Innovation will be key to accelerating the clean energy transition and reaching a net zero economy. Edison Energy is following the latest innovations in decarbonization across technologies, projects, and programs, from conception through completion.
The big picture
Global cement production makes up approximately 7% of annual greenhouse gas (GHG) emissions through the burning of quarried limestone. Researchers have now found a way to make cement production carbon neutral by using limestone grown with microscopic algae, or microalgae.
The research team was recently awarded a $3.2 million grant from the U.S. Department of Energy’s (DOE) Advanced Research Projects Agency–Energy (ARPA-E)
How it works
Concrete is produced by forming a paste made of water and portland cement, which is the most common and widely used cement globally. Materials such as crushed stone, gravel, or sand are then added, with the mixture hardening into concrete.
Portland cement is produced by extracting limestone from quarries and burning it at high temperatures, which releases large amounts of carbon dioxide (CO2). Replacing quarried limestone with biologically grown limestone creates a net carbon neutral way to produce portland cement.
In addition, ground limestone is often used as a filler in portland cement, typically replacing 15% of the mixture. By using biologically grown limestone instead of quarried limestone as the filler, portland cement could become net neutral and potentially carbon negative by pulling CO2 from the atmosphere and storing it permanently into the concrete, according to researchers.
The inspiration behind the innovation comes from coral reef structures. These structures are formed when each individual stony coral organism secretes a skeleton of calcium carbonate – a main component of limestone.
The researchers decided to cultivate coccolithophores, a species of microalgae that can create calcium carbonate deposits during photosynthesis. Microalgae can survive in both warm and cold freshwater and marine systems, making them the perfect candidates for cultivation on land or water. Just 1 to 2 million acres of open ponds would be needed to produce all the cement the U.S. needs.
Notably, biogenic limestone can be produced in real time, while natural limestone can take several million years to form.
Why it matters
Concrete is the most produced material in the world. Twice as much concrete is used in construction as all other building materials combined. Ton for ton, its global usage is twice that of steel, wood, plastics, and aluminum combined.
If all cement-based construction globally were replaced with biogenic limestone cement, it would stop 2 gigatons of CO2 annually from being released into the atmosphere. Another 250 million tons of CO2 would be pulled out of the atmosphere and stored in the cement.
Researchers believe that replacing quarried limestone with a biogenic version could also improve air quality, reduce environmental damage, and increase equitable access to building materials.
The research team was recently selected by the HESTIA program (Harnessing Emissions into Structures Taking Inputs from the Atmosphere) to develop and scale up the manufacturing of biogenic limestone-based portland cement.
Minus Materials, Inc., a CU Boulder startup, has helped commercialize the product with financial support from investors and corporate partnerships. The limestone is currently available in limited quantities.
Stay tuned for the next installment of the Energy Edge Innovation Series!