Multiscale investigation of calcined clays for stabilisation of natural clays

Recently, calcined clays have emerged as a viable Supplementary Cementitious Material (SCM) in structural concrete. In contrast, less knowledge exists on the use of clay-based SCM as a binder for stabilisation of natural clays. This study investigates the partial replacement of conventional binders, i.e. Ordinary Portland Cement (CEM I) and lime, with calcined kaolinites for stabilising a natural sensitive clay, aiming to achieve mechanical strength and microstructural evolution comparable to a traditional lime–cement mix (50:50). A holistic approach is adopted to investigate properties across length scales using Electrochemical Impedance Spectroscopy (EIS), miniature Cone Penetration Tests (mCPT), and synchrotron-based X-ray phase-contrast nano-holo-tomography (nano-CT). The results indicate that mixes with up to 20% replacement of conventional binders with calcined clay exhibit comparable strength and material properties to traditional lime–cement stabilised samples, while offering potential reductions in CO2 emissions. The findings further indicate that pore water availability is a key factor influencing hydration and the resulting mechanical properties in binder-mixed clays. This depends on the proportions of lime, cement, and calcined clay relative to the natural water content, with cement having the greatest influence on water demand. Consequently, the binder composition in stabilisation of soft clays can be optimised to achieve enhanced performance by considering the water retention characteristics and reactivity of the components in the mix, ultimately leading to improved mechanical strength.