Development of characterisation models for incremental permanent deformation model for asphalt concrete in confined compression

Abstract

Permanent deformation modelling research at North Carolina State University has produced the so-called incremental model that fits the primary and secondary regions in permanent strain growth. Triaxial repeated load permanent deformation tests are conducted on Federal Highway Administration-Accelerated Loading Facility and NY9.5B mixtures to evaluate the effects of temperature, stress, and load time on permanent deformation and, therefore, to determine the form of the incremental model to account for these effects. The test results suggest that the slope in the log(ϵ_vp)−log(N) plot is constant regardless of these three major factors. This observation provides the basis for two modelling approaches: the functionalised model and the shift model. The functionalised model is formulated by expressing the coefficients of the incremental model in terms of the reduced load time and deviatoric stress. The shift model, based on the time-temperature–stress superposition principle, utilises the strain mastercurve and reduced load time and deviatoric stress shift functions. A composite loading test that is composed of varying load times and deviatoric stresses is proposed as the model calibration test. It is found that the permanent strain growth under the complex loading histories predicted by the calibrated models is in good agreement with the measured permanent strain growth.

Keywords:

• permanent deformation
• rutting
• incremental model
• functionalised model
• shift model
• time-stress superposition

Acknowledgements

This research is sponsored by the Federal Highway Administration under project No. DTFH61-08-H-00005, Hot Mix Asphalt Performance-Related Specifications Based on Viscoelastoplastic Continuum Damage Models. The authors gratefully acknowledge the FHWA's support.