Although alkali-activated materials (AAMs) show great promise as viable substitutes for Ordinary Portland Cement (OPC), they face numerous challenges in achieving widespread market acceptance. These challenges include the intricate chemistry of AAMs, technological and environmental complexities, inconsistency in the availability and quality of raw materials, and the absence of a well-established value chain for AAM production. Furthermore, legislative and regulatory frameworks are often lacking or unfavorable, and economic concerns related to scalability and competitiveness continue to pose barriers. Social acceptance remains limited, often due to unfamiliarity with the material and skepticism about its long-term performance. This chapter presents findings from various international research and development projects focused on advancing AAM technology. It highlights the pivotal role of pilot-scale trials in assessing the feasibility of AAM implementation, identifying technical and logistical challenges, and guiding further innovation. Additionally, the chapter showcases successful case studies and industrial applications of AAMs, positioning them as sustainable, high-performance alternatives to both traditional OPC and ceramic-based construction materials.

Although alkali-activated materials (AAMs) are promising low-carbon binders, their broader use is limited by pronounced volumetric instability, especially early-age autogenous shrinkage. Zinc oxide (ZnO) is known to retard conventional cementitious systems, but its potential to regulate shrinkage in AAMs through reaction-kinetics control remains insufficiently understood. Here, nano-ZnO was incorporated into alkali-activated fly ash/slag pastes (AAFS) to examine its effects on shrinkage behavior, reaction kinetics, internal relative humidity, and reaction-product evolution. Increasing nano-ZnO dosage progressively prolonged the setting time and delayed the main heat-release peak, indicating effective regulation of early reaction kinetics. This delay reduced early water consumption and helped maintain a higher internal relative humidity, thereby mitigating self-desiccation-induced autogenous shrinkage. XRD and FTIR results further suggested the possible formation of calcium zincate hydrate and delayed development of C-(A)-S-H/N-(C)-A-S-H gels. As a result, 3% nano-ZnO reduced the 7-d autogenous shrinkage by approximately 58% (from 7985 to 3337 με) and decreased the 14-d drying shrinkage by approximately 15% under the tested conditions. These findings indicate that nano-ZnO can act as a reaction-kinetics modifier for mitigating the shrinkage of AAFS in the early age.

Numerical models are helpful vehicles for understanding and describing the engineering properties of construction materials. With the rapid development of both computational capabilities and theoretical insights into chemical reactions, there have been increasing research activities around the globe and raising demands for computational methods that describe different characteristics of alkali-activated materials. In this Chapter, we summarized the collective efforts performed on modelling and simulation of alkali-activated materials in the past two decades and highlighted the most relevant results and advances in the aspects of atomistic simulation, thermodynamic modelling, kinetics modelling, microstructure simulation, and multi-scale modelling. It can be concluded that pioneering work on modelling and simulation of alkali-activated materials has been conducted with fruitful results. However, there are still deficiency gaps and challenges in modelling and simulation of alkali-activated materials, especially in comparison with PC-based materials.

Alkali-activated materials (AAMs), as eco-friendly alternatives to Portland cement (PC), have attracted increasing attention of researchers and users in the past decades. Despite the eco-friendly nature of AAMs, doubts about these materials as an essential ingredient of concrete exist, regarding, for example, their volume stability. One possible volume change concerns autogenous shrinkage. Autogenous shrinkage is the self-created volume reduction of materials due to chemical reactions without the need for substance or heat exchange with the environment. If the autogenous shrinkage of a binder material is too large, cracking might happen, which will seriously impair the durability of concrete. The aim of this chapter is to provide a state-of-the-art review on the autogenous shrinkage of AAMs. The different characteristics and mechanisms of autogenous shrinkage of different AAMs are reported. Corresponding shrinkage-mitigating strategies are summarized. Existing models to simulate and predict the autogenous shrinkage of AAMs are reviewed. Remarks are then given on testing methods of autogenous shrinkage, which link back to the determination of the magnitude of autogenous shrinkage of AAMs. Connections between autogenous shrinkage and other deformations such as drying shrinkage, thermal deformation and creep are also discussed. Research gaps and outlook on future research in this field are given in the end.

In recent years, blast-furnace slag (BFS) composite cement, which partially replaces ordinary Portland cement (OPC) with a by-product from the manufacture of iron, has been widely used in civil engineering due to its numerous advantages. Although the mechanical properties and durability of BFS concrete are excellent, there are still some issues that need to be addressed – for example, significant drying shrinkage. To mitigate the drying shrinkage, a shrinkage-reducing agent (SRA) is one important kind of admixture that is usually added to cementitious materials. One type of SRA – non-ionic surfactant – was proven to be capable of mitigating the drying shrinkage of OPC concrete, but whether it is also effective in BFS concrete is still unclear. In this study, the influences of a commercial non-ionic surfactant (Sika® Control-40) on the surface tension, hydration process and pore structure of BFS cement pastes are studied experimentally. Mechanical properties and deformation of both BFS cement paste and concrete are also measured. The test results show that the addition of SRA results in lower compressive and flexural strength, higher porosity and lower hydration rate of BFS cement paste. With the addition of non-ionic surfactant, drying shrinkage of BFS cement paste and concrete is significantly reduced.

Calcium-sodium aluminosilicate hydrate (C-(N)-A-S–H) gels are the primary phases in alkali-activated slag (AAS) systems and govern paste-scale microstructural evolution. Conventional models assume cross-linked and non-cross-linked C-(N)-A-S–H gels with Ca/(Si + Al) > 0.67 and Al/Si < 0.25. However, several studies have reported Al-rich gels (Al/Si > 0.25) in both AAS and in alkali-activated blends with lower calcium content, whose nanostructure and chemistry remain insufficiently resolved. In this study, four amorphous Al-rich C-(N)-A-S–H gels spanning Al/Si = 0.31–0.57 and Ca/Si = 0.56–1.04 were synthesized to enable two orthogonal comparisons: (i) varying Al/Si at constant Ca/Si to isolate Al-for-Si substitution effects, and (ii) varying Ca/Si at constant Al/Si to probe calcium role on network connectivity. Comprehensive characterization revealed the coexistence of local structural environments characteristic of C-(N)-A-S–H/C-A-S–H, (N,C)-A-S–H, and N-A-S–H-like gel domains without the formation of crystalline secondary phases. ²⁹Si NMR revealed a progressive increase in Q⁴(mAl)-rich sites with increasing Al incorporation, while the relative proportion of the C-(N)-A-S–H/C-A-S–H environments decreased with decreasing Ca/Si ratio. ²⁷Al NMR confirmed tetrahedral Al coordination, with chemical shifts varying with Ca/Si ratio, reflecting changes in interlayer charge-balancing. Octahedral Al was detected exclusively in gels with a higher Al/Si at 0.5, indicating the formation of more highly polymerized aluminosilicate environments under high-Al conditions. ²³Na NMR revealed chemical shifts of − 5.81 to − 6.21 ppm, correlating strongly with the Na/Al ratio. Collectively, the findings demonstrate that gels with Al/Si > 0.25 deviate from classical tobermorite-like structures and exhibit increasingly polymerized and structurally heterogeneous aluminosilicate environments.

The increasing demand for sustainable development in engineering practice has triggered researchers to explore solutions to reduce the CO₂ footprint caused by Portland cement (PC) production. Alkali-activated concrete (AAC), made by alkali activation of industrial by-products, poses to be a sustainable alternative to traditional Portland cement concrete. Despite vast studies on its material properties, there is still insufficient knowledge on the structural performance of reinforced AAC members, which impedes its widespread application. Bond between concrete and embedded reinforcement is critical for the structural behaviour of reinforced members, including crack propagation (crack opening and crack spacing), load carrying capacity, deformational capacity and seismic resistance. In this chapter, a critical review on the bond behaviour between AAC and reinforcement is given. A vast variety of tests have been used for studying the AAC-reinforcement bond. Similar to traditional PC concrete, different setup configurations and specimen geometries affect not only the measured bond strength, but also the nature of the bond response. Therefore, in this review different bond tests are discussed, focusing on application of both conventional steel and fibre reinforced polymer (FRP) as reinforcement. Given that AAC is a wide class of materials with largely varying mechanical properties, this study systematically classifies bond results based on different types of precursors used. Furthermore, numerical methods to predict AAC flexural response as well as the applicability of existing PC concrete design codes are summarized. It is concluded that AAC beams show comparable short-term bond behaviour with traditional PC concrete of the same strength class. Although the design codes for traditional concrete turn out to be usually applicable for the AAC-reinforcement bond, opposite trends were also reported. Finally, whereas the short-term behaviour has been widely investigated for AAC bond, systematic studies dealing with its long-term behaviour are lacking. Time dependent effects must be considered when developing reliable guidelines and recommendations for future structural design of AAC.

The introduction of alkali-activated concrete (AAC) technology to the construction industry represents a significant step toward a sustainable development and a cleaner environment by reducing environmental pollution. Currently, its application is relatively limited compared to traditional Portland cement based concrete (PCC). However, AAC has a remarkable potential for future growth and innovation despite several associated challenges and limitations. The current Chapter highlights recent progress in AAC mix design and its mechanical properties, paving the way for a broader application. The universally recognized international standards and codes for AAC, its mix design and evaluation of its long-term performance are still emerging. Unlike conventional PCC, AAC encompasses a wide class of materials with wide varying chemical composition and reaction mechanisms, depending on the choice of constituent materials (precursors and alkali activators). The mechanical properties, while diverse, reflect the flexibility of the material in response to different compositions and curing conditions. Though, non-uniformity makes consistent AAC usage challenging on the scale of PCC. Nevertheless, ongoing research and development efforts by RILEM TC 294-MPA are dedicated to tackling these challenges and enhancing the efficacy and widespread adoption of AAC technology.

Woody biomass fly ash (WBFA) is the main by-product of woody biomass energy production. However, its use in cementitious materials remains limited due to its low intrinsic reactivity, largely associated with the scarcity of aluminosilicate phases. At the same time, the high alkalinity and sulphur content in WBFA make it a promising component for formulating cement-free binders without additional chemical activators, when combined with highly reactive precursors. This study investigates the reaction mechanisms and microstructural evolution of binders based on WBFA and ground granulated blast furnace slag (BFS), with the aim of elucidating their synergistic interactions and optimizing performance. Binary pastes with varying WBFA/BFS ratios mixed with water were prepared and characterized by isothermal calorimetry, pore solution analysis, XRD, FTIR, TGA, SEM-EDS, and MIP. The results show that, although increasing WBFA content initially delayed hydration by limiting the dissolution of reactive species, it markedly enhances long-term reactivity and strength through sustained release of alkali and sulphate. The main hydration products are C-(A)-S-H gels, ettringite, Friedel's salt, and hydrotalcite, with their amount and assemblage strongly governed by the WBFA/BFS ratio. Reaction kinetics analysis and thermodynamic modelling confirm the dual role of WBFA as both a reactive precursor and internal alkali/sulphate activator. Among the formulations studied, the mixture with a WBFA/BFS ratio of 50:50 exhibited the best overall performance, achieving the highest compressive strength and lowest porosity. These findings clarify the reaction mechanisms in WBFA-BFS binary pastes, providing practical guidance for designing WBFA-based, cement-free binders for sustainable construction applications.

Among the various examples of sustainable construction materials explored in scientific literature, alkali-activated materials excel as one of the most mature and reliable solutions for large scale applications. It consists on the combination of an alkaline source in liquid or solid state, and a partially-to-fully amorphous solid precursor. The combination of these components leads to the obtainment of a hardened material which resembles Portland-cement based products. The performance and durability of these alternative binders is highly dependent on their components and production methods, and multiple laboratorial- and industrial-scale examples have shown their capability of outperforming conventional building materials. Practical challenges with variations in chemistry and mineralogy of raw materials, and the global utilization of prescriptive standards for structural building materials, hinder a wider utilization of these binders, and the efforts of the scientific and applied industry communities in overcoming these barriers is detailed throughout this report. This chapter provides an overview of alkali-activated binders, summarizing the main characteristics of their components, their reaction mechanisms, their challenges, and the expected advances of the technology with respect to one-part binders.

Because building materials are intended to provide durable and safe structures, they are subject to strict regulations designed to ensure that they do not pose a hazard during their use. But they must also not be harmful to humans or the environment at the end of their life cycle, regardless of whether they are reused, recycled, or disposed of in a landfill. The requirements that building materials/products must meet vary around the world, but all countries have at least some minimum requirements, whether through regulations, mandatory standards, certification procedures, and/or monitoring at construction sites. In Europe, regulations and standards are based on what is known as the “materials-based” approach, meaning that standards define not only the technical requirements, but also the materials from which products are made. Other parts of the world use the so-called “performance-based approach”, meaning that products must have a certain performance regardless of the materials from which they are made. The “materials-based” approach could present some obstacles or barriers for alkali activated products when it comes to providing the documentation needed to bring such products to the market, as there are no EN standards for alkali-activated products so far. The aim of this chapter is to provide information on the legislation for building materials in general but with a focus on alkali activated materials (AAM) around the world and to provide guidance on how to approach the subject.

Alkali-activated concrete (AAC) is a sustainable alternative to ordinary Portland cement concrete, but its large-scale structural performance remains insufficiently understood, particularly in terms of long-term durability. To ensure safe application, continuous monitoring of AAC structures is essential. This paper develops and validates ultrasonic-based damage indicators (DIs) intended to support future lifetime monitoring of precast AAC bridge members. Full-scale laboratory tests were performed on two prestressed AAC beams and a solid slab consisting of three beams with embedded piezoelectric sensors. Active ultrasonic measurements collected throughout loading were processed to derive two DIs: (1) reduction in waveform coherency using direct wave interferometry to indicate crack initiation, and (2) relative wave velocity obtained from an arrival-time picker to track crack propagation. The waveform coherency-based DI consistently identified the onset of cracking at or even before the first visible cracks appeared in digital image correlation (DIC) images, while the velocity-based DI provided a qualitative measure of crack propagation and orientation. Both indicators responded sensitively once degradation developed, enabling early warning of structural deterioration. The validated DIs are intended to inform the development of a lifetime monitoring scheme on a pilot precast AAC bridge on a Dutch national road. This study also provides a practical pathway toward risk-informed operation and broader adoption of AAC in bridge applications.

This chapter serves as a concise introduction to the State-of-the-Art Report on the Mechanical Properties of Alkali-Activated Materials (AAMs) in construction. It emphasizes the important role of mechanical properties in shaping AAM research and highlights key areas of exploration, including the impact of raw materials on mixture design, fresh properties, and a broad range of mechanical characteristics. Additionally, it outlines the structure of the book, guiding readers through its extensive coverage of theoretical foundations, practical insights, and emerging standards for AAMs. Overall, it sets the stage for understanding how AAMs can significantly advance sustainable construction practices.

Carbonation of recycled cement paste powder (RP) has been widely explored for CO₂ sequestration. However, the cementitious reactivity and mechanical performance of carbonated recycled cement paste powder (CRP) remain insufficient, limiting its effective utilization as a supplementary cementitious material (SCM). To address this limitation, this study proposes a two-step carbonation-ultrasonic modification strategy to transform RP into a nano-reinforced, highly active SCM. In the first step, controlled gas-solid carbonation induces the preferential formation of needle-like aragonite whiskers on RP surfaces. Subsequently, liquid-phase ultrasonic treatment detaches these whiskers while exposing the underlying silica-rich layer. The resulting liquid-solid suspension is directly incorporated into cement paste without further separation. Ultrasonic dispersion converts surface-grown aragonite into nanoscale fillers and nucleation sites, while the exposed silica-rich layer exhibits enhanced pozzolanic reactivity, collectively accelerating C-S-H nucleation and early hydration. This synergistic physical-chemical activation significantly refines pore structure. Consequently, the 28 d compressive strength increases by 37.1% relative to RP and by 26.75% compared with ordinary Portland cement (OPC). The proposed approach provides a scalable pathway for the high-value utilization of RP while simultaneously contributing to CO₂ sequestration and low-carbon cementitious systems.

This chapter introduces the classification of AAMs, the terminology used in the following chapters and provides the notation of abbreviations.

Concrete is an ageing viscoelastic material exhibiting both elastic (instantaneous) as well as viscous (time-dependent) deformation under loading conditions (either external or internal). There is a limited number of studies focused on the time-dependent response of alkali-activated concretes (AACs) under loading/unloading conditions. Creep of AAC is a complex phenomenon, which is influenced by exposure conditions of the material, including the loading magnitude, temperature, relative humidity, thermal and drying histories; as well as chemical composition and phase assemblages (e.g., type and amount of reaction products) present in the cementitious matrix. AAC has shown very vibrable creep behaviors, due to different raw materials and processes using during their production. Creep studies on room temperature cured slag-based AAC usually show high creep; however, creep studies of different AACs, including fly ash-based and fly ash-slag-blended, indicate that elevated temperature curing could be a suitable mitigation strategy for reducing creep. This is associated with the development of a more mature microstructure in the material, due to an accelerated reaction kinetics and a consequent increase in strength and lower creep. However, applying a curing temperature above 80 °C causes thermal defects and cracks which increases the creep. For most aluminosilicate-based AACs that produced with fly ash, metakaolin and their blends with a small amount of ground granulated blast furnace slag, the recommended curing method is to use thermal curing at about 60 °C. In addition, curing time and initial loading time are also important. It must be noted that because of the complexity of raw materials properties and mix proportions, there is no universal method for all types of AACs. The existing creep prediction models for Portland cement-based concretes cannot be transferred and adopted in AACs directly due to the distinct nature of hydration products. Therefore, more studies investigated the creep at both small size and full-scale of AACs are urgently needed.

Designing hydrogel-based composites for internal curing in cementitious systems remains challenging due to the persistence of polymer phases as discrete particles, which leads to hydrogel-related pore formation and reduces mechanical properties. In this study, a basalt-polyacrylamide hydrogel composite (BCPA) was engineered by introducing micron-sized basalt particles as physical crosslinking centers to construct a polymer-particle interface whose stability is responsive to the surrounding ionic environment. Upon exposure to the ion-rich cement pore solution, cation adsorption on basalt surfaces is proposed to weaken the original polymer-basalt association, leading to a proposed interfacial self-debonding process and inferred redistribution of polyacrylamide segments within the cement matrix. This interfacial evolution induces a transition of the polymer phase from a discrete particulate state to a dispersed segmental configuration, thereby altering the structural response of the hydrogel composite after incorporation. As a consequence, hydrogel-related marcopores are markedly suppressed. The inferred redistribution of polymer segments allows internal curing functionality to be retained while enabling a refined pore structure that can be readily accommodated by hydration products. At a dosage of 1 wt%, BCPA reduces 7-day autogenous shrinkage by approximately 75% and decreases cracking area by nearly one order of magnitude, while limiting compressive strength loss within 20%, substantially lower than the approximately 44% loss observed for the chemically crosslinked polyacrylamide reference (a typical internal curing agent). These findings suggest that regulating interfacial interactions to modulate polymer state evolution offers a promising strategy for designing hydrogel composites that reconcile shrinkage mitigation with mechanical integrity in cementitious systems.

Alkali-activated slag (AAS) has attracted increasing attention as a sustainable alternative to Portland cement due to its significantly lower carbon footprint and promising mechanical and durability performance. However, despite these advantages, the widespread application of AAS is still hindered by several challenges. Among them, efflorescence―manifested as white deposits on material surfaces—remains one of the most common and persistent issues, adversely affecting both the aesthetic quality and long-term durability of materials. Mitigating efflorescence is therefore critical for the practical implementation of AAS binders. This study systematically investigated the influence of K on the efflorescence of AAS pastes prepared using NaOH and KOH solutions. Incorporating K in the activator significantly suppressed efflorescence: a 25% substitution decreased it by 59%, while substitutions above 50% achieved reductions exceeding 98%. The underlying mechanisms were elucidated through analysis of phase assemblage, gel chemistry, pore structure, and carbonate formation. K exhibited higher binding strength and capacity than Na within the gel, effectively decreasing the concentration of free alkalis available for efflorescence. Moreover, saturated K₂CO₃ solutions showed much lower equilibrium relative humidity than Na₂CO₃, rendering K-based systems more hygroscopic and less prone to efflorescence under ambient conditions. A K substitution of approximately 40% was predicted to substantially suppress efflorescence. These findings highlight the pivotal role of K in enhancing the durability of AAS binders.