Concrete Canoes

Civil Engineers Host Student Competition

August 1, 2007

Engineering students in the 20th annual American Society of Civil Engineers national concrete canoe competition, show off their latest canoe boat models. The concrete canoes float because a cubic foot of water weighs 62-point-4 pounds. A cubic foot of concrete composite concrete mix weighs 45-point-6 pounds -- thatýs almost 20 pounds lighter than water. Adding foam plus the concrete, then makes its lighter than water, so the whole canoe will float.

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BACKGROUND: The American Society of Civil Engineers sponsors an annual Concrete Canoe Competition. The event provides students of engineering with a practical application of the principles they learn in the classroom, along with important team and project management skills. It also challenges their knowledge, creativity, and stamina, while showcasing the versatility and durability of concrete as a building material. The 2007 event was held June 14-16 at the University of Washington in Seattle.

ABOUT THE COMPETITION: The annual concrete canoe competition dates back to late 1969, when engineering professor Clyde Kessler had his students build a canoe out of concrete. Since then, the event has expanded significant, with more than 200 universities participating each year in regional competitions. The winners of those move on to the national competition: the 'Olympics of civil engineering.' Teams must design their concrete canoes from scratch. The competition has four parts, each accounting for 25% of the final score: a technical paper, a technical presentation, a final product judging, and the concrete canoe race. The latter has five different events: a pair men and women's sprint, a pair men and women's slalom, and a four-person co-ed sprint.

WHATEVER FLOATS YOUR BOAT: Concrete canoes can float thanks to Archimedes' Principle. Archimedes was an ancient Greek mathematician who figured out that a body immersed in a fluid is pushed up by a force equal to the weight of the displaced fluid. This is called buoyancy; an object will float if its buoyancy is greater than its weight, and will sink if its weight is greater than its buoyancy. The shape and position of the body affects the strength of the force pushing up on the body. So a concrete canoe placed on end in water will sink because the weight of concrete is greater than that of the displaced water. However, in its normal position, the weight of the canoe depends on its total volume, since it includes all the air inside it. So the average weight is less than that of the water displaced, and the canoe floats.

WHAT IS CONCRETE? Concrete is a common construction material used in pavement, architectural structures, foundations, roads, parking structures, and brick/block walls. It consists of cement mixed with water and an aggregate (a space filler). Concrete used for sidewalks, for example, use larger, heavier aggregates like rocks, gravel, or sand, but for concrete canoes, the teams use very light materials: glass bubbles, fly-ash, or silica fume. Concrete hardens after mixing and placement because the water reacts with the cement -- a chemical process known as hydration -- and this bonds all the components together to create a stone-like material. About six billion cubic meters of concrete are made each year, and in the US it is a \$35 billion industry that employs more than two million workers. The American Society of Civil Engineers contributed to the information contained in the TV portion of this report.

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Did you know?...

In 1848, Joseph Louis Labot of France built a ferro-concrete boat now housed in the Brignoles Museum. And a Dutch concrete boat built in 1887 was still in use at the Amsterdam Zoo as late as 1967.