Air-coupled ultrasonic mapping of stimulated autogenous self-healing and repair effectiveness within concrete mixtures

Due to the high risk of cracking, the adequate repair of concrete structures has become equally important to the design of cementitious mixtures. As these repairs should provide a certain level of safety to the user, the assessment of the regained performance needs to be confirmed. Air-coupled ultrasound combines a non-destructive character together with a fast and easy application. Within the present study, two main objectives are pursued. One is the use of air-coupled receivers as a step towards a fully non-contact methodology. Additionally, the effectiveness of air-coupled ultrasonic mapping is applied to both self-healing mixtures and manually repaired specimens. Additionally, two different ultrasonic frequencies are adopted. The results show that air-coupled ultrasonic mapping enables to monitor the processes of cracking, self-healing and repair within the entire cross-section through a point-by-point measurement. Moreover, the use of different frequencies demonstrates the increased sensitivity of the higher frequencies to follow-up these mechanisms. Lastly, from the material point of view, the mixture with 1% SAP revealed the highest self-healing capacity, whereas the manual repair through polyurethane was superior to all self-healing blends.