Evaluation of concrete self-healing with different fly ash contents and cracking ages by means of ultrasonic pulse velocity and compressive strength tests

This study aims to analyze the self-healing of concretes with different fly ash contents. The concrete specimens with different amounts of fly ash in the composition of the cements were subjected to cracking at 7 days and 28 days of age. The cracking was generated by the application of 80% of the rupture load by compression for 2 min. After cracking, twelve wetting and drying cycles were performed to favor the development of self-healing. Each 7-day cycle (168 h) consisted of 78 h of immersion in lime-saturated water and 90 h of exposure to the laboratory environment. The analysis of the phenomenon occurred through the ultrasonic pulse velocity and compressive strength tests at the cracking dates and after the last wetting and drying cycle. In the samples submitted to cracking at 28 days of age, the reductions in ultrasonic pulse velocity after the cracking process was directly proportional to the fly ash content in the concrete. The reduction in ultrasonic pulse velocity due to cracking was 3.7% for cement with higher fly ash content, while cement without the presence of this mineral addition had a reduction of 1.9%. The compressive strength test was not an adequate technique to visualize the effects of concrete self-healing. The main contribution of the study was to prove that a non-destructive test can be applied to monitor the concrete self-healing. Also, the study showed the importance of crack age in the efficiency of self-healing in concretes with different fly ash contents. © 2021, The Author(s), under exclusive licence to Springer Nature Switzerland AG part of Springer Nature.