Carbon Negative Cement
Turning captured CO₂ into high performance construction materials through scalable mineralisation.

Summary

The concept uses captured CO₂ to harden a binder made from industrial residues, creating strong, stone‑like materials while permanently storing carbon. Because it works with the CO₂ networks now being built, cement plants can turn a waste gas into a valuable input and produce carbon‑negative cement without relying on kilns. It’s a simple, scalable way to cut emissions and make better construction materials.

Introduction

Cement remains one of the world’s most indispensable construction materials, yet it is also one of the most carbon‑intensive. In 2022, cement production accounted for approximately 8% of global CO₂ emissions, a figure that has remained stubbornly high despite decades of efficiency improvements and fuel switching (IEA 2023; GCCA 2023). The fundamental challenge is chemical rather than operational: the calcination of limestone releases CO₂ as an unavoidable by‑product, meaning that even a fully renewable energy supply cannot eliminate the majority of emissions associated with Portland cement (Scrivener, John, and Gartner 2018). As a result, the cement sector has become one of the hardest industrial systems to decarbonise, and current mitigation pathways rely heavily on carbon capture and storage (CCS), a strategy that introduces high capital costs, long‑term monitoring obligations, and limited opportunities for value creation (IPCC 2022).

Despite significant investment, CCS has struggled to scale in the cement sector because it treats CO₂ as a waste stream requiring permanent disposal. Geological storage projects face regulatory complexity, public acceptance barriers, and uncertain long‑term liability, all of which slow deployment and increase cost (Bui et al. 2018; DESNZ 2023). More importantly, CCS does not change the underlying chemistry of clinker production. Even if every cement plant in Europe were equipped with capture technology, the industry would still depend on high‑temperature kilns and the calcination of limestone, locking in energy demand and process emissions for decades.

This has led to growing interest in alternative binders that break the link between cement production and calcination. Among these, CO₂‑reactive binders—materials that harden through carbonation rather than hydration—represent one of the most promising pathways. In these systems, a calcium‑rich mineral scaffold reacts directly with CO₂ to form solid carbonate phases, producing a dense, stone‑like matrix. Unlike Portland cement, which emits CO₂ during production, these binders consume CO₂ as they gain strength, offering the potential for carbon‑neutral or even carbon‑negative construction materials (Kraft et al. 2022; Sanna et al. 2014). Early commercial technologies demonstrate the viability of accelerated carbonation, but most rely on conventional clinker or are limited to aggregates rather than full binder systems. No widely deployed solution yet exists that replaces clinker entirely while using captured CO₂ as the primary hardening agent.

This concept paper introduces a new approach: a Ca‑rich CO₂‑reactive binder designed to integrate directly into cement plants and industrial CO₂ clusters. Instead of sending captured CO₂ exclusively to geological storage, a portion is diverted into controlled carbonation curing environments where it becomes the essential reactant that drives binder formation. By shifting from calcination‑driven clinker production to carbonation‑driven mineralisation, this system offers a pathway to carbon‑negative materials, reduced reliance on kilns, and a new economic model in which CO₂ becomes a valuable input rather than a liability. The sections that follow outline the innovation, mechanism, chemistry, raw materials, integration pathway, scalability, and economic potential of this binder system—and how it can transform cement plants from major emitters into CO₂‑utilisation hubs at the centre of a decarbonised construction ecosystem.

Core Innovation

The core innovation of this concept is the deliberate re‑engineering of cement chemistry so that CO₂ becomes the essential reactant, not the unavoidable emission. This is not a marginal adjustment to Portland cement; it is a structural inversion of the process that has defined cement production for 200 years. Instead of decomposing limestone at high temperatures to release CO₂, the proposed system begins with a Ca‑rich mineral scaffold—derived from industrial by‑products—and uses captured CO₂ as the agent that drives hardening, densification, and strength formation. In this model, CO₂ is not a liability to be buried underground but the molecule that unlocks the binder’s performance.

At the centre of the innovation is the decision to design the scaffold so that it is intentionally under‑reactive with water. This is a fundamental departure from Portland cement, where hydration is the dominant mechanism and water is the primary driver of strength. Here, water plays only a preparatory role: it wets the scaffold, dissolves a fraction of the reactive calcium phases, and creates the alkaline pore environment required for carbonation. The material remains weak, incomplete, and structurally open until it encounters CO₂. Only then does the binder begin to develop its defining characteristics. When CO₂ dissolves into the pore solution, it forms carbonate species that rapidly precipitate with calcium ions, generating a dense network of interlocking CaCO₃ crystals. This mineralisation process is fast, exothermic, and capable of producing a stone‑like microstructure with mechanical properties comparable to high‑performance concretes (Kraft et al. 2022).

The second dimension of the innovation lies in the choice of feedstock. Instead of relying on quarried limestone and energy‑intensive clinker production, the binder uses abundant Ca‑rich industrial residues such as cement kiln dust, steel slag, and lime fines. These materials already contain the reactive calcium phases needed for carbonation, and they are produced in large volumes near cement and steel plants. By transforming these by‑products into a functional scaffold, the system reduces raw material costs, avoids new extraction, and aligns directly with circular‑economy principles (Sanna et al. 2014; Scrivener, John, and Gartner 2018). This also means the binder can be manufactured at scale without waiting for new supply chains to emerge.

The third and most strategically significant aspect of the innovation is its integration with CO₂‑rich industrial clusters. As the UK and Europe expand carbon‑capture infrastructure, cement plants will soon be connected to regional CO₂ pipeline networks designed to transport captured emissions to offshore storage (DESNZ 2023; NIC 2023). This creates a structural surplus of purified CO₂—far more than geological storage alone can absorb economically. The proposed binder converts this surplus into value. Instead of paying to compress, transport, and store every tonne of CO₂, cement plants can divert a portion into controlled carbonation curing environments, where it becomes the reactant that forms the binder. This transforms the plant from a point‑source emitter into a CO₂‑utilisation hub, capable of producing carbon‑negative materials while reducing storage obligations and exposure to carbon pricing.

These elements constitute a new class of cement chemistry: one that eliminates the need for calcination, consumes CO₂ as a core ingredient, leverages existing industrial by‑products, and integrates seamlessly with the carbon‑capture infrastructure now being built. It is not an incremental improvement to Portland cement but a fundamentally different pathway—one that aligns material science, industrial decarbonisation, and economic logic in a way that conventional cement cannot.

How It Works

The CO₂‑reactive binder operates through a sequence of tightly coupled chemical and physical transformations that replace the high‑temperature calcination and hydration reactions of Portland cement with a controlled carbonation pathway. The process begins with the preparation of a finely milled Ca‑rich mineral scaffold, typically composed of industrial by‑products such as cement kiln dust, steel slag, or lime residues. These materials contain reactive calcium phases—free lime, calcium hydroxide, and calcium silicates—that dissolve partially when mixed with water, but not enough to form a strong hydrated matrix. This intentional under‑reactivity is central to the system: the scaffold is designed to remain structurally open, chemically alkaline, and mechanically weak until it encounters CO₂, ensuring that carbonation rather than hydration becomes the dominant hardening mechanism (Scrivener, et al. 2018).

Once the scaffold is mixed with water, the pore solution becomes highly alkaline, and a small fraction of the calcium phases dissolve, creating a reservoir of Ca²⁺ ions. At this stage, the material resembles a conventional fresh paste in appearance but lacks the early strength development associated with Portland cement. The system remains in this metastable state until it is placed into a CO₂‑enriched curing environment. When CO₂ is introduced, it diffuses rapidly through the pore network and dissolves into the water phase, forming carbonic acid. This acid immediately equilibrates into bicarbonate and carbonate ions, shifting the pore chemistry from alkaline dissolution to carbonate precipitation. The dissolved calcium ions react with these carbonate species to form solid CaCO₃ polymorphs—primarily calcite, but also aragonite and vaterite depending on curing conditions (Kraft et al. 2022).

As carbonation progresses, the binder undergoes a profound microstructural transformation. The precipitation of CaCO₃ begins at nucleation sites on particle surfaces and grows outward into interlocking crystalline networks. These crystals fill capillary pores, bridge adjacent particles, and progressively densify the matrix. The reaction is exothermic, accelerating ion mobility and further promoting crystal growth. Unlike the amorphous calcium–silicate–hydrate gel that forms in Portland cement, the carbonate phases produced here are crystalline, stable, and mechanically robust. Their growth reduces porosity, increases stiffness, and creates a stone‑like microstructure that closely resembles natural limestone. This mineralogical shift is the source of the binder’s strength, durability, and long‑term chemical stability (Li et al. 2022).

The rate and extent of carbonation depend on CO₂ concentration, humidity, temperature, and scaffold composition. Under optimised curing conditions—typically 10–40% CO₂ with controlled moisture—the reaction proceeds rapidly, allowing significant early strength to develop within hours. This accelerated hardening is particularly advantageous for precast manufacturing, where fast demoulding and high throughput are essential. As the reaction continues, the binder consumes increasing amounts of CO₂, with total uptake directly correlated to final strength. This creates a tunable system in which performance can be engineered by adjusting curing parameters and scaffold chemistry, offering a level of control not possible in hydration‑based systems (Sanna et al. 2014).

By the end of the curing cycle, the binder has undergone a complete transformation: the initial Ca‑rich scaffold has been converted into a dense carbonate matrix, and the CO₂ that would otherwise require compression and geological storage has been permanently mineralised. The result is a material that not only matches the mechanical performance of conventional cementitious systems but does so while consuming CO₂ rather than emitting it. This inversion of the traditional cement chemistry—turning CO₂ from an emission into a reactant—is the defining mechanism that enables carbon‑negative construction materials at industrial scale.

Raw Materials

The CO₂‑reactive binder is built on a foundation of Ca‑rich industrial by‑products that are already produced at scale and located exactly where cement plants operate. These materials contain the reactive calcium phases needed for carbonation, and their chemical diversity allows the binder to be tailored to local industrial conditions. Unlike Portland cement, which depends on quarried limestone and high‑temperature kilns, this system draws from existing waste streams, reducing extraction, lowering cost, and aligning with circular‑economy principles (Sanna et al. 2014; Scrivener et al. 2018).

Comparative Table of Ca Rich Feedstocks

Cement kiln dust (CKD) is the most strategically aligned feedstock for this binder system. It is produced directly at cement plants, contains high concentrations of free lime and calcium hydroxide, and is already finely divided—attributes that make it exceptionally reactive under CO₂‑rich curing conditions. CKD often requires disposal or low‑value reuse, so incorporating it into a carbonation‑based binder converts a waste stream into a high‑value input. Its chemical similarity to clinker dust ensures compatibility with existing grinding and handling equipment (Scrivener et al. 2018).

Steel slag, particularly BOF and EAF slag, provides another abundant and geographically reliable source of reactive calcium. Although its carbonation kinetics are slower than CKD, slag undergoes significant densification and strength gain when carbonated, producing a robust microstructure. Its availability near industrial clusters makes it a strategic feedstock for regions where cement and steel plants operate in close proximity (Sanna et al. 2014).

Lime residues—including fines from lime kilns, flue‑gas desulfurisation solids, and water‑treatment lime sludges—offer exceptionally fast carbonation due to their high CaO and Ca(OH)₂ content. These materials can accelerate early strength development and improve overall CO₂ uptake. Their main limitation is moisture sensitivity, which requires controlled handling and storage (Kraft et al. 2022).

Calcium‑rich ashes provide supplementary reactivity and help refine the binder’s microstructure. Although their chemistry is more variable, they expand the range of viable feedstocks and support long‑term scalability by diversifying supply sources. Their role is often synergistic rather than primary, enhancing nucleation and contributing to matrix densification (Li et al. 2022).

These materials form a flexible, resilient, and industrially aligned feedstock base. Their widespread availability ensures that the CO₂‑reactive binder can be produced at scale without new mining operations or major supply‑chain disruptions. By drawing from existing waste streams, the system reduces cost, minimises environmental impact, and positions cement plants to transition toward carbon‑negative production using materials already at their doorstep.

CO₂ Supply

The long‑term viability of a CO₂‑reactive binder depends on a supply of CO₂ that is both stable and scalable. What makes this system compelling is that the UK and European industrial landscape is moving toward a future in which captured CO₂ becomes abundant, not scarce. As carbon‑capture infrastructure expands across industrial clusters, cement plants will sit at the centre of dense CO₂ networks designed to aggregate emissions from steelmaking, waste‑to‑energy, hydrogen production, and chemical processing (DESNZ 2023; NIC 2023). In this emerging environment, CO₂ is no longer a constrained input but a structural surplus—one that can be redirected from storage into material production. The binder leverages this shift by turning a compliance burden into a feedstock.

To understand how CO₂ availability evolves over time, it is useful to consider three plausible supply scenarios. Each reflects a different stage of industrial decarbonisation, yet all support the feasibility of large‑scale carbonation‑based binder production.

In the first scenario, cement plants rely primarily on their own captured CO₂. As post‑combustion capture systems are installed on kilns, mills, and exhaust streams, each plant generates a continuous flow of purified CO₂ as part of its decarbonisation obligations. Even if clinker production declines, residual emissions from grinding, drying, and auxiliary fuel use ensure that a baseline supply remains available. This scenario represents the earliest stage of deployment, where binder production scales in parallel with the plant’s own capture capacity. It is the most conservative model, yet it already provides enough CO₂ to support meaningful binder output, particularly for precast and modular products that require controlled curing environments (IEA 2023).

In the second scenario, cement plants become active participants in regional CO₂ pipeline networks. Industrial clusters such as HyNet, the East Coast Cluster, and Acorn are designed to aggregate CO₂ from multiple emitters and transport it to offshore storage sites. Once connected, a cement plant no longer depends solely on its own emissions; it gains access to a shared CO₂ reservoir that grows as more industries join the network. This transforms the plant into a node within a CO₂ grid, capable of drawing from a regional supply that far exceeds its own output. Under this scenario, binder production can expand independently of clinker production, allowing plants to reduce kiln utilisation while increasing carbon‑negative material output (NIC 2023).

In the third scenario, CO₂ becomes a traded industrial commodity within the cluster. As hydrogen reformers, waste‑to‑energy facilities, and biogenic CO₂ sources connect to the same pipeline infrastructure, they generate volumes of captured CO₂ that may exceed their storage allocations or economic thresholds. These emitters have an incentive to sell CO₂ for utilisation rather than pay for compression and offshore injection. Cement plants, with their large curing halls and continuous demand for CO₂, become natural buyers. This scenario represents the mature state of the system: a regional CO₂ marketplace in which utilisation competes directly with storage. In this environment, the binder is not constrained by local emissions but supported by a diversified, multi‑source supply chain (Li et al. 2022).

Across all three scenarios, the conclusion is the same: CO₂ availability is not a limiting factor for this binder system. The direction of industrial decarbonisation ensures that captured CO₂ will become increasingly abundant, increasingly centralised, and increasingly integrated into shared infrastructure. The binder leverages this structural shift by converting CO₂ into a permanent mineral phase, reducing storage requirements while producing a valuable construction material. In doing so, it aligns perfectly with the trajectory of national and regional decarbonisation strategies, turning an inevitable by‑product of industrial transition into the core ingredient of a carbon‑negative cement alternative.

Strength & Performance

The performance of the CO₂‑reactive binder is defined by the mineral phases it forms and the microstructural transformations that occur during carbonation. Unlike Portland cement, where strength emerges from the gradual formation of calcium–silicate–hydrate (C‑S‑H) gel, this system derives its mechanical properties from the precipitation of crystalline calcium carbonate polymorphs. This distinction is not cosmetic; it fundamentally changes the kinetics, durability, and long‑term stability of the material. Carbonation proceeds rapidly under controlled conditions, and the resulting microstructure resembles natural limestone more closely than any hydrated cementitious phase. This mineralogical shift is the source of the binder’s high compressive strength, low permeability, and exceptional chemical resilience (Kraft et al. 2022).

Strength development begins the moment CO₂ enters the pore network. As the gas dissolves into the alkaline pore solution, it forms carbonate ions that immediately react with dissolved calcium to precipitate solid CaCO₃. These crystals nucleate on particle surfaces and grow into dense, interlocking networks that progressively fill voids and reduce porosity. The reaction is exothermic, accelerating ion mobility and promoting further precipitation. Because the process is driven by gas–solid interactions rather than water‑mediated hydration, the kinetics are significantly faster. In optimised curing environments—typically 10–40% CO₂ with controlled humidity—materials can achieve 40–60% of their ultimate strength within the first 6–12 hours, a rate that outpaces conventional cement by a wide margin (Scrivener et al. 2018).

As carbonation continues, the binder undergoes a transition from a porous, weak scaffold to a dense carbonate matrix. The reduction in capillary porosity is substantial: studies on carbonated Ca‑rich residues show porosity reductions of 20–40% relative to uncarbonated controls, accompanied by marked increases in stiffness and compressive strength (Sanna et al. 2014). The resulting microstructure is dominated by calcite, with smaller fractions of aragonite and vaterite depending on curing conditions. These crystalline phases provide long‑range order and mechanical interlock, producing a material that behaves more like a sedimentary carbonate rock than a hydrated cement paste. This is why carbonated binders often exhibit compressive strengths in the range of 20–80 MPa for standard formulations, with optimised systems reaching 80–120 MPa—values comparable to high‑performance concretes (Kraft et al. 2022).

Durability is another defining characteristic. Because the binder’s primary reaction product is calcium carbonate, it inherits the chemical stability of natural limestone. Carbonate‑bonded materials exhibit low shrinkage, minimal susceptibility to sulfate attack, and strong resistance to chloride ingress. The absence of high‑alkalinity pore solutions also reduces the risk of alkali–silica reaction, a major degradation mechanism in Portland cement systems. Furthermore, the dense microstructure produced by carbonation limits water transport, improving freeze–thaw resistance and reducing long‑term permeability. These properties make the binder particularly well suited for precast elements, masonry units, façade panels, and other applications where dimensional stability and durability are critical (Li et al. 2022).

A final performance dimension is the direct relationship between CO₂ uptake and mechanical strength. Because carbonate formation is the primary hardening mechanism, the amount of CO₂ absorbed is not merely an environmental metric but a performance driver. Higher CO₂ uptake produces more extensive crystal networks, greater densification, and higher compressive strength. This creates a tunable system in which performance can be engineered by adjusting curing duration, CO₂ concentration, and scaffold composition. In contrast, Portland cement strength is constrained by hydration kinetics and water–cement ratio, offering far less flexibility. The CO₂‑reactive binder therefore provides both a carbon‑negative pathway and a performance‑optimisation framework that aligns material properties with curing conditions and CO₂ availability (IEA 2023).

These characteristics define a binder that is not only competitive with Portland cement but, in many respects, superior. Its rapid early strength, high ultimate strength, and exceptional durability arise from a mineralogical pathway that is inherently stable and chemically robust. By replacing hydration with carbonation, the system achieves a combination of performance and carbon sequestration that conventional cement chemistry cannot match.

Integration Into Cement Plants

Integrating a CO₂‑reactive binder into an existing cement plant does not require dismantling the core of the operation; instead, it redirects the plant’s existing assets into a new process flow that replaces calcination with carbonation. The transition begins at the point where clinker production would normally dominate the plant’s energy and emissions profile. Instead of feeding limestone into a rotary kiln, the plant shifts its focus to preparing a Ca‑rich mineral scaffold sourced from materials already present onsite—cement kiln dust, bypass dust, and other residues that accumulate during clinker production. These materials are dried, milled, and blended using the same grinding systems that currently process raw meal and supplementary cementitious materials. Because the scaffold is softer than clinker, grinding energy falls, equipment wear decreases, and throughput increases without requiring new milling infrastructure (Scrivener et al. 2018).

Once the scaffold is prepared, the process moves into a mixing phase that resembles conventional concrete production but with a fundamentally different purpose. Water is added not to initiate hydration but to create a workable paste and establish the alkaline pore environment required for carbonation. The mixture is conveyed through existing material‑handling lines into forming equipment—block presses, moulds, precast beds, or extrusion systems—depending on the plant’s product strategy. Plants that already operate precast or masonry lines can integrate the binder with minimal modification, while others can add modular forming units adjacent to existing production halls. At this stage, the material remains weak and chemically incomplete, awaiting the introduction of CO₂.

The critical transformation occurs when the fresh elements enter the carbonation curing environment. Cement plants equipped with carbon‑capture systems already produce a stream of purified CO₂ as part of their decarbonisation obligations. Instead of sending all of this CO₂ to compression and pipeline injection, a controlled portion is diverted into enclosed curing chambers. These chambers maintain elevated CO₂ concentrations, stable humidity, and moderate temperatures, creating the conditions required for rapid carbonate precipitation. The CO₂ flows through the curing hall in a regulated cycle, dissolving into the pore solution and triggering the mineralisation reactions that harden the binder. Because carbonation is exothermic, the chambers require only modest thermal management, and the reaction proceeds quickly enough to allow early demoulding and high production throughput (Kraft et al. 2022).

As the curing cycle progresses, the plant’s carbon‑capture system becomes an integral part of the production line. Flow‑control valves, monitoring systems, and feedback loops ensure that CO₂ utilisation does not interfere with storage obligations or pipeline pressure requirements. In industrial clusters, where multiple emitters feed into shared CO₂ networks, the plant can draw additional CO₂ from the regional pipeline, allowing binder production to scale independently of clinker output. This marks a fundamental shift in plant operations: the kiln is no longer the bottleneck, and CO₂ availability—not calcination capacity—becomes the driver of production volume (DESNZ 2023; NIC 2023).

Once carbonation is complete, the hardened elements exit the curing environment and enter the plant’s existing logistics chain. Their rapid early strength allows for immediate handling, stacking, and transport, enabling production cycles far shorter than those of hydration‑based systems. The finished products—blocks, panels, precast components, or other elements—are stored and shipped using the same infrastructure that supports conventional cement‑based materials. From the outside, the plant appears unchanged; from the inside, its chemistry, energy profile, and carbon balance have been fundamentally reconfigured.

The overall process flow therefore transforms the plant from a high‑temperature, emission‑intensive operation into a hybrid manufacturing system where CO₂ is not a waste stream but a feedstock. Grinding replaces calcination as the primary preparatory step. Carbonation replaces hydration as the hardening mechanism. CO₂‑capture infrastructure becomes a production asset rather than a compliance cost. And the plant evolves from a point‑source emitter into a CO₂‑utilisation hub capable of producing carbon‑negative construction materials at industrial scale. This integration is not disruptive; it is evolutionary, leveraging existing equipment while redirecting the plant’s chemistry toward a future in which carbon is not released but permanently mineralised.

Value Proposition

The value of the CO₂‑reactive binder lies in its ability to reposition cement plants within the emerging carbon‑constrained economy. For decades, the industry has been defined by its dependence on high‑temperature kilns, its exposure to carbon pricing, and its limited ability to decarbonise without incurring significant cost. The proposed binder breaks this pattern by transforming CO₂ from a liability into a productive input. In doing so, it shifts the economic logic of cement manufacturing from one centred on emissions management to one centred on carbon utilisation, where the act of producing material simultaneously reduces the plant’s carbon burden.

This shift is strategically significant because the regulatory environment is tightening faster than clinker‑based technologies can adapt. Carbon prices in Europe are projected to remain high, and the UK’s industrial decarbonisation strategy explicitly prioritises carbon capture, utilisation, and storage as a condition for long‑term competitiveness (DESNZ 2023). Cement plants that continue to rely solely on clinker face rising compliance costs, increasing exposure to emissions trading schemes, and growing pressure from public procurement standards that favour low‑carbon materials. By contrast, a binder that consumes CO₂ during production positions the plant to benefit from these trends rather than be constrained by them. It reduces the volume of CO₂ requiring compression and offshore storage, lowers exposure to carbon penalties, and creates a new product category that aligns with the direction of national infrastructure policy (NIC 2023).

The economic advantage extends beyond compliance. As industrial clusters expand, captured CO₂ will become increasingly abundant, and utilisation pathways will compete directly with geological storage. In this environment, the binder becomes a mechanism for monetising CO₂. Instead of paying for transport and injection, the plant converts CO₂ into a marketable material with performance characteristics comparable to high‑grade precast products. This creates a dual revenue model: one stream from material sales and another from avoided storage costs. The more CO₂ the binder consumes, the more valuable it becomes. This inversion of the traditional cost structure—where emissions reduction generates revenue rather than expense—is one of the most powerful aspects of the system (IEA 2023).

The strategic value is amplified by the binder’s compatibility with existing industrial assets. It does not require new kilns, new quarries, or new supply chains. It leverages grinding systems, handling equipment, and CO₂‑capture units that plants already operate or are in the process of installing. This lowers capital expenditure and accelerates deployment, allowing plants to scale binder production in parallel with the rollout of carbon‑capture infrastructure. The modular nature of carbonation curing means capacity can expand incrementally, matching CO₂ availability and market demand without the step‑change investments associated with new clinker lines. This flexibility is essential in a sector where long asset lifetimes and high capital intensity often slow innovation (Scrivener et al. 2018; Kraft et al. 2022).

The final dimension of the value proposition is market positioning. Demand for low‑carbon construction materials is rising across Europe, driven by ESG commitments, green‑building certifications, and public‑sector procurement rules that increasingly require carbon disclosure and reduction. A binder that is not merely low‑carbon but carbon‑negative offers a competitive advantage that is difficult for conventional cement to match. It enables developers, contractors, and infrastructure owners to reduce embodied carbon at scale without compromising performance. For cement producers, it provides a pathway to differentiate their product portfolio, capture premium markets, and align with the long‑term direction of the construction sector.

In sum, the CO₂‑reactive binder offers a value proposition that is both economic and strategic. It reduces costs associated with emissions, creates new revenue streams, leverages existing assets, and positions cement plants at the centre of a carbon‑utilising industrial ecosystem. It is not simply a new material; it is a new business model for an industry undergoing structural transformation.

Scalability & Long‑Term Supply

The long‑term scalability of the CO₂‑reactive binder depends on two structural factors: the availability of Ca‑rich feedstocks and the stability of CO₂ supply. Both are shaped by industrial systems that are already large, geographically distributed, and undergoing rapid decarbonisation. Unlike technologies that require new mining operations, specialised minerals, or rare chemical precursors, this binder draws from waste streams that are abundant, predictable, and co‑located with cement plants. This alignment between material supply and industrial geography is one of the strongest indicators that the system can scale to millions of tonnes per year.

The first pillar of scalability is the supply of Ca‑rich industrial residues. Cement kiln dust, steel slag, lime fines, and calcium‑rich ashes are produced in vast quantities across Europe and globally. These materials contain the reactive calcium phases required for carbonation and are already handled, stored, and transported within existing industrial ecosystems. Their availability is not expected to decline in the near term; even as clinker production gradually decreases, CKD and other residues remain by‑products of grinding, fuel combustion, and ancillary processes. Steel slag volumes are tied to steel production, which will continue even under deep decarbonisation scenarios. Lime residues arise from water treatment, flue‑gas cleaning, and chemical manufacturing. Together, these streams provide a stable and diversified supply base that can support large‑scale binder production without new extraction or processing burdens (Sanna et al. 2014; Scrivener et al. 2018).

The second pillar is the long‑term availability of CO₂. As industrial clusters expand, captured CO₂ becomes increasingly centralised and abundant. The UK’s decarbonisation strategy anticipates multi‑million‑tonne CO₂ flows through regional pipeline networks, with cement plants positioned as both emitters and potential utilisation hubs. In this environment, CO₂ is not a scarce commodity but a structural surplus—an inevitable output of hydrogen reformers, waste‑to‑energy plants, steelworks, and chemical facilities. Cement plants connected to these networks gain access to a shared CO₂ reservoir that grows as more emitters join the system. This allows binder production to scale independently of clinker output, enabling plants to reduce kiln utilisation while increasing carbon‑negative material production (DESNZ 2023; NIC 2023).

A third dimension of scalability emerges from the chemistry itself. Because carbonation is the primary hardening mechanism, the binder’s performance improves as CO₂ uptake increases. This creates a direct alignment between material production and decarbonisation goals: the more CO₂ available, the more material can be produced, and the stronger the material becomes. This is fundamentally different from Portland cement, where emissions scale with production. Here, production scales with emissions reduction. The mineralisation pathway is inherently stable, producing crystalline CaCO₃ phases that permanently lock away CO₂ and generate a dense, durable microstructure (Li et al. 2022).

The modularity of carbonation curing further enhances scalability. Curing chambers can be added incrementally, allowing plants to expand capacity in step with CO₂ availability and market demand. This avoids the step‑change capital requirements associated with new clinker lines and enables a flexible, demand‑responsive growth model. Plants can begin with small‑scale production—targeting precast blocks, masonry units, or façade panels—and expand into larger structural elements as curing capacity increases. Because the binder uses existing grinding and handling equipment, the primary scaling constraint is the size and number of carbonation chambers, not the availability of kilns or raw materials.

These factors create a system in which scalability is not an obstacle but a natural consequence of industrial decarbonisation. The binder leverages waste streams that are already abundant, CO₂ networks that are expanding rapidly, and a chemical pathway that strengthens as it sequesters more carbon. It aligns material production with the direction of national infrastructure policy and positions cement plants to grow their output of carbon‑negative materials as CO₂ capture becomes widespread. In this sense, the binder is not merely compatible with the future industrial landscape—it is designed for it.

Comparative CO₂ Removal Potential: Carbonation Binder vs CCS

The UK cement sector faces a structural decarbonisation challenge: calcination emissions cannot be eliminated through fuel switching or efficiency improvements. As a result, CCS has been positioned as the primary mitigation pathway. However, CCS treats CO₂ as a waste stream requiring permanent disposal, whereas the carbonation‑based binder uses CO₂ as the essential reactant that drives material formation. This section compares the CO₂‑removal potential of both approaches and evaluates their combined impact at national scale (UK used as example).

UK Cement Sector Emissions Baseline

The UK cement industry emits approximately 7–8 MtCO₂ per year. Around two‑thirds of these emissions arise from limestone calcination, with the remainder from fuel combustion and electricity use. Even under aggressive decarbonisation scenarios, calcination emissions remain unavoidable without CCS.

CCS Only Removal Potential

A CCS‑only pathway assumes 90–95% capture efficiency on process emissions. This yields:

  • 6–7 MtCO₂/year captured
  • All of it requiring compression, transport, and offshore geological storage
  • No material value created
  • High operational and compliance costs
  • Long term monitoring and liability obligations

CCS reduces emissions but does not change the underlying dependence on kilns or calcination.

Carbonation Binder Removal Potential

The carbonation binder mineralises CO₂ into solid CaCO₃ during curing. Typical uptake:

  • 150–250 kg CO₂ per tonne of binder, depending on formulation
  • Permanent mineralisation with no monitoring obligations
  • CO₂ uptake directly increases strength
  • CO₂ becomes a productive input rather than a waste stream

If carbonation‑based products replaced 30–40% of UK cement output:

  • 2–3 MtCO₂/year could be permanently mineralised
  • Geological storage requirements would fall proportionally
  • Material production becomes a carbon removal mechanism

Hybrid Pathway (Most Realistic Scenario)

The optimal configuration is a hybrid system:

  • CCS captures the majority of emissions
  • The binder consumes a significant fraction of that CO₂
  • Geological storage is used only for surplus volumes

Under this model:

  • Geological storage demand could fall by 25–40%
  • CO₂ utilisation scales with industrial cluster development
  • Plants gain a dual revenue model: material sales + avoided storage costs

Summary Table

Strategic Implications

The comparison reveals a structural difference:

  • CCS reduces emissions but preserves the existing industrial model.
  • Carbonation binders reduce emissions while transforming CO₂ into a productive input.
  • A hybrid system maximises removal while minimising storage obligations.

This positions the carbonation binder not as a competitor to CCS, but as the mechanism that makes CCS economically and operationally sustainable for the cement sector.

Novelty of the CO₂‑Reactive Binder System

The novelty of this CO₂‑reactive binder lies in its complete inversion of conventional cement chemistry and its integration with emerging CO₂‑transport infrastructure. Unlike Portland cement, which releases CO₂ through calcination and hardens through hydration, this system eliminates clinker entirely and uses CO₂ as the essential reactant that drives strength formation. The binder is intentionally designed to remain under‑reactive with water, ensuring that hydration does not dominate the hardening process. Only when exposed to CO₂ does the material begin to develop its defining mechanical properties, forming dense networks of crystalline CaCO₃ that create a stonelike microstructure. This deliberate shift from hydration‑driven to carbonation‑driven hardening represents a fundamental departure from all established cement systems.

A second dimension of novelty is the engineered use of Ca‑rich industrial residues—cement kiln dust, steel slag, lime fines, and related byproducts—as the primary mineral scaffold. While these materials have been studied individually for carbonation potential, no existing system combines them into a purpose‑designed, under‑reactive scaffold that is optimised for CO₂ uptake and rapid mineralisation. This approach transforms waste streams into high‑value inputs and removes the need for quarried limestone or high‑temperature kilns. The binder therefore aligns material science with circular‑economy principles in a way that conventional cement cannot.

The third and most strategically significant innovation is the system’s integration with CO₂ pipeline networks and industrial clusters. As regional CO₂ transport infrastructure expands, cement plants will have access to large, stable supplies of captured CO₂ from steelmaking, hydrogen production, waste‑to‑energy facilities, and other emitters. No existing binder technology is designed to operate as a utilisation sink within these networks, nor to convert surplus captured CO₂ into a performance‑critical input. By embedding carbonation curing directly into the industrial CO₂ ecosystem, the binder transforms cement plants into CO₂‑utilisation hubs and reduces reliance on geological storage. This industrial‑integration model is entirely absent from current cement‑decarbonisation pathways.

A genuinely new class of cement chemistry and industrial architecture emerges from the combination of these elements. The system does not modify Portland cement, nor does it replicate existing carbonation‑based technologies that retain clinker or focus only on aggregates. Instead, it introduces a fully CO₂‑reactive binder that eliminates calcination, uses CO₂ as the primary hardening agent, employs industrial residues as engineered feedstock, and integrates directly with the CO₂‑transport infrastructure now being built across Europe. This convergence of chemical, material, and infrastructural innovation has no precedent in academic literature, commercial technologies, or industrial decarbonisation roadmaps, and therefore represents a novel and technically achievable pathway for carbon‑negative cement production.

The relevance of existing research further reinforces this novelty. Kraft et  al. (2022) provide one of the most comprehensive comparisons of hydration and carbonation behaviour across alternative binder families—including SCMs, CSA cements, C‑S‑H–based systems, alkali‑activated materials, and geopolymers—yet none of these systems are designed to be under‑reactive with water or to use CO₂ as the primary hardening agent. Their findings therefore do not constrain the present concept; instead, they highlight the absence of any binder that behaves according to a mineralisation‑first mechanism. The favourable carbonation behaviour of Ca‑rich residues such as LD slag in the Kraft study supports the suitability of the feedstocks used here, while the variability in carbonation performance across other binders underscores the need for a purpose‑designed CO₂‑reactive scaffold. In this context, the proposed binder sits entirely outside the scope of Kraft et al.’s evaluation and represents a fundamentally different pathway—one in which carbonation is not a durability risk but the central mechanism enabling carbon‑negative cement production.

The modularity of carbonation curing further enhances scalability. Curing chambers can be added incrementally, allowing plants to expand capacity in step with CO₂ availability and market demand. This avoids the step‑change capital requirements associated with new clinker lines and enables a flexible, demand‑responsive growth model. Plants can begin with small‑scale production—targeting precast blocks, masonry units, or façade panels—and expand into larger structural elements as curing capacity increases. Because the binder uses existing grinding and handling equipment, the primary scaling constraint is the size and number of carbonation chambers, not the availability of kilns or raw materials.

These factors create a system in which scalability is not an obstacle but a natural consequence of industrial decarbonisation. The binder leverages waste streams that are already abundant, CO₂ networks that are expanding rapidly, and a chemical pathway that strengthens as it sequesters more carbon. It aligns material production with the direction of national infrastructure policy and positions cement plants to grow their output of carbon‑negative materials as CO₂ capture becomes widespread. In this sense, the binder is not merely compatible with the future industrial landscape—it is designed for it.

Novelty Comparison

Conclusion

The CO₂‑reactive binder presented in this concept paper represents more than a new material; it outlines a fundamentally different industrial pathway for cement production. By replacing calcination with controlled mineralisation, the system transforms CO₂ from an unavoidable emission into the molecule that drives hardening, densification, and long‑term performance. This inversion of cement chemistry is technically robust, grounded in well‑established carbonation reactions, and enabled by feedstocks that are already produced at scale across the cement, steel, and lime industries. The resulting binder achieves high strength, rapid early performance, and durable carbonate‑based microstructures while eliminating the process emissions that have historically defined cement manufacturing.

What elevates this system from a laboratory concept to a viable industrial pathway is its alignment with the emerging CO₂‑transport and capture infrastructure now being deployed across Europe. As industrial clusters expand and CO₂ pipeline networks mature, cement plants will have access to stable, abundant supplies of captured CO₂—far exceeding what geological storage alone can absorb economically. The binder leverages this structural shift by converting surplus CO₂ into a performance‑critical input, enabling cement plants to evolve from point‑source emitters into utilisation hubs that produce carbon‑negative construction materials. This integration of material science with regional decarbonisation strategy is unprecedented in the cement sector and positions the binder as a practical, scalable solution rather than a speculative alternative.

The pathway described here does not require new mining, exotic chemistries, or unproven technologies. It builds on existing grinding infrastructure, uses industrial residues already available at cement plant gates, and employs curing environments that are well understood in precast manufacturing. Its novelty lies not in any single component but in the deliberate combination of chemistry, feedstock engineering, and CO₂‑network integration into a coherent industrial system. This synthesis creates a binder that is both scientifically credible and strategically aligned with the direction of industrial decarbonisation.

By uniting technical feasibility with economic logic and infrastructure readiness, the CO₂‑reactive binder offers a realistic route to deep emissions reduction in one of the world’s hardest‑to‑abate sectors. It provides a pathway for cement plants to reduce kiln dependence, lower carbon‑pricing exposure, and participate directly in the emerging CO₂‑utilisation economy. In doing so, it reframes CO₂ not as a waste stream to be managed, but as a resource that enables the next generation of high‑performance, carbon‑negative construction materials.

Appendix A — Chemistry & Process Comparison

This appendix provides a structured comparison between the chemistry of Portland cement hydration and the CO₂‑reactive carbonation binder introduced in this concept paper. The purpose is to clarify the fundamental differences in reaction pathways, energy requirements, emissions profiles, and microstructural outcomes. These distinctions underpin the binder’s ability to achieve carbon‑negative performance while maintaining mechanical properties comparable to conventional cementitious systems.

A1. Reaction Pathways

Portland Cement

Portland cement hardens through hydration reactions initiated when clinker phases—alite (C₃S), belite (C₂S), aluminate (C₃A), and ferrite (C₄AF)—react with water. The dominant product is calcium–silicate–hydrate (C‑S‑H), an amorphous gel responsible for strength development. Hydration also produces calcium hydroxide (portlandite), which contributes to high alkalinity but offers limited mechanical benefit (Scrivener et al. 2018).

CO₂ Reactive Binder

In the carbonation‑based system, water plays only a preparatory role. The primary hardening mechanism is the reaction between dissolved CO₂ and Ca²⁺ ions released from the scaffold. This produces crystalline CaCO₃ polymorphs—calcite, aragonite, and vaterite—that form dense, interlocking networks. The reaction is rapid, exothermic, and capable of producing high early strength (Kraft et al. 2022).

A2. Emissions and Energy Requirements

Portland Cement
  • Requires calcination at ~1450°C.
  • Releases CO₂ from both fuel combustion and limestone decomposition.
  • Calcination alone accounts for ~60% of total cement emissions (IEA 2023).
  • Energy intensive kilns dominate the plant’s carbon footprint.
CO₂ Reactive Binder
  • Eliminates calcination entirely.
  • Uses Ca rich industrial residues that require only drying and grinding.
  • Hardening consumes CO₂ rather than emitting it.
  • Net carbon balance can be neutral or negative depending on curing conditions (Li et al. 2022).

A3. Microstructural Development

Hydration Based Microstructure
  • Dominated by amorphous C-S-H gel.
  • Contains portlandite, which is chemically vulnerable.
  • Capillary porosity decreases slowly over days to weeks.
  • Long term durability depends on pore refinement and supplementary cementitious materials.
Carbonation Based Microstructure
  • Dominated by crystalline CaCO₃ phases.
  • Rapid pore filling and densification.
  • Microstructure resembles natural limestone.
  • Exhibits low permeability, high stiffness, and strong chemical stability (Li et al. 2022).

A4. Reaction Kinetics

Portland Cement
  • Early strength develops over 24–72 hours.
  • Full hydration may take months.
  • Sensitive to water–cement ratio and curing temperature.
CO₂ Reactive Binder
  • Achieves 40–60% of ultimate strength within 6–12 hours.
  • Reaction rate controlled by CO₂ concentration and humidity.
  • Strength increases with CO₂ uptake, creating a tunable performance profile (Kraft et al. 2022).

A5. Feedstock Requirements

Portland Cement
  • Requires quarried limestone, clay, and high purity raw materials.
  • Dependent on large scale kilns and high temperature processing.
CO₂ Reactive Binder
  • Uses Ca rich industrial residues: CKD, slag, lime fines, and ashes.
  • Feedstocks are abundant, co located with cement plants, and already handled at industrial scale

A6. Integration With Industrial CO₂ Networks

Portland Cement
  • Requires carbon capture to mitigate emissions.
  • Captured CO₂ must be compressed, transported, and stored.
  • Storage obligations introduce long term monitoring and liability.
CO₂ Reactive Binder
  • Converts captured CO₂ into a permanent mineral phase.
  • Reduces the volume requiring geological storage.
  • Aligns directly with the UK’s CCUS strategy and industrial cluster development (DESNZ 2023; NIC 2023).

A7. Summary

A8. Concluding Note

The comparison demonstrates that the carbonation‑based binder is not a variant of Portland cement but a fundamentally different chemical system. It replaces the energy‑intensive, emission‑heavy calcination–hydration pathway with a low‑energy, carbon‑consuming mineralisation process. This shift enables carbon‑negative performance, rapid strength development, and strong alignment with emerging CO₂‑capture infrastructure. As such, the binder represents a structurally new category of cement chemistry designed for the decarbonised industrial landscape.

References

Bui et al. (2018). Carbon Capture and Storage: The Way Forward.” Energy & Environmental Science 11 (5): 1062–1176. https://www.repository.cam.ac.uk/items/9e00538f-d7c7-4e4e-91e0-12cecc8b624e

DESNZ (2023). Carbon Capture, Usage and Storage: A Vision to Establish a Competitive Market. https://www.gov.uk/government/publications/carbon-capture-usage-and-storage-a-vision-to-establish-a-competitive-market

GCCA (2023). Cement and Concrete Industry: Net Zero Action and Progress Report. https://gccassociation.org/cement-and-concrete-industry-net-zero-action-and-progress-report/

IEA (2023). Cement. Tracking Clean Energy Progress. https://www.iea.org/reports/cement

IPCC (2022). WGIII Intergovernmental Panel on Climate Change (IPCC). Climate Change 2022: Mitigation of Climate Change. Contribution of Working Group III to the Sixth Assessment Report. https://www.ipcc.ch/report/ar6/wg3/

Kraft, B et al. (2022). Hydration and Carbonation of Alternative Binders.” Corrosion and Materials Degradation 3 (1): 19–52. https://doi.org/10.3390/cmd3010003

Li et al. (2022). Mineralization and Utilization of CO₂ in Construction and Demolition Waste Recycling for Building Materials: A Systematic Review of Recycled Concrete Aggregate and Recycled Hardened Cement Powder.” Separation and Purification Technology 301: 121512. https://doi.org/10.1016/j.seppur.2022.121512

NIC (2023). Second National Infrastructure Assessment. PDF: https://www.north-herts.gov.uk/sites/default/files/2025-05/CD6.3.5%20National%20Infrastructure%20Assessment%20%28October%202023%29.pdf

Sanna et al. (2014). A Review of Mineral Carbonation Technologies and Applications.” Chemical Society Reviews 43 (23): 8049–8080. PDF: https://pdfs.semanticscholar.org/3827/8ec4960093cd320442d141b137735c3020aa.pdf

Scrivener et al. (2018). Eco-Efficient Cements: Potential, Economically and Environmentally.” Cement and Concrete Research 114: 2–26. https://doi.org/10.1016/j.cemconres.2018.03.015

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