Mechanical behavior of unbound granular road base materials under repeated cyclic loads

Abstract

This paper aims to report the mechanical behavior of crushed rock base (CRB) and hydrated cement treated crushed rock base (HCTCRB) as granular road base materials subjected to repeated cyclic loads from Repeated Loads Triaxial (RLT) tests with various stress paths in order to improve more understanding of such Western Australian roads based materials on mechanistic-empirical pavement design and analysis. As is well known, pavement surface rutting, longitudinal and alligator cracks are normally the main cause of damage in flexible pavements. The factors contributing to such damage are the excessive irreversible deformation of base layers and the behavior of a mechanical response of unbound granular materials (UGMs) under traffic loads which at the moment are not well understood. In this study, the shakedown concept was utilized to describe and determine limited use of CRB and HCTCRB subjected to different stress conditions. This concept is a theoretical approach used to describe the behavior under RLT tests. It utilizes macro-mechanical observations of the UGM's response and the distribution of the vertical plastic strain in the tested material. When the shakedown limit of an UGM is known, the limitations of the accumulated plastic strain in an unbound granular layer which causes rutting can be predictable. In this paper, compacted CRB and HCTCRB samples were subjected to the various stress condition defined by the stress ratio (the ratio of a vertical major stress, σ1 and a horizontal minor stress, σ3) in order to simulate the real condition of pavement. The study revealed that road base defined the working stress ratio of a pavement structure and that after a large number of traffic loads, deterioration will occur. Moreover, the mechanical responses were investigated and the limit ranges of using UGMs in pavements were determined.