Exploring the mechanical response of low-carbon soil improvement mixtures

As society moves towards decarbonisation, it is important to assess the hydromechanical behaviour of binders that could offer a low-carbon alternative to Portland cement in ground improvement technologies. This work considers two such alternatives: one still largely unexplored (metakaolin-based geopolymers) and a better known one (colloidal silica). Results from unconfined compressive strength, permeability tests, undrained monotonic and cyclic triaxial tests on granular soils (sand and silty sand) treated with those two binders are presented and discussed, emphasizing similarities and differences with the response of similar soils treated with other conventional and unconventional binders. Effects of silt content, curing conditions and soil/binder ratios are examined. Both colloidal silica and metakaolin-based geopolymer significantly improve the mechanical properties of the treated soils, although the geopolymer results in a stronger and stiffer material. Both treatments reduce much the permeability of the treated soil, but the reduction achieved with colloidal silica is larger.