How To Make A Concrete Canoe
What you’ve just watched is a video overview of the National Concrete Canoe Competition (NCCC), hosted this year by the University of Nevada, Reno, in mid-June.
In this week’s print Newscripts column, I wrote about NCCC, a contest established in 1989 to give civil engineering students experience in real-world problem solving. Concrete’s used in infrastructure all over the world, including airport runways, buildings, and bridges. The heavy building material, however, is not typically used in boats. And floating is not its specialty.
But it is possible to give concrete buoyancy. And that’s the challenge at the heart of NCCC. People are always asking how concrete can possibly float, says Erik Bjornstrom, a fourth-year civil engineering student at Cal Poly, San Luis Obispo. The answer, he says, lies in the aggregates that get added, and to a lesser extent, the admixtures.
As I mention in this week’s column, concrete is a stew of cement (which is limestone-based), aggregates like crushed stone, and chemicals (the admixtures) that impart various properties to the material. Adding lightweight aggregates such as glass beads instead of heavier ones like gravel helps make concrete float. Air-entraining admixtures (which include surfactants) create air bubbles in concrete, making it lighter.
Bjornstrom, who’s also the project manager of this year’s winning NCCC team, says building a concrete canoe is a long, arduous process. A few teammates are responsible for coming up with the mixture for the canoe. This year, Bjornstrom told me, those folks tested some 160 concrete formulations before settling on a winner. The final material has to be “strong enough, light enough, and workable for volunteers” to be able to mold the seafaring vessel.
The actual molding gets carried out on Casting Day, when volunteers pour the concrete over a canoe-shaped mold and carefully smooth it down. At Cal Poly, some 50 students help out over a 4- to 5-hour period to get the concrete in place, Bjornstrom says. This year, the team’s canoe was made of three concrete layers and two reinforcement layers (made of fiberglass mesh and carbon fiber mesh, respectively). NCCC rules state that no more than 50% of your canoe’s thickness can be made of reinforcement materials, Cal Poly’s project manager adds.
To see some footage of students casting a concrete canoe, check out this excellent video from the University of Illinois. It also tells a little about the history of NCCC.
And if you’re wondering: Yes, concrete canoes are harder to steer than regular ones. Bjornstrom says it’s almost like driving a car without power steering. The heft of the vessel makes it difficult to change directions, especially when paddling on one side or the other. Cal Poly seemed to figure out how to control its boat this year, though. The team won three out of the five NCCC boating races.