Microcapsule-based self-healing cement stabilised clay

The in-situ mixing of soft clays with cementitious binders is a common soil stabilisation method for a wide range of underground construction applications, varying from the improvement of foundation ground to the construction of earth retaining walls within the framework of excavation works. However, it is shown that the mechanical and transport properties of cement stabilised clay change considerably when subjected to aggressive environments. Therefore, there is a need to improve the resilience of cement stabilised clay against mechanical and environmental stresses. The development of self-healing cement stabilised clay could provide more reliable materials that are likely to reduce the maintenance and repair costs. Microcapsule-based self-healing approaches have been investigated recently. The mechanism of self-healing microcapsule system is that when cracks propagate in the cementitious matrix, they rupture the microcapsules, leading to the release of healing agents into the crack volume. The objective of this paper is to investigate the self-healing performance of cement stabilised clay incorporating microcapsules. In this study, microencapsulated sodium silicate was incorporated in cement stabilised kaolin clay and the healing agent reacts with the calcium hydroxide in the cementitious matrix to form the calcium-silicate-hydrate gel to heal the cracks. Properties investigated were the distribution and release of microencapsulated sodium silicate, the permeability, and microstructure of the stabilised clay samples. CT scan and scanning electron microscopy analysis revealed the rupture of microcapsules and the generation of healing products around the microcapsules. The effective healing of cracks was verified by the recovered permeability properties of microcapsule-containing stabilised clay samples.