Various tools to cut the carbon footprint of concrete have been proven in countries around the world. Combining these tools could cut concrete-related emissions by about three-quarters, yet no country is using them all. That ought to change.
That was the argument Sabbie Miller, a professor at the University of California, Davis, a faculty scientist at Lawrence Berkeley National Laboratory and faculty director of the Materials Decarbonization and Sustainability Center, brought to campus this month for the second Energy Solutions Forum of the semester.
“We are consuming on a rough order of magnitude 30 billion metric tons of concrete every single year on the planet,” Miller said.
Concrete goes into houses, roadways and sewer systems, and producing it accounts for roughly 8% of global human-generated carbon dioxide emissions, she said, and making the materials that go into the built environment accounts for about 15%. None of that counts the construction itself. Cement, a key ingredient in concrete, is responsible for a large part of concrete’s emissions.
Three changes, none of them new
Miller’s group at UC Davis tested what would happen if every country matched the best practice another country had already proven.
They found that cleaner, more efficient kilns would cut concrete’s emissions by about 20% by 2100.
Better-graded aggregate and wider use of supplementary materials would cut emissions by more than 30%.
Choosing stronger, more durable materials while staying inside existing building codes would cut more than 10% of emissions.
Stacked together, she said, those three stages would reduce greenhouse gas emissions from concrete by roughly 75%. And the figure assumes no new technology, only wider use of what already works.
“There are strategies already out there,” Miller said. “We just might not be implementing them to the fullest extent yet.”
But even that approach fails to reach zero by 2050.
The last stretch of Miller’s talk turned to a speculative idea: using the built environment itself to store captured carbon dioxide, in cements that harden by absorbing CO2, and in synthetic aggregate, biochar and timber. Scaled against how much of these materials the world consumes, she said, that could meet the carbon storage targets set by the Intergovernmental Panel on Climate Change.
Why it hasn’t happened
Asked how far the aggregate strategy can go before concrete simply needs cement, Miller agreed that concrete can never be cement-free.
“We can’t get it to net zero cement because we need something to hold everything together,” she said. But most of the world still mixes concrete with two sizes of crushed rock, leaving gaps that cement paste must fill. Canada uses three. Brazil uses four on many projects.
“I don’t know why [the] U.S. has kind of been hung up on two,” she said.
Another question turned to economics and whether cost ultimately forces the choice of method. Some strategies, Miller said, are not viable without subsidies through carbon credits. Others are already cheaper and still go unused. Reuse is the clearest example: a recent California study found that repurposing industrial buildings into housing could cut 40% of the state’s anticipated emissions from housing.
Miller said the barrier in that case is who pays and who benefits.
“Who owns the structure, who’s using the structure, who’s actually getting the benefit of not replacing the structure,” she said. “They end up being different entities.”
An overlooked source of greenhouse gases
“We tend to think about the key main sources of greenhouse gases being fossil fuels that we burn, automobiles and airplanes,” said Christopher Barile, the chemistry professor who coordinates the forum. “There’s actually a significant fraction of greenhouse gases that comes from industrial materials. And so concrete is really a big one, probably steel’s number two. And these are processes that are really hard to decarbonize.”
Attendees include students, faculty and interested members of the community. Among those listening were Mick Hitchcock, the biochemist and philanthropist who founded the series, and Scott Bassett, associate dean of the College of Science.
Coming this fall: The Energy Solutions Forum closes its fall semester on Nov. 18 at 4 p.m. with Taylor Wilson, applied nuclear physicist and founder of Prometheus Industries and Talos Materials, on the future of nuclear energy technologies. The series is free and open to the public, and registration is .
