Automated and Continuous Monitoring of Freeze-Thaw Damage in Concrete Using Embedded Piezoelectric Transducers

In this paper, we propose to monitor the evolution of damage in freezethaw cycles tests using embedded ultrasonic piezoelectric transducers. The transducers are used in emitter-receiver pairs. Concrete specimens were subjected to 70 freeze-thaw cycles of 12 h in temperature ranges from -20 degrees C to +17 degrees C and the monitoring system automatically and continuously recorded ultrasonic signals every 5 min. With such rich information, it is possible to monitor the difference between recorded signals during freezing and thawing phases, as well as transition times between these two phases. Several indicators were extracted from the recorded signals to evaluate the level of degradation of the concrete, including the traditional wave velocity and the first wave amplitude of the recorded signals as well as Coda wave parameters. The results show that the first wave amplitude is a more sensitive indicator of early freeze-thaw damage than the traditionally used wave velocity. Coda wave interferometry (CWI) also proves to be an interesting and complementary indicator to better understand the freeze-thaw damage mechanism in concrete.