Beyond the surface: Coupling water permeability assessments to X-ray micro-computed tomography for evaluation of self-healing on lime-based mortars

Self-healing, a promising solution to cementitious structures' main problem - cracking, involves complex dynamics influenced by factors like crack type, size, and binder material. Existing tests lack a comprehensive approach to describe it. This study coupled the results of X-ray micro-computed tomography (micro-CT) to water flow tests and optical microscopy to obtain 3D crack volume analysis, water permeability, and crack widths, respectively. Three binder formulations - a pure cement, a 50 % lime - 50 % cement and a 33 % lime - 67 % metakaolin mix - were selected to test the method's accuracy across different mortars. On average, pure cement samples exhibited the best healing efficiency in all tests, albeit not significantly. Interestingly, neither water flow nor microscopy measurements could be correlated to crack volume changes, suggesting different aspects of selfhealing were captured. Micro-CT analysis provided clarification, revealing that self-healing predominately occurred at the surface. Additionally, the precipitation of self-healing products at the pore-crack interface led to certain pores becoming disconnected from the original crack. Therefore, the measured volume change of the crack appeared to be larger than the actual precipitation of healing products. Given the different limitations encountered on all tests, the use of coupled tests is encouraged for future studies.