Climatic Considerations in New AASHTO Flexible Pavement Design

Abstract

This research is undertaken to study and assess carefully the effect of climatic factors on the new American Association of State Highway and Transportation Officials (AASHTO) design for flexible pavements. Climatic factors considered include seasonal changes in the subgrade moisture content and the annual variations in the ambient temperature. Through a sensitivity analysis of the new AASHTO equation, the change in the structural number required to offset a reduction in the subgrade resilient modulus due to an increase in moisture content is evaluated; an adjusted structural number is thus calculated. The impact of the ambient temperature on the asphalt‐concrete layer is evaluated by considering the interactive result of temperature and fatigue damage; the concept of weighted effective dynamic modulus is thus used. A rational method is proposed to select the appropriate asphalt grade to minimize both low‐temperature cracking and rut depth. By knowing the asphalt grade and the mix properties, the weighted, effective asphalt‐layer coefficient is calculated. An example to illustrate how climatic considerations can be incorporated into the AASHTO design is presented.