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2006-2007 HIGHLIGHTS








Cover of the 2007 Annual Report
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Gregory Harrington, Michael Collins, Becky Hoffmann, Andy Jacque, Alice Yuroff and Becky Manning.

From left: Professor Gregory Harrington, Pathobiological Sciences Professor Michael Collins, State Lab of Hygiene Advanced Microbiologist Becky Hoffmann, CEE PhD student Andy Jacque, and Pathobiological Sciences Research Associate Alice Yuroff and Senior Scientist Becky Manning. (Large image)

Civil and Environmental Engineering

To your health:
Studying bacteria growth in drinking water

In Professor Gregory Harrington’s lab, water samples swish gently through tabletop vessels in a way that mimics fluid flow through a pipe. However, the samples aren’t just ordinary water: They comprise special mixtures of sanitized water and a group of disease-causing bacteria called Mycobacterium avium complex, or MAC.

Researchers have found MAC in public water-distribution systems, as well as in household plumbing and drinking water. However, the U.S. Centers for Disease Control and Prevention lists the number of human infections from the bacteria as “non-reportable” and limited primarily to immuno-compromised people.

Previous studies have focused on detecting MAC and determining the quantity of the bacteria present in water-distribution systems, says Harrington. In controlled laboratory studies, he hopes to learn what conditions favor their presence—or absence.

Each of his tabletop vessels, or biofilm reactors, is filled with MAC-spiked water exposed to different piping materials and temperatures. As these water samples circulate, Harrington and graduate student Andy Jacque study whether MAC grow in the water, and whether they grow on tiny copper, cast iron or PVC coupons—samples that represent common water-distribution-system materials.

“If we can determine what conditions favor their absence, then maybe we can come up with engineering designs that prevent their occurrence in water,” says Harrington, whose work is part of an American Water Works Association Research Foundation-funded collaboration with colleagues in the UW-Madison School of Veterinary Medicine and the Wisconsin State Laboratory of Hygiene.

Concrete samples provide clues
to coated rebar health

Much like the skeleton offers physical support within the human body, a steel reinforcing bar, or rebar, adds strength and stiffness to such concrete structures as bridge decks and building foundations. As is the case with the body, when that rebar skeleton begins to corrode, the concrete around it breaks down, too.

Many accelerated laboratory studies have shown that a properly applied epoxy coating on rebar can extend the life of reinforced concrete structures like bridge decks.

But what does a two-year laboratory study mean for a bridge that’s supposed to last 50 years? “The only way we can answer that question is to actually measure the performance of the bars in the field,” says Professor José Pincheira. “And for that, we have to wait many years.”

Enter four Minneapolis-area bridges, built in the late 1970s and early 1980s with reinforced concrete that contains epoxy-coated rebar. Researchers conducted a 1996 study to assess the rebar condition; recently, the Minnesota Department of Transportation asked Pincheira and Assistant Professor Fratta to perform a follow-up.

The duo used several minimally invasive measurement techniques to identify areas in which the rebar likely was corroded. They pulverized small concrete samples taken from those areas and analyzed their makeup to assess the rate at which humidity and road salt—two factors in rebar corrosion—penetrated the concrete.

Considering such variables as weather and traffic frequency, Pincheira and Fratta compared their results with the 1996 data—giving the state of Minnesota a better idea about the service life of its bridges and making a unique field-research contribution to the study of reinforced concrete.

Finely tuned asphalt mixes
may reduce roadway wear and tear

Using laboratory simulation tools that, in a matter of hours, replicate years of roadway wear and tear, Professor Hussain Bahia can evaluate the durability of asphalt customized with various additives. “The conventional asphalts are not meeting our needs—and the problem we face is that the refineries cannot easily and economically produce better asphalts,” he says.

A secondary market 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.

With funding from the Federal Highway Administration, the National Cooperative Highway Research Program, the Wisconsin Department of Transportation, and private industry, he develops tools to evaluate modified-asphalt resistance to such damage as wheel-path rutting, fatigue cracking, and thermal cracking—all of which ultimately cost taxpayers to repair. “We try to understand what the additive is doing inside the asphalt,” he says.

In addition, Bahia 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.

His results enable asphalt manufacturers to develop new and improve existing asphalt additives. They also provide state departments of transportation the information they need to customize asphalt specifications for specific conditions, such as roads with high traffic flow 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,” says Bahia.

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