The Move Toward Sustainable Concrete
Fortunately the last two decades have seen a marked increase not only in the construction industry's awareness of climate change but also its awareness of the carbon footprint of traditional concrete. This has led to a growing push for green concrete solutions, both from industry players and from government administrations across the US and the globe. "The concrete mix of 20 years ago is not the concrete mix of today," LeMonds says. "The low carbon concrete space has had significant uptake since the 2000s."
Across the market there are a wide variety of sustainable concrete solutions. Many innovations include the replacement of traditional Portland cement, which emits large amounts of CO2 in the cement production process, with cementitious materials and the incorporation of recycled aggregates.
"Sustainable concrete often replaces a portion of Portland cement with alternative materials like fly ash, slag, or natural pozzolans," LeMonds says. "These substitutes reduce CO2 emissions and resource consumption."
Portland-limestone cement is a popular alternative that is blended with a higher limestone content than traditional cement, reducing CO2 emissions by 5 to 10%on average.
"The concrete mix of 20 years ago is not the concrete mix of today."
"It's kind of like baking bread," says Erin Winston, structural project manager for HKS. "You use the same materials, but with various ratios you get very different results." Rather than dictate the exact mix it uses on projects, HKS provides performance benchmarks and lets local producers who often closely guard their proprietary mixes-decide how to achieve them.
Holcim's OneCem Portland limestone cement, for instance, is manufactured with 10% finely ground high-quality limestone, resulting in a 10% lower embodied carbon. It has been rigorously tested and can be used in virtually any application-from residential construction to large-scale infrastructure.
Much of the embodied carbon in cement comes from the heating process in manufacturing, "because a lot of those kilns don't use high-quality energy sources; they're using coal or dirty coke that create the most emissions," Getz says.
Concrete producers are beginning to take action on this front. By the end of the year Holcim will be sourcing 40% of its energy needs at its 350 US facilities from renewable sources like wind and solar. "The goal is to drive transformative change," LeMonds says. "You can end up with extremely low carbon concrete if you add low carbon electricity into the mix.”