"There is no substitute for Victory"
by Rich Shimano
Each year, schools design, build, and race full-size canoes made entirely of reinforced concrete. These canoes are judged in regional competitions (such as our ASCE Pacific Northwest Regional Conference) based on design and construction quality, written presentation of work performed, and racing performance. The "best" canoe from each region then moves on to a professionally sponsored national competition.
Concrete canoes generally range in length from 8 feet to 24 feet and can weigh as little as 50 pounds or as much as 1000 pounds. These two-person canoes are paddled on a quarter-mile flatwater course by the same engineering students who built them. The fact that students have been building and racing canoes since engineering students first built a concrete canoe at the University of Illinois in 1970 implies that such a project is not mere folly but can significantly contribute to the technology of concrete while providing valuable research and management experience to eager students.
Concrete is an economical, commonly available building material which, unlike plaster, gains strength in water. With proper design and construction, durable and seaworthy craft can be constructed at a cost which can be competitive with respect to the use of other building materials.
Since Joseph-Louis Lambot patented his wire-reinforced concrete boats in 1847, concrete has been used for many commercial maritime products. Most notably, concrete ships were constructed in great numbers during World War II because of the extremely high cost and difficulty involved in obtaining steel and other traditional ship-building materials.
However, for smaller, human-powered craft such as canoes and kayaks, concrete can pose many interesting and difficult structural challenges because of the smaller hull dimensions and "carved" hull shape typically needed to yield a lighter weight craft with efficient mobility. Hence the engineering challenge lies in finding lighter, stronger, concretes to be used more sparingly in efficient designs which meet both the serviceability and safety needs of people.
By solving problems related to the "exotic" use of concrete in canoe construction, it is hoped that problems in more conventional applications of concrete may also be solved.
But will it float?
Archimedes' Principle ensures that a medium such as water will provide a buoyant force equal to the weight of the medium displaced. Imagine a sealed one-gallon plastic milk jug filled one-third of the way with common beach sand. Will it float in the ocean? Certainly, but only because the weight of the jug and the sand was designed to be less than the weight of a gallon of sea water.
In the same way, the shape of a concrete canoe must be carefully designed so that the total weight of the canoe and its occupants will not exceed the volume of water displaced when the canoe is partially submerged to its ideal waterline.
Additionally, each canoe will be required to float when completely filled with water in order to meet a state safety regulation which is imposed on canoes in general.
Some schools will use "high-tech" concretes which are less dense than water in order to meet this requirement. Others will put permanent flotation material at the bow and stern of the canoe which, in conjunction with the volume of the canoe itself, will displace enough water to offset the total weight of the canoe.
What did you learn in school today?
Classroom instruction is extremely valuable in providing the knowledge needed to use concrete as a structural material. But with the hands-on experience from the concrete canoe contest, this knowledge can be more readily utilized and appreciated because students will associate such knowledge with personal experiences.
For example, reading about the use of superplasticizers to reduce water demands in a concrete mix might leave a slight impression on one's mind. However, the experience of adding such an admixture to a damp, crumbly concrete mix, and watching the mix transform into a flowing material will leave an indelible impression which will find practical use in an engineering student's professional career.
Lower water content can help reduce the extent of shrinkage cracking, but the use of chemicals such as superplasticizers can cause thermally-induced cracks early on due to the excess heat generation that they cause. Again, the experience of a terribly cracked canoe or an extremely muggy curing tent under which the canoe is stored after concrete placement will never leave a student's mind.
Furthermore, students will learn the value of teamwork while feeling a sense of pride in their workmanship. In a classroom setting, students might compete against one another to achieve high test scores; however, in the canoe project, students will work together and share their experience and knowledge to create a tangible product whose quality will depend on the contributions from all involved.