Carbon emissions set in cement?

The cement industry is the definition of “hard to abate,” but the challenge of reducing carbon emissions from our most-used construction material is breaking the traditional mold.

An exciting corollary of the push to decarbonize human activities is that it is forcing industries that have been the foundation of modern society — such as cement, steel, mining, and chemicals — to take a fresh look at their operations. Concrete, for example, the mix of aggregates and high-carbon-emitting cement that shelters, supports, elevates, tunnels, and bridges for humanity, must maintain its reliable, solid qualities, but the industry is investigating how its constituent parts and processes could be reimagined for a low-carbon world.

Ian Riley, CEO of the World Cement Association, says that some 20 years ago, the industry recognized that its emissions — at that stage, CO₂, dust, and nitrous oxides (NOx) were given almost equal weight — were a threat to its social license and sustainability. Much was achieved, especially in China, the world’s biggest cement producer accounting for 55% of global output, to reduce the dust and NOx factor. The energy efficiency of the limestone mining and coal-fired kiln processes has also been improved by 30% over recent decades, resulting in lower carbon emissions. Fuel switching to biomass or refuse-derived fuel — burning baled waste to generate electricity — a strategy deployed particularly in Europe, yielded further CO₂ reductions. And cutting the concentration of “clinker” in cement from 84% to a global average of around 70% also had a significant effect.

But the cement industry is still a significant emitter of CO₂, responsible for some 8% of global emissions, according to an article in the journal Nature — and clinker is the clincher behind cement’s hard-to-abate label.

Why are cement industry CO₂  emissions so hard to abate?

The calcination of limestone produces two-thirds of carbon emissions from the cement industry. “Clinker is made by heating limestone to 1,450 degrees Celsius,” explains Riley, “which causes the limestone to decompose into calcium oxide and CO₂. So, the process uses a lot of energy, but even worse, it gives off a lot of CO₂.”

And although cement makes up only about 12% of the volume of most concrete (it’s the substance that binds the usual aggregate of fine and coarse rocks), it is almost entirely responsible for the carbon footprint of concrete, which is why the two terms “cement” and “concrete” are often used interchangeably when talking about carbon emissions from concrete as a building material.

Another barrier to abatement is the cost of the various mitigation technologies relative to the price of concrete, which is at best sold at margins of 5-10%.

As an energy technology company, Baker Hughes is working to apply the technical knowledge and expertise it has developed over many years of helping to decarbonize the oil and gas industry to industries such as cement and steel production. Nikhil Khurana, the company’s Decarbonization Engagement Leader, acknowledges the cost constraints on cement, saying, “If you consider that producing one ton of clinker generates 0.8 ton of CO₂, the abatement cost of creating green cement today is around $100 per ton. So, the price of cement would have to increase by around $80-$100 per ton — or double its current price.” 

And global standards for the composition of cement and concrete are necessarily cautious about adapting to new cementitious products. Standards that deliver strength, resilience, and reliability of building materials are essential to the safety of people living in or in the lee of concrete structures — think multi-story buildings, dams, freeways. New technologies that use strengthening additives to substitute for some of the clinker in cement or geopolymer binders to replace cement completely have frequently come up against a concrete wall of hard-fought regulation that resists their adoption.

On the other side of the wall, net-zero-carbon commitments by companies and countries, along with emerging carbon-price regimes, are gradually creating demand for new low-carbon products — an environment in which new technologies can scale and be validated for use in construction. Ingenuity and new possibilities are reaching for the skyscraper, sizing up oil wells for lining with new blends, and even channeling entirely new revenue streams for the cement industry.

Putting a new spin on the carbon-bedeviled cement mix(er)

Riley is placing his informed bets on three technologies to decarbonize cement and concrete: i) increased use of supplementary cementitious products in cement and concrete, ii) synthetic aggregates made from CO₂ and with a negative CO₂ footprint, and iii) direct carbonation of concrete which absorbs CO₂ and improves strength. He says cement producers in areas with access to Kaolin are investing their own money — as opposed to being kickstarted by government funding — in the Swiss-developed LC³, or limestone calcined clay cement, which combines 50% clinker with 30% calcined clay (produced by heating kaolinites such as china clay or paper sludge waste), 15% limestone and 5% gypsum. 

According to Baker Hughes experts, other technologies available today to help decarbonize the manufacturing process include the use of hydrogen to produce heat and waste heat recovery systems.

Argos, the fourth largest cement producer in Latin America, has repurposed one kiln at its Colombian plant to process kaolin. Riley also cites a Portuguese company, Cimpor, having built a greenfield LC³ plant in Ivory Coast. “I think we’re going to see most of the majors and regional companies looking seriously at the potential for calcined clay, but to make the economics work, they have to secure the reserves in the right place. Otherwise, it becomes pretty much unfeasible,” says Riley. In LC³’s favor is that the technology is proven, the standards are already beginning to change to accommodate the new blend, and depending on geographical access to the new, comparatively inexpensive material, Riley says that “the economics look attractive in some cases, in others they look acceptable.”

The upshot for the climate is that LC³ represents a 40% reduction in carbon emissions compared to OPC (Ordinary Portland cement), which uses 95% clinker and 5% gypsum, and a significant reduction on already modified cement mixes that have reduced the clinker component to 70%.

Riley says a large range of other mixers are in the early stages of testing and validation, but that some of the most interesting are in the category of concrete-strengthening additives — he mentions graphene and hybrid nanotubes — which need only be applied in small amounts to have a reinforcing effect that reduces the need for high concentrations of carbon-releasing clinker in cement, or the amount of cement in concrete.

Carbon capture, utilization, and storage

Carbon capture, utilization, and storage (CCUS) solutions will definitely play a key role in decarbonization of the hard-to-abate sectors. Some emissions will be stored, for example, in underground geological formations, others will be transformed into a variety of value-added products such as chemical building blocks. As Khurana says, “Partnerships and cooperation on CCUS technological solutions are crucial to succeed in the quest for carbon neutrality. For instance, building more and more use cases for captured carbon will be important.”

The cement industry has potential use for captured CO₂, in that concrete absorbs CO₂ as it cures, and it can be made to absorb more than the usual quantity of CO₂ if it is injected with the gas during batching and mixing or if it is cured in, say, a chamber filled with the gas. The Intergovernmental Panel on Climate Change (IPCC) reports that the uptake of CO₂ in cement infrastructure (also known as carbonation) can offset around half the carbonate emissions from current cement production.

An even more promising use for captured carbon in the concrete industry is the production of synthetic aggregates, dubbed “permanent carbon capture” by purveyors such as Blue Planet. “These are aggregates made out of CO₂ and calcium oxide, which have a very large negative carbon footprint,” explains Riley. He continues, “Even using conventional cement, you wind up with minus 500 kilos per cubic meter instead of plus 200 kilos as a carbon footprint for the concrete.” Riley is optimistic about this potential sequestering bonanza but views it as still in the early stages of development, among other promising technologies.

Collaboration: cementing new relationships

Riley says the cement industry has undergone a transformation in its approach to sustainability in recent years, in that, “We’ve always thought of cement as being the problem, and therefore that cement would have to provide the solution, but that’s not the only way of doing it.” Today, he says, the industry sees the possibilities of cooperation and collaboration along the building supply chain and across different industries.

The global Energy Transitions Commission, a coalition of leaders in the energy landscape whose aim is to accelerate the transition to a net-zero-emissions future, also believes in the synergies that might be achieved through cross-industry collaboration. Together with the World Economic Forum, it established the Mission Possible Platform to address the challenges of hard-to-abate sectors. Working groups are being formed for seven industries, including steel, plastics and chemicals, and cement. As the energy transition is at the heart of Baker Hughes’ strategy, it decided to act and engage. In July 2021, when the Concrete Action for Climate group was inaugurated as a Mission Possible Partnership, Baker Hughes joined to help formulate a roadmap to decarbonization.

Mette Munkholm, an executive who has worked with oil majors to meet their business objectives while reducing carbon emissions and driving the digital transformation of their operations, is Baker Hughes’ representative to the group. She says, “We’re keen to be part of what it would take to create the environment in which low-carbon cement will work.”

Part of that is contributing to policy settings in different jurisdictions that support and encourage the industry to decarbonize. Munkholm points to the EU which has already established one of the world's largest funding programs for the demonstration of innovative low-carbon technologies that can be deployed by the cement industry.

HeidelbergCement, for example, is committed to offering carbon-neutral concrete across its product portfolio by 2050 at the latest. It’s supported in its ambitions by European projects such as carbon capture and storage (CCS) at its Norcem subsidiary in Norway; first envisaged in 2011 and partly funded by the Norwegian government, the CCS plant will become operational in 2024 and will capture around 400,000 tons annually, or half of the carbon generated by cement processes, and transport it to underground storage beneath the North Sea. HeidelbergCement is also one of the strategic partners in the EU-funded Low-Emissions Intensity Lime And Cement project, now in the scale-up phase known as LEILAC2, which is piloting another method, Direct Separation Technology, for capturing CO₂ at its Hannover cement plant in Germany.

On the market-demand side for captured CO₂, HeidelbergCement has also partnered with Dutch innovators OmegaGreen, to investigate the potential for large-scale absorption of CO₂ in cultivating algae at its Safi cement plant in Morocco. The intention is to add the high-nutrition algae to feed for livestock. [1]

Another approach, in this case to seed demand for tried and tested low-carbon cement, is for an industry such as oil and gas to demonstrate the use case for the product in its operations.  “Baker Hughes sees a possibility to contribute to such a demand signal,” says Munkholm, which could have the dual outcome of helping to lower the carbon footprint of participating oil and gas partners while giving a highly visible real-world demonstration of the viability of low-carbon cement.

Policy mortar will help connect the supply chain

How much of the cost of lowering emissions from cement and, therefore, from concrete will be borne by consumers of the products will likely depend on the policy settings that each country adopts. Riley says that “In Sweden today, you can get a premium for low-carbon concrete, but elsewhere it’s harder to find examples.”

He says developers and the construction industry have until recently been one step removed from demand for low-carbon products: “For example, a lot of tech companies have set themselves a goal of net-zero, so when they build new offices or data centers they want those to be net-zero as well.” In principle, he says, they’re willing to pay a premium for a lower carbon concrete, but in practice, the company with the net-zero commitment is not handling procurement.

“If you can connect those dots, you can get to a point where they are willing to pay a little extra, and in the context of the overall project, the premium is not very large — it hardly makes any difference at all,” says Riley.

The recent budget of the UK government made it a legal requirement for national infrastructure projects to take into account the UK’s 2050 net-zero target. As a result, says Riley, “We do see contractors that are working on infrastructure projects in the UK starting to look at how they can achieve that.” In this way, the carbon value chain is encouraged to integrate with the economic value chain for low-carbon goods.

Policies are critical to create demand signals for low-carbon products from hard-to-abate industries. Setting the right policies in relation to cement would allow markets to set a price premium for low-carbon concrete, which in turn would allow industry to expedite solutions such as repurposing kilns in response to reduced demand for clinker, or blending captured CO₂ with green hydrogen to create new fuels such as green methane. Waste heat systems could also be used to recover unused heat sources.

Munkholm says her discussions so far with cement corporations participating in the Cement for Climate Action group indicate that the industry is intent on developing those technologies that deliver significant emissions reductions. “Like Baker Hughes, they need to be sure that there is a real effect, that the maths work — it must be a real outcome for the planet.”