The whole process must be repeated several times in order to optimise the thicknesses of each layer and this may need to be repeated to investigate different pavement types. Each layer is given a Structural Number, and the total of the Structural Numbers of each layer in the system must exceed the required Structural Number derived from the loading conditions.Ĭompleting the Structural Number calculations can be tedious, particularly where the loading conditions are uncertain or where the pavement design must be optimised. The AASHTO 1993 method evaluates the structural strength contribution of each layer in the pavement system based on its thickness and stiffness. This takes the form of an overall Structural Number. This empirical equation is used to determine the total structural strength required to resist the proposed traffic loads. The AASHTO 1993 method is based on an empirical equation developed from road performance information gathered from the AASHTO Road Test.

An example to illustrate how climatic considerations can be incorporated into the AASHTO design is presented.Flexible pavement design according to the AASHTO 1993 guide can be very time consuming.

By knowing the asphalt grade and the mix properties, the weighted, effective asphalt‐layer coefficient is calculated. A rational method is proposed to select the appropriate asphalt grade to minimize both low‐temperature cracking and rut depth. 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. 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. Climatic factors considered include seasonal changes in the subgrade moisture content and the annual variations in the ambient temperature. 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.

Flexible pavement design aashto example