Permanent Deformation in Asphalt Concrete

Abstract

Permanent deformation in asphalt concrete pavements manifests itself as depressions along the wheel paths, ruts. The prediction of rut depth requires a knowledge of materials characteristics that relate the asphalt concrete permanent strains to stress and temperature. This paper analyzes the character of permanent strains as inferred from a creep/recovery test. It is shown that the separation of the strains into the time‐independent elastic and plastic strains and the time‐dependent viscoelastic strains requires tests with various times to unloading. The analysis is illustrated with the results of a series of uniaxial compression creep/recovery tests on one asphalt concrete mixture. The tested material exhibits temperature‐dependent elastic and plastic strains that are proportional to the level of stress. The time‐ and temperature‐dependent viscoelastic strains are nonlinearly related to the stress level and stress history. An approximate constitutive equation that disregards this nonlinearity is presented.