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Study of the Effects of Rrest Time and Loading Time on Viscoplastic Strain of Asphalt Concrtee

Jahangiri, Behnam | 2015

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 47181 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Tabatabaei, Nader
  7. Abstract:
  8. Asphalt concrete exhibits viscoelastic and viscoplastic behavior which is dependent on rate and temperature. To model this behavior, various mechanical modelshave been presented in which total strain, as the response of the applied stress, is decomposed by various researchers to recoverable and permanent strains.Accumulation and expansion of permanent response result in rutting which is a dominant and prevalent distress in hot mixed asphalt (HMA) in hot climates. The available models are not capable of accurately calculate the viscoplastic strain under cyclic loading.
    To close this gap, recovered viscoelastic strain at rest (unloading) period was introduced. This parameter accounted for the effect of dislocation and reorientation of aggregates during rest time and their tendency to approach the primary position (before applying load). In this study, cyclic creep and recovery loading patterns with varying partial unloading (or rest) times and partial unloading stresses in sinusoidal and trapezoid shapes were designed and applied on cylindrical HMA specimens in lab. Different amounts of recovered viscoelastic strain achieved from experiments helped by characterization of constitutive equations.
    Hardening relaxation equation used at this study was a function of recovered viscoelastic strain. This equation reduced the hardening occurred in material due to loading. The viscoplastic strain rate increased in the next loading cycle. Application of correction parameter in the hardening relaxation equation resulted in modification of Perzyna viscoplastic model. In case of thecyclic creep and recovery experiments carried out in this study, average error of viscoplastic strain estimation by Perzyna model was reducedto 9%
  9. Keywords:
  10. Asphalt Mixture ; Rutting ; Cyclic Loading ; Viscoplastic Strain ; Viscoelastic Strain ; Hardening Relaxation Equation

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