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Review

Alkali-Activated and Geopolymer Systems Through the Lens of Resource Efficiency

by
Nilofar Asim
1,*,
Marzieh Badiei
2 and
Khadijehbeigom Ghoreishi
1
1
Centre for Applied Science and Primary Industries, Wintec, Hamilton 3240, New Zealand
2
Independent Researcher, Mashhad 91777-35843, Iran
*
Author to whom correspondence should be addressed.
Resources 2026, 15(5), 66; https://doi.org/10.3390/resources15050066
Submission received: 17 March 2026 / Revised: 1 May 2026 / Accepted: 5 May 2026 / Published: 8 May 2026
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Abstract

Although geopolymer and alkali-activated binders are promoted as low-carbon OPC alternatives, their resource-centric performance remains complex and geographically dependent. This review examines these systems from a resource-efficiency perspective and evaluates alkaline activator demand; precursor availability, including fly ash, slag, calcined clays, and mining residues; and embodied energy across mix designs and curing regimes. Recent mechanical and durability analyses, together with life cycle assessments, reveal important trade-offs in alkali-activated geopolymer systems. Customized precursors may unintentionally compromise their inherent resource efficiency, while the declining availability of industrial waste increasingly competes with alternative waste valorization processes. Developing one-part activator systems and implementing data- or machine-optimized mix designs capable of handling extremely highly variable waste streams will be necessary to achieve meaningful reductions in mineral consumption, energy demand, and emissions. The study reframes these binders as enablers of urban mining and industrial symbiosis. Policy changes toward resource-oriented governance, including performance-based standards, carbon-responsive procurement, and more transparent end-of-waste legislation, are also needed to promote a circular material economy. Strategic, large-scale deployment requires the integration of regional resource mapping with predictive performance modeling to navigate resource constraints in the construction sector.

1. Introduction

Since the construction industry has a major impact on energy consumption, greenhouse gas emissions, and extraction of raw materials, alternative binder systems that support circular resource strategies are needed [1,2]. Among these, alkali-activated geopolymer technology is becoming increasingly popular as an efficient way to develop more environmentally friendly building materials [3,4,5,6,7].
Waste management has frequently been considered a secondary benefit of conventional sustainable material techniques, which have primarily focused on enhancing performance and reducing carbon emissions [8]. However, from a resource-centric perspective, alkali-activated and geopolymer systems are viewed as integrated resource management technologies with the ability to change industrial material cycles, not just as alternatives to OPC [9,10,11]. Alkali-activated geopolymers are low-carbon aluminosilicate binders that are produced by chemically activating precursors rich in silica and alumina using alkaline solutions.
Although the durability and mechanical performance of the alkali-activated materials and geopolymers have been widely demonstrated, a systematic evaluation from a resource-centric perspective still remains underdeveloped.
Alkali-activated geopolymers are synthesized through dissolution-polycondensation reactions, forming binding phases such as the calcium-aluminosilicate-hydrate (C-A-S-H) or sodium-aluminosilicate-hydrate (N-A-S-H) gels, depending on the composition of the activator and the chemistry of the precursor [12,13]. These systems provide greater thermal stability, increased resistance to chemical degradation, and compressive strengths that are on par with ordinary Portland cement. However, their greater strategic potential lies in their ability to integrate a variety of secondary resources as functional components, as well as in performance metrics [14,15].
Fly ash and ground granulated blast furnace slag (GGBS) have historically dominated the precursor landscape because of their availability and reactivity [16]. However, these byproduct streams have gradually decreased as a result of the continuous decarbonization in the metallurgical and energy sectors, which has limited the traditional alkali-activated geopolymer supply chains [17]. Diversification toward other aluminosilicate sources, such as the calcined clays, mining wastes, waste glass, biomass ash, and construction and demolition waste, is becoming more crucial for maintaining the progress [6,18,19,20,21].
The significant physicochemical heterogeneity of these alternative feedstocks has a direct impact on the reaction routes, gel chemistry, dissolution kinetics, and long-term durability. Therefore, rather than simply making the material substitutions, precursor selection and mixture design must be considered as linked resource-reaction optimization challenges.
The alkali-activated geopolymers serve as platforms for the material valorization within the larger industrial networks under this resource-centric framework. In a multi-criteria optimization space that includes durability, mechanical performance, environmental effects, energy use, and economic feasibility, precursor sourcing, activation chemistry, and processing methods become interdependent variables [17].
The diversity of secondary resources creates opportunities for industrial symbiosis and the development of geographically tailored formulations, but it also presents obstacles, especially with regard to supply chain consistency, regulatory approval, and compositional uncertainty. However, the use of these systems is limited by the current prescriptive criteria for cementitious materials. Therefore, it is crucial to advance the data-driven mix design frameworks and performance-based standards in order to facilitate the flexible use of a variety of precursors.
The thermodynamic modeling and machine learning-assisted mixture optimization are two emerging computational methods that show promise for accelerating the systematic resource integration [22,23,24]. Figure 1 presents the development process for geopolymer cement.
Using a resource-centric approach, this study examines the trends in precursor availability, chemical reactivity, sustainability implications, and system integration challenges to provide current insights into the alkali-activated and geopolymer systems. Unlike most reviews that focus mainly on the performance or emissions reduction, this review integrates resource availability, activator burden, regional constraints, and life-cycle implications to address a gap in the literature. This perspective reframes these materials as components of infrastructure for the circulation of resources rather than just as low-carbon substitutes for cement.

2. Materials and Methods

The Elicit platform, created by Ought, Inc., was used for the literature search and data extraction in this review using the following process: (1) To find the relevant papers from Elicit’s database of more than 125 million academic articles, a research question was entered into its semantic search system; (2) topical alignment, rather than simple keyword matching, was used by Elicit’s transformer-based relevance classification model to rank the papers; (3) the most important papers were evaluated according to the inclusion/exclusion criteria for the review; (4) key data points (such as sample kinds, results, and methodology details) were systematically extracted from the chosen studies using Elicit’s data extraction feature; and (5) all AI-generated claims were checked against the original source papers, and the authors manually reviewed and edited all extracted content before it was included in the manuscript.
This review does not represent a complete quantitative meta-analysis and is limited by the variations in the study quality, methodology, and regional context.

3. Principles of a Resource-Centric Perspective

3.1. Limitations of Purely Chemistry or Performance-Based Classifications

Available studies do not particularly address the limitations of classifying the alkali-activated geopolymer-based solely on chemistry or performance. However, based on the more general issues discussed in the literature, a number of important limitations can be determined. According to Kriven et al. [17], the wide variety of precursors and their complicated chemistry significantly affect the technical performance of geopolymers and alkali-activated products, indicating that classifications based only on chemistry would not properly reflect this complexity.
They observed that when working with new waste materials, each system requires a systematic study to understand its chemistry, including long-term durability.
This suggests that knowledge from the well-studied precursors cannot be directly applied to new systems. According to the studies, present classification methods have a number of unacknowledged drawbacks.
Constraint on resource availability: Since the traditional precursors gradually run out, classifications based on the specific chemical compositions may become out of date due to the limited and decreasing availability of certain precursors, particularly the furnace slag and coal fly ash in some regions [17].
Performance variability: Waste materials can significantly vary in their properties, particularly those from different sources or seasons, which makes performance-based classifications difficult because of their inconsistent properties [17].
Regulatory barriers: Studies show that market needs are not sufficiently met by the current classification systems [26]. According to Kriven et al. [17], alkali-activated geopolymers have not fallen within the scope of harmonized standards (hEN) so far, indicating that the current classification systems are insufficient for regulatory approval.
Nevertheless, the available literature does not fully address the different theoretical or practical limitations of the classification systems based on chemistry versus performance. Further research on the classification techniques is required for an in-depth study of this issue.

3.2. Circular Economy, Waste Valorization, and Regional Resource Contexts

Alkali-activated geopolymer exhibits strong integration across multiple dimensions with waste valorization, circular economy concepts, and regional resource utilization [18,27,28].
Considering the tremendous amount of globally produced solid waste [1] and the critical need for waste valorization, the utilization of various solid wastes in the production of alkali-activated geopolymer and the reduction of 35–50% of resource consumption in the construction industry are perfectly aligned with the circular economy principles [8,29].
Waste materials (natural or industrial) [30] can be valorized differently, such as an inert filler, a reactive material, or a supplier of alkali [31]. Meanwhile, geopolymerization can be used for the toxic waste immobilization applications [32,33,34,35,36].
Studies have found that not only does the precursor availability vary geographically (such as blast furnace slag and coal fly ash) [17], but also their properties depend on the geographical location and the season [30]. The findings reveal that regional variations significantly affect the implementation methods.

3.3. Reframing Alkali-Activated Geopolymer Systems as Resource-Management Technologies

Alkali-activated and geopolymer systems should be viewed not only as alternative binder materials but also as comprehensive resource-management technologies. Recent studies emphasize the need for a conceptual and terminological reclassification to better reflect their exceptional recycling potential and wider industrial relevance [1].
These materials enable the large-scale incorporation of industrial byproducts, positioning them as active agents in waste valorization rather than passive construction materials.
Beyond their structural role, alkali-activated geopolymers serve as versatile chemical platforms capable of processing diverse waste resources. Their reactive matrices can immobilize, consolidate, and stabilize hazardous or complex residues by functioning as reactive precursors, inert fillers, or alkali suppliers [31,32]. This multi-functionality expands their significance from material performance to secondary resource utilization and environmental remediation.
Economically, alkali activation facilitates the upgrading of low- or negative-value wastes, transforming the landfill-bound materials into marketable products, sometimes even into high-value functional materials [14,17].
Meanwhile, these materials exhibit remarkable adaptability, finding use in diverse fields such as membrane technology, water treatment, catalysis, and specialty functional applications [14,15,37].
Importantly, through tailored processing strategies, alkali-activated systems contribute to the strategic resource security by enabling the utilization of precursors with the limited availability or complex compositions [17]. All of this evidence supports interpreting alkali-activated and geopolymer systems as integrated platforms for resource valorization, in which binding is one among several functional outcomes, rather than as binders that incidentally consume waste materials.

4. Precursor Resources

From a resource-centric perspective, precursor resources provide critical insights into how industrial byproducts can be classified and leveraged for alkali-activated and geopolymer systems. This perspective emphasizes not only the opportunities these materials offer in terms of sustainability and circularity but also the challenges associated with their variability, supply dynamics, and integration into established production systems.
Table 1 demonstrates the relationship between precursors’ and activators’ technical characteristics and their environmental performance and strategic challenges for resource-centric assessment.
This evolution reflects the broader industrial shift toward resource diversification and the valorization of secondary materials within low-carbon construction frameworks.
Although the studies offer significant insights into compositional characteristics and final material characteristics, they only provide specific limited compositional fingerprints for the detailed oxide-balance data (SiO2-Al2O3-CaO-Fe2O3-alkalis) for different resource categories (Table 2).
Conventional liquid activators [51] are a critical resource limitation in alkali-activated geopolymer systems, sometimes overshadowing the sustainability benefits of employing waste precursors, with significant resource and life cycle inventory (LCI) impacts. Table 3 presents a summary of the conventional liquid activators (NaOH, KOH, and sodium silicate) and their resource/LCI implications.

5. Resource Availability, Logistics, and Regionalization

The long-term sustainability of cement alternatives depends on the ability to navigate the complex and often unpredictable nature of seasonal and geographical resource availability. Alkali-activated and geopolymer systems, in particular, rely on the secondary materials whose supply is influenced by industrial cycles, regional infrastructure, and shifting environmental regulations.
Regarding temporal mismatch and resource transitions, conventional industrial byproducts such as steel slag and coal ash are decreasing as a result of the world’s transition to green energy [17]. As a result, there is a temporal mismatch whereby established waste streams are disappearing while geopolymer technology is preparing for expansion. Figure 2 presents the shift from conventional precursors to emerging waste-based resources and the need to adapt to supply limitations.
This shift highlights the importance of regional resource mapping, one-part systems, and AI-assisted mix design for sustainable implementation.
In order to make up for the loss of traditional minerals during the transition to underutilized resources, research is turning to readily available mine tailings that contain aluminosilicate and other locally generated industrial wastes [17].
Furthermore, the importance of regionalization is clear, since the sustainability of the system depends significantly on regional constraints on the supply of the byproducts. Since transportation distances can significantly affect the final energy and carbon footprint, sources that provide comprehensive regional resource assessments are needed to ensure that the materials are provided locally [17,30,47].
Finally, one of the main challenges lies in the management of the strategic material flows, which requires an understanding of the long-term evolution of the industrial byproduct streams and their potential competition with alternative valorization routes.
To preserve the net environmental advantages of these binders in a resource-constrained sector, it is essential to adopt the system-level modeling frameworks and region-specific resource strategies [8,17,22].
The ongoing reduction in the conventional feedstocks calls for a transition toward locally available precursors, including mine tailings, natural or calcined clays, and construction and demolition waste. However, this shift requires careful balance, since the environmental benefits of alternative materials can differ due to the energy-intensive pre-processing or long-distance transport. Achieving sustainability; therefore, requires moving beyond a one-size-fits-all approach toward a model that aligns regional geological resources with the tailored processing technologies optimized for the local conditions.

6. Environmental and Circularity Assessment of Resource Pathways

Evaluating the sustainability of the alkali-activated and geopolymer systems requires a comprehensive environmental and circularity assessment, integrating life cycle assessment (LCA) data with an analysis of the trade-offs among the competing material options [56,57,58,59,60,61]. Such assessment frameworks help to clarify how the resource pathways influence overall carbon savings, energy efficiency, and material circularity, providing a basis for making informed decisions on precursor selection and process optimization.
In comparison with the ordinary Portland cement, industrial byproducts continuously provide the greatest environmental benefits due to their lower CO2 equivalent emissions and lower energy usage [2].
However, natural materials like metakaolin require energy-intensive thermal pretreatment (calcination), which greatly increases their carbon footprint and can even surpass the OPC criteria.
In the life cycle assessment of alkali-activated geopolymer, the alkaline activator is a crucial factor. Sodium silicate, or water glass, is frequently the main source of a system’s global warming potential (GWP).
Based on the studies, the important strategic concepts include the activator factor, in which the choice of the activator often has a greater impact on the environment than the precursor.
Regarding hybrid solutions, a rational combination of high-reactivity precursors (such as metakaolin) and low-grade, waste-derived sources is recommended to combine the mechanical performance with sustainability.
Furthermore, regionality plays a critical role, as the local energy grid and the transportation distances of the precursors and activators have a significant impact on the LCA results.
Ultimately, the findings show that significant circular economy value can be generated by adopting the alkali-activated geopolymer systems, whereby the low-value materials (caused by landfill taxes) can be upgraded into high-value construction materials [1,8,17,28,62].
After discussing resource availability and environmental trade-offs, the following section focuses on how precursor chemistry affects performance characteristics and offers systematic strategies to transform variable waste streams into high-performance materials.

7. Resource-Sensitive Performance and Adaptive Design Strategies

7.1. Mechanical Performance

The mechanical properties of alkali-activated and geopolymer binders vary considerably depending on the precursor family and the blending strategy adopted. Differences in the reactivity, particle morphology, and calcium-aluminosilicate composition of the raw materials control the formation and structure of the binding gels, which determine the compressive strength development, fracture behavior, and long-term stability.

7.1.1. Mechanical Performance by Precursor Class

Alkali-activated geopolymer systems’ performance is associated with the characteristics of the resource classes they originate from. Variations in the precursors’ chemistry, mineralogy, and physical quality directly influence the resulting materials’ mechanical strength, durability, and workability. Understanding these relationships is critical for designing mixtures that combine optimal performance with sustainable resource utilization.
Regarding industrial byproducts, the compressive strength range of these systems is typically between 30 and 80 MPa. Due to the rapid formation of the C-A-S-H gels, slag-based systems specifically achieve an early-age strength that is about 30% higher than that in fly ash systems [8,22,63].
In the case of natural precursors, because of their high reactive alumina content and enhanced pozzolanic activity after the thermal treatment, metakaolin-blended geopolymers show significantly higher compressive strength than the fly ash-only systems [17,22].

7.1.2. Role of Blending on Mechanical Properties

Furthermore, a blended system allows for the optimization of Si/Al and Ca/Si ratios through the systematic combination of high-reactivity precursors (such as metakaolin) with supplementary waste materials like slag or red mud, thereby balancing the high mechanical performance with sustainability goals [22].

7.1.3. Processability, Curing, and Application Modes

Finally, although emerging and alternative precursors offer special advantages, such as maintaining over 90% compressive strength at 250 °C, they often lack the sufficient reactive alumina to form a stable framework; consequently, co-precursors such as fly ash, metakaolin, or calcium sulfoaluminate cement are required [22].
The transition to waste-derived systems presents important chemical and mineralogical complications absent from the traditional binders. Each new waste stream must be thoroughly studied in order to fully understand its unique reaction kinetics and long-term durability, as these materials differ depending on the season and geographic location.

7.2. Resource-Sensitive Durability Issues

7.2.1. Carbonation Resistance

It is known that durability is a variable that is significantly influenced by the precursors’ and activators’ chemical composition. Regarding carbonation, because high-alkali systems are especially dependent on the relatively high rates of carbonation, this is an important challenge for the alkali-activated geopolymer systems [17].

7.2.2. Alkali-Silica Reaction and Leaching

Similarly, the sensitivity to the alkali-silica reaction (ASR) is significantly increased when the reactive aggregates and high-alkali activators are combined [22].
Leaching is also a critical factor because some of the compounds in the waste-derived precursors leach easily under the exceptionally alkaline conditions, and even the materials that are considered inert may exceed the regulatory limits if activated [17].

7.2.3. Chemical Resistance and Long-Term Stability

Finally, in terms of chemical resistance, improvement of the N-A-S-H network through optimized molar ratios can reduce pore connectivity and greatly increase the resistance to acid corrosion and sulfate attack [17,22].
Instead of addressing the sustainability and structural performance as separate goals, the study by Sri Mohan Kumar et al. [22] highlights a shift toward the predictive durability assessment.
Researchers may simultaneously anticipate a material’s carbon footprint and structural durability by utilizing the AI-enhanced life cycle assessment and merging the traditional LCA with the real-time durability data.
Durability, on the other hand, is based on the resource chemistry rather than only on the physical strength. Chemical breakdown or corrosion are examples of degradation that frequently result directly from the specific precursors (raw materials) used in the mixture.
Developers can pre-calculate how various chemical mixtures will behave over the decades by using predictive models. This prevents the early failure of a low-carbon material selection, which would result in higher environmental costs for the replacement or repair of the material.

7.3. Processability and Applications

7.3.1. In Situ Versus Precast Applications

The resource and precursors are responsible for the alkali-activated geopolymer processability and applications. Regarding the in situ versus precast applications, to speed up the strength development, precast elements frequently use the fly ash-slag blends and high-temperature curing (60–80 °C).
On the other hand, ambient curing is preferred in in situ applications, requiring careful control of the activator concentrations to allow for slower reaction kinetics [17,22].

7.3.2. 3D Printing and Rheological Control

Furthermore, in the context of 3D printing, precise rheological control is necessary for this new application. In order to ensure that the material is printable, the activator concentration and temperature must be precisely controlled to modify the workability and setting times [17,22,52].

7.3.3. Repair Mortars and Curing Requirements

Additionally, for the repair mortars, alkali-activated systems’ rapid setting time and excellent chemical resistance make them ideal for repairing infrastructure (like the sewage tubes) [17].
Finally, regarding the curing requirements, in contrast to the acid-activated (ASP) systems, which can cure at room temperature, the alkali-activated geopolymer typically require relatively increased curing temperatures (40–90 °C) [22].

7.4. Strategic Blending and Hybrid Gel Approach

7.4.1. Strategic Blending and Hybrid Gel

Different strategies are adopted to transform the variable waste materials into the high-performance materials. Some of the important strategies for the alkali-activated geopolymer systems are highlighted below.
Strategic Blending and the Hybrid Gel Approach: This approach creates hybrid gel systems by combining the reactive, high-calcium precursors (like slag and GGBS) or reactive alumina sources (like metakaolin) with low-reactivity waste.
Regarding the synergies in chemistry, the dual-gel system (N-A-S-H + C-A-S-H) is produced by the high-Ca precursors, which densify the material’s microstructure, fill the pores, and boost its early strength [22,42].

7.4.2. Contaminant Encapsulation

Furthermore, this strategy enables control of the contamination because the blending allows for the encapsulation; during the dissolution and hardening process, hazardous heavy metals in the waste are chemically and physically sealed within the geopolymer matrix [17,41].

7.4.3. Co-Precursors for Low-Alumina or Low-Reactivity Wastes

Finally, to provide the required alumina framework for structural stability, waste glass (low aluminum) could be combined with the co-precursors such as fly ash, metakaolin, or calcium sulfoaluminate cement [22].

7.5. Pre-Treatment: Performance vs. Environmental Cost

7.5.1. Thermal Treatment

Pre-treatment Performance vs. Environmental Cost: It is known that the physical and chemical treatments can boost the precursor reactivity. However, they involve significant trade-offs in energy and cost.
Regarding thermal treatment (calcination), the clays (such as kaolinite) can be heated to about 700 °C to produce the highly reactive metakaolin; however, if the process is not optimized, it might eliminate the CO2 savings and increase the expenses up to fivefold ($550/ton vs. $100/ton for slag) [17,22,43].

7.5.2. Chemical Treatment

Similarly, chemical treatment has the potential to eliminate some pollutants, such as organic debris, heavy metals, or particular salts, which could otherwise hinder the dissolution of the silica and alumina or prevent the geopolymerization process. Enhancing the chemical or physical characteristics of an ore or waste enables it to meet the performance and safety requirements that would otherwise prohibit its utilization in construction [22].

7.5.3. Mechanical Grinding and Combined Activation Strategies

Furthermore, mechanical (grinding) processes show that reducing the particle size increases the surface area, which speeds up the reaction kinetics and enhances the final compressive strength [17,22].
Finally, regarding the combined strategies, although combining the thermal and chemical activation and ultrafine grinding can produce the densest matrices, a strict cost–benefit analysis is required to ensure that the environmental cost is worth the performance gain.

7.6. Adaptive Design Frameworks: AI and Machine Learning

7.6.1. Artificial Neural Networks and Predictive Models

Artificial neural networks (ANNs) dominate (37% of studies) in the compressive strength prediction using MLP, LSTM, CNN, and DNN algorithms (Table 4).
These tools enable real-time quality control and parameter optimization, such as adjusting the sodium hydroxide concentration to account for the variations in waste chemistry. Because static recipes are no longer effective due to the regional and seasonal variations in waste materials, the industry is shifting toward machine learning (ML), thermodynamic modeling frameworks, and performance-based standards.
Table 4 summarizes the dominant computational frameworks. ANNs account for 37% of applications, primarily in compressive strength prediction.

7.6.2. Thermodynamic Modeling Tools

Thermodynamic Modeling GEMS, FactSage: Simulate the different chemical phase formation and reactions before any materials are physically mixed in the lab. The Chemical Reality Check: ML models are often black boxes, and the sources emphasize that they must be combined with thermodynamic modeling to ensure that the predicted mixtures are chemically realistic and scalable.
Standardization: Helps manage the lack of standardization in the silica-based precursors, fly ash, and slag by simulating their chemical behavior across the different regions.

7.6.3. Multi-Objective Optimization and LCA Integration

Multi-Objective AI Genetic Algorithms (GA), PSO Particle Swarm Optimization, NSGA-II, and LCA LCC models: Integrates the life cycle assessment (LCA) with durability data to find the sweet spot between the lowest carbon footprint and the longest lifespan.
Optimization Workflow: Uses trained ML models like the ANNs as a predictive engine within an optimization loop to iteratively search for the optimal set of mixture proportions.

7.6.4. Data Limitations and Intellectual Property Barriers

Although methods like transfer learning are being increasingly used to transfer the knowledge from the fly ash systems to less-studied precursors, an important challenge is that the work frequently relies on small datasets. At the same time, potential conflicts with a company’s intellectual property may further restrict data access and application. Despite the distinct technological advantages of machine learning (ML) frameworks in managing resource variability, their economic implementation remains constrained by the conflict between corporate confidentiality and regulatory transparency. While these models can considerably enhance complex mix design optimization, regulatory bodies often demand full disclosure of proprietary formulations, which poses a significant challenge for industries seeking to protect their intellectual property.
Bridging the gap between research and large-scale industrial utilization requires improvements in variability control, the integration of life cycle assessment (LCA) tools, and the standardization of mix design protocols. Meanwhile, the most promising future pathway for developing robust and cost-effective formulations lies in combining ML techniques with thermodynamic modeling, thus ensuring both scientific performance and practical scalability [22].

7.7. Standardization, Policy, and Market Framing Around Resources

The existing standardization frameworks, largely designed for the traditional Portland cement systems, present considerable barriers to the widespread adoption of alkali-activated and geopolymer materials, as well as to the broader advancement of the innovative waste-valorization technologies [26]. Updating these frameworks to reflect the material diversity, regional variability, and measurable sustainability criteria will be crucial for positioning these technologies within the future circular construction markets.
The adoption of the varied, unconventional precursors is hindered by the fact that many international standards are still prescriptive rather than performance-based, requiring particular components such as a minimum clinker content. This material-specific strategy effectively protects established companies and discourages the use of local waste streams by forcing novel binders through time-consuming and costly individual assessment processes (such as the European Technical Assessment) [17].
The standardization gap mentioned in the research is highlighted in Table 5, which compares the current regulatory environment for the traditional ordinary Portland cement (OPC) with innovative alkali-activated geopolymer materials.
The main strategy for incorporating novel materials such as the alkali-activated/geopolymer systems into the worldwide market is to shift from prescriptive to performance-based standards. The new frameworks should classify materials according to their chemical function and reactivity (e.g., Si/Al ratio and amorphous content) rather than defining a binder by its origin (e.g., fly ash). Strategic policy tools, such as carbon credits, landfill tax, and Leadership in Energy and Environmental Design (LEED)-style procurement requirements, are needed to support this shift by rewarding the high-impact resource combinations. Regulators have the ability to convert the alkali-activated/geopolymer from specialized research projects into low-carbon, economically viable infrastructure solutions by internalizing the environmental costs of conventional materials and accelerating the end-of-waste certification procedure [17,22].

8. Future Directions in Resource-Centric Alkali-Activated Geopolymer Research

Future alkali-activated geopolymer research is shifting toward a resource-centric strategy that considers municipal and industrial waste as strategic assets rather than disposal issues. This shift is supported by three pillars:
•
Systematic mapping of resources (precursors): In order to solve the temporal mismatch caused by a decreasing supply of conventional materials such as coal fly ash and blast furnace slag, research has to give the highest priority to the systematic mapping of global and regional precursor inventories. Researchers can develop dynamic databases that monitor the availability and quality by region and season by mapping a variety of materials, including biomass ash, mining tailings, and volcanic rock [17,22,30].
•
Standardized characterization: To ensure that industries have access to materials despite geographical variation, standardized characterization techniques must be established in order to establish reliable global networks for raw materials [17,22,30].
•
Digital tools and AI infrastructure: Artificial neural networks (ANNs) are identified as a main tool for modeling the complex nonlinear relationships in diverse waste materials. By simulating phase assemblages, thermodynamic modeling tools like GEMS and FactSage help maximize precursor reactivity and reduce the need for trial-and-error tests. ANNs and deep neural networks are examples of advanced models used to forecast a mix’s durability and mechanical qualities based on chemical inputs. In order to improve performance prediction, hybrid predictive platforms combine data-driven artificial intelligence with physics-based thermodynamic modeling. By integrating Building Information Modeling (BIM) with life cycle assessment (LCA) methods, sustainability and structural durability may be monitored in real time during a project’s life cycle [22,24,63].
•
Circular Economy Integration: Alkali-activated and geopolymer materials play an important role in advancing industrial symbiosis, enabling the transformation of waste from sectors such as glass manufacturing, energy production, and agriculture into valuable building materials. This role extends into broader frameworks of territorial metabolism and urban mining, where construction and demolition wastes are repurposed to create high-performance products. Such valorization processes can significantly reduce raw material consumption by up to 50%, while simultaneously mitigating waste generation and environmental impact [1,8,9,69].
To support the large-scale utilization of secondary resources in construction value chains, future efforts should focus on close collaboration between researchers, industry stakeholders, and policymakers. In particular, the establishment of clear and practical end-of-waste criteria will be essential to facilitate market acceptance and regulatory approval of these alternative materials as legitimate, high-quality construction resources [9,17].

9. Conclusions

Based on the comprehensive analysis, the transition from the ordinary Portland cement to alkali-activated geopolymer materials represents more than a shift to alternative binders; it reflects a broader move toward resource management technologies capable of addressing multiple sustainability challenges simultaneously.
In order to fully utilize this potential, regulatory agencies require a shift from the recipe-based regulations to resource-oriented, performance-based standards that evaluate the materials based on their structural performance and chemical reactivity rather than their origin.
Complementary policy initiatives, including landfill taxation, industrial symbiosis incentives, and digital resource inventories, could reduce barriers associated with waste variability and supply uncertainty. Together, these developments can help position the alkali-activated and geopolymer systems as a meaningful part of the low-carbon, circular construction sector.

Author Contributions

N.A.: Conceptualization; Writing—original draft and review; M.B.: Writing—original draft and review; K.G.: Review and Editing. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

No new data were created or analyzed in this study.

Acknowledgments

During the preparation of this work, the authors used the Elicit platform (developed by Ought, Inc., Oakland, California, USA) to identify relevant literature and extract key information from research articles. The authors also used QuillBot (developed by QuillBot Inc., Chicago, Illinois, USA) to enhance the language and readability of the manuscript. All outputs generated by these tools were critically reviewed and edited by the authors. The authors take full responsibility for the accuracy, integrity, and originality of the content presented in this manuscript.

Conflicts of Interest

The authors declare no conflicts of interest.

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Resources 15 00066 g001
Figure 1. The geopolymer cement development method [25].
Figure 1. The geopolymer cement development method [25].
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Figure 2. Resource transition and adaptive response in alkali-activated geopolymer systems.
Figure 2. Resource transition and adaptive response in alkali-activated geopolymer systems.
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Table 1. Integrated Resource Assessments: LCA, Strategic Challenges, and Technical Performance.
Table 1. Integrated Resource Assessments: LCA, Strategic Challenges, and Technical Performance.
Precursor CategorySpecific Material ExamplesAvailability and Supply ContextPerformance and Durability CharacteristicsEnvironmental Impact and LCA FindingsProcessing and Strategic Trade-OffsReference
Industrial ByproductsCoal fly ash (low/high Ca), ground granulated blast-furnace slag (GGBFS), red mud (bauxite residue), silica fume, ferro-nickel slag, marble dust.Decreasing availability in regions transitioning from coal/blast furnaces; geographically concentrated slag production.Mechanical Strength: 30–80 MPa; slag achieves 30% higher early strength than fly ash. Risks: carbonation and alkali-silica reaction (ASR).Superior performance: 80–90% CO2 reduction; 60–70% energy reduction (up to 97% GWP reduction in specific cases).Requires grinding and milling for particle-size optimization; high heterogeneity requires source-specific study.[8,17,29,30,31,38,39,40,41,42]
Natural and Thermally Treated ResourcesMetakaolin, calcined clays, natural pozzolans, volcanic tuffs, diatomite, volcanic rock/ash.Abundant in clay-rich or volcanic regions; generally not a waste stream; higher cost ($550/ton vs. $100/ton for slag).Mechanical Strength: 30–80 MPa; noted for high reactive alumina. Durability: high thermal stability (up to 1000 °C); lower ASR risk.Mixed profile: 40–60% CO2 reduction; can occasionally exceed Portland cement GWP due to calcination energy.Requires high-intensity thermal treatment (~700 °C) and grinding; sensitive to Al/P ratios.[17,22,30,43]
Emerging and Challenging WastesMine tailings, biomass ashes (rice husk ash, almond shell ash), dredged sediments, sewage sludge ash, CDW (recycled concrete/brick/glass).Widely available globally but underutilized; highly variable by location and seasonal cycles.Specialized performance: over 90% strength retention at 250 °C; often requires co-precursors (FA/MK) to form a stable framework.High circularity: upgrades waste from a negative value (−100€/ton) to market value; 35–50% reduction in abiotic resource consumption.Complex pre-treatment; potential leaching of hazardous/radioactive materials; requires ML-optimized mix designs.[1,8,17,21,22,30,31,44,45,46,47,48,49]
Alkaline ActivatorsNaOH, KOH, sodium silicate (water glass).Global supply bottleneck: Current supply only allows for replacing ~7% of Portland cement.Critical for dissolution-polycondensation; concentrations must be adjusted to control reaction kinetics and rheology.High impact: major contributors to the system’s total GWP and embodied energy; sodium silicate is the primary GWP source.Research is shifting toward one-part “just-add-water” solid activators and waste-derived alkalis from biomass.[6,9,10,12,13,14,15,16,17,18,21,22,23,24,41,42,47,50,51,52]
Table 2. Data on various resource categories of alkali-activated geopolymer [17,22,31].
Table 2. Data on various resource categories of alkali-activated geopolymer [17,22,31].
System TypePrimary Gel PhaseChemistry and Precursors Performance Characteristics
Low-calciumN-A-S-H or K-A-S-HAluminosilicate framework (e.g., metakaolin, Class F fly ash).Superior fire resistance, chemical stability, and durability in aggressive environments.
High-calciumC-(A)-S-H or hybrid gelsCalcium-rich (e.g., Slag/GGBFS).Accelerates early-age strength development; similar to Portland cement hydration products.
Blended systemsHybrid N-A-S-H/C-A-S-HCombinations of various precursors (e.g., fly ash + slag).Allows for precise tuning of reaction kinetics, workability, and final property envelopes.
Table 3. Conventional liquid activators: resources and sustainability implications [17,21,22,50,51,53,54,55].
Table 3. Conventional liquid activators: resources and sustainability implications [17,21,22,50,51,53,54,55].
Activator Topic Resource and Sustainability Implications
Environmental impactActivators (especially sodium silicate/water glass) are the largest contributors to GWP and embodied energy in the life cycle of these materials.
Supply constraintsGlobal supply of sodium hydroxide is a major bottleneck; currently, only about 7% of Portland cement could be replaced by geopolymers due to limited activator supply.
One-part systemsDevelopment of solid just-add-water activators is seen as essential for mainstream adoption, as it improves safety, logistics, and shelf life.
Alternative ConceptsResearch is shifting toward waste-derived alkalis (e.g., from biomass ashes such as rice husk) and carbonate-based activators to reduce costs and carbon footprints.
Table 4. Some Adaptive Design Frameworks in AAS [17,22,23,24,64,65,66,67,68].
Table 4. Some Adaptive Design Frameworks in AAS [17,22,23,24,64,65,66,67,68].
Technology Primary RoleKey Algorithms/ToolsMain Limitation
Artificial Neural Networks (ANN)Property prediction (strength, durability)MLP, LSTM, CNN, DNN, ANFISSmall datasets (<200 points); needs transfer learning
Thermodynamic ModelingChemical Phase Simulation GEMS, FactSageComplex Input Requirements 
Multi-Objective AILCA + durability optimizationGA, PSO, NSGA-IIIP conflicts with proprietary formulations
Table 5. Standardization gap for the ordinary Portland cement (OPC) vs. innovative alkali-activated geopolymer materials [17,22,26].
Table 5. Standardization gap for the ordinary Portland cement (OPC) vs. innovative alkali-activated geopolymer materials [17,22,26].
FeatureOrdinary Portland Cement (OPC)Alkali-Activated/Geopolymer
Primary StandardHarmonized Standards (hEN/ASTM): Broadly recognized and an industry standard.Individual Assessments (ETA/EAD): Requires specific, often costly, case-by-case approval.
Basis of design Prescriptive: Mandates specific ingredients (e.g., minimum clinker content).Performance-Based: Relies on measurable outcomes (e.g., strength, durability).
Market Entry Direct: Instant CE marking or ASTM compliance for established grades.Delayed: Lengthy approval processes due to the lack of harmonized codes.
Waste Integration Limited: Restricted to specific approved SCMs (e.g., specific fly ash classes).High Potential: Can valorize diverse, non-standardized industrial waste streams.
Risk Liability Outsourced: Compliance with prescriptive standards provides a legal defense.Internalized: Liability is often managed through vertical integration and custom testing.
Sustainability Credit Incremental: Focuses on modest clinker reduction.Radical: Enables 80–90% $CO2 reduction and high waste diversion.
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Asim, N.; Badiei, M.; Ghoreishi, K. Alkali-Activated and Geopolymer Systems Through the Lens of Resource Efficiency. Resources 2026, 15, 66. https://doi.org/10.3390/resources15050066

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Asim N, Badiei M, Ghoreishi K. Alkali-Activated and Geopolymer Systems Through the Lens of Resource Efficiency. Resources. 2026; 15(5):66. https://doi.org/10.3390/resources15050066

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Asim, Nilofar, Marzieh Badiei, and Khadijehbeigom Ghoreishi. 2026. "Alkali-Activated and Geopolymer Systems Through the Lens of Resource Efficiency" Resources 15, no. 5: 66. https://doi.org/10.3390/resources15050066

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Asim, N., Badiei, M., & Ghoreishi, K. (2026). Alkali-Activated and Geopolymer Systems Through the Lens of Resource Efficiency. Resources, 15(5), 66. https://doi.org/10.3390/resources15050066

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