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Abstract

This review examines the reintegration of lower-grade clays into industrial applications, with a focus on ceramics, cementitious binders, and infrastructure materials as key sectors for sustainable transformation. It compiles current research and experimental insights to understand how such materials, often overlooked due to variable composition or limited reactivity, can be adapted to meet sector-specific performance requirements. In ceramic tile production, low-grade clays demonstrate varying degrees of sintering efficiency and thermal shrinkage, compared to traditional kaolin, offering viable paths for cost reduction. In cement applications, contrasts between kaolinite-based and limestone calcinated clay (LC³) reveal trade-offs in strength development, shrinkage behavior, durability, and CO₂ emissions. The review critically examines technical constraints, including mix variability, curing sensitivity, and activation thresholds, while emphasizing the need for regulatory adaptation and economic feasibility. In infrastructure applications, lower-grade clays have demonstrated promising adaptability for use in road base stabilization, where their plasticity and compaction behavior outweigh the demands for high purity. Their mineralogical variability influences moisture sensitivity and load-bearing performance, yet tailored mix designs and hybrid systems can mitigate these effects. The review underscores that while durability and regulatory compliance remain key challenges, these clays offer viable alternatives for low-carbon construction in regions with abundant local deposits. Through a synthesis of empirical findings and methodological analysis, this work contributes to the strategic valorization of underutilized clay sources and supports the advancement of resource-efficient material design.

Keywords

Clay resource scarcity ceramic industry cement industry sustainable practices

Introduction

The industrial value of clay-based materials has long hinged on the availability of high-rich deposits, which remain foundational in ceramics, cementitious systems, and construction.¹ However, growing concerns over resource depletion, environmental sustainability, and economic viability are forcing a systematic reevaluation of how clay is sourced, processed, and applied across sectors. Clays’ capacity to undergo thermal transformation into nontoxic, durable products has positioned them as important raw materials for industrial use. Although the materials are environmentally friendly, their manufacturing process presents significant challenges.² Over the centuries, technological advances have expanded their use, refining their role in diverse industrial applications.³ However, the rising pressure burdens this sector with the demands for increasing eco-friendly solutions.^4,5

Kaolinite-rich clays, renowned for their fine particle size, chemical stability, electrical properties, and thermal resistance, have become indispensable for both traditional uses and advanced technological applications. Historically, regions such as the United Kingdom, China, and Ukraine have been rich sources of kaolinite,⁶ but extensive mining activities have reduced the availability of these high-purity resources. With declining reserves and supply chains disrupted by geopolitical issues, industries are driven to explore alternative clay sources, including excavated waste clays.⁷ However, these substitutes often contain impurities that require adjustments to preserve product quality and performance.⁸

The environmental impact of clay mining adds to the complexity, as large-scale extraction disrupts ecosystems, destroys habitats, and causes soil erosion. As a result, it is essential to adopt more sustainable extraction techniques and efforts in land restoration after mining.⁹

This review investigates the shift from high-purity kaolin to alternative clay sources, including the reuse of clay-based industrial residues. It analyzes how key industries are innovating to preserve material performance while lowering costs and minimizing environmental impact.

Most previous studies focus on isolated improvements without offering integrative frameworks or cross-sector synthesis. Furthermore, optimistic narratives about novel binders (e.g., geopolymers, LC³ systems) often obscure technical and economic limitations that hinder broader applicability. Thus, this review aims to:

Map the current strategies for transitioning away from kaolin across key industries,

Analyze performance claims,

Identify systemic challenges to implementation, including standardization, resource variability, and process compatibility, and

Offer future directions for research and industrial integration.

By consolidating insights across disciplines and articulating both benefits and constraints, the study aims to provide a balanced and technically grounded perspective that supports sustainable material transitions.

Resource challenges

Kaolinite, a mineral primarily composed of aluminum silicate, serves as a key component in traditional construction and building materials production. Its high alumina and silica content makes it especially valuable in the manufacture of porcelain ceramic tiles,¹⁰ Portland cement (PC),¹¹ and refractory materials. The rapid growth of the construction sector, particularly in emerging economies, has intensified demand for durable building materials. In turn, this surge has accelerated the depletion of premium-grade kaolinite deposits, raising concerns about the resource sustainability. These clays are geographically constrained and unevenly distributed, and decades of extraction have diminished reserves in key regions. Europe, for example, has experienced a marked decline in accessible high-quality clay, prompting industries to seek alternative sources.¹² Ukraine was once a leading supplier of ceramic-grade kaolinite, exporting to countries like Italy and Spain, where its purity and consistency made it ideal for porcelain tile production.^13,14 However, ongoing conflict has disrupted supply chains, leading manufacturers to diversify sourcing strategies.¹⁵ Among others, Serbia has emerged as a substitute supplier, with kaolinitic and illitic clay deposits undergoing mineralogical and performance assessments to evaluate their suitability for ceramic applications in southern Europe. These efforts have led to the inclusion of Serbian clays in tile production mixes in countries such as Italy and Spain, as detailed in recent studies.^16,17 Local deposits are also being evaluated to reduce reliance on imports, though variations in mineral quality often necessitate adjustments in processing. As other neighboring countries enter the supply chain, regional collaboration has become increasingly important in mitigating the effects of resource scarcity.

According to the Mineral Commodity Summaries 2025,¹⁸ global production in 2024 included approximately 44,000, 21,000, and 4300 metric tons of kaolinite, bentonite, and Fuller’s earth, respectively. Contributions of individual countries to the total output of these materials are illustrated in Figure 1.

Figure 1.

Distribution of global production by country for clays: (a) kaolinite, (b) bentonite, and (c) Fuller’s earth.

The latest edition of the Study on the Critical Raw Materials for the EU¹⁹ highlights that most kaolin clay consumed within the EU is directed toward ceramics, paper manufacturing, and other industrial applications, as illustrated in Figure 2. The primary sources of clay imports into the EU include Ukraine, China, Turkey, India, and Germany.¹⁹

Figure 2.

The applications of kaolin clay within the EU.

Clay extraction poses significant environmental challenges, including land degradation, deforestation, and the disturbance of local ecosystems. Despite ongoing recultivation efforts, mining practices have left lasting impacts, including extensive excavation pits and altered landscapes, that complicate long-term sustainability.^20,21 Increasingly stringent environmental regulations^22,23 may further restrict extraction techniques, posing additional challenges to accessing remaining kaolinite reserves.²⁴ On a positive note, restoration initiatives have led to the development of protected habitats for rare plant and animal species.²⁵

The depletion of high-grade kaolinite not only raises sustainability concerns but also affects the economics of raw material supply. As industries shift toward alternative sources or lower-quality variants, production costs may rise, ultimately impacting the pricing of ceramics and cement.

Industrial applications of alternative and lower-grade clays

The increasing scarcity of high-purity kaolinite has prompted industrial sectors to explore alternative clay sources as well as the reuse of mineral-rich byproducts and post-consumer materials. The low-grade clays, often dismissed due to their higher impurity levels and suboptimal mineralogy, offer significant potential when carefully characterized and strategically applied. This section highlights how underutilized clay deposits are being repurposed in technically viable ways to meet industrial demands. Additionally, it also briefly examines how waste materials are being integrated into the ceramics industry, cementitious systems, and road construction.

Ceramic industry

The ceramic industry has traditionally depended on kaolinite-rich clays for their adequate plasticity, consistent rheology, whiteness, and thermal stability during firing, all essential properties for manufacturing high-quality products such as porcelain tiles, sanitaryware, and refractory materials. These same characteristics, particularly the controllable flow behavior and shape retention, make kaolinite an ideal material for extrusion-based 3D printing of ceramics, where precise deposition and dimensional stability are of interest.²⁶ However, with accessible high-grade deposits becoming increasingly scarce, manufacturers are driven to rethink traditional practices.²⁷

Lower-grade clays with elevated iron content, varied particle sizes, and mixed mineralogy are gaining interest as partial or full replacements of kaolinite. These materials, sourced from local deposits or mining overburden, often contain illite, montmorillonite, and other silicate phases that influence behavior during shaping and firing.^17,28,29 Furthermore, considerable research has been conducted on the applications of kaolinite and its partial substitution with illitic clays in fast-firing production of ceramic tiles.¹⁰ Studies have examined the impact of clay purity on product performance, with findings indicating that while high-kaolinite clays provide superior characteristics, lower-grade clays can be effectively utilized through material optimization techniques.¹⁶ These clays are being upgraded to meet industrial standards through advanced beneficiation techniques, including selective flotation and magnetic separation, which effectively remove iron-bearing oxides.^30,31 Additionally, lower-grade clays inherently contain complementary minerals such as feldspar and quartz, which contribute to maintaining the essential characteristics of ceramic products.¹⁶ For instance, Italian tile manufacturers have successfully integrated Serbian clays, known for their lower kaolinite content, into their production lines by fine-tuning firing temperatures and regimes, thereby preserving product quality despite the change in raw materials.^16,17 Clay blends with montmorillonite, illite, or chlorite demand tailored sintering curves, while fluxing agents like feldspar compensate for reduced vitrification potential.²⁷ Optimizing firing protocols and controlling particle size remain critical for minimizing defects such as warping, bloating, or undesirable coloration.³² Table 1 provides an overview of the effects of lower-grade clays compared to kaolinitic clays in ceramic formulations.

Table 1.

Properties of ceramic materials using different clay grades.

Property	High-grade kaolinitic clay	Lower-grade clay (illite, montmorillonite, chlorites)
Plasticity index	Low (5–27)^33,34	Low to high (5–58)^33,35−37
Drying shrinkage	Low (5–7%)^17,38,39	Sometimes lower—includes spreading,^40,41 often higher—requires control (5.9–9.5%)⁴²
Dry modulus of rupture	3.6–4.7 MPa⁴³	0.8–0.9 MPa⁴¹
Firing temperature	∼1200–1350 °C⁴⁴	Often lower (950–1200 °C)^32,45
Firing shrinkage	3–7%^17,29	0.4–2.6%^32,35
Color after firing	White or light beige⁴³	Reddish, buff, or gray depending on Fe/Ti content and firing temperature¹⁶
Thermal expansion	Consistent and predictable⁴⁶	Variable—requires testing for compatibility⁴⁷
Fired modulus of rupture	High (76–80 MPa)^43,48	Lower; can be improved with fluxes or secondary additives (2– 60 MPa)^35,49
Vitrification potential	Excellent^44,48	Moderate; requires fluxing agents^32,47
Availability and cost	Limited, expensive⁶	More abundant, cost-effective³²
Environmental benefit	Lower (more processed)⁵⁰	Higher (less processed, often locally sourced)⁵¹

Furthermore, industrial waste, such as broken ceramics and tiles, is being reintegrated into production to reduce reliance on virgin raw materials. The potential of unconventional materials, such as agricultural residues (e.g., rice husk ash⁵² applied in traditional firing-based processes and mining tailings utilized through geopolymerization,⁵³ as partial clay substitutes, is under active investigation, enhancing both the diversification and resilience of the raw material base (Figure 3).

Figure 3.

Sustainable practices in the ceramic industry: innovations in low-kaolinite clay utilization.

Current research efforts are focused on developing synthetic and alternative materials that replicate the functional properties of kaolinite-rich clays. One notable advancement in this field is the rise of geopolymer ceramics, which harness aluminosilicate-rich industrial byproducts (e.g., fly ash) to replicate the structural behavior of conventional kaolinite-based systems.⁵⁴ Although still in the experimental stage within ceramic applications, geopolymerization presents a promising avenue for reducing dependence on virgin clay resources. However, further studies are needed to address key challenges, including instability in aqueous environments, ongoing geopolymerization reactions, and potential depolymerization over time, which may compromise the durability and performance. Considering that ceramic production accounts for approximately 1% of Europe's total industrial emissions,⁵⁵ these emerging technologies support broader goals of decarbonization and circular material use.

Within the refractory sector, kaolinite-rich clays remain essential due to their high thermal stability, melting point, and resistance to structural degradation under extreme temperatures. Historically, high-grade kaolinite deposits were preferred for such applications, valued for their purity and predictable performance. However, increasing resource constraints and environmental considerations have shifted attention toward lower-grade clay alternatives. Although traditionally overlooked, lower-grade kaolinitic clays offer considerable potential when subjected to target processing. Despite their inclusion of impurities, such as quartz, mica, hematite, and organic matter, advanced treatments can significantly enhance their suitability for refractory use.¹⁷ This shift supports cost-effective and sustainable production while reducing dependency on high-grade reserves. The strategic utilization of underused materials contributes to waste minimization and lowers the environmental footprint of clay extraction and processing. Moreover, the aluminosilicate framework of clays exhibits structural flexibility that enables the partial substitution of chemically analogous waste-derived materials, without significantly compromising performance or reactivity. One example is the incorporation of ceramic tile manufacturing waste, aligning with principles of industrial symbiosis and closed-loop resource management.

Binder systems in construction

Roman cement, also referred to as natural cement, was first identified in England during the late 18th century. It was manufactured through the calcination of marl stone, a sedimentary rock formed by the simultaneous deposition of calcium and carbonate, and clay, resulting in a naturally homogeneous blend. This cement was highly prized for its rapid-setting characteristics, making it particularly suitable for specialized construction tasks.⁵⁶ In 1824, artificial cement was developed by firing a mixture of limestone and clay,⁵⁶ mimicking the mineralogical composition of marl. To regulate and extend the setting time, gypsum was incorporated into the mixture, an innovation that ultimately led to the development of what is now known as Portland cement (PC). The calcined blend of limestone and clay forms clinker, the primary intermediate product in this manufacturing process.

As environmental awareness has grown, so too has concern over the environmental footprint of PC production. Producing one ton of ordinary Portland cement (OPC) consumes approximately 4750 MJ of energy and releases around 832 kg of CO₂.⁵⁷ These emissions predominantly stem from the clinkerization process, where limestone is calcined at high temperatures, as well as from electricity-intensive grinding operations and transportation of raw materials. A breakdown of the relative contributions of these processes to total energy consumption and CO₂ emissions is illustrated in Figure 4.

Figure 4.

Contribution of individual processes to (a) total energy consumption and (b) total CO₂ emissions per ton of Portland cement produced.

As a fundamental pillar of global infrastructure, the cement industry is under significant burden for its carbon footprint, contributing 7–8% of worldwide anthropogenic CO₂ emissions.⁵⁸ To reduce energy consumption and emissions in cement manufacturing, industrial byproducts such as slag, biomass ash, and silica dust are being employed, along with alternative clays and minerals, to mitigate the depletion of kaolinite reserves.^59–61 Studies on eco-friendly cement formulations have demonstrated that LC³, employing abundant low-grade clays and limestone, can decrease emissions while ensuring strong structural performance.^62,63 Furthermore, the integration of organic and inorganic waste materials has demonstrated promising potential in enhancing the usability of lower-grade raw materials.⁵⁹

Innovations such as selective mining, resource mapping, and waste reduction improve kaolinite usage efficiency, while recycling concrete and byproducts reduces reliance on raw materials. Additionally, synthetic alternatives mimicking kaolinite offer a promising path for sustainable, high-quality cement production.⁶⁴

According to SRPS EN 197-1:2011⁶⁵ and SRPS EN 197-5:2021,⁶⁶ these materials can be officially added to cement in the following proportions: up to 95% by mass for granulated blast-furnace slag (CEM III), up to 35% for fly ash, and up to 10% for silica dust.

It is worth emphasizing that the incorporation of selected waste-derived materials can improve the mechanical performance of cementitious systems by improving packing density, promoting pozzolanic reactions, and refining microstructural characteristics.⁶⁷ Consequently, the pursuit of a sustainable alternative that significantly reduces clinker content without sacrificing performance remains ongoing. A promising solution is LC³ cement, composed of 50% clinker, 30% calcined clay, 15% limestone, and 5% gypsum.⁶² Notably, most clays with low carbonate content are capable of undergoing pozzolanic reactions.⁶⁸ Figure 5 illustrates the distinctions between the production processes of PC and LC³ cement.

Figure 5.

The production processes of Portland and LC³ cement (adapted from⁶⁹).

The production of LC³ cement requires approximately 2987 MJ of energy and results in the emission of around 559 kg of CO₂ per ton of cement.⁵⁷ These values account for the clinkerization process, the calcination of clay, electricity used for grinding, and the transportation of raw materials. The contribution of each of these processes to the total energy consumption and CO₂ emissions is illustrated in Figure 6.

Figure 6.

Contribution of individual processes to (a) total energy consumption and (b) total CO₂ emissions per ton of LC³ cement produced.

LC³ cement has a longer setting time compared to PC.⁷⁰ Nonetheless, when the same water-to-cement (w/c) ratio and cement content are applied, the mechanical properties of concrete produced with LC³ cement are on par with those made using PC. Moreover, the durability properties of LC³-based concrete are superior to those of PC-based concrete.⁷¹

Studies have also shown that the capital investment required to establish a new LC³ production plant is lower than that for an OPC plant of similar capacity.⁶² If limestone were also calcined in LC³ production, the mechanical properties would likely improve further, as a higher degree of calcination is generally associated with increased strength.⁵⁷ Despite its compelling environmental benefits and favorable mechanical performance, LC³ systems face several limitations that constrain their broader adoption. A key challenge lies in the variability of performance stemming from differences in the mineralogical composition and quality of available clays, which directly affect pozzolanic reactivity and strength development.⁷² The calcination process demands precise temperature control, as both over- and under-calcination can diminish reactivity and compromise binder efficiency.⁷³ Additionally, LC³-based concretes exhibit heightened sensitivity to curing conditions compared to traditional PC systems. Inadequate curing, particularly in dry or hot climates, can hinder strength gain and increase permeability due to the slower hydration kinetics of clinker and the pozzolanic reaction of calcined clay and limestone.⁷⁴ Geographic limitations in the availability of suitable kaolinitic clays, coupled with underdeveloped infrastructure for clay processing and quality assurance in certain regions, further restrict scalability.⁷⁵ From a regulatory standpoint, LC³ has yet to be fully integrated into many national and international cement standards, posing institutional barriers to widespread commercialization.⁷⁶ These technical, logistical, and policy-related constraints underscore the need for continued research, regional material optimization, and harmonized regulatory frameworks to support the successful implementation of LC³ as a viable low-carbon alternative to conventional PC (Table 2).

Table 2.

Comparison of kaolinite-based cement and LC³ cement.

Parameter	Kaolinite-based cement	LC³ cement
Compressive strength (MPa)	40–55 MPa at 28 days⁷⁷	Comparable or higher: 45–65 MPa at 28 days⁷⁸
Early strength development	Moderate⁷⁹	Enhanced due to the synergy of limestone and reactive clay⁸⁰
Durability	Prone to carbonation and chloride ingress⁸¹	Superior resistance to chloride penetration⁸²
Shrinkage	Moderate to high⁸³	Lower shrinkage due to the filler effect of limestone⁷⁰
CO₂ emissions	High (due to full clinker content)⁸⁴	Up to 40% reduction compared to OPC⁷⁰
Composition	Clinker + metakaolin + gypsum⁸⁵	Clinker + calcined clay + limestone + gypsum⁸⁵
Pozzolanic activity	Depends on the clay type and activation⁸⁶	Optimized with metakaolin-rich clays^72,73
Production cost and environmental burden	Higher production cost and significant environmental impact due to high energy input and clinker content⁸⁷	Lower cost and reduced environmental footprint owing to partial clinker replacement and lower calcination temperatures⁸⁸

Calcined clay and limestone can be incorporated directly into cement or added separately to concrete mixtures. Research⁸⁹ revealed that substituting PC with a blend of calcined clay and limestone (maintaining a 2:1 ratio) at replacement levels of 30% and 45% effectively reduces both autogenous and drying shrinkage, while preserving compressive strength. This blend also significantly enhances the concrete durability. Furthermore, partial replacement of PC with 10% calcined palygorskite or kaolinite has demonstrated notable effects on compressive strength. Strength gains were observed with palygorskite calcined at 800 °C, whereas kaolinite proved effective even at 600 °C, with performance improving as calcination temperature increased.⁹⁰ In this context, kaolin exhibited superior pozzolanic activity at lower temperatures compared to palygorskite, likely due to its transformation into metakaolin, a well-established concrete additive. Metakaolin is known to enhance compressive strength when used to replace up to 15% of the cement mass,⁹¹ with its optimal transformation occurring within the 450–850 °C temperature range.⁹²

The geopolymerization process presents a sustainable and innovative alternative to conventional cement production.⁹³ It involves the chemical activation of aluminosilicate-rich materials, using alkaline solutions, resulting in the formation of geopolymer binders characterized by a three-dimensional silico-aluminate network. Unlike traditional cement manufacturing, this process operates at substantially lower temperatures, thereby reducing energy consumption and minimizing carbon dioxide emissions.⁹⁴ Geopolymer cements exhibit excellent mechanical strength, long-term durability, and resistance to chemical attack, making them well-suited for a wide range of construction applications. By mitigating the environmental impact of PC, geopolymer technology offers a promising pathway toward more sustainable infrastructure development.⁹⁵

Despite their low carbon footprint and high early strength, geopolymers face several critical limitations that impede their large-scale adoption in the construction industry. A key economic challenge in geopolymer production lies in the high cost of alkali activators, particularly sodium silicate and sodium hydroxide, which can account for up to 50% of the total binder cost. This significantly undermines the cost competitiveness of geopolymers relative to OPC.⁹⁶ In addition, while geopolymers exhibit excellent durability in controlled laboratory settings, their long-term performance under real-world environmental conditions (such as freeze-thaw cycles, carbonation, and chloride penetration) remains uncertain and often inconsistent.⁹⁷ These concerns raise questions about their suitability in aggressive or variable climates. Furthermore, the absence of unified international standards for geopolymer composition, testing, and structural design continues to hinder their acceptance in mainstream construction practices.⁹⁸ Without clear regulatory pathways, design codes, and performance benchmarks, geopolymers remain largely confined to niche applications or research environments. Addressing these technical, economic, and institutional barriers is essential for the broader deployment of geopolymer technology in sustainable infrastructure.

In summary, while LC³ cement and geopolymer systems offer promising pathways for low-carbon construction, their implementation is far from universally optimized. LC³ formulations, for instance, are highly sensitive to the quality and reactivity of calcined clays, the proportioning of limestone, and the fineness of grinding—all of which can vary considerably across production sites. Beyond laboratory validation, achieving consistent field performance hinges on precise mix design and tightly controlled curing environments. In resource-constrained settings, these requirements may hinder scalability or compromise mechanical reliability.

Similarly, the practical deployment of geopolymers faces challenges stemming from the variability of precursor materials such as fly ash and metakaolin, which often exhibit heterogeneity in amorphous phase content and elemental composition. These inconsistencies can significantly influence reactivity and binder performance. Moreover, the alkali activation process requires stringent control over pH levels and curing conditions, which may not be compatible with standard infrastructure workflows. This is particularly problematic in cold climates or high-humidity environments, where achieving optimal curing parameters becomes more complex and less predictable. Both systems also face economic hurdles. LC³ production requires new grinding configurations and quality control for clay beneficiation, while geopolymer technology remains commercially fragmented, with limited standardized testing and certification pathways. These barriers underscore the need for sector-specific feasibility studies before asserting general superiority.

Clay-Based alternatives in road applications

In geotechnical applications, clay-rich soils—even those with inconsistent mineralogy—are used for subbase stabilization and slope support when modified with lime, cement, or supplementary additives. Lower-grade clays, when properly blended and cured, may be used for road construction and geotechnical applications. Applications in road foundations and landfill liners benefit significantly from the low permeability and high shear strength of geopolymer binders, which enhance structural integrity and reduce the risk of leachate migration or subgrade failure. For instance, montmorillonite clayey soils incorporating fly ash and rice husk ash activated by sodium hydroxide (NaOH) to form geopolymer up to their respective optimal contents significantly enhance all their mechanical properties.⁹⁹

As a foundational activity within civil engineering, road construction has historically depended on the extensive consumption of natural resources, including aggregates, water, and energy-intensive materials, contributing to environmental degradation and resource depletion. Each day, significant volumes of materials are employed to develop new transportation routes and to rehabilitate or maintain existing infrastructure. In regions where low-bearing capacity soils are naturally present at construction sites, these can be stabilized to meet the structural requirements of road sub-base layers.^100–103 Among these materials, kaolin clay plays a vital role in the construction of pavement and base layers, serving as a locally available resource with promising potential for infrastructural applications (Figure 7). During road construction, it is common to encounter native soils with insufficient low-bearing capacity, rendering them unsuitable for base and subbase applications. A widely adopted solution in soil stabilization, whereby various binders are introduced to alter the mechanical behavior of natural soils. Finely powdered kaolin has proven to be an effective stabilizer for lateritic soils,¹⁰⁴ which are typically unsuitable for road infrastructure. When used with clay-rich soils, kaolin clay enhances unconfined compressive strength (UCS) compared to unstabilized samples, while also boosting overall bearing capacity and mitigating shrinkage-swelling issues frequently encountered in clays from cold climate regions.¹⁰⁵ Furthermore, kaolin clay has demonstrated its potential as an effective stabilizing agent for lateritic soils by reducing the plasticity index (PI) and enhancing both strength and moisture resistance. These improvements support its use either as a standalone stabilizer or in combination with cement-based binders.¹⁰⁶ When nanostructured kaolin is combined with cement, it significantly increases the California bearing ratio (CBR) of lateritic soils,¹⁰⁷ offering an additional indicator of improved load-bearing performance.

In 2023, Europe produced 269 million tonnes of asphalt, making it the most commonly used material for paving.¹⁰⁸ During the asphalt mix production, natural kaolin may be used in various particle sizes and for different purposes. Silica sand, generated as a byproduct of kaolin mining or beneficiation processes,¹⁰⁹ can be repurposed as a fine aggregate in the production of hot mix asphalt.¹¹⁰ Adding dehydroxylated kaolin (metakaolin) in the shares from 0% to 10% of the fine aggregate’s weight enhances the stiffness of hot mix asphalt mixtures.¹¹¹ Nano clay, particularly nano kaolin, is widely regarded as the most prevalent nanomaterial for modifying bituminous materials due to its cost-effectiveness and natural abundance. It shows great potential for enhancing the physical and rheological properties of the modified binder under both unaged and aged conditions.¹¹² The incorporation of bitumen as a binder in asphalt mix production notably enhances rutting resistance, with an optimal dosage of 5% yielding the most effective performance improvements.¹¹² However, the asphalt industry remains one of the most environmentally intensive sectors, primarily due to its high energy demands and extensive consumption of natural aggregates. A promising strategy to mitigate this environmental footprint is the adoption of warm mix asphalt (WMA) technology, which enables production at lower temperatures and reduces energy use. The addition of nano-sized kaolinite to WMA has been shown to further improve its mechanical properties, reducing Marshall flow and rutting depth while significantly increasing indirect tensile strength, Marshall stability, and compressive strength. These enhancements position nano-kaolinite-modified WMA as a more sustainable and high-performance alternative for pavement applications.

Besides its various uses in the asphalt industry, kaolin is often implemented for rigid pavement construction, i.e., in concrete for paving purposes. In addition to the previously discussed applications of kaolin in structural concrete, metakaolin, when used as a partial replacement for cement in polymer concrete, accelerates setting time compared to conventional cement pastes. However, this modification tends to reduce workability while enhancing compressive strength.¹¹³ Pervious concrete, as a modern and innovative paving material with increasing application, can also be produced with kaolin as a supplementary cementitious material (SCM). In fiber-reinforced pervious concrete, increasing fiber content beyond 10% may enhance compressive strength, but it is not recommended when aiming to improve split tensile strength.¹¹⁴

Finally, kaolin is a versatile and valuable material in road construction, with applications spanning all phases—from subgrade stabilization and base layers to surface treatments and finishing. However, sustainability is one of the primary goals in road construction development, and reducing the usage of natural materials is one of the most intensive activities. Although the use of kaolin itself promotes sustainability in road construction (using it as a binder it is possible to use materials that would otherwise have unfavorable properties), reducing the use of kaolin in the road construction sector can be desirable for cost savings, sustainability, or to improve performance depending on the application (e.g., as a filler asphalt mix, in cement, for soil stabilization, etc.). There are several practical strategies to reduce its use (Figure 8): (a) using alternative, sustainable materials that have similar or better properties (fly ash¹¹⁵ (1) of ground granulated blast furnace slag¹¹⁶ as a binder in soil stabilization, using geopolymers as a binder in pavement base layers,¹¹⁷ using different kind of waste materials as a filler in asphalt¹¹⁸; (b) optimizing mix design to reduce filler demand to determine the ideal blend of aggregates and binder in asphalt¹¹⁹ and (c) updating design and procurement standards to allow or encourage the use of alternative materials over kaolin. Among various stabilization strategies, the use of alternative binders such as LC³ cement emerges as the most promising. Experimental results indicate that LC³-stabilized clay soil exhibits mechanical performance comparable to that of Ordinary Portland Cement (OPC).¹²⁰ Furthermore, estimates presented in¹²¹ suggest that substituting OPC with LC³ for the expansive subgrade of a 1-km two-lane road could yield substantial environmental benefits, saving approximately 350 GJ of thermal energy, 12594 kWh of electrical energy, and CO₂ emissions by around 2740 kg of carbon.

Shared strategies and implementation constraints

Across applications, the strategic use of lower-grade clays aligns with the goals of resource conservation, local material valorization, and circular design. However, successful implementation depends on:

Material Characterization: Variability in mineralogy and reactivity requires advanced mapping and consistent quality control,

Processing Adaptations: Firing adjustments, additive blending, and refining steps are often necessary to meet industrial thresholds,

Design Compatibility: Performance metrics—such as thermal expansion, shrinkage, and mechanical strength—must align with end-use requirements, and

Infrastructure and Cost: Decentralized clay sources may face transport, processing, and scalability challenges that affect industrial uptake.

Figure 7.

Kaolin's role in promoting sustainable road and pavement construction practices.

Figure 8.

Kaolin's role in promoting sustainable road and pavement construction practices.

A unified framework for testing and benchmarking properties across different clay grades could accelerate their integration, ensuring performance without compromising design standards.

The industries are actively striving to optimize energy consumption across production processes to reduce both environmental impact and operational costs. An additional focus lies in recycling and reusing materials to establish a closed-loop system, reducing waste and limiting resource extraction. These approaches underscore the industry's dedication to sustainability while tackling the challenges of resource depletion (Figure 9). To address the environmental impact of clay mining, various sustainable practices are being explored:

Post-extraction recultivation initiatives are crucial for restoring ecological balance. Case studies from various countries demonstrate successful reclamation practices, turning abandoned extraction sites into arable land or natural habitats²⁵; and

The ceramics and cement industries are actively pursuing methods to recycle waste materials. Incorporating fly ash, slag, or other industrial byproducts can reduce dependence on virgin raw materials while lowering greenhouse gas emissions.^122,123

Figure 9.

Shared improvement strategies from the cement and ceramic industry.

The ceramic and cement industries are experiencing a significant transformation as they face the twin challenges of depleting high-quality kaolinite reserves and increasing environmental demands.¹²⁴ In response, both sectors are pioneering innovative approaches that not only address resource scarcity but also significantly reduce ecological footprints. These efforts span material science breakthroughs, process optimizations, and systemic changes in production paradigms, reflecting a growing commitment to sustainability.

While the road pavement, ceramic, and cement industries have distinct operational frameworks, they share common challenges and are adopting overlapping strategies to promote sustainability. Energy efficiency stands out as a critical focus area, with the building materials production sectors investing in waste heat recovery systems to harness and reuse thermal energy from kilns, achieving efficiency gains of up to 30%.¹²⁵ Incorporating renewable energy sources such as solar and wind power into manufacturing operations represents a collaborative effort to decrease dependence on fossil fuels and curb greenhouse gas emissions.¹²⁶

Land restoration and recultivation efforts are also gaining traction as industries acknowledge the long-term environmental consequences of clay extraction. Abandoned mining sites, once barren and ecologically degraded, are being rehabilitated into productive landscapes. In the UK, for example, former kaolin mines have been transformed into thriving nature reserves, supporting biodiversity and serving as models for sustainable land management.¹²⁷ Techniques like phytoremediation, which involves planting native vegetation to restore soil health, and the construction of sedimentation ponds to prevent water contamination, are becoming standard practices in post-mining rehabilitation.

Circular economy principles are further unifying the industries, with material recycling emerging as a cornerstone of sustainable production (Figure 9). Demolition waste, including crushed concrete and ceramic fragments, is being repurposed in new manufacturing cycles, closing the loop on resource use.¹²⁸ Collaborative supply chains are also forming, enabling industries to share waste streams, such as using ceramic waste in cement formulations, thereby minimizing waste and maximizing resource efficiency. These shared strategies highlight a collective commitment to sustainability, driven by innovation and cross-sector collaboration.

The shared strategies across the ceramic, cement, and road construction industries underscore a paradigm shift toward systemic sustainability. The proposed innovations, such as geopolymerization and LC³ cement, offer distinct advantages over traditional methods by leveraging industrial byproducts (e.g., fly ash, slag) and low-grade clays to create high-performance materials with a minimal environmental footprint. Geopolymer binders, for instance, eliminate the need for high-temperature kilns entirely, reducing energy consumption by up to 60% and CO₂ emissions by 80% compared to conventional cement.^129,130 These advancements are not merely incremental improvements but transformative solutions that decouple material performance from resource intensity. The cross-industry adoption of these practices—such as using ceramic waste in concrete¹³¹ or repurposing mining byproducts for road stabilization¹³²—demonstrates their versatility and scalability. By prioritizing circularity, these models reduce landfill burdens, lower extraction pressures, and create synergies between sectors, fostering a collaborative ecosystem for sustainable development. The added value lies in their ability to meet stringent performance standards while advancing the UN Sustainable Development Goals (SDGs), particularly SDG 9 (Industry, Innovation, and Infrastructure) and SDG 12 (Responsible Consumption and Production).

Geopolymerization is another key area of innovation, initially driven by the cement and mortar industries, and later adopted by the road construction and ceramics sectors to advance their own technologies.

Conclusions

The exploration of lower-quality clays as alternative raw materials in the construction materials sector presents a compelling opportunity to enhance sustainability, reduce environmental impact, and diversify resource streams. As demonstrated in the comparative tables, these clays—often sourced from mining tailings, agricultural residues, or underutilized geological deposits—exhibit sufficient pozzolanic activity and compatibility with blended cement systems, particularly when processed appropriately. Their integration into formulations such as LC³ cement or geopolymer binders can significantly lower CO₂ emissions and reduce reliance on high-grade kaolinitic clays.

However, several barriers hinder widespread adoption. Technically, variability in mineral composition and reactivity demands tailored processing and quality control protocols, which may not be feasible for all production scales. Logistically, the decentralized nature of these resources complicates supply chain integration. Moreover, the lack of standardized testing frameworks and performance benchmarks for these materials creates uncertainty for manufacturers and regulators alike.

Policy-making plays a pivotal role in overcoming these challenges. Incentivizing the use of marginal clays through regulatory frameworks, subsidies, and inclusion in public procurement standards can accelerate industrial uptake. Establishing certification pathways and supporting regional mapping of clay deposits would further enable informed decision-making and resource planning. Looking ahead, future research should focus on:

Developing robust characterization methods for heterogeneous clay sources.

Creating adaptable processing technologies that can accommodate mineralogical variability.

Integrating digital tools such as soft sensors and digital twins to optimize material performance and lifecycle assessment.

Fostering interdisciplinary collaboration between geologists, material scientists, and policy experts to align technical innovation with regulatory evolution.

By addressing both the technical and institutional dimensions, the construction sector can unlock the latent potential of lower-quality clays—transforming what was once considered waste into a cornerstone of sustainable infrastructure.

Footnotes

ORCID iDs

Milica Vasić

Ivanka Netinger Grubeša

Paul Awoyera

Author contributions

Conceptualization, M.V.V, I.B, P.A, and I.N.G.; methodology, M.V.V, I.B, and I.N.G.; writing—original draft preparation, M.V.V, I.B, P.A, and I.N.G.; writing—review and editing, M.V.V, I.B, P.A, and I.N.G.; visualization, M.V.V, I.B, and I.N.G. All authors have read and agreed to the published version of the manuscript.

Funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This research was funded by the Ministry of Science, Technological Development and Innovation of the Republic of Serbia (Contract number 451-03-136/2025-03/ 200012). This study was funded under “Circular Economy in the Construction Industry,” financed by the University North, Croatia.

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Data availability statement

The data reported in this review paper are available in the cited references.

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Clays in transition: Addressing resource challenges and sustainable innovations in the construction sector

Abstract

Keywords

Introduction

Resource challenges

Industrial applications of alternative and lower-grade clays

Ceramic industry

Binder systems in construction

Clay-Based alternatives in road applications

Shared strategies and implementation constraints

Conclusions

Footnotes

ORCID iDs

Author contributions

Funding

Declaration of conflicting interests

Data availability statement

References