Development of a Viscoplastic Constitutive Model using Rate-Dependent Yield Criterion for HMA in Compression

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Title: Development of a Viscoplastic Constitutive Model using Rate-Dependent Yield Criterion for HMA in Compression
Author: Yun, Taeyoung
Advisors: Dr. Y. Richard Kim, Committee Chair
Dr. Roy H. Borden, Committee Member
Dr. Murthy N. Guddati, Committee Member
Dr. S. Ranji Ranjithan, Committee Member
Abstract: This dissertation presents a uniaxial viscoplastic constitutive model that is capable of capturing the rate-dependent hardening-softening behavior of hot-mix asphalt (HMA) subject to compressive loading. Experimental support for such behavior is also given. In the constitutive model, Perzyna’s over-stress theory and a rate dependent hardening-softening function are used as the flow rule and yield stress function, respectively. A comprehensive material experimental program is performed to identify the characteristic behaviors of HMA, including dynamic modulus test, monotonic test, repetitive creep and recovery test, and flow number test under various loading conditions. From the dynamic modulus test, it is confirmed that the dynamic modulus of HMA in compression is the same as that in tension-compression; however, it is shown that the dynamic modulus is especially dependent on confining pressure at conditions where the material is softest (high temperatures and low frequencies). Further, it is found that when affected by confining pressure, that the modulus increases as the confining pressure increases. It is also confirmed that the time-temperature superposition principle holds true regardless of loading type, severity of damage or viscoplastic strain, as evidenced by a series of constant strain rate tests and repetitive creep and recovery tests. A finding previously undocumented for HMA that is found in this experimental research, is that the resistance to viscoplastic flow, the yield stress, shows rate-dependent hardening and softening behavior. The rate-dependent hardening and softening of the yield stress explains the significant increase of viscoplastic strain in the repetitive creep and recovery tests with long rest periods or with short loading pulses relative to those with short rest periods or long loading pulses. The flow number test and tests combining repetitive creep and recovery and flow number tests are conducted to verify the model. The results indicate that the developed model is capable of accounting for the effects of rest period and loading sequence on viscoplastic strain development. These characteristics cannot be adequately captured with existing HMA viscoplastic models.
Date: 2008-12-03
Degree: PhD
Discipline: Civil Engineering

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