Cementing a More Sustainable Future

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.

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.

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)