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.

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.

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.

Under the directives of the RILEM Technical Committee 294-MPA, this publication reports on the findings of an interlaboratory study that tested fiber-reinforced GGBFS-based alkali-activated concrete (FRAAC), with participants from Belgium, India and Slovenia. The research also elaborates prediction models for the tensile splitting strength of GGBFS-based FRAAC. This research endeavoured between 2020 and 2024 to find a globally reproducible FRAAC mix that could attain the required mechanical strength and workability criteria. The primary goal of the interlaboratory study was to generate FRAAC without the use of superplasticizers in order to maintain an S4 class consistency slump and achieve the desired 28-days cube compressive strength of 40 MPa. Steel and PVA fibers were determined to be incorporated to the GGBFS-based AAC mix at 0.3 and 0.1% volume fractions, respectively, through iterative interlaboratory investigations. Experimental program was conducted to examine the compressive and tensile splitting strength of these FRAAC combinations at different curing ages, ranging from 1 to 720 days. The findings indicate that while there were a few interlaboratory variations in the mechanical properties, the FRAAC produced was uniform across all participants. The desired compressive strength of 40 MPa was attained by GGBFS-based FRAAC with both steel and PVA fibers at 28 days. Although FRAAC containing steel fibers exhibited the higher early compressive strength, FRAAC prepared with steel and FRAAC prepared with PVA both demonstrated a 720-days compressive strength of about 61 MPa. The FRAAC mixes with steel fiber additions exhibited a tensile splitting strength that was approximately 30% higher than the mix with PVA fibers. Nonetheless, at all ages, the tensile splitting strength of both FRAAC mixes was clearly higher than 2 MPa. These results support reliable and consistent experimental findings, which allude towards FRAAC as a sustainable substitute for conventional Portland cement concrete.

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.

Several exoskeletons have been developed and increasingly used in clinical settings for training and assisting locomotion. These devices allow people with severe motor deficits to regain mobility and sustain intense and repetitive gait training. However, three factors might affect normal muscle activations during walking: the assistive forces that are provided during walking, the crutches or walker that are always used in combination with the device, and the mechanical structure of the device itself. To investigate these effects, we evaluated eight healthy volunteers walking with the Ekso, which is a battery-powered, wearable exoskeleton. They walked supported by either crutches or a walker under five different assistance modalities: bilateral maximum assistance, no assistance, bilateral adaptive assistance, and unilateral adaptive assistance on each leg. Participants also walked overground without the exoskeleton. Surface electromyography was recorded bilaterally, and the statistical parametric mapping approach and muscle synergies analysis were used to investigate differences in muscular activity across different walking conditions. The lower limb muscle activations while walking with the Ekso were not influenced by the use of crutches or walker aids. Compared to normal walking without robotic assistance, the Ekso reduced the amplitude of activation for the distal lower limb muscles while changing the timing for the others. This depended mainly on the structure of the device, and not on the type or level of assistance. In fact, the presence of assistance did not change the timing of the muscle activations, but instead mainly had the effect of increasing the level of activation of the proximal lower limb muscles. Surprisingly, we found no significant changes in the adaptive control with respect to a maximal fixed assistance that did not account for subjects' performance. These are important effects to take into careful considerations in clinics where these devices are used for gait rehabilitation in people with neurological diseases.