Permanent Deformation in Flexible Pavements with Unbound Base Courses

Abstract

Permanent deformation of the unbound base and subbase layer of a flexible pavement is one of the damage types that can require extensive maintenance. To be able to predict the development of permanent deformation, two options can be considered. The first is the development of models that allow the prediction of permanent deformation as a function of the applied stresses, the number of load repetitions, and the material characteristics and moisture regime. The second is the determination of stress conditions at which no significant permanent deformations develop. Such a stress level is, of course, dependent on the material characteristics, the degree of compaction, and the moisture content. The development of such a “shake down limit” for unbound base materials made of mixtures of recycled concrete and masonry is the topic of this paper. It has been found that the allowable ratio of applied vertical stress at a given confining stress level and the vertical stress at failure at that same confinement level depend to some extent on the composition of the mixture of crushed concrete and crushed masonry but mainly on the degree of compaction; ratios between 0.45 and 0.61 were found. Furthermore, it was possible to estimate the parameters controlling the resilient, as well as the failure behavior from physical parameters such as gradation, mixture composition, angularity of the particles, and the degree of compaction. The relationships indicate that performance-related specifications for the materials as investigated still can be based on well-known parameters that can easily be assessed in a short period of time and at a low cost.