Many of you joined us in welcoming our first edition to the Eco-Home family at the Silo Eco-Home groundbreaking. This post will be the first in a series of articles exploring the specific green components of the Silo Eco-Home. Today's discussion: Concrete.
An EF5 tornado creates a lot of debris. In fact, in Greensburg the estimate rang in about 87,000 truck loads. By mass, concrete comprised a significant percentage of this debris. As Greensburg continues to refine our approach to sustainable natural disaster recovery, we've found a good re-use for our old foundations, basements, driveways, and sidewalks. We've relocated it to the walls of The Silo Eco-Home.
But, how green is concrete? Like all building materials, concrete's green profile is a point of contention. Another blog, Inhabitat.com, covered the environmental pros and cons of building with concrete in a past article. Here are their conclusions:
"Worldwide, concrete is the most widely-used construction material with over ten billion tons produced annually. In the US, the dubious manufacturing process churns out over two tons of concrete per person per year with a heavy CO2 burden – in total about 7% of global CO2 emissions come from concrete production.
At the same time, the material possesses a unique structural efficiency and inherently green qualities like a capacity to reduce recurring embodied energy, high solar thermal performance, low maintenance requirements and high durability. Variations of concrete with high solar reflectance are considered for heat island mitigation, and with no-offgassing, concrete is an interior finish that meets IAQ standards. Substituting Portland cement with fly ash, using recycled aggregate and a locally fabricated supply can reduce concrete’s environmental impact."
With a foundation, walls, roof, and garage of concrete, our primary objective when designing the Silo Eco-Home was to reduce its carbon footprint. So, we put our heads together with Armour Homes' owner, Dave Moffitt, to reimagine a greener future for concrete construction.
The image (borrowed from the Portland Cement Assocation) to the right shows the typical mixture for concrete. In the Silo Eco-Home we have replaced the 41% gravel component with crushed concrete salvaged after the storm. The result is a less energy intensive concrete building. The aggregate was sourced no more than a few miles away from where it was crushed; no new material was extracted to produce the concrete; and we diverted thousands of pounds of concrete from the landfill. As an added feature, we've also used 30% fly ash (a by-product of coal combustion) in the cement mixture.
So, how green is concrete? Well. All we can say is that after a natural disaster it's a readily available resource. And in Greensburg, Kansas, waste hasn't been an option since we settled in 1886.
On a related note, we would like to give kudos to our local concrete supplier Heft & Sons LLC for making such a service available.