Far-field radar NDT technique for detecting GFRP debonding from concrete

A radar nondestructive testing (NDT) technique using an airborne horn antenna operating in the far-field condition is developed for detecting damages such as debonding and concrete cracking in glass fiber reinforced polymer (GFRP)-wrapped concrete columns. The far-field airborne radar (FAR) NDT technique is advantageous for distant measurement in practical applications where contact/near-contact measurement becomes an issue. In this technique the radar antenna operates in inverse synthetic aperture radar (ISAR) mode. Laboratory measurements at the frequency range 8–18 GHz are made on artificially damaged GFRP–concrete specimens for a preliminary validation of this technique. Collected frequency–angle measurements are further processed by the fast backprojection algorithm to render range–cross-range imagery for damage detection. From the reported measurements and imaging results the proposed FAR NDT technique is conceptually validated; the potential of this technique is shown in identifying defects and debonding in the GFRP–concrete interface regions of the concrete columns wrapped with these composite materials.