- Trial lecture starts at 10.15
- Public defence starts at 12.15.
Title of trial lecture: "Performance testing of asphalt concrete mixtures"
Assessment committee:
- Professor Nicole Kringos
- Dr. Ing.-habil Sabine Leischner
- Head of committee: Professor Jing Zhou, UiA
Supervisor in the doctoral work:
- Associate professor Ephrem Taddesse, UiA
Summary of thesis
Characterization of Asphalt concrete materials in damage and undamaged state
Asphalt paved roads worldwide amount to more than 3.5 times the diameter of the sun. These vital infrastructures have limited-service life due to distress or damage from traffic and environmental loads. As a top road surface layer, asphalt concrete is one of the most important road building materials with unique chemical, physical and mechanical properties. The mechanical properties are viscoelastic, viscoplastic, fatigue cracking, and fracture under different loading scenarios. These load-related responses exhibit complex relationships, and existing characterization methods were insufficient to measure, control and model their coupling.
This thesis explored the linear and nonlinear behaviors of asphalt concrete in a two-stage laboratory testing process over a wide range of temperature, frequency, loading. The first phase focused on the response of asphalt concrete under small-applied load (i.e., linear viscoelastic behavior). In this phase, the time – Temperature, and Pressure -dependent responses of asphalt concrete was modeled and validated in uniaxial (1D) and triaxial (3D) stress states. Furthermore, two commonly used test protocols (Indirect tensile and axial compression) were compared and correlated in one-dimension loading case for practical application.
The second phase examined the destructive/damage testing under compression, tension and tension-compression loading scenarios. Permanent deformation (or rutting) and fatigue cracking damage were investigated, with emphasis on the interaction between them. It was affirmed that rutting is the cause of surface fatigue cracking, other than thermal cracking.
In general, the thesis contributions can be summarized in four important areas: the stress-dependency of linear viscoelastic response, correlating indirect tensile and uniaxial compression test method for linear viscoelastic responses, a novel approach to investigating fatigue and rutting damage interaction, and in-depth exploration and proposal for effective measuring and modeling of permanent deformation and fatigue damage interaction.
The thesis presents a substantial laboratory finding and valuable data, and novel insights into several areas for research, a comprehensive discussion on the need for damage interaction asphalt concrete. A ‘system approach’ of design and service-life prediction of pavements is sought to be the philosophy for complex systems like road infrastructure. Developing a ‘unified’ mathematical damage prediction and design model that takes environmental and traffic loads as input is the task outlooked by this thesis for future study.
What to do as an online audience member
The disputation is open to the public. To follow the trial lecture and the public defence online, register on Zoom.
We ask online audience members to join no earlier than 10 minutes in advance. After these times, you can leave and rejoin the meeting at any time.
Opponent ex auditorio:
Deadline for the public to pose questions is during the break between the two opponents. Questions ex auditorio can be submitted to Emma Horneman.