Paddling Concrete to a Win


Rocks sink. This simple law of nauture makes the phrase “National Concrete Canoe Competition” sound like the title of a Monty Python skit. In fact, the competition, held by the American Society of Civil Engineers, features student teams that put their engineering know how into keeping concrete boats afloat.
One of these teams, the Concrete Canoe team at California Polytechnic State University, San Luis Obispo, has won the contest for two consecutive years. This year they’re gunning for a third win.
Concrete Canoe competitions started in the 1960s in the United States and are steadily taking hold in countries around the world. After all, understanding concrete is an integral part of civil engineer’s education. The US National competition involves judging concrete boat entrants in four areas. There’s the canoe itself, an oral presentation, a design paper, and the paddling race.
The key to Cal Poly team’s wins is in the recipe. Concrete is made of three ingredients: an aggregate (usually a mixture of stones and sand), cement, and water.
“We don’t mess with the water,” said Mason Breipohl, the team’s project manager and a junior at the university. “We use super lightweight aggregate, glass microspheres, and chemical admixtures that help boost certain properties. But at the end of the day it’s a lot of testing and trial and error till you find that perfect mix.”
The result is a concrete that is definitely lighter than water. But the buoyancy comes with a price: It’s a good deal less strong than the concrete used by industry. Breipohl and his team make up for it by using eight steel cables that run the length of the canoe. “They act as an additional safety factor and help relieve some of the stress,” Breipohl said.
Cal Poly team is also very careful about moving and transporting the canoe, using plenty of extra straps and foam to secure it in its trailer.
The team doesn’t get to coast on their past glories and just reuse their boat, or their recipe, for that matter. The contest rules change each year, and the team is always striving to maintain their advantage. “A lot of schools are coming for us, so we try to stay one step ahead,” Breipohl said.
This year there’s a focus on sustainability, so the San Louis Obispo team created a new recipe that forgoes Portland cement, which is used in the vast majority of industrial concrete. “We felt it would be really impressive if we could entirely remove that and use recycled byproducts instead,” Breipohl said. “We’re definitely proud of it, and hoping we can set the bar for sustainability and show people what can be done.”
To emphasize the sustainable theme, the team has decorated this year’s concrete canoe with elements from Norse mythology, specifically Yggdrasil, the tree of life. “We seal it and sand it, give it a nice smooth finish,” Breipohl said. “It glides across the water pretty well.” Their previous winning canoe drew inspiration from Van Gogh’s Starry Night.
They also tweaked the canoe’s maneuverability. Though they won last year’s competition, there was room for improvement. “Last year, during the four person race, the tail was sagging a little low to the water line,” Breipohl said. “Water was coming in over the sides.” To fix the problem, this year’s boat is a little wider in the back—a solution they arrived at after much 3D modeling.
The new canoe has already shown its superiority in the water. In the Pacific Southwest Conference, hosted by San Louis Obispo in early April, the team placed first.
Though Cal Poly engineering prowess is clearly what’s put them in the lead, there’s another element that gives the team an advantage. “We’re fortunate being in San Louis Obispo,” Breipohl said. “We have beautiful weather and a lake to practice in all the time—we’re paddling four times a week.”
Michael Abrams is a technology writer based in New Jersey.
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