Major construction firms team up to get the carbon out of concrete

The Climate Group’s ConcreteZero initiative will set standards and create markets for low-carbon concrete. Experts say its early goals are well within reach.

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A consortium of construction firms, property developers and building engineers plans to use their collective heft to drive down the carbon emissions of one of the world’s most ubiquitous building materials. As part of the new ConcreteZero initiative, 17 companies have pledged to bring the proportion of low-emissions” concrete they use to 30 percent by 2025 and 50 percent by 2030. The companies — which include major European construction firms such as Laing O’Rourke, Mace, Skanska UK and Willmott Dixon; property owners and developers such as Canary Wharf Group and Grosvenor; and engineering firms such as Buro Happold and Thornton Tomasetti — say they’ll use only zero-carbon concrete by 2050

That 2050 goal is a bold one that will be hard to achieve. Production of cement, the raw material in concrete, accounts for between 7 and 8 percent of global carbon emissions today, due both to the fossil fuels used in its high-heat production and the chemical composition of the raw materials and processes that make it. These emissions have been rising, not only because of the ever-increasing demand for concrete for buildings, roads and bridges but also because the carbon-intensity of global cement production is increasing, according to recent research.

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The International Energy Agency has tracked1.8 percent annual increase in the carbon-intensity of global cement production from 2015 to 2020, a trend line that is moving in the opposite direction of the 3 percent annual declines IEA says the industry must achieve to be on track with its net-zero by 2050 goal. 

But the options to reduce the carbon-intensity of concrete — the combination of cement and gravel, sand and other aggregate materials that is mixed with water and poured into forms that harden into rocklike rigidity — are broadly available, practical and cost-effective today, building decarbonization experts say. 

That’s why Climate Group, the U.K.-based nonprofit leading the ConcreteZero initiative, is enlisting concrete-using companies in demanding lower-carbon methods and materials and setting the definitions and standards for what counts as low” and zero”-emissions concrete. 

It’s time for concrete targets to reduce carbon emissions in years, not decades,” Jen Carson, Climate Group’s head of industry, said in a statement on Monday. ConcreteZero is signaling to the industry that the biggest buyers want the industry to innovate and act now.” 

ConcreteZero is modeled on similar Climate Group initiatives that have enlisted corporations to pledge to boost their use of renewable energy and, more recently, to commit to sourcing a rising quantity of low-carbon steel, another major source of global carbon emissions that will be hard to decarbonize.

Boosting demand for concrete that carries a lower embodied carbon” footprint will be a vital step in driving the concrete industry to invest in the alternatives available today that could allow ConcreteZero members to hit their goals through 2030, said Victor Olgyay, a principal in the carbon-free buildings practice of nonprofit think tank RMI. (Canary Media is an independent affiliate of RMI.) 

Today, there are ways to cost-effectively reduce the climate impact of cement and, by extension, concrete, by 50 percent with essentially no cost,” Olgyay said in a Monday interview. The trick is not to try to reduce the energy- and chemistry-derived carbon emissions of making cement, which are still in the early stages of technological development, but to concentrate on reducing how much cement is used in the concrete going into construction. 

The low-hanging fruit for reducing concrete’s embodied carbon impact 

Engineers and architects can reduce the proportion of cement in a number of ways, Olgyay said. One is to use higher-quality aggregate that imparts more structural integrity to the concrete that’s made with it, he said. 

Another is by using what’s called supplementary cementitious materials” to replace a portion of the cement used in different mixes of concrete. Fly ash from coal plants and slag from steel mills are the most common alternatives and are being put to use by some major cement and concrete companies such as Cemex. But rice husks, ground glass and several other alternatives can replace anywhere from 10 to 40 percent of the cement,” Olgyay said. 

However, there are barriers to making these shifts, Olgyay went on to explain. The first is that concrete is a structural material that holds up buildings, and engineers are very cautious about messing around with the mix.” 

Convincing concrete specialists such as ConcreteZero members Byrne Bros. and Morrisroe to designate standards for concrete mixes that use varying proportions of these alternative aggregates and cementitious materials for different purposes could help eliminate this barrier. The U.S.-based Structural Engineering Institute has published guidelines on how to avoid the overuse of concrete to reduce carbon impact. Similarly, the mixes employed for high-strength concrete used in bridges or skyscrapers are very different than that used to pave sidewalks, Olgyay said. 

The second barrier to more widespread adoption is that there’s currently not a lot of demand” for lower-carbon concrete, he said. That puts relatively little pressure on the ready-mix” companies, which combine cement with the various sources of aggregate materials available locally to serve regional construction needs, to seek out or invest in alternative materials. 

Efforts like ConcreteZero’s could play a valuable role in boosting this demand, Olgyay said. So too will regulatory pushes like the U.S. federal government’s call to the concrete and asphalt industries to provide lower-emissions materials for federal construction projects, or the state-by-state policies mandating lower-carbon concrete standards for government contracts. 

Setting the standards for measuring the carbon footprint of different concrete materials and mixes is also needed to provide transparency between concrete makers and buyers, Olgyay added. Luckily, environmental product declarations that assess the embodied carbon footprint of different mixes of cement and concrete are generally available, with those provided by the Embodied Carbon in Construction Calculator (EC3) tool serving as today’s gold standard. 

Three or four years ago, virtually nobody was talking about this in the construction industry,“ said Andrew Himes, director of collective impact at the Carbon Leadership Forum, the nonprofit group that developed the methodology behind the EC3 tool. But the understanding that up to half of a building’s lifetime carbon impact is tied up in the materials used to build it, not just the energy used to heat, cool, light and otherwise operate it, has changed that situation dramatically, he said. 

Cement production: The tougher part of decarbonizing concrete

Reducing the carbon emissions associated with making Portland cement, the type of cement used in most of the world’s concrete, will be more challenging, Olgyay said. Making Portland cement involves heating kilns to temperatures of greater than 1,400 degrees Celsius, a level of heat that’s hard to achieve without burning fossil fuels. And the raw material of cement, limestone or calcium carbonate releases carbon as part of the process that transforms it into clinker,” a precursor material to cement, accounting for between 50 to 65 percent of cement production’s total emissions. 

Various methods are being explored to reduce emissions without altering the fundamental formula for making Portland cement, Olgyay said. Canadian startup CarbonCure has developed a technique of injecting carbon dioxide captured from emitting sources into concrete as a means of storing the carbon and strengthening the concrete, for example.

Still others are looking at ways to reduce the amount of energy needed for the heating portion of this carbon emissions profile or to switch to carbon-neutral sources of energy. Others are exploring alternative materials to calcium carbonate that won’t emit carbon dioxide when heated to form cement. More esoteric concepts include using living organisms to grow” cement.

These new chemistries for cement are very interesting, but they’re emerging technologies,” Olgyay said. In the meantime, he said, existing methods to reduce the carbon intensity of concrete should be the industry’s focus, rather than waiting for cost-effective means to capture and store the carbon emissions from their facilities to achieve the final reductions necessary to achieve zero-carbon goals. 

That makes for some uncertainty on how to reach this end goal, he said. But in the meantime, the group’s 2025 and 2030 goals are both easily achievable and broadly in line with” targets set by the United Nations’ Intergovernmental Panel on Climate Change for reducing greenhouse gas emissions at a pace and scale needed to limit the most catastrophic harms of climate change.

Jeff St. John is director of news and special projects at Canary Media.