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Lowering Concrete Manufacturing Emissions and Optimizing the Design of the Built Environment

Allen Hamblen
President and CEO of CalPortland

No matter the type of infrastructure, concrete construction provides a sustainable and resilient built environment, which is an important part of the PCA Roadmap to Carbon Neutrality. What is commonly considered construction involves four separate phases: design, construction, use, and end-of-life. Much like earlier steps in the value chain, the carbon intensity of construction can be reduced through optimization within each of these phases.

Optimizing concrete mixtures

Manufacturing concrete today is a complex process. From the generic concrete of residential applications to innovative ultra-high strength concrete for the tallest buildings and longest bridges in the world, concrete manufacturing requires stringent quality control and an understanding of the characteristics and properties of local materials. Along with cement, aggregate and water, most concrete today uses supplementary cementitious materials (SCMs) – admixtures and additives – that improve the properties of concrete for various situations. There are almost a limitless number of concrete formulations to meet the needs of engineers, contractors, owners, and others.

After water, concrete is the second most consumed material on the planet, which is why it’s such a critical step in the value chain to reach carbon neutrality. The cement industry’s Roadmap targets improved mix designs that optimize every single component within concrete – and by optimizing the manufacture of concrete and creating hyper-specific mixes, we can reduce emissions. By switching from prescriptive specifications to performance specifications, producers have the flexibility to design for the application of the project rather than for a specification that may be overdesigned for the use. With dozens of inputs and outputs, leveraging both conventional and machine-based tools allows producers to transition from a set menu of default mixtures to designing tailor-made mixtures using the right materials at the right time for the right application.

A cubic yard of concrete today represents about 500 pounds of CO2. By utilizing optimized mix designs, that same cubic yard of concrete will represent 364 pounds of CO2 by 2030, 273 pounds by 2040 and less than 200 pounds by 2050, a reduction in intensity of 60%. That concrete will still have the same strength and durability consumers have come to expect but with lower life cycle emissions.

Reducing direct emissions from concrete manufacturing and transportation

Making concrete requires energy, and delivering concrete requires energy.

Manufacturing concrete accounts for only about 5% of the total CO2 footprint of concrete. As the grid is supplied with more renewable energy, concrete production facilities will see a 100% reduction in the CO2 footprint.

Concrete manufacturers have committed to transitioning from diesel powered to zero emissions fleets to transport their products. Today, transportation accounts for about 6% of the total CO2 footprint of concrete, with a targeted goal of 3% by 2050 – a 50% reduction in delivery energy.

Avoiding overdesign

Given the ubiquity of concrete, it’s important to optimize how it’s used. Optimization in the design phase takes a whole life building design approach and utilizing performance specifications to lower carbon in the built environment is one approach to avoiding overdesign.

Every structure is designed on basic principles like strength, stiffness, stability, durability, and long-term performance. This Roadmap encourages a rational approach to avoid the wasteful one-size-fits-all approach that is the unknowing default selection of many designers. Keeping building codes updated to include the use of performance specifications addresses overly conservative designs that provide a false sense of security. Despite advances in building codes and design, this remains an issue.

Concrete’s wide range of performance characteristics allows for structural systems to be optimized by simply considering the size, shape and spacing of structural components. A common example is the use of higher strength concretes to decrease slab depths.  Similarly, high strength concrete can allow either reduced column sizes or wider spacing between the columns. While the cement content will vary based on mix design, the overall structural system can be optimized with a lower carbon footprint.

This Roadmap envisions that optimization in the design and construction phase can achieve construction efficiencies of 10% by 2030, 20% by 2040, and 30% by 2050. Optimized construction also means reducing waste on the job site and eliminating returned concrete. Today, more than 5% of concrete is returned from construction sites; with more precise design and by limiting excess materials at the job site, our targets for returned concrete are 4.25% by 2030, 3.25% by 2040, and 2.5% by 2050.

By working with concrete manufacturers, stakeholders, urban developers and contractors, we can lower concrete’s carbon footprint, achieve carbon neutrality, and build a more sustainable built environment for the next generation.

Reducing Emissions and Optimizing Materials Used in Cement Production: The Second Link in the Carbon Neutrality Value Chain

Rick Bohan
Vice President, Sustainability for the Portland Cement Association

The Roadmap to Carbon Neutrality, introduced by the Portland Cement Association, outlines a value chain approach to reach carbon neutrality across the built environment. The first two links in this value chain directly relate to operations at cement plants. Most Americans will never see clinker, the first step in the value chain, or cement, the main ingredient in the concrete we use to build our roads, structures and critical infrastructure.

Cement is a binder that, when mixed with water and aggregates, forms the durable and resilient material we know as concrete. Optimizing the ingredients in cement not only enhances the benefits of cement-based products, but also reduces the carbon intensity of cements. Cement producers are building on their proven legacy of lowering emissions to continue cutting greenhouse gases (GHG) while further increasing their energy efficiency.

Increasing supplementary cementitious materials

Cement includes clinker with finely ground limestone, inorganic processing additions, and precisely controlled amounts of sulfate. By optimizing what goes into cement, we can reduce emissions from material processing – for example, replacing some of the clinker with limestone or industrial byproducts like slag or fly ash, reduces the carbon intensity of cement while creating a product with the same strength, durability, and resiliency we’ve come to expect from concrete.

Currently, cements have a clinker to cement ratio of more than 90%. The remaining material, gypsum, limestone, and processing additions can be partially replaced with supplementary cementitious materials (SCMs). This directly reduces the CO2 from clinker production. SCMs include slag, fly ash and silica fume. In many cases, these are industrial byproducts that would otherwise be landfilled. Proper amounts of SCMs can improve durability and address the harmful chemical reactions caused by some aggregates.

Tomorrow’s cements are targeting lower clinker to cement ratios. Cements today include less than 5% of SCMs, but the industry is targeting increasing SCM amounts to 10% in 2030, 15% by 2040 and 20% by 2050.

Leveraging new cement blends

Portland cement specifications limit the amount of limestone that can be added in cement to just 5%, but portland-limestone cement (PLC) specifications allow for the addition of up to 15% limestone, fly ash or slag, which leads to a reduction in CO2 emissions.

There is a tremendous opportunity to increase the use of PLC, but in many cases, institutional inertia presents one of the greatest obstacles to widespread use. This Roadmap is an approach to accelerating the acceptance and adoption, not only of these proven materials, but also an approach to accelerating the adoption of the standards and specifications providing a pathway to their use.

Standards for the cement industry are the common language that producers, users and consumers speak to ensure consistency and uniformity. Different cement standards provide cement users a variety of options and choices. Ultimately harmonizing these unique standards will provide an even greater degree of flexibility.

For more than a century, educating producers, users, consumers, the government, academia, contractors, the construction industry, and the general public has been the hallmark of PCA; it is even more important today to educate stakeholders on all the options available with cement blends and their sustainable benefits.

Organizations such as ASTM International and the American Association of State Highway and Transportation Officials play a critical role in developing. Updating these standards is key to helping the cement and concrete industry achieve carbon neutrality.

Cement producers can create more efficient and sustainable clinker and cement, but collaboration to update regulations and increase awareness of these materials will be required before the market will embrace them.

Optimizing Clinker Composition: the First Link in Reaching Carbon Neutrality

Monica Manolas
President, Ash Grove South, a CRH Company

In October, the Portland Cement Association released its Roadmap to Carbon Neutrality, which outlines an approach that leverages the entire value chain to lower emissions. The first link in that value chain is clinker; clinker is a binding agent that is the precursor to cement, the key ingredient in concrete.

While most Americans will never see clinker unless they visit a cement plant as it is an intermediate product, it is essential to cement manufacturing. The key chemical reaction to produce clinker is responsible for more than 60% of CO2 emissions from cement production. There is currently no way around this “chemical fact of life” and no viable alternative to clinker that can be produced at the scale society needs. There are, however, opportunities to optimize energy use, shift away from traditional fossil fuels, and utilize carbon capture technology to avoid emissions.

Decarbonated raw materials

Clinker starts with quarried materials like limestone, clay, shale, and sand that must be heated and processed. To reduce these emissions, manufacturers can use decarbonated raw materials that have already been processed to no longer contain CO2. These materials often end up in landfills, so in addition to avoiding processing emissions, these materials are also brought into the circular economy.

Today, these materials represent less than 5% of cement manufacturers’ raw material input; with the right policies, that could be doubled. By 2050, the industry is targeting replacing virgin raw materials with at least 10% decarbonated raw materials.

Fuel switching

Clinker production requires material temperatures of nearly 3,000 degrees Fahrenheit, and those temperatures can only be achieved with combustion. The industry’s current fuel mix includes 60% coal and petcoke, with alternative fuels making up only a fraction of the current fuel mix. These alternative fuels range from cellulosic biomass to non-recycled plastics, residuals from paper and cardboard recycling, and agricultural wastes – all opportunities to give spent materials a second, productive life.

Current regulations limit the use of non-hazardous secondary materials, even when those materials can be beneficially used in lieu of fossil fuels. Cement plants are already equipped to use alternative fuel materials. With the right policies and regulations, alternative fuels could make up 50% of the industry’s fuel mix.

The industry is also advocating for the use of “transition” fuels, like natural gas, while renewable fuel sources become available at scale. Displacing traditional fossil fuels with natural gas in the near-term cuts CO2 combustion emissions by 24%. With the right infrastructure investment, cement producers can switch to renewable sources of electricity like wind and solar to eliminate CO2 created from fossil fueled power plants.

Improving energy efficiency

Cement manufacturing is already one of the most energy efficient industrial processes – with today’s technologies operating above 80% thermal efficiency. Producers are constantly looking for new opportunities to improve, and many cement plants are U.S. EPA ENERGY STAR certified for performing in the top quartile.

Using modernizations, upgrades, machine learning, and artificial intelligence the goal is to reduce the 3.84 MM BTU of energy it takes to produce one metric ton of clinker by more than 25%.

Carbon capture

In the long term, carbon capture, utilization and storage (CCUS) is a critical part of cutting emissions in cement production. CCUS effectively captures CO2 to either be used to produce new materials or be safely and permanently sequestered. While at-scale CCUS will take significant research and development efforts, the industry continues to advocate for the right policies and investments to make carbon capture an integral part of any cement plant.

Clinker is the first step in a value chain that results in the concrete infrastructure we experience every day. Working to implement actions and policies and research and investment that bring down emissions at the cement plant is crucial for the industry to reach carbon neutrality and be a part of creating a more sustainable built environment.

Achieving Carbon Neutrality Across the Concrete Value Chain

Michael Ireland
President and CEO at Portland Cement Association

Portland Cement Association has recently announced the release of its Roadmap to achieve carbon neutrality across the concrete value chain by 2050. The cement and concrete industry is committed to addressing climate change and reducing emissions, and this Roadmap to Carbon Neutrality will guide us on our ambitious and critical decarbonization journey.

To reach this goal, the U.S. cement industry has aligned and PCA is gathering a coalition of thought leaders, researchers and stakeholders along the value chain that make this Roadmap a reality. Only by working together as an industry can we hope to realize the multitude of solutions that must be developed across policies and regulations, technology and innovation and demand generation. There is a strong need for broad collaboration even beyond the industry, and we are leading on bringing the right people to the table.

Importantly, many of the solutions included in the Roadmap are products, technologies and approaches that exist today – lower carbon cement and concrete are available today. By bringing together partners across the value chain, we intend to shift mindsets and increase awareness and adoption of these solutions.

The U.S. cement industry aligning under a formal and measurable commitment to reduce emissions comes at a critical time in our country. The construction sector is poised for growth, with the U.S. predicted to add another 121 billion square feet of buildings by 2050, the equivalent of constructing New York City every year for the next 20 years. This doesn’t account for the trillions of dollars the country is poised to spend reviving infrastructure, rehabilitating existing roads and bridges, and expanding construction in growing cities. Development at this scale means the cement and concrete industry has a once-in-a-generation opportunity to set a global example on building sustainably, utilizing new approaches, and advocating for updated technology.

America’s cement producers have a strong culture of innovation and are in constant pursuit of finding efficient ways of producing the high-quality cement our nation needs for homes, highways, hospitals and infrastructure. The Roadmap accelerates industry alignment and identifies challenges and barriers that must be addressed in order to achieve carbon neutrality. It enables our member companies and partners along the concrete value chain to address climate change and continue building a better future, shaped by concrete. We invite stakeholders to join this ambition to realize carbon neutrality across the full concrete value chain.

Learn more about the Roadmap here.