CCUS is an acronym you’ll see more of in the years to come. It stands for “Carbon Capture, Utilization & Storage.” Some technologies capture and sequester CO2 before it enters the atmosphere. There are also technologies involving direct air capture. Direct injection into ready-mix concrete at the plant is another possibility.

Atmospheric Warming

It is excess carbon dioxide in the atmosphere that drives the nascent CCUS sector. How exactly does CO2 impact the earth’s atmosphere? Together, nitrogen and oxygen account for 99% of dry air. By contrast, carbon dioxide accounts for a mere 0.04%. At such low concentrations, how does CO2 manage to warm the atmosphere?

The phenomenon is explained by the way CO2 interacts with the sun’s energy. Nitrogen and oxygen do not interfere with infrared energy radiating out into space. The simplicity of their molecular structure is a key reason. Unfortunately, carbon dioxide does absorb infrared energy, heating the atmosphere in the process. This is because CO2’s wavelength of 2k to 15k nanometers overlaps with the wavelength of infrared energy. the latter range from 700 to 1 million nanometers.

Penn State Prof. David Tilley suggests this analogy, “If someone my size drinks two beers, my blood alcohol content will be about 0.04 percent.” That’s about the level where the body starts feeling alcohol’s effects. At a concentration of 0.04%, the atmosphere starts to feel the adverse effects of carbon dioxide.

While we can reign in DUI with laws, global carbon emissions cannot be legislated out of existence. It requires nothing less than steadfast cooperation among nations. One human family is dependent on a single atmosphere.

Since CO2’s effect is cumulative, it is appropriate to analyze emissions over time. Since 1975, the five nations emitting the most carbon are, in order, the United States, China, Russia, Germany, and the UK. CCUS mitigation is well underway across the United States, Europe, and the UK, but less so in China and Russia.

CCUS Commitments in Cement and Concrete

Cement production is carbon intensive. Pressure on the industry increases as net-zero pledges proliferate. Worldwide, researchers continue to chip away at the industry’s carbon emissions. They do so in diverse ways.

Cement-related

• Deploy SCMs to reduce the amount of Portland cement needed in concrete mixes.

• Use alternative energy sources to operate kilns - electric, biomass, recycled plastic

• Prevent kiln-generated CO2 from reaching the atmosphere

Concrete-related

• Use less concrete by making it stronger

• Inject CO2 into concrete mixes

• Develop advanced aggregates and alternatives

A Rising Tide of CCUS Strategies

To analyze the impact of each new carbon mitigation strategy, it's necessary to look at the totality of the atmosphere. No single technology will be the magic bullet.

Novel Solutions

As a result, the scramble is on to find novel ways to limit CO2 in the atmosphere. For example, CO2Rail intends to deploy specialized rail cars to snatch CO2 from the air.

MIT’s electroswing adsorption system is effective at atmospheric CO2 concentrations. That’s just 0.04%. The concept features a large, specialized battery that absorbs CO2 as it is being charged.. The battery then releases the CO2 as it is being discharged. Current limits on discharging cycles are being addressed.

Solid sorbent technologies overcome certain energy and regeneration drawbacks of amine-based CO2 absorption. Researchers are exploring CO2 capture via zeolites and metal organic framework (MOF) membranes. Ionic liquids are another possibility.

CCUS & Concrete: Capacity in the Pipeline

The concrete industry gets the credit for the largest carbon sequestration “project” on the planet. It’s called carbonation. This is the chemical process by which atmospheric CO2 reacts with calcium hydroxide. The chemical reaction yields calcium carbonate and water:

Ca(OH)2 + CO2 → CaCO3 + H2O

The process begins on the concrete's surface, gradually working its way inward.

Another way to deal with carbon dioxide is to reduce its production from the start. The industry already uses alternate fuels to fire cement kilns. Blended cements reduce the need for the energy-intensive clinker produced by the kilns. Alternative binders reduce the amount of Portland cement required. Portland limestone cement (PLC) is now being widely adopted. Additives like graphene strengthen concrete, reducing the amount required for a given project.

Ultimately, CCUS is a vital component in the battle to limit atmospheric carbon.

One study estimates that Europe accounts for 56% of current CCUS capture capacity. The United States and Canada account for another 40%. India accounts for another 3%, with China at 0%. The problem? Europe only accounts for 4% of the global cement production, with China at more than 50%.

Decarbonization Pathways

Firing cement kilns accounts for half of carbon emissions. The other half is from calcination. Achieving net-zero emissions will require carbon capture during cement production. Various CCUS technologies appear promising. However, they are often expensive, sometimes doubling costs. Processes need to be refined and scaled upward.

Currently, multiple CO2 capture technologies are in the pipeline at large-scale projects:

• Mineralization

• Post-combustion amine scrubbing

• Oxy-fuel combustion

Mineralization delivers carbon sequestration without the complexities and costs associated with underground storage.

Potential Potholes on the Road to Decarbonization

Cost and CCUS commitment are current obstacles. Cement producers must get onboard en masse to effectuate change. At present, just two companies, Lafarge Holcim and Heidelberg Cement account for 73% of the CCUS capacity in the pipeline. Going forward, the economies of scale may lower costs at these large companies.

In the cement/concrete industry, there is no silver bullet to carbon capture. More technological breakthroughs are vital during this challenging journey toward carbon neutrality.

Policy Support & Government Initiatives

Policy support is essential to decarbonizing the cement industry. Governments must incentivize carbon capture to achieve the prodigious goals set for 10, 20, 30 years from now. Thus far, Europe leads the way.

However, the United States took a significant step forward in August 2022. The Inflation Reduction Act became the federal government’s largest response ever to climate change. Various incentives and initiatives will drive 2030 GHG emissions to levels 32-42% below those of 2005.

Ultimately, policy support is vital among the planet's most prolific cement producers.

About PACA

The Pennsylvania Aggregates and Concrete Association (PACA) keeps its members and the general public informed of the latest industry developments. PACA’s staff welcomes questions about your upcoming concrete project. Please contact us at your earliest convenience.