Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Civil and Environmental Engineering

First Advisor

John B. Metcalf


The two primary objectives of the research were to derive constitutive models for the interfaces of flexible pavement layers, and to determine the effects of the mechanical properties of interfaces on pavement performance. A simple constitutive model was derived for the asphalt-to-asphalt interfaces using data provided by laboratory direct shear tests at several normal load levels. In the model, the shear displacement and stress are proportional until the shear strength of the interface is reached. After failure, a friction model represents realistically the interface condition. The test results proved that, if a tack-coat is not applied between layers, the shear strength at the interface and the shear stress-displacement relationship depend on the magnitude of the normal stress acting on interface with tack-coat. Fatigue tests at constant normal to shear stress ratio indicated a longer life for the interfaces with tack-coat. Field shear tests at several levels of normal load indicated that asphalt surface layers bond well to soil-cement bases. Failure at these interfaces appears due to shear in the cement stabilized material. The field tests proved that, due to their very high resistance to movement, asphalt surface layers can be considered to be fully bonded to granular base layers. The interface constitutive models were integrated into the ABAQUS finite element model in order to determine the effects of interface condition and the horizontal loads on the stress-strain field in a road structure. The study proved a significant impact of the interface condition on pavement life.