The effect of curing conditions on the hydromechanical properties of a metakaolin-based soilcrete

Abstract

An attractive approach to reduce the carbon dioxide footprint of deep soil mixing (DSM) is to replace Portland cement-based binders by geopolymers based on metakaolin. Safe design requires a good understanding of the mechanical and hydraulic properties of the improved ground, but very little is known about metakaolin–soil mixtures. For instance, shrinkage during curing is a significant issue for metakaolin-based concretes but has not been previously studied in soilcretes. In this work the permeability and strength of sand- and silty sand-based metakaolin soilcretes are studied under different curing conditions. The development of microcracks induced by geopolymer shrinkage is confirmed through a microstructural study using mercury intrusion porosimetry, scanning electron microscopy and X-ray computed tomography. The influence of microporosity and binder filling on permeability and strength is clarified adapting well-established soil models. A modified Kozeny–Carman formulation is proposed for permeability. A mixture ratio model is calibrated to represent strength. In general, the metakaolin-stabilised materials present excellent mechanical and hydraulic properties, although these are very sensitive to curing conditions.