Monitoring the self-healing evolution of cementitious mixtures with superabsorbent polymers through air-coupled ultrasound

Self-healing cementitious composites including superabsorbent polymers (SAPs) have been studied as an alternative to costly, labour-intensive repairs. Whereas the assessment of the healing ability can be performed through a variety of testing methodologies, an in-situ evaluation requires the adoption of a non-destructive technique in order to maintain the present infrastructure. Additionally, the assessment method should be easily applicable for reasons of time efficiency. Thanks to their sensitivity to the elastic properties, ultrasonic waves have enabled the evaluation of the regained mechanical performance, without interfering with the microstructure. While coupled ultrasonic measurements are an established procedure, the use of air-coupled ultrasound provides the advantage of omitting the transducers’ coupling. As the coupling is a time-consuming task and imposes a certain variability between performed measurements, the adoption of air-coupled ultrasound would lead to a significant improvement of the evaluation method. Therefore, a comparison between both techniques using various mortar mixtures was performed.