Book Description

Abstract: The new Mechanistic-Empirical Pavement Design Guide (MEPDG) provides a state- of-the-art and practice pavement design procedure that eradicates the AASHTO 1993 empirical design procedure deficiencies. Huge advancements with respect to traffic input, material characterization and environmental impact are incorporated in the MEPDG. The AASHTO 1993 design procedure is based on empirical equations derived from the AASHO Road Test conducted in the late 1950's in a test track in Ottawa, Illinois. The test provided very useful information for the design of pavement at that time. However, with the present advancement in materials and dramatic increase in traffic volumes, this empirical design procedure started to show massive drawbacks. The MEPDG is a more comprehensive design procedure that incorporates sophisticated models for pavement response calculation, material properties variations with respect to environmental conditions and pavement performance predictions. The mechanistic part of the design procedure is the pavement response calculation and the empirical part of the method is the pavement performance prediction. Incorporating these models allows the MEPDG of producing pavement design sections that are cost-effective and perform better than those designed using the AASHTO 1993 design procedure for a given life span. With the initial introduction of the MEPDG in 2004, almost every State Highway Agency (SHA) in the United States and several road authorities around the world exerted efforts to understand and plan to implement the MEPDG according to their own local conditions. It was hence found necessary to explore the new design procedure according to Egyptian local conditions. The objectives of the research is to prepare a body of accurate and readily usable environmental data for Egypt for MEPDG input, compare the effectiveness of both design methods and assess the sensitivity of MEPDG predicted performance with respect to variations in inputs. Weather data files for major Egyptian cities were extracted from available data sources and prepared for direct input in the MEPDG. The preparation of data was done using a computer application especially developed in this research program to comprehensively and rationally complete this task. A comparative study was then done between the two design methods. Five pavement sections were designed using the AASHTO 1993 design procedure and then evaluated using the MEPDG for three traffic levels. These five sections were chosen to best represent the majority of Egypt. A sensitivity analysis was then conducted to investigate the predicted behavior of fatigue cracking and rutting with respect to variations in environmental conditions, traffic levels, AC layer thickness and properties, granular base (GB) layer thickness and subgrade strength. Comparing both design methods revealed that pavements designed under the AASHTO 1993 do not perform equally at the end of their design life. Terminal Present Serviceability Index (PSI) values are different for different traffic levels and locations. Predicted fatigue cracking and rutting showed a similar trend to terminal PSI values. The AASHTO 1993 was also found to over-estimate pavement layers thicknesses. Predicted fatigue cracking showed high sensitivity to design inputs under the scope of the study. Environmental conditions and traffic loading were also found to be the most influential input parameters on the selected pavement performance indices. Unexpected results for predicted rutting lead to further investigation and MEDPG rutting prediction model was evaluated with respect to an Egyptian rutting prediction model. Rutting prediction model adopted by MEPDG produced lower values for permanent strain compare to the Egyptian rutting model and further calibration for the MEPDG rutting prediction model was found necessary.