We love concrete, maybe you don’t know it, but look around. It forms the basis of almost everything built. Think of it as liquid rock. Simply pour it into any shape you want so you can put whatever you want on top of it or underneath. We have been playing around with the stuff since Roman days, where they used it to move water and armies and erect buildings to show their dominance over nature. I have to tell you that my wife, whose Italian grandfather and aunt have made concrete for their entire lives, can make a mean batch. A couple thousand years and not too much has changed, from the concrete’s point of view at least.

Sure, we made it stronger and prettier over time but recently concrete has learned to do more with less. Cement which is the “glue” that binds all the aggregates together turns out to be the problem. Fly ash, a waste product of burning coal in power plants can replace up to 30% of the cement and actually improve the strength of concrete in some applications.  Slag is another waste product, this time from the production of steel that also has been proven to effectively replace some of our old friend cement.

This is a big deal because the biggest problem with concrete is that its production puts at lot of carbon into the air. More specifically, portland cement is made from limestone (CaCO3) which you strip off the carbon (CO2) in coal fired furnaces to produce calcium oxide (CaCO). 5% of all CO2 emissions are from just the making of cement. Those coal fired furnaces (418 lbs. coal per ton of cement) can now be supplemented by burning biomass. Not all carbon is equal. If you mine it and it goes into the atmosphere then you are adding to the problem, if you use waste plant material that will simply decay, that carbon is already in the environment.

These are good tricks, but there are more. Concrete as it turns out not only releases CO2 in its production but over time reabsorbs some of it again. New formulas are being tested that will absorb a lot more, most famously an experiment on the new replacement bridge in the Minnesota’s Twin Cities. Maybe in time an even bigger chunk of carbon could be grabbed out of the sky.

Concrete is a big part of our urban landscape, it absorbs a lot of the heat of the day and makes our urban environment much hotter in the summer. This heat makes us turn up the ac, which uses a lot of energy, which ultimately makes it hotter still. New concrete formulas help alleviate this frustrating cycle. White concrete used for hardscapes reflects a lot more of the sun rather holding that heat, and porous concrete pavers can actually help cool an outdoor space by letting water evaporate.

The next trick is inside. Good engineering is now taking advantage of concrete’s ability to hold heat to make our building more energy efficient. By placing structural walls inside the building’s envelope concrete can regulate indoor temperatures by absorbing heat when the building warms up and releasing it later, when the heat is needed.

andrew michler, leed ap | a smarter building
www.baosol.com

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