CONCLUSIONS AND CONSIDERATIONS In the end, because of the forgiving nature of concrete, the mixes turned out great. The most difficult part in the casting exercise was the amount of water to use. Concrete is proportioned by weight and volume so depending on the precision of the strength needed, the contractor or builder will choose. Because we were trying to get a precise replicable object, we proportioned by weight as well, allowing us to use the same amount of water every time. The amount of water to vary from participant to participant, but within 1/4 of an ounce. The ratio we ended up using was a very common 1:2:3, meaning 1 part cement, 2 part sand, 3 part gravel, in that order, which theoretically achieves a strength of 4500 psi. To achieve that strength we used .3-.5 parts water, where we chose to use 1 part water, as a more fluid mix was needed. We could have gotten away with using a higher aggregate mix in order to lower the cement ratio even further. Something else we could have tried to reduce the amount of cement in our mix ratio was reducing the angularity of our aggregate, or using rounder aggregate. A sphere uses the least surface area to enclose a given volume. Blue Planet has a 100% carbon sequestered aggregate which is much rounder because of the way the C02 forms to produce the synthetic aggregate. After a quick analysis of the objects cast by Dougal Heap, using only Blue Planet aggregate and taking into account the CO2 of the cement and sand the net embodied carbon of the objects would be -19 grams of CO2. But with the coated aggregate, which is the majority of the material we used in the casting experiment, the embodied carbon would go from 27 grams to 12 grams. The Concrete Canvas was an awkward scale of material to truly get into interesting experiments. It tends to be too thick for the size of the material. We believe at a workable scale of at least 2'x2' the material would have been more appropriately scaled for the thickness of what we were experimenting with. It would allow smoother curves, the experimentation of more functional objects like tables, stools and vases, and an ease of fabrication and workability. Concrete Canvas donated the 5mm sample, which, in hindsight, I would have definitely requested the 3mm sample.
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