Constitutive behaviour of a clay stabilised with alkali-activated cement based on blast furnace slag

Abstract

Alkaline cements have been extensively tested for soil stabilisation in the last decade. However, only a few studies have focused on the assessment of such performance by establishing the constitutive behaviour of the cement. In this paper, we focus on the mechanical behaviour, using triaxial testing of a clay with high water content stabilised with an alkali-activated binder and the subsequent prediction of the experimental stress–strain response using a kinematic hardening constitutive model initially developed for natural clays. Monotonic consolidated undrained triaxial tests were conducted on reconstituted and stabilised clay specimens cured for 28 days to evaluate the effects of cementation on the overall shear behaviour. Alkali-activated binder was synthetised from blast furnace slag and sodium hydroxide. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD) were performed to study the microstructure, whereas leachate analyses were performed after 28 and 90 days of curing to investigate the contamination potential. The main product formed was calcium aluminosilicate hydrate (C-A-S-H) with a low CaO/SiO₂ ratio, and no risk of soil contamination was found. The compressibility and undrained shear strength in the pre-yield state was found to be independent of the initial mean effective stress (<i>p</i>’₀), unlike what was observed in the post-yield state, where the shear strength seemed to be affected by <i>p</i>’₀. The model provided reliable predictions of the experimental results and captured the main features of the artificially cemented clay for the tested <i>p</i>’₀ range. Such studies are fundamental to establish adequate confidence in such alternative binders—an essential aspect if their use is to become widespread in the near future.