Carbon Negative Concrete???

As Industrial Design major who’s future career will most likely consist of creating a wide variety of products, something that is a big concern for me is creating environmentally friendly products. I don’t want to just create things that will eventually just create more waste and end up in a landfill polluting our Earth. I also don’t want to help perpetuate environmentally harmful manufacturing processes like those used to make cement that release tons of greenhouse gases into the atmosphere.  So when I heard about the Calera process I was very interested and wanted to look into it more to see if this was actually an effective and sustainable method for capturing and storing carbon.

The Calera Corporation developed the Calera process to sequester CO2 from our environment in a way that is actually sustainable and effective over time. They then used this process to create a superior form of concrete that mimics the form of calcium carbonate that marine animals use to create their hard shells. The Calera process results in the production of the vaterite polymorph which is stable when stored in the absence of water. When water and other proprietary additives are added to the vaterite polymorph, a cement reaction occurs in which the vaterite transforms via a dissolution and reprecipitation reaction to form another polymorph of calcium carbonate known as aragonite. This conversion of vaterite to aragonite results in a material with high strength, just as natural systems like mother of pearl are also constructed from the aragonite polymorph of calcium carbonate.

Concrete is the most widely used man-made material in the world. Concrete is made of roughly 80% aggregate (sand and gravel), 10-15% cement, and the remainder air, water, and additives. The Calera process can permanently mineralize carbon into either fine or coarse aggregates or a supplementary cementitious material that can be used to create building materials such as concrete. The standard process for manufacturing Portland cement generates large amounts of CO2 both from the fuel used to heat the raw materials as well as from the conversion of CaCO3 to CaO, which releases CO2. Because of this, concrete made from Portland cement carries a CO2 footprint of approximately 0.8-1.5 ton CO2/ton cement, translating to roughly 537 pounds of CO2/cubic yard of concrete! Calera SCM both captures carbon from one source and avoids carbon emissions from another. Concrete made with 20% cement replacement with Calera SCM, and 20% cement replacement with fly ash would have carbon footprint of negative 1146 pounds of CO2/cubic yard of concrete. This is a carbon savings of 1683 pounds of CO2/cubic yard of concrete compared to standard concrete. “With projected U.S. Portland cement consumption at nearly 200 million metric tons by 2020, a 20% market penetration with a SCM replacement level of 50% would reduce CO2 emissions by 30 million metric tons.” Which is far more than the reduction that would be accomplished by supplementing fly ash as a replacement for some portions of Portland cement used in regular concrete mix.

The carbon capture method employed by Calera, is also unique because it has many possible inputs including: fly ash, brines, waste water, and flue gas. In capturing CO2 and other emissions from flue gas, Calera’s carbonate mineralization technology uses solid and liquid sources of alkalinity, such as fly ash, wastewaters, and brines. The outputs of the process are clean air, fresher water, and solid materials that can be used as an aggregate or supplementary cementitious material. Another concern that often comes up in the conversation of carbon capture is how efficient is it, especially since you are trying to capture and manipulate a gas in this process. In its pilot landing facility, the Calera process regularly observes Carbon capture rates greater than 50% and has even reached rates of over 90%.