Evaluation of Ground-Penetrating Radar for Detecting Defects in Concrete at Early Ages (05-0936) - MP-23
Sathaporn Lek-udom, Cleveland State University
Paul A. Bosela, Cleveland State University
Norbert Joseph Delatte, Cleveland State University

Ground-coupled radar systems provide a radiated pulse with more energy to penetrate deeper than air-coupled radar. The classical problem of Ground Penetrating Radar (GPR) data interpretation is caused by its oscillatory nature as well as the complicated nature of the test structure. Other subsurface sensing and imaging techniques such as, Impact-Echo (IE), Ultrasonic (UT), and Infrared Thermography (IT) methods, are often recommended as complementary methods to GPR. The purpose of this study is the use of a ground-coupled radar system for detecting specific defects in early age concrete test slabs. In addition, the study compares the results with those obtained using the IE method. Fourteen 1.14 x 1.14 x 0.286 m. (45 x 45 x 11-1/4 in.) test slabs with various basic simulated defects were cast. At various points during the cure cycle, the wave speeds were measured using the GPR device and the compressive strength test was measured. The results showed that GPR was able to detect depth of the plain concrete slab after 21 days. Also, the moisture content of the concrete affects the GPR results. The presence of top rebar, an air gap on top of the rebar, air voids and honeycomb beneath the top rebar were detected but an air gap between the bottom rebar, the presence of bottom rebar, and the location of the bottom of the slab having multiple layers of rebar could not be identified. The IE method was recommended as a complementary method.