The Silo Series: Concrete
Friday, February 20, 2009 at 12:05PM by Mason Earles 
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.
Reader Comments (3)
Thanks for posting this. I was thinking about that when I first heard about Greensburg and saw the show on Planet Green. There was so much rubble left over, but so much of it could be considered a free resource to use (such as all the wood, metal and concrete). I hope much of it has been reused and recycled into new uses and was not just landfilled.
When I first heard about Greensburg's plan I was instantly enthralled and always daydream about moving there to start a green business. One of the first things I thought of was that someone there should open a salvage yard where they collect reusable archetectural pieces, woods, and other materials that can be sold for a fraction of the cost of a new item, to both reuse the damaged goods from the tornado and help residents find local matierals for rebuilding.
I'm on my town's new Environmental Task Force which is trying to evaluate and improve our environmental programs, so I have pointed out Greensburg's General Plan as an example of the great things they're doing and what we should be considering. Thanks for leading the way. I don't know if I'll ever actually move to Greensburg, but I am a close observer of your progress and really hope to see more of the tv show return this year.
IMHO (i.e., unscientifically) the durability of concrete outweighs any cons in its production.
It is not the aggregate that is the problem from a sustainability standpoint; it is the portland content and lifespan of the building. Soil cements are actually quite green when the building is designed to last in excess of 100 years and then actually remains standing. Too often they are torn down to make way for a neww concrete structure. Lowering portland content is also doable, it some cases it can be eliminated entirely.