formation of more crystalline cementitious products, which accelerated the bridging (cementation) effect between lime–slag and clay particles.

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