Residual Strength of Impact-Damaged CFRP Used to Strengthen Concrete Structures

Although previous research has demonstrated the improvement in performance of reinforced concrete structures enhanced with externally applied carbon fiber reinforced polymers (CFRP), the effect of transverse impact damage on the strength of the CFRP enhancements is unknown, and no guidelines have been provided that describe which impact events warrant CFRP repair or replacement. The impact events, such as dropped tools, collisions, and low-speed projectiles may cause critical damage to the epoxy matrix and fibers that is undetectable through visual inspection. The purpose of this research is to provide insight into the level of transverse impact needed to initiate critical damage in wet layup CFRP enhancements, which will serve as a guideline for inexpensive and immediate damage assessments. To simulate a variety of impact events, impactors (tups) of different sizes and shapes were dropped from several heights. The impacts were performed with a guided drop-weight apparatus, designed to achieve free-fall behavior. The results show that impacts that only cause indention of the FRP surface do not significantly affect the tensile strength, but impacts that cause crushing of the epoxy (seen as whitish areas) can indicate as much as a 63% residual tensile strength. Furthermore, for the test conditions considered, tests showed that impacts with a peak impact pressure greater than 21 MPa (3,000 psi) reduced the tensile strength of the CFRP.