We talk with leading educators in the field of asphalt technology in an effort to tune in to academia on important industry issues.
Dallas N. Little is Regent’s Professor and the Snead Chair Professor at Texas A&M University. He is a Distinguished Member of the American Society of Civil engineers.
What drew you to civil engineering, and in particular, transportation?
I was attracted to civil engineering through a strong program at the U. S. Air Force Academy. In graduate work at the University of Illinois, I became very interested in material engineering because of great professors and that interest continued to gain momentum during my years at Texas A&M. I was fortunate enough early in my academic career to be a part of some very interesting projects such as a National Science Foundation grant to understand the chemical and rheological processes responsible for damage and damage-healing in asphalt. I think engineering materials to meet the demands of the environment to which the infrastructure is subjected is simply fascinating and certainly challenging.
How can we improve asphalt-aggregate mixture design analysis procedures?
The answer requires contributions from the practitioner and the researcher, from the experimentalist and the theoretician and mutual respect for the importance of all components. I think we are making good progress in implementing a more mechanistic approach along with good science. We will always have to rely on and appreciate design and construction experience and the skill of the contractor, but I think we can all agree that a clearer understanding of the “reason why” things work moves us in the right direction and makes us more efficient.
What do you feel are the best ways to assess asphalt-aggregate bond strength and durability in the presence of moisture?
In order to assess the sensitivity to moisture of a specific mixture we are pretty much forced to use a process that mimics what happens in the field. That is why we rely on tests such as AASHTO T-283 or the Hamburg test. After all, so many factors influence moisture damage at so many length scales. This in no way diminishes the role of materials science in helping understand the fundamental reasons for improving adhesive and cohesive bond strengths based on, for example, surface energy and aggregate micro-texture measurements. This is how we make fundamental improvements by first understanding the mechanism that activates a better bond.
How important is the process of “healing” in asphalt performance?
Recovery during rest periods following damage or “healing” has been a key component of my research since I began with a National Science Foundation grant to study healing in 1985. At that time very few recognized healing. Today we have made a lot of progress with respect to understanding the role of chemical healing in the damage process. It has a very important role and I am happy to say that since the mid-1980s many excellent researchers across the world, including several of my former students, have contributed to our understanding.
Where should today’s engineering students focus their research in the asphalt field?
Asphalt is a complex material and in its complexity rests intrigue in terms of research. Its response to load is time and temperature-dependent, it comprises many chemical functional groups that dictate how it changes with age, and how it reacts with aggregate to form the familiar composite that is a mainstay of our highway infrastructure. There is plenty of room for better understanding of the fundamental mechanisms that define how asphalt behaves under load and over time. As we improve our analytical skills with tools that offer higher and higher resolution, we can continue to make a better product.