New Innovation Drives Down Carbon Dioxide Emissions from Cement

Cement is the most ubiquitous manufactured product on planet Earth. It’s typically combined with gravel, sand, and water, then poured into molds laced with steel bars to make steel-reinforced concrete. That concrete is widely used in buildings, bridges, roads, wastewater systems, and virtually every other element of the built environment. The global cement industry is also a prodigious carbon dioxide emitter. For every ton of cement produced, nearly a ton of carbon dioxide is emitted. If the industry were a country, it would be the world’s third largest carbon dioxide emitter, behind China and the US. Efforts are underway to drive down those emissions, but first, let’s take a look at why the industry emits so much carbon.

The dominant type of cement produced by the global industry is known as Portland cement. It’s made by combining limestone and other raw materials, grinding up those materials, and then heating the mix in high-temperature kilns. The kiln heating is done to induce a chemical reaction that drives carbon out of the limestone, which then combines with oxygen, and is released as carbon dioxide. That reaction accounts for two-thirds of the carbon dioxide emissions attributable to Portland cement manufacturing. The remaining one-third is due to energy consumption, mostly to heat up the kilns, but some energy is also needed for grinding, material handling, and transportation.  

One obvious opportunity to drive down those carbon dioxide emissions is to use new forms of cement whose production and use results in far lower emissions, widely referred to as “green cement.” Indeed, the University of California, San Diego (UCSD), recently announced that a research team, led by structural engineering professor Yu Qiao (pronounced like “ciao”), developed an innovative technique for making green cement by mixing sand or soil filler with a polymer binder.

The UCSD team’s recipe for green cement consists of 96% filler, by weight, with 4% polymer binder. The binder may be either regular epoxy or thermoset polyester plastic. Compared to ordinary Portland cement, producing the UCSD product releases 95% less carbon dioxide. Furthermore, the materials required cost less than Portland cement.

The key problem the UCSD team faced was that conventional mixing techniques just aren’t good enough to thoroughly mix up the filler and binder. They could get around this problem by using excessive amounts of binder, in the range of 10% to 15%, but that would make the cement impractically expensive. Instead, the UCSD researchers found they could reduce the amount of binder down to 4% by pressurizing the filler and binder mixture to 10,000 to 15,000 pounds per square inch (psi). At that pressure, capillary forces drive the binder into the most critical spaces between the filler grains.

The UCSD researchers tested the material that emerged from their pressure cylinders and determined that it was so strong it didn’t need to be combined with water, gravel, and steel reinforcing bars like Portland cement. This cement was ready to be used in construction as is. For example, steel is used to reinforce concrete in order to improve its ability to resist bending forces. When the UCSD team ran a flexural strength test, they observed that their green cement was able to resist much higher bending forces than steel-reinforced concrete. They also found that their green cement achieved compressive strength comparable to high-strength concrete.

The UCSD researchers also expect their green cement to feature excellent water and corrosion resistance, weatherability, and thermal stability, just like concrete made with Portland cement. It would appear that there are many reasons to anticipate that the UCSD green cement would be a superior product to steel reinforced concrete.

According to Professor Qiao, he is investigating opportunities to commercialize his team’s new product. He plans to start out in the precast market, where the cement can be mixed, poured into molds, pressurized, and cured under controlled conditions. The precast parts would then be shipped to job sites. His laboratory is capable of producing 500-pound parts. He’s planning on starting with bridge panels and other infrastructure parts, as the codes and standards for these parts are less restrictive than for building components. In theory, his team does have a process for the mold-in-place market, but he wants to succeed in the precast market first. Qiao says he is currently “evaluating whether to keep doing R&D to better develop the technique versus beginning commercialization now.” Should he decide to go the commercialization route, he’s yet to decide whether to license an existing cement producer to use his team’s process or to start a new company.

Qiao and his team will have to choose their business model carefully, as there are many barriers to market entry for a green cement product. Perhaps the biggest barrier is one that’s as formidable as, well, a 30-foot high reinforced-concrete wall: Portland cement has been the dominant technology in the construction market for over a century, and many building codes and standards require Portland cement for concrete construction, whether or not there are alternatives that can do the job just as well. Another major barrier is that cement specifiers and consumers (think architects, engineers, developers, and builders) are notoriously risk averse. It can take years of reliability tests and field experience to persuade them to try a new construction product. In the absence of public policies driving them towards low carbon materials, they have little motivation to go outside of their comfort zone, or to select a costlier alternative (apparently, this isn’t a problem for UCSD green cement, but could be for other green cements).

Despite these imposing barriers, a few green cement products are already on the market. Two early entrants include Zeobond and Solidia Technologies. Zeobond claims the ability to reduce carbon dioxide emissions as much as 60% by replacing some of the Portland cement in its concrete mix with alternative materials, like flyash from coal-burning power plants. Solidia claims to reduce emissions up to 70% by producing a new kind of cement that mixes with carbon dioxide instead of water to make concrete. Ideally, at some point in the future, the carbon dioxide the company uses would be recovered from the exhaust streams from coal-burning power plants and other industrial sources. Neither company appears to have made a major dent in the market so far.

Given the importance of cutting cement-industry carbon dioxide emissions as well as the handful of alternative products either available now or on the way, it’s time to start chipping away at those barriers. Building industry professionals, on your next project, how about replacing some of the Portland cement with green cement where allowed by building code? Investors, get ready for new opportunities in an exciting market. Climate activists, it’s time to start lobbying to change building codes so that they continue to protect public safety while allowing more flexibility in cement selection. And for the rest of us, watch for green cement, perhaps even UCSD’s product, to show up in a project near you soon.