FAQs

The Roadmap is the documentation of the path that the U.S. cement industry and greater construction value chain will use in reaching carbon neutrality throughout the value chain by 2050.

The Roadmap is a document that includes the targets, the timeframes, the technologies, and the policy needs along each step of the value chain that will get the cement industry to carbon neutrality by 2050.

Carbon neutrality occurs when CO₂ emissions from the production of concrete are offset by at least an equal amount of CO₂ reductions.

With full support in these areas, the industry can reach carbon neutrality sooner. While the cement and concrete industry has made consistent progress in reducing the carbon intensity of its products across the value chain, reaching carbon neutrality will require significant advances in technology, policy, infrastructure, and markets. Without those policies and support, it will take the industry more time and possibly jeopardize reaching the goal.

Reaching carbon neutrality requires support in a wide variety of areas including funding research and development, regulation and permitting, credit for carbon reduction levers, community acceptance, market acceptance, performance-based standards, procurement based on cradle-to grave life cycle analysis, low-carbon infrastructure, and a secure and level playing field.

The cement industry cannot do it alone. The industry is asking everyone involved throughout the value chain to help reach this goal by re-thinking their role, by setting their own bar higher, by pushing their own envelope further, and by helping advocate for the policies the cement and concrete industry need to reach carbon neutrality. The industry is asking everyone involved throughout the value chain to help advocate for the policies needed to reach carbon neutrality.

Everyone has a role to play. The academic, the architect, the builder, the contractor, the engineer, our government, the homeowner, the material scientist, the manufacturer, the owner, the policymaker, and the researcher, will all be at the forefront but there are hundreds of others that can support these efforts.

The value chain includes clinker, cement, concrete, construction, and the use of concrete as a carbon sink. The value chain is a microcosm of a circular economy. Clinker, the first step in the value chain, is an intermediate product within the cement manufacturing process. Cement, the second step, is a blended mixture of clinker and gypsum along with potentially many other materials like limestone and other processing additions. Concrete, the third step, is a mixture of cement, water, fine and coarse aggregates, and chemical and mineral admixtures. Concretes today also commonly include, fly ash, slag, and other materials. Construction, the fourth step, is the built environment. Concrete construction includes airports, buildings, bridges, runways, streets, sidewalks, tunnels, and many more structures. The fifth and final step in the value chain is the use of concrete as a carbon sink. Concrete absorbs CO₂ throughout its lifetime and even after it is demolished.

The U.S. cement industry contributes 0.17% CO₂eq to the global production of CO₂. The EPA Inventory of U.S. Greenhouse Gas Emissions and Sinks notes current (2019) total U.S. emissions of 6.6 GtCO₂eq. Using the same calculation procedure, the U.S. cement industry contribution to U.S. CO₂eq emissions is 1.25%.

The manufacture of cement relies upon the transformation of calcium carbonate into calcium oxide. That reaction produces CO₂ and without that reaction, there can be no clinker, hence no Portland cement. In the U.S. more than 60% of the CO₂ emissions from cement manufacturing are generated by this chemical reaction called calcination. PCA and the industry calls this calcination reaction the industry’s “chemical fact of life”. In addition, the chemical reactions to produce clinker require material temperatures of nearly 2,800 degrees Fahrenheit or 1,500 degrees Celsius. (For comparison, the surface temperature of the sun is 10,000 degrees Fahrenheit or 5,500 degrees Celsius.) The only way to achieve those high temperatures is through fuel combustion. In the U.S., just under 40% of the CO₂ emissions from cement manufacturing are generated from fuel combustion.

The CO₂ generated from combustion can be reduced through the transition from traditional fossil fuels like coal, petcoke, and natural gas to alternative fuels including biomass, secondary materials, and renewable energy sources and also from increased fuel efficiency in the manufacturing process. PCA also anticipates that hydrogen and other transformative fuels and transformative technologies will play a role. The CO₂ generated from the chemical reaction or chemical fact of life can be reduced by incorporating decarbonated raw materials, including slag and fly ash, as feedstocks. These are materials that have already been processed and no longer contain CO₂. Additionally, increasing the use of recycled materials diverts these materials from landfills.

The CO₂ associated from cement can be reduced or avoided by replacing a portion of the clinker with limestone, inorganic processing additions, supplementary cementitious materials, and by manufacturing and transporting cements using zero emission rail and truck transport. PLCs have been available for decades and can reduce the CO₂ footprint of today’s cements by up to 10%. Blended cements using fly ash and slag can also reduce CO₂. Shifting from prescriptive specifications to performance-based specifications provides designers more flexibility also reduces or avoids CO₂.

The CO₂ associated from concrete and concrete production can be reduced or avoided using PLCs and other low-carbon blended cements, supplementary cementitious materials, admixtures to optimize concrete mixtures, and by manufacturing and transporting concrete and concrete products using zero-emissions electricity, rail, and truck transport.

Concrete mixtures can be optimized by increasing the use of SCMs and using machine learning algorithms and artificial intelligence to discover the optimal mix design for specific applications and to identify the optimal sequencing, scheduling, and delivery of concrete and concrete products. Optimized concrete mixtures and concrete products provide the best strength and durability performance requirements and the most sustainable performance for specific individual applications. Quality assurance and acceptance testing of fresh concrete can also be optimized. Optimization ultimately provides better performance with less variability.

Optimization is about “shifting the curve” and “shaping the curve” regarding performance. Shifting the curve means bringing the slow adopters and less than average performers into the median or average range, bringing the median or average adopters and performers into the above average range, and allowing the above average performers to push the envelope even further through innovation and discovery. In many cases this means simply removing the obstacles that slow adopters and average performers face. Shaping the curve means bringing the below average and average adopters much closer to and always chasing the above average adopters and performers. It is about setting the bar higher and pushing the envelope further.

Using building construction as an example, optimization in the design phase is exemplified by the Whole Building Design Guide developed by the National Institute of Building Sciences. Optimized construction envisions the use of Building Information Modeling (BIM) and full-life cycle analysis techniques that incorporate energy efficiency, resource efficiency, resiliency, project-life, indoor air quality, and adaptability into the circular economy. The guiding principles for high-performance buildings and infrastructure include employment of integrated design principles, optimization of energy performance, protection and conservation of water, enhancement of indoor air quality, reduction of the environmental impact of materials, and the assessment and consideration of climate change risks. Each of these principles can be met through concrete construction. Design optimization considers the initial structure use as a starting point while providing the flexibility to adapt to the structure’s future uses. Strength, stiffness, stability, slab depth, column size and spacing, and framing considerations can all be optimized for future adaptability.

The CO₂ associated with the construction phase can be reduced or avoided through life cycle-based procurement policies, zero-waste materials management, and end-of-life reuse and recycling of concrete materials.

Construction can be optimized using innovative construction techniques like additive manufacturing, a zero-waste construction site, advanced sequencing, and scheduling, zero emission deliveries and zero-emission construction material handling equipment, on-site robotics, and the use of drones. These and many other innovations can all reduce the carbon footprint in the construction phase.

The use phase of a building accounts for 88-98% of the life cycle global warming potential. Research by MIT indicates that using concrete lowers the use phase global warming potential impacts up to 10% and lowers the life cycle global warming potential impacts up to 8% in comparison to buildings that are not concrete.

Crushed concrete can be recycled and re-used as aggregate in new concrete mixtures thereby saving the energy required to quarry and process virgin aggregate. Further, over time recycled concrete continues to absorb and sequester CO₂ (see discussion about concrete as a carbon sink).

Concrete and live growing trees share something in common; they both absorb CO₂. Trees and plants use CO₂ to produce the food they need through photosynthesis. Concrete absorbs CO₂ from the moment that it sets throughout its entire life through a process called carbonation. Air contains about 0.04% or 400 ppm of CO₂. That CO₂ naturally diffuses into concrete and reacts with the calcium hydroxide and other hydration products in concrete to form calcium carbonate. This reaction is irreversible.

The absorption of CO₂ by concrete depends primarily on the concrete surface area exposed to the atmosphere, the amount of water and moisture available, the permeability of the concrete, and the length of exposure. For example, an above grade concrete wall will slowly absorb CO₂ throughout its life. If that concrete wall is removed, reduced into smaller aggregate-sized particles, and exposed to the atmosphere in a stockpile, it will absorb CO₂ more quickly due to the higher surface area. The crushed concrete can then often be recycled as aggregate. Various models using the compressive strength of the concrete, the type of structure, the type of exposure (exposed to rain vs. sheltered from rain, indoor vs. outdoor, with or without cover, in ground or out of the ground) have been developed to calculate the degree of carbonation. The U.S. EPA is currently evaluating what is known as the Tier I model for incorporation into the National Inventory Report. Current estimates indicate that approximately 10% of the CO₂ generated during the manufacture of cement and concrete can ultimately be absorbed over the life of a concrete structure.

CCUS (carbon capture, utilization, and storage) is an integral part of the Roadmap and includes a range of technologies that capture CO₂ as the first step and then either transforms the CO₂ into a useful product or sequesters (permanently store) the CO₂. While some commercial scale projects are being implemented in other industries and countries, the use of CCUS in the cement industry, like other industries, is still in the research and development stage. The cement industry is currently evaluating the use of solvents, sorbents, membranes, oxyfuel combustion, oxyfuel calcination, calcium or carbonate looping, algae capture, direct separation reactor technology, and other carbon capture and related technologies in cement plants worldwide.