Enhanced Portland Cement Concrete Fatigue Model for StreetPave

Abstract

The Portland Cement Association (PCA) pavement thickness design method for jointed concrete pavements is mechanistically based and consists of both fatigue and erosion analyses. It determines the minimum slab thickness required for a given set of site and design conditions on the basis of both fatigue and erosion criteria. At the heart of the fatigue analysis is the fatigue model, which establishes the number of allowable load repetitions for a given stress ratio [ratio of flexural edge stress caused by the application of wheel loads to the portland cement concrete (PCC) slab flexural strength]. The PCA fatigue model is based on data derived from beam fatigue tests conducted in the early 1950s and 1960s. The model estimates the conservative lower-bound estimate of the allowable number of load applications at a given stress ratio (i.e., it incorporates a high degree of reliability–-approximately 90% or higher). Although this may be desirable for high-volume, high-traffic pavements, it is too conservative for low-volume roads or street pavements. The PCA pavement thickness design method currently is being used in the American Concrete Pavement Association (ACPA) pavement design software, StreetPave. StreetPave incorporates the PCA's pavement thickness design methodology in a Windows-based user platform. ACPA commissioned a study to expand, improve, and broaden the current PCA fatigue model by including reliability as a parameter for predicting PCC fatigue damage and by calibrating the enhanced model with additional fatigue data from recently completed studies. An enhanced fatigue model was then developed.