AUTOMATED PAVEMENT SUBSURFACE PROFILING USING RADAR: CASE STUDIES OF FOUR EXPERIMENTAL FIELD SITES

Abstract

Accurate knowledge of pavement layer thicknesses and material properties is important to pavement management. Often this information is unknown or records are inaccurate, inaccessible, or out of date. The traditional method for obtaining pavement layer data is core sampling, which is time-consuming, labor-intensive, and intrusive to traffic; it also provides information only at the core location. The capability of ground-penetrating radar to provide accurate and continuous pavement layer thickness and property information has been investigated. Four Texas Strategic Highway Research Program asphalt pavement test sites were tested with radar. The accuracy of the radar predictions for asphalt thickness was within plus or minus 0.32 in. using the radar data alone, and within plus or minus 0.11 in. when one calibration core was used per site. The accuracy of the radar predictions for base thickness was within plus or minus 0.99 in. The nominal layer thickness ranged from 1 to 8 in. of asphalt and 6 to 10 in. of base. The actual asphalt layer thickness was shown to vary by more than 20% from values assumed from prior records and earlier cores. These variations have been shown to lead to errors of up to 95% in base moduli back-calculated from falling weight deflectometer data. The radar results were shown to be repeatable over time and independent of survey speed at up to 40 mph. The radar data were analyzed automatically using software that operated directly on the raw radar waveforms and produced numerical layer thickness profiles. The resulting predictions were correlated with direct in situ measurements and core and material samples. The results of this project have shown that ground-penetrating radar data, when properly analyzed, can provide highly accurate measuremnets of pavement layer properties for project- and network-level applications.