United States Department of Transportation
i
A comprehensive characterization of asphalt mixtures in compression.
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2013-08-01
[PDF-2.81 MB]
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Abstract:Permanent deformation (i.e., rutting) is one of the major distresses in asphalt pavements, and it consists of
irrecoverable deformation due to viscoplastic flow and viscofracture fatigue damage. The mechanisms of rutting have not
been well addressed due to the complexities of asphalt mixture including (a) distinctions between compression, extension,
and tension; (b) rate and temperature dependence; (c) dilative volumetric change; (d) frictional material with cohesion;
(e) inherent anisotropy due to preferential aggregates’ orientation; (f) crack-induced anisotropy due to crack growth;
(g) strain hardening during viscoplastic accumulation; and (h) strain softening during viscofracture evolution.
In this project, all of the aforementioned fundamentals of asphalt mixtures were simultaneously characterized by a
comprehensive viscoplastic-fracture mechanistic model, which was incorporated with (a) a modified effective stress to
consider the inherent anisotropy and the crack-induced anisotropy due to viscofracture cracking in compression; (b) a
smooth and convex Generalized Drucker-Prager (GD-P) yield surface; (c) a non-associated viscoplastic flow rule; (d) a
rate- and temperature-dependent strain hardening rule; and (e) a viscofracture evolution that was modeled by an
anisotropic damage density-based pseudo J-integral Paris’ law. The model parameters were related to fundamental material
properties that were measurable and understandable for civil engineers. A systemic testing protocol including five
individual test methods were proposed to determine the model parameters and material properties. The test protocol was
demonstrated to be efficient, as one asphalt mixture could be completely characterized within 1 day. The GD-P yield
surface model was validated by octahedral shear strength tests at different normal and confining stresses. The GD-P model
was able to characterize the full range of the internal friction angles from 0 to 90 degrees. In contrast, the widely used
Extended Drucker-Prager (ED-P) model can only be used for a material that has an internal friction angle less than 22
degrees due to the convexity criterion of the yield surface.
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