Humans' favorite thing to consume is water. Our second favorite thing to consume is cement. It’s the integral component of concrete, a material ubiquitous in buildings and sidewalks the world over.

Cement is the truly hard matter of the decarbonization game. It was one of the reasons I argued for the necessity of Carbon Dioxide Removal (CDR) in February, because decarbonizing the supply chains of heavy industry like concrete and steel will take time.

But it needs to start now: for every ton of cement produced, a little under the same amount of carbon dioxide goes into the atmosphere. Cement accounts for ~7% of total global emissions. The US is the third largest producer of cement but has the most carbon-intense cement production in the world, due to high clinker-to-cement ratios in US cement plants. Clinker (it sounds bad, right?) is a binding substance in cement that is produced in the cement kilning stage, and amounts to more than half of cement's emissions.

In short, it takes a lot of thermal energy to manufacture cement, and it will be difficult to decarbonize.

The first lever of this heavy lift will be the government, because 40% of all concrete in the United States is procured by the public sector, and more than half of that is procured by state and local governments.

That puts the government in a market-making position.

But before we go deeper on what those policies would look like, let’s talk about the emerging tech.

There are two main ways to reduce concrete’s net carbon pollution: (1) develop a new low or zero carbon process for producing cement, which is the major CO2 emitting component of concrete. (2) use it as a vehicle to absorb and store CO2 that would otherwise be emitted.

Green Cement:  Startups like Sublime Systems, Chement, and Brimstone Energy are developing ways to reduce or eliminate emissions from cement production. Sublime and Chement substitute fossil-fired kilns with electrochemical processes, eliminating direct heat emissions and making cement’s inherent chemical CO2 emissions much easier to clean up. Brimstone eliminates process CO2 emissions by swapping out (clinker-adjacent) limestone for calcium silicate, which does not release CO2.

Concrete as Carbon Storage:  CarbonCure and CarbonBuilt inject CO2 into fresh concrete for storage, reducing the final product’s net carbon intensity. By adding into the standard cement mixing process, this kind of tech avoids needing to revamp the concrete supply chain.

However, not all approaches are going to work. NREL authored a recent paper that found some tech in this category can lead to net emissions, because they can require more cement to make their concrete as durable as the standard stuff.

Now, back to policy that will help scale green concrete:

At the Federal level, a recent Executive Order included a national Buy Clean initiative that would begin to move the government to procure lower-carbon materials, including concrete. The General Services Administration, which oversees $75 billion in annual contracts, will now require federal contractors to use climate-friendly concrete and asphalt in the agency’s major projects.

States are taking action too. Each one produces concrete and there is a growing movement for state-level Buy Clean policies, which have passed in Washington (2021), Minnesota (2021), Colorado (2021), New York (2021), California (2021), and Oregon (2022).

Buy Clean is an important start, but most of these policies are laying the foundation for actual procurement later. They focus on setting standards for Environmental Product Declarations, so that government agencies can develop procurement standards, and industry can report embodied carbon in a uniform, verifiable way.

New York could move ahead of the pack with the proposed Climate Forward Concrete Leadership Act, which would add performance incentives for industry when they exceed minimum carbon thresholds and a process for expedited approvals - less than 6 months - for new low carbon concrete materials.

We need bolder action.

For a green cement startup to truly break into market, it needs the financing to build and operate capital-intensive cement plants. But the status quo cement industry is dominated by a handful of giant multinationals that will use their pricing power, supplier relations, and political connections to keep new entrants out– unless policy provides enough stick and carrots to truly transform the market.

What we need is something like a Low Carbon Concrete Standard that puts increasing limits on the allowable carbon content of concrete. We need governments to enter into Green Concrete Purchase Agreements (GCPA) with producers to buy clean at a particular volume and price. A GCPA would enable new cement manufacturers to secure the financing they need, to build new facilities and compete with incumbent producers. And we need regulators to focus more on performance outcomes (see NRDC’s new policy handbook for low carbon concrete procurement) rather than prescribing exactly what kinds of materials are permitted.

Green concrete is not as sexy as a Model 3, but it is the hard stuff that needs to get done. After all, if Elon thinks single lane underground tunnels (Google: Hyperloop) are a realistic solution to traffic, he'll need some good cement. Tweet that!