Investigating permanent deformation of bituminous mixtures designed using particle-packing based gradation and mastic optimization

Abstract

Aggregate gradation plays a critical role in the performance of asphalt mixture, specifically the permanent deformation response. A rational aggregate gradation design can provide an interlocked coarse aggregate skeleton which can be effectively filled with bituminous mastic, resulting in improved resistance to permanent deformation. The objective of the study is to develop an aggregate skeleton with minimal disruptive aggregate interactions using particle-packing design approaches. Further, the influence of aggregate gradation on the permanent deformation behavior of bituminous mixtures is investigated. Six distinct gradations are formulated using three design methods: one based on conventional principles and two employing particle-packing approaches. One of the particle-packing approaches considers the geometrical interaction among the aggregate fractions implicitly by controlling size ratio, and the other one accounts for the geometric interactions explicitly through analytical formulations. In addition, the analytical formulation is used to identify the critical sieve in the gradation which contributes to mixtures’ permanent deformation. Dry rut wheel tests and repeated creep and recovery tests with a trapezoidal loading protocol are performed on all mixtures at \(60\,^\circ \)C to evaluate their permanent deformation behavior. A trapezoidal creep-recovery test protocol is adopted instead of the generally followed testing approach. A linear viscoelastic model is used to predict the strain response, and retardation time is computed from the linear viscoelastic model parameters. Further, retardation times are correlated to the permanent deformation characteristics of the mixtures. The study finds that mixtures with an optimized coarse aggregate structure, which can hold sufficient mastic, exhibit better resistance to permanent deformation.