by AARON GRUDOWSKI, Illinois Tech Civil Engineering Student, Concrete Canoe Captain | March 2, 2017
Each year, roughly 200 ASCE Student Chapters go head to head in the annual Concrete Canoe Competition, where student engineers design, construct, and race a canoe made of concrete against other university teams. This year, we’re once again following the Illinois Tech team as they try to make it to Nationals in Colorado this June 17-19.
It’s been almost one year since the 2016 Great Lakes Student Conference. And one year since our concrete canoe crumbled into hundreds of tiny little pieces as we prepared to race it in front of 19 other schools.
After such a disastrous performance last year, I was nervous about this year’s canoe. What if we didn’t finish on time? What if it completely failed like last year?
The one thing that hasn’t changed, though, is the team standing in our way of going to Nationals. As always, the University of Wisconsin—Madison, is ranked as the number one team going into the year. But with all of our hard work and dedication in every other aspect of the competition, maybe, just maybe, we can sink their hopes and beat them.
Unlike the year before, we set a much stricter timeline for ourselves. Upon arrival at IIT for the fall 2016 semester, the Concrete Canoe team immediately went in and prepared the shop for the upcoming year.
Over the course of the next few months, Rafal, our team’s other captain, dedicated most of his free time to designing a mold for the canoe. The two main restrictions were the length and width of the ship (22’x36” maximum). His resulting design was an 18-foot hull with a width of 28 inches, ensuring that it met guidelines and provided enough stability during the competition. Using SOLIDWORKS 3D software, Rafal carefully designed every curve and edge of the canoe. Nothing less than perfection would suffice.
Learning from Last Year
The other task that we focused on for most of first semester was figuring out a good mix design to use to construct the canoe. Typically, true concrete has a strength of 2,000-4,000 pounds-per-square-inch (psi), and high strength concrete can withstand 4,000-6,000 psi. With the addition of materials that aided in canoe buoyancy, a typical well-made concrete canoe has a strength of a little more than 2,000 psi. For the 2016 conference, our canoe had a mere 800 psi, which may have played an itty bitty part in our canoe’s destruction.
The rocks and dirt we get to play with — I mean the cement and other materials that we use to construct the boat — fall into several categories. The main structural components are the cementitious materials, which consist of cement, fly ash, and silica fume. When mixed with water, these materials react and form a paste that binds the other materials together. The other main components are aggregates, admixtures, reinforcement, and, of course, water.
Blood, sweat, and aggregates
Teams use many different types of aggregate, ranging from sand to hydrated lime. The main aggregates that we use are 3M Glass Bubbles, Cenospheres, and lightweight shale. Larger aggregates decrease the surface area that the cement paste must cover, which reduces cracking and shrinking. The shale in our mixture serve as the large aggregates, while the 3M Glass Bubbles and Cenospheres are used to increase the buoyancy of the concrete. Their low densities make them lighter than water, which in turn keeps the canoe above the surface, although nothing could save last year’s poor ship.
This year, the ASCE added a new rule. Each team’s mixture had to be composed of 25% shale by volume. Although this helps increase strength, it also increases the density of the mixture, which can potentially lead to buoyancy issues.
There are two types of reinforcement used, which include primary and secondary. The primary reinforcement is composed of a carbon fiber or wire mesh spread across the length of the canoe. The holes in the mesh allows the layers of concrete to bind to one another through the mesh, greatly increasing the strength. Secondary reinforcement consists of fibers made from carbon fiber, steel, nylon, or other similar materials. Our team utilizes carbon fiber fibers to reduce cracking and permeability while also increasing shatter-resistance of the mixture.
The final component, admixtures, have different uses. There are accelerants, retarders, water reducers, superplasticizers, and corrosion inhibiting admixtures. The admixture that we use is a combination water reducer and superplasticizer. Basically, its function is to reduce the amount of water and, in turn, the water-cement ratio. Water actually decreases the strength of concrete, so if we can decrease the amount we use, it is very beneficial.
After about twenty different mixtures and hours spent in a lab testing their compressive and tensile strengths, we finally found one that would keep our hopes of making it to Nationals afloat (haha, get it?).
So, we’re ready to cast now, right? Well, not quite. Next, it was time to cut out the cross sections for the mold. The canoe had to be cast by Saturday February 18 or else there would not be enough time for proper curing. This year, we decided to try something different. Instead of just creating a male mold like last year, we decided on both a male and female mold in order to increase the uniformity of the canoe’s thickness. Also, it would allow us to pour the concrete instead of place it on the mold. In the end, it would drastically help improve our canoe, but it would also increase the difficulty of the process.
So into the wood shop we went to cut out the cross sections for the mold. The CNC cutter sliced through the wood like butter, knocking out the cross sections until there were only 6, 5, 4, …, uh oh. With only four sections left, the CNC cutter stopped working. And just our luck, it would take a few days to fix. Out came the hand saws, and after an extra few hours of work, the cross sections were done.
RACING AGAINST TIME
We were scheduled to cast the canoe Saturday at 4 p.m, and it was already Thursday… and we still had two entire molds to construct. Thursday and Friday came and went, and we might as well have slept in the canoe shop. Saturday morning arrived, and the drills were drilling and the hammers were hammering, but at 4:00 PM, there was still work left to do.
Thoughts raced through my head. “Would we have to push back casting? Would we be unsuccessful again?” It was too hard to know what would happen, but we pressed on, knowing that time was running out.
check back next week for Part 2 of the Concrete Canoe saga, where we’ll hear about the team’s progress in the competition.
For last year’s coverage of the Concrete Canoe and to learn more about Illinois Tech, click here.