How To Make Concrete From Atmospheric Carbon

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Concrete, steel, and myriad other construction materials we take for granted are leading sources of atmospheric carbon dioxide (CO2). The good news is that concrete can be made from the trillions of tons of excess CO2 in the atmosphere.

San Jose, California-based Blue Planet has developed a technology that captures CO2 at the smokestacks of energy and other manufacturing plants. And it has a chemical process for pulling CO2 out of the air that can extend the emission-reducing benefits of building with atmospheric carbon.

One Leg of a Carbon-Cutting Stool

Humans need to deploy a variety of strategies to reduce atmospheric CO2 while still enabling people to make and deliver the basic goods that people need. Strategies include carbon capture, land management and reforestation, carbon reductions from improved manufacturing processes, and the elimination of fossil fuels-based airline and shipping fuel, which can be replaced with fuels made from atmospheric carbon.

Blue Planet’s technology in just one approach, a method for mining the air to recapture two centuries of excess CO2, could help kickstart a new infrastructure and building industry that cleans the planet while improving lives around the world. New cities, home designs, and on-demand printed products assembled from carbon atoms are just a few of the outputs that will help human carbon reduction achieve its pressing goals.

Blue Planet’s first construction project was a big one. It has provided CO2-based concrete to build a new terminal and runways at the San Francisco International Airport. During the construction process, a team from Stanford University conducted a study comparing the Blue Planet concrete mix with conventional concrete. The research team concluded that the Blue Planet mix could reduce CO2 emissions by up to 48 percent over standard concrete.

But the technology is still working toward large-scale deployment. When it achieves massive scale, Blue Planet believes it can make concrete carbon-neutral — or even carbon-negative — removing more CO2 than the concrete takes to produce.

The Chemistry of Cement

As Healthy Climate Alliance founder Peter Fiekowsky explained during in recent Earth911 interview, Blue Planet’s CO2-capture process results in a limestone aggregate, or gravel, that is used in concrete mix instead of newly mined materials. The process currently uses carbon captured from power plants, but procedures to capture carbon directly from the air are being developed. Fiekowsky said that, “so far, it looks like it’s not going to be very expensive and still be profitable even when it belongs to a tube straight out of the air.”

Blue Planet’s process uses less energy than making traditional concrete. It also adds two important innovations that make it much more efficient. Unlike other CO2 capture technologies that focus on producing purified CO2, Blue Planet skips that energy-intensive step to turn its CO2 into CO3, calcium carbonate, which is better known as limestore. The company takes spent concrete materials and coats the fragments with CO3 to make the raw materials for new concrete, which it calls “CO2NCRETE.”

A fragment of stone is covered by layers of limestone (CO3) to create concrete material.

The CO3 coating of the fragments acts as a carbon sink, locking the CO2 into layers of material like an oyster shell or plankton in the ocean. The CO2NCRETE is 44 percent CO2, removing it from recirculation for thousands of years. It mimics a biological process that has been responsible for carbon sequestration for millions of years.

Blue Planet’s technology will continue to evolve. And competitors, such a team at the University of Augsburg in Germany, are looking at using other forms of captured carbon to make carbon-fiber reinforced cement forms that will make buildings more resilient during earthquakes, as well as longer-lived. Buildings have an uncanny ability to adapt as times change, as author Stewart Brand has argued.

The possibilities for atmospheric carbon, however, do not end at concrete and building materials. Fuel, plastics, and many other materials can be made from captured CO2. If we see this as a source of solutions, the CO2 crisis becomes tractable and practical to solve, because there is money to be made while delivering products and fuels that carry lower carbon footprints. Buildings are a natural place to store CO2; we simply haven’t recognized the opportunity until now.

Cleaning up our atmospheric mess can be the basis for kickstarting new industries.

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Taylor Ratcliffe

Taylor Ratcliffe is Earth911's customer support and database manager. He is a graduate of the University of Washington.

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