Assessment of the CFRP–Concrete Interface Integrity of Original Champlain Bridge Diaphragms through Nondestructive and Semidestructive Testing

Abstract

Externally bonded fiber-reinforced polymer (FRP) composites have been widely adopted for the rehabilitation of aging bridge infrastructure in recent decades. The major reasons for the utilization of these materials in bridge rehabilitation include strength, durability, lightweight nature, design flexibility, and quick installation. However, deterioration of the bonded interface between the concrete substrate and the FRP—or between individual layers of a multilayer composite—can significantly impact the structural performance of the strengthened member or system. Therefore, it is necessary to evaluate the effectiveness and accuracy of condition assessment techniques to ensure satisfactory performance over the intended service life of the structure. This paper presents a visual inspection and detailed assessment of three full-size diaphragms from the Champlain Bridge in Canada. The diaphragms were strengthened with externally bonded carbon fiber–reinforced polymer (CFRP) sheets 5 years before the bridge was decommissioned as a result of extensive degradation after 57 years in service. The condition assessment includes nondestructive (acoustic tapping and infrared thermography) and semidestructive (direct pull-off) testing to identify surface and subsurface issues including CFRP delamination, material incompatibility, discoloration due to corrosion, interfiber cracks, and fundamental problems arising from the construction of the bridge diaphragms and installation of the CFRP. The results of 490 pull-off tests, comprising the largest single database of its kind to date, generally confirmed the results of nondestructive tests that aimed to locate hidden defects behind the strengthening layers. Microscopy of failed surfaces provides additional insights into the condition of the bond line in defective regions. Premature deterioration of bridges is one of the critical challenges faced by the engineering sector in Canada. One such structure is the Original Champlain Bridge in Montreal, which exhibited signs of significant damage to structural components including the girders, deck, diaphragms, and foundation elements. Following a series of extensive but ultimately unsuccessful rehabilitative measures, the historic Champlain Bridge was eventually replaced at a cost to taxpayers of over $4 billion (CAD). The primary goal of this study is to investigate and understand the performance and integrity of the carbon fiber–reinforced polymer (CFRP) strengthening technique applied to three diaphragms in the bridge through various nondestructive and semidestructive methods. Even though CFRP is commonly used to strengthen bridges globally, comprehensive studies on its long-term bond performance are lacking from the literature. This paper presents findings from an assessment of the condition of the CFRP strengthening system using visual inspections and nondestructive testing (NDT), followed by semidestructive direct tension pull-off tests on one diaphragm. The outcomes of this work will be beneficial in understanding the advantages and limitations of various NDT techniques for assessing damage in critical concrete members strengthened with CFRP.