The first microcapsule-based self-healing cement–bentonite cut-off wall materials

Abstract

Despite the extensive use of cement–bentonite in contaminated land containment applications, there are still many challenges related to durability. The development of self-healing cement–bentonite materials could provide more resilient, sustainable and reliable cut-off walls with significantly enhanced durability, reduced maintenance costs, enhanced safety and protection against sudden or undetected failure. The objective of this study was to develop self-healing cement–bentonite cut-off wall materials incorporating microcapsules. Microencapsulated sodium silicate, as a healing agent, would be released into cracks when the microcapsules rupture as a result of any damage incurred, and would react with the cement–bentonite matrix to fill and heal the cracks. Novel microcapsules with switchable mechanical properties developed for self-healing cement applications were employed here. The results demonstrated the enhanced average crack mouth healing and recovered permeability performance provided by the microcapsules compared to control cement–bentonite samples. X-ray microcomputed tomography and scanning electron microscopy were applied to investigate the self-healing process of the microcapsule-containing cement–bentonite system. The microstructural analysis confirmed the survivability, uniform dispersion and crack-triggered rupture of the microcapsules, as well as the release of the healing agent and the generation of hydration products within the cracks. These are promising results for the application of the microcapsule-based system for self-healing cement–bentonite cut-off wall materials.