Design Comparisons Using the New Mechanistic-Empirical Rigid Pavement Design Guide

Traditionally, pavement design has been based on empirical observations and extrapolations from the AASHO Road Test from the 1950s. However, due to changing materials, loadings and highway needs, these observations and extrapolations become more and more obsolete in the current design method. The forthcoming Design Guide under development in NCHRP Project 1-37A introduces a new mechanistic-empirical (M-E) pavement design method. M-E design uses basic engineering mechanics as well as performance observations to create functions that should more accurately predict the distress of a pavement structure over its design life. When any new design method is developed, there is a need to compare the new approach versus existing practice. The purpose of this research was to compare the new M-E approach versus an existing empirical methodology, the 1993 AASHTO Design Guide, to determine what impact the new approach has on rigid pavement design in terms of final design slab thickness. This paper documents the process of comparing the new M-E design approach to the existing AASHTO method. Design comparisons were executed for 125 different sets of conditions and it was found that slab thicknesses from the new design approach were typically 9 percent thinner when using the new M-E Design Guide