In-Depth Evaluation of Novel Condition Assessment Techniques for FRP-Strengthened Concrete Structures

Using fiber-reinforced polymer (FRP) composite materials to externally retrofit civil infrastructure is a viable long-term rehabilitation technique. However, ensuring the structural integrity and performance of the bond line between the composite materials requires cost-effective condition assessment methods. This paper presents a comprehensive study on the implementation of multiple nondestructive testing (NDT) techniques, ranging from inexpensive tools to highly advanced equipment, for detecting and quantifying discontinuities in FRP-strengthened concrete elements. The testing program included six concrete prisms strengthened with multiple layers of carbon-FRP sheets with artificially introduced defects. The following NDT techniques were used for assessment: acoustic tapping, shearography, and two techniques based on infrared thermography. At the microscale, defect size distribution was analyzed using microcomputed tomography (micro-CT) (high-resolution imaging technique) NDT techniques. The results provide valuable insights into interfacial and interlaminar defects, bond quality, and thickness. The study also highlights the challenges in adopting certain advanced NDT techniques for field inspection of externally bonded FRP materials. The findings from this work underscore the importance of data fusion from multiple NDT methods to inform decision-making and maintenance strategies for critical structures.