Transforming Industrial Waste into Low-Carbon Cement: A Multi-Criteria Assessment of Supplementary Cementitious Materials for Sustainable Concrete Design

Abstract

The cement industry accounts for nearly 8% of global anthropogenic CO₂ emissions, driven largely by energy-intensive clinker production. Valorising industrial and agricultural waste as Supplementary Cementitious Materials (SCMs) presents a viable mitigation strategy, aligning decarbonisation goals with circular-economy principles. This review employs a two-stage screening process and the Evaluation based on Distance from Average Solution (EDAS) method to assess 27 SCMs across technical, environmental, economic, and regulatory dimensions. The results establish a clear hierarchy: fly ash and metakaolin ranked highest, followed by ground granulated blast furnace slag, silica fume, and calcined clay. Life cycle assessment confirms these top-performing SCMs can reduce the global warming potential of cement production by 50–90% compared to ordinary Portland cement. While established SCMs like fly ash offer a balanced profile in durability, CO₂ reduction, and cost, the framework also identifies regionally abundant materials such as steel slag, bagasse ash, red mud, and Rice Husk Ash (RHA), which possess significant potential but require further processing and standardisation. The findings underscore that material consistency, robust regional supply chains, and performance-based standards are critical for large-scale SCM adoption, providing a replicable framework to guide industry and policy stakeholders in accelerating the transition to low-carbon, waste-valorised cement technologies.

1. Introduction

Cement production is paramount for modern-day infrastructure advancement, serving as the backbone of the global construction sector. However, it is one of the major carbon-intensive industries, contributing approximately 7–8% of CO₂ emissions [1,2], largely due to the calcination of limestone and the fossil fuel energy required for clinker production [3,4]. Despite advancements such as dry-process kilns, the production of ordinary Portland cement (OPC) still requires 3.0–6.0 GJ of energy per ton and remains heavily dependent on non-renewable fuels, thereby exacerbating emissions and accelerating resource depletion [5,6]. With global cement demand exceeding 4 billion tonnes annually and projected to rise in line with urbanisation and infrastructure development, emissions from the sector are expected to increase unless transformative mitigation strategies are implemented [7,8]. Technological advances, such as alternative fuels, carbon capture and storage (CCS), and high efficiency kilns, present partial mitigation but encounter scalability, cost, and regulatory hurdles [1,8,9]. Beyond carbon emissions, cement production contributes to land degradation, air pollution, and resource depletion, highlighting the urgent need for sustainable alternatives.

Reducing the environmental impact of cement requires transformational changes in both material usage and process design. One of the most effective approaches to reduce the carbon footprint of cement is the partial substitution of clinkers with supplementary cementitious materials (SCMs). SCMs derived from industrial and agricultural by-products such as fly ash, ground granulated blast furnace slag (GGBFS), silica fume, red mud, rice husk ash, and calcined clays, not only improve the durability and performance of concrete but also provide an environmentally sound outlet for large waste streams. Integrating SCMs into cement systems addresses two critical challenges simultaneously [10,11]: reducing GHG emissions and diverting industrial waste from landfills, thereby aligning with circular economy principles [12] and global sustainability goals such as SDG 7 (Affordable and Clean Energy), SDG 9 (Industry, Innovation, and Infrastructure), and SDG 12 (Responsible Consumption and Production) [13,14,15,16].

Although numerous studies have investigated the properties of specific SCMs [10,11,17,18,19], a comprehensive, comparative framework that evaluates both established and emerging materials across technical, environmental, regulatory, and economic dimensions remains limited. Previous reviews have often focused on a narrow set of materials or relied heavily on qualitative expert opinion, limiting their applicability in decision-making. Moreover, while established SCMs like fly ash and GGBFS are widely standardized [14,15], emerging alternatives such as bagasse ash, steel slag, and geopolymers present both opportunities and challenges due to variability in composition, processing requirements, and regulatory acceptance. This study advances the field by applying a two-stage systematic screening process combined with a robust multi-criteria decision-making (MCDM) method: Evaluation based on Distance from Average Solution (EDAS) to assess 27 potential SCMs. Each material is evaluated across technical performance, environmental impact, economic feasibility, and standards compliance, providing a balanced perspective that goes beyond single-criterion assessments) [20,21,22]. By integrating life cycle assessment (LCA) results with MCDM analysis, this work establishes a clear ranking of SCM suitability while identifying regional opportunities and supply risks. The study thus contributes a replicable framework that informs policymakers, researchers, and industry stakeholders, offering a practical roadmap to decarbonize cement production, valorize industrial waste, and accelerate the transition to low-carbon, resource-efficient concrete technologies.

2. Methods and Data Sources

2.1. Mapping Industrial Waste and Its Characteristics

The generation of industrial waste is increasingly becoming a major environmental concern that requires urgent mitigation due to the pace of global industrialization. These wastes vary in their composition, geographic distribution, disposal practices, and volume thereby posing different levels of environmental and health threats. Beyond prevalent waste management issues known, some industrial residuals present unique prospects for valorization in the construction sector specifically as potential SCMs or alternative raw materials. For example, mineral-rich wastes like fly ash, blast furnace slag, red mud, and iron ore tailings are well known for their latent hydraulic or pozzolanic properties and high content of reactive oxides such as Al₂O_3, SiO₂, and CaO [14,15]. There is a need to understand the global industrial sources, generation trends, and current disposal challenges of such wastes to assess their viability in sustainable cement design.

Table 1. General overview of the different industrial waste.

Waste Type	Global Availability & Key Regions	Primary Sources	Current Disposal Issues	References
Mining Waste	~1.4 billion tonnes/year of iron ore tailings; major producers include Brazil, China, and Australia.	Iron ore, coal, and other mineral extraction activities.	Tailings are often stored in dams; risk of dam failures and toxic leachate contaminating water bodies.	[23]
Fly Ash & Slag	Significant quantities from coal-fired power plants and steel, especially in the U.S., China, and India.	Combustion of coal in thermal power plants.	Contains heavy metals; improper disposal leads to air and water pollution; limited recycling in construction.	[24]
Chemical Waste	Global widespread; significant in chemical manufacturing hubs like the U.S., Germany, and China.	Chemical manufacturing, pharmaceuticals, and laboratories.	Hazardous nature; challenges in treatment and disposal; risk of soil and water contamination.	[25]
E-Waste	Electronic waste is also known as e-waste. Over 70% of global ends up in China; significant amounts also in India and Nigeria.	Disposed electronic devices/parts from consumers and industries.	Laid-back recycling leads to environmental pollution and health hazards; lack of proper infrastructure.	[26]
Textile Waste	countries with large textile industries are the major contributors. These countries include Bangladesh, India, and China.	Textile and dyeing industry.	Wastewater contains dyes and chemicals; solid waste disposal issues; informal recycling.	[27]
Paper Mill Waste	Abundant in countries with large paper industries like the U.S., Canada, and Finland.	Pulp and paper manufacturing industries.	Sludge disposal challenges; chemical residues in wastewater; air emissions.	[28]
Plastic Waste	Plastic waste is a global issue; prominent producers include the U.S., China, and European countries.	Plastic manufacturing and packaging industries.	Non-biodegradable nature; accumulation in landfills and oceans; recycling challenges.	[29]
Radioactive Waste	Produced in countries with nuclear power plants and medical facilities; notable producers include the U.S., France, and Russia.	Nuclear power generation, medical isotope production, and research laboratories.	Long-term storage challenges; risk of radiation leaking; high cost of disposal.	[30]
Biomedical Waste	Abundant in countries with large healthcare sectors like the U.S., India, and China.	Hospitals, clinics, and pharmaceutical industries.	Risk of infection; improper disposal leads to environmental pollution; need for specialized treatment.	[31]
Construction Debris	High volumes globally; especially in fast growing regions like Asia and the Middle East.	Construction, renovation, and demolition activities.	Large volumes; limited recycling; most times ends up in landfills; potential for hazardous materials.	[32]
Hazardous Waste	High in Asia-Pacific, North America, and Europe due to rapid industrialization and legacy adulteration.	Chemical manufacturing, metal processing, and electronics industry.	Improper disposal leads to soil and groundwater contamination, health risks, and illegal dumping.	[33]
Industrial Sludge	Predominant in industrialized countries; increasing in Asia and Latin America.	Wastewater treatment, metal processing, mining.	Landfilling raises environmental issues; drying and incineration are energy intensive.	[34]
Asbestos Waste	persistent in Russia, China, India, Brazil; legacy waste in many banned countries.	Construction, shipbuilding, automotive industries.	Hazardous to health when airborne; disposal requires strict handling and encapsulation.	[35]
Food Processing Waste	Globally generated, particularly high in North America and Europe; significant production losses in developing regions.	Food and beverage industry, agriculture.	Causes methane emissions in landfills; underused in bioenergy or composting.	[36]
Packaging Waste	High volumes in EU, North America; rapid growth in Asia-Pacific.	Manufacturing, retail, logistics.	Plastic-based materials resist degradation; recycling rates are low; leads to aquatic pollution.	[37]

offers a combined overview of the major types of industrial waste that exist in the built environment. It details their primary origin, geographic prevalence, and the environmental management concerns associated with each of them; this serves as the foundation for evaluating their sustainability and technical applicability potential in concrete production systems.

The information presented in Table 1 highlights the diversity, scale, and environmental importance of industrial waste streams arising from key sectors such as metallurgy, energy, chemicals, construction and mining. These wastes differ not only in geographic distribution and volume but also in their chemical composition and management issues. Mining activities, especially iron ore abstraction, generate vast number of tailings, which, if not properly managed, will result in disastrous long-term contamination of aquatic environments and failures of containment systems. Likewise, coal combustion residuals like fly ash and boiler slag are produced in large amount and contain minute quantity of metals that pose environmental hazards when disposed inappropriately. Although such materials have shown potential as SCMs, there are still irregularities in their utilization due to issues that include: logistical constraints, variable quality and limited recycling infrastructure. The treatment practice of waste from chemical and pharmaceutical industries is more complex and pose continuous dangers to groundwater and soil. While the prompt turnover of electronic devices has increased the generation of e-waste, significant amount is exported to regions lacking adequate recycling infrastructure thereby compounding ecological and human health risks. Textile, paper, and food processing industries also contribute considerably to solid and liquid waste with high or chemical and organic loadings whereas construction and demolition activities continue to produce vast volumes of inert debris, much of which ends up in landfills.

Within this wide-ranging waste, specific waste types like fly ash, red mud, blast furnace slag, and mine tailings are of special interest due to their mineralogical compatibility with cementitious formulations. These materials are rich in aluminosilicates and have calcium-bearing phases which offer viable pathways to reduce clinker demand and thereby mitigate CO₂ emissions and high energy consumption in cement production [10,12]. While fly ash and slags have established partial incorporation in commercial concrete systems, the valorization of other industrial residues such as red mud and tailings is still evolving and being supported by innovations in activation chemistry and geopolymer synthesis [13,24]. However, effective integration of these waste materials requires careful assessment of their long-term performance, environmental safety, and phase stability. Concerns such as lack of harmonized standards, heavy metal leaching, and heterogeneity in composition continue to be significant barriers [23,38]. Addressing these concerns calls for a structured framework that accounts for material reactivity, local waste availability, regulatory alignment and processing needs. This will be essential for both resource efficiency and emission reduction goals. It will also support the alignment of waste management strategies with broader sustainability and circular economy principles.

2.2. Two-Stage Screening and Classification of SCMs from the Industrial Waste Pool

The transition toward sustainable concrete design necessitates the strategic valorization of industrial by-products as viable SCMs. In response to the environmental burden of clinker production and industrial waste accumulation, the integration of industrial by-products, agricultural residues, and engineered pozzolan SCMs offers a dual environmental benefit: reducing landfill pressures and lowering the carbon footprint of cementitious systems [2,11]. However, the applicability of these materials is not universal and varies significantly depending on their chemical composition, reactivity, processing requirements, and regional availability.

This section outlines a two-stage systematic screening process designed to identify and characterize industrial by-products, agricultural residues, and engineered pozzolan with potential SCM applications. While most materials considered in this study originate from industrial and agricultural residues (e.g., fly ash, rice husk ash, red mud), some such as calcined clay and metakaolin are not waste materials but rather engineered pozzolans derived from thermally activated natural clays. Their inclusion is justified in their high performance, emerging availability in developing markets, and increasing relevance in low-carbon cement strategies such as LC3 (limestone calcined clay cement) systems [39]. This is further classified in Table 2. In this study, the term “Geopolymer Binders” refers to alkali-activated materials produced from industrial by-products such as fly ash, GGBFS, or metakaolin. While geopolymers are often studied as alternative complete binders (not just SCMs), their inclusion here reflects their SCM-like use in blended systems or partial replacement scenarios in emerging low-carbon technologies.

Geopolymers are not a singular material, but rather a class of binders whose performance, cost, and CO₂ footprint depend heavily on precursor and activator type [40]. As such, their origin is categorized separately in Table 2 and Supplementary Material (Section S1), with caution applied to their comparability against traditional SCMs.

2.2.1. Initial Screening and Eligibility Assessment

The first stage involves an extensive classification of materials based on their source, availability, prevalent region, and disposal challenges. Table 2 presents this classification, which includes both well-established SCMs such as fly ash, silica fume, ground granulated blast furnace slag (GGBFS), and metakaolin, as well as emerging materials like red mud, biomass ash, waste glass powder, and ceramic dust [14,41]. Each material is assigned to one of three categories based on existing literature: Established SCMs (already broadly adopted and standardized), Promising SCMs (have potential but limited standardization or application), and Exploratory SCMs (under research, with preliminary feasibility).

Table 2. Emerging industrial by-products, agricultural residues, and engineered pozzolan SCMs.

S/N	Material	SCM Classification	Global Availability & Key Regions	Primary Sources	Current Disposal Issues	Material Origin	References
1	Fly Ash (FA)	Established	~750 million tonnes annually; major producers: China, India, USA	Coal-fired power plants	Landfill disposal; heavy metal contamination	Industrial by-product	[42]
2	Ground Granulated Blast Furnace Slag (GGBFS)	Established	~300–360 million tonnes annually; major producers: China, India, USA	Steel and iron industries	Underutilized; landfill accumulation	Industrial by-product	[42]
3	Silica Fume (SF)	Established	~1.5 million tonnes annually; produced in silicon-producing countries	Silicon and Ferrosilicon industries	Inhalation risk; ultrafine particle disposal	Industrial by-product	[42]
4	Red Mud (Bauxite Residue)	Promising	~170 million tonnes annually; major producers: Australia, China, Brazil	Alumina production	Highly alkaline; pond storage risks	Industrial by-product	[43]
5	Rice Husk Ash (RHA)	Established	~70 million tonnes annually; producers: China, India, SE Asia	Rice milling	Open burning; air pollution	Industrial by-product	[44]
6	Palm Oil Fuel Ash (POFA)	Established	~7 million tonnes annually; major producers: Malaysia, 7Indonesia, T8hailand	Palm oil mills	Groundwater contamination; poor awareness of reuse potential	Industrial by-product	[42]
7	Bottom Ash (BA)	Promising	~1934 million tonnes annually; major producers: USA, EU	Coal-fired power plants	Groundwater leaching; low reuse rates	Industrial by-product	[42]
8	Waste Glass Powder (WGP)	Promising	~11.5 million tonnes in USA; higher globally	Post-consumer glass	Alkali-silica reaction; landfill dumping	Industrial by-product	[45]
9	Marble Dust Waste (MDW)	Exploratory	Significant in India, Italy, Turkey	Marble cutting and polishing	Dust pollution; underutilized	Industrial by-product	[46]
10	Flue Gas Desulfurization Gypsum (FGDG)	Exploratory	~30 million tonnes annually in the USA	Coal power with desulfurization units	Leaching risks; storage problems	Industrial by-product	[46]
11	Ceramic Dust Waste (CDW)	Promising	High in China, India, Spain	Ceramic tile manufacturing	Landfill disposal; reuse unexplored	Industrial by-product	[46]
12	Napier Grass Ash (NGA)	Exploratory	Biomass-producing countries	Biomass combustion	Underutilization; disposal in landfills	Agricultural residue	[47]
13	Biomass Ash	Promising	Regions using biomass energy (e.g., Brazil, India)	Biomass combustion	Heavy metal leaching; landfill disposal	Agricultural residue	[48]
14	Calcined Clay	Established	Abundant in India, Brazil, Africa	Calcined kaolinitic clay	Mining and energy-intensive processing	Engineered pozzolan	[49]
15	Aspiration Dust	Exploratory	Found in industrial processing zones	Dust from industrial collectors	Inhalation hazard; fine particle management	Industrial by-product	[50]
16	Bagasse Ash	Promising	Common in Brazil, India, Thailand	Sugarcane processing	Groundwater pollution risk; landfill accumulation	Agricultural residue	[51]
17	Boiler Slag	Promising	Found in thermal power regions (e.g., China, USA)	Coal-fired boilers	It contains heavy metals; poor reuse	Industrial by-product	[52]
18	Egg Shells	Promising	Global; large poultry-producing nations	Poultry processing	Odor; organic contamination risk	Agricultural residue	[53]
19	Metakaolin (MK)	Established	Global (especially where kaolin clay is found)	Calcined kaolinite clay	Calcination emissions	Engineered pozzolan	[54]
20	Copper Slags	Exploratory	Common in Chile, India, China	Copper smelting	Heavy metal leaching	Industrial by-product	[55]
21	Other Non-Ferrous Slags	Exploratory	Countries with base metal smelting (e.g., Canada, China)	Zinc, lead, aluminum, nickel smelting	Toxic metal leaching; landfill accumulation	Industrial by-product	[56]
22	Lead/Zinc Slags	Exploratory	Common in China, Australia, USA	Lead and zinc smelters	Toxicity; environmental contamination risks	Industrial by-product	[57]
23	Blast Furnace Dust	Promising	Major steel-producing nations (e.g., China, India, Germany)	Steel production	Airborne hazard; landfill accumulation	Industrial by-product	[58]
24	Steel Slag	Promising	~200 million tonnes annually; found globally	Steel plants	Heavy metal leaching; landfill dumping	Industrial by-product	[59]
25	Geopolymer Binders	Established	Dependent on industrial waste supply (FA, GGBFS, MK)	Fly ash, slag, metakaolin	Early-stage adoption; production variability	Engineered binder (composite of by-products)	[60]
26	Oil-Based Mud	Exploratory	Oil-producing regions (e.g., Middle East, USA, Russia)	Drilling waste from oil rigs	Hydrocarbon contamination; classified hazardous waste	Industrial by-product	[61]
27	Kaolinitic Waste	Promising	Found in mining countries like Brazil, USA, UK	Kaolin mining	Dust pollution; poor valorization	Industrial by-product	[62]

Table 2. Emerging industrial by-products, agricultural residues, and engineered pozzolan SCMs.

S/N	Material	SCM Classification	Global Availability & Key Regions	Primary Sources	Current Disposal Issues	Material Origin	References
1	Fly Ash (FA)	Established	~750 million tonnes annually; major producers: China, India, USA	Coal-fired power plants	Landfill disposal; heavy metal contamination	Industrial by-product	[42]
2	Ground Granulated Blast Furnace Slag (GGBFS)	Established	~300–360 million tonnes annually; major producers: China, India, USA	Steel and iron industries	Underutilized; landfill accumulation	Industrial by-product	[42]
3	Silica Fume (SF)	Established	~1.5 million tonnes annually; produced in silicon-producing countries	Silicon and Ferrosilicon industries	Inhalation risk; ultrafine particle disposal	Industrial by-product	[42]
4	Red Mud (Bauxite Residue)	Promising	~170 million tonnes annually; major producers: Australia, China, Brazil	Alumina production	Highly alkaline; pond storage risks	Industrial by-product	[43]
5	Rice Husk Ash (RHA)	Established	~70 million tonnes annually; producers: China, India, SE Asia	Rice milling	Open burning; air pollution	Industrial by-product	[44]
6	Palm Oil Fuel Ash (POFA)	Established	~7 million tonnes annually; major producers: Malaysia, 7Indonesia, T8hailand	Palm oil mills	Groundwater contamination; poor awareness of reuse potential	Industrial by-product	[42]
7	Bottom Ash (BA)	Promising	~1934 million tonnes annually; major producers: USA, EU	Coal-fired power plants	Groundwater leaching; low reuse rates	Industrial by-product	[42]
8	Waste Glass Powder (WGP)	Promising	~11.5 million tonnes in USA; higher globally	Post-consumer glass	Alkali-silica reaction; landfill dumping	Industrial by-product	[45]
9	Marble Dust Waste (MDW)	Exploratory	Significant in India, Italy, Turkey	Marble cutting and polishing	Dust pollution; underutilized	Industrial by-product	[46]
10	Flue Gas Desulfurization Gypsum (FGDG)	Exploratory	~30 million tonnes annually in the USA	Coal power with desulfurization units	Leaching risks; storage problems	Industrial by-product	[46]
11	Ceramic Dust Waste (CDW)	Promising	High in China, India, Spain	Ceramic tile manufacturing	Landfill disposal; reuse unexplored	Industrial by-product	[46]
12	Napier Grass Ash (NGA)	Exploratory	Biomass-producing countries	Biomass combustion	Underutilization; disposal in landfills	Agricultural residue	[47]
13	Biomass Ash	Promising	Regions using biomass energy (e.g., Brazil, India)	Biomass combustion	Heavy metal leaching; landfill disposal	Agricultural residue	[48]
14	Calcined Clay	Established	Abundant in India, Brazil, Africa	Calcined kaolinitic clay	Mining and energy-intensive processing	Engineered pozzolan	[49]
15	Aspiration Dust	Exploratory	Found in industrial processing zones	Dust from industrial collectors	Inhalation hazard; fine particle management	Industrial by-product	[50]
16	Bagasse Ash	Promising	Common in Brazil, India, Thailand	Sugarcane processing	Groundwater pollution risk; landfill accumulation	Agricultural residue	[51]
17	Boiler Slag	Promising	Found in thermal power regions (e.g., China, USA)	Coal-fired boilers	It contains heavy metals; poor reuse	Industrial by-product	[52]
18	Egg Shells	Promising	Global; large poultry-producing nations	Poultry processing	Odor; organic contamination risk	Agricultural residue	[53]
19	Metakaolin (MK)	Established	Global (especially where kaolin clay is found)	Calcined kaolinite clay	Calcination emissions	Engineered pozzolan	[54]
20	Copper Slags	Exploratory	Common in Chile, India, China	Copper smelting	Heavy metal leaching	Industrial by-product	[55]
21	Other Non-Ferrous Slags	Exploratory	Countries with base metal smelting (e.g., Canada, China)	Zinc, lead, aluminum, nickel smelting	Toxic metal leaching; landfill accumulation	Industrial by-product	[56]
22	Lead/Zinc Slags	Exploratory	Common in China, Australia, USA	Lead and zinc smelters	Toxicity; environmental contamination risks	Industrial by-product	[57]
23	Blast Furnace Dust	Promising	Major steel-producing nations (e.g., China, India, Germany)	Steel production	Airborne hazard; landfill accumulation	Industrial by-product	[58]
24	Steel Slag	Promising	~200 million tonnes annually; found globally	Steel plants	Heavy metal leaching; landfill dumping	Industrial by-product	[59]
25	Geopolymer Binders	Established	Dependent on industrial waste supply (FA, GGBFS, MK)	Fly ash, slag, metakaolin	Early-stage adoption; production variability	Engineered binder (composite of by-products)	[60]
26	Oil-Based Mud	Exploratory	Oil-producing regions (e.g., Middle East, USA, Russia)	Drilling waste from oil rigs	Hydrocarbon contamination; classified hazardous waste	Industrial by-product	[61]
27	Kaolinitic Waste	Promising	Found in mining countries like Brazil, USA, UK	Kaolin mining	Dust pollution; poor valorization	Industrial by-product	[62]

2.2.2. Detailed Classification and Selection of SCMs

The second stage of screening involves the evaluation of these materials based on critical cementitious performance indicators. The identification and qualification of potential SCMs from industrial by-products, agricultural residues, and processed natural materials rely on a comprehensive set of performance and sustainability indicators. Each criterion plays a distinct role in determining whether a material is technically viable, environmentally beneficial, and practically implementable in cementitious systems. The screening criteria are elaborated below:

• Pozzolanic or Latent Hydraulic Activity

Pozzolanic activity refers to the ability of siliceous or aluminosilicate materials to chemically react with calcium hydroxide [Ca (OH)₂] in the presence of water, forming secondary cementitious compounds such as calcium silicate hydrate (C–S–H) and calcium aluminate hydrate (C–A–H). These hydration products enhance long-term strength, impermeability, and durability of concrete. In contrast, latent hydraulic activity describes the intrinsic capacity of certain materials, such as ground granulated blast furnace slag (GGBFS), to harden in water but requiring activation through the alkaline environment of cement paste. The degree of pozzolanicity or hydraulicity is typically evaluated using standardized procedures, including the Chapelle test, the strength activity index (SAI), and the Frattini test, in accordance with ASTM C618 [63]. Materials such as silica fume, Class F fly ash, and rice husk ash exhibit strong pozzolanic behavior, whereas metakaolin, calcined clays, and GGBFS display either latent hydraulic or combined pozzolanic–hydraulic reactivity [14,64].

• Oxide Composition (SiO₂, Al₂O₃, CaO)

The chemical composition of an SCM, especially the proportions of aluminum oxide (Al₂O₃), silicon dioxide (SiO₂), and calcium oxide (CaO), plays a key role in its reactivity and compatibility with the traditional Portland cement. These oxides contribute to the formation of C–S–H, C–A–H, and other useful hydration compounds that influence the durability and compressive strength of concrete. For example, a high content of reactive silica and alumina improves pozzolanic activity, whereas a balanced combination with calcium oxide can promote early-age strength development through latent hydraulic reactions. Fly ash general contains 40–60% SiO₂ and 20–30% Al₂O₃, while GGBFS is rich in CaO (30–50%), making both highly recommended SCMs when combined with Portland cement [10].

• Fineness (Particle Size Distribution and Surface Area)

The fineness of an SCM calculated in terms of particle size distribution (PSD) and specific surface area (e.g., Blaine fineness or BET surface area) directly impacts its reactivity, water demand, and ability to fill voids in cementitious matrices. The finer the particles, the larger the surface area for reaction thereby giving more room for packing denser binder matrix, which contributes to lower porosity and enhanced mechanical strength. For example, silica fume, with a particle size less than 1 µm and surface area over 20,000 m²/kg, is highly reactive and improves both strength and durability in high-performance concretes. In contrast, coarser materials such as bottom ash require mechanical grinding to reach optimal fineness. Target fineness values for SCMs are typically >300 m²/kg for Blaine fineness, depending on the type of material [19,65].

• Compatibility with Cement Chemistry

A suitable SCM must be integrated efficiently with the hydration kinetics and chemical equilibrium of ordinary Portland cement (OPC) without activating undesirable reactions. Incompatibility may lead to reduced strength gain, delayed setting, or even issues related to expansion. One prevalent concern is the alkali-silica reaction (ASR), where amorphous silica in some SCMs (e.g., waste glass powder) reacts with alkalis from cement, forming expansive gels that damage concrete. Therefore, pre-treatment or particle size control may be required to mitigate ASR hazards. Compatibility can also be influenced by the SCM’s chloride and sulfate contents, which can affect durability and reinforcement corrosion. Proper chemical and mineralogical characterization ensure that the SCM does not interfere with OPC hydration or compromise structural integrity [15,39].

• Availability and consistency

For real-world and commercial-scale use, SCMs are expected to be available in significant quantities and display relatively stable composition across production batches. Availability is influenced by logistical feasibility, industrial activity levels, and regional distribution. A good example is fly ash; it is abundantly available in coal-dependent countries like China, India, and the United States, but its availability is declining with the transition away from coal-fired power. Consistency, particularly in oxide composition and fineness, is critical for predictable performance. SCMs from uncontrolled processes (e.g., biomass ash or red mud) often show high variability, requiring pre-treatment, blending, or quality monitoring protocols [11,65].

• Environmental and economic benefits

SCMs must provide net environmental benefits over traditional Portland cement by reducing greenhouse gas emissions, conserving raw materials, and minimizing solid waste accumulation. Life cycle assessment (LCA) tools have consistently shown that the partial replacement of clinker with SCMs can reduce embodied CO₂ by 20–60%, depending on the substitution rate and material type [2]. For instance, using GGBFS or fly ash can offset energy-intensive clinker production, while also diverting industrial waste from landfills. From an economic standpoint, SCMs sourced as industrial by-products are often less costly than Portland cement and can contribute to financial savings in waste management and production. However, economic feasibility is region-specific and depends on collection, processing, transportation, and market demand [12].

• Regulatory and standards compliance

To ensure safe and durable application in concrete, SCMs must meet regulatory specifications defined by international and national standards. These standards cover loss on ignition (LOI), chemical composition, fineness, pozzolanic activity, and performance metrics such as strength development and durability. Widely adopted standards include ASTM C618 (for fly ash and natural pozzolans) [63], ASTM C989 (for GGBFS) [66], and EN 197-1 (for common cements incorporating SCMs) [67]. Materials not yet covered by these standards (e.g., red mud, waste glass powder) require robust research facts and performance testing to support their acceptance. Regulatory acceptance is crucial for market penetration and for meeting construction code requirements in infrastructure projects [15,68].

Table 3. International standards governing SCMs: product-level specifications and cement-level conformity criteria.

Standard Code	Region	SCMs Covered	Key Criteria (Concise)	Standard Type	Reference
ASTM C618	USA/widely used globally	Coal fly ash & raw/calcined natural pozzolans for use in concrete	Chemical & physical limits for fly ash/natural pozzolan (classification into Classes, requirements for SiO2 + Al2O3 + Fe2O3, LOI, moisture, SO3, strength/activity index and physical tests). See official scope/details.	Product/admixture standard (SCMs for concrete)	[63]
ASTM C989/C989M	USA	Ground Granulated Blast Furnace Slag (GGBFS) (slag cement)	Defines strength grades (e.g., Grades 80/100/120), chemical limits (sulfide/sulfate), fineness/activity index and compressive strength requirements for slag cement used as a cementitious material.	Product/slag cement specification (SCM/cementitious material)	[66]
ASTM C1240	USA	Silica fume for use in cementitious mixtures	Chemical and physical minimums (SiO2 content typically ≥85% by mass, limits on moisture, LOI; specific test/packing/conformity rules).	Product standard (silica fume for concrete/cementitious mixes)	[69]
EN 450-1 (BS EN 450-1:2012)	Europe	Fly ash for concrete (Type II addition under EN 206)	Requirements for siliceous fly ash used directly in concrete: reactive SiO2 (method reference to EN-196/EN-197 [67]), combined oxides (SiO2 + Al2O3 + Fe2O3), LOI categories (A/B/C—typical limits in EN practice; e.g., Category A ≈ ≤5%, B ≈ ≤7%, C ≈ ≤9%), chloride ≤ 0.10%, SO3 ≤ 3%, fineness/conformity rules. (EN 450-1 is the product standard for fly ash as a concrete addition.)	Product standard SCM used directly in concrete (Type II addition)	[70]
EN 15167-1	Europe	GGBFS (ground granulated blast furnace slag) for use in concrete, mortar and grout	Chemical & physical property limits, quality control and conformity criteria for GGBFS used directly in concrete (i.e., Type II addition). EN 15167-1 sets reactivity/activity test requirements and acceptance classes.	Product standard—SCM used directly in concrete (Type II addition)	[71]
EN 13263-1 (BS EN 13263-1)	Europe	Silica fume for concrete (by-product of silicon/ferrosilicon production)	Defines chemical/physical requirements for silica fume used as a Type II addition: typical SiO2 ≥ 85% and high specific surface (EN gives ranges/requirements; conformity/test methods included).	Product standard SCM used directly in concrete (Type II addition)	[69]
EN 197-1	Europe	Common cement composition & conformity criteria (lists allowed constituents, e.g., fly ash, GGBFS, natural pozzolans)	Specifies cement types (CEM I, CEM II, CEM III, …) and permissible constituents and proportions (i.e., cements containing SCMs). EN 197-1 governs cements (their composition & conformity), not the direct-use product requirements for raw SCMs in concrete is in EN 450-1 [70]/EN 15167-1 [71]/EN 13263-1 etc [69].	Cement standard (composition & conformity for cement that include SCMs as constituents)	[67]
EN 206 (supporting standard)	Europe	Concrete standard—defines additions/Type I (inert) & Type II (pozzolanic/latent hydraulic)	EN 206 specifies how Type II additions are treated in concrete (and references EN 450-1 [70], EN 13263 [69] etc. for product requirements). It is useful to cite when discussing how SCM product standards relate to concrete practice.	Concrete standard (links product standards to concrete use)	[72]
IS 3812	India	Pulverised fuel ash (fly ash) used in cement, mortar & concrete	Specifies chemical and physical requirements, pozzolanic activity, particle size, LOI limits and testing procedures for fly ash used as pozzolana or for partial cement replacement in concrete/cement manufacture.	National product standard SCM used in cement & concrete	[73]
BS 8615	UK/UK adoption	Natural pozzolans (natural pozzolana & calcined natural pozzolana)	Provides production, chemical composition, reactivity/durability and conformity requirements for natural pozzolans to be used with Portland cement (references EN-197-1) [67]. Useful for RHA/pozzolanic agricultural ashes in UK context.	National/product standard SCMs (natural/calcined pozzolanas)	[74]
NBR 12653	Brazil	Pozzolans (e.g., rice husk ash, metakaolin)—classification & test limits	Brazilian ABNT standard that gives pozzolanic index limits, LOI/moisture limits and grinding/fineness guidance for agricultural/other pozzolans intended for cement replacement; widely referenced in RHA/regional SCM studies.	National product standard—SCMs/pozzolans	State-of-the-art reviews on RHA and pozzolans reference NBR-12653 when reporting Brazilian limits and test methods [75].

These standards not only govern performance benchmarks but also influence regional SCM availability, blending proportions, and long-term durability considerations.

presents international standards governing SCMs focused on both product-level specifications and cement-level conformity criteria.

2.3. MCDM Frameworks (EDAS)

To identify the most suitable SCMs, this study applied the Evaluation based on Distance from Average Solution (EDAS) method [76], a robust multi-criteria decision-making (MCDM) technique. Key evaluation criteria included reactivity, scored from 1–10 based on the Strength Activity Index (SAI) or equivalent ASTM C618 tests [63], and environmental benefits, scored by normalizing reported life-cycle assessment (LCA) global warming potential (GWP) reductions onto a 10-point scale. To ensure an objective weighting of these criteria, the entropy method was applied, which determines weights based on the inherent variation within the dataset itself, thereby minimizing subjective bias.

EDAS is particularly advantageous for sustainability assessments because it evaluates alternatives relative to the average performance across multiple criteria, providing a balanced and replicable ranking system. The EDAS procedure involves the following steps [38]:

Step 1: Decision Matrix Construction

A decision-making matrix $X={\left[x_{ij}\right]}_{m\times n}$ presented in Equation (1) is constructed to evaluate $m$ different SCM alternatives, against $n$ distinct criteria. In this matrix, each element $x_{ij}$ represents the performance of the ith alternatives) with respect to jth criterion.

$$X={\left[x_{ij}\right]}_{m\times n}=\left[\begin{array}{cccc}{x}_{11}& x_{12}& \dots & x_{1n}\\ x_{21}& x_{22}& \dots & x_{2n}\\ \dots & \dots & ..& \dots \\ x_{m1}& x_{m2}& \dots & x_{mn}\end{array}\right]$$

(1)

where $m$ is the number of SCM alternatives, and $n$ is the number of evaluation criteria.

Step 2: Average Solution Calculation

For each criterion $j$, the average value is calculated as:

$${AV}_j={\displaystyle \frac{{\sum }_{i=1}^m{x}_{ij}}{m}}$$

(2)

Step 3: Positive and Negative Distances from Average (PDA and NDA)

For each alternative $i$ and criterion $j$:

$${PDA}_{ij}=\left\{\begin{array}{c}\max \left(0,{\displaystyle \frac{x_{ij}-{AV}_j}{{AV}_j}}\right) B\\ \max \left(0,{\displaystyle \frac{{AV}_j-x_{ij}}{{AV}_j}}\right) NB\end{array}\right.$$

(3)

$${NDA}_{ij}=\left\{\begin{array}{c}\max \left(0,{\displaystyle \frac{{AV}_j-x_{ij}}{{AV}_j}}\right) B\\ \max \left(0,{\displaystyle \frac{x_{ij}-{AV}_j}{{AV}_j}}\right) NB\end{array}\right.$$

(4)

Step 4: Weighted Aggregation of PDA and NDA

Using criterion weights $w_j$ (derived via the entropy method), the weighted sums are computed as the Weighted Sum of PDA (Equation (5)) and NDA (Equation (6))

$${SP}_i=\sum _{j=1}^n\left(w_j\times {PDA}_{ij}\right)$$

(5)

$${SN}_i=\sum _{j=1}^n\left(w_j\times {NDA}_{ij}\right)$$

(6)

Step 5: Normalization

The aggregated PDA and NDA are normalized as ${SP}_i$ and ${SN}_i$ in Equations (7) and (8) respectively

$${NSP}_i={\displaystyle \frac{{SP}_i}{\mathrm{m}\mathrm{a}\mathrm{x} \left({SP}_i\right)}}$$

(7)

$${NSN}_i=1-{\displaystyle \frac{{SN}_i}{\mathrm{m}\mathrm{a}\mathrm{x} \left({SN}_i\right)}}$$

(8)

Step 6: Appraisal Score Calculation

Finally, the appraisal score (AS) for each alternative is obtained as:

$${AS}_i={\displaystyle \frac{N{SP}_i+{NSN}_i}{2}}$$

(9)

Step 7: Ranking of Alternatives

SCMs are ranked according to their ${AS}_i$ values, where higher scores indicate better overall suitability. This EDAS-based framework allows simultaneous consideration of multiple criteria: including pozzolanic reactivity, chemical composition, environmental benefit, economic feasibility, and standards compliance; providing a transparent, quantitative method for prioritising SCMs in sustainable cement production.

3. Results and Discussion

3.1. Screening Outcomes and Hierarchy of SCMs

This comprehensive two-phased screening design helps to distinguish SCMs that are immediately applicable from those that necessitate further investigation or process optimization. It forms the groundwork for the multi-criteria assessment presented in the subsequent section, where SCMs are critically evaluated for their potential contribution to sustainable, low-carbon concrete technologies.

Table 4. SCM Suitability Scoring Matrix.

S/N	Waste Material	Pozzolanic/Hydraulic Reactivity	SiO2/Al2O3/CaO Content	Fineness	Cement Compatibility	Availability & Consistency	Environmental Benefit	Standards Compliance	Total/70
1	Fly Ash (FA)	9	9	8	9	10	10	9	64
2	GGBFS	9	9	7	9	9	9	9	61
3	Silica Fume (SF)	10	10	10	8	6	8	8	60
4	Red Mud	5	6	6	5	9	7	3	41
5	Rice Husk Ash (RHA)	8	9	6	8	8	9	7	54
6	Palm Oil Fuel Ash (POFA)	7	8	7	7	7	6	6	48
7	Bottom Ash (BA)	5	6	5	6	8	7	5	42
8	Waste Glass Powder (WGP)	7	8	7	3	7	8	5	45
9	Marble Dust Waste (MDW)	3	3	6	6	7	6	4	36
10	FGDG	6	7	6	7	7	7	6	46
11	Ceramic Dust Waste (CDW)	4	6	3	6	6	3	4	32
12	Napier Grass Ash (NGA)	6	7	7	6	3	8	4	41
13	Biomass Ash	6	7	6	6	6	8	5	44
14	Calcined Clay	9	9	8	9	8	8	9	60
15	Aspiration Dust	4	5	5	5	6	6	3	34
16	Bagasse Ash	7	8	6	7	6	9	6	49
17	Boiler Slag	5	6	3	6	7	7	4	39
18	Egg Shells	3	3	4	4	6	3	2	25
19	Metakaolin (MK)	10	10	9	9	8	9	9	64
20	Copper Slags	6	7	6	6	3	7	5	40
21	Other Non-Ferrous Slags	5	6	5	5	6	6	4	37
22	Lead/Zinc Slags	4	5	4	4	5	5	3	30
23	Blast Furnace Dust	5	6	5	5	6	6	4	37
24	Steel Slag	7	8	7	7	8	8	6	51
25	Geopolymer Binders	9	9	8	9	7	9	7	58
26	Oil-Based Mud	3	4	4	3	5	5	2	26
27	Kaolinitic Waste	8	9	7	8	7	8	7	54

The result shows a definite hierarchy among the screened SCMs, reflecting distinctions in pozzolanic activity, physical characteristics, chemical composition, and environmental performance. Based on cumulative scores, the materials are classified into four categories: Top performers (≥60), high Suitability (50–59), moderate Suitability (40–49), and low Suitability (<40).

presents the result of SCM suitability scoring matrix. Each material is rated across the seven SCM selection criteria, with scores from 1 (lowest) to 10 (highest). The Scoring Framework is presented in Supplementary Material (Section S1).

• Top Performers (Scores ≥ 60)

• Fly Ash (64) and Metakaolin (64) rank highest due to their high pozzolanic reactivity, fine particle size, and extensive field performance. They both meet ASTM C618 standards and substantially reduce CO₂ emissions [66,77,78]. Metakaolin is gotten from calcined kaolinite clay; it enhances early strength, durability, and chloride resistance [79,80].
• GGBFS (61) (Ground Granulated Blast Furnace Slag) is a latent hydraulic binder known for its long-term strength gain and durability benefits. It is widely available and used in sustainable concrete systems [81,82].
• Calcined Clay (60) and Silica Fume (60) are high-reactivity SCMs. Calcined clay, especially kaolinitic varieties, provides exceptional pozzolanic activity and is promising for low-carbon cements [83]. Silica fume, though less available, offers high strength and low permeability in small dosages [64].

• High Suitability (Scores 50–59)

These SCMs exhibit strong potential but may require further optimization or standardization for broader adoption.

• Geopolymer Binders (58) and Rice Husk Ash (57) are innovative and emerging SCMs. Geopolymers are synthesized from aluminosilicate-rich wastes under alkaline activation. Its present full cement replacement prospective and outstanding mechanical properties [84,85]. Rice husk ash, when properly calcined, contains amorphous silica and exhibits strong pozzolanic activity [86].
• Kaolinitic Waste (54) perform well due to favorable mineralogy [87].
• Steel Slag (51) and Palm Oil Fuel Ash (50) show good chemical composition and environmental benefits. Nonetheless, both require further processing like grinding and stabilization to address free lime and improve fineness [88,89].

• Moderate Suitability (Scores 40–49)

SCMs in this tier possess partial pozzolanic properties or compositional advantages but face constraints in reactivity, variability, or environmental risk.

• Bagasse Ash (49) and Waste Glass Powder (45) contain amorphous silica but are susceptible to alkali-silica reaction unless finely ground. When processed correctly, they can improve durability and reduce permeability [90]. Bagasse ash is a sugar industry byproduct that requires fine grinding but enhances strength and durability.
• FGDG (46) and Biomass Ash (44) offer decent pozzolanic reactivity. Biomass ashes vary substantially in composition depending on feedstock and combustion method [86,87].
• Copper Slag (40) possess alumina and iron oxides but may introduce impurities or heavy metals that require treatment [55,91].
• Napier Grass Ash (41) and Bottom Ash (42) can serve as regional SCMs when finely processed but show slower pozzolanic activity compared to fly ash [92,93].

• Low Suitability (Scores < 40)

These materials generally exhibit poor reactivity, inconsistent quality, or elevated environmental risks, limiting their application as active SCMs.

• Boiler Slag (39) and Ceramic Dust Waste (32) contain silica and calcium but possess poor reactivity and it is not consistent in supply [52,94].
• Aspiration Dust (34), Lead/Zinc Slags (30), and Oil-Based Mud (26) have reduced reactive phases and often contain toxic elements, restricting their safe application in cement [95,96,97].
• Eggshells (25) are composed mainly of calcium carbonate and lack pozzolanic phases, making them more appropriate as fillers than active SCMs [53].

Although both materials originate from the steel industry, GGBFS is a latent hydraulic material formed during iron production and is widely accepted as a high-performance SCM. In contrast, steel slag is a by-product of steel refining, often containing free lime (CaO), periclase (MgO), and unreacted oxides, which can cause volumetric instability unless treated. GGBFS has broader global standardization (ASTM C989) [66], whereas steel slag’s use in cement is still under research due to variability and leaching risks [98]. This ranking incorporates technical, environmental, and practical potential. Top-tier SCMs like Fly Ash (FA), Ground Granulated Blast Furnace Slag (GGBFS), Silica Fume (SF), Metakaolin (MK), and Calcined Clay (CC) demonstrate superior pozzolanic or latent hydraulic reactivity, rich reactive silica and alumina content, and adequate fineness which are the major characteristics for strength development and improved durability in cementitious systems [11,99]. For instance, FA and GGBFS are greatly used due to their favorable particle size distribution and long-term availability from coal combustion and iron production, respectively, which make them reliable SCMs [100]. Silica Fume, despite lower availability, ranks high due to its ultrafine particles and extremely high SiO₂ content, significantly enhancing strength and durability [101]. Metakaolin and Calcined Clay also have significant score as they offer high pozzolanic activity and comply with global standards such as ASTM C618 [63] and EN 197-1 [49]. Environmental benefits were also a key consideration; high-ranking materials often deter substantial waste streams from landfills while reducing CO₂ emissions by replacing clinker, thus encouraging circular economy goals [2]. Standards compliance further strengthens the ranking, as materials that meet ASTM, BS EN, or local regulatory criteria are more possible for large-scale implementation. Lower-ranking materials may still be feasible in specific environments or regions but necessitate further development to meet performance and safety benchmarks. Materials like Rice Husk Ash (RHA) and Palm Oil Fuel Ash (POFA) demonstrate strong potential due to their extraordinary amorphous silica content and environmental benefits derived from agricultural waste valorization, though variability in combustion methods may impact consistency [102,103]. Conversely, materials such as Red Mud, Bottom Ash, and Bauxite Residue are limited by lower reactivity, higher content of heavy metal, or alkali concerns, which may hamper their performance and acceptance in standard cement formulations [104,105]. Similarly, waste glass powder and steel slag are not so promising due to reasonable pozzolanic properties but require careful preprocessing to mitigate alkali-silica reaction [106]. Ultimately, this multi-criteria assessment aligns with sustainable construction goals and global efforts to reduce the carbon footprint of the cement industry [1].

3.2. Performance Analysis of Top-Ranked SCMs

Among the screened SCMs, five materials emerged as top performers: Fly Ash (FA), Ground Granulated Blast Furnace Slag (GGBFS), Silica Fume (SF), Calcined Clay (CC), and Metakaolin (MK). Their ranking was based on cumulative scores across technical, environmental, and regulatory criteria (Table 4). These materials are either industrial by-products or engineered pozzolans, and their use substantially improves the environmental footprint and durability of concrete systems.

Fly Ash remains one of the most widely used SCMs, particularly in regions with coal-based energy infrastructure. It offers excellent workability and long-term strength benefits, though its pozzolanic reaction is slower, necessitating optimization in early-age strength formulations. However, its availability is tightly coupled with the coal power sector, which is rapidly declining in decarbonization pathways. Conversely, GGBFS, sourced from iron and steel manufacturing, performs exceptionally well in aggressive environments, providing sulfate and chloride resistance. It is less pozzolanic but more hydraulic than FA and is preferable for large-scale marine or underground applications. Notably, GGBFS availability may be constrained as the steel industry transitions from blast furnaces to electric arc furnaces, reducing slag output.

Silica Fume, though used in small quantities (5–10%), offers exceptional performance in ultra-high-strength and low-permeability concretes. It is ideal for chloride-rich or freeze–thaw environments. Its effectiveness comes from its high surface area and amorphous SiO₂ content, yet its limited availability and high cost—due to densification and transportation—hinder broader usage. Calcined Clays, especially those used in LC³ systems, are attractive due to their wide geological availability and moderate processing energy. They are particularly suitable in developing countries where industrial by-products are scarce. However, variation in kaolinite content and the need for calcination infrastructure remain practical challenges. Meanwhile, Metakaolin, an engineered high purity pozzolan, offers superior reactivity, sulfate resistance, and early gain strength, especially where durability is prioritized. It outperforms GGBFS in sulfate-rich environments but is costlier due to controlled processing and constrained kaolin deposits.

Despite their high performance, implementing these SCMs at scale involves navigating economic, infrastructural, and policy barriers. FA and GGBFS face declining or geographically skewed availability, while SF and MK pose cost constraints. CC offers scalability potential but requires kiln retrofitting and local clay characterization. To accelerate adoption, performance-based standards, incentives for local sourcing and processing, and harmonized SCM regulations across jurisdictions are needed. Further, market adaptation will depend on regional resource logistics, lifecycle policy integration (e.g., carbon pricing), and investment in supply-chain infrastructure. In the broader context of circular economy and decarbonization goals, hybrid SCM strategies—combining materials like FA + MK or CC + limestone—present a resilient path forward.

These top five SCMs are summarized in

Table 5. Summary of the comparative assessment of SCMs.

SCM	Strength Contribution	Durability	LCA GWP (kg CO2-eq/Ton)	Availability	Main Limitation	Usage Case Study
Fly Ash	Abundant, good long-term strength, eco-friendly	High	50–200	Declining	Variable quality, slow early strength	Mass concrete, blended cements
GGBFS	High durability, consistent quality	Very High	50–150	Regional	Alkali activation needed	Marine and sulfate-resistant concrete
Silica Fume	High strength, low permeability	Very High	90–200	Limited	Workability, handling. Expensive, densification issues	High-performance/ultra-high-strength concrete
Calcined Clay	Abundant clay sources, good reactivity	High	350–450	Broad	Calcination, purity. Moderate strength gain, variability in kaolinite	Low-carbon cement blends (e.g., LC3)
Metakaolin	Very high reactivity, improves durability	High	400–600	Niche	Expensive, energy-intensive processing	Precast, white concrete, specialty applications

, which consolidates data from literature regarding strength contribution, durability, life-cycle environmental impact, and limitations. These SCMs have been widely adopted and studied over decades, and their effectiveness is well documented in literature [39]. Future updates to this matrix may further integrate under-researched materials as additional performance and availability data become available.

3.3. Multi-Criteria Selection of SCMs for Sustainable Concrete Applications

SCMs provide a bridge between conventional cement production and sustainable applications in the construction industry [10,107,108]. Each material presents advantages and limitations, making trade-offs inevitable. The most suitable SCMs combine high pozzolanic reactivity, favorable chemical composition, fineness compatible with cement systems, broad availability, and cost-effectiveness, while also supporting energy savings and emissions reduction. Economic feasibility is a key determinant. Low-cost options such as fly ash, ground granulated blast furnace slag, and rice husk ash benefit from established production systems and integration into existing supply chains [2]. Calcined clay and metakaolin show strong technical performance but require thermal activation at 700–900 °C, raising processing costs [109]. High-cost or limited-scale SCMs such as silica fume and treated red mud face specialized handling and logistical barriers [39,110].

Regional variability further complicates adoption: fly ash remains economical in coal-dependent regions like China and India but is increasingly scarce and costly in Europe and North America [111,112,113,114]. To address these trade-offs systematically, the EDAS-based multi-criteria decision-making framework was applied to the five top-performing SCMs identified in the screening phase: fly ash, metakaolin, ground granulated blast furnace slag, calcined clay, and silica fume. Each was evaluated across ten weighted criteria including durability, CO₂ reduction potential, cost, standards compliance, availability, alkali–silica reaction mitigation, carbon avoidance credit, blending ease, and circularity contribution (

Table 6. Comprehensive multi-criteria evaluation of key SCMs.

SCM	Durability Enhancement	Environmental Impact (CO2 Saving)	Economic Viability	Standards Compatibility	Global Availability	Long-Term Strength Gain	ASR Mitigation Potential	Carbon Avoidance Credit	Ease of Blending & Use	Resource Circularity Impact	References
Fly Ash	4	5	4	5	5	5	5	5	5	5	[5,115,116,117,118,119,120,121,122,123,124]
GGBFS	5	5	4	5	3	4	4	4	4	4	[1,108,125,126,127,128,129]
Silica Fume	5	4	2	5	2	5	5	3	3	2	[10,49,130,131,132,133,134]
Calcined Clay	4	4	5	3	4	3	2	3	3	4	[16,39,135,136,137]
Metakaolin	5	3	2	3	2	4	3	2	3	3	[99,138,139,140,141,142,143,144]

).

The results show that fly ash achieved the highest appraisal score due to its balanced performance across durability, cost, and emissions reduction, as well as strong compliance with standards. GGBFS and silica fume followed closely, excelling in durability and resilience, though each faced economic or supply constraints. Calcined clay demonstrated strong potential in regions with abundant deposits, while metakaolin offered superior reactivity but ranked lowest among the five in economic feasibility. A radar chart (Figure 1) highlights these trade-offs, showing fly ash as the most balanced material, while silica fume and metakaolin exhibited strong technical attributes but weaker economic and logistical profiles.

Overall, the comparative evaluation confirms the importance of context-specific SCM selection. While fly ash remains optimal in coal-dependent regions, calcined clay or agricultural residues may be more viable where industrial by-products are scarce. By applying multi-criteria evaluation to inherent material characteristics rather than relying solely on expert opinion, this study provides a transparent and replicable framework for identifying SCMs suited to sustainable concrete applications.

The weights of the criteria are presented in Figure 2; it is obtained using the entropy method (see Section S2 in Supplementary Materials for details). These criteria comprehensively address the chemical properties, technical performance, environmental impact, economic feasibility, and practical implementation aspects required for sustainable concrete design.

The EDAS method revealed that Fly Ash is the most suitable SCM based on the ten criteria evaluated, significantly outperforming the other alternatives (Figure 3). GGBFS and Silica Fume showed comparable performance, ranking second and third respectively. Calcined Clay ranked fourth, while Metakaolin, despite its excellent pozzolanic properties, ranked last due to its performance across the weighted criteria set. This comprehensive evaluation provides concrete designers with a clear preference order for SCM selection based on a balanced assessment of chemical, technical, environmental, economic, and practical factors.

3.4. Performance Potential of Under-Explored SCMs

While widely accepted SCMs such as fly ash, GGBFS, and silica fume consistently dominate the top ranks in the EDAS framework, several moderately scoring SCMs; notably steel slag, bagasse ash, red mud, and rice husk ash (RHA) which demonstrate significant potential for sustainable concrete production, especially when evaluated under region-specific conditions. Although their industrial uptake remains limited, ongoing innovations in processing and activation techniques continue to enhance their technical viability and sustainability credentials.

• Technical Barriers

Steel slag often exhibits low early-age reactivity, delayed setting, and volume instability arising from the presence of free lime (f-CaO) and magnesia (f-MgO). These characteristics can lead to expansion and microcracking if the slag is not adequately stabilized [59,145]. Bagasse ash, a by-product of sugarcane processing, typically suffers from high loss on ignition, uneven calcination, and irregular particle size, all of which reduce its pozzolanic reactivity [146]. Similarly, red mud generated from alumina refining presents challenges related to high alkalinity, heavy-metal leaching, and variable chemical composition, which can adversely affect the workability and setting of cementitious systems [147]. For RHA, the main obstacles involve controlling the combustion temperature to retain amorphous silica, achieving sufficient fineness, and reducing unburned carbon, as excess crystallinity diminishes reactivity and increases water demand [148].

• Recent Advances Mitigating Barriers

Technological modifications have substantially improved the performance of these under-explored SCMs. For instance, aqueous carbonation of steel slag enhances pozzolanic reactivity while sequestering CO₂ and reducing the leaching of alkaline earth metals [13,145]. Controlled re-burning and fine grinding of bagasse ash can transform it into a reactive pozzolan capable of achieving compressive strengths comparable to or exceeding those of conventional concrete at 28 days [146,149]. Likewise, red mud, when used in limited proportions (10–20%) or combined with GGBFS in binary systems, can improve compressive strength, chloride resistance, and microstructural density [13,147]. In the case of RHA, optimized calcination (600–700 °C) and mechanical activation yield high-reactivity amorphous silica, enabling up to 15% cement replacement without compromising long-term strength [148,150].

• Regional Relevance and Substitution Potential

The valorisation of these SCMs offers pronounced regional advantages. In sugar-producing regions across Asia, Africa, and Latin America, bagasse ash is abundantly available and can replace declining fly-ash resources.

Steel slag presents strong prospects in industrialized regions with active steel production, where its use can reduce landfill volumes and embodied carbon simultaneously [59]. RHA is highly suited to agrarian economies such as India, Thailand, and Nigeria, where rice milling generates large volumes of husk residues. Conversely, red mud is particularly relevant in alumina-producing nations such as China, India, and Australia, where it can alleviate the environmental burden of bauxite residue storage [13].

• Implications for the EDAS Framework

Integrating these under-explored SCMs into the evaluation framework provides strategic diversification for future cement decarbonization. Expanding the assessment criteria to include preprocessing energy demand, regional abundance, and environmental risk mitigation can elevate the relative scores of materials such as bagasse ash, RHA, red mud, and steel slag. By incorporating these mid-tier SCMs, the EDAS methodology extends beyond confirming established industrial trends, positioning it as a decision-support tool for identifying emerging, regionally appropriate low-carbon cement technologies.

3.5. Regional Supply Dynamics, Risks, and Policy Pathways for SCM Adoption

The adoption of supplementary cementitious materials (SCMs) extends beyond technical performance to encompass critical issues of regional supply, policy alignment, and infrastructure readiness. Their availability is intrinsically shaped by local industrial profiles, regulatory frameworks, logistical capacity, and natural resource distribution [12,15]. While established materials such as fly ash (FA), ground granulated blast furnace slag (GGBFS), and metakaolin (MK) are proven clinker alternatives, their large-scale deployment is increasingly constrained by uneven supply, declining production, and regulatory bottlenecks [18].

A primary concern is the dwindling availability of fly ash, historically a cornerstone SCM. As coal-fired power plants are phased out in the transition to cleaner energy, fly ash production has fallen sharply in the European Union, with similar trends emerging in North America and parts of Asia. This creates significant challenges for cement producers long dependent on its cost-effectiveness. Compounding this, regional disparities profoundly influence SCM access. In sub-Saharan Africa and Southeast Asia, the absence of large-scale steel or silicon industries limits the supply of GGBFS and silica fume. Conversely, these regions generate substantial agricultural residues such as rice husk ash, palm oil fuel ash, and bagasse ash that remain underutilized despite their proven potential. Industrialized nations like China, India, and South Korea have better access to GGBFS and silica fume due to robust industrial sectors, though these supply chains remain vulnerable to market fluctuations and export restrictions.

To systematically address these supply constraints, policy instruments should prioritize R&D and standardization for underutilized SCMs such as agricultural ashes, steel slags, and red mud. This entails a crucial shift towards performance-based specifications rather than prescriptive compositional limits, which would accelerate the validation and integration of emerging SCMs within regional contexts. Presently, infrastructural gaps pose a significant barrier to this transition. Pre-treatment and grinding facilities for processing these industrial and agricultural residues are often absent in resource-rich regions [10,16], creating valorization bottlenecks. This is exacerbated by a lack of coordinated investment in logistics and regional supply networks, which increases costs and supply variability. These challenges are compounded by regulatory misalignment. Building codes and standards continue to favour a narrow set of traditional SCMs, hindering the formal integration of emerging alternatives even when their technical performance is well-documented.

Overcoming these multi-faceted barriers requires adaptive, region-specific strategies. Local sourcing must be prioritized by valorizing regionally abundant residues, such as bagasse ash in Brazil or rice husk ash in India. Hybrid binder systems, which combine complementary SCMs like calcined clay with limestone, can enhance resilience by reducing reliance on single sources. Policy frameworks must accelerate this transition by incentivizing waste-to-resource pathways through tax credits, carbon pricing, and subsidies for preprocessing. Simultaneously, coordinated investment in grinding capacity, logistics, and distribution networks is critical to establishing reliable SCM supply chains. In sum, the sustainable adoption of SCMs hinges not only on technical merit but on securing their reliable and cost-effective availability. Anticipating supply risks, aligning policy with performance-based standards, and investing in enabling infrastructure at regional and global levels are essential to cementing the role of SCMs in a low-carbon future.

4. Conclusions

This study demonstrates that valorising industrial and agricultural wastes as supplementary cementitious materials (SCMs) offers a viable pathway for decarbonising cement production. By applying a two-stage screening process and the EDAS multi-criteria decision-making framework to evaluate 27 candidate materials across technical, environmental, economic, and regulatory dimensions, a clear performance hierarchy was established. Fly ash and metakaolin ranked highest, followed by GGBFS, silica fume, and calcined clay, with life cycle assessment confirming their potential to reduce the global warming impact of cement by 50–90% compared to ordinary Portland cement.

Beyond ranking individual materials, the analysis underscores that successful SCM adoption is heavily context-dependent, influenced by supply-side risks, regional industrial activity, and policy frameworks. While fly ash remains a reliable option in some economies, calcined clays and agricultural residues offer greater long-term promise in regions with abundant natural resources but limited industrial by-products.

The primary contribution of this work is a replicable, evidence-based framework that integrates material science with sustainability metrics and policy considerations. Rather than prescribing a universal solution, it enables a portfolio approach where regionally appropriate SCMs are selected to balance performance, availability, and economic feasibility. By providing a quantitative and transferable method for evaluating emerging alternatives, this study helps close the critical gap between research validation and industrial acceptance. Embedding such a strategy into policy and practice can accelerate the transition toward a low-carbon, circular cement industry and strengthen global progress toward climate goals.