Use of GPR and MASW to Complement Backcalculated Moduli and Design Life Calculations

Nondestructive deflection testing by means of the falling weight deflectometer is one of the most reliable and established methods for evaluating the structural capacity of pavements. However, there are several factors that can influence the moduli values obtained through the backcalculation process and the resulting calculated design life or required overlay thickness. Some of the difficulties associated with backcalculation include constructing a suitable pavement model due to the as-built variations in layer thicknesses in addition to determining the modulus for thin asphalt layers. Many researchers have reported success when using ground penetrating radar (GPR) to determine flexible pavement layer thicknesses. Recently, the Multi-Channel Analysis of Surface Waves (MASW) technique has been shown to provide accurate nondestructive estimates of the in-situ asphalt concrete modulus. In this study, nondestructive deflection testing in addition to GPR and MASW testing was performed along a 200 m test section and across the transverse width of the traffic lane to establish variations in thickness and moduli. Backcalculation was performed with and without GPR thickness data resulting in a 40% variation in modulus. The modulus obtained via GPR data provided a significantly better estimate to the recorded MASW modulus. Using the 1993 AASHTO Guide for Design of Pavement Structures, the difference in modulus and thickness between GPR and non GPR data resulted in nearly a two inch difference in required overlay thickness. The results obtained using the new Mechanistic-Empirical Pavement Design Guide (MEPDG) identified considerable differences in rutting performance, but only minute differences in asphalt fatigue.