We talk with leading educators in the field of asphalt technology in an effort to tune in to academia on important industry issues.
Dr. Walaa Mogawer, P.E., Ph.D., F. ASCE is a professor of Civil and Environmental Engineering, and Director of the Highway Sustainability Research Center (HSRC) at the University of Massachusetts Dartmouth.
What drew you to civil engineering, and in particular, transportation?
When I was a child I had the unique opportunity to visit one of the largest civil engineering marvels of the world, the Egyptian pyramids. The enormity and brilliance of these structures drove my desire to learn more about the design and construction of large scale structures. Not surprisingly this prompted me to focus my career in civil engineering. It wasn’t until my graduate studies that I became more focused in the transportation discipline. I had enrolled in a pavement design course, which I found to be fascinating, challenging, and unlike the typical civil engineering curriculum.
What are you discovering from your research on re-refined engine oil bottoms (REOB), also known as vacuum tower bottoms?
It is difficult to make universal conclusions about the effect of REOB on the performance of asphalt binders and mixtures. Many variables influence the properties of an asphalt binder modified with REOB including the REOB source, dose of REOB utilized and virgin binder to which it is added. Not all the asphalt binder sources utilized could be modified with REOB to meet a specific performance grade regardless of dosage used. For the sources that could be modified, binder rheology results indicated that REOB modified binders showed increased aging relative to straight run binders. This trend increased as higher dosages of REOB were used.
How has using an Accelerated Loading Facility (ALF) improved your Superpave and mix design research?
A primary objective of the ALF pavement study performed by FHWA from 1993 to 1999 was to validate the Superpave high and intermediate temperature asphalt binder specifications. The study validated the specification at high temperatures but two polymer modified asphalt mixtures tested yielded discrepancies with the specification. This finding led Kevin Stuart of the FHWA to develop the first test for asphalt binders that incorporated a rest period. This ultimately led to the development of the Multiple Stress Creep Recovery test used today.
What are some of the advantages of using a high performance thin lift overlay incorporating high RAP content and warm mix asphalt technology?
High performance thin lift overlays are generally used in applications where a higher level of rutting and fatigue resistance is required. These types of mixtures generally require higher binder content and the use of polymer modified asphalt. This modified asphalt is typically more expensive than unmodified asphalt. This coupled with the fact that more binder is required, could lead to an initial higher cost relative to other conventional pavement preservation strategies. Using high amounts of reclaimed asphalt pavement (RAP) and warm mix asphalt (WMA) technologies have been utilized in an effort to produce a more cost effective but similar performing overlay mixture. Due to the use of RAP, the amount of virgin binder required is less due to the re-use of binder in the RAP. This inherently leads to costs savings as less virgin materials are being used. Moreover, incorporating WMA in the mixtures can provide the benefits of improved mixture workability, fuel cost savings at the plant, reduced emissions at the plant and field, improved compaction at lower temperatures, increased haul distances and longer paving season.
Where should today’s engineering students focus their research in the asphalt field?
The asphalt field today is very dynamic so today’s engineering students must be prepared to adapt accordingly. Research efforts should always focus on the critical needs and issues of the industry at that time. Current hot topic issues include: sustaining our roads and consequently minimizing the use of new natural resources, energy harvesting from pavements, increased use of recycled materials (RAP, RAS & GTR), asphalt rejuvenators, REOB and warm mix asphalt. Moreover, more emphasis needs to be placed on validating laboratory research results to actual field performance. In my opinion this is currently lacking and represents a major disconnect in research.