Can the Concrete Jungle Sink CO2?

By the time today’s preschoolers hit middle age, the number of buildings on the planet is projected to double. An already unprecedented wave of urban migration will continue to grow, with two-thirds of the world’s population flocking to cities not yet on the map. And while sun and wind may power much of this new construction, the whopping majority will be built with roughly the same material used to construct the Pantheon nearly 2000 years ago—concrete.

Concrete involves three main components: water, aggregate (rock, sand, or gravel), and a binding agent to hold it all together. Portland cement, the most common binder, accounts for more annual carbon emissions than every country on the planet, except for the U.S. and China. Kate Simonen, an architect and founder of the Carbon Leadership Forum, notes that embodied emissions—those released from the manufacturing of industrial materials—are going to rise, at least as a percentage of the overall impact. “As building codes become more stringent and the electrical grid decarbonizes, the relative proportion of impact due to material production increases.”

But is it possible to clean up concrete’s supply chain? A new bill in New York is not only betting on it, but also that it’s scalable, with the right policies to nudge the industry forward.

Building on the state’s landmark climate bill passed last spring, the proposed legislation requires that carbon emissions from concrete become the determining factor, after cost and structural considerations, when selecting bids for state contracts. There are many ways to lower concrete emissions, from decades-old low-tech solutions to new technologies that use carbon in the production process itself. The idea is to incentivize suppliers to measure how much CO2 their concrete mixes emit, which they have no obligation to report currently. Then, suppliers must use any available fix to reduce emissions without ballooning costs, catalyzing a race to what was once considered far-fetched: affordable, carbon-sinking concrete.

Governments are the largest purchasers of concrete. By changing the procurement process of the country’s third-largest economy, the bill hopes to cause a ripple effect, as suppliers sell cleaner products to other markets. It would also launch the state on a path to reduce industrial emissions while continuing to decarbonize electrification. “Everyone knows that producing more renewable energy is better than burning more fossil fuels,” says Assembly Member Robert Carroll, the bill’s sponsor. “But most people don't know the difference between cement and concrete or how carbon-intensive they are to create. It's a huge issue if we're going tackle climate change.” 

Knowing the carbon footprint of a particular mix is a first step, according to Jeremy Gregory, the Executive Director of the Concrete Sustainability Hub at MIT. To do this, companies can create an Environmental Product Declaration (EPD), what amounts to a nutritional label about a product’s environmental impact. Until recently, creating EPDs required several months and independent, individual verification. Given that a single concrete plant produces hundreds if not thousands of different mixes, developing EPDs for an entire plant was both time-consuming and expensive.

Digital automation, however, is becoming a trend in the sector and is lowering costs. In 2013, Climate Earth, an emissions analytics company, designed an EPD generator that enables concrete plants to create reports for new mixes within seconds after an initial setup period. Central Concrete, a West Coast subsidiary of U.S. Concrete, became the first plant in the country to create EPDs for all its mixes, and Eastern Concrete may follow suit in the Northeast. This past November, the Carbon Leadership Forum published the first free, cloud-based tool to calculate embodied emissions for construction projects, using EPDs as raw data and making it easier for architects and engineers to understand the performance and embodied emissions of materials.

Making EPD declarations mandatory will create incentives to find similar solutions. “Measurement matters,” says Gregory. “Reporting and publicizing the environmental impact of materials will lead to companies wanting to differentiate themselves from bigger emitters.”

New York’s proposal builds on these advances, as well as a handful of new polices enacted on the West Coast, to jumpstart a market around low-carbon concrete. The City of Portland now requires all concrete suppliers to submit EPDs for city contracts, while Marin County just published the first low-carbon concrete building code in the country. At the state level, California’s Buy Clean Act set maximum carbon thresholds for a range of building materials and may include concrete with an amendment this year.

Carroll and a growing number of cosponsors are hoping to make New York the first state to use competition to target emissions from concrete manufacturing. The bill would award contracts to suppliers who demonstrate the greatest carbon reduction with the lowest prices. Companies who deploy carbon capture and utilization (CCU) technologies in the production process would be further prioritized, with an eye to hastening the development and adoption of carbon-negative mixes.

Several startups are attempting to commercialize CCU in concrete manufacturing. CarbonCure Technologies and Solida, the most established of the set, are both partnering with large-scale cement manufacturers like Lafargeholcim to test and review CCU. Others have conducted noteworthy demonstrations, like Blue Planet’s carbon-sinking aggregate used in parts of San Francisco International Airport. CO2Concrete projects that its plant will produce 10 tons of concrete a day while cutting CO2 by nearly 70%. And Calgary-based Carbon Upcycling, which absorbs carbon to strengthen fly ash, a cement substitute, that can reduce emissions by up to 40%, is setting up a second plant in New York with support from New York State’s Energy Resource and Development Authority (NYSERDA).

“As architects and engineers, we have to think of ourselves as sink-builders,” says Bruce King, a structural engineer and driver of the Marin County code change. “We have to store more than we use.” The industry, King says, knows this is coming. “It’s a matter of habit and inertia. We throw in extra cement that isn’t structurally required.”

Still, changing the way a large state like New York procures concrete is a gargantuan task that involves multiple state agencies and reversing decades of standard practice. Comparing functional performance, environmental performance, and cost is a complicated process with no one-size-fits-all-projects solution. There’s also the question of whether suppliers will take kindly to an EPD mandate and preferential treatment for carbon-cutting companies. And yet, for New York to meet its climate goals, as well as the nation and the world, addressing industrial emissions is paramount. According to Simonen, who’s been leading the charge on lowering embodied emissions for over a decade, waiting is not really an option. “We simply don’t have time to approach this in a linear fashion.”