Research Report: Inspecting FRP Composite Structures with Nondestructive Testing

Structural plastics and composites such as fiber reinforced polymers (FRP) represent a broad class of materials finding increased use in bridge and highway related applications. These materials offer important advantages, including corrosion resistance and formability. A number of bridge-related research and construction projects involving composites have begun at TxDOT and in other states and countries in the recent years, demonstrating the rapidly expanding use and interest in these materials.

As the use of composites is implemented in TxDOT structures, TxDOT must conduct quality assurance testing to ensure structural integrity of the products, much in the same way TxDOT already does with steel and composite structures. Nondestructive testing, especially the acoustic emission method (AE) offers great promise for inspecting FRP structures to ensure integrity. AE testing is used very successfully in quality assurance testing of pressure vessels, and research is needed to adapt this method to the type of composite structures that will be used in highway applications and to consider other methods that might be suitable to structural composites.

This research involved testing of large structural elements to determine the effectiveness of AE and other methods in quality assurance testing of composite structural elements for highways and to develop a protocol for quality assurance testing that could be applied to actual composite members. Damage was induced in these structures so that performance and results could be evaluated under different conditions. Secondary bonds and connections were tested and joints in various locations were evaluated.