"Climatic Consideration in the New AASHTO Equation for Flexible Pavements", Adnan A. Basma and T. I. Al-Suleiman, American Society of Civil Engineers, Transportation Engineering Division, ASCE, Vol. 117, No. 2, Mar./Apr. 1991, pp. 210-223.


This research was undertaken to carefully study and assess the effect of climatic factors on the new 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 structure number required to offset a reduction in the subgrade resilient modulus due to an increase in moisture content was evaluated, thus, an adjusted structure number is calculated. The impact of the ambient temperature on the asphalt concrete layer was evaluated by considering the interactive result of temperature and fatigue damage, thus, the concept of weighted effective dynamic modulus was 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.

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