Adoption of Limestone Calcined Clay Cement and Concrete in the U.S. Market

Key Findings:

• Limestone calcined clay cement is a promising alternative to portland cement and one of the best solutions emerging for reducing carbon emissions from the cement industry. Under the current state of technology development, the carbon intensity of limestone calcined clay cement is 40% lower than portland cement. Calcined clays can be combined with limestone to produce blended cements or be used as a supplementary cementitious material in place of portland cement in concrete.

• Because 46% of cement purchased in the United States is used in public construction projects, federal, state, and local governments can achieve major emissions reductions by shifting their cement and concrete purchases to limestone calcined clay cement. We analyzed four market adoption scenarios and their associated emissions reduction potentials based on government-funded procurement. Shifting half of government purchases to limestone calcined clay cement could cut 7.3 million metric tons (Mt) CO2 annually. This accounts for approximately 9% of the U.S. cement industry’s total CO2 emissions in 2021.

• If we take into account usage of limestone calcined clay cement in non-public construction projects, the potential impact of its adoption in the U.S. market more than doubles.

• Limestone calcined clay cement is cost effective, with production costs up to 25% lower than portland cement due to savings in energy and materials.

• Limestone calcined clay cement can help enable other decarbonization options for the cement sector. The lower temperatures (800oC) required in its production compared to portland cement (1,500oC) offer substantially improved process energy efficiency, which in turn opens the path for electrifying clay calciners. When combined with thermal energy storage options and renewable and other clean energy sources, this can lead to even greater emission reductions, approaching zero-emission scenarios.

• Governments, cement companies, concrete companies, and the non-governmental organization (NGO) community can help overcome technical, standards and codes, policy, market, and other barriers and increase the adoption of limestone calcined clay cement in the United States.

Cement manufacturing is one of the most energy- and carbon-intensive industries in the world, contributing around 7% of global carbon dioxide emissions (i.e., more than the food, beverage, paper, and non-ferrous metals industries combined). Cement is a key ingredient in concrete, the widely used building material, and its production will continue to rise globally in the coming years, especially in the global south. Decarbonizing the cement sector will, therefore, be essential to achieving the objectives of the Paris Climate Agreement, under which the world’s countries committed to reduce their greenhouse gas emissions to net zero by 2050.

This report evaluates the potential of limestone calcined clay cement as a sustainable alternative to portland cement in the United States. We estimate the carbon reduction potential of different adoption rates (10%, 20%, 30%, and 50%) of limestone calcined clay cement by government and private cement users in the U.S. market in 2021, highlight the opportunity to realize these emissions reductions by shifting cement purchases for public construction projects, identify barriers, and offer recommendations to increase adoption. Compared to portland cement, limestone calcined clay cement reduces emissions, performs as well, and is more cost-effective (25%) due to savings in energy and materials.

Cement is manufactured by heating limestone to a high temperature to create lime and carbon dioxide. The lime is further heated to produce clinker (an intermediate product), which is mixed with other materials to produce portland cement. Cement, a key binding agent, is mixed with aggregate and water to produce concrete, a widely used building material. The CO2 emissions from the cement industry can be reduced by (IEA and WBCSD 2018, Goldman et al. 2023): Improving energy efficiency; Improving material efficiency (e.g., by replacing portland clinker to produce blended cements, substituting portland cement with supplementary cementitious materials (SCMs) to produce concrete); Using alternative binding materials; Switching from traditional fuels to alternative fuels; Using decarbonized, alternative raw materials, and feedstocks; Using electrochemical production processes; Implementing carbon capture, utilization and storage.

Calcined clays represent a material efficiency approach that offers one of the best decarbonization opportunities for the sector, with substantial reductions in new carbon emissions possible, especially when combined with other decarbonization approaches like increased energy efficiency and electrification. Calcined clays can be combined with limestone and used to produce blended cements or be used as an SCM instead of portland cement in concrete. Calcined clays can use existing equipment, such as rotary kilns, reducing capital expenses, and they already enjoy acceptance in the standards community.

Limestone calcined clay cement is a low-carbon replacement for portland cement and can reduce CO2 emissions by up to 40%, under the current state of technology development. It has undergone rigorous testing and been shown to perform as well as portland cement, while costing 25% less to produce due to savings in energy and material use. In addition, it offers adequate mechanical qualities (e.g., durability), making it appropriate for a variety of structural applications, including pavements, highways, residential and commercial buildings, and other infrastructure. Limestone calcined clay cement is globally scalable.

The use of limestone calcined clay cement has been studied in several countries around the world, including India, Brazil, Colombia, and Cameroon. This report discusses case studies from seven countries. Overall, limestone calcined clay cement is projected to account for more than one-quarter of cement use in the world by 2050 (IEA and WBCSD 2018).

In the United States, the use of calcined clays has been very limited despite abundant clay deposits in many regions of the country, but there is growing interest. U.S. CO2 emissions can be reduced by 7.3 Mt annually by shifting half of federal, state, and local government procurement toward limestone calcined clay cement. This is equivalent to eliminating greenhouse gas emissions from driving 1.7 million gasoline-powered cars annually. The United States is the fourth-largest producer of cement in the world, producing about 91 Mt of portland cement and masonry cement in 2023 (USGS 2024). Sales of cement in 2023 were around $16 billion (USGS 2024). At the state level, Texas, Missouri, California, and Florida have the highest cement production, in that order, and Texas, California, and Florida consume the most cement (USGS 2024). Of the total amount (110Mt) of cement consumed (produced and imported) in the United States, 46% was used in public construction projects (PCA 2016), (i.e., about 47 Mt of cement). Three-quarters (75%) of public procurement is from state and local governments, with the remaining 25% from the federal government (Hasanbeigi and Khutal 2021). The U.S. cement industry emitted around 80 Mt of CO2 in 2021 (calculated based on data from the U.S. Geological Survey (USGS) 2023 and U.S. Department of Energy (DOE) published in 2022).

We conducted a scenario analysis using four scenarios to describe the adoption rate of limestone calcined clay cement by government and private cement users in the U.S. market in 2021—low (10% adoption across the market), medium (20%), high (30%), and transformative (50%)—and estimate the carbon reduction potential for each scenario. Even higher adoption rate scenarios may be possible based on market conditions over time. Based on this analysis, U.S. government (federal, state, and local) purchases of cement for construction can result in the emission reductions presented in Table ES-1.

Table ES-1. Summary of CO2 reduction potential of limestone calcined clay cement used by government procurement in the United States

Limestone calcined clay cement, a blended cement, produced by fossil fuel-based conventional calciners offers a 40% reduction in emissions over conventional portland cement. Electrification of the clay calciner, when powered by renewable energy, can help produce zero-emission calciner clay. If this zero-emission calcined clay is used in limestone calcined clay cement production, then the emissions reduction can be as high as 50%. According to the U.S. Department of Energy (DOE) Pathways to Commercial Liftoff: Low- Carbon Cement report, electrification of precalciner/kiln technologies used in conventional portland cement production may achieve up to a 35% reduction in carbon emissions (Goldman et al. 2023). Thus, if clinker is also produced by an electrified precalciner/kiln using renewable or clean process heat and is coupled with zero-emission limestone calcined clay, then the limestone calcined clay blended cement would achieve about 70–75% emissions reduction compared to conventional portland cement.

Maturation of the calcined clay technology over time to include higher than 45% replacement rates in blended cement and concrete mix design efficiencies can further bring the total emissions reduction potential to 80% or higher in zero-emissions scenarios (compared to business as usual). Carbon capture, utilization, and storage (CCUS) can then be employed to reduce emissions further. These estimates underscore the importance of advancing research, development, demonstration, and commercial deployment of electrification technologies for the cement sector through the Inflation Reduction Act (IRA 2022), the Concrete and Asphalt Innovation Act (2023), and other policy initiatives. Advancing such opportunities in the United States showcases American leadership in green manufacturing and demonstrates how innovation can transform this sector in other large cement-producing countries like China and India and globally. Governments, cement companies, concrete companies, and the NGO community can help overcome barriers and increase adoption.

Some of the key barriers to adoption of calcined clays as an SCM in concrete and in a blended cement like limestone calcined clay cement and potential solutions to address those barriers are also discussed in this report.

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