Carbon Removal Technology in Ready-Mix Concrete

The carbon removal technology in ready-mix concrete refers to innovative approaches and processes that aim to reduce or eliminate the carbon footprint associated with the production and use of concrete. Traditional concrete production involves the emission of carbon dioxide (CO₂) during the manufacturing of cement, which is a key ingredient in concrete.

Carbon removal technologies focus on various strategies to mitigate or offset these emissions, thereby contributing to the reduction of greenhouse gas emissions and the overall environmental impact of concrete production. It’s crucial to note that cost estimates provided herein below can change over time as technologies mature, economies of scale are realized, and new innovations emerge.

Additionally, government incentives, regulatory frameworks, and market demand can influence the financial feasibility of these technologies. As such, conducting thorough feasibility studies and cost analyses for specific carbon removal technologies in ready-mix concrete projects is essential to determine accurate investment requirements.

Some carbon removal technologies in ready-mix concrete include:

I- Carbon Capture and Utilization (CCU): This involves capturing CO2 emissions from industrial processes, such as cement production, and then converting or utilizing the captured CO₂ for beneficial purposes, such as in the production of aggregates or synthetic materials. The investment required for CCU technologies can vary widely depending on the specific technology used and the scale of implementation. Large-scale carbon capture facilities, especially those integrated with industrial processes, can involve substantial upfront costs, ranging from hundreds of millions to several billion dollars. The cost per ton of CO₂ captured can vary significantly but may range from $50 to $150 or more.

Here’s an elaboration on CCU in the context of the concrete industry:

a. Capture of CO₂: In the cement and concrete production process, a significant amount of CO₂ is emitted due to the calcination of limestone (a key ingredient in cement) and the combustion of fossil fuels for energy. CCU technologies involve capturing these CO₂ emissions before they are released into the atmosphere. Different capture methods can be employed, including chemical absorption, adsorption, and membrane separation.

b. Utilization of Captured CO₂: Once captured, the CO₂ can be used or converted into valuable products, reducing the net emissions from concrete production. Some common CCU strategies in the concrete industry include:

1. Mineralization: Captured CO₂ can be reacted with alkaline materials, such as certain types of industrial waste or natural minerals, to form solid carbonates. These carbonates can potentially be used as supplementary cementitious materials in concrete production.
2. Carbonate Precipitation: CO₂ can be directly injected into concrete mixes during mixing, where it reacts with calcium hydroxide to form calcium carbonate. This process, known as carbonation curing, enhances the mechanical properties of concrete and locks in the captured carbon
3. Enhanced Weathering: Crushed silicate minerals, when exposed to CO2 and water, can naturally undergo a weathering process that binds CO2 into solid carbonates. This concept could be applied to concrete or its raw materials to capture and store CO₂.
4. Algae Cultivation: Some researchers are exploring the use of captured CO2 to cultivate algae, which can be harvested and used for various purposes, including biofuel production.
5. Synthetic Fuel Production: Captured CO₂ can be used as a feedstock for producing synthetic fuels, such as methane or methanol, through chemical reactions.
6. Concrete Products: CO₂ can be incorporated into concrete products like precast blocks or panels, sequestering carbon within the material.

CCU Benefits and Challenges: CCU in the concrete industry offers several potential benefits, including:

• Reduced Emissions: CCU can lead to a significant reduction in the net carbon emissions associated with concrete production. • Resource Efficiency: By utilizing captured CO₂ in valuable products, the industry can reduce the demand for virgin resources. • Product Innovation: CCU can lead to the development of new types of concrete with enhanced properties or novel applications. • Climate Mitigation: CCU contributes to mitigating climate change by preventing the release of CO₂ into the atmosphere.

However, there are also challenges to consider, such as the technical feasibility of the capture and utilization processes, scalability, cost-effectiveness, and potential impacts on the overall performance and durability of concrete products.

Carbon Capture and Utilization presents a promising avenue for reducing the environmental impact of the concrete industry. As research and development in CCU continue, it’s important to carefully assess the economic viability, technical feasibility, and long-term sustainability of various CCU strategies to ensure their effective integration into the concrete production process.

II- Carbon Offsetting: This approach involves balancing out the carbon emissions generated during concrete production by investing in projects that remove or prevent an equivalent amount of carbon dioxide from the atmosphere. These projects can include reforestation, soil carbon sequestration, or investing in renewable energy sources. The cost of carbon offsetting can vary depending on the type of offset project and location. Reforestation projects, for instance, can have lower costs per ton of CO₂ offset, often ranging from $5 to $30. However, the costs can vary based on factors like land availability, maintenance, and the chosen offset standard.

The cement industry has been exploring various carbon offsetting cases and initiatives to reduce its carbon footprint and contribute to mitigating climate change. Here are a few examples of carbon offsetting cases experienced by the cement industry:

a. Reforestation and Afforestation: Many cement companies have invested in reforestation and afforestation projects as a form of carbon offsetting. Trees absorb carbon dioxide from the atmosphere through photosynthesis, helping to counterbalance the emissions from cement production. These projects can involve planting trees on degraded land, deforested areas, or even on reclaimed mine sites.

b. Renewable Energy Investment: Some cement manufacturers have committed to using renewable energy sources, such as wind, solar, or hydroelectric power, to power their production facilities. By transitioning away from fossil fuels, these companies reduce their direct carbon emissions and contribute to a cleaner energy grid.

c. Carbon Capture and Storage (CCS): While still in its early stages, some cement companies are exploring the potential of carbon capture and storage technologies. These technologies capture carbon dioxide emissions from cement plants and other industrial sources and then store or utilize the captured carbon dioxide, effectively preventing it from entering the atmosphere.

d. Waste Heat Recovery: Cement production involves high-temperature processes that generate waste heat. Some companies are implementing waste heat recovery systems to capture and repurpose this heat for power generation, reducing the need for additional energy sources and consequently lowering emissions.

e. Circular Economy Practices: Cement companies are increasingly looking into circular economy practices such as using alternative fuels from waste materials in cement kilns. By replacing traditional fossil fuels with waste-derived fuels, both emissions and waste disposal are reduced.

f. Carbon Offsetting Projects: Cement companies often invest in external carbon offsetting projects, such as supporting renewable energy projects in communities, promoting energy efficiency initiatives, or contributing to projects that capture or prevent carbon emissions, like landfill gas collection systems.

g. Emission Reduction in Logistics: Cement companies are also considering emission reductions in their supply chain and logistics. This includes optimizing transportation routes, using more fuel-efficient vehicles, and adopting sustainable practices to minimize the carbon footprint associated with raw material transportation.

h. Carbon Markets and Trading: In some regions, carbon markets and trading systems exist where industries can purchase carbon credits from projects that have achieved verified emissions reductions. Cement companies can participate in such markets to offset a portion of their own emissions.

The cement industry accounts for approximately 7% of total greenhouse gas emissions. A single carbon credit represents the reduction, avoidance, or removal of 1 metric ton of CO₂ from operations or the atmosphere. These credits serve a dual purpose: motivating companies to lower their emissions and acting as a catalyst for their ongoing emission reduction efforts.

The voluntary carbon credit market expanded to reach a value of USD 1 billion in 2021, and this growth trajectory is projected to persist. Noteworthy corporations such as Amazon, Shopify, Stripe, Microsoft, BMO, GM, Audi, and Square have actively engaged in purchasing carbon credits. Forecasts indicate that the market is set to burgeon, potentially attaining a valuation of USD 100 billion by the close of the current decade.

In this context, the concrete industry stands poised to make a substantial contribution in fulfilling the mounting demand for carbon credits.

The core process of generating carbon credits revolves around adhering to an approved methodology that undergoes rigorous testing and validation of a technology. This methodology is subject to meticulous scrutiny by an independent third party, Vera. This scrutinized approach outlines how CO₂ infusion into concrete leads to the creation of carbon credits.

Central to the carbon credit generation process is meticulous data collection. Revenues stemming from the carbon credit sales are meticulously divided and then redistributed among the creators of these credits. A producer initiates their engagement with the carbon reduction system, which involves reducing cement content in concrete while incorporating CO₂. This strategic utilization of resources generates carbon credits that are subsequently sold, resulting in a shared revenue stream for the producer.

What sets these carbon credits apart, particularly those derived from the utilization of CO₂ in concrete, is their distinct trading dynamics. These credits command notably higher prices in the carbon market compared to the average rates typically paid for carbon credits. This premium valuation is attributed to the credits’ exceptional attributes of enduring permanence and stringent verifiability.

To provide a tangible illustration, envision a concrete producer involved in pouring approximately 40,000 m3 of concrete. Within this scenario, assuming a price tag of $100 per credit and a 5% reduction in cement content, the producer stands to accrue up to $25,000 in revenue from carbon credits. This underscores the significant financial potential harnessed through participation in carbon credit trading.

As the cement industry continues to face pressure to reduce its environmental impact, carbon offsetting will likely remain an important part of their sustainability initiatives.

III- Alternative Binders: Research is ongoing to develop alternative binders that require less or no cement in concrete production. These binders can be made from waste materials or byproducts and may have lower carbon emissions associated with their production. The development and implementation of alternative binders are still evolving, and the cost can vary based on the binder’s composition, availability of feedstock materials, and production methods. While specific cost figures per ton of CO2 reduction may not be readily available, the investment can include research and development costs as well as potential adjustments to manufacturing processes.

Here are some common examples:

a. Fly Ash: Fly ash is a byproduct of coal-fired power plants and contains silica and alumina. When mixed with lime or alkalis, it can react to form a binding matrix. It is commonly used as a supplementary cementitious material in concrete production.

b. Slag: Slag is a byproduct of the iron and steel industry. It contains a high amount of calcium, silica, and alumina. Ground granulated blast furnace slag (GGBFS) can be used as a binder to create cementitious properties.

c. Metakaolin: Metakaolin is calcined kaolin clay, which is rich in alumina and silica. When used as a binder, it can enhance early strength and durability. It’s often used in high-performance concrete mixes.

d. Silica Fume: Silica fume is an ultra-fine byproduct of silicon and ferrosilicon alloy production. It’s used as a supplementary cementitious material to improve strength, durability, and reduce permeability.

e. Calcined Clay: Calcined clay, similar to metakaolin, is clay that has been heated to high temperatures to activate its pozzolanic properties. It’s a key ingredient in LC3 (Limestone Calcined Clay Cement).

f. Natural Pozzolans: Natural pozzolans like volcanic ash and pumice have been used historically as cementitious materials. They react with calcium hydroxide to form cementitious compounds.

g. Alkali-Activated Binders: These binders use alkaline solutions to activate industrial waste materials like slag, fly ash, or natural pozzolans. They form a binder matrix similar to cement but with lower carbon emissions.

h. Hydraulic Lime: Hydraulic lime is produced by burning limestone with lower temperatures than those used for Portland cement, resulting in reduced carbon emissions. It can be used for masonry and plaster applications.

i. Magnesium Oxide: Magnesium oxide can be used as a binder, often in combination with other materials, to create carbon-reduced construction products.

j. Bio-based Binders: Some researchers are exploring bio-based binders made from agricultural waste or byproducts, aiming for sustainable and low-carbon alternatives.

Each alternative binder has its own advantages and limitations, and Holderchem can assist in the choice and supply of the binder, which depends on factors such as the desired application, local availability of materials, performance requirements, and environmental considerations.

IV- Carbon-Reduced Cement: Some companies are developing cements with reduced carbon emissions. For instance, there are low-carbon and carbon-neutral cements that aim to lower the carbon content of concrete while maintaining its performance. The costs associated with producing carbon-reduced cement can vary depending on the specific formulation, production methods, and market conditions. Carbon-reduced cements may have slightly higher production costs compared to traditional cements, but the exact cost per ton of CO₂ reduction can vary widely.

LC3, which stands for “Limestone Calcined Clay Cement,” is a type of cement that aims to reduce carbon emissions compared to traditional Portland cement. LC3 is developed by substituting a significant portion of the clinker (the main ingredient in Portland cement production) with calcined clay and limestone. This innovative cement formulation has the potential to substantially reduce carbon dioxide emissions associated with cement production.

LC3 is designed to address the high carbon footprint of conventional cement production, which is primarily attributed to the process of clinker production. The production of clinker requires heating limestone and other raw materials to very high temperatures, which releases a significant amount of carbon dioxide as a byproduct. By utilizing calcined clay and limestone as partial replacements for clinker, LC3 reduces the amount of clinker needed in the cement, leading to lower carbon emissions.

The exact carbon reduction achieved by LC3 can vary based on factors such as the specific formulation, production methods, and local conditions. However, LC3 has the potential to achieve substantial carbon dioxide emission reductions, with estimates suggesting that it could reduce emissions by up to 30-40% compared to traditional Portland cement.

LC3 has gained attention as a more environmentally friendly alternative to conventional cement due to its potential to lower the overall carbon footprint of construction materials. However, like any new technology, its implementation depends on factors such as market acceptance, availability of raw materials, regulatory support, and economic viability.

In addition to LC3 (Limestone Calcined Clay Cement), there are several other types of carbon-reduced cements and cementitious materials that aim to lower carbon emissions in comparison to traditional Portland cement. Here are a few examples:

a. Geopolymer Cement: Geopolymer cement is produced by activating aluminosilicate materials, such as fly ash or slag, with an alkaline solution. This process avoids the high-temperature clinker production of traditional cement, resulting in significantly reduced carbon emissions. Geopolymer cement can achieve comparable performance to Portland cement while using industrial byproducts.

b. Belite-Rich Calcium Sulfoaluminate Cement (CSA): CSA cement is made by combining calcium sulfate, bauxite, and limestone. It produces less carbon dioxide during production compared to traditional cement. Belite-rich CSA cement is an advancement that uses higher proportions of belite and lower levels of aluminate, further reducing the carbon footprint.

c. Magnesium Oxide Cement: This type of cement is produced from magnesium oxide, derived from natural minerals or industrial processes, and can be mixed with other materials like sand and cellulose fibers to create a binder. It has lower energy requirements during production and can be a carbon-reduced alternative.

d. Recycled Glass Powder Cement: Ground recycled glass can be used as a partial replacement for cement in concrete mixes. This reduces the demand for clinker and raw materials, contributing to carbon emissions reduction.

e. Calcium Aluminate Cement (CAC): While not entirely carbon-free, calcium aluminate cement has lower embodied carbon compared to Portland cement due to its lower limestone content. It’s used in specialized applications where rapid setting and resistance to high temperatures are required.

f. Silica Fume-Blended Cement: Silica fume, a byproduct of silicon production, can be added to cement blends to improve strength and durability while reducing the carbon footprint. Silica fume requires less energy to produce compared to clinker.

g. High-Volume Fly Ash Cement: By using a high volume of fly ash as a supplementary cementitious material, carbon emissions can be reduced since fly ash is a waste byproduct of coal-fired power plants. This approach lowers the need for clinker in cement production.

h. Alkali-Activated Binders: Alkali-activated binders utilize alkaline solutions to activate industrial waste materials such as slag, fly ash, and natural pozzolans. These binders can offer similar performance to Portland cement while emitting fewer greenhouse gases.

It’s important to note that the availability, performance, and cost-effectiveness of these carbon-reduced cement alternatives can vary based on factors such as regional materials, technology maturity, and specific application requirements. As the field of sustainable construction evolves, ongoing research and development efforts are contributing to the emergence of new and improved carbon-reduced cement options.

V- Circular Economy Practices: Incorporating recycled materials into concrete production can have relatively lower costs compared to some other technologies. However, these costs can still vary based on factors such as the availability and quality of recycled materials, transportation, and processing.

Here are a few examples that illustrate how using recycled materials can have relatively lower costs compared to other carbon reduction technologies:

a. Recycled Aggregate: Instead of using entirely new quarried aggregates, crushed concrete from demolished structures can be used as recycled aggregate in new concrete mixes. This approach eliminates the need for mining raw materials, reducing extraction costs and associated environmental impacts. While the processing and transportation of recycled aggregate may incur some costs, they are often lower than those for extracting and processing new aggregates.

b. Fly Ash and Slag: These are byproducts of industrial processes, such as coal combustion and steel production. When used as supplementary cementitious materials in concrete, they can replace a portion of cement, reducing both raw material costs and carbon emissions. Because fly ash and slag are often considered waste materials, they can be obtained at relatively low or even no cost, making them an economical choice.

c. Recycled Concrete: Demolished concrete structures can be crushed and processed to create recycled concrete aggregate (RCA). This RCA can then be used to produce new concrete, reducing the need for virgin aggregates. The cost of processing and using recycled concrete is generally lower than that of mining and processing new aggregates.

d. Recycled Steel and Fibers: Incorporating recycled steel in the form of steel fibers or reinforcement bars can lower the embodied carbon of concrete structures. Recycled steel is often readily available from salvaged buildings or industrial processes. While there might be some processing costs, using recycled steel can be cost-competitive with new steel, especially if it’s locally sourced.

e. Recycled Plastic: In some cases, waste plastic can be incorporated as a partial replacement for sand in concrete mixes. While this technology is still evolving and might have certain limitations, it illustrates how unconventional recycled materials can be used to reduce costs associated with traditional raw materials.

f. Recovered Water: Using treated wastewater as mixing water in concrete production is another form of recycling. It helps conserve freshwater resources while also reducing the need for energy-intensive water treatment processes. The cost savings from using reclaimed water can contribute to the overall cost-effectiveness of concrete production.

It’s important to note that while using recycled materials in concrete production can offer cost advantages, there are also factors to consider, such as material quality, consistency, and potential regulatory requirements. Additionally, the availability of recycled materials might vary depending on local circumstances. Proper testing and quality control measures should be in place to ensure the performance and durability of concrete mixes containing recycled materials.

VI- Enhanced Concrete Mix Design: Optimizing mix designs to reduce cement content can be a cost-effective approach, as it might involve adjusting the proportions of aggregates and supplementary cementitious materials. The cost per ton of CO₂ reduction can vary but is generally considered to be on the lower end of the spectrum.

Enhanced concrete mix design is indeed a valuable approach to reducing the carbon footprint of concrete production. By optimizing the mix proportions and incorporating supplementary cementitious materials, this strategy can offer both environmental and economic benefits. Here’s a comment on this approach:

Optimizing concrete mix designs to reduce cement content is a sustainable and pragmatic method for curbing carbon emissions. By carefully adjusting the ratios of cement, aggregates, and supplementary cementitious materials like fly ash, slag, or silica fume, the industry can achieve substantial reductions in cement consumption without compromising the structural integrity or performance of the concrete. This not only lowers the environmental impact associated with cement production but also conserves natural resources.

Furthermore, this approach is often considered cost-effective compared to some other carbon reduction technologies. While the specific cost per ton of CO₂ reduction can vary based on factors such as material availability, local market conditions, and transportation costs, the overall expenses are generally manageable. The use of supplementary cementitious materials often reduces the reliance on cement, which can be a significant cost driver in concrete production

However, it’s important to recognize that achieving optimal results through enhanced concrete mix design requires careful consideration of factors such as material compatibility, mix workability, and long-term durability. Proper testing and quality control are essential to ensure that the resulting concrete maintains the required strength, durability, and performance characteristics.

In conclusion, enhanced concrete mix design is a pragmatic approach that aligns well with sustainable construction practices. By reducing cement content and incorporating supplementary cementitious materials, the industry can effectively contribute to carbon reduction goals while also benefiting from potential cost savings. It’s a strategy that showcases the potential for innovation within the industry, where environmental responsibility and economic viability can go hand in hand.

VII- Carbonation Curing: Carbonation curing can be relatively cost-effective since it utilizes carbon dioxide that is captured from the atmosphere or other sources. The costs may primarily involve infrastructure adjustments to implement the curing process, and the cost per ton of CO₂ captured could be moderate. On average, producers using Carbonation Curing in the production of Ready Mix reduce cement content by 4-6% with no compromise on concrete quality or performance. Alternatively, they can choose to increase the concrete strength without increasing the cement content.

Ready-mix producers can also rejuvenate the cement-based materials and water within their slurry tank, transforming them into valuable resources through upcycling. As a result of a CO₂-induced reaction, ultrafine suspended solids form in reclaimed water. These solids, which are rendered stable by CO₂, play a beneficial role in bolstering the strength of concrete in newly formulated mixes and can thus be reused as binding agents in fresh concrete blends, enhancing concrete performance or allowing for a reduction in the quantity of cement required. Furthermore, it is important to note that CO₂ treated reclaimed water serves to mitigate the erratic fluctuations in properties of freshly mixed concrete, a consequence often observed when unprocessed reclaimed water slurry is employed in the production of new concrete.

On average, producers rejuvenating the cement-based materials and water within their slurry tank by injecting in the slurry water carbon dioxide, reduce cement content by around 3% with no compromise on concrete quality or performance.

Here’s a more detailed elaboration on carbonation curing:

Carbon Curing Process Overview:

a. Concrete Placement: Carbonation curing is applied after concrete has been placed and initially cured. During the curing period, concrete undergoes hydration, where cement particles react with water to form calcium silicate hydrate gel, which provides strength to the material.

b. Exposure to CO₂: After the initial curing period, the concrete is exposed to a carbon dioxide-rich environment. This can be achieved by enclosing the concrete in a controlled environment with elevated levels of CO₂ or by using techniques like wet curing with CO₂-saturated water.

c. Carbonation Reaction: The carbon dioxide reacts with the calcium hydroxide (Ca(OH)₂) present in the concrete, resulting in the formation of calcium carbonate (CaCO₃). This reaction consumes the calcium hydroxide and carbon dioxide, producing water as a byproduct. The conversion of calcium hydroxide into calcium carbonate leads to densification and strengthening of the concrete matrix.

Benefits of Carbonation Curing:

a. Enhanced Strength and Durability: Carbonation curing leads to the formation of additional calcium carbonate crystals within the concrete’s microstructure. This contributes to improved compressive strength, abrasion resistance, and durability of the material over time.

b. Reduced Permeability: The densification of the concrete matrix through carbonation results in reduced permeability, making the concrete less susceptible to the ingress of moisture, chemicals, and aggressive agents that could cause deterioration.

c. CO2 Sequestration: Carbonation curing effectively captures and sequesters carbon dioxide within the concrete. This process enhances the sustainability of concrete production by utilizing captured CO₂ and reducing its emissions footprint.

d. Energy Efficiency: Carbonation curing often requires lower energy inputs compared to traditional heat-based curing methods. It can be applied at ambient temperatures, reducing the need for additional energy for heating.

Considerations and Challenges of Carbonation Curing:

• The depth of carbonation depends on factors such as concrete composition, curing conditions, and the availability of calcium hydroxide. Therefore, carbonation curing may not penetrate deep into thick concrete elements.

• The process is relatively slower than heat-based curing, so it might not be suitable for applications requiring rapid strength gain.

• Carbonation curing might not be suitable for environments where carbonation-induced corrosion of reinforcing steel could be a concern.

Carbonation curing is a sustainable technique that simultaneously improves concrete performance and contributes to CO₂ capture and utilization. Its ability to enhance strength, durability, and sustainability makes it an attractive option for construction projects seeking environmentally friendly practices. However, careful consideration of project-specific requirements and potential challenges is necessary for successful implementation.