ABSTRACT
Empirical pavement design methods resulting from the AASHO Road Tests are still the most adopted around the word. Since their development, asphalt properties have greatly improved and advances in the theories of mechanics enhanced the ability to predict the response of pavement materials. However, layer coefficients for asphalt mixtures have not been updated to accommodate these advances and pavement structures are currently designed using inaccurate values. The objective of the study presented in this paper was to present a four-step procedure for determination of structural layer coefficients for asphalt mixtures, considering their viscoelasticity and temperature-dependency. Layer coefficients were calculated for thirty-eight (38) HMAs and most of the values were above the single layer coefficient suggested in the original design guide. Moreover, the variability of the new values indicates the ability of the procedure to discern the behavior of different materials. Five HMAs were randomly selected for a simple design exercise of two structures generally used in Michigan for low and high traffic volume roads. The original AASHTO 1993 layer coefficients were initially adopted, then the two structures were re-designed using the new structural coefficients and the AASHTOW are Pavement ME design software (Level 1 analysis). Results indicate that the thinner pavement structures obtained using the new structural coefficients are still overdesigned if compared with those obtained with the latest and more accurate Pavement ME design methodology.
