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.

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.

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.

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

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.

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.

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.

Society is urging the public and private sectors to adopt sustainable measures to mitigate global warming. In response, the construction industry is exploring alternative binders to reduce its carbon footprint. Yet, durability concerns and regulatory gaps remain unresolved for this new generation of binders. In contrast, another potential path to decarbonization may lie in the built heritage. Standing the weathering of time, Egyptians, Phoenicians, and Romans relied on lime-based binders to create future-proof buildings before Portland cement was invented. However, as most lime applications were empirical and undocumented, the current bottleneck lies in the limited availability of scientific data—needed to establish lime as a sustainable and structurally viable material. Thus, this study investigated four mortar mixtures commonly used in masonry structures, monitoring key properties such as mechanical strength, permeability, and carbon capture capacity for six months. Results indicate that mixtures with higher air lime content exhibited lower strength, primarily governed by carbonation. Permeability tests confirmed air lime’s breathability, which favored carbon capture, as demonstrated through phenolphthalein and thermogravimetric analysis. Within the monitoring period, lime-cement groups absorbed more carbon dioxide earlier than others, likely due to interactions between hydration, carbonation, and water evaporation, which led to faster carbonation rates. Finally, an extended monitoring is recommended for future studies.

Alkali-activation is a technically sound pathway to valorize industry wastes and by-products, and there has been a burgeoning interest in evaluating the potential of waste streams and/or by-products from different industries as precursors for alkali-activated materials production. In the context of sustainable construction materials, as well as other industrial systems, the use of such non-conventional precursors addresses the challenges associated with the global availability and management of such resource streams. This includes the availability of alternative valorisation routes, the life cycle implications of using waste streams, and the pragmatic issues around incorporating a wide range of precursor materials for future proof this technology. In this chapter an overview of studies utilizing alternative precursors for producing alkali-activated cements is presented, analyzing the characteristics of each resource, and identifying the links between mix design formulations and the performance of the alkali-activated materials produced with them. This in order to elucidate the existing knowledge gaps to facilitate the widespread uptake of such resources as key precursors for producing this type of cements.

The use of fibers to address tensile cracking in alkali-activated concrete (AAC) is a topic of ongoing research. The addition of fibers enhances the tensile and flexural characteristics of all types of concrete including AAC. However, the mixing process, the setting time, and the workability are compromised due to the presence of fibers in the hardened matrix. There are different material categories of fibers such as steel, synthetic, carbon, and organic fibers that can impart different characteristics depending on the intended usage of concrete. The present chapter reviews the different types, orientations, dosages, and geometric properties of fibers included in AAC. along with the effects of fiber addition on the mix design, mixing and curing procedure of concrete, as well as the fresh and hardened characteristics of fiber-reinforced alkali-activated concrete (FRAAC). The use of statistical models to predict the mechanical characteristics of FRAAC is also discussed. Finally, the chapter presents the advantages, disadvantages, and safety precautions for this material followed by recommendations for practical usage.

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.

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.

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.

Cementitious materials can achieve desirable strength development and reduced cracking potential under moist or immersed conditions. However, in this work, we found that alkali-activated slag (AAS) pastes can crack underwater, with a higher silicate modulus showing more pronounced cracking. Chemically, the C-(N-)A-S-H gel in the paste with a higher silicate modulus showed a higher Na/Si ratio and a higher leaching loss of Na, which led to more significant structural changes and gel deterioration underwater. This triggered the propagation of cracks initially present in the material. Physically, the paste with a higher silicate modulus featured a denser microstructure, lower water permeability and higher pore pressure, which resulted in a steeper gradient of pore pressure in the matrix. Consequently, the concentration of tensile stress was simulated at the centre and the corner of the cross-section of the sample. As this simulated concentrated stress exceeded the flexural strength of AAS pastes, significant fractures at the centre and spalling at the corner occurred, consistent with the experimental observation. This work not only elucidated the cracking mechanisms of AAS materials underwater but also provided new insights into mixture designs for these materials under high-humidity conditions.

Alkali-Activated Concrete (AAC) is considered as a promising alternative to conventional Portland Cement Concrete (PCC) due to its potential to reduce environmental impacts. However, its application in practical engineering is limited by, among others, insufficient understanding of the long-term structural behaviour of reinforced and prestressed AAC elements. To address this, a series of experiments were conducted on composite girders to investigate the long-term flexural behaviour. The composite girder is formed by a prefabricated prestressed AAC inverted-T girder with cast-in-situ ACC topping concrete. The midspan deflection of two composite girders, subjected to self-weight and additional sustained loading, were measured over a 9-month period. Subsequently, flexural tests under four-point bending configuration were performed at the age of 9 months and the reference age of 28 days. The results showed that the specimens tested at 9 months exhibited reduced initial stiffness, decreased cracking load and larger crack widths in the precast prestressed girder compared to those tested at 28 days. The reduction in stiffness likely stems from decreased elastic modulus and structural cracking. Meanwhile, the lower cracking load arises from prestress losses caused by ongoing (restrained) shrinkage and creep, consistent with AAC material test observations. Larger crack widths observed in the precast girder may result from a degradation of bond between AAC and prestressing strands over time. The distinct failure patterns of the 9-month specimens (anchorage failure for sample subjected to self-weight only and flexural failure for sample exposed to additional sustained load), highlighted the role of creep on bond behaviour between prestressing strands and AAC, particularly as a function of varying stress levels at the level of strands. Finally, analytical models were applied to evaluate the prestress loss and flexural behaviour of the specimens. The effective prestressing force and cracking loads at both testing ages were overestimated when the effects of (partially) restrained deformations between precast and cast-in-situ AAC were neglected. More accurate analytical predictions were achieved when these long-term effects and the level of restraint in the composite girder were considered.

Non-hydraulic lime (also known as air lime) is an ancient carbonatable binder that has regained attention due to its carbon sink potential. Besides lower CO2 emissions during production, air lime also absorbs carbon dioxide during its hardening process. Yet, the challenge with non-hydraulic lime (and alternative binders in general) lies in the absence of data, standards, and replicable studies. For instance, air lime is often used in masonry mortars, where volume stability (shrinkage and creep) is required to ensure structural safety, but research on this issue remains scarce. Therefore, the objective of this study was to apply existing frameworks to experimentally measure the total creep (EN 12390–17:2019) of non-hydraulic lime-containing mortars. Four groups were analyzed, with non-hydraulic lime contents of 100 %, 67 %, 50 %, and 0 % (binder volume). Specimens were subjected to three different curing conditions and then loaded and monitored for up to 240 days. The results showed that (i) unlike Portland cement, non-hydraulic lime mortars needed more time to develop strength under natural environmental conditions; (ii) the phenolphthalein test did not accurately monitor the carbonation depth of air lime-rich mortars; (iii) air lime-rich systems showed less shrinkage, possibly due to carbonation-induced expansion; and (iv) air lime-rich groups exhibited greater creep strains, confirming their high deformability. These findings demonstrate that air lime-containing mortars exhibit a distinct time-dependent behavior, highlighting the need to adapt existing standards for more accurate and reproducible long-term performance assessments.

Efflorescence is a significant aesthetic and structural issue for alkali-activated materials (AAMs). This study addressed this issue at the aggregate level for the first time. The results indicated that substituting sand with aluminosilicate-based lightweight fine aggregate (LWFA) by 20 % or 50 % in volume reduced the efflorescence of alkali-activated slag (AAS) mortars by 14.6 % or 43 %, respectively. The mitigation mechanisms of LWFA were proposed in terms of gels, pore solution and microstructure. Specifically, the pozzolanic reaction of LWFA provided gels with additional Si and Al, which contributed to binding Na⁺ in the pore solution, thereby reducing the available Na for efflorescence formation. Combined with its internal curing effect, LWFA densified the surrounding pastes, which hindered the transport of ions and water, thus limiting the formation of efflorescence products. Furthermore, the incorporation of LWFA enhanced the flexural strength of mortars without significantly compromising compressive strength.

Existing research on the mechanisms affecting the strength of cementitious materials primarily focuses on the composition and properties of cement hydration products, often overlooking the interactions between different products. This study presents a systematic experimental and theoretical investigation into the mechanical properties of cementitious materials, emphasizing the interactions between crystal and gel products driven by crystallization pressure. A new mechanism based on crystallization pressure is proposed to explain the impact of the interactions between hydration products on the strengths of cementitious materials. Experiments were conducted by immersing specimens in solutions with tailored ion concentrations (including water, isopropyl alcohol, ethanol, and solutions of calcium hydroxide and calcium acetate) to vary the crystallization pressure. The flexural and compressive strengths of these specimens were then tested. An analytical model was developed and validated against the experimental data. Both experimental and calculated results demonstrate a negative correlation between crystallization pressure and strength. Specimens subjected to crystallization pressures of 101.7 MPa and 147.8 MPa showed reductions in flexural strength of 19.34 % and 30.65 %, respectively, and decreases in compressive strength of 10.00 % and 14.41 %, compared to control specimens with zero crystallization pressure. These results suggest that ion concentrations in the pore solution alter the crystallization pressure, which in turn affects the interactions between crystal and gel products and strength of cementitious materials. This study provides insights into the mechanisms of strength degradation due to moisture in porous materials.

This research investigated the use of wood biomass fly ash (WBFA) as a key component in developing low-carbon cementitious materials. WBFA was first subjected to water pretreatment and grinding to remove metallic aluminum and free lime, reducing expansion and cracking risks. Characterization of WBFA showed its high calcium and alkali-bearing phases but limited aluminosilicates. Dissolution test showed WBFA had strong alkalinity, suggesting its role as an activator for aluminosilicate-bearing minerals. A novel cement- and chemical-free binary binder was developed using 50 % treated WBFA and 50 % blast furnace slag (BFS). Paste with a water-to-binder ratio of 0.4 achieved 40 MPa compressive strength at 60 days. The use of superplasticizer significantly improved flowability, allowing the water-to-binder ratio to be reduced to 0.25, which resulted in compressive strength up to 58 MPa at 60 days. Calcium aluminate silicate hydrates (C-A-S-H) gels and ettringite were identified as the main reaction products in the pastes.