219 / 2022-06-10 15:01:07

Detection of CFRP-concrete bond defects by using electrical measurements

CFRP-concrete,Interface,Defect Detection,Electrical Measurement,Parallel Circuit

To extend the service life of a reinforced concrete (RC) structure, carbon fiber reinforced polymer (CFRP) laminates with a high strength to weight ratio and excellent corrosion resistance are extensively used to strengthen deficient structures. However, due to the poor construction, overloading or harsh environments, a series of defects at the CFRP-concrete interface may cause serious structural safety problems. In this study, a detecting protocol based on the electrical measurement is proposed to effectively locate defects at the CFRP-concrete interface. Since the electrical conductivity of bonding defects is significantly different from the intact region in the CFRP-concrete interface, the electrical measurement could be used to detect the bonding defects. It was found that the current pathway in the interfacial defects could be equivalent to a parallel circuit (Fig. 1), which can help to assess detailed information about the defects.



Based on the equivalent circuit, an analytical model (Fig. 2) was established to assess the number, location and size of defects by analyzing the resistance distribution curves (Fig. 3). The length of defects had been quantified by determining a reliable defect edge coefficient mathematically and statistically (Fig. 4). The investigation of high-efficiency electrode arrangement was also carried out. Using comparatively small electrode intervals and distances between electrodes and the bonding interface could improve the detection precision. To reduce the interference effect from the steel reinforcement, the electrodes should be arranged as far as possible from the stirrups. Additionally, it was also found that the defect severities could be assessed by the comparison of minimal resistances. The outcomes of this study can be served as a possible methodology for evaluating the bond defects between CFRP and concrete.



Meanwhile, to apply the proposed method in practice, steel reinforcement's quantified effects on detecting accuracy were determined. Since the reinforcement cage in concrete would change electrical field distribution in concrete, the variation of the electrical field leads to the unexpected current pathway that flowed from defects to electrodes, which may change the resistance distribution curves. Experimental results indicated that the number and location of longitudinal reinforcement had less impact on detecting the number and location of defects (Fig. 5). In the contrast, the stirrups would result in the misidentified defect locations. Because of this, the analytical model was modified to assess the detailed information of defects and showed satisfactory accuracy.



The detection methodology based on the electrical measurement is promising to continuously monitor the bond performance of the CFRP-concrete interface under the hygrothermal environment. However, there are some limitations that remain and further studies are needed for the practical implementation of this proposed method. For example, the relationship between mechanical properties and electrical responses of adhesive under hygrothermal aging is not developed yet. Meanwhile, to achieve non-destructive detection, the embedded depth of electrodes in concrete should be investigated so that the use of external-paste electrodes on the surface of the concrete can be realized. Also, it is important to visualize the electrical results in the future, which is necessary to achieve the resistivity tomography of the bond layer.