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An innovative gradient finishing technique on University of Wisconsin's interior inlays gave an aesthetic edge.

On the journey to the American Society of Civil Engineers' (ASCE) 2011 National Concrete Canoe Competition, some students towed their canoes more than 2000 miles across the country. Some worked through holiday breaks to keep on schedule. And some practiced paddling through frigid mountain rivers for hours on end—all for the chance to compete at the University of Evansville in Evansville, Ind., in June.

The annual contest challenges students to put their knowledge and creativity to practical use, and tests their project management skills. The teams spend hundreds of hours working on their canoes. If they win a regional conference competition, they qualify for the national event.

Teams are judged in four parts with equal weight: a design paper, oral presentation, final product, and the canoe's performance in five different races. This year, the top three teams took home a combined $9000 in scholarship money for their respective civil engineering programs.

“This year's requirements limited the amounts of certain kinds of recycled materials, and forced the students to think beyond glass spheres,” said Mark Valenzuela, associate professor in the Department of Mechanical and Civil Engineering at the University of Evansville and a home team adviser. All concrete mixes were required to contain at least two sustainable aggregate sources, each making up at least 25% of the total amount of aggregate. Only one could be glass microspheres.

University of Evansville's home team experimented by adding corn husks and corncobs—locally abundant materials in Indiana—to the concrete for its canoe, Crux Scrutum. When the corn's sugar content created an unexpected retarding effect, the students settled on ceramic spheres, chopped nylon, and chopped plastic bottle caps.

This year, ASCE's Committee on National Concrete Canoe Competitions permitted students to use reactive aggregates. Water/cement ratio and air content requirements were removed, although the teams still had to correctly calculate air content.

Paddling to victory

Engineering students from 24 universities met for the aquatic showdown in Evansville. They spent two intense days setting up, displaying their canoes, and making academic presentations. Then the teams waited a few more hours for morning thunderstorms to pass before they could finally race at John James Audubon State Park in Henderson, Ky.

For the second year in a row, California Polytechnic State University, San Luis Obispo, won first place, but not with the same students. In fact, without a single returning team member, the new group faced a steep learning curve. “We had to teach ourselves the techniques and methods that had been used before, and put in a lot of extra hours for mistakes we made along the way,” said captain and project manager Chad Inlow.

Their efforts produced a 208-pound canoe, Cetacea, named for a biological order of marine mammals. Its thin hull was reinforced with aircraft cable encased in a Teff on sheath.

They used Latex to add tensile strength to the hull, which also helped reduce density by frothing and adding air content when mixed. Unfortunately, the air content took the form of large, unstable bubbles, so the team added an air-entraining admixture as a stabilizing agent. But to meet the competition's minimum density requirement of 55 pounds per cubic foot without reducing tensile strength or stability, they also added an air-detraining admixture.

The team found an innovative way to meet its sustainable aggregate requirement. “We brainstormed for weeks trying to come up with a new aggregate, but nothing seemed to match the requirements—strong, relatively lightweight, sustainable, light-colored. For those two weeks, everything I looked at was a potential aggregate,” Inlow recalled. After he was inspired during a trip to the restroom, the team decided to use 600 pounds of ground porcelain from crushed toilets.

But Cetacea's aesthetics were its strongest asset. The winning canoe features an inlaid rail, plus one curved and one square bulkhead. It is decorated with more than 30 brightly-colored graphics, including cast-in-place and precast tiles. 3D elements, an intricate coral piece and a turtle, grace each bulkhead.