Green Cement

The companies and technologies looking to decarbonize our built environment

If you’re anything like me, you probably don’t spend a ton of time thinking about cement. It might be in the roads we drive on and the shopping centers and buildings we frequent, but it just blends into the background. It’s just sort of there.

If you stop for a second and think about it for a moment, you’ll realize that cement plays a huge role in the world we’ve built. It’s in our roads and bridges, our buildings and schools, the foundations of our homes. It’s virtually everywhere. But being everywhere can come with a carbon cost. It’s estimated that cement emits anywhere from 6-8% of global carbon dioxide emissions every year, which would make cement production the third or fourth largest emitter in the world if it were a country, comfortably behind China and the US, and sitting either right above or right below India, depending on the year and the data source you look at.

What is cement?

Cement is most useful as the primary input into concrete, the composite building material which is the most widely used building material on the planet. In fact, the only substance that we consume more of than concrete each year is water.

Most of the cement we produce is what’s known as Portland cement, which was developed in England in the early 1800s. Portland cement is the default standard industry cement, so standard in fact, that it is used in nearly 98% of global concrete production today. The production of Portland cement is carbon intensive by nature of the chemistry needed to produce it. Limestone is heated to over 2500 degrees Fahrenheit, which is such high heat that it requires lots of carbon emitting fuel to produce. Then, the chemical reaction produces a mixture of lime known as “clinker”, which is used to make the Portland cement, and carbon dioxide, which is emitted as waste.

The nature of the chemical reaction process doesn’t leave much room for reduced emissions through efficiency. For the most part, if you want the clinker, you’re going to have to take the carbon dioxide that comes with it.

How can we make cement green?

There are, of course, a few methods for reducing the carbon intensity of Portland cement. The first is utilizing fly ash in the mixture. Fly ash is a toxic byproduct of the coal burning process that can result in severe lung disease in humans and animals through exposure. Although fly ash used to be released into the atmosphere, today the US requires fly ash be captured and stored on site at the coal-fired power plants which produce it. When mixed in with lime and water, fly ash forms a Portland cement-like compound that reduces the carbon intensity from the chemical reaction process. An additional benefit is that this process also removes fly ash from the storage locations where it is sometimes kept in a less than secure manner, causing negative health impacts in neighboring communities.

While the removal of fly ash from these storage locations is a positive, coal plant closures in the US and globally threaten the supply of fly ash into the future. In the US, coal power plant capacity peaked in 2011 and has been declining steadily ever since. By the end of 2020 over a third of the total US coal capacity had been shut down. Utilizing the fly ash that has already been produced by the coal-fired power plants is certainly a solution but may not be a long-term one.

There are plenty of startups and small firms in this space that have been making a lot of progress towards green cement over the last few years that claim to be the long-term solution. Sioneer, a startup based in Stockton, in California’s Central Valley, has developed a technology that allows the fly ash to be replaced in the process with a treated, recycled glass, which they produce.

Another California based startup, Blue Planet Systems, pulls carbon dioxide from power plants and mixes it with calcium from recycled concrete. This process, which mimics the earth’s natural process of storing carbon in rocks, creates a “synthetic” limestone, which can then be used in the production of cement.

CarbonCure, another startup firm based on the Atlantic coast of Canada, has their own solution. By injecting carbon dioxide directly into concrete during the mixing process, it is chemically converted into a calcium carbonate which remains embedded within the concrete for thousands of years. If this carbon dioxide were captured from some other emitting process, this could serve as a method to sequester it and prevent it from reaching the atmosphere. As an added bonus, the calcium carbonate actually serves to strengthen the concrete.

All of these processes are slightly different, but the idea is the same. Inject carbon into the mixing process, trapping the carbon in the cement where is stays for a very long time. This is somewhat similar to carbon sequestration techniques such as planting trees, which keeps carbon in the organism rather that in the atmosphere. Carbon storage in rocks is a natural process of the earth, and controlling it through one of the mechanisms employed by these startups could be crucial step in lowering the carbon dioxide levels in the air.

What’s Stopping the Deployment?

On the whole, the construction industry is an incredibly risk-averse field, and for good reason. Structural engineers often do not want to use salvaged or recycled materials as are present in some of the potential solutions due to an inability to completely control the source material. They also can be weary about taking the risk on a “first-of-its-kind” project, without the right financial incentives. No one wants to be the engineer that stamped or signed off on the first ever bridge built from any new material, no matter how similar it may be to existing materials. Although green cement has been laboratory tested to the same overall strength as traditional Portland cement, structural engineers see too much personal risk to their careers and reputation, and the community, to deploy green cement without any push from outside agencies like government policy or regulation.

There is also the issue of cost. Green cement can cost anywhere from 75%-140% more per ton than Portland cement. However, cement is not the only input into concrete, and concrete is not the only input into construction. If the cost of cement were increased by 100%, it is estimated that the overall cost of building a new home should only increase by 0.25%-0.75%. Of course, who bears this cost is key. A cement supplier could get run out of business if the cost of their product went up by 100%, but a home builder could more easily sneak a half-a-percent surcharge into the total cost of a new home. Determining a cost structure that works for all of the players within the supply chain will be key to the equation.

Why Stay Optimistic?

Green cement is still a nascent technology and has a long way to go down the cost curve. However, just like residential solar installation has fallen from nearly $8/watt in 2010 to close to $2/watt today due to innovations all throughout the supply chain, deployment of green cement can help these companies down the learning curve. As the companies producing green cement scale, their costs will fall and their efficiencies will rise, and the cost premium of green cement will begin to decline.

The commitments from cities, states, and companies are also encouraging. While some of these commitments lack the willingness to back them up, some organizations are walking the walk. LinkedIn’s 245,000 square foot corporate headquarters in Silicon Valley was built with green cement and sustainable concrete. This model could be the push needed to convince other firms and jurisdictions that they can meet their carbon reduction goals through the building process. The developers, engineers, architects, contractors, subcontractors, superintendents, and workers all came away from the job site with green cement experience to add to their skillset and product offerings for the next clients who may enquire.

At the end of the day, green cement doesn’t drive the cost of building much higher. When carbon neutral substitutes reach cost parity, history tells us to watch out, because they’re coming a lot faster than we think.