Asphalt concrete creep as related to rutting

Rutting is one of the major modes of distress in flexible pavements. It is caused by plastic deformation that can occur in any of pavement layers. Historically, rutting of asphalt concrete has been considered a mix design and/or construction problem. Furthermore, current methods of mix design are independent from pavement thickness design procedures. The focus of this paper is on permanent deformation of asphalt concrete layer. The primary objective is to develop a methodology for characterization of rutting potential of asphalt mixtures that can be easily implementable at state highway agencies. Permanent deformation characterization procedures are to be based upon parameters that can be integrated into mechanistic pavement design procedures. A mechanistic methodology is developed for permanent deformation characterization of asphalt paving materials. Rheological properties of hot mix asphalt (HMA) are thoroughly studied by means of a simple creep test that is originally developed by Shell researchers. Procedures are developed in order to account for nonlinear, viscoelastic, and viscoplastic deformation components of HMA. Results indicate that structural arrangement of pavement layers has a significant influence on rutting performance of the HMA layer. Findings of this study can be easily implemented in an integrated mix-thickness design procedure.