On the use of non-destructive testing for the measurement of self-healing in lime-based mortars

The study of self-healing construction materials has increased in popularity over the last couple of decades. Nevertheless, most research has predominantly focused on cement-based materials and work on other type of binders such as lime-based mortars remains rather limited. Despite the multiple testing methods available to assess the efficacy of self-healing, these techniques are not always suitable for materials of different mechanical strengths and  behavior. In order to further expand the knowledge on self-healing beyond the high-strength cement-based materials, self-healing has been studied on low-strength binders. Here it is shown how the use of non-destructive testing with ultrasonic pulse velocity (UPV) can help determine the self-healing capacity of low-strength mortars. A hydrated-lime:metakaolin mortar mix and cement mix were cast and damaged after 7 days of curing. The samples were damaged under compression using 70 % of the average compressive strength. Before and after damaging, the samples were tested by UPV and superficial cracks were studied by microscopy. The samples were then placed under wet-dry cycles of 1 hour wet/23 hours dry or submersion for 28 days and tested again. As healing proceeded, an increase in the UPV was observed. Microscopy measurements confirmed visually the self-healing of cracks in all samples. The mechanical strength of both formulations was similar after healing when compared to a non-damaged and non-healed sample. These results show the necessity for techniques that are tailored to the mechanical nature of the different studied materials and opens up the possibility of further investigating self-healing in a wider variety of construction materials.