Microstructural analysis of healing efficiency in highly durable concrete

Abstract

Abstract Micro-crack damage is a prime cause for deterioration of concrete structures. Previous studies have demonstrated that concrete has the capability to self-heal from micro-cracks when it is exposed to specific environmental conditions. Several traditional techniques have been used to evaluate the recovery of mechanical properties and qualitative magnitude of crack healing. Therefore, there is a need to develop a more analytical understanding of crack healing by studying geometrical aspects of the internal void structure. In this study, microcapsules containing sodium silicate as a healing agent and polyurethane as shell material are used at different content to facilitate concrete self-healing; mechanical and non-destructive tests are used to evaluate strength recovery. X-ray tomography images were reconstructed into a 3-dimensional section to evaluate the closure of cracks and self-healing potential via porosity, sphericity, reduction of crack width and volumetric size analysis, as well as through the Structure Model Index to identify various geometrical aspects during the healing progress. XRD analysis was also used to evaluate the chemical composition and consumption of calcium cations as a result of the new formation of C-S-H gel. An in-house fabricated mould was used for crack development through the entire volume of the sample, homogenously. The results demonstrated that cracks up to 122 µm were effectively healed with a crack repairing rate of up to 60%.