MODE I FATIGUE AND FRACTURE OF THE CARBON FIBER REINFORCED POLYMER TO CONCRETE BONDED INTERFACE
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Abstract
As wet, lay-up fiber reinforced polymers (FRP) continue to gain popularity in the redesign and retrofit of reinforced concrete structures; it becomes imperative to fully define the interaction between these materials. Until recently, the main body of FRP research focused on the flexural and shear strengths of the FRP to reinforced concrete system. However, in order to fully determine the capabilities of the structural system, the ability of the FRP to reinforced concrete bond to transfer the loads must be thoroughly investigated. The preliminary research on defining the behavior of the FRP to concrete bond (deemed the interface in earlier studies) primarily used two types of testing methodologies, the double cantilever beam (DCCB) and the three point bending beam. Recently, the Single Contoured Cantilever Beam (SCCB) was proposed for materials that exhibit brittle failure and are weak in tension. The overreaching goal of the current study is to better define the behavior of the bonded interface of reinforced concrete and carbon fiber reinforced polymers (CFRP). The study will utilize the surface profile 3 (SP 3) as the finished substrate surface and ascertain its effect on the system as it pertains to Mode I fracture and fatigue. The work is presented as three main contributions (journal articles) that address fracture of the concrete to CFRP bonded interface, an analytical model (FE) of the SCCB system, and fatigue of the concrete to CFRP bonded interface. A limited study on durability of the interface subjected to Mode I fatigue is also presented in Appendix B. In Chapter 2, the fracture behavior of the bonded interface using the SP 3 surface profile is investigated. Nine specimens with varying compressive strengths were tested to failure. The analysis shows that the critical strain energy release rate is a function of both the compressive strength of concrete and the mix design. A comparison of the results to past works was utilized to validate the current study results. The third chapter presents an analytical study (finite element) for fracture of the concrete to CFRP bonded interface. The model utilizes the ABAQUS® defined cohesive element to model the delamination of the interface. The results illustrate the ability of the cohesive element to effectively model the interface with a two percent difference in critical load between the model and the lab results. The fourth chapter provides a foundational work on the fatigue life of the concrete to CFRP bond interface. For this objective, the SCCB was subjected to a cyclic loading of multiple loads for a load ratio of 0.5 and a frequency of five hertz. The results were then used to formulate a modified Paris Law equation for the prediction of fatigue life for the 0.5 load ratio and five hertz frequency. The resulting analysis provided the material constants of B and m as 2 x 10-8 and 3, respectively. Additionally, it was discovered that while shallower than fracture, the failure occurred predominantly in the substrate.