Non-Destructive Identification of GFRP Rebar Using Spatial Averaging of GPR Radargrams

This study presents the development of a non-destructive Glass Fiber Reinforced Polymer (GFRP) rebar identification technique for reinforced concrete structures based on Ground Penetrating Radar (GPR) B-scan images (radargrams). Conventional steel rebars are vulnerable to corrosion, and the consequential weakening of concrete from the inside can lead to the catastrophic failure of concrete structures. In addition, even when corrosion is detected, the damage is far advanced, leading to costly repairs and maintenance. Recently, GFRP rebars have been gaining interest because of their lightweight, non-corrosive, and high tensile strength characteristics, combating the limitations of conventional steel rebars. GPR is one of the non-destructive inspection techniques for concrete structures using electromagnetic waves. The existence, location, and diameter of steel rebars can be identified using the electromagnetic waves reflected from steel rebars owing to the significant differences in dielectric constants between concrete and steel rebars. However, for GFRP rebars, it becomes challenging because the dielectric constant difference between GFRP rebars and concrete is much less than that of steel rebars. Thus, in this study, the GPR-based GFRP rebar identification technique is developed by averaging multiple radargrams obtained from adjacent line scanning paths (spatial averaging). Concrete specimens were fabricated by inserting actual GFRP rebars with various diameters. Then, the existence and location of the GFRP rebars were estimated using GPR radargrams. The performance of the developed technique was evaluated qualitatively by calculating the standard deviation of the noise component. The results indicate that GFRP rebars are more clearly identified using the developed technique.