Detecting debonding flaws at the epoxy-concrete interface and evaluating deterioration under outdoor exposure condition of near-surface mounted CFRP strengthening beams using the Impact-echo method

• Main Authors: Chia–Tsung Hsieh, 謝嘉聰
• Other Authors: 林宜清
• Format: Others
• Language: zh-TW
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/53ygyv

博士 === 國立中興大學 === 土木工程學系所 === 104 === This thesis discusses the feasibility of using the impact–echo method (IE method) to evaluate the debonding flaws at the epoxy–concrete interfaces and the deterioration under outdoor exposure conditions of near-surface mounted carbon fiber reinforced polymer (NSM CFRP) strengthening beams. To clarify the characteristics of the stress wave propagation caused by impact forces on NSM CFRP structures, both numerical and experimental studies were performed on the bar-like epoxy specimens with and without CFRP bars and NSM CFRP strengthening beams with various debonding statuses at the epoxy–concrete surfaces. The numerical analysis revealed that the impact responses in the bar-like epoxy specimens with and without CFRP bars were initiated by the first few cross-sectional vibration modes, and the IE test verified this result. The numerical analysis and experimental study indicated that for NSM CFRP strengthening beams without debonding flaws, the impact response spectra each featured one high-amplitude peak at the fundamental mode frequency, referred to as the dominant frequency. When debonding occurred at the epoxy–concrete interfaces of NSM CFRP strengthening beams, the impact responses revealed that the dominant frequencies decreased significantly. When the dominant frequencies instead increased to levels nearly equal to those of the fundamental frequencies of the bar-like epoxy specimens, the epoxy thoroughly debonded from the concrete interfaces. Finally, the strengthening surfaces of the NSM CFRP strengthening beams were exposed to outdoor environments; IE and loading tests were conducted when the beams were exposed to the outdoor environment for 4, 8, 12, and 48 months. The result indicated that prolonged outdoor exposure generated the debonding flaws at the epoxy–concrete interfaces, which caused a significant decrease in the dominant frequencies of the IE spectra. The loading test result revealed a decrease in the load-carrying capacity due to debonding damages at the epoxy–concrete interfaces. According to the characteristics of the aforementioned impact responses, the IE method is capable of detecting the debonding flaws at epoxy–concrete interfaces and can evaluate the deterioration of the NSM CFRP strengthening beams under prolonged outdoor exposure.