Real-Time Structural Health Monitoring of Concrete Using the Non-Linear Ultrasonic SPC-I Technique

Continuous monitoring is the most desirable approach for ensuring the health/integrity of concrete structures. It is particularly difficult to monitor concrete structures due to their non-linear nature and random distribution of constituents. Evaluation of properties of concrete as a heterogeneous composite has been performed by various techniques ranging from highly sophisticated physicochemical characterization to mechanical tests. The linear ultrasonic techniques generally measure the time-of-flight or the attenuation of a propagating wave. In recent years, the non-linear ultrasonic techniques have been proven to overcome some of the challenges during concrete curing monitoring. In this investigation, ultrasonic testing is carried out on concrete prism specimens. The specimens are placed in a 4-point loading machine and stressed until failure. Ultrasonic signals are propagated through the specimens using tuned PZT transducers in a transmission mode. The ultrasonic testing is carried out in a continuous real-time way to allow real-time prediction of specimen deterioration before its catastrophic failure. The results show that the traditional linear ultrasonic techniques (such as the first-arrival technique and signal attenuation) cannot detect concrete deterioration before its failure . However, the non-linear ultrasonic technique, i.e., the Sideband Peak Count-Index (SPC-I), is sensitive enough to detect concrete deterioration before its failure. Therefore, the SPC-I technique can be deployed for continuous reliable monitoring of concrete structures.