As builders of ICF homes, we at ORC will always be one of the first to praise the benefits of concrete as a primary building material. It’s superior in many ways when compared to its more mainstream counterparts, from its resilience against natural disasters and pests, to its impressive lifespan of 30-100 years. Its highly durable, and has a high thermal mass, which makes it a great option when building with energy efficiency in mind.
However, the environmental impacts of the production process of cement–and by extension concrete–shouldn’t be overlooked. Despite its sustainability in the field, cement still has a massive carbon footprint, putting out .93 lbs of CO2 into the atmosphere per pound created. To put that in perspective, around 4 billion tons of cement are produced globally each year.
The Making of Concrete
Currently, the primary ingredient in most concrete mixtures is Portland Cement. This cement is itself made from calcium, iron, silicon, and aluminum, which can present as a combination of materials like limestone, chalk or shells, and clay, iron ore, or silica. Supplementary Cementitious Materials (SCMs) such as fly ash, are often added as well to help improve the durability of the cement, or to decrease the amount of heat that’s needed to produce it. These ingredients are then fired at high temps, and the resulting product is finely ground into a powder.
This powder–cement–is then mixed with water and an aggregate like rock or sand in order to create concrete.
Because of the impact of this production process on the environment, sustainability advocates have begun to look at many alternatives. Some have proposed enhancing the process, as with SCMs, while others have looked to other materials entirely, like with mycelium composite, as we showcased in our previous newsletter.
But regardless of the alternative, the strength, durability and thermal mass are all important considerations to make when looking to use or create them.
Hempcrete, which is made from hemp fibers, water and lime, holds up as a worthy contender for certain applications. While it can only bear loads of 72.5-507.6 psi and so requires structural support, it is highly insulating with an R-Value of 2.4-4.8 per inch, compared to the 0.1-0.2 per inch R-Value of concrete. Because of its natural materials, it’s biodegradable and even carbon negative, which means it absorbs more CO2 than is put out during its production process.
Fly ash is already used as an SCM in much of traditional cement, but Ashcrete takes it to a whole other level by using it as the main ingredient. Fly ash, bottom ash, and other residual materials from coal production are upcycled and combined with acid and an aggregate to create a product that is not only highly similar to concrete in texture, but also in strength. Ashcrete boasts a compressive strength of >3000 psi, matching traditional concrete, which has a compressive strength of 3000-4000 psi.
According to its main manufacturer, Ashcrete Technologies, they may also be able to trap CO2 in the ash, which would provide an additional solution to the CO2 problem traditional concrete production poses.
Do as the Romans Do
Efforts to create a more sustainable and environmentally friendly solution to modern concrete also have researchers looking to the past. Ancient Roman structures like the Colosseum, the Pantheon–which sports the world’s largest un-reinforced concrete dome– and their aqueducts may provide those solutions.
Like the concept of using fly ash in today’s concrete, the Romans used volcanic ash, also known as pozzolana. It should be noted that this was of course a locally available resource due to Rome’s geographic position. The Romans would use the pozzolana in a hot mixing process with quicklime and seawater, and these materials would then react and create particles known as “lime clasts.”
While modern researchers once thought that these lime clasts were imperfections in the manufacturing process, they later realized that they actually gave Ancient Roman concrete self-healing properties. When the cured concrete is exposed to water, the presence of the lime clasts promote the growth of calcium carbonate crystals, which then fill in any cracks or weathering the concrete may have sustained.
While alternatives like these may not be applicable on a large scale yet, its important to consider now how they and others can be applicable in ICF construction in the future, especially as society begins to move away from less sustainable materials. Imagine ICF block filled entirely with Ashcrete instead of traditional concrete. We as a company would love to be able to implement alternatives as the become further improved, researched and available.
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