The objectives of this research were to determine the feasibility and practicality of pulsed electromagnetic wave (radar) technology for locating and measuring voids beneath reinforced and nonreinforced concrete pavements and to identify or develop techniques for processing the radar's return signals. The Georgia Institute of Technology researchers adapted available radar equipment, originally developed for the detection of nonmetalic mines, for the location of voids beneath pavements. Mathematical models and algorithms were developed for analyzing return signals from pavements, base materials, and voids; and a microcomputer was selected for processing the data. The radar equipment and data processing system were then evaluated by laboratory controlled measurements and field measurements conducted on a specially constructed outdoor test lane 72 ft long by 8 ft wide of 9-in. thick portland cement concrete, with and without steel, reinforcing over a dense-graded aggregate base. The findings of this study indicate that it is feasible and practical to use radar technology for locating and measuring voids beneath pavements, both reinforced and nonreinforced. It has also shown that the signal returns can be processed in the field by microcomputer with the resulting capability of longitudinal void location within 6 in. and void depth determinations up to 8.5 in. with a standard deviation of less than 0.5 in. Temperatures above 70F limit the measurement capability of the equipment used in the study. Prior to extensive field use, the influence of environmental conditions, such as high temperatures, should be documented, and the equipment should be designed and built to withstand normal field handling and transportation conditions. (Author).
Abstract