CIVIL AND ENVIRONMENTAL ENGINEERING

Prof. Lawrence Bank (right, with graduate student Dushyant Arora) is studying composite strips that can be used to strengthen aging bridges temporarily. (36K JPG)

Rehabilitating a better bridge

Hundreds of aging bridges are nearing the end of their useful lives. But replacing them is costly. What's a bridge owner to do? Professor Lawrence Bank has come up with a solution — temporarily strengthening them by using composite strips attached to the underside of the bridge. Wisconsin, for instance, has hundreds of concrete bridges that were built 60 or 70 years ago. Many of the bridges are still functional, but are deteriorating.

From Bank's perspective, these kinds of bridges are ideal candidates for fiber-reinforced polymer (FRP) plates, or strips, that can be attached to the underside of the bridge. The plates are held in place by fasteners that are shot into the concrete by a power-actuated fastening gun (similar to a pneumatic nail gun). The sheer force of shooting the fastener with a nail gun creates a bond between the fastener surface and the concrete, making for a secure connection.

A key factor in using the FRP plates is a bridge's "sufficiency number," which is an overall assessment of a bridge's condition. Bridges are typically assessed on measures such as the load they can hold, their width, safety features such as guardrails, and their general condition, according to Bank. A bridge with a sufficiency number below 50 is usually slated for replacement. But by utilizing the FRP plates, a bridge's sufficiency number can be improved enough to forestall its total replacement.

City, village and town governments own many of these deteriorating bridges. For some communities, replacing more than one or two bridges at any one time could be too costly. Using FRP plates would allow local governments to spread out their bridge replacements over several years.

An upgrade for asphalt

Longstanding asphalt specifications may fall by the wayside in light of a new report by Professor Hussain Bahia. The report highlights several changes to national standards that will result in better-performing asphalt that uses more new and emerging materials.

The main finding of the study is that current American Association of State Highway and Transportation Officials specifications for performance-graded asphalt binders underestimates the potential performance of modified asphalt binders. The report proposes changes to national specifications, including six new standard testing protocols, two new machines (one of which is under patent application) and a new asphalt grading system to be used nationally.

Bahia's research group has focused on studying the best methods of evaluating asphalts modified with additives such as plastics, polymers and recycled tires.

"We have developed new methods to study storage stability, workability and resistance of asphalt to heavy traffic conditions," Bahia says. "The proposed standards include criteria to account for traffic volume, traffic speed and pavement structure in selecting modified asphalts."

The report is of particular interest to materials engineers in state highway agencies as well as to materials suppliers and paving contractors responsible for modifying asphalt binders for hot-mix asphalt pavement construction.

For this project, Bahia worked with the Asphalt Institute, a research center for the Association of Asphalt Producers, and the National Center for Asphalt Technology, a research center for the National Asphalt Pavement Association located at Auburn University. The research study and subsequent report were funded by a $1 million grant from the National Cooperative Highway Research Program.

Annihilating anthrax

Professor Marc Anderson has developed a method to keep grocery store fruits and vegetables fresher. Now his research shows promise to ward off deadly strains of anthrax.

Fruits, vegetables and flowers spoil due to exposure to ethylene, a naturally occurring hormone. But Anderson's research has shown that titanium dioxide can be used as a catalyst to break up ethylene into carbon dioxide and water vapor, prolonging the shelf life of produce and flowers. Anderson's research has found its way into grocery stores, where a device called Bio-KES can be installed to keep produce fresher for longer.

Nearly the same process, it turns out, proves effective in fighting anthrax spores. Anderson discovered that ultraviolet photons used to break down ethylene can be used to tear apart nearby water molecules. The byproduct of that reaction — hydroxyl ions — attacks and destroys pathogens such as anthrax. Anderson's findings have led to the development of a flat box that can be affixed to a ceiling and draw in eight cubic feet of air per minute. Tests have shown that more than 90 percent of the pathogen spores, such as anthrax, sucked into the box are destroyed by the use of ultraviolet photons.