Small Beam Bond Test Method for CFRP Composites Applied to Concrete

This paper presents the development of a test method that can be used to test the bond capacity of carbon fiber-reinforced polymer (CFRP) composites bonded to concrete. The rationale for the selection of the test method is described along with the results of the experimental work used to refine the test configuration and procedures. The research objectives were to develop a test method that (1) can be used to evaluate the durability of the FRP-concrete bond (adhesion failure mode); (2) facilitate multiple replicate for statistical validation; (3) is simple to conduct; and (4) provides comparative results that are easy to interpret. The method utilizes a small concrete beam modeled after the modulus of rupture test, which is typically used to measure concrete tensile strength. A number of small beam sizes and loading configurations were considered during the investigation. The final recommended specimen configuration is $4\times 4\times 14\text{in}\text{.}$ $\left(100\text{mm}\times 100\text{mm}\times 356\text{mm}\right)$ beam with a half-depth saw cut at midspan. A 1 in. (25 mm) wide by 8 in. (203 mm) long CFRP strip is applied to the tension face of the beam over the saw cut. The specimen is loaded until failure with a single concentrated load at midspan over a 12 in. (305 mm) span. For durability testing, samples are prepared with the same materials and exposed to the desired accelerated conditioning protocol. Companion unexposed samples are also tested and the relative decrease in capacity is reported as the load to failure of the exposed specimen to that of the control specimen.