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 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.

The present research investigated the hydration characteristics of model (C₃S-C₃A-gypsum-blast furnace slag) and real cement slag pastes at an early age, and emphasis was laid on the interaction of gypsum, aluminate phases dissolved from both C₃A and slag. Two additional peaks arose during the decelerating stage of calorimetric measurement. The first one was originated from the renewed aluminate reaction between C₃A and gypsum, while the second one was attributed to the reaction between aluminate phase dissolved from slag and gypsum. High alumina content in slag promoted the aluminate reactions between gypsum and C₃A. On the other hand, the reaction between slag and gypsum was suppressed because of the addition of C₃A. Besides, factors affecting the optimal sulfate requirement of cement slag paste, e.g., C₃A content in cement clinker, slag substitution level, and slag chemistry, etc. were analyzed. The authors believed that the results found in this paper provided essential insights to quantitatively understand the early-age aluminate interactions of gypsum, C₃A as well as blast furnace slag in cement slag paste.

Municipal solid waste incineration (MSWI) bottom ash (BA) is widely available and has been increasingly explored for sustainable concrete production. While it is commonly used in Ordinary Portland Cement (OPC)-based concrete, its application in alkali-activated concrete (AAC) remains rare. This study developed a new AAC using MSWI BA as coarse aggregate to evaluate whether this represents a more sustainable application pathway compared to its use in conventional concrete. To address issues associated with metallic aluminum (Al) in MSWI BA, a NaOH-based pre-treatment was applied to reduce its content and minimize surface cracking and volume expansion in AAC. The incorporation of treated MSWI BA increased the overall porosity of AAC. The interfacial transition zone (ITZ) surrounding MSWI BA exhibited characteristic microstructural features. While previous studies suggested that MSWI BA-induced porosity may enhance freeze-thaw resistance in OPC concrete, the opposite trend was observed in AAC. The increased pore volume, irregular pore shapes, and MSWI BA-related microcracking reduced freeze-thaw durability. Despite these challenges, the developed AAC retained mechanical performance within strength class C30/37 and achieved a substantially lower carbon footprint compared to OPC and CEM III/B concretes. Leaching assessments further confirmed that the developed AAC complied with environmental standards and did not release harmful contaminants. Overall, these findings demonstrate that MSWI BA is a promising coarse aggregate for AAC.

The application of alkali-activated materials (AAM) based on metakaolin, fly ash and ladle furnace slag in seismic retrofitting of beam-type unreinforced masonry (URM) walls with textile reinforced mortars (TRM) was investigated in this study. Additionally, a combined seismic and energy retrofitting scheme comprising an extruded polystyrene (XPS) thermal insulation, alkali-activated or traditional cementitious mortar and styrene-butadiene rubber (SBR)-coated glass-fiber textile was studied on beam-type URM walls. A total of 12 wall specimens made of perforated fired-clay bricks were subjected to in- and out-of-plane cyclic tests. Seismic retrofitting with AAM-based TRM led to a substantial increase of load-bearing capacity, up to 70 %, while the combined energy and seismic retrofitting increased the energy dissipation capacity by at least 8 times for both in- and out-of-plane loading. Durability of the TRM jackets consisted of SBR-coated glass-fiber textile and AAM mortar was studied experimentally and at the matrix-fiber interface with Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS). A severe impact of the AAM mortar mix in fresh state on SBR-coated glass-fiber textile was quantified through a set of uniaxial tensile tests and confirmed at a microscopic level. Alkali-activated materials pose a great potential in becoming an effective and environmentally friendly alternative to traditional cementitious materials in structural repair and retrofitting applications. However, to systematically utilize the AAM-based TRM strengthening configurations studied here, the addressed durability issues need to be resolved.

Previously, the lack of a thermodynamic database for N-(C-)A-S-H gel limited the application of thermodynamic modeling to alkali-activated fly ash (AAFA). This study pioneers thermodynamic modeling of AAFA using a recently developed thermodynamic dataset for N-(C-)A-S-H gel. The reaction products, pore solutions and reaction kinetics of AAFA pastes were experimentally determined. Based on the reaction kinetics, the composition of the solid phases and the pore solution of AAFA were modeled over time. The results showed that the simulated compositions of the solid reaction products and pore solution match closely with the experimental results, especially for the sodium hydroxide-activated system. Moreover, modeling results point out the potential presence of minor reaction products (e.g., C-(N-)A-S-H gel, microcrystalline ferrihydrite, Mg-containing phases) undetectable by experimental techniques. The study also demonstrated that thermodynamic modeling accurately captured the amount of bound water in reaction products, highlighting its robustness in both qualitative and quantitative analysis.

This work evaluated the reactivity and leaching potential of municipal solid waste incineration (MSWI) bottom ash as supplementary cementitious material (SCM) and precursor for alkali-activated materials (AAM). The chemical composition of the amorphous phase in MSWI bottom ash was found to be in the same range as that of Class F coal fly ash. The reactivity of MSWI bottom ash as SCM and AAM precursor was tested to be much lower than that of blast furnace slag, but similar to that of Class F coal fly ash. The method of thermodynamic modeling was found useful in providing references for the mix design of MSWI bottom ash-based AAM. Grinding MSWI bottom ash into powder for the application of SCM and AAM precursor increased its leaching potential. Based on the findings of this study, recommendations were provided on how to use MSWI bottom ash to prepare blended cement pastes and AAM.

To better understand early stiffening of AAS pastes, distinctive microstructural features by varying the silicate modulus (Ms) have been visualized with in-situ microscopy. In addition, the activation reaction was monitored with multiple approaches, while solid and liquid phases in hydrating AAS were characterized separately. In silicate-activated AAS, it was found fine granules of reaction products are intensively dispersed in the activator solution, leading to a less flocculated system. Compared to hydroxide-activated AAS, the development of interparticle connections was limited at early ages, whereas reaction products were detected with much smaller grain size, less crystalline phase, and higher Al incorporation. Results indicate that the stiffening of hydroxide-activated AAS is attributed to the formation of a well-percolated network through solid reaction products. Instead, massive fine granules of reaction products dispersed in the pore solution continuously develop, which may intensify the interparticle interactions and macroscopically results in the stiffening of a silicate-activated AAS.

The production of cement and concrete contributes significantly to global greenhouse gas emissions. Alkali‐activated concretes (AACs) are a family of existing alternative construction materials that could reduce the current environmental impact of Portland cement (PC) production and utilisation. Successful applications of AACs can be found in Europe and the former USSR since the 1950s and more recently in Australia, China and North America, proving their potential as construction materials. However, their utilisation is limited presently by the lack of normative and construction guidelines. Raw materials’ non‐uniform global availability and variable intrinsic properties, coupled with the lack of specific testing methods, raise questions regarding reproducibility and reliability. The mechanical and chemical behaviour of AACs has been investigated extensively over the past decades, strengthening its potential as a sustainable substitute for traditional PC‐based concrete. Although a wide amount of studies demonstrated that AACs could meet and even exceed the performance requirements provided by European design standards, a classification of these broad spectra of materials, as well as new analytical models linking the chemistry of the system components to the mechanical behaviour of the material, still need further development. This report gives an overview of the potential of alkali‐activated systems technology, focusing on the limitations and challenges still hindering their standardisation and wider application in the construction field.

A deeper insight into SO₃/Al₂O₃ ratio including the contribution of alumina in slag at early age is required to ensure a properly sulfated slag cement. In this paper, to investigate the effect of gypsum and alumina of slag, emphasis was laid on the hydration characteristics of C₃S-gypsum-slag system during the early age, of which slag was synthesized in the laboratory with varying Al₂O₃ contents from 3.69 to 18.19 wt%. The duration of dormant period during the hydration of C₃S depended on Al₂O₃ content of slag significantly; however, the amount of silicate reaction before the onset of aluminate reaction was independent of slag chemistry and gypsum content added. The rate of aluminate reaction was controlled by the availability of reactants, SO₄²⁻ and Al³⁺ ions in particular, which were sourced from gypsum and slag, respectively. Calcium monosulfoaluminate only occurred in mixture when slag contained a high amount of Al₂O₃ (18.19 wt% in this study) at early age, and its formation proceeded continuously at the expense of ettringite. Sulfur rich species incorporated in slag started to participate into aluminate reaction after the main hydration peak of C₃S, and it played a similar role to gypsum.