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Improving asphalt could pave the way to cost savings, U researcher says

December 2002
From the CTS Report

With more than 90 percent of all paved U.S. highways topped with asphalt at a cost of $10 billion each year, research into bituminous materials has never been more important. In fact, University of Minnesota civil engineering assistant professor Mihai Marasteanu estimates that just a 1 percent reduction in costs could save $100 million annually.

Marasteanu presented his latest research October 30 as part of the CTS fall faculty seminar series in a lecture titled "Update on Bituminous Materials Characterization."

During the presentation, Marasteanu pointed out that asphalt pavement research has undergone a significant change during the past 12 years, shifting from primarily empirical methods to mechanical-based scientific methods. The goal has been to bring asphalt research to levels similar to those used in other engineering areas, ultimately providing a critical link between basic theories and actual pavement performance.

Many of the changes have been prompted by increases in traffic, changes in the way oil is processed, and significant advancements in laboratory experiments, computing, and other advanced research tools.

Though Marasteanu acknowledges that rutting, fatigue cracking, and low temperature are among the most common "distress mechanisms" for asphalt pavement, he has also found the often-overlooked elements of aging and moisture sensitivity to be just as important. "There are a number of issues that still need a lot of clarification," he said, noting the ever-evolving compositions of asphalt mixtures.

For instance, Marasteanu observed, the properties of asphalt binder, an organic material, irreversibly change when exposed to oxygen, heat, or solar radiation. As a result, the asphalt "ages" as its mechanical properties, adhesion to aggregate, and moisture sensitivity also change.

According to Marasteanu, current research trends are moving in two main directions, modeling fundamental material behavior and developing parameters for pavement design and pavement performance. Future research, he added, needs to examine the interaction between different distress modes (e.g., where does fatigue cracking end and thermal cracking begin?), transition behavior, and asphalt-aggregate interaction fundamentals.

Marasteanu has been the principal investigator on four Mn/DOT projects studying the properties of asphalt mixtures.