Concrete is everywhere. It is popular for buildings and infrastructure because of its compressive strength. Add rebar, and you add tensile strength—resulting in a material that can carry weight without cracking and resist bending or being pulled apart.
It Started With the Romans
The ancient Romans used lime, volcanic rock, and stone aggregate to produce underwater structures that remained intact after over 2,000 years. The magnificent dome of the Pantheon in Rome was built with concrete, unreinforced. That's a testament to both the material used and the design.
We usually see concrete in the form of building foundations, highway surfaces, and bridges. A few decades ago, there was a worldwide shortage of cement—the binder in concrete that holds the aggregate together—because of a building boom in China. Making cement is a highly energy-intensive process. Lime has to be heated to a very high temperature to create a material that, when mixed with water, creates a tight bond that cures quickly and maintains its strength over a long period.
Build Better
Estimates vary, but most sources say cement production produces about 10% of global greenhouse emissions. Global temperatures rise due to carbon emissions, leading to more storms, flooding, and drought. Global temperature rise has contributed to the extinction of hundreds of species and is the driving force behind much of the migration we are seeing worldwide. It takes a global village built with green concrete to mitigate the problems and improve future generations' lives.
There are two ways to improve the carbon footprint of concrete. 1) Use renewable energy to make it, and 2) use different, less energy-intensive materials. In other words, make greener concrete.
MIT reports on a startup, Sublime Systems, that uses electrochemistry and renewable energy rather than fossil fuels in the concrete-making process. The company facility in Massachusetts can make nearly 250 tons of concrete a year and is on a path to produce 100 tons per day.
A recent story in the Washington Post describes one startup's solution to the concrete problem. "Brimstone, a 35-person startup, has developed a different cement-making method. Instead of baking limestone, it starts with carbon-free silicate rock. Chemically extracting calcium oxide from silicate does not release carbon dioxide. A byproduct of the process is magnesium that can absorb CO2 from the atmosphere."
"Hempcrete," or concrete made with hemp, also shows promise as a much less energy-intensive way to make concrete. It doesn't require heat to manufacture, and the hemp plant is a fast-growing, hardy, and abundant plant that is a renewable resource. Hemp is a good insulator as well. It is gradually working its way into the mainstream, and its use is included in the U.S. building code and international residential building codes.
A startup that is building a demonstration project in Oahu called Yummet wants to take ocean water and solid waste to produce clean water, hydrogen, and biochar, a product used as a soil amendment and in Yummet’s green concrete product. The company claims that its concrete is “negative carbon producing” because of how it is manufactured and the materials used. Tests show the concrete to be more than twice as strong as traditional concrete.
All of this may be like drops in a concrete bucket, but to make a difference and make a profit, companies have to scale to solve the problem of substantial greenhouse gas emissions. To measure the scale of the problem, globally, we use about 30 billion tonnes of concrete and 4 billion tonnes of cement per year.
Shop Locally
Locally, Contra Costa County publishes a Green Building Materials Resource List that is very helpful for finding local sources of green concrete and other green building materials. The Contra Costa County Solid Waste & Recycling site also shows photos of various green building materials on its website and a demonstration display. You can look before you buy!
Photo: Dome of the Pantheon in Rome. Photo by Jim Gunshinan.
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