Fracture mechanics method for mode-iinterface evaluation of FRP bonded to concrete substrates

There is a pressing need for development and implementation of advanced materials and methods for rehabilitation of infrastructure worldwide. To this end, externally bonded fiber-reinforced polymer or plastic (FRP) composites to concrete for repair and strengthening has been proven to be an effective technology, but uncertainty remains with durability and long-term performance of the interface bond, requiring developments for effective testing and analysis methods. This paper describes the favorable attributes and implementation of a new experimental fracture approach known as the single contoured cantilever beam (SCCB) specimen to evaluate fracture energy of the FRP-concrete interface. This study describes the design and fabrication of the SCCB specimen; calibration tests to obtain constant compliance rate change and avoid measurements of crack lengths; and application to fracture tests under Mode-I loading to obtain interface fracture energies for glass fibers bonded to both normal and high-performance concretes. A total of eight specimens for each concrete type were initially tested at time zero, followed by a total of 18 specimens, nine for each concrete type, after being conditioned at 28 degrees C and 50% relative humidity for 25, 50, and 75 days, respectively. The results showed increase in fracture energy with time for the conditioned specimens relative to those tested at time zero, due mainly to continued strength gains of both concrete and bonding resin. The significance of this study is the potential practical application of the SCCB specimen for durability investigations of FRP-concrete interfaces, as will be reported in the future, using changes in fracture toughness as a measure of degradation and leading to development of design guidelines.