Decarbonizing the Cement Industry: Technological, Economic, and Policy Barriers to CO₂ Mitigation Adoption

Abstract

The cement industry accounts for approximately 7–8% of global CO₂ emissions, primarily due to energy-intensive clinker production and limestone calcination. With cement demand continuing to rise, particularly in emerging economies, decarbonization has become an urgent global challenge. The objective of this study is to systematically map and synthesize existing evidence on technological pathways, policy measures, and economic barriers to four core decarbonization strategies: clinker substitution, energy efficiency, alternative fuels, as well as carbon capture, utilization, and storage (CCUS) in the cement sector, with the goal of identifying practical strategies that can align industry practice with long-term climate goals. A scoping review methodology was adopted, drawing on peer-reviewed journal articles, technical reports, and policy documents to ensure a comprehensive perspective. The results demonstrate that each mitigation pathway is technically feasible but faces substantial real-world constraints. Clinker substitution delivers immediate reduction but is limited by SCM availability/quality, durability qualification, and conservative codes; LC₃ is promising where clay logistics allow. Energy-efficiency measures like waste-heat recovery and advanced controls reduce fuel use but face high capital expenditure, downtime, and diminishing returns in modern plants. Alternative fuels can reduce combustion-related emissions but face challenges of supply chains, technical integration challenges, quality, weak waste-management systems, and regulatory acceptance. CCUS, the most considerable long-term potential, addresses process CO₂ and enables deep reductions, but remains commercially unviable due to current economics, high costs, limited policy support, lack of large-scale deployment, and access to transport and storage. Cross-cutting economic challenges, regulatory gaps, skill shortages, and social resistance including NIMBYism further slow adoption, particularly in low-income regions. This study concludes that a single pathway is insufficient. An integrated portfolio supported by modernized standards, targeted policy incentives, expanded access to SCMs and waste fuels, scaled CCUS investment, and international collaboration is essential to bridge the gap between climate ambition and industrial implementation. Key recommendations include modernizing cement standards to support higher clinker replacement, providing incentives for energy-efficient upgrades, scaling CCUS through joint investment and carbon pricing and expanding access to biomass and waste-derived fuels.

1. Introduction

Cement production is one of the most significant industrial sources of carbon dioxide (CO₂), accounting for an estimated 7–8% of global CO₂ emissions in recent years [1]. In 2023, global fossil fuel and cement emissions reached a record high of approximately 36.8 gigatons (Gt) of CO₂, with the cement industry contributing roughly 2.7–2.9 Gt CO₂ [1,2]. The high emissions result from both the energy-intensive clinker production process and the calcination of limestone (process emissions), roughly in a 40:60 energy-to-process split [3,4]. This means that merely switching to green energy will not fully decarbonize cement; therefore, fundamental changes in raw materials and processes are required [3]. Demand for cement continues to grow due to urbanization and infrastructure development, especially in emerging economies.

Reducing CO₂ emissions from cement production is challenging because a significant portion of emissions arises from the calcination of limestone, a chemical process intrinsic to cement production [4]. This process releases CO₂ that cannot be mitigated solely through traditional methods like process modifications or energy innovation. Furthermore, multiple inadequacies in traditional cement production, particularly related to outdated technologies and poor operational management, can lead to significant additional CO₂ emissions [5]. These inadequacies include low thermal efficiency, suboptimal process control, lack of waste heat recovery (WHR) and insufficient maintenance practices, all of which exacerbate fuel consumption and emission levels. These not only hinder the overall productivity of cement plants but also lead to higher fuel and electricity consumption, greater thermal energy losses, and ultimately increased CO₂ emissions. The primary factors contributing to additional CO₂ emissions in the cement industry include the following:

• Inefficient production processes: Wet and semi-wet kiln technologies consume significantly more thermal energy than dry processes. Transitioning from wet to dry processes can reduce energy consumption by 13% and fuel use by 28% [6].
• Outdated machinery: Reliance on obsolete equipment lacking modern energy-saving and emission-reduction technologies leads to higher energy consumption and CO₂ emissions.
• High-carbon fossil fuels and inappropriate raw materials: Utilizing fuels with high carbon content, such as coal and unsuitable raw materials, increases combustion-related CO₂ output.
• Excessive thermal losses: Significant heat losses occur through exhaust gases and kiln surfaces, resulting in wasted energy. Studies have shown that about 40% of the total input energy is lost through waste gas and heat dissipation on the surface of the rotary kiln [7].
• High clinker-to-cement ratios: Clinker production accounts for over 90% of the CO₂ emissions in cement production. Reducing the clinker content in cement by substituting it with alternative materials can significantly lower emissions [8].

These factors collectively contribute to the substantial CO₂ emissions associated with cement production. Addressing them through technological upgrades, process optimization, and material substitution is essential for reducing the industry’s carbon footprint. The cement industry generates CO₂ from four different sources [9]. The largest share of emissions, accounting for approximately 40% to 60%, arises from limestone (CaCO₃) decomposition into lime (CaO), the main constituent in cement production [4]. About 30% to 40% of the total CO₂ emissions are from burning fossil fuels in the pyro-processing unit, including the preheater, calciner, and kiln, as shown in Figure 1. The remaining emissions are from electricity used in the mills and air coolers [10,11].

The International Energy Agency (IEA) projects global cement demand could increase by 12–23% by 2050 compared to 2018, with strong growth in regions like South Asia and Africa [3,12]. Without mitigation, this demand surge would proportionally raise CO₂ emissions. Recognizing the urgency, the Global Cement and Concrete Association (GCCA) has pledged a net-zero cement industry by 2050 to align with the Paris Agreement [3]. Achieving this will require deploying multiple CO₂ reduction strategies in parallel. Over the past two decades, extensive research has explored how to reduce the carbon footprint of the cement industry and the IEA cement roadmap outlines four key decarbonization strategies for reducing CO₂ emissions in the cement industry [9,13,14].

Figure 2 illustrates four core strategies to mitigate CO₂ emissions in cement production. These include (i) Clinker Substitution, which involves replacing a portion of clinker with supplementary cementitious materials (SCMs) such as fly ash, slag, or calcined clay. Each 1% reduction in clinker factor can lower CO₂ emissions by approximately 0.8% [15]; (ii) Energy Efficiency Improvements through kiln upgrades, adoption of dry-process technology, and implementation of WHR systems. It can reduce thermal energy use by 10–20%, lowering fuel-related CO₂ emissions [16]; (iii) Alternative Fuels, where fossil fuels are replaced by lower-carbon options like biomass, refuse-derived fuels (RDF), used tires, or other low-carbon waste. This can reduce CO₂ from fuel combustion by 20–40%, depending on substitution rates [17]; and (iv) Carbon Capture, Utilization, and Storage (CCUS), which captures CO₂ from flue gases and stores it underground or converts it into usable products. It has the potential to reduce process emissions by 50–90%, especially for calcination-related CO₂ [18]. These strategies represent practical and scalable approaches for reducing the industry’s carbon footprint.

The Cement Technology Roadmap IEA [11] estimated that by 2050, alternative fuels and clinker substitution could contribute around 24% of the required emissions reduction. According to Zhang, et al. [19], energy efficiency improvements offer a potential solution to reduce approximately 0.26 Gt of CO₂ emissions by 2050, which accounts for roughly 3% of the total cumulative CO₂ emissions. Despite the need for further exploration, CCUS technology can potentially reduce approximately 65–80% of the GHG emissions generated by cement plants [20]. While exact contributions vary by scenario, it is clear that no single measure is sufficient; an integrated approach is needed. Numerous studies have demonstrated the technical feasibility of each mitigation measure [10,19,21,22,23,24], as follows: blended cement with lower clinker content can perform equivalently in many applications; modern kiln upgrades and WHR can significantly cut energy use; and oxy-fuel or amine-based capture can theoretically remove >90% of CO₂ from flue gas [3]. However, implementation on the ground has lagged. Global clinker substitution averaged only around 27% in 2020 [8]. Alternative fuels provide just about 18% of cement kiln energy worldwide, though >50% in some EU plants [3], and only a handful of pilot CCUS projects are underway in the cement sector. The slow adoption is due to a combination of technical, economic, and policy-related barriers. For instance, many regions lack suitable SCM supplies or standards, efficiency retrofits can be capital-intensive, CCUS remains costly and unproven at full scale, and policy support, e.g., carbon pricing or mandates, is often insufficient or inconsistent [15,25]. These barriers are multifaceted and interrelated, requiring holistic analysis.

Traditional mitigation pathways, such as energy efficiency improvements, alternative fuels, CCUS, and clinker substitution, are insufficient for deep cement decarbonization. Consequently, recent high-level assessments emphasize the need for disruptive low-carbon cement technologies that differ from incremental measures. Emerging options include alkali-activated binders such as geopolymers, limestone calcined clay cement (LC₃), magnesium and calcium-silicate-based cements that can mineralize CO₂, as well as electrochemical and plasma-assisted processes designed to bypass the traditional high-temperature kiln route. Electrified clinker production replaces combustion with electrochemical or plasma heating. The electrolysis of limestone yields calcium hydroxide with a pure CO₂ byproduct for capture, eliminating process emissions [26]. Plasma-heated kilns demonstrate fossil-free clinker, resulting in nearly pure CO₂ off-gas, simplifying capture and improving clinker reactivity [27]. These approaches bypass the limited gains of efficiency improvements by removing fuel-related emissions entirely. Process re-engineering for CO₂ Capture approaches, such as the Low Emissions Intensity Lime and Cement (LEILAC) indirect calciner, employs electrically heated reactors to calcine limestone in a pure CO₂ atmosphere, enabling inherent capture of decomposition emissions [28,29]. Unlike post-combustion CCS retrofits, this design-integrated method represents a step-change pathway for emission reduction by fundamentally reconfiguring the cement production process.

Cement recycling, or circular cement, innovative research has shown that old concrete can be recycled into new cement. Dunant, et al. [30] demonstrated an electric arc furnace process using waste paste with steel recycling, producing recycled clinker without added cost. Powered by renewables, this approach could achieve near-zero emissions, surpassing traditional aggregate recycling. Novel low-carbon binders offer transformative alternatives to Portland cement. Alkali-activated materials (geopolymers), carbonatable binders, and calcium sulfoaluminate or belite-rich cements reduce CO₂ by altering clinker chemistry and feedstocks. Studies report that geopolymer cements can emit 70–80% less CO₂ than traditional Portland cement [31]. These novel cements reduce the limestone calcination step and can even uptake CO₂ during curing, unlike incremental use of SCMs, which still rely on Portland clinker. Although barriers persist, including standards, supply constraints, and scaling challenges, recent pilot demonstrations and targeted investments highlight their potential to redefine cement decarbonization pathways and enable deep emissions reductions [28].

Despite the wealth of literature on cement decarbonization, relatively few studies focus on the barriers and challenges that hinder the widespread implementation of mitigation strategies. Most publications examine individual technologies, e.g., a new SCM or a capture technique, in isolation or model theoretical scenarios. There is a need for integrative analyses that consider the socio-technical context, including economic viability, regulatory frameworks, and stakeholder acceptance [2]. This paper provides a comprehensive review and evaluation of the barriers preventing effective CO₂ mitigation in the cement industry.

2. Methodology

This study adopts a Scoping Review approach, designed to provide a comprehensive overview of the breadth of existing research rather than a quantitative meta-analysis. The scope and objectives of the review were clearly defined and focused on cement decarbonization pathways and obstacles to minimize selection bias. The methodology involved systematic identification, screening, and thematic synthesis of relevant peer-reviewed journal articles, technical reports, and policy documents. This approach allowed us to map key themes, identify knowledge gaps, and capture the diversity of research addressing cement industry decarbonization. Figure 3 presents the methodological framework of the literature review conducted in this study. The process includes an iterative literature search, selection based on relevance and credibility, thematic extraction of barriers and enablers, and synthesis into a comprehensive narrative covering clinker substitution, energy efficiency, alternative fuels, and carbon capture strategies.

Before conducting the main literature research, we carried out a preliminary scoping review of high-impact journal articles and technical reports on cement decarbonization to identify the most commonly used terminology. We then analyzed keyword frequency within the academic databases (Scopus, Web of Science, Google Scholar, etc.) and industry sources to determine which terms consistently appeared in studies addressing CO₂ mitigation. This exercise guided the selection of our core search terms, “cement”, “cement industry”, “CO₂ emissions reduction”, “clinker substitution”, “energy efficiency”, “alternative fuels”, “carbon capture”, “decarbonization”, “barriers”, and “policy” and ensured these terms captured the technical, economic, and policy dimensions of the topic. We combined these keywords with Boolean operators (AND, OR) and applied truncation, e.g., decarbon to broaden the search and include variant expressions. This structured approach was supplemented by handsearching reference lists and consulting expert bibliographies to minimize the risk of missing relevant studies. The search did not impose strict date or language limits but gave priority to recent studies (past 10–15 years) while including seminal earlier works. Instead of rigid inclusion/exclusion criteria, studies were selected based on topic relevance and source credibility, consistent with best practices in qualitative narrative reviews that emphasize comprehensive coverage and analytical flexibility.

The literature review included peer-reviewed journals, industry and NGO reports, regulatory documents, and relevant books and conference proceedings covering environmental science, cement policy, and energy. Initial screening excluded irrelevant topics, with selection based on relevance to CO₂ mitigation barriers rather than citation metrics. To maintain balance and minimize bias, sources reflected diverse geographic contexts and addressed both challenges and proposed solutions. The total number of sources reviewed after screening and deduplication is 83 sources: 73 peer-reviewed journal articles (83%), 8 technical/industry reports (9%), and 7 policy/standards documents (8%). This selection provides comprehensive coverage of academic research, industry practices, and policy perspectives, providing a robust foundation for the analysis.

Data Extraction

Selected sources were read in full, and key information on mitigation challenges and enablers was recorded. This information was organized using an inductive, thematic approach. First, passages describing obstacles or enabling factors were coded according to broad categories: technical/technological issues, economic and financial considerations, regulatory/policy factors, and socio-organizational constraints. Next, these codes were mapped onto the main cement decarbonization pathways of interest. Specifically, the analysis focused on synthesizing insights in the following areas:

• Clinker and material substitution: barriers related to alternative cement chemistries and SCMs, e.g., quality/performance concerns, supply of raw materials.
• Energy efficiency improvements: obstacles to upgrading kilns and processes, e.g., capital costs, operational complexity, and expertise gaps.
• Carbon capture, utilization, and storage: issues in deploying capture technologies in cement plants and transport/storage infrastructure, e.g., technological readiness, high costs, and regulatory support.
• Alternative fuels: challenges in replacing fossil fuels with biomass or waste-derived fuels, e.g., fuel availability, handling and process compatibility, emissions regulations.

We then analyze the technological, economic, and policy barriers for each approach and synthesize findings to draw recommendations and outline remaining research gaps. This process is depicted in Figure 1, illustrating the stepwise approach from review to evaluation to recommendations.

3. Overview of Key Studies on Barriers to CO₂ Mitigation in the Cement Industry

The reviewed literature presents a broad spectrum of research methodologies, geographic contexts, and disciplinary perspectives, collectively offering a comprehensive view of the multifaceted barriers to CO₂ mitigation in the cement industry.

Table 1. Overview of studies on barriers to CO₂ mitigation in the cement industry.

Authors/References	Scope	Key Findings	Strengths	Limitations	Barrier Category
Benhelal, et al. [32]	Global review of CO2 reduction technologies in cement.	The review finds that economic, policy and logistical barriers, rather than technical barriers, are the primary causes. Shown technologies, such as clinker substitution, alternative fuels and carbon capture, are not widely adopted.	Comprehensive synthesis highlighting the gap between technical, policy and practical adoption.	No original data; broad focus with limited regional detail.	Economic/policy highlights financing and regulatory hurdles as the main bottlenecks.
Miller, et al. [33]	Complete value-chain and circular-economy analysis of cement emissions across production, use, and end-of-life.	The study identifies that cement accounts for about 7% of global GHG emissions; it emphasizes that deep decarbonization measures require lifecycle strategies beyond production, including circular design and green public procurement.	Holistic, cross-sectoral perspective covering the entire lifecycle.	High-level overview with limited discussion of costs and implementation challenges.	Policy/economic focuses on circular-economy policies, procurement incentives and market mechanisms.
Griffiths, et al. [2]	Systematic review on cement and concrete decarbonization using a socio-technical systems framework	The study concludes that technological innovation alone cannot decarbonize cement; supportive economic, social and policy environments are essential.	Holistic integration of technical and socio-economic factors	Comprehensive synthesis with limited depth on individual barriers.	Multiple emphasizes that technical, economic and policy factors are inseparable.
Ige, et al. [34]	Meta-review of system dynamics (SD) modeling studies for cement CO2 mitigation.	The study finds that existing SD models focus on technical solutions but often overlook real-world implementation barriers.	Highlights modelling gaps and the need for integrated approaches.	No case validation; minimal stakeholder input; relies on existing literature.	Technical, with a primary focus on the inadequacy of existing modeling tools.
Marinelli and Janardhanan [35]	Empirical multi-criteria decision analysis (Best–Worst Method) to green cement in India using expert rankings to rank decarbonization barriers.	The study identifies top barriers (low corporate commitment, skill shortages, financial gaps) and recommends R&D support, workforce training, green financing, and public procurement policies as alleviation strategies.	Provides Country-specific insights with expert-driven prioritization of barriers. Moderate to high fills the gap in emerging market data.	Small expert sample; findings may not generalize beyond the context.	Economical emphasizes financing and organizational capacity constraints.
Cavalett, et al. [36]	Lifecycle assessment and scenario modeling of 15 European cement mitigation strategies by 2050.	The study shows that combining alternative fuels, energy efficiency and clinker substitution can reduce emissions by about 50% by 2050; net zero requires carbon capture.	Data-rich with robust LCA and strong scenario analysis	Region-specific and assumes a stable policy context. Not capture global diversity.	Technical/economic highlights, technological limits of current options and cost implications.
Habert, et al. [37]	Techno-economic assessment of CO2 reduction potential under Factor 4 targets.	The study finds that the capital-intensive nature of cement production is a core barrier; it emphasizes that deep decarbonization needs significant financial/policy support.	Data-driven; identifies financial constraints ahead of trend.	Slightly outdated; social or policy dynamics underexplored.	Economic focuses on the cost barrier to technology adoption.
Busch, et al. [38]	Comprehensive case study of Net-Zero Cement mandate (SB 596) in California, analyzing six decarbonization strategies for cement/concrete using policy analysis and stakeholder input.	The study identifies outdated building codes and low market demand as key barriers and suggests policy performance standards and green procurement to drive adoption.	Real-world policy context with stakeholder engagement.	Limited to a proactive policy jurisdiction (California) and may not transfer directly to other regions.	Policy emphasizes regulatory reform and market-pull measures.
Barbhuiya, et al. [25]	Comprehensive roadmap analysis of the global cement sector to achieve net-zero carbon by combining technological innovations, strategy roadmaps, and policy frameworks.	The study identifies barriers like short policy horizons and inadequate R&D funding in both developed and emerging economies.	Integrates technology and policy to provide a comprehensive strategic vision.	Recommendations are general; lacks detailed quantitative scenario modeling.	Policy/economic—stresses regulatory vision and funding as critical gaps.
Habert, et al. [39]	A critical review of environmental impacts and decarbonization strategies for cement and concrete.	The study finds no single solution, advocates a portfolio approach, such as material substitution, alternative fuels, energy shifts, and CCS. The study highlights that some measures may increase other environmental impacts.	Balanced LCA perspective with global scope.	Conceptual review; lacks new modeling or empirical evidence.	Technical, analyzes technological and the need for complementary options.

synthesizes the most influential peer-reviewed studies published, detailing their scope, findings, and critical evaluation. This tabular summary serves as the foundation for identifying prevailing themes, contradictions, and gaps in current knowledge.

The literature consistently agrees that a lack of technical solutions does not constrain the cement industry’s decarbonization, and numerous viable mitigation strategies have been identified [32]. However, a recurring theme is the disconnect between technical feasibility and practical implementation, with economic, organizational, and policy barriers slowing progress in every region. Notably, early studies and recent analyses alike underscore that financial barriers, high capital costs, and uncertain returns on investment make companies hesitant to adopt innovations without strong incentives [25]. This happens repeatedly across contexts. For instance, the cement sector in China has long had the technology to improve efficiency but lacked financing mechanisms and policy support to deploy it at scale [40].

At the same time, some contrasts emerge in emphasis. In developing countries, internal factors such as corporate commitment and skill gaps are identified as the top barriers to green practices [35], whereas many global studies place policy and market conditions at the forefront, for example, the need for carbon pricing, subsidies, or updated standards [25,38]. This suggests a contextual nuance emerging economies may struggle first with awareness, knowledge, and organizational readiness, while advanced economies hit barriers related to regulatory frameworks and economic incentives. Nonetheless, both contexts ultimately face financial constraints and risk aversion when adopting expensive new technologies. Another subtle inconsistency is in the outlook on technology deployment. Optimistic perspectives like Miller, et al. [33] and Busch, et al. [38] assumed that existing or near-commercial technologies, if supported by aggressive policy and design innovation, can bring cement to net zero. In contrast, more critical analyses, such as Cavalett et al. [36], indicated that without breakthroughs or massive CCUS roll-out, current measures only achieve roughly half of the needed reduction, suggesting that deeper decarbonization might require both strong policies and new technological leaps. This highlights a tension in the literature on whether the carbon problem in cement industry is primarily a policy failure not rewarding available solutions or a technology gap needing new solutions like novel cement or carbon capture at scale. Many studies implicitly conclude it is a mix of both, calling for integrated approaches combining innovation, investment, and policy reform [2,38].

Areas needing further research are repeatedly noted. Several authors point out the need for real-world demonstration projects and data on novel low-CO₂ cement and carbon capture in cement plants to reduce uncertainty for both industry and regulators [38]. There is also a call for better economic and policy analysis, e.g., how carbon pricing, subsidies, or green procurement can effectively overcome the cost barrier; current literature provides conceptual support but lacks detailed case studies on the successful implementation of such levers in cement [20]. Integration of social factors is another gap, while broad reviews acknowledge issues like stakeholder resistance and conservative construction codes. Detailed research on how to shift these through education, revised standards, etc., is limited [15,25]. Moreover, models and scenario studies would benefit from incorporating adoption barriers; as Ige, et al. [34] noted, many models assume deployment without adequately modeling the decision-making barriers. As we advance, bridging this gap between engineering solutions and social science insights is crucial. This means interdisciplinary research that pilots new technologies in cooperation with industry, evaluates policy pilot programs such as low-carbon concrete mandates in public works, and actively involves stakeholders like engineers, architects, financiers, and regulators in crafting viable pathways. Such efforts would address the inconsistencies in the current literature by testing which strategies truly work in practice, thereby moving the cement industry closer to a credible, achievable route for CO₂ mitigation.

4. Overview of CO₂ Mitigation Strategies in the Cement Industry

In this section, we examine the four primary strategies for CO₂ mitigation in cement production and analyze the technical, economic, and policy barriers associated with each. The strategies are (1) Clinker substitution, (2) Energy efficiency improvements, (3) CCUS, and (4) Alternative fuels. For each, we review the state-of-the-art approaches and then discuss the challenges hindering their implementation.

4.1. Clinker Substitution (Low-Carbon Cements)

Portland cement, traditionally composed of up to 95% clinker, has long dominated the global construction market [11]. However, in light of climate change imperatives, the decarbonization of the cement industry strategy increasingly emphasizes clinker content reduction through the use of SCMs. These include industrial byproducts such as fly ash, ground granulated blast furnace slag (GGBFS), silica fume, and calcined clays like metakaolin, as well as naturally occurring pozzolans including volcanic ash, rice husk ash, and ground glass [17,41,42,43,44]. Replacing clinker with SCMs significantly reduces both process-related and fuel-derived CO₂ emissions. Ref. [10] reported that producing one ton of clinker requires about 3.70 MJ of energy and releases 0.79 tons of CO₂, with limestone calcination accounting for nearly 58% of the environmental impact of the cement industry [45].

Quantitative studies have reinforced the environmental benefits of SCMs. Shah et al. estimated that the widespread use of traditional and novel SCMs could reduce CO₂ emissions by up to 1.3 Gt annually, nearly half of global cement-related emissions. This underscores the huge mitigation potential of clinker substitution. Similarly, Knight, et al. [46] developed mathematical models to optimize SCM-to-cement ratios in concrete mixtures, finding that optimal ratios can significantly lower greenhouse gas (GHG) emissions. For instance, a limestone SCM-to-cement ratio of 0.17 kg/kg in 30 MPa concrete yielded 1.6 times fewer emissions compared to a 0.42 kg/kg ratio. Beyond emissions reduction, SCM-blended cements maintain high durability and performance, improving resistance to sulfates, lowering permeability, and improving long-term strength [17,43,44,47]. Importantly, SCMs require substantially less energy to process compared to traditional clinker, contributing to additional energy savings [48].

SCMs also offer economic benefits due to lower or negative acquisition costs, often being sourced from industrial waste products [49] and a highly effective strategy for improving the CO₂ performance of cement [50]. The 2023 Cement Industry Sustainability Initiative’s Getting the Numbers Right (GNR) data indicate that CO₂ emissions per ton of cementitious material have declined by 25% since 1990 [51]. The Inter-American Development Bank (IDB) guidelines report that cement plants are responsible for substantial CO₂ emissions, and implementing best-practice measures can significantly reduce these emissions per ton of cement produced [52].

4.1.1. Technical Barriers

The primary technical challenge that hinders the adoption of clinker substitutes in cement production is the availability and quality of SCMs. Traditional SCM sources like coal fly ash and blast-furnace slag are limited and geographically concentrated. With coal power phasing down in some regions, fly ash supplies are declining [8]. Slag availability depends on steel production and is also finite. In many developing countries, these materials are scarce, forcing reliance on imported SCMs or local natural pozzolans, which may have variable quality. New SCM options, such as calcined clays from abundant clays, are promising but require additional processing calcination at approximately 700 °C and optimization of mix designs [8].

Additionally, different SCMs impart varying properties, such as slower early strength gain for fly ash cement, which may necessitate changes in construction practices (longer curing) or chemical admixtures. Another technical barrier is the low technology readiness of novel binders. While basic blending is mature (TRL 9), more radical alternatives like alkali-activated binders or limestone calcined clay (LC₃) cement are at the pilot stage. Many emerging SCM-based cement formulations still have low levels of technology readiness and lack extensive field validation [8]. For example, alkali-activated (geopolymer) cement shows good lab performance, but scaling their production and ensuring long-term durability data remains an ongoing research area [25]. Scaling up any new cement chemistry to industrial production is non-trivial, as Zajac, et al. [53] found, and even converting captured CO₂ into mineralized cementitious material faces challenges when moving from lab to an industrial scale.

4.1.2. Economic Barriers

Economic challenges remain a critical constraint to the widespread adoption of SCMs in cement production. Blended cements often offer cost savings primarily due to the high energy intensity and capital costs of clinker production. Regional SCM availability and supply chain logistics heavily influence their economic viability [54,55]. In areas where SCMs must be transported over long distances, high logistics costs can undo both the financial benefits and the environmental advantages [9,56]. Certain SCMs, such as high-purity silica fume and metakaolin, are costly and limited in supply, making them suitable only for niche applications. Moreover, the cement industry’s commodity-driven nature fosters a conservative market, where producers hesitate to shift formulations without clear demand or policy-driven incentives [9,56]. A study by Ripley et al. found that replacing 30% of clinker with lower-cost materials could reduce cement production costs by a few percent while cutting emissions by approximately 17%. Thus, the main economic barrier is not cost inefficiency but ensuring reliable supply chains for SCMs.

Capital investment in clinker-centric infrastructure and existing procurement contracts creates further resistance to change. Additionally, the opportunity cost of SCMs, particularly when they are in demand for competing applications like fly ash in concrete or soil stabilization, can increase prices, especially in supply constrained markets [54,55]. Small-scale cement producers are especially disadvantaged, lacking the economies of scale or capital to invest in new blending or grinding equipment [25]. Limited market awareness and acceptance of blended cements further hinder investment in innovation and capacity expansion [57].

4.1.3. Policy and Regulatory Barriers (Clinker Substitution)

A major barrier to accelerating clinker substitution in the cement industry lies in the limitations of current policy and regulatory frameworks. Historically, building codes and technical standards such as ASTM, EN, and similar national specifications have restricted the type and amount of SCMs permissible in cement and concrete formulations. These prescriptive standards primarily endorse a narrow range of SCMs such as fly ash, ground granulated blast furnace slag (GGBFS), silica fume, natural pozzolan, and limestone [8]. While these materials are widely recognized, many innovative or regionally abundant SCMs, including calcined clays, recycled glass powder, and biomass ash, remain excluded from established codes. This omission restricts producers from commercializing blended types of cement using alternative SCMs and discourages engineers and contractors from specifying them in construction projects.

Although a shift toward performance-based standards where material use is guided by the desired concrete performance rather than strict composition limits offers a promising alternative, global adoption remains slow and fragmented. Despite existing for decades, performance-based standards have not been widely implemented due to regulatory inertia, lack of harmonized testing methods, and resistance from traditional market stakeholders [8]. There is also an urgent need to accelerate the standardization of new SCMs, including clear guidelines for classification, testing, and integration into cement blends. In addition to regulatory constraints, policy incentives for using low-clinker cement remain weak. Most jurisdictions do not mandate or financially support the procurement of low-carbon cement in public infrastructure, missing a critical opportunity to stimulate demand. Governments can play a key role by introducing regulations that limit landfilling or incineration of viable industrial byproducts, thereby encouraging their use in cement production [58]. Yet many such policies focus narrowly on limestone substitution, neglecting the broader SCM landscape [17].

Compounding these issues are knowledge gaps and uncertainty among stakeholders, contractors, designers, and regulators who often perceive blended cement as inferior to traditional Portland cement. Overcoming this barrier requires sustained education, demonstration projects, and industry–government collaboration. In conclusion, unlocking the full decarbonization potential of clinker substitution requires policy reform, regulatory modernization, standardized acceptance of a broader SCM portfolio, and confidence-building among end-users [25]. By applying a Scoping Review approach, this study synthesizes the current state of knowledge and highlights research gaps that warrant further systematic investigation.

4.2. Energy Efficiency in Cement Production

Improving the energy efficiency of cement production is a foundational mitigation strategy. Thermal energy (for heating the kiln) and electricity (for grinding and plant operations) contribute around 30–40% of the CO₂ emissions of cement [3]. Over the past decades, the industry has made improvements in most developed-world kilns, which have shifted from outdated wet-process kilns to modern dry-process kilns with preheaters and precalciners, cutting energy use per ton clinker substantially [59]. Best available technology (BAT) modern kilns operate at approximately 3.0 GJ/ton clinker thermal energy, approaching the theoretical minimum [11]. Nevertheless, efficiency improvements remain essential, especially in regions with older plants. Efficiency measures include upgrading preheater configurations, installing high-efficiency burners, enhancing insulation, using WHR to generate electricity, utilizing variable frequency drives and efficient motors for grinders, improving process control and optimization and reducing clinker over-burning [17,60]. The IEA estimates that efficiency gains could contribute around 10–15% of the required CO₂ reduction in a 2 °C scenario by 2050 [19]. Notably, efficiency measures often come with co-benefits of cost savings on fuel or electricity, making them no-regrets options.

4.2.1. Technical Barriers

Many cement plants have already implemented the most straightforward efficiency upgrades so that remaining gains can be incremental and sometimes site-specific. The theoretical minimum energy is approximately 1.8–1.9 GJ/ton for clinker (the chemical reaction requirement), meaning even perfect technology cannot eliminate that portion [11,61,62]. Thus, there is a diminishing returns effect, and it is increasingly challenging to squeeze out further considerable energy savings after adopting known best practices [25]. However, in developing countries, a significant share of production still uses suboptimal technology, e.g., small-scale vertical shaft kilns or older designs due to slower capital turnover; upgrading or replacing these is a technical and financial challenge. Another barrier is that some efficiency improvements involve process complexity or operational risk. For instance, operating at the very low end of heat consumption could risk incomplete clinker reactions or quality issues if not carefully managed [25]. Introducing advanced controls or novel techniques like using electric plasma torches for part of heating can be technically challenging and unproven at scale. The integration of WHR systems faces practical issues, too because not all plants have sufficient thermal output or a favorable layout for WHR, and dust in exhaust gases can foul heat exchangers if not appropriately designed [63]. In summary, the technical potential for energy efficiency is finite and many plants are already relatively efficient. Further substantial improvements may rely on innovative technologies (e.g., electrified heating, which transfer emissions to the power sector) that are still in R&D.

4.2.2. Economic Barriers

Energy efficiency projects in cement often have attractive paybacks since fuel is a major cost; yet, economic problems still exist. Capital cost is a primary one and upgrading a kiln preheater tower or installing a WHR generation system requires significant investment and may necessitate plant downtime. Cement is a low-margin commodity, so securing internal funds for such retrofits competes with other business needs. Particularly for smaller or financially strained cement companies (or state-owned plants), the upfront cost can be prohibitive without external support [25]. Even when economically justified long-term, companies might delay upgrades due to short-term pressures or uncertainty about future market conditions. Another economic barrier is the so-called “Efficiency gap,” where split incentives exist. For example, if plants operate under short-term leases or management contracts, operators might not invest in improvements whose benefits accrue mostly beyond their tenure.

Additionally, in some regions, energy prices (fuel and electricity) are subsidized or artificially low, reducing the economic incentive to save energy. For instance, if coal is very cheap, a company might not see enough cost savings to justify investing in a new burner or heat recovery unit. Conversely, rising fuel prices or carbon costs improve the business case for efficiency, which is an important dynamic. There is also the risk that retrofitting old plants for efficiency might be less cost-effective than building new, efficient plants, but new builds are constrained by demand and capital cycles. Thus, some analysts highlight a “valley of death” for funding mid-life retrofits. On a positive note, many efficiency measures are modest in cost: upgrading motors, variable speed drives, better-grinding media, etc., can often be carried out gradually as part of maintenance, and these have been happening. Nonetheless, the economic barrier lies in achieving deep efficiency improvements beyond the low-hanging fruit.

4.2.3. Policy Barriers

Governments can influence industrial energy efficiency through regulations and incentives. One barrier is the lack of stringent energy performance standards for cement plants. Unlike some appliance or vehicle sectors, industrial energy use is often not mandated by efficiency standards. Absent requirements and improvements depend on the initiative and economic rationale of the company. Policies like energy audits, benchmarking, and disclosure can drive firms to identify savings, but their impact varies. Subsidies or low-interest loans for efficiency upgrades can help overcome capital barriers, but such programs are not universally available.

In some cases, regulatory frameworks accidentally discourage efficiency. For instance, if electricity produced from WHR cannot be sold to the grid or credited, companies have less incentive to install WHR [64]. Moreover, where carbon pricing exists, it puts a price on inefficiency via higher emissions costs. However, in many regions, carbon prices are still too low or absent to change investment decisions materially [65]. On the flip side, overcapacity in specific markets led governments to enforce the shutdown of older, inefficient kilns as a policy measure to both control emissions and excess supply [66,67,68]. Such measures highlight policy influence but also come with economic side effects. Another barrier can be operational regulations or labor issues implementing new tech like AI-based process control, which may face resistance or require retraining staff (a social barrier intersecting with policy if labor regulations impede changes).

Additionally, achieving energy efficiency requires knowledge transfer and technical assistance, especially for smaller local producers; the lack of extension programs or industry associations to disseminate best practices is a soft barrier. In sum, stronger policy signals could hasten efficiency improvements, but currently, they are uneven. The voluntary initiatives of the cement industry, such as the Cement Sustainability Initiative of the WBCSD, have played a role in knowledge sharing and benchmarking. Yet, not all companies participate or meet targets.

Overall, energy efficiency is a critical first step in decarbonization—it can yield immediate emissions reductions and cost savings. Most technical fixes are mature and well-understood; the challenge is ensuring they are universally adopted. The barriers are primarily economic, i.e., access to capital, payback in low-margin contexts, and structural, i.e., older plants in developing regions and lack of policy push. As Barbhuiya, et al. [25] noted, optimizing energy use is a complex but necessary task and balancing CO₂ reduction with maintaining performance and cost is an ongoing challenge requiring continuous innovation. Efficiency alone cannot bring cement down to net zero, but without efficiency, other measures like CCUS or alternative fuels would have to work much harder. Therefore, addressing these barriers through financing mechanisms, technical support, and appropriate regulation is an integral part of the overall strategy.

4.3. Carbon Capture, Utilization, and Storage

CCUS refers to a suite of technologies aimed at trapping CO₂ from industrial emitters and either storing it permanently or utilizing it in products, e.g., carbonating concrete or converting it to chemicals. In cement production, CCUS is one of the few options capable of dramatically reducing emissions up to approximately 90% capture, even while using conventional raw materials and fuels, because it addresses the process CO₂ from calcination, which cannot be eliminated by energy measures alone [3]. Therefore, it is seen as a necessary component for deep decarbonization or net-zero cement scenarios. Several capture methods are under development for cement kilns, including post-combustion capture using solvents similar to power plant CO₂ scrubbers; oxy-fuel combustion, for instance, burning fuel in oxygen to achieve a CO₂-rich exhaust for easier capture; and calcium looping, a process that uses limestone-based sorbents to take CO₂ from flue gas [69]. CCUS is one of the primary measures to reduce the carbon emissions of cement production, which is strongly favored by the cement industry [70]. A handful of pilot and demonstration projects are in progress, e.g., the LEILAC project in Europe testing direct calciner capture [71] and the project of Norcem in Norway aiming to capture about 400,000 tCO₂/year from a cement plant by 2024 [72]. Despite this progress, CCUS in cement is still at an early stage relative to the industry’s scale and no full-scale cement plant has integrated CCS into regular operation as of 2025.

4.3.1. Technical Barriers

Cement CCUS faces significant technical challenges. First, cement kiln flue gas has a relatively lower CO₂ concentration, which is about 20% by volume compared to some other industries, making capture less efficient (especially for solvent-based post-combustion capture) [15]. The presence of dust and impurities (SOx, NOx) in the exhaust can degrade solvents or sorbents, requiring robust gas cleanup. Oxy-fuel combustion (which yields nearly pure CO₂ exhaust) involves major modifications to the kiln and air separation units and has not yet been demonstrated at full cement kiln scale. The integration of capture units into existing cement plants is a complex constraint. The need to maintain kiln heat balance and potential impacts on clinker chemistry must be managed [15]. Moreover, capturing CO₂ is only part of the chain since transport and storage/utilization infrastructure is required. Many cement plants are not located near suitable CO₂ storage sites, meaning captured CO₂ would need to be compressed and transported (via pipelines, trucks, or ships) to a storage reservoir. This is a logistical challenge, especially for inland plants. Utilization options (CCUS) such as using CO₂ for curing concrete or making chemicals are currently limited in scale and the global demand for CO₂ in such applications is small relative to cement emissions [15]. Thus, most captured CO₂ would require storage, which in turn demands careful site selection, monitoring, and long-term liability management issues that extend beyond the cement plant itself. The reliability and operational stability of CCUS are other concerns, as cement plants operate continuously, and any capture system must do the same without causing frequent outages. The technology risk is still high, and CCUS has not yet been sufficiently proven to be suitable for large-scale use in cement [15]. This lack of full-scale demonstration means there are uncertainties in performance, especially regarding how capture processes might affect kiln operation; for example, oxy-fuel requires new designs for clinker coolers and potentially alters NOx chemistry [23,32,69,73,74].

4.3.2. Economic Barriers

Perhaps the most prohibitive barrier for CCUS in cement is cost. Carbon capture is inherently energy-intensive: capturing about 90% of CO₂ from a cement kiln could raise the plant’s energy consumption by roughly 25–40% (for solvent regeneration or oxygen production) [15]. This translates to a drastically higher fuel requirement or electricity use, adding expense. Studies consistently find that implementing full CCS would increase the marginal cost of cement production significantly, with one estimate being by 2–3 times the current clinker cost [15]. In concrete terms, if baseline cement costs are around $60–$100/ton, CCS could add on the order of $50–$100 per ton. Post-combustion capture costs about $60 per ton CO₂ captured, which for a typical cement (approximately 0.8 t CO₂/ton) would be roughly $48 added per ton of cement [3]. This would make cement significantly more expensive, posing competitiveness concerns, especially in markets without carbon pricing. The cement industry, being cost-sensitive and globally traded, fears erosion of market share if one producer incurs CCS costs while others without CO₂ constraints do not have a classic carbon leakage problem [75]. Additionally, the capital investment for CCS, i.e., capture plant, compressors, and pipeline contribution, is enormous. A full-scale CCS retrofit can cost hundreds of millions of dollars for a single plant [76]. Companies are unlikely to undertake such investments without strong financial incentives or mandates. Economic viability might improve if carbon prices reach high levels, for example $100/tCO₂ or if low-cost capture technologies emerge, but currently, the business case is very weak. As a result, virtually all ongoing CCS projects in cement rely on public funding, subsidies, or expectations of future regulations. Even utilization pathways face economic issues and CO₂-derived products often cannot compete with conventional products unless subsidized or if CO₂ is nearly free. In summary, high costs, both operational (energy) and capital, are the most significant barriers for the cement industry to adopt CCUS [77]. Without a carbon price or policy that shifts these economics, companies have little financial incentive to deploy CCS at scale.

4.3.3. Policy and Societal Barriers

To overcome economics, strong policy support is essential, yet it is currently insufficient in most regions. Carbon pricing or emissions trading can, in theory, make CCS cost-competitive if the price per ton of CO₂ saved is above the capture cost. However, many carbon markets (EU ETS, etc.) have prices that, while rising, are only recently approaching levels that could justify CCS. Modeling for China’s cement industry indicates that CCS is only adopted when a substantial carbon tax is imposed, as otherwise, it never becomes cost-competitive [78]. This aligns with real-world behavior: no company will deploy CCS without policy drivers.

Additionally, policies are needed to build CO₂ transport and storage infrastructure, something individual cement firms cannot do alone. Government coordination to develop CO₂ hubs, pipeline networks, and storage sites (perhaps serving clusters of industries) is crucial. Regulatory frameworks for CO₂ storage (permits, monitoring, liability) must also be in place; in many countries, these are still nascent. For instance, long-term liability for stored CO₂ (who is responsible if leakage occurs decades later?) remains a thorny issue that governments need to clarify to give companies confidence [15]. Public acceptance is another concern because large-scale CCS projects sometimes face public opposition due to fears of CO₂ leakage or simply NIMBYism against pipelines and injection wells. The cement industry thus needs not only a favorable policy but also public trust that CCS is safe and necessary. Outreach and education can help mitigate misconceptions, but until the public sees successful CCS in action, doubt may remain. Another barrier is the lack of inclusion of cement CCS in policy planning relative to power sector CCS. Many governmental decarbonization plans emphasize power and maybe steel CCS, but not all have concrete plans for cement, which can lead to cement being left out of funding opportunities or R&D programs [79]. On the utilization side, policy could help by setting standards that allow or encourage CO₂-cured concrete or by treating carbon-derived products favorably, but these are in their infancy. Finally, international policy coordination, like the EU’s Carbon Border Adjustment Mechanism (CBAM), might reduce carbon leakage concerns by levying a tax on imported cement for its carbon content [80]. This could indirectly support domestic producers investing in CCS by protecting them from unfair competition, but such mechanisms are still evolving and may introduce their complexities [81].

In summary, CCUS could enable deep emissions cuts in cement—potentially capturing 50–90% of a plant’s CO₂. However, the barriers are formidable, detailed as follows: technically, it is complex and unproven at full scale; economically, it is highly costly, doubling to tripling production cost without significant offsets [15]; and policy-wise, it demands robust governmental intervention and public acceptance, which are not yet entirely in place. As experts have pointed out, without substantial incentives or carbon pricing, CCS in cement will not be deployed [78]. Therefore, overcoming CCUS barriers will likely require treating cement like a hard-to-abate sector that receives targeted support (similar to how some countries fund CCS for industrial clusters). Until then, CCUS in cement remains more of a future promise than a near-term solution. Importantly, while CCUS can mitigate most emissions from an individual plant, it does not address other issues like increased resource/energy use or the need for secure CO₂ storage for centuries. Those broader considerations mean CCUS should be pursued alongside, not in lieu of, the other mitigation strategies.

4.4. Alternative Fuels (Fuel Switching)

The cement industry has long utilized alternative fuels, defined as any non-traditional fuel that replaces coal or petcoke to reduce its reliance on fossil fuels and, in some cases, to lower net CO₂ emissions. Common alternative fuels include biomass residues, e.g., rice husks, palm kernel shells, sugarcane bagasse, RDF from municipal solid waste, used tires, waste oils and solvents, and even sewage sludge. Using these in cement kilns can cut CO₂ emissions in two ways: (1) if the alternative fuel is biomass-based, its carbon is biogenic and part of the natural carbon cycle often considered carbon neutral, and (2) even for non-biogenic wastes, it avoids emissions that would occur if that waste decomposed in a landfill like methane generation or was incinerated without energy recovery. Additionally, co-processing waste in cement kilns provides a waste management service, destroying hazardous components and reducing landfill volumes. In Europe, alternative fuels already supply, on average, approximately 60% of kiln energy [82], with some plants exceeding 90%. However, globally, the thermal substitution rate is much lower, estimated at approximately 18% on average, meaning there is substantial room to increase alternative fuel use [82,83]. The GCCA’s 2050 roadmap envisions alternative fuels, including a large biomass component and some hydrogen, playing a significant role in decarbonization [3].

4.4.1. Technical Barriers

Cement kilns are versatile in that they can accept a wide variety of fuels, but ensuring stable kiln operation on heterogeneous alternative fuels is a challenge. Alternative fuels often have different calorific values, moisture content, and combustion characteristics compared to coal. For instance, biomass generally has lower energy density and higher moisture, which can reduce flame temperature. Wastes can contain components like chlorine and metals that might cause kiln system build-ups or affect clinker chemistry. To use alternative fuels extensively, plants may need modifications, e.g., special feeding systems to introduce fuels at the precalciner or main burner, shredders for waste, dosing systems for precise feed rates, and advanced control systems to manage combustion. There is also a limit to how much certain fuels can be used before adverse effects occur. High chlorine content from plastics and certain biomass can lead to corrosion or excessive bypass dust needing disposal. Alkalis from some waste can affect product quality. While many European plants have solved these issues with robust kiln management and installing chlorine bypasses using an appropriate mix of fuels, some plants, especially older or smaller ones, may not be equipped to handle a broad alternative fuels portfolio. Another technical barrier is ensuring continuous supply; kilns need a steady heat input 24/7, so intermittent availability of particular alternative fuels like seasonal biomass requires either storage or a diversified fuel mix. Moreover, preprocessing requirements for some alternative fuels, such as drying high-moisture biomass, shredding municipal waste to uniform RDF fluff, etc., are technical steps that add complexity and require energy input. When considering novel future alternative fuels such as hydrogen or electrification, hydrogen could be used in burners to eliminate CO₂ from combustion, but its production is currently expensive and requires new burner designs. Electrification, such as plasma torches, is still experimental and would shift emissions to the power sector [84,85]. Both would require significant re-engineering of kilns and are not yet proven in real cement processes. Thus, technically, while substitution between 20 and 40% of energy with alternative fuels is relatively straightforward, pushing to very high rates over 80% or using 100% unconventional fuels brings increasingly difficult technical hurdles to maintain clinker quality and kiln integrity.

4.4.2. Economic Barriers

The economics of alternative fuels can vary widely. In some cases, alternative fuels are cheaper than coal; for instance, waste fuels might come with a tipping fee that the waste generator pays the cement plant to take it, effectively causing a negative fuel cost. This scenario, common with hazardous waste or in regions with high landfill taxes, can make alternative fuels extremely attractive economically [83]. However, in other cases, the processing and handling costs of alternative fuels can outweigh the fuel savings. Setting up an alternative fuel system requires capital investment for feed equipment, storage, and possibly preprocessing facilities. Operating costs include sorting, drying, and grinding waste to make it usable. If a cement plant has to buy biomass (like wood chips) in competition with other industries (power plants, etc.), the price can be significant and subject to supply fluctuations. Many alternative fuels have lower energy content, so more volume is needed, raising transport costs. A persistent barrier in some regions is simply access to a reliable alternative fuel supply chain. Suppose local waste management infrastructure is lacking; for example, there is no system to collect and sort municipal waste or agricultural residues. In that case, the cement plant cannot readily procure enough alternative fuels or may need to import them, which can be costly and logistically complex. On the flip side, stringent waste regulations can indirectly subsidize alternative fuel use, e.g., if landfill disposal is expensive, waste producers will pay cement plants to take RDF.

In regions where landfilling is cheap and unregulated, there is little economic incentive for waste to go to cement kilns. Biomass availability is similarly variable because some countries have surplus agri-residues, which could be cheap fuel, while others have scarce biomass because it is already used as cooking fuel or soil amendment. Thus, the economics are site-specific. Another factor is that increasing alternative fuels might slightly reduce a plant’s throughput or increase maintenance due to more frequent shutdowns to clean build-ups, which are economic penalties that are not always quantified. However, studies generally show moderate use of alternative fuel yields net savings or is cost-neutral, whereas pushing to very high alternative fuel rates can have diminishing returns. The cost of innovation is also a barrier to hydrogen or novel synthetic fuels. Currently, the cost is prohibitively high relative to coal; hydrogen can be several times more expensive per unit of energy. Without subsidies or a carbon price, there is no business case for such switches yet. In summary, while alternative fuels can often save money or at least break even, especially when including waste disposal fees, the initial investments and ongoing operational complexities are the main economic hurdles. For some smaller producers, these hurdles deter them from even starting alternative fuel usage, especially if coal is readily available and cheap.

4.4.3. Policy and Regulatory Barriers (Alternative Fuels)

Policy plays a crucial role in alternative fuel adoption. Waste management policies are central if regulations encourage waste-to-energy and discourage landfilling through bans or taxes. Cement kilns have a strong incentive to co-process waste. Such policies have driven high alternative fuel usage in Europe. In contrast, where environmental regulations are soft, cement plants might use cheaper but dirtier fuels like petroleum coke without consequences, and municipalities may prefer landfilling waste over sending it to kilns. Therefore, alternative fuel uptake remains low. Also, some countries have regulations that restrict the burning of particular waste due to air quality concerns. Cement kilns do have advanced air pollution control, and their high temperatures can destroy organics effectively. Still, public perception or regulatory caution can limit permits for using waste like tires or industrial sludges. Emissions standards need to be met regardless of fuel; certain alternative fuels can increase emissions of NOx, SOx, or other pollutants if not managed, potentially violating permits. Thus, plants might avoid those alternative fuels if compliance is an issue.

On the other hand, clear guidelines and streamlined permitting for alternative fuel use can facilitate adoption. Biomass policy also matters if biomass is designated as carbon neutral. It makes using biomass fuels desirable for meeting CO₂ targets since their emissions might be counted as zero in inventories [86]. Some jurisdictions provide credits or renewable energy certificates for industrial biomass usage, which can further incentivize it. Safety and handling regulations can also be a barrier because storing large quantities of waste fuel may trigger additional requirements, such as fire safety, odor control, etc., adding to the compliance burden. Another angle is supply chain and quality standards for alternative fuels: establishing protocols for RDF quality—such as calorific value, maximum chlorine, etc.—helps cement plants trust the fuel and use it effectively. Without standards, variability in waste fuel quality can be a deterrent. Social acceptance is relevant here as well—local communities might oppose cement plants burning waste, fearing toxic emissions, even if emissions are within limits. Transparent communication and monitoring are needed to address these concerns. In some cases, misperceptions like confusing cement kiln co-processing with incineration have slowed alternative fuel programs. Government incentives like grants for alternative fuel system installation or carbon credits for each ton of fossil CO₂ avoided via biomass could remove some barriers but are not yet widespread. Additionally, looking forward, the policy might need to encourage new alternative fuels like hydrogen or electrification by funding R&D or pilot projects because the market alone will not drive those until costs fall.

In summary, alternative fuels represent a practical decarbonization route that is already making an impact and can be expanded further. It primarily addresses the fuel-related (energy) portion of emissions, which is roughly 30–40% of total cement CO₂ [3]. Replacing 100% of fossil fuel with biomass would theoretically eliminate those combustion emissions though process emissions remain, and partial replacement yields proportional savings. The barriers are centered on fuel preparation, consistent supply, investment in handling systems, and regulatory enabling conditions. Many of these barriers have been overcome in best-practice regions (e.g., Western Europe), demonstrating that high alternative fuel usage is achievable given the right incentives and know-how. For the regions that are still lagging, addressing waste management frameworks, building public–private partnerships to ensure supply, and sharing technical experience can significantly improve uptake. It is also worth noting that while alternative fuels reduce fossil CO₂, their overall mitigation effect depends on the sustainability of biomass sourcing, no deforestation, etc., and proper management of waste-derived fuels to avoid toxin emissions. Thus, a balanced and well-regulated approach is needed. With such an approach, alternative fuels can serve as an important bridge strategy, cutting emissions now while longer-term solutions like CCUS or new cement are developed.

5. Discussions

To synthesize insights from the literature, Figure 4 presents a logical relationship diagram, mapping the main low-carbon cement technology pathways alongside their respective strengths, weaknesses, key barriers, and commonly applied analysis methods, thereby providing a structured overview of the technological landscape.

As shown, while clinker substitution and energy efficiency offer near-term, lower-cost opportunities, pathways such as CCUS and novel binders face higher technical and economic barriers, underscoring the importance of complementary analysis methods to evaluate and inform targeted policy and investment.

In reviewing the literature and analyzing current industry practices, several critical research gaps and areas have emerged that must be addressed to accelerate cement sector decarbonization, where existing literature or data are insufficient. These gaps span technical innovation, data standardization, pilot demonstration needs, policy design, and lifecycle integration. Addressing these challenges will be essential to overcoming current uncertainties and unlocking the full mitigation potential of low-carbon cement strategies. This section categorizes the research gaps into technical, informational, and policy domains.

Low-Carbon Clinker and SCM Innovation Gaps: While clinker substitution has made significant advances, substantial innovation gaps remain in developing and characterizing new SCMs and alternative low-carbon clinkers. Materials such as calcined clays, agricultural residues, and construction waste fines have shown promise. Still, systematic research into their properties, scalable processing methods, and performance in multi-SCM blends is limited. The behavior of ternary and quaternary blended cement under diverse curing regimes remains poorly understood. Similarly, alkali-activated systems incorporating multiple SCMs require further study [8]. Alternative low-CO₂ clinkers like belite-rich and calcium sulfoaluminate cement also face obstacles related to industrial scalability and long-term durability validation. Barbhuiya, et al. [25] demonstrated laboratory-scale CO₂ mineralization technologies, but scaling these processes for industrial use presents substantial logistical and technical challenges. Research must focus on improving the technology readiness of these novel binders, including large-scale pilot trials and real-world durability monitoring. Additionally, economic processing routes for local raw materials, such as low-temperature clay calcination and fly ash beneficiation, must be developed to ensure a sustainable and geographically diversified SCM supply chain.

5.1. Standardization and Comparability of Data

A critical barrier to the effective evaluation of cement decarbonization strategies is the lack of standardized metrics and comparable datasets. Current life cycle assessments (LCA) vary widely in system boundaries; some include concrete carbonation uptake and supply chain emissions, while others do not, making cross-study comparisons difficult. There is an urgent need to harmonize LCA frameworks, especially regarding how carbon uptake occurs during a life cycle structure [78]. For instance, Wu, et al. [1] demonstrated the significant role of carbonation, yet it is inconsistently factored into global mitigation scenarios. Another gap lies in future demand assumptions: whether high- or low-demand pathways are used dramatically alters technological deployment outlooks. A standardized scenario framework is needed for apples-to-apples comparisons.

Additionally, regional granularity remains a major gap; while global aggregates dominate, region-specific data on material availability, costs, technological barriers, and regulatory environments, especially for emerging economies, are lacking. Latin American studies by Camargo-Bertel, et al. [87] showed that local solutions can differ dramatically from global averages. To build credible mitigation roadmaps, more granular data across diverse geographies is essential. Without this standardization and localization of data, policymakers and industry leaders risk making decisions based on incomplete or misleading global assumptions, hampering targeted, effective action.

5.2. Full-Scale Demonstrations and Pilot Data

Another persistent research gap lies in the limited availability of full-scale demonstration projects and operational data for key cement decarbonization technologies. Many promising strategies, including CCUS and novel cement, remain confined to laboratory or small pilot trials. As of now, no cement plant has operated a continuous, full-scale CCS unit, though the Norcem project in Norway is expected to pioneer this by the mid-2020s [70,72]. Until multiple full-scale project demonstrations occur across different geographies and operational conditions, uncertainties around integration, capture efficiency, and operational disruptions will persist. Similarly, hydrogen-fueled kiln trials, although announced, are yet to generate extensive peer-reviewed findings. Even emerging technologies such as AI-driven process optimization lack concrete evidence linking them to substantial CO₂ reductions. Bridging this gap demands greater collaboration between academia, industry, and governments to fund and support large-scale pilots.

Furthermore, demonstration projects should address long-term performance monitoring, particularly for low-clinker or novel concrete structures. Without empirical pilot data, many mitigation strategies remain perceived as high-risk, limiting their broader adoption [15]. Therefore, full-scale trials are a foundational step towards validating scalable, low-carbon cement pathways.

5.3. Policy and Market Mechanisms Analysis

Effective policy and market mechanisms play an essential role in cement decarbonization, yet substantial research gaps persist in understanding their design and impacts. While carbon pricing is commonly advocated, uncertainty remains over the specific price thresholds needed to make technologies like CCS viable in the cement sector. Similarly, the global implications of emerging policies, such as the EU CBAM, on trade patterns and carbon leakage have not been sufficiently explored [81]. Comparative policy analyses are also limited; understanding why policies such as landfill taxes successfully drove alternative fuel adoption in Germany but failed elsewhere could yield valuable insights. Furthermore, financing mechanisms for decarbonization projects such as climate finance programs, green bonds, and blended finance models remain underexplored. Interdisciplinary research linking engineering, economics, and political science is needed to design effective incentives, equitable financing frameworks, and public engagement strategies [25]. Public acceptance issues surrounding CCUS and waste-derived fuels are also insufficiently studied and require dedicated social science research to facilitate community buy-in and mitigate opposition. Bridging these gaps will better enable policymakers and industry leaders to craft robust, equitable strategies for cement sector decarbonization globally.

5.4. Life Cycle and Cross-Sector Interactions

Finally, cement decarbonization research must extend beyond the plant boundary to address interactions across the broader construction value chain. There is a substantial gap in integrating cement decarbonization strategies into full building LCA. Decisions regarding building design, material efficiency, and end-of-life recycling significantly impact total embodied emissions and must be considered alongside cement formulation changes [88]. The balance between using larger quantities of low-carbon cement and optimizing the use of high-carbon cement through efficient design needs to be better evaluated using comprehensive life cycle modeling. Additionally, cross-sectoral coupling opportunities remain underexplored. For example, utilizing waste heat from cement production for neighboring industries or employing captured CO₂ for curing new concrete products could unlock circular economy benefits. Initial estimates suggest that direct CO₂ mineralization can only offset a fraction of cement emissions, highlighting the need for integrated system approaches rather than isolated technical fixes [15]. Moreover, advancing demolition and material recovery strategies could further reduce cement’s lifecycle emissions footprint.

As academic and industry researchers work on these gaps, there is a need for collaboration, e.g., global data-sharing initiatives on cement plant performance, international research networks on alternative binders, such as the LC₃ project on limestone calcined clay cement and joint government–industry working groups on policy design for heavy industry decarbonization. Many of the perceived barriers can only be truly addressed by empirical evidence from deployment [15]. This review echoes the call to the researchers and others that a systemic approach combining technical innovation with policy and market innovation is needed and that some areas, like digital construction methods enabling material efficiency, are under-researched but potentially impactful [1]. By addressing these research gaps, future studies can provide the missing pieces that allow stakeholders to confidently implement the full suite of mitigation strategies and track progress.

5.5. Cross-Cutting Barriers to CO₂ Mitigation Strategies

Across the four major CO₂ mitigation strategies examined, several recurring barriers emerge. As summarized in

Table 2. Cross-cutting barriers to CO₂ mitigation strategies in the cement industry.

Barrier Theme	Clinker Substitution	Energy Efficiency Improvements	Alternative Fuels	CCUS	Description and Evidence
High Capital Costs	Moderate; cost of SCM processing facilities, quality control,	High; kiln upgrades, digital systems, and WHR.	Moderate; fuel preprocessing, upgrades.	Very High; capture units, transport and storage infrastructure	Upgrading existing kilns, adding waste-heat recovery, or switching to more efficient grinding technologies requires significant investment. CCUS installations are currently priced comparable to building a new plant, and their revenue streams remain unclear. Even plant upgrades to enable clinker substitution or high-replacement SCMs can be capital-intensive when additional drying, calcination, or material-handling systems are required.
Supply Chain Constraints	High; availability and logistics of SCMs like slag, fly ash, and calcined clays	Moderate; supply of modern equipment, spare parts.	High; biomass/waste availability, logistics and co-processing plants.	High; CO2 transport pipelines, storage sites, and infrastructure gaps	The availability and consistent quality of SCMs such as fly ash, slag, calcined clay, and natural pozzolans limit clinker substitution. Alternative fuel supply chains require reliable sourcing, preprocessing and storage; biomass, waste-derived fuels, and hydrogen are often unavailable at scale. CCUS also depends on transport and storage infrastructure, which is scarce or non-existent in many regions.
Restrictive regulations and standards	Moderate; standards limiting clinker replacement levels	Low–Moderate; lack of mandatory efficiency targets.	High waste legislation, permitting issues, and co-firing regulations	Very High lack of CO2 pricing, liability for storage, and unclear policy support.	Construction codes and cement standards often limit the allowable proportion of alternative binders and discourage the use of low-carbon cements. Regulations governing the co-processing of waste-derived and biomass fuels can be prohibitive or inconsistent across jurisdictions. The absence of clear permitting processes for CO2 transport and injection slows CCUS projects.

, high capital costs remain a central challenge, particularly for kiln upgrading, fuel-processing systems and CCUS deployment. Supply chain constraints, including limited availability of SCMs, biomass and CO₂ transport, and storage networks, further hinder widespread adoption. In addition, regulatory and policy limitations, such as clinker content restrictions, waste co-firing regulations and insufficient support for carbon storage, reinforce these challenges. By synthesizing these common themes into a unified framework, it becomes clear that overcoming financial, infrastructural, and policy-related barriers will be essential for achieving meaningful decarbonization in the cement industry.

Capital costs and return-on-investment constraints are consistently highlighted as critical barriers. Habert et al. and Barbhuiya et al. Barbhuiya, et al. [25] highlight that the cost of implementing CCUS is comparable to building an entirely new cement plant, making its adoption difficult to justify within the sector. Supply chain constraints are also recurrent, as noted by Benhelal et al. Benhelal, et al. [32] and Barbhuiya et al. Barbhuiya, et al. [25], who point to variability in the quality and availability of SCMs alongside immature logistics for waste-derived fuels, and the scarcity of CO₂ transport with storage infrastructure. Regulatory and standards-related barrier is evidenced in Busch et al. Busch, et al. [38], which identifies outdated building codes and weak market demand, and Marinelli and Janardhanan Marinelli and Janardhanan [35], who highlight fragmented regulations and limited institutional capacity as obstacles to adoption. Collectively, these studies validate the three cross-cutting themes identified in the matrix and provide policy and practice-oriented insights for overcoming barriers to CO₂ mitigation in the cement industry.

While multiple research gaps hinder progress toward cement decarbonization, their prioritization is essential to guide policymakers, industry, and researchers. These gaps can be categorized into short-term and long-term needs. Short-term priorities include scaling clinker substitution through secure supply chains of SCMs such as calcined clays, slag, and fly ash. Further work is required on standardization and performance testing to enable widespread adoption. Energy efficiency improvements through digital optimization, advanced process control, and waste heat recovery remain pressing, particularly for existing plants in emerging economies. In parallel, alternative fuel integration demands better logistics and preprocessing systems to ensure stable quality and emissions compliance. Long-term priorities focus on CCUS, where demonstration projects and infrastructure development remain critical. In addition, novel low-carbon binders, such as geopolymers, belite-rich, and CSA cements and circular cement concepts, such as cement recycling, face challenges in durability evidence, codes, and feedstock availability. Research must also address systemic barriers such as CO₂ transport networks, market creation mechanisms, and policy harmonization. This prioritization highlights the need for immediate, scalable measures while sustaining innovation pipelines for transformative, next-generation solutions to achieve deep decarbonization.

6. Conclusions and Recommendations

By applying a scoping review approach, this study synthesizes the current state of knowledge and highlights research gaps that demand further systematic investigation and empirical validation. The results show that significant CO₂ reductions are technically achievable in the cement sector through four decarbonization strategies: clinker substitution, energy-efficiency improvements, alternative fuels, and CCUS. While these strategies are well-established, the analysis reveals that successful implementation depends on more than technical capability; it centers on addressing economic, regulatory, and organizational barriers across all strategies. Clinker substitution offers the most immediate and low-cost reductions, with each 1% reduction in clinker lowering CO₂ emissions by approximately 0.8%. Yet, adoption is constrained by the limited supply and variable quality of SCMs, restrictive construction codes and the slow qualification of new binders. LC₃ shows promise where suitable calcined clays and logistics exist, but material supply and durability remain as blockages. Energy efficiency measures, such as WHR, advanced process controls, and modern kiln upgrades, can further lower the carbon intensity of the sector.

However, capital intensity, downtime risks, and diminishing returns in modernized plants constrain uptake. The barrier is particularly dominant in developing countries that use outdated technologies. Alternative fuels, such as biomass and RDF, can meaningfully reduce combustion emissions. However, their deployment depends on reliable supply chains, consistent calorific value and preprocessing requirements, as well as regulatory or public resistance, which are weak in many regions, influencing their adoption. Also, the development of integrated waste management systems and infrastructure remains essential. CCUS exclusively addresses process emissions from calcination and can achieve deep reductions. Its deployment remains limited due to high capital intensity demands, integration complexity and restricted access to CO₂ transport-and-storage networks. Costs also remain high-priced without policy support.

Across all pathways, cross-cutting barriers persist as follows: (i) financing and risk, high upfront costs, thin margins, carbon pricing and uncertain returns discourage investment in low-margin businesses; (ii) codes, standards, data, outdated regulations, fragmented LCA and plant data, and slow SCM qualification; and (iii) supply chain and capability feedstock logistics for SCMs and low-carbon fuel logistics, permitting throughput, and workforce expertise, or quality assurance limitations. These themes indicate that bundled, multi-instrument interventions, policy, finance, standards, and capacity building are required rather than technology-only solutions. Social barriers, such as limited stakeholder awareness and resistance to new materials, further constrain progress. Beyond these established mitigation strategies, this review emphasizes the growing importance of disruptive low-carbon cement technologies innovations, such as circular cement recycling, process re-engineering electrified indirect calciners, such as LEILAC, and novel low-carbon binders like geopolymers, LC₃, CSA/belite formulations. These technologies have the potential to offer near-zero-carbon emissions but remain at an early stage of commercialization, facing feedstock-supply challenges in scale and therefore require demonstration projects, standards development, permit accelerated research, targeted investment, piloting, and policy support. In light of the above, this study proposes the following strategic recommendations:

• Enable Clinker Substitution and Process Optimization (Short-term): Move to modernize cement standards and construction codes to accommodate higher SCM usage; prioritize the adoption of best-available technologies for thermal efficiency, grinding technologies upgrades, and process advance controls to capture short-term gains.
• Support Alternative Fuel Adoption (Short-term): Reform regulations to enable safe co-processing of biomass and waste-derived fuels in cement kilns. Invest in fuel preprocessing, build reliable supply chains and stakeholder engagement to build trust and secure social licenses.
• Accelerate CCUS Development (Long-term): Support public–private investment frameworks for pilot, demonstration projects and coordinated investment in CO₂ transport and storage infrastructure. Implement policy instruments, such as carbon pricing or tax credits, to reduce commercial risk and improve commercial feasibility.
• Strengthen Policy Support and Collaboration (Long-term): Implement green procurement mandates and comprehensive carbon pricing; harmonize standards and data practices; and promote international cooperation to publicize global best practices and support technology transfer.

By implementing these integrated actions with strong policies, financial support, and data-driven planning, both industry and policymakers can overcome the identified barriers and position the cement sector toward deep decarbonization while sustaining economic and social progress and supporting sustainable development goals. In conclusion, no single pathway is sufficient. Overall, achieving deep emission reductions in cement production requires a portfolio approach that combines short-term and long-term improvements with transformative innovations. Future research should focus on scaling disruptive low-carbon binders, advancing CCUS integration, strengthening SCM and fuel supply chains, and improving life cycle assessments and techno-economic modeling to support global sustainable development goals.