Understanding the Value of Comprehensive Material, Performance Models and Real Failure Modes in Modern Rigid Pavement Designs

Abstract

Rigid pavements traditionally have been designed using either empirical or mechanistic-empirical methodologies. Historically, common design methods included AASHTO (1993 and 2008) and the PCA Method (now known as Street Pave or Pavement Designer). These design methods were calibrated using a relatively limited number of pavements with slab dimensions of 12ft (3.5m) wide and 15ft (4.5m) long, different traffic levels, local climate conditions and materials and construction practices from the era of the testing. In addition to these methods, modern methods including bonded and unbonded concrete overlays and slabs with optimized geometry are becoming increasingly common. While historical methods might provide appropriate designs for certain geometries (slabs sizes), applications and locations like those to which they were calibrated, the appropriateness of their application should be in question (e.g., AASHTO 93’s limit of testing to a certain amount of ESALs and climatic conditions). Mechanistic performance methods allow the incorporation of new materials and conditions, but understanding the mechanistic principle that the method is trying to extrapolate and the resulting failure mode of this new condition is an important consideration. This paper contrasts historical and modern rigid pavement design methods and their results, with an emphasis on illustrating when historical designs might yield unconservative and possibly dangerous or incorrect designs because of their lack of consideration of comprehensive performance models.