How much embodied carbon is in your portfolio?
Assuming your buildings were constructed with concrete or steel, the answer is likely high. But future additions to your portfolio don’t have to follow the same path. Architects are starting to push for concrete and steel with lower embodied carbon because these materials have massive carbon footprints. The global steel sector alone accounts for 10% of the world’s carbon dioxide emissions, according to Architect magazine, and concrete contributes another 6-11%.
But today, alternatives exist that can lower the carbon footprint of new buildings. Read on to discover how better buildings are built.
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Why There’s a Carbon Problem with Building Materials
For both concrete and steel, the embodied carbon problem lies in the way these materials are manufactured.
“The key ingredient of concrete is limestone that’s heated to about 4,000 degrees C., which is done with the burning of fossil fuels,” explained Sara Neff, director of sustainability for Lendlease. “Then, there’s also carbon trapped in that substance that off-gasses, which releases additional carbon.”
Steel is typically made in blast furnaces powered by coke, a purified version of coal. Burning coal releases carbon dioxide.
Both materials require energy-intensive production methods. However, today’s architects have greener choices than what existed just a few years ago.
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How to Make Greener Concrete and Steel
Today’s marketplace features lower carbon choices for both concrete and steel.
Electric arc furnace (EAF) steel mills run on electricity rather than relying on burning fossil fuels, which means they can be as green as the electricity mix supplying them. Lower carbon steel also typically contains a higher percentage of recycled steel.
Lowering the carbon footprint of concrete can take the form of one of two strategies:
- Material substitution replaces part of the concrete’s Portland cement content with fly ash, slag, silica fume or other products.
- Carbon sequestration injects carbon dioxide into concrete mixes to sequester it.
Neither can fully cancel out the concrete’s carbon footprint, but material substitution in particular is promising because different materials can also improve the concrete’s performance.
“High slag concretes are some of the best concretes that we’ve worked with,” said Eamonn Connolly, director of engineering for McHugh Engineering Group.
McHugh Concrete, in partnership with its ready-mix supplier Oremus and mix designer Master Builders Solutions, recently developed a greener concrete mix using slag for The Reed, a multifamily residential building in Chicago developed by Lendlease. The concrete mix replaces up to 60% of the concrete’s Portland cement with slag, a waste product formed in blast furnaces during steel production.
“From a building owner’s perspective, you’re getting not only sustainability, but durability,” Connolly said. “High slag mixes have one-third less embodied carbon than traditional concretes and we’re getting superior performance in terms of strength, stiffness and durability.”
High slag concrete mixes are denser. The concrete has fewer voids in it, which means less ingress of water and chloride ions, Connolly explained.
“Over time, that penetrates deeper into the rebar and causes corrosion. With a more dense and less permeable mix, you have less attack on the rebar, so your structure lasts longer,” he said.
Building with Greener Materials
How can you start incorporating lower carbon concrete and steel in your upcoming projects? Ask, Neff advised. Lendlease sets embodied carbon targets for each of its new buildings that reflect what materials are available regionally. Use online calculators, such as the Embodied Carbon in Construction (EC3) calculator or OneClick, to calculate the embodied carbon of building materials and set goals for reduction. Ask suppliers for EPDs for their products and compare them to baseline values to reach your reduction goals.
“Get started!” Neff urged. “Tackle what’s most important. Maybe you don’t want to do a full lifecycle cost analysis because that’s not in the budget. Focus on the steel and concrete—we know that’s where the most impactful parts of our emissions are. You don’t need a full LCA to reduce the carbon of your concrete and steel—that can be done now. The goal is to just get started. Don’t wait around.”
Read next: 7 Pathways to Greener Construction
