Empirically Yours

Clams Inspire Pollution-free Cement


Cement manufacturing is killing us. Cement making around the world releases so much carbon dioxide that if it were a country, it would be the third biggest source of CO2 pollution after China and the U.S.

Worse, CO2 in the air is still increasing. As measured at the CO2 observatory on top of Mauna Loa, the level of this gas was up 0.7% from October 2022 to October 2023. 

If we do nothing and continue making cement by the traditional method, it will worsen climate disruptions. But maybe we can learn something from clams and oysters, who have been making their cement-hard shells from seawater one atom at a time for hundreds of millions of years.

There are two sources of polluting CO2 from making cement. The first is the CO2 released when the raw material limestone (calcium carbonate)is heated in kilns to make calcium oxide, the key ingredient in cement. CO2 is also released from the fossil fuel burned to heat the kilns. Just in time, many startup companies are testing new methods that minimize or eliminate one or both of these sources of CO2.

Two companies — Terra CO2 Technologies, in Golden, Colorado, and Brimstone Chemical Manufacturing, of Oakland, California — have kicked limestone out of the recipe and use other rocks: silicates like granite or basalt. Terra and Brimstone realized that the silicate rocks, which cover 80% of the Earth’s surface, could substitute for limestone. Silicates contain calcium but they don’t release CO2 when they are processed to make what the industry calls a “supplementary cementing material.” Pilot plants are being built in Texas and Nevada, respectively. The companies claim their methods will be 70-80% cleaner than traditional processes — and the cement or concrete produced should absorb CO2 from the air. 

Cement companies that use the traditional method are starting to pay attention because Brimstone recently received an independent endorsement certifying that its cement is structurally and chemically identical to old-fashioned cement. This is essential for the new cement to gain the acceptance of the cement and concrete industry.

Another company’s recipe, Carbon-Built Inc., of Los Angeles California, makes concrete blocks without heating rocks. What, no kiln? Their secret process captures a mineral binder from calcium-rich waste materials from “undisclosed industrial sources.”. (Maybe they are burning biomass material.) CO2 is added during the formation of the block to complete the reaction that yields conventional concrete. They claim a 70 to 100% reduction in CO2 emissions. They are already making concrete blocks at a factory in Alabama. With other partners, they are making blocks with CO2 captured from the air.

Yet another company, Sublime Systems Inc., in Boston, Massachusetts, uses electricity to split water (into an acid and a base) which reacts to dissolve calcium from silicate rocks. Calcium oxide is formed but it quickly reacts with the silicate material to form good, old-fashioned calcium silicate hydrate, which is of course cement as we’ve always known it. There is no kiln, just electricity. They have a pilot plant up and running in Massachusetts. The “sublime cement” they make passed all the industry tests and has been endorsed by the industry, like Brimstone.

Fortera, located in San Jose, California, has a way to double the yield of today’s cement factories. Fortera captures CO2 from one end of a conventional kiln and minerals from the other end and recombines them in a special solvent to make a stable form of cement. The process captures and reuses almost all of the CO2 that is generated in the kiln, doubling the yield compared to traditional methods. A pilot plant is being built in Redding, California.

Prometheus Materials, based in Colorado, is making concrete blocks starting with light and algae in a process they call “photosynthetic bio-cementation.”’ Yes, they use light to drive the growth of algae in very large tanks in simulated seawater with trace nutrients and CO2. This is essentially the process used by shellfish. Calcium carbonate forms and after mixing with “natural binders and aggregates” it becomes bio-concrete. Their process avoids essentially all of the emissions of the traditional method. They will begin selling precast products like concrete blocks next year.

These companies are cleaning up a product we all use but it is just one of the big planet-wide clean-ups we need to implement. Remember from our brief trip to Hawaii that CO2 is still increasing in our air. Until we take action to first slow and eventually reverse air pollution, the consequences will soon be utterly impossible to ignore. Weird weather will continue around the world with droughts, floods, vast wildfires, tornados and frequent hurricanes. Warming oceans will continue to melt ancient ice in Greenland and the north and south poles and sea level rise will reshape the shapes of continents.

Does anyone believe we could get through all this without a vicious economic contraction?

We’ve burned through fossil energy for more than 200 years to build ourselves a large industrial civilization. But unless we decarbonize our economy, Earth will choke us, flood us, or burn us. Fortunately, we can learn from mollusks how to make cement without air pollution since they do it all the time in the ocean without polluting the air.

Richard Gelinas, Ph.D., whose early work earned a Nobel prize, is a senior research scientist for the Institute for Systems Biology. He lives in Lakebay.