Cement's climate cost may be solved with a different kind of rock
Cement rarely comes up in conversations about climate change, yet the industry produces roughly as much carbon dioxide as all the passenger cars on the planet. A new study proposes a surprisingly straightforward fix: swap out the rock that cement is made from.
Using a different type of rock as the raw material could cut energy use by more than 40% and slash associated carbon emissions by over 80%. The research, led by Jeff Prancevic, a geologist at UC Santa Barbara, and Cody Finke from Brimstone Energy, Inc., offers a potential solution to the cement industry's significant carbon footprint.
Cement production and CO2 emissions
Portland cement, the kind used in virtually all modern construction, is responsible for around 4.4% of global greenhouse gas emissions. This surprising statistic often goes unnoticed due to cement's lack of visibility compared to cars or power plants.
"Cement barely registers in the public mind as a major driver of climate change, but the CO2 emissions from cement production are similar to all the world’s passenger cars," Prancevic said. The issue lies in the raw material: cement currently relies on limestone, which is chemically about half CO2. When heated to produce quicklime, the key ingredient in cement, CO2 is released directly into the atmosphere.
Around 500 kg of CO2 escapes per metric ton of cement produced, before even accounting for the energy used in the process. This method, refined over more than a century, is essentially baked-in carbon emissions.
A different rock, a different chemistry
The study asks a direct question: what if the calcium came from somewhere else? The researchers investigated calcium-rich silicate rocks, such as basalt and gabbro, as a replacement for limestone.
Unlike limestone, silicates don't store carbon in their chemical structure, so processing them doesn't release CO2 in the same way. The first step was checking the availability of these rocks. Using geological maps, the team found quantities sufficient to supply cement production for several hundred thousand years at current rates.
"Not all of that basalt is easily accessible, but the numbers suggest that calcium from basalt is virtually inexhaustible," Prancevic said. The team then modeled the energy and emissions profile of silicate-based cement production, finding that the theoretical minimum energy requirement was less than 60% of what limestone processing demands.
Using natural gas as an energy source, minimum CO2 emissions per ton of cement could fall from 609 kg to around 50 kg, depending on the specific rock type. Even with average grid electricity and current unoptimized processes, the approach would cut emissions by more than 25% compared to conventional methods.
Iron and aluminum from basalt
One of the more striking findings is what comes out of the process alongside cement. Basalt contains iron and aluminum in addition to calcium. The ratio of calcium to iron in basalt happens to be almost exactly the ratio in which society consumes cement and steel.
This means both materials could potentially be produced from the same rock, with little waste of either. On top of that, basalt contains roughly 20 times more aluminum than current global consumption levels, opening up new production opportunities.
Producing multiple valuable materials from a single feedstock is a major reason the silicate route is more efficient. It resembles a more integrated industrial system, rather than a single-purpose process generating one product and a lot of CO2.
Changing an entrenched industry
Despite its appeal, this approach faces a formidable obstacle: the cement industry has been doing things the same way for well over a hundred years. "The construction industry is built around Portland cement, from design to placement to maintenance," Prancevic said.
"Even subtle changes in standards are painstakingly considered and are slow to be adopted. This is exactly why we’ve focused on technology to make the same Portland cement builders are used to."
Lower-carbon alternative cements have existed for decades but haven’t displaced conventional cement due to insufficient financial incentives. Switching would also require changes to established supply chains and building standards.
By producing standard Portland cement from a different rock, the silicate approach sidesteps that barrier. It can slot into existing infrastructure rather than requiring the industry to rebuild around something new.
Cement is also cheap, at around $150 per ton. Any new production method will need to demonstrate meaningful cost savings or at least parity to gain real traction.
Experimenting with new technologies
Prancevic's co-authors at Brimstone Energy are working to bring the technology to market. The paper is also an invitation to the wider research community to experiment with new technologies to accelerate cement decarbonization.
"This paper is really a call for other researchers to experiment with new technologies to accelerate cement decarbonization because there is the potential to solve a climate problem as big as cars simply by sourcing calcium from a different rock," Prancevic said.
"I’m surprised that it’s taken so long for this solution to be considered," he concluded.
The study is published in the journal Communications Sustainability. Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.
