Self-healing assessment of cementitious mortars through air-coupled ultrasound

Abstract

The adoption of self-healing cementitious materials has gained attention as an alternative to costly and labour-intensive manual repairs. Cementitious blends possess an inherent ability to repair formed cracks through so-called autogenous healing. Whereas the efficiency of autogenous healing remains limited as moisture needs to access the cracks, the healing capacity can be improved through the inclusion of superabsorbent polymers (SAPs). To encourage the use of these self-healing blends within the construction industry, an assessment of the healed state is necessary to ensure a structure’s safety. The requirements for such evaluation method comprise the ability of assessing the regained mechanical performance, while maintaining the structural capacity of the member under study. A non-destructive method that has proven its potential is the application of ultrasonic waves, which are sensitive to the elastic properties of the material they travel through. Coupled ultrasound is currently most often used, while air-coupled ultrasonic measurements allow to reduce the occurring coupling variability. In this study, the self-healing evolution of cementitious mixtures with and without SAPs was assessed through coupled and air-coupled ultrasound. A comparison between both techniques confirmed the potential of air-coupled ultrasound, paving the way for automated self-healing evaluations.