Minnesota Department of Transportation
The Minnesota Local Road Research Board (LRRB) funded a project to evaluate the usefulness of ground-penetrating radar (GPR) in evaluating Minnesota roads. A literature search was first performed to review the applications of ground-penetrating radar (GPR) to highway applications. These applications include calculating layer thickness, estimating asphalt density, determining aggregate base moisture content, identifying stripping within asphalt layers, detecting air voids and vertical cracks, identifying subsurface anomalies, and analyzing rutting mechanisms. The relative accuracy of using GPR as opposed to traditional field tests was assessed. A simple laboratory calibration was performed to estimate the thickness of a concrete slab to within 10%. Finally, a sensitivity study was performed to determine the dependence of various output parameters (minimum layer thickness, maximum depth of penetration, horizontal resolution, reflection coefficients, layer thickness, and air void thickness) on input parameters (antenna frequency and dielectric constant). GPR was successful in identifying total asphalt thickness on CSAH 61 in Pine County, and moderately successful in determining base thickness and identifying the underlying, original concrete roadway in select locations. The surveys were not successful in differentiating asphalt course thicknesses. The surveys also identified potential regions of stripping. GPR was not successful in locating near-surface bedrock or peat deposits on CSAH 48 in St. Louis County, because of the presence of a geo-textile membrane.
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