Finely tuned asphalt mixes may reduce roadway wear
In the 1950s, Route 66 set the standard for the lazy, laid-back way in which travelers meandered from Chicago to Los Angeles and points in between. At the same time, a landmark highway-pavement study in Ottawa, Illinois, set design standards for the types of pavement on which truckers and tourists traveled the country for years to come.
Now, nearly 60 years later, an ever-increasing army of car and truck drivers pounds the pavement—less to have a good time than to make good time—and highway pavement materials like asphaltic concrete aren’t bearing that load.
“The conventional asphalts are not meeting our needs—and the problem that we face is that the refineries cannot easily produce better asphalts,” says Civil and Environmental Engineering Professor Hussain Bahia. “There are limitations on their equipment, economics, and their procedures that limit the capability of modifying asphalt at the refinery.”
In response, an emerging secondary market now offers a massive menu of asphalt modifiers designed, in theory, to boost the performance of asphalt pavement.
Bahia is an expert in determining which additives work best. “There is a need, not only for evaluating new materials for their initial performance, but also for how they resist damage,” he says.
With funding from the Federal Highway Administration, the National Cooperative Highway Research Program, the Wisconsin Department of Transportation, and private industry, Bahia’s group draws on laboratory simulation tools that, in a matter of hours, replicate years of roadway wear and tear. “We bring the bigger world into our lab and try to simulate the exact climate and traffic conditions and give an assessment of how the material will perform,” he says.
The simulation tools enable his group to evaluate such pavement damage as wheel-path rutting, fatigue cracking, and thermal cracking. “We can show anyone who might be interested that additives can be used to enhance resistance to all of these distresses that result in closing the roads for replacing or maintaining them,” he says.
Key to this research is new National Cooperative Highway Research Program software that enables highway engineers to analyze specific pavement and additive choices and predict roadway response. “The demand from climate and traffic and the new software is really opening the opportunity for scientific advancement in producing better asphalts,” says Bahia.
Bahia also studies ways that modified asphalt mixes can contribute to safer driving conditions. For example, during a rainstorm, a porous asphalt mix can drain water through the pavement, reducing the likelihood that drivers will skid on slick, puddled roadway surfaces. Though porous asphalts are not new, Bahia’s studies focus on “sustainable” asphalt choices, or those that last longer and require less repair.
In addition, he and colleagues are studying how to use additives to decrease asphalt production temperature—and cut down on noxious fumes—during road construction. At room temperature, asphalt is a semisolid. To build a road with it, construction crews need heat the asphalt only to the point that they can roll it smooth. This new, more environmentally friendly asphalt is called warm asphalt mix and the UW-Madison group is helping to define the effects of certain additives on the mix temperature.
Ultimately, Bahia’s research enables asphalt manufacturers to develop new and improve existing asphalt additives. The results also provide state departments of transportation the information they need to customize asphalt specifications for specific conditions, like roads with frequent heavy truck traffic or those that experience wide temperature swings. “We give them very specific information about how we think the material is improving the asphalt, and by how much” he says.