The Science of Sustainability

Cementing a More Sustainable Future

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Clarke Snell is a builder, a dreamer, and a 50 year-old student bent on saving the planet — one house at a time.

As an architecture graduate student at the University of North Carolina at Charlotte, Snell is tackling what he sees as the greatest challenge of our time: climate change. Armed with a firm belief that sustainable design can help slow the warming trend, he and his fellow students have set their sights on tackling a major climate change culprit: concrete.

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The geopolymer cement mix developed at UNC Charlotte uses recycled fly ash from coal plants. Photo courtesy Clarke Snell.

Concrete accounts for somewhere between 5-8% of the world’s total carbon dioxide emissions. It’s the most widely used building material on the planet.  We produce nearly three tons of the stuff, per person, every year.  From buildings, to bridges, to bathroom countertops, concrete is here to stay.

The question is: what are we going to do about it?

One answer is eco-friendly geopolymer cement, which can reduce the carbon footprint associated with concrete by up to 90%.

Cement and concrete are often used interchangeably, but they are actually two separate products.  For starters, cement is an ingredient used to make concrete. You can’t make traditional concrete without cement.  Conventional cement (also known as Portland cement) is a very fine powder typically made by burning limestone and other minerals at temperatures over 2,500°F.

Concrete is the mixture of aggregate (a combination of sand, gravel or crushed stone), and a paste material comprised of water and cement.  Through a process called hydration, the cement and water harden with the aggregate, binding the mixture into a rocklike mass that can be shaped and set as needed.

As history can attest (see, Roman empire) concrete is strong, durable, and relatively easy to transport.  But there’s a caveat: making one ton of concrete releases a ton of carbon dioxide into the atmosphere. Literally.

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UrbanEden's concrete walls help keep the building warm in the winter and cool in the summer. Photo courtesy Clarke Snell.

Here’s the good news:  There is a viable alternative– and Snell and his team at the University of North Carolina at Charlotte are already using it.

A biennial competition sponsored by the Department of Energy challenges schools from around the world to design and build energy efficient, solar powered homes.  The UNC Charlotte team wanted to use concrete for its durability and strong insulation properties, but they didn't like the carbon emissions associated with producing Portland cement – the glue that holds concrete together.

So they used a geopolymer composite material made from fly ash to replace the conventional Portland cement.  Fly ash, or flash, is a recyclable by-product from coal power plants that is both strong and durable.  The flash creates a binding material that, when combined with certain activating chemicals, can be used to make concrete.

The new material looks and performs like conventional concrete but doesn’t have to be burned at 2,500°F, thereby skirting most of the associated carbon dioxide emissions.  As student Project Manager Clarke Snell says, “If emulated in all building projects, this small, essentially plug and play substitute, would be world changing.”

UrbanEden under construciton at the 2013 Solar Decathlon competition. Photo Credit: Eric Grigorian/U.S. Department of Energy Solar Decathlon

UrbanEden under construciton at the 2013 Solar Decathlon competition. Photo Credit: Eric Grigorian/U.S. Department of Energy Solar Decathlon

 

Additional information about use of geopolymer based cement developed by Dr. Brett Tempest at UNC-Charlotte – (Link)

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Category: Chemistry, Energy, Engineering, Environment, Video

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David Huppert

About the Author ()

As a producer/reporter for UNC-TV, David Huppert has spent the last 6 years immersing himself in the Old North State's culture and folklore, consuming as much of state's rich legacy (and barbecue) as possible. David returns to UNC-TV after a one-year hiatus in NYC where he produced for CBS This Morning. Since 2000 David has produced pieces for public television (UNC-TV, Charlie Rose) and commercial news (CBS, FNC’s The O’Reilly Factor, CNBC). When he’s not telling stories for television, David is either working on a documentary about Alaska’s Wrangell-St. Elias National Park, or gallivanting around North Carolina with his wife, @mediumish. You can follow him @hupdiggs and at vimeo.com/davidhuppert
  • Lindsey Hoshaw

    Clarke Snell is so charismatic and hearing the story of the UNC Charlotte house through his perspective was great. Plus, who knew that concrete could have such a big impact on climate change? Very engaging video.

  • mansa musa

    I am all from green solutions to earth's problems.My question is how do the two materials compare cost-wise? I alway find sustainable, eco-friendly initiatives are – initially – expensive something that the general mass will always be reluctant to adopt.

  • Kevin Russell

    Yes, Cemex of Mexico like many other large producer of concrete is a massive emitter of CO2, but it is HempCrete which is going to shine here using Contour Craftings innovation, ultimately with nanocellulose which can also be made from hemp biomass.