by: Kayla Carey and Andrew Primo | October 27, 2022

Cement is a powdery substance that can be mixed with sand, water, and gravel to form concrete.

Most people are familiar with cement, the key ingredient in concrete, but few are likely aware of how foundational this material is to contemporary life. Buildings, roads, bridges, canals, sidewalks, railways, ports, power lines, wind, and solar farms… nearly all infrastructure requires cement and lots of it. The International Energy Agency estimates that nearly 4.3 billion tons of cement were produced in 2021 alone, making enough concrete to build the equivalent of over 2,800 Hoover Dams.

And this number will only grow. By mid-century, the global population is expected to approach 10 billion people, over two-thirds of whom will live in cities, according to the UN Department of Economic and Social Affairs. Add to that the massive buildout of electricity, renewable energy, efficient transportation, and carbon capture infrastructure required to support a decarbonized society, and the need for a significant increase in today’s already record-high cement production levels becomes abundantly clear.

Why are cement emissions so difficult to reduce?

There is, however, a fatal catch to this skyrocketing demand: cement, as it is produced today, has a tremendous greenhouse gas footprint. And decarbonizing isn’t as simple as substituting coal with renewable energy or electrifying vehicles. At least half of all emissions generated from the production of Portland cement (the global standard) are released during production through the creation of “clinker,” one of the primary steps in cement production.

Clinker is produced in giant kilns, where limestone and other minerals are superheated to temperatures up to 2,700 degrees Fahrenheit.  The chemical byproduct of this process is tremendous amounts of carbon dioxide (CO₂): in the United States,  one metric ton of CO₂ is emitted for every metric ton of Portland cement produced. Because of the difficulty in avoiding the process emissions from this critical step in production, cement is considered a “hard-to-abate” industry.

Clinker production requires high heat and releases carbon dioxide as waste. Image Source: Cement Association of Canada

With such huge volumes of cement produced each year at such high emission rates, the cement industry has become one of the most carbon-intensive on the planet, contributing approximately 2.4 billion metric tons of CO₂. That’s more than all aviation and maritime shipping emissions combined, and these will only continue to increase unless rapid steps are taken to reduce cement’s carbon intensity.

How can we reduce cement’s hard-to-abate emissions?

With the increasing demand for infrastructure paired with the urgency for decarbonization, how can the cement industry balance this paradox? Unsurprisingly, there is not a single or simple solution.

The Global Cement and Concrete Association’s (GCCA) 2050 Net-Zero Roadmap identifies several actions that the cement industry can adopt to slash greenhouse gas emissions and limit the most severe consequences of climate change. These strategies include:

• Improving operational efficiency;
• Switching to less carbon-intensive fuel sources;
• Replacing traditional limestone-derived clinker with alternative materials; and
• Deploying carbon capture utilization and storage (CCUS) technologies.

Each pathway can have a significant impact on lowering the carbon intensity of cement; however, only a couple of technologies can reduce the troublesome emissions released during clinker production – clinker replacement and CCUS.

Clinker Replacement: In certain applications, clinker can be at least partially replaced with alternative products called supplementary cementitious materials (SCMs). Typical SCMs are byproducts of industrial processes, such as coal and steel production; however, transitions in these industries, such as the closing of coal-fired power plants and the shift to more efficient steel-production furnaces, have limited the availability of these commonly used SCMs, creating a gap between supply and demand. Some companies have launched demonstration projects to produce additional clinker replacements, such as fly ash harvested from landfills and naturally occurring substances—known as “natural pozzolans”—like volcanic ash. But producing and treating these materials so that they can be used in cement is complicated and expensive, and they have not yet reached the scale needed to meet the worsening SCM supply void.

Carbon Capture Utilization and Storage: CCUS—in which the CO₂ released in clinker production is captured and stored or used in other applications—is another key approach to reducing cement’s process emissions. Very few CCUS projects currently exist, especially at cement plants. Nearly all CCUS projects worldwide are still in the pilot phase as the technology faces substantial implementation challenges and is extremely cost-prohibitive. 

Nearly 4.3 billion tons of cement were produced in 2021, which is enough concrete to build the equivalent of over 2,800 Hoover Dams. 

Leveraging the Voluntary Carbon Market

For hard-to-abate sectors to meet net-zero targets on time, they must work together to employ a mix of proven and emerging technologies, such as clinker replacement and CCUS. But how can the industry overcome existing economic and technical challenges to scaling these technologies? The voluntary carbon market could be an important lever in bringing new SCMs to market and making CCUS more economically viable.

Today, there are a growing number of opportunities for the cement industry to generate voluntary carbon credits. One of the most trusted carbon offset registries, the Climate Action Reserve, recently announced the development of a Low-Carbon Cement Protocol that will incentivize the production of innovative SCMs to address the current supply gap. In addition to tax incentives, new opportunities are also emerging to generate carbon credits from CCUS projects. The cement industry can leverage the voluntary carbon market to direct much-needed financing to the sector and accelerate the road to decarbonization. 

About the Authors

Kayla Carey is a Manager for Program Development, specializing in decarbonization for hard-to-abate sectors. With experience in sustainability management and energy policy, she helps energy and industrial clients navigate environmental markets and develop new quantitative methodologies. She holds a master’s degree in Environmental and Natural Resources Policy and a Bachelor of Arts in Ecology and Evolutionary Biology, both from the University of Colorado Boulder.

Andrew Primo is a Manager on ClimeCo’s Program Development team, based out of Denver, Colorado. He assesses the feasibility of new emission reduction projects in hard-to-abate sectors, including heavy industry, waste management, and shipping. He works with corporate partners and carbon registries to develop new technical methodologies for carbon crediting programs.