Development of an Innovative Non-Destructive and Field-Oriented Method to Quantify the Bond Quality of Composite Strengthening Systems on Concrete Structures.

Astrid Billon-Filiot,Marc Quiertant,Romain Maurin,Jean-Marie Hénault,Frédéric Taillade,Jean-Claude Renaud,Karim Benzarti

doi:10.3390/ma13235421

Abstract

Over the last 30 years, structural reinforcement and retrofitting with externally bonded composite materials have proven to be efficient and cost-effective solutions to increase both the safety and the lifespan of civil engineering structures, including nuclear power plants. The effectiveness of the strengthening system highly depends on the level of adhesion between the fiber-reinforced polymer (FRP) composite material and the concrete surface. Therefore, on-site evaluation of the bond quality is critical to assess the performance and predict the durability of the system in place. The direct tension pull-off test is most commonly used to quantify the adhesion level, but this standardized method has many drawbacks. In the present study, it is proposed to evaluate the bond properties by using a nondestructive test (NDT) derived from the standard pull-off test. This innovative test enables the measurement of an interfacial “stiffness” which may be used as a bond quality criterion. This paper gives an insight into the performance of the proposed NDT method, when applied in laboratory conditions to concrete slabs reinforced with bonded pultruded carbon FRP plates (CFRP). Three different epoxy adhesive systems with a broad range of Young’s moduli were used for the specimens’ preparation, in order to vary the stiffness of the concrete/CFRP interface. The purpose was to simulate different levels of interfacial adhesion that could be observed for a single adhesive system. It was shown that the test method was able to detect differences in the interface stiffness beyond experimental uncertainties, and it should therefore enable the detection of differences in the bond quality for a given adhesive system as well. The sensitivity of the NDT was then discussed, and its detection capabilities were predicted for standard field conditions. In the last part, strain measurements were collected during the NDT, thanks to distributed optical fiber sensors (DOFS) embedded in the adhesive joints of the strengthened specimens. An analysis of the strain profiles was found to provide complementary information on the quality of the adhesive bond.

Highlights

IntroductionReinforcement systems based on externally bonded fiber-reinforced polymer (FRP) materials are commonly used [1,2,3]
For civil engineering applications, reinforcement systems based on externally bonded fiber-reinforced polymer (FRP) materials are commonly used [1,2,3]
The size of the area mechanically affected by the ND pull-off loading was rather small, which confirmed that the ND pull-off test could be performed on small test panels

Summary

Introduction

Reinforcement systems based on externally bonded fiber-reinforced polymer (FRP) materials are commonly used [1,2,3]. A high quality of adhesion implies, obviously, that the bond layer does not present macroscopic defects like voids or cracks, which may initiate critical flaws and lead to the premature failure of the assembly. Such defects can be detected using simple nondestructive test (NDT) methods like hammer inspection, or by more sophisticated methods involving mechanical-wave-based techniques (impact-echo [4], acoustic emission, ultrasonic inspection [5] and impedance measurements [6])

Methods

Results

Conclusion