An annual competition put on by the
American Society of Civil Engineers, the goal is to build and race a
canoe made out of
concrete. Individual Concrete Canoe
challenges have been something of an
ASCE tradition since the 60's, but weren't done on a national,
playoff bracket based scale until 1988. There are now 20 regional competitions that allow the first and second place teams to go on to the national competition.
Placing is based mostly on the quality of the canoe's design and presentation. 25% of the points go to the design paper, 15% to oral presentation, 10% to the canoe display, and 10% to the canoe itself. Placing in races determines the other 40%, with five different races done: Men's and Women's Distance, Men's and Women's Sprint, and coed Slalom. Each team has to have a presentation on how their canoe was designed and made, presented with a theme of their choice: pirates, race cars, great American presidents, etc.
Instead of being mixed out of the usual pebbles and sand, the concrete to be used for canoes is specially designed by each team. Carbon fiber, glass microspheres, graphite, microballoons, and other light weight, strong materials are commonly used. Teams usually end up with concrete that is itself much lighter than water, and the only condition on the concrete mixture is that it must be 75% (by mass, not size) Portland cement.
Surprisingly, using concrete in waterborne vehicles isn't a new idea; it was first tried in 1848 for the boats on Joseph Louis Lambot's French estate, and several "unsinkable" concrete battleships and aircraft carriers were designed during WWII and the Cold War. Besides the Concrete Canoe Competition, there is lots of other research being done on using concrete as a light and strong construction material. University of Alabama Huntsville (along with their own Concrete Canoe team) is working on, believe it or not, concrete to be used in space. Researchers there believe that concrete mixtures will eventually be lighter and more flexible than the graphite-epoxy composites used in aerospace now. They also point out that concrete's inert nature would make it more resilient to forces like radiation and atomic oxygen erosion, further showing the possibility of its use.