This paper introduces a new permanent deformation model proposed from a research study recently conducted at the University of Illinois aimed at characterizing the deformation behavior of unbound aggregate materials used in pavement base/subbase applications. Sixteen different aggregate materials, commonly used for base/subbase applications in the state of North Carolina were tested in the laboratory for shear strength and permanent deformation behavior. An analysis framework was established to consider the strong correlation that commonly exists between permanent deformation and shear strength characteristics. Accordingly, the trends of permanent strain accumulations from repeated load triaxial tests were captured in a new rutting model developed by taking into account the shear stresses applied at certain fractions, i.e., 25%, 50% and 75%, of the shear strength properties of these materials under similar loading conditions. Finally, justification has been provided to highlight how this model would present an improvement over the unbound aggregate rutting damage model currently used in AASHTO's mechanistic-empirical pavement design approach. Physical significance of individual model parameters has also been analyzed in this paper, and inferences regarding expected values of these parameters have been drawn. It is concluded that the proposed model has the ability to predict deformation characteristics of aggregate materials by incorporating number of load cycles, shear strength and stress state components.
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