Glass fiber-reinforced polymers (GFRPs) have received increasing attention in recent years\ndue to their overall performance of light weight, low cost and corrosion resistance, and they are\nincreasingly used as reinforcement in concrete structures. However, GFRP material has low elastic\nmodulus and linear elastic properties compared with steel bars, which introduces different bonding\ncharacteristics between bars and concrete. Therefore, a reliable monitoring method is urgently needed\nto detect the bond slip in GFRP-reinforced concrete structures. In this paper, a piezoceramic-based\nactive sensing approach is proposed and developed to find the debonding between a GFRP bar\nand the concrete structure. In the proposed method, we utilize PZT (lead zirconate titanate) as\ntwo transducers. One acts as an actuator which is buried in the concrete structure, and the other\nacts as a sensor which is attached to the GFRP bar by taking advantage of machinability of the\nGRRP material. Both transducers are strategically placed to face each other across from the interface\nbetween the GFRP bar and the concrete. The actuator provokes a stress wave that travels through\nthe interface. Meanwhile, the PZT patch that is attached to the GFRP bar is used to detect the\npropagating stress wave. The bonding condition determines how difficult it is for the stress wave\ntraveling through the interface. The occurrence of a bond slip leads to cracks between the bar and\nthe concrete, which dramatically reduces the energy carried by the stress wave through the interface.\nIn this research, two specimens equipped with the PZT transducers are fabricated, and pull-out tests\nare conducted. To analyze the active sensing data, we use wavelet packet analysis to compute the\nenergy transferred to the sensing PZT patch throughout the process of debonding. Experimental\nresults illustrate that the proposed method can accurately capture the bond slip between the GFRP\nbar and the concrete.
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