Each year the UofT Concrete Canoe Team continues its research into the development of high tensile strength, low density, workable concrete. The mix must also adjust to the always-changing mix rules of the competition.
With a composite flexural strength of 10.5 MPa and a density around 80% that of water, our team boasts one of the most highly developed concrete mixes of all schools involved in the competition. Concrete Basics
Concrete is usually a mix of cement (and/or other binders such as fly-ash), aggregates (such as sand or gravel), water, and admixtures (such as viscosity-decreasing super plasticizers).
The chemical reaction that takes place in concrete is called a hydration reaction. In this process minerals in cement react with water and bind the aggregates in the mix together. This reaction is relatively slow, and there is a period of time, called the curing period, while it proceeds and releases heat.
Our current mix uses Federal white cement, metakaolin, flyash type C, amorphous calcium aluminosilicate (VCAS) and Cembinder colloidal nano-silica as binders, Siscor hollow glass spheres, K1 glass microspheres and Expancel expanded polymer microspheres as aggregates, and acrylic polymer latex, high-range water reducer, air-entrainer and poly(vinyl alcohol) as admixtures.
The canoe is constructed from alternating layers of low density concrete and carbon fibre. The carbon fibre, along with ultra-high molecular weight polyethylene ‘Dyneema’ fibres incorporated into the concrete mix, help increase the tensile strength of the canoe. Recent Testing
Our team has in recent years tested the addition of poly(acrylic acid), poly(vinyl alcohol), various latexes, silane admixtures, Expancel plastic spheres, binders (flyash, blast furnace slag, silica fume, metakaolin, amorphous calcium aluminosilicate, aqueous nanosilica), various coloured pigments, Ipanex, Kalmatron, and various plastic and mineral fibres to the mix.