Summertime, and the living is easy, at least for me and Future Spouse. We suddenly found our respective travel schedules sufficiently curtailed that we will both be in the same place for almost an entire month. Inconceivable! Leisure time is the ultimate novelty, and frankly, we're unaccustomed to that luxury. Lest we be reduced to sneering at each other's writer's block and heaving crockery about to relieve the boredom, we took the opportunity to explore our new hometown. Friday night, we saw an outdoor performance of Hamlet staged in the Hollywood Forever Cemetery, right smack in front of the tomb of Douglas Fairbanks (the event inspired a fluffy little piece at Huffington Post on "10 Things I Hate About Hamlet"). And Saturday night, we experienced "Dining in the Dark" (you can read more about our experience here).
Jen-Luc Piquant skipped out on those festivities in favor of consorting with her swashbuckling pirate mates over kegs of spiced rum (because everyone's got a little "Captain" in them, even faux-French avatars). There was much reminiscing over last month's Concrete Canoe Competition, an annual three-day event sponsored by the American Society of Civil Engineers (ASCE). Basically, teams of engineering students from universities all over the country compete to design and build the best canoe made out of concrete. The idea is to provide engineering students with a practical application of classroom principles, along with vital 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."
It's true, concrete is one of most common and versatile construction materials, used in pavement, buildings, foundations, roads, parking structures, and so forth. That explains why it's such a huge industry: about six billion cubic meters of concrete are made each year (at least per the most recent data from 2005), with a market value of around $35 billion. It also accounts for more than two million jobs. Its versatility is due in part to the fact that it can be mixed in so many different ways, to achieve different desired properties for specific uses. Almost all concrete is essentially cement mixed with water and some sort of aggregate (space filler); it hardens thanks to a chemical process called hydration, in which water reacts with the cement and bonds all the components together into the final stone-like material we know and love. That aggregate can contain just about anything. The concrete used in sidewalks, for instance, uses larger, heavier aggregates like rocks, gravel or sand. With the advent of carbon nanotubes, it's become more commonplace to mix them into the cement aggregates for added strength. But to build concrete canoes, far lighter materials are favored as aggregates: teams use things like glass bubbles, fly ash, or silica fume.
And yes, the canoes really do float, a compelling example of Archimedes' Principle in action: a body immersed in a fluid is pushed up by a force equal to the weight of the displaced fluid. You remember Archimedes. He was a Greek mathematician, famous for all kinds of things, but among the most oft-repeated tales is how he came to the aid of his friend, Hiero, king of the Greek city of Syracuse. Hiero suspected that a goldsmith charged with making him a royal crown -- one assumes he needed a spare -- had kept some of the gold provided for himself, and mixed in silver to ensure the weight of the final crown matched that of the original lump of gold provided. He didn't want to melt the crown down to discover the truth, but the thought just nagged at him, and he asked Archimedes to help.
Inspiration hit one day as Archimedes lowered himself into one of the public baths in the city and noticed displaced water flowing over the sides of the tub. Legend has it that he was so excited with his insight, he leapt out of the tub and ran (naked?) through the streets of Syracuse yelling, "Eureka! Eureka!" ("I found it! I found it!")
A theoretical insight must be backed up by experiment, so Archimedes took a lump of gold and of silver, each weighing the same as the king's crown, although the lump of silver was much larger because silver is lighter than gold. He put each lump in a vessel filled to the rim with water, and noted that the larger amount of silver caused more water to overflow than the lump of gold, because there was more material, even though both weighed the same. He concluded that a solid material will push away an amount of water equal to its own bulkiness (volume). So if the king's crown were indeed made of pure gold, it would have to displace the same amount of water as the lump of pure gold that weighed the same. Unfortunately for the dishonest goldsmith, the crown made more water overflow than the pure lump of gold, proving that the goldsmith had added silver to the crown to make it bulkier. The goldsmith's fate was probably not a happy one.
This property is known as buoyancy: an object will float if its buoyancy is greater than its weight, and will sink if its weight is greater than its buoyancy. It must be said that the shape and position of a given object plays a vital role here: a concrete canoe placed on end in water will sink because the weight of the concrete is greater than that of the displaced water. But in its normal position, the weight of the canoe depends on its total volume, and this includes all the air inside it. So the average weight is less than that of the water displaced, and the canoe floats. It's weird, but true, like many counter-intuitive concepts in physics. And let's face it -- it's also pretty cool. (According to Wikipedia, the competition rules allow teams to insert concrete-covered, non-structural foam pieces in their canoes so that the canoes float after being submerged. Hmmm. Seems like a bit of cheat to me.)
Concrete in some form or another dates back to 5600 BC Serbia (Bora! would be so proud), evidenced by the discovery of remnants of a hut with a floor made of red lime, sand and gravel. In China, the pyramids of Shaanxi (thousands of years old) contain a mixture of lime and volcanic ash or clay, and the Assyrians and Babylonians also used clay as cement in their concrete. Builders in the Roman Empire preferred concrete made from quicklime, pozzolanic ash, and an aggregate mad from pumice (similar to modern Portland cement concrete). They also figured out that adding horse hair made concrete less likely to shrink, while adding blood -- you heard me: blood -- made the concrete more frost-resistant. The Egyptians liked to different and opted for lime and gypsum cement -- although in all seriousness, the variations probably had as much to do with available materials in the different regions as anything else.
For some reason, though, the various formulas for concrete were lost for roughly 13 centuries, before a British engineer named John Smeaton pioneered the use of Portland cement in concrete in 1756. (He used pebbles and powdered brick as aggregate.) It was only matter of time before someone got the idea to build a boat out of concrete, and it finally happened in 1848: a Frenchman named Joseph Louis Labot built a boat out of ferro-concrete that is still on display at the Brignoles Museum. Forty years later, the Dutch got into the act, with a concrete boat that proved so durable, it was still in use at the Amsterdam zoo as recently as 1967,
But racing concrete canoes? Who'd a thunk it? An engineering professor named Clyde Kessler, that's who. Back in 1969, he hit upon the notion of requiring his engineering students to build a canoe out of concrete. Word spread to another professor at nearby Purdue University, John McLaughlin, who challenged Kessler and his students to a competition. Since then, the event has expanded significantly, with more than 200 universities participating each year in regional competitions around the US (and that's not counting the other competitions occurring worldwide), and a magazine devoted entirely to concrete canoes. The winners of those move on to the national competition, considered to be the "Olympics of civil engineering," in much the same way that the annual International Physics Olympiad is the "Olympics of physics" -- except the national canoe competition isn't international. Still, the winning team does get to compete in the Dutch Concrete Canoe Challenge, to be held in the Netherlands this September.
Quite a bit of work goes into these designs; these are not fly-by-night creations. Top teams spend months on the project. They must design the canoes from scratch, usually creating the hull/overall shape with the aid of a computer design program. A styrofoam mold is made, and the particular concrete mix is designed.
Individual techniques vary, but in general, here's what happens. When it's time to actually build the canoe, the mold is covered with Crisco (so that it can be easily separated from the completed canoe) and a layer of cement is laid, followed by a fiberglass mesh to give more strength to the structure and also supply some tension to make the cement a bit more flexible, so it doesn't crack. (Stanford University's team built a canoe that cracked in half during a competition in the mid-1990s; strangely, the school hasn't competed since.) Then another layer of cement is applied, and another layer of fiberglass mesh, topped with one more cement layer. The entire canoe is then "cured" -- a process of hardening the concrete.
The team members also practice paddling, using a fiberglass model until the concrete canoe is ready, at which point they practice in the concrete craft to get a feel for it. This is key. In a 2006 article in Concrete Canoe Magazine, John Gilbert reminisced about that first race in Illinois in 1971: "Concrete canoes are not like their tamer counterparts made from aluminum or fiberglass. These canoes had minds of their own and needed to be coaxed wheedled, and urged around the course. And just when one felt one had control of the situation, one was liable to be tossed unceremoniously into the water by a none too subtle roll." The losing team (Purdue) learned the hard way: Know your boat if you want to win.
There are five different racing events in the competition: a men's pair, a women's pair, a men's slalom, a women's slalom, and a four-person co-ed sprint. The race might offer the most pulse-pounding excitement (especially for the poor sods who must paddle the sometimes unwieldy concrete canoes), but it only accounts for about 25% of the final score. There is also a technical paper, a technical presentation, and a "final product judging." Scanning over the technical papers, it's obvious that some real, hard science goes into these designs.
This year, the competition was held June 14-16 in Seattle, hosted by the University of Washington, and the University of Wisconsin, Madison, won for the fifth year in a row. The University of Florida placed second, with the University of Nevada, Reno, finishing a close third. It's not just a symbolic victory either: the winning teams receive scholarships of $5000, $2500 and $1500, respectively -- although, divided four ways, that doesn't amount to much, considering the months of work that goes into preparing for the competition. (I note with sadness that the City College of New York placed dead last out of 18 teams, perhaps because the only place to practice paddling is in the East River. And that's just, like, gross.)
If canoes just don't float your boat (oh, stop me before I pun again!), there's always the Great Northern Toboggan Race, a similar event intended to challenge the creativity of engineering students. It's been going on since 1974, and instead of designing and building concrete canoes, the students build toboggans with a metal frame and a running surface made completely out of concrete. Per Wikipedia, the resulting contraption must weigh less than 300 pounds, have a working braking system, and be fitted with a roll bar to protect its five passengers. It's a bit more elaborate than the canoe competition, in that teams also choose a theme for their sled -- drawn from pop culture or based on the home university and its location -- and compete dressed in costumes that match the theme. Sometimes even the toboggan design contains elements of the theme. That's Jen-Luc's kind of competition: she's got her pirate outfit all ready to go, the minute a toboggan team opts to be buccaneers.
Great article!
By the way, photos on the asce site show some canoes carrying extra flotation material taped onto the gunwales, probably to pass the 'swamp' test shown in other photos. It certainly makes sense to require that the canoe not sink when overturned, given that the lake is 60 to 100 feet deep in places.
Other fields of engineering do something similar. Mechanical engineering has done various human powered devices in the past and will be doing a window-washing robot next year. Automotive engineers build a small race car. Just like with the canoes, competition includes design reports and presentations as well as racing.
Posted by: CCPhysicist | July 18, 2007 at 12:46 PM
Nice article. EUREKA!
Posted by: Concrete | January 05, 2008 at 01:09 AM