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 study proposes a novel strategy in which lightweight aggregates (LWAs) are pre-soaked in the alkaline activator, enabling them to function simultaneously as internal curing reservoir and reactive participants in alkali-activated slag (AAS) mortar. Owing to the improved chemical compatibility between the stored liquid and the surrounding pore solution, activator pre-soaking reduced reaction retardation and promoted a more gradual and sustained liquid release compared with conventional water pre-soaking. Consequently, self-desiccation and the associated autogenous shrinkage were more effectively mitigated. The restrained cracking tendency of AAS mortar was also markedly reduced, accompanied by a transition in the post-peak fracture response from brittle to more ductile behaviour. In addition, the latent reactivity of the LWA was exploited through the release of Si and Al species, which promoted reaction-product formation and densification near the LWA-paste interface. As a result, the lack of measurable 1-day strength observed with water pre-soaking was largely overcome, and the elastic modulus was better preserved. These findings, together with the simplified practical implementation of this method, support activator pre-soaking as a promising preconditioning approach for LWA-incorporated AAS systems.

This study presents the interlaboratory results on the autogenous deformation of alkali-activated slag (AAS) and alkali-activated metakaolin (AAMK) paste and mortar, obtained by the RRT3 Expert Group of RILEM technical committee (TC) 294-MPA. The primary objective was to examine the autogenous deformation magnitudes of these two systems and validate the applicability and reproducibility of the corrugated tube method for these materials. To ensure comparability, all five laboratories used slag and metakaolin distributed from the same batches and followed common target mixture formulations and standardized measurement protocols. Sand and the commercial chemicals used to prepare the activators were sourced locally, but all complied with the specified common requirements. Moreover, the effect of aggregates on the autogenous deformation was estimated with two analytical models. Our results show that the corrugated method exhibited good reproducibility and reliability in measuring the autogenous deformation of AAS paste, which ranged between 4600 and 5500 μm/m at 7 days, with a variation below 10%. AAS mortar showed autogenous deformation approximately 2100 μm/m at 7 days, about 60% below that of the corresponding paste, demonstrating the significant restraining effect of aggregate at a sand-to-paste mass ratio of 1.03. AAMK systems showed much larger scatter and a common biphasic response comprising early expansion followed by shrinkage. However, the initial expansion diminished before final setting time, indicating that the expansion is more associated with chemical or thermal deformation. When referenced to the final setting time, the AAMK paste exhibited substantially smaller deformation than AAS, with values ranging from approximately −900 to 0 μm/m by the end of the 7-day test. This study seeks to promote the standardization of autogenous shrinkage testing protocols for AAMs and enhance the understanding of their deformation behaviors.

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.

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.

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.

The formation of micro-cracks due to restrained shrinkage is a significant concern for the durability and in-service implementation of alkali-activated materials (AAM). These cracks develop as a result of partial or total restrained deformations which occur when the material's properties are still evolving, and the deformation rate is high. This makes AAM especially susceptible to cracking during this critical early stage, leading to potential long-term durability issues. Therefore, it is particularly crucial to understand their restrained shrinkage behavior and early-age cracking risk. This chapter discusses two approaches for assessing the cracking sensitivity of AAM with a particular focus on the empirical method. It reviews the existing testing devices for evaluating restrained shrinkage and cracking in AAM, and compares and discusses key findings from the literature.

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.

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.

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

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.

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.

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.

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.

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.

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.

Although air lime is a carbonatable binder with high carbon sink potential, reproducible research remains hindered by the limited availability of lime-oriented standards and openly accessible datasets. These limitations prevent the consolidation of fundamental knowledge and reinforce the perception of lime mortars as highly variable and empirical materials. This study addresses this gap by implementing a FAIR-aligned (Findable, Accessible, Interoperable, Reusable) and reproducible workflow for the characterization of air lime-containing mortars. Four mixtures were monitored for up to 364 days to assess fresh, physical, and mechanical properties under defined conditions. All experimental metadata and datasets are openly published in a structured repository. Results show that air lime-containing mixtures exhibited longer setting times, higher open porosity, greater carbonation depths, and lower compressive strength. Length change measurements indicate hydration-carbonation interactions, particularly in lime-cement systems. By combining experimental characterization with a FAIR-aligned and reproducible workflow, this work supports more transparent, resource-efficient research practices.

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.

Purpose – The Netherlands is one of the frontrunners in green concrete with innovative pilot projects and institutional settings (e.g. concrete agreement). However, mainstreaming green concrete needs to further overcome economic, institutional, technical and social barriers. Especially, demand-side organizations can play a critical role by setting environmental standards and project prioritization. In this regard, this study aims to understand how demand-side organizations can stimulate green concrete adoption in the construction sector by using the multi-level perspective (MLP) framework. Design/methodology/approach – The MLP framework was chosen to understand the dynamics between socio-technical elements that shape the transition. This research uses a qualitative research approach by interviewing 12 key experts in the Dutch concrete industry based on their expertise and experience. Interviewees were identified based on the snowballing technique. Subsequent thematic analysis reveals strategies for accelerating green concrete adoption. Findings – Key findings emphasize the need to promote diverse cement types tailored to specific applications, accelerate the development of alternative supplementary cementitious materials (SCM), create aggregate demand for near-mature innovations and provide large-scale testing for radical innovations. Practical implications – This research provides construction stakeholders with a framework for identifying leverage points where policy alignment and market demand can jointly drive innovation diffusion. Social implications – This study highlights the necessity of integrating incremental and radical innovations to meet greenhouse gas reduction targets. Originality/value – This study contributes to the construction management field by translating transition theory into operational insights for project-based organizations and demand-side actors.