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 is usually a mix of cement (and/or other binders such as metakaolin), 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 CRH White Portland Cement, Metakaolin, White Silica Fume, and Slag Cement as cementitious materials, Nycon PVA RECS15 8mm fibers, Poraver expanded glass microspheres, Norlite aggregate, and 3M K1 & K37 glass microspheres as aggregates, and X-seed super-plasticizer, MasterSure Z60 workability retaining admixture, Euclid VISCTROL viscosity modifying admixture, and MasterGlenium high-range water reducer as admixtures.
The canoe is constructed from alternating layers of low density concrete and carbon fibre. The carbon fibre, along with the fibres incorporated into the concrete mix, help increase the tensile strength of the canoe.
In recent years, our team has tested the addition of fiberglass, poly(acrylic acid), poly(vinyl alcohol), silane admixtures, 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. We sometimes also use grey cement/silica fume for concrete colouring and use various Interstar Ready Mix Colors for aesthetic purposes.