Comparison of AASHTO 1993 and MEPDG considering the Egyptian climatic conditions

Abstract

The current flexible pavement design system in Egypt was adopted primarily from the AASHTO 1993 Design Guide. It is an empirical design method based on the results of the late 1950s AASHO Road test with many limitations. Thus, the Mechanistic-Empirical Pavement Design Guide (MEPDG) which is now called Pavement ME Design was developed to overcome those limitations. Unlike the AASHTO 1993 method, MEPDG considers the variation in moisture and temperature on the mechanical properties of the pavement layers. The main objective of this paper is to compare the AASHTO 1993 and MEPDG methods based on a recently developed Egyptian climatic data. The AASHTO 1993 method was used to design the thickness of a typical flexible pavement structure, using two different levels of traffic (low and high) and two different types of subgrade strength (weak and strong). Then, the AASHTO 1993 designed structures were simulated with MEPDG to predict performance over 20 years of service life. The comparative analysis of AASHTO 1993 design guide and MEPDG revealed that although all pavement sections in this study were designed with the AASHTO 1993 method for the same serviceability loss, they exhibited different performance as predicted by MEPDG. The variation of the MEPDG-predicted performance of the AASHTO 1993 designed pavement structures increased with the increase in traffic level and decrease in the subgrade strength. This variation was different for different climatic conditions. For the Egyptian conditions, the predominant distress was rutting. Finally, the climatic conditions showed a significant effect on distress occurrence and time to failure, especially the AC rutting.