Technical Approach for Pavement Evaluations
EPIC offers two proprietary pavement evaluation services, Pavement Voids Analysis (PVA) and Pavement Composition Analysis (PCA). From PCA, two additional services were developed -- Pavement Thickness Analysis (PTA) and Relative Compaction Profile (RCP). All services are based on sophisticated, automated analysis of ground penetrating radar (GPR) signals collected using innovative GPR hardware. The new technology is such a departure from the traditional uses of GPR that it is referred to by the trademark name, Hyper Optics, meaning that the wavelength of the electromagnetic waves used in the scanning traces is longer than visible light waves. The following paragraphs summarize the use of Hyper Optics in pavement evaluation.
Hyper Optics uses the basics of electromagnetic theory with innovative system identification and mathematical modeling to give new meaning to existing GPR signals. The first step in getting more information from the GPR is to engineer the hardware to collect a "clean" signal by addressing such issues as noise-to-signal ratio, jitter, amplitude stability, temperature stability, and bounce. Second, as with any scientific instrument, you must calibrate the radar. Third, you must have software capable of analyzing signals to recognize the patterns that occur when interlayer voids are present (PVA) and to account for signal variations due to the relative amounts of air, liquid, and solids in the layer (PCA). Using a successive approximations approach, the PCA software seeks convergence of the measured trace to one of 6 models. Material properties are extracted from the model after convergence.
From PVA, EPIC provides the pavement owner with a color-coded voids map of the scanned area covering full lane width. The map provides the GPS coordinates, depth, and volume of voids.
From PCA, EPIC provides the pavement owner with a color-coded map depicting a selected material property. For example, maps can be produced which show layer thickness, asphalt content, total unit weight, percent air, voids in the mineral aggregate, permeability, evaporable water content, and porosity. In addition, a Relative Compaction Profile (RCP) map can be produced without taking the calibration and verification cores needed for the other properties cited.