A Continuum Coupled Moisture-mechanical Constitutive Model for Asphalt Concrete

The presence and flow of moisture degrade engineering properties of asphalt concrete as part of thermodynamic, chemical, physical, and mechanical processes. This detrimental effect is referred to as moisture damage. The aim of this dissertation is the development of physically based constitutive relationships along with a computational tool for the fundamental analysis of combined mechanical and moisture induced damage of asphalt concrete. Such a tool can greatly contribute to an improved material selection procedure and give insight into the various damage inducing mechanisms in asphalt concrete.

In this dissertation, thermo-hygro-mechanical constitutive relationships are developed based on the principle of virtual power and laws of thermodynamics in order to simulate moisture-induced damage of asphalt concrete. An evolution function is proposed to consider the detrimental effect of moisture diffusion and presence inside the material. The effect of pore water pressure is incorporated using Biot?s coefficient. The Continuum Damage Mechanics (CDM) theory is extended to Continuum Moisture-Mechanical Damage Mechanics (CMMDM) to incorporate the moisture degradation effect and couple it to the mechanical response of asphalt concrete. The proposed moisture damage constitutive relationships are implemented in the Pavement Analysis using Nonlinear Damage Approach (PANDA) finite element (FE) package to model the moisture damage effect on the complex environmental-mechanical response of asphalt concrete. The developed constitutive relationship and framework are validated over different loading scenarios and a range of experimental measurements.

The developed constitutive relationship and framework are applied to simulate pavement performance. The focus is on investigating the effects of various moisture conditioning periods on permanent deformation (rutting) and fatigue damage of asphalt pavements.

The constitutive and computational models are used to develop a framework for the simulation of the effect of moisture on the microstructural response of asphalt concrete. This framework explicitly incorporates the material microstructural distribution and properties. The developed framework is used to perform two-dimensional (2D) and three-dimensional (3D) micromechanical simulations in order to study and investigate the capability of the proposed constitutive relationships to predict the microstructural response of asphalt concrete under combined effect of moisture diffusion and mechanical loading.