Anisotropic Behavior of Bituminous Mixtures in Road Pavement Structures

Abstract The compaction of bituminous mixture during road pavement construction induces anisotropic properties. However, bituminous mixture is generally considered isotropic. This article presents the investigations on the anisotropic behavior of a bituminous mixture in a road pavement structure. A pavement block (55 by 46 by 28 cm) was sawn and extracted from a highway in France. Cylindrical specimens were cored and sawn from the middle layer of this block in three directions: longitudinal direction I, vertical direction II, and transversal direction III. Complex tension/compression modulus tests were performed at the University of Lyon/Ecole Nationale des Travaux Publics de l’Etat (ENTPE) laboratory to investigate the anisotropic behavior of the bituminous mixture. These tests consist in measuring axial stress and radial strains when sinusoidal axial strain, with an amplitude lower than 10−4 m/m, was applied on the specimen. Tests were performed on the specimens cored in Directions I, II, and III at nine temperatures and six frequencies. For each specimen, the complex modulus E* and complex Poisson’s ratios ν* in two perpendicular diameter directions were measured. Thus, the complex modulus in the three directions (EI*, EII*, and EIII*) and six complex Poisson’s ratios (νI-II*, νI-III*, νII-I*, νII-III*, νIII-I*, νIII-II*) could be obtained and investigated. The Time Temperature Superposition Principle was verified for both the norm and phase angle of E* and ν*. The anisotropic properties of material were studied by comparing the three E* and six ν*. The obtained results reveal an anisotropic behavior of the bituminous mixture. The different E* and ν* respected the Time Temperature Superposition Principle with the same shift factor. In addition, the rheological tensor was shown to be symmetric. The experimental results were simulated using the anisotropic three-dimensional version of the “2 Springs, 2 Parabolic elements and 1 Dashpot” (2S2P1D) linear viscoelastic model. A unique normalized curve can be considered for E* and ν*. The stability of the material behavior was also investigated within the tested frequency–temperature range.