Evaluations of Pavement Thickness and Modulus Using Spectral Analysis of Surface Waves

Currently the Arkansas State Highway and Transportation Department has no non-destructive testing (NDT) device to measure the thickness of various components of pavement systems. When pavement thicknesses are needed in Falling Weight Deflectometer (FWD) analyses and similar pavement life studies they must be determined by physical drilling or coring of the pavement structure. This is very costly alternative which provides only spot measurements at the locations selected for coring. It could also lead to premature pavement deterioration in the vicinity of the coring if the patching of the pavement is not performed correctly. Ideally, pavement thickness would be determined at each location where FWD measurements are made in a non-destructive manner. While several alternative NDT techniques could be used to determine pavement thickness, only one is currently available that can measure pavement thicknesses and simultaneously provide an estimate of dynamic moduli in a cost effective manner. Two NDT techniques that are most commonly used to make thickness measurements are Spectral Analysis of Surface Waves (SASW) and Ground Penetrating Radar (GPR). GPR has been used with great success in areas where there is no ground water table present and concentrations of plastic fines are very low. While the GPR device can make rapid measurements, the presence of either of these complicating conditions severely affects the accuracy of the GPR device in determining pavement thicknesses. Additionally the GPR device only measures changes in material conductivity to determine interfaces and does not do a good job in predicting the absolute value of that conductivity which could be correlated to the modulus or density of the material in the sampled cross-section. The use of SASW to determine thickness and modulus of pavement sections has been widely reported for over 15 years. Its use has been limited by highway departments, however, because the existing SASW hardware is cumbersome and time consuming to set up in the field and the technique requires highly trained technicians to interpret the results. The goal of this research is to create a truly portable and self contained device with associated software that would make the process of determining pavement thicknesses quick, easy and accurate for moderately trained highway personnel. Such a device would have the potential for replacing the FWD device altogether.