Performance-Based Models for Flexible Pavement Structural Overlay Design

Performance of flexible pavement has long been recognized as an important parameter in the design of flexible pavements. Pavement surface condition evaluated using visual inspection is periodically done to assess pavement performance over time. A distinct performance curve is then constructed for each pavement structure that relates the pavement surface condition to service time or accumulated $80\mathrm{kN}$ equivalent single axle load applications. The presented flexible pavement overlay design models are constructed using performance curve parameters to provide an adequate overlay thickness at any given future time. The undertaken approach attempts to compensate an existing pavement structure for the loss in performance (strength) that it has endured over a specified service time. In essence, this approach is similar to the mechanistic methods of overlay design that make a compensation for the loss in a particular strength indicator such as the commonly used deflection method. Therefore, compensation is made for the loss in performance as represented by appropriately selected performance curve parameters. Performance parameters are then converted into equivalent relative strength indicators, which are in turn converted into equivalent overlay thicknesses. The relative strength indicators deployed in this paper are the structural number and gravel equivalent used by the American Association of State Highway and Transportation Officials and the California Department of Transportation design methods of flexible pavement, respectively.