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 oil 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. (c) 2007 Elsevier Ltd. All rights reserved.