Concrete is one of the primary contributors to global carbon emissions, mainly due to the widespread use of Portland cement. Transitioning to more sustainable binder alternatives is therefore very crucial. The potential advantages of using wood biomass fly ash (BFA) as a sustainable precursor in the manufacturing of alkali-activated concrete is investigated in this study. Several biomass fly ashes (BFA1, BFA2, BFA3, and WA4) were characterised to identify the most suitable candidate for CO₂ sequestration. Focusing on the existence of reactive Ca- and Mg-bearing phases, the selection was based on both chemical composition and phase analysis using XRF and XRD, followed by a free lime content analysis. Among these investigated ashes, BFA1 showed the most interesting characteristics, particularly in regard to its possible CO₂ absorption capacity.
The selected biomass fly ash (BFA1) underwent a two-stage pretreatment process intended to improve its environmental performance as well as to improve its use in alkali-activated concrete. The first step involved a water-interaction treatment. This treatment was primarily meant to prevent the generation of hydrogen gas, an issue that typically originates from the reaction of metallic aluminium in the ash with the alkaline environment. In addition to that, this treatment also enables the immobilisation of heavy metals. The second pretreatment was an accelerated carbonation pretreatment. This is mainly focusing on an increase in the CO₂ sequestration by transforming reactive CaO and Ca(OH)₂ into stable carbonates such as calcite. In addition to carbon absorption, this carbonation process contributed further to the immobilisation of heavy metals.
The effectiveness of each of these methods was assessed. The main assessment criteria were the reduction in heavy metal concentration, removal of metallic aluminium, and overall carbonation efficiency. Both treatments effectively dropped heavy metal levels to below the Dutch Soil Quality Limit (SQL). Furthermore, the combination of both treatments proved most successful for totally mitigating metallic aluminium content. Hereby resolving major challenges for the safety of including BFA into concrete. The carbonation of the ash was carried out through two routes, a dry route and a wet route (L/S = 0.3). The effectiveness of the wet carbonation method exceeded the gas-solid method by achieving complete carbonation in just eight hours. In contrast, the gas-solid approach was significantly slower, and after two months, total carbonation was nevertheless not achieved. The persistent presence of free lime confirmed the limited efficiency of the gas-solid route. The CO₂ absorption capacity of BFA1 was eventually determined to be 6.59% by weight, highlighting the effectiveness of the wet carbonation method in facilitating carbon sequestration.
Combining QXRD, ICP-OES dissolution, FTIR and isothermal calorimetry allowed for the assessment of the reactivity of the pretreated BFA1 samples. Raw BFA showed the most reactivity among the various treatments, based on its largest cumulative heat release from the isothermal calorimetry test. Its finer particle size distribution and lower degree of particle agglomeration were mostly responsible for this increased reactivity. Raw BFA also showed the highest dissolution levels of alumina and silica in the ICP-OES test, further confirming its superior chemical reactivity in alkaline environments. On the other hand, the samples that underwent carbonation treatment showed a reduction in reactivity. This was clear from the lower total heat generated in the isothermal calorimetry tests and the lower dissolution of reactive elements in the ICP analysis. In addition to that, FTIR spectra showed the presence of gel-like structures in both water-treated and carbonated BFA1 samples, demonstrating the initial formation of reaction products. These early reactions reduce the reactivity of the material by consuming some of its available reactive content, thereby influencing the reactivity during subsequent alkaline activation.
Following the pretreatment process of the ash, the water-carbonation-treated BFA was incorporated into alkali-activated concrete mixtures by partially replacing slag at varying replacement levels. These concrete mixtures were developed and tested in order to meet the requirements for the production of sidewalk pavement blocks. Mechanical testing showed that a 25% replacement level of slag with treated BFA was sufficient to satisfy the compressive strength class of C30/37, as defined in the regulation. The reference mix (AAC-REF) reached a compressive strength of 49 MPa, while the mix including 25% pretreated BFA showed a slightly lower strength of 46 MPa. Durability testing showed that the treated BFA significantly lowers freeze-thaw resistance. The mass loss resulting from freeze-thaw after 28 cycles increased from 3.63 kg/m² in the AAC-REF sample to 5.66 kg/m² in the BFA-containing mix at the 25% replacement level, a significant reduction in the long-term durability under freeze-thaw conditions.
Paste samples were prepared to analyse the impact of BFA addition on the microstructure and phase composition. FTIR analysis of the paste determined the degree of polymerisation, showing a slightly increased polymerisation degree in the BFA-containing paste. QXRD and TGA were applied to determine the amount of reaction products formed after alkali activation. Both pastes contained similar types of reaction products, but the reference paste contained a greater amount of amorphous phases. Lastly, SEM analysis was performed to examine morphological and compositional changes due to the incorporation of BFA. BFA incorporation resulted in the development of micro-cracks between the BFA grain and the surrounding matrix and within the BFA particle itself. SEM-EDX point analysis revealed that the reaction gel consisted mainly of C–A–S–H, although the BFA-containing specimens had a larger Ca/Si ratio, likely due to the high calcium level in the BFA and the existence of calcite.
A life cycle assessment (LCA) was conducted to measure the environmental benefits of including water-carbonation-treated BFA, with a focus on lowering its carbon footprint. The results showed that replacing 25% of slag with pretreated BFA reduced CO₂ emissions by 21.28% relative to the reference mix, which consisted of 100% slag. This shows the potential of using BFA as a sustainable alternative precursor in an alkali-activated system.
Finally, this thesis demonstrates that pretreated biomass fly ash can be utilised in alkali-activated binder systems, especially under combined water and carbonation treatments. Although these treatments might slightly reduce the reactivity of the ash, their environmental benefits, including CO₂ sequestration, metallic aluminium elimination, and heavy metal immobilisation, provide strong justification for their incorporation in sustainable building materials.

The Dutch Climate Act (2019) requires a substantial reduction in greenhouse gas (GHG) emissions, targeting a 49% reduction by 2030 and 95% by 2050. The construction sector, which is responsible for 15% of the Netherlands' CO2 emissions, largely relies on concrete, a material that contributes up to 8% of global CO2 emissions, primarily due to cement production. Transitioning to sustainable concrete is vital for meeting these climate targets. This study explores how demand-side organisations, particularly purchasers, can facilitate the adoption of green concrete in the Netherlands by establishing environmental standards and prioritising sustainable materials in construction projects.

This research utilises qualitative methods, including literature reviews, stakeholder interviews, and case studies of both conventional and green concrete projects. The findings emphasise the importance of promoting the 'cement with purpose' concept, generating demand for near-mature innovations, providing extensive testing for emerging innovations, and contributing to the development of alternative materials beyond slag. At the project level, the successful adoption of green concrete is associated with clear sustainability targets, strong engineering capabilities, client willingness to accept risks, and the strategic use of pilot projects.

The study proposes a conceptual framework, the Green Concrete Adoption Strategy for Purchasers (GCAS-4P), which combines strategic and practical insights to assist demand-side organisations in advancing the green concrete transition. It also highlights the need for further research to consider supplier perspectives and broader regional transitions.

Cement production for concrete is responsible for 5-8% of the global anthropogenic emissions, making it essential to search for alternative binders. This study focuses on alkali-activated materials (AAMs) as a potential replacement for Portland Cement (PC) to reduce carbon emissions. The practical implementation of AAMs in the construction industry faces challenges, particularly related to volume instability caused by drying shrinkage. Drying shrinkage is linked to both water loss through evaporation and the hydration process. The underlying mechanism of drying shrinkage in AAMs is not well understood yet, hindering their widespread application.

The aim of this study is to advance the understanding of the drying shrinkage mechanism in AAMs, by considering the contribution of the pore size distribution and gel characteristics of AAMs. A detailed analysis is performed to identify the governing parameter related to the drying shrinkage mechanism. This is done by controlling the pore size distribution and total porosity at moment of exposure, while differences in the gel composition were obtained. Moreover, the impact of different mix design parameters of blended AAMs on drying shrinkage behaviour, weight loss, microstructural development, flexural and compressive strength are investigated. The selected mix design parameters in this study include slag-to-fly-ash ratio (1, 0.7 and 0.5), curing time (3, 7, 14 and 28 days) and Na₂O wt.% content (4 and 5 wt.%).

Results from the study indicate that drying shrinkage in AAMs is influenced by factors beyond water loss, diverging from the observed correlation in PC. The study highlights important findings related to mix design parameters. In terms of the slag-to-fly-ash ratio, an increase in ground granulated blast furnace slag (GGBFS) content correlates with reduced drying shrinkage, weight loss, refinement of the pore structure and total porosity. Regarding curing time, prolonged curing durations lead to decreased drying shrinkage and weight loss, coupled with improved flexural and compressive strength. As for activator content, an increased amount of activator refines the pore structure, resulting in reduced total porosity, weight loss, and increased compressive strength. However, drying shrinkage remains relatively constant over the 56 days exposure.

Based on the starting point that the pore size distribution of selected samples at the moment of exposure to drying was controlled, it is suggested that gel characteristics, i.e. reaction products, rather than pore size distribution, govern the drying shrinkage phenomenon in AAMs. Comparative analyses underscore the influence of homogeneous reaction products, a higher atomic Ca/Si ratio and the availability of sodium and silicate from the activator. At the moment of exposure, the type of gel is more crucial than the quantity, as demonstrated by the sample with more reaction products exhibiting greater drying shrinkage in the analysis.

The drying shrinkage mechanism in AAMs is strongly correlated with microstructure and the nature of reaction products. The comprehensive results of this study suggest that the gel characteristics have an crucial role as a driving force in the mechanism of drying shrinkage. The study underscores the substantial influence of mix design parameters on drying shrinkage, offering valuable insights for the practical implementation of AAMs in construction. This research marks a significant step forward in enhancing our understanding of this complex phenomenon for AAMs.

The study provides several recommendations for future research, including extending the range of mix design parameters and curing times to evaluate the findings of this study, assessing the rate of reaction of mixtures and considering the impact of drying on the exposed pore structure. Furthermore, the application of N₂ adsorption to detect the smaller range of pores in AAMs, the determination of the influence of internal relative humidity on drying shrinkage, and the investigation of cracking potential of AAMs related to drying shrinkage are also suggested.

Alkali-activated fly ash (AAFA) is being increasingly acknowledged as an eco-friendly binder free of Portland cement, valued for its low carbon footprint and promising engineering properties. However, the application of AAFA has been limited due to its unstable and uncontrollable engineering properties, which are closely tied to its microstructure. The microstructure of AAFA can be affected by several factors, including the intrinsic properties of fly ash, the types of alkaline activators, the mixture and curing regime. These factors can lead to various reactions, resulting in diverse microstructures, and thus a wide range of engineering properties. A deep understanding of the relationship between these influencing factors and the resulting microstructure is essential to bridge the gap between the mixtures and their corresponding engineering properties. Although the effects of these factors on the microstructure of AAFA have been extensively investigated experimentally, there is currently no numerical model capable of simulating the chemical reactions and microstructural development of AAFA. As a result, the reactions and microstructure, and thus the engineering properties of AAFA, remain unpredictable for a given mixture. Simulating the reactions and microstructural development would enable the customization of mix designs to achieve desired engineering properties, thereby promoting the application of AAFA. Therefore, the aim of this research is to simulate the reaction process and development of the microstructure of AAFA.
Thermodynamic modeling is a robust approach to simulate chemical reactions. However, the main challenge in thermodynamic modeling of AAFA lies in the lack of a thermodynamic database of its primary reaction product, N-(C-)A-S-H gel, which varies in Si/Al and Ca/Al ratios. Developing such a database requires accurate determination of the chemical compositions of N-(C-)A-S-H gels, which is difficult to achieve with conventional experimental techniques. Therefore, this research addresses this challenge by utilizing molecular dynamics simulations to determine the chemical compositions of N-(C-)A-S-H gels. By simulating the polymerization process that mimics actual reactions, the atomic structures of N-(C-)A-S-H gels with various Si/Al and Ca/Al ratios were constructed. According to the simulation results, it is proposed that N-(C-)A-S-H gels with a Si/Al ratio of 1-3 and a Ca/Al ratio of 0-0.5 can represent the chemical compositions of N-(C-)A-S-H gel in a mature AAFA paste.
After determining chemical compositions, synthesis of pure N-(C-)A-S-H gels is the second step to determine their thermodynamic data. However, synthesizing N-(C-)A-S-H gel with a Si/Al≥2 at a high pH (corresponding to the alkalinity range of pore solutions in AAFA paste), posed a double challenge. To address this issue, using a concentrated solution with an initial Si/Al ratio higher than the target is the key. Following this approach, N-(C-)A-S-H gels with a Si/Al ratio of 1-3 and a Ca/Al ratio of 0-0.5 were synthesized successfully and characterized by using XRF, XRD, FTIR, and TGA techniques. Subsequently, the solubility of the synthesized N-(C-)A-S-H gels was measured through a dissolution test. A thermodynamic database of N-(C-)A-S-H gels with various Si/Al and Ca/Al ratios was established for the first time, encompassing not only the solubility, but also the Gibbs free energy, heat capacity, entropy, enthalpy, and molar volume. This established thermodynamic database is the key to performing thermodynamic modeling to simulate the reactions of AAFA.
Coupled with the reaction kinetics determined by isothermal calorimetry and SEM-EDS analysis, the thermodynamic modeling of AAFA was performed for the first time to investigate the formation of reaction products and the phase assemblage of AAFA over time in GEMS software. The sodium hydroxide-activated system showed a close consistency between the modeling and experimental data regarding phase assemblage and pore solution chemistry, while for the sodium silicate-activated system, the simulated ion concentrations in the pore solution showed discrepancies compared to the experimental results. This discrepancy may be attributed to the high ionic strength in the sodium silicate-activated system, limitations in thermodynamic data of N-(C-)A-S-H gel and thermodynamic modeling approach itself.
To simulate the microstructure of AAFA, GeoMicro3D model, originally designed for alkali-activated slag, was extended to adapt to AAFA. To achieve this, first, the dissolution of fly ash in an alkaline solution was investigated experimentally, from which prediction functions were developed to describe the dissolution rate of Si and Al, accounting for the intrinsic characteristics of fly ash, solution pH, and temperature. The developed functions can accurately predict the dissolution behavior of fly ash, aligning well with the experimental results. Then, the GeoMicro3D model was extended by equipping with the thermodynamic database of N-(C-)A-S-H gels and the prediction functions for the dissolution of fly ash. GeoMicro3D was employed to simulate the reaction process and the 3D microstructural development over time of the sodium hydroxide-activated fly ash paste. The distribution of various phases in a 3D microstructure of AAFA can be captured and visualized over time. The simulated degree of reaction of fly ash and the porosity of AAFA were in good agreement with the corresponding experimental data. Furthermore, GeoMicro3D can well simulate the pore solution chemistry over time, consistent with the experimental results.
To sum up, the reaction and microstructure evolution of AAFA were investigated using multiple simulation techniques in this work. The extended GeoMicro3D model developed in this research paves the way for simulating the microstructure and the pore solution chemistry for any given AAFA mixture. This advancement contributes to a deeper understanding of the relationship between the AAFA mixture and the resulting microstructure. Furthermore, the mechanical properties, transport properties and durability of AAFA can be further evaluated based on the simulated microstructure constructed by using the extended GeoMicro3D. This model enables industries to effectively manage fly ashes of varying qualities and customize AAFA to meet specific engineering requirements. This not only improves the utilization of fly ash but also promotes the sustainability of construction practices.

With growing concern for global warming, the electricity industry is actively promoting the transition from coal to renewable energy sources. Due to the carbon neutrality of wood biomass energy, it has become one of the most popular options of renewable energy sources. However, the by-products resulting from biomass combustion, particularly wood biomass fly ash (WBFA), have not received sufficient attention. Direct disposal of WBFA poses environmental threats and causes pollution. From the perspective of the construction industry, the energy transition has led to a scarcity of coal fly ash (CFA) that is intensively used as supplementary cementitious materials (SCMs) in construction industry. With the increasing demand for raw materials in construction industry, it is of great interest to explore whether WBFA can be integrated as a new material in construction industry. This motivates the initiative of this research, driven by significant industry demand.

This thesis aims to enlarge the utilization efficiency of WBFA by recirculating WBFA as a valuable mineral to develop sustainable low-carbon cementitious materials. Prior to the experiment, a literature review on the properties of WBFA and current WBFA utilization methodologies in cementitious materials are summarized. An application-oriented WBFA classification was proposed, providing a guideline for the utilization of WBFA in preparing cementitious materials.

For the experimental research, three types of WBFA were initially characterized and screened based on their physicochemical properties, i.e., the content of unfavoured metallic aluminum and reactive components. One type of WBFA with representative properties was selected as the most suitable candidate for further investigation. To remove the metallic aluminum in WBFA, a two-step pretreatment method is proposed. The feasibility of WBFA for binder formulation was then evaluated through dissolution tests.

Based on the characteristics of WBFA, two types of binders were proposed. In chapter 4, considering the high alkalinity of WBFA, WBFA was used to enhance the reaction of aluminosilicates. An innovative clinker-free binary binder with WBFA and blast furnace slag (BFS) was developed. The effects of different WBFA to BFS ratios on reaction kinetics, hydration products, and microstructure evolution were studied. Following this, WBFA was further used as a mineral additive for BFS replacement in BFS blended cement. The effects of WBFA on both BFS and cement reactions were comprehensively studied using different characterization techniques. These two chapters together provide new solutions for the valorization of WBFA in novel binder formulations.

The carbonation of WBFA-containing binders investigated in chapter 4 and 5 was studied in chapter 6. The carbonation kinetics of pastes were calculated based on the carbonation depth development. It was found that in WBFA-BFS binary pastes, mixture with 50% of WBFA and 50% of BFS showed the best carbonation resistance, although the carbonation coefficient was much larger than cement pastes. When WBFA was introduced in BFS blended cement, it was observed that there was a decreased carbonation resistance in pastes with more WBFA. By analysing the microstructure evolution, it was concluded that pore connectivity played the key role in governing the carbonation process of pastes. Further grinding of WBFA to reduce its porous structure was recommended to reduce the pore connectivity and improve the carbonation resistance of pastes with WBFA.
The environmental impact evaluation is of great significance for waste utilization in the construction industry, as it can, to a certain extent, help quantify the sustainability of specific products. In chapter 7, bio-ash bricks and bio-ash composite cement were developed based on the mixtures studied in Chapters 4 and 5, respectively. A cradle-to-gate life cycle analysis (LCA) was conducted to evaluate the contribution of integrating WBFA for the production of these construction products. Possible improvements regarding further reducing the environmental impact of these products are discussed.

In summary, this thesis offers novel options for the utilization of WBFA in the construction sector as a binder component. Binary paste containing up to 70% WBFA demonstrates satisfactory mechanical properties for low-strength applications. In BFS-blended cement, substituting up to 30% of BFS with WBFA enhances early compressive strength, only a 7.67% reduction in compressive strength after 90 days. These findings indicate high utilization efficiency for WBFA. The investigations in the reaction kinetics and microstructure evolution of pastes with different WBFA to BFS ratios in the binders yield valuable insights into the function of WBFA in binder reaction. This knowledge can serve as a valuable reference for engineering practitioners seeking to customize the properties of these binders. The development of building products such as bio-ash bricks and bio-ash cement exemplifies the conversion of WBFA into construction materials. This emphasizes the notable ecological advantages of WBFA as a resource for the construction sector, highlighting the academic and industrial interests in utilizing WBFA for the development of sustainable low-carbon cementitious materials.

Climate change is the main global concern today, triggering a transformative shift in several sectors, especially the construction industry. High carbon emissions during Portland cement (PC) production necessitate a gradual shift toward more environmentally friendly alternatives, such as alkali-activated materials (AAMs). AAMs offer a promising, low-carbon solution for the production of alternative building materials. Introduction of these materials, however, require certification backed by well-documented test results. The widely used EuroCode 2 (EN 1995-1-1) (EC2) for PC concrete currently lacks guidelines for the use of AAC. Experimental data and reliable models for estimating long-term mechanical properties, especially creep and shrinkage phenomena, are still missing. The aim of this thesis is to evaluate creep behaviour of AAC, clarify underlying mechanisms and develop a creep model that takes into account specific microstructural and nanoscale properties of alkali-activated paste....

The development of an efficient and sustainable transportation system is crucial for the effective functioning of economies. Concrete, a widely used material for road construction, poses significant environmental challenges. A sustainable alternative is to use alkali-activated concrete (AAC) for road construction. However, the aggregates used in AAC are generally mined, contributing to the negative environmental impact. To address this concern, municipal solid waste incineration (MSWI) ashes, specifically MSWI bottom ash (BA), can be utilised to replace natural aggregates. Thus the construction of pavements using sustainable concrete facilitates its growing demand without burdening the environment.

This research focuses on the utilisation of municipal solid waste incineration bottom ash (MSWI BA) aggregates in AAC for potential application in pavements. The study was divided into five phases: aggregate characterisation, mechanical performance evaluation, long-term performance study, microstructure analysis, and life cycle assessment (LCA) analysis. The physical properties of MSWI BA aggregates indicated that the aggregates are porous and weak. Nonetheless, these aggregates showed comparable properties to natural aggregates and can still be used for pavement application. However, the metallic aluminium in the MSWI BA aggregates releases hydrogen gas leading to concrete cracking and swelling, thus, hindering its use in various applications. To address this concern, alkaline pre-treatment using sodium hydroxide solution was employed in this research. An optimal replacement level of 30% was chosen based on the effectiveness of the pre-treatment in removing metallic aluminium and the compressive strength of AAC containing MSWI BA aggregates.

In the next phase of the research, the mechanical and long-term performance of AAC with optimum replacement level was evaluated. The results demonstrated that the concrete satisfied the mechanical performance requirements for pavements. However, the freeze-thaw resistance of the AAC was below the norm requirement due to the air voids and associated cracking, which was confirmed through scanning electron microscopy (SEM) and X-ray computed tomography analysis.

SEM analysis revealed reactive phases in the MSWI BA aggregates and poor aggregate-matrix bonding for the coarser fraction compared to the finer aggregate fraction, leading to decreased mechanical performance. Despite these findings, the AAC containing MSWI BA aggregates satisfied the majority of the norm requirements, indicating its potential for road pavement application. However, evaluating the environmental impact of adding MSWI BA aggregates in concrete is essential. The life cycle assessment analysis demonstrated that the optimal MSWI BA sample exhibited better environmental effects, indicated by a lower environmental cost indicator value compared to AAC and ordinary Portland cement concrete samples with similar performance.

In conclusion, the pre-treatment method utilised in this research is optimal for a replacement level of 30% of gravel with MSWI BA aggregates. The AAC with 30% replacement level meets all the mechanical property requirements stipulated by the norm for pavement application, exhibits good air void distribution, and has limited environmental impact owing to the lower ECI value. This study evaluated the feasibility of applying MSWI BA aggregates in AAC for pavement application and showed promising results.

Geopolymer concrete, a relatively new building material has been suggested as an alternative to Ordinary Portland Cement (OPC) based concretes for within the building sector, due to it having a relatively low CO2 emission during production. An issue with geopolymer concrete however, is that high amounts of early age creep, shrinkage and decrease in elastic modulus over time has been observed which in conjunction with the existing research on geopolymer concrete having been predominantly conducted in laboratory settings, leads to questions about the applicability of these findings and thus the use of geopolymer concrete as a replacement for OPC based concretes in concrete structures. To address this issue, this study makes use of Fiber Bragg Grating (FBG) fiber optic sensors, placing them within reinforced steel which in turn are placed inside geopolymer concrete to obtain data that is more applicable to real world settings compared to prior findings observed within laboratory settings.
Four precast prestressed geopolymer concrete girders are produced and rebars containing FBG fiber optic sensors are placed prior to casting. Measurements before and after the release of prestressing are analysed to determine the apparent transmission length of the prestressing strands and compared to methods defined by Eurocode EN 1992-1-1. The applicability of these guidelines is evaluated, as these are intended for use with conventional concretes. The changes in strain over time, and elastic modulus changes during curing of the precast girder is monitored and analysed, focusing on the effect of time dependent changes of the concrete to the effectiveness of the prestressing forces. The girders are combined with a geopolymer concrete topping to form two beams and one slab. The beams are subject to a flexural test and a shear test respectively. The slab undergoes a cyclic loading test before being tested in two critical point load locations in two separate tests. The FBG measurements gained during the tests are evaluated using analytical methods.
The results show that the FBG fiber optic sensors integrated into steel rebar can deliver strain measurements in locations conventional strain sensors cannot be applied. The FBG data suggests that conventional concrete transmission length guidelines are applicable to this geopolymer concrete mixture. As the FBG-integrated rebars were all placed in the same location in the precast girder cross section, the strains measured by these FBGs are only representative of concrete near the core of the girder, where the concrete is not exposed to drying conditions. And because this geopolymer concrete is susceptible to drying, the difference between measurements and expected values such as the elastic modulus and the drying shrinkage can be explained by the low amount of drying that the concrete in the core of the girder experiences. Due to the positioning of rebar in the cross section of the precast girder in this study, crack initiation during the flexural test was not detected. The occurrence of cracks is detected in the measured strains as it diverged from the linear elastic model during the crack propagation phase. This shows that the cross sectional position of the sensors is important for the desired function and role of concrete in-situ FBG monitoring.
Overall, the data that the (rebar-integrated) FBG strain sensors can provide can be of great use towards the larger task of bringing geopolymer concrete structures to a real life application. In-situ FBG strain data of the precast prestressed girders provide additional information into the application of this SCGC mixture in larger scale structural elements. This data is a useful addition to the data gained through conventional methods, and results from lab testing. FBG monitoring can provide strain data from the core of structural elements, giving an insight of the behaviour during curing and (destructive) testing that is otherwise difficult to obtain.

Alkali-activated material (AAM) is one of the most attractive alternatives to ordinary Portland cement (OPC). Recently, more and more research interests are devoted to durability performance. In cold areas, freeze-thaw resistance is a crucial durability factor for concrete. However, the understanding of the freeze-thaw resistance of AAMs is minimal. Accordingly, the subject of this thesis is drawn forth. The main aim of this study was to investigate the effects and mechanisms of using admixtures (SAP and AEA) to improve the freeze-thaw resistance of alkali-activated slag (AAS).
Regarding the general properties, such as workability and mechanical properties, it was found that the influence of adding SAP or AEA is acceptable. Then, the air-void systems created by SAP and AEA were reconstructed and characterized by the micro-CT scan. It was found that both SAP and AEA successfully entrained air voids into AASM, while the characteristics of the resultant air-void system were quite different. Further analysis on the surface condition of AASM undergoing 28-day sealed curing or preconditioning procedures in the CDF test, and the ASTM C672 test revealed that AASM shows a considerable surface microcracking potential. Samples sealed for 28 days showed a considerable extent of microcracking due to autogenous shrinkage. Samples that underwent 14-day drying after 7/14 days’ curing showed significant microcracking due to autogenous shrinkage and drying shrinkage. With the addition of SAP, the cracking caused by autogenous shrinkage was minimized, but the cracking caused by drying was only slightly reduced. With the addition of AEA, there was only a minor improvement in surface integrity.
The freeze-thaw resistance of AASM with or without the addition of SAP or AEA was investigated in the form of surface scaling damage by a modified CDF test. Plain AASM showed poor surface scaling resistance mainly attributed to the pre-existing surface microcracking. The addition of SAP and AEA successfully improved the surface scaling resistance of AASM. The improvement was more significant by adding SAP due to the effect of improving surface integrity. Based on the SAP mixtures, a good correlation was found between the SAP air-void system and the resultant surface scaling resistance. The final cumulative surface scaling generally decreased with higher entrained air content, denser air voids distribution, and smaller air voids size. A preliminary logarithm model was developed for the relationship between the reduction in surface scaling and the equivalent water/binder ratio and the air-void system. Finally, upscaling tests on the concrete scale also found that the addition of SAP improved the surface scaling resistance of AASC.
Overall, in this study, the freeze-thaw resistance of AAS was successfully improved by the SAP and AEA. The effects of adding SAP/AEA and the related factors on the selected properties of AASM were revealed. The mechanisms behind these observations were also understood and generated a series of further research possibilities. It is hoped that these findings and observations can give some guidance to the industrial applications of AAS and some inspiration to the scientific community.

Concrete made with Portland cement has good behaviour under compressive stress, but it is weak in tension. Cracking caused by tension is a typical problem in concrete practice. High autogenous shrinkage at early ages is one of the causes of cracking, especially in high/ultra-high performance concrete. In that stage shrinkage is strongly related to the decrease of relative humidity (RH) inside the concrete. To minimize the probability of cracking induced by autogenous shrinkage at early age, internal curing, which can provide moisture inside the concrete, has been proposed. Several internal curing agents, such as Super Absorbing Polymers (SAP) and saturated lightweight aggregate (LWA), are utilized in high performance concrete and have shown good results for mitigating autogenous shrinkage. The use of these agents, however, also have some drawbacks. Searching for an alternative internal curing methods for ultra-high performance concrete remains a challenge....

In recent years, considerable attention has been given to the utilization of municipal solid waste incineration (MSWI) bottom ash as a mineral resource for construction materials. MSWI bottom ash is the primary residue discharged after incinerating municipal solid waste. The generation of MSWI bottom ash is increasing dramatically with the wide application of waste incineration techniques. Different methods have been proposed to improve the quality of MSWI bottom ash and make it suitable as supplementary cementitious material (SCM) or precursor for alkali-activated materials (AAM). However, there is no systemic guidance on how to select quality-upgrade treatments for MSWI bottom ash. When using MSWI bottom ash to prepare blended cement pastes and alkali-activated pastes, the optimal mix design is usually found by trial and error. Very little information is available in the literature regarding the reaction of MSWI bottom ash as SCM and AAM precursor. The contribution of MSWI bottom ash to the microstructure formation and strength development of blended cement pastes and alkali-activated pastes is not very well understood.
The goal of this research is to develop knowledge that can be used to support the application of MSWI bottom ash as a mineral resource for construction materials. Based on this knowledge, a strategy for using MSWI bottom ash produced in the Netherlands (4-11 mm) as raw material to produce blended cement pastes and alkali-activated pastes is proposed. This research consists of the following parts:
1. Quality-upgrade treatments of as-received MSWI bottom ash
As-received MSWI bottom ash cannot be used directly as SCM and AAM precursor due to its large particle size and presence of metallic aluminum (Al). Mechanical treatments consisting of grinding and sieving were studied and selected to reduce the particle size and the metallic Al content of as-received MSWI bottom ash. The effectiveness of the mechanical treatments used to reduce the metallic Al content of MSWI bottom ash is strongly influenced by the distribution of metallic Al in bottom ash particles. Most metallic Al separated during mechanical treatment comes from the coarse particles. The metallic Al embedded in the particles smaller than 0.5 mm is difficult to be removed via mechanical treatments (see Chapter 3).
2. Development and microstructure analysis of blended cement pastes and alkali-activated pastes
The reactivity and leaching potential of mechanically treated MSWI bottom ash (MBA) are studied. This information is used in the development of blended cement pastes and alkali-activated pastes. A dissolution test is proposed to assess the reactivity of MBA as AAM precursor. The reactivity of MBA as SCM and AAM precursor is similar to that of Class F coal fly ash (FA), but much lower than that of blast furnace slag (BFS). The leaching of antimony (Sb) and sulfate from MBA is above the threshold value prescribed in Dutch Soil Quality Decree. The dosage of MBA in blended cement pasts and alkali-activated pastes should be controlled to prevent excessive leaching of contaminants into the environment (see Chapter 4).
The reactivity of MBA is determined by the content and the chemical composition of its amorphous phase. The amorphous phase of MBA has a chemical composition within the same range as that of the amorphous phase of FA. Given that the reactivity of MBA is close to that of FA, previous experience with the mix design of Class F coal fly ash-based pastes is used as a reference for the mix design of MBA-based AAM. Additionally, thermodynamic modeling is used to predict the assemblage of reaction products and the composition of pore solution in alkali-activated MBA paste when changing the Na2O content in the activator. The modeling results are also used to guide the mix design of MBA-based AAM (see Chapter 4).
When water treatment and NaOH solution treatment are part of the mixture preparation procedure, the compressive strength of the blended cement pastes and alkali-activated pastes made from MBA is close to that of the pastes prepared with the same amount of FA (Chapters 5 and 6). The metallic Al that cannot be removed during mechanical treatments can be oxidized by treating MBA in water or NaOH solution at room temperature. Apart from reducing metallic Al content, water treatment and NaOH solution treatment also slightly change the mineralogical composition of MBA.
Blending water-treated MBA (WMBA) with Portland cement paste leads to changes in the reaction products and microstructure. WMBA delays clinker hydration on the first day but enhances clinker hydration at later ages. The reaction products of WMBA contribute to the strength development of blended cement pastes (see Chapter 5).
NaOH solution-treated MBA (CMBA) is used together with BFS to prepare alkali-activated pastes. CMBA retards the reaction of BFS during the first seven days but promotes the reaction of BFS at later ages. Adding CMBA into alkali-activated pastes changes the reaction products and microstructure. The reaction products of CMBA contributes to the strength development of alkali-activated pastes (see Chapter 6).
3. Environmental impact assessment of blended cement pastes and alkali-activated pastes
Compared with Portland cement paste, blended cement pastes and alkali-activated pastes prepared using MSWI bottom ash SCM and AAM precursor have lower environmental impacts, especially in the impact category of global warming (see Chapter 7).
This research deepens the understanding of the reaction of MSWI bottom ash as SCM and AAM precursor. This study also demonstrates how to use MSWI bottom ash to prepare blended cement pastes and alkali-activated pastes by considering the chemical and physical properties of MSWI bottom ash. Since the MSWI bottom ash used in this research has chemical and mineralogical compositions within the same range as the MSWI bottom ash reported in the literature, the knowledge developed in this work stimulates the utilization of MSWI bottom ash produced in other regions as SCM and AAM precursor for construction materials.

In 2016 the Paris agreement was adopted by 196 parties. The main goal of this agreement is to obtain a climate-neutral world in 2050. The CO2 emissions should decrease as soon as possible to achieve this goal. Concrete is the world's most used building material, and with good reason, it provides cheap, solid and reliable products used for over 200 years. However, concrete is responsible for 5-10 % of the yearly CO2 emissions worldwide. These emissions are mainly because of cement production, the binding agent of concrete. Therefore, to lower the CO2 emissions from concrete, it is most effective to opt for an alternative binder. This research focuses on alkali-activated materials (AAMs), where an alkali-activated binder has replaced cement. This binder consists of a precursor and an alkaline activator. The materials most commonly used as precursors are blast furnace slag and fly ash, waste products. The production of these materials is not nearly enough to replace cement. Therefore, there is a need for alternative precursors. Volcanic materials can be an alternative precursor, and some have been successfully applied in AAMs before. However, since volcanic materials come in different forms, validation of a wide range of volcanic materials.

This research has investigated four European aluminosilicate volcanic materials: trass, phonolite, perlite and pumice. Each of these materials has been assessed on their particle size, chemical composition and microstructure to determine whether they exhibit (pozzolanic or latent hydraulic) reactivity. All four materials classify as inert. For trass and phonolite, the lack of reactivity is most likely because of their lack of amorphous phases (around 30% and 5%, respectively). For perlite and pumice, it is because of the too coarse particles.
The reactivity of trass and phonolite is enhanced by calcination, and the reactivity of perlite and pumice is enhanced by grinding. Determination of the reactivity shows that calcination had no or a negative effect on the reactivity of trass and phonolite. Most likely because of the lack of calcium and magnesium in these materials. Ground pumice does show an increase in reactivity. However, not sufficient to be classified as reactive. Ground perlite does show reactive behaviour and is classified as pozzolanic, less reactive.

Ground perlite and BFS are used as precursors in mortar to assess the contribution of perlite to compressive strength development. It shows that perlite contributes to the strength of mortar when combined with a sodium silicate and sodium hydroxide activator. Likely, the sodium silicate is necessary to delay the alkalinity of the mixture. This alkaline delay makes that perlite does not form a layer of hydration products over the particles, making it impossible for perlite to react further and contribute to the compressive strength. TGA measurements found that because of the silicates that perlite contributes to the mixture, the hydration products become denser, which seem to cause higher strength. However, it is also found that silicates from sodium silicate solution are more effective in providing silicates than perlite is.

Of all four materials, only perlite seems to be reactive enough to contribute to the strength of alkali-activated binders as precursors. Volcanic materials cannot be considered to be one material, and each one has to be assessed individually.

Research about alkali-activated materials or geopolymers has increased in the past decade as they are regarded as a potential replacement to cement-based materials. This is due to the fact that alkali-activated materials possess several advantages over cement-based materials, and the most important one is that they are more sustainable to the environment, as they have less CO2 emissions, less energy consumption during the production process, and the use of byproducts as a binder.
The main aim of this work is to develop a mixture that has superior buildability properties with an open time of two hours or more. In order to achieve this, the effect of admixtures, specifically retarders and viscosity modifying admixtures had to be studied. The use of admixtures in geopolymer has been regarded as a complex subject because multiple factors influence their effect on the mixture, like: binders used and their percentages, alkaline activator used, and liquid to binder ratio.
In this work, the effect of 3 retarders: sucrose, sodium chloride, and sodium borate on the setting time, flowability, and yield stress development was studied. Moreover, the effect of those retarders was studied with the addition of viscosity modifying admixtures: nano-clay (attapulgite), xanthan gum, sodium carboxymethyl starch, and sodium carboxymethyl cellulose on the same properties.
The binders and the alkaline activator used were fixed through out the entire work. the binder composed of 60% fly ash, 20% blast furnace slag, and 20% glass wool. The alkaline activator consists of sodium hydroxide and sodium silicate with a SiO2/Na2O ratio of 1.5.
The addition of sucrose didn’t lead to any delay in the setting time. While both sodium chloride and sodium borate delayed the setting time, increased the flowability, and improved the extrudability of the mixtures. Out of the viscosity modifying admixtures, attapulgite had the most positive effect as it improved the thixotropic behaviour of all the mixes and improved the yield stress. Sodium carboxymethyl starch and cellulose almost had the same effect on the all the mixtures as they both improved extrudability and the yield stress in a similar trend. Xanthan gum was considered a poor admixture to be added to this mixture as it led to significant dryness which led to loss in fluidity which affected both flowability and extrudability.
The most suitable design was the B3lbA0.5 mixture which has 3% borax and 0.5% attapulgite and a liquid to binder ratio of 0.45. It had an initial setting time of more than 8 hours, flowability was maintained for 2.5 hours and it remained extrudable for 2 hours. Its yield stress ranged from 1360.87 Pa to 1977.78
Pa. After 28 days, it had a flexural and compressive strength of 5.72 MPa and 30.42 MPa respectively. Moreover, the flexural and compressive strength of 3D printed prisms was tested in the vertical and horizontal direction on the 7th day. The results showed that the flexural strength of the 3D printed prism tested in the vertical direction was the highest compared to the cast prism and 3D printed prism tested in the horizontal direction by 0.29% and 0.43% respectively. While the compressive strength of 3D printed cube tested in the horizontal direction was higher than both the cast cube and the 3D printed cube tested in the vertical direction by 0.24% and 0.32% respectively. The strength results indicate that
the mixture could be used in structural applications. The tensile bond strength was 0.69 MPa and the failure occurred near the glue, meaning that the interface is stronger than the material. In 3D printed concrete, usually the interface between the layers is the weakest point, however due to the addition of attapulgite the interface was strengthened. This explains why the compressive strength in the horizontal direction was higher than the vertical one as the interface was no longer the weak link in the specimen. The mixture’s buildability wasn’t optimal as the bottom layer had a slight big deformation and it had only
ten layers of printed material, but that is reasonable since the open time is 2 hours. This means that for big spans this mixture can be useful as it can be printed for a long period of time and its yield stress will develop.
In order for the mixture to be printable, it had to have an initial setting time higher than three hours, a spread diameter between 150-200mm and a yield stress above 1400 Pa. The above mentioned results
fall within the range of values that were needed to have a printable mixture. However, after printing the mixture it was concluded that a spread diameter of 150-180mm and a yield stress above 1600 Pa would be more suitable for both printability and buildability, because when the spread diameter was above
180mm and the yield stress was lower than 1600 Pa, the mixture’s viscosity impacted the buildability.

Alkali activated concrete is seen as possible contender to alleviate the environmental footprint of the concrete industry. The goal of this research is to evaluate the extend to which ground granulated blast furnace slag and calcined clay-based alkali activated concrete can be utilized in concrete revetment applications with equal performance in freeze-thaw and sulfate attack resistance and lower environmental impact compared to blast-furnace slag cement concrete. This research uses a combination of ground granulated blast furnace slag and calcined clay as precursor blend which is combined with sodium silicate and sodium hydroxide activator solution. An upscaling methodology is used such that differences in material behavior between each upscaling step (paste, mortar, concrete) is explained. Mix designs are developed with the Taguchi method.The alkali activated concrete mix designs develop good compressive strength, where both mix designs reach over 12MPa after 24 hours of ambient curing and over 37MPa after 28 days of ambient curing. It fulfills the requirement for revetment products and outperforms cement concrete.The water absorption is on the high side. It does not fulfill the requirement, but the high value is attributed to non-optimal compaction as the concrete phase uses a special vibration and pressure compaction machine, which does not represent the compaction enabled in a factory process as the reference concrete also fails to meet this requirement.Freeze-thaw performance of the alkali activated mortar is sufficient as 5 of 9 mortar mix designs meet the requirement from the CDF test. Inclusion of calcined clay and the effect of the modulus clearly results in worse freeze-thaw performance due to more difficult compaction, higher absorption and more interconnected pores resulting in more scaling as the de-icing solution can penetrate further in the specimens. Freeze-thaw of the alkali activated concrete and reference concrete is insufficient with large amount of scaling at the end of the test, partially attributed to compaction. However, the retarding scaling behavior of alkali activated concrete indicates good long term performance.Sulfate attack performance is tested at mortar level where specimens are exposed to 10 % MgSO4 solution for 14 days. No degradation is visible in terms of scaling and compressive strength. Slight formation of ettringite is observed, thus it is recommended to extend the testing period.LCA is performed on product level and does not consider service life and recyclability. The alkali activated concrete mix designs show the potential to reduce the milieukostenindicator with 48 % to €5,72 and reduce the CO2 emissions with 63% towards 48kg per m3 produced concrete. These are significant reductions, but for full validation of environmental footprint performance of alkali activated concrete, service life and recyclability should also be involved in the calculations.The research proves that alkali activated concrete is a very interesting alternative for cement concrete in revetment products where the saturated Dutch GGBFS market can be alleviated partially by substitution of calcined clay. However, to apply the alkali activated concrete in revetment products, more research should be carried out with regards to durability, curing methods, recyclability and service life.

Alkali-activated Materials (AAMs), including those classified as geopolymer, are obtained through the reaction between a solid precursor and an alkaline solution. Compared with ordinary Portland cement (OPC) binders, these materials maintain comparable mechanical properties but have the advantage of reducing greenhouse gas emissions and utilization of industrial by-products and residuals which helps to meet sustainability goals. AAMs are thus considered an environment-friendly construction material with great potential for next-generation concrete.
AAMs are inherently brittle. The low ductility of AAMs makes them prone to cracking and corresponding performance degradation, which is detrimental to their durability. Based on the concept of strain-hardening cementitious composite (SHCC), one solution relates to a family of fiber-reinforced composites that have high tensile ductility and multiple-cracking characteristics, i.e., strain-hardening geopolymer composite (SHGC). While much effort has been taken to develop conventional SHCC, scientific and technical knowledge of SHGC is still in the very early stage of development. This PhD project deals with the development of a cement-free strain-hardening geopolymer composite (SHGC) as a high-performance construction material using industrial wastes and by-products through alkaline activation technology:
The fracture properties and other mechanical properties of the alkali-activated slag/fly ash (AASF) paste as the matrix for SHGC were experimentally tested. The microstructure and chemistry of the reaction products were investigated to understand the fracture mechanism. It was found that the fracture properties of pastes are strongly related to the chemical composition (Ca/Si ratio) of the main reaction product, i.e., C-(N-)A-S-H gel. The fracture properties were also found to be dominated by a cohesion/adhesion-based mechanism. Furthermore, the compressive strength of AASF paste is primarily determined by its capillary porosity.
The fiber/matrix properties, including chemical bonding energy, initial frictional bond, and slip-hardening behavior of fiber during the pullout process were also experimentally studied. The chemistry and microstructure of the reaction product in the fiber/matrix interfacial transition zone (ITZ) were characterized. Their influence on the interface bonding properties was also investigated. It is found that the chemical bonding between PVA fiber and AASF matrix increases with increasing Ca/Si and Ca/(Si+Al) ratio of C-(N-)A-S-H gel. Hence, changing the slag content and the alkali activator Ms appears to be an effective way to modify chemical bonding. Unlike the formation of portlandite near the PVA fiber surface in conventional SHCC, a high-Ca C-(N-)A-S-H phase was formed in the fiber-matrix ITZ of SHGC. This explains the higher chemical bonding energy found in SHGC compared to that in conventional SHCCs. Furthermore, the adhesion mechanism of the PVA molecule in reaction products was studied using MD simulation. The study suggests that the adhesion between PVA fiber and C-(N-)A-S-H gel is primarily due to electrostatic interactions rather than van der Waals interactions.
Based on the result of fracture properties of the matrix and fiber/matrix interface properties, the SHGC is then systematically developed following a micromechanics-based design approach. The experimentally-attained matrix and interface properties served as input for the numerical micromechanics model to simulate the crack bridging behavior. Through the micromechanical modeling, the optimal fiber length and volume were selected and the behavior of mixtures with different fiber/matrix combinations was predicted. With this approach, researchers and materials engineers can design and tailor future SHGC more efficiently than by using the commonly used trial-and-error method.
Finally, the environmental impact of the SHGC with the most promising performance was also evaluated. This evaluation was conducted using a cradle-to-gate life-cycle assessment (LCA) of SHGC compared to that of conventional SHCC materials. The developed SHGC demonstrates a very promising environmental profile. It has a significant reduction of the global warming potential (GWP) and a lower or similar total environmental impact compared to conventional SHCC materials. In addition, the results also provide recommendations for further improvements in mixture design for the future development of SHGC.
This study successfully developed a sustainable slag/fly ash-based SHGC with a lower carbon footprint than conventional SHCC. It is considered a good example to utilize industrial by-products as secondary resources and at the same time contribute to a circular economy. Furthermore, this study helps to understand the fracture properties of AAMs. It also clarifies the adhesion mechanism of PVA fiber in AAMs. All of these give promising guidance for researchers and engineers to design fiber-reinforced AAMs with required fracture properties and interface bonding properties. In particular, it contributes to the design and tailoring strategies for high-performance composite, for instance, SHGC, through proper mixture design.

In this research work, the possibility of self healing of surface micro-cracks under the fog curing conditions has been studied for early age concrete. Coda Wave Interferometry (CWI) technique has been implemented to detect the micro cracks in concrete caused due to the cyclic loading. 30 load cycles has been for varying load levels and it's effect on the mechanical properties has been analyzed for early age concrete.

This research aims to improve the sustainability of Dutch prestressed concrete railway sleepers. Approximately 100.000 to 200.000 sleepers are used every year, corresponding to 12.000 to 24.000 tonnes of concrete. This will be done by replacing cement with an alkali-activated binder. The cement industry is responsible for approximately 5 to 7% of the global CO2 emission, whereas the alkali-activated binder uses no cement. Instead, by-products will take over the role of cement in concrete, activated by high pH alkalies. This research can be subdivided into four parts: Deciding the requirements, designing for the mechanical properties, determining the durability properties and conducting a Life Cycle Analysis (LCA). The main requirements follow the product specification of the railway infrastructure manager ProRail. Some requirements on manufacturability follow from a market consult. Ground granulated blast furnace slag is used as a precursor due to its availability in the Netherlands, unlike other potential candidates. An iterative mix design procedure is conducted to come to three mixes, meeting the requirements for the fresh concrete and the mechanical properties. The three mixes differ based on the binder content and activator dosage. Nineteen different mixes are designed, of which the final three meet all the mechanical and manufacturability requirements. These three mixes are subjected to tests to determine non-required mechanical properties, such as the tensile strength or the material’s elastic modulus. Finally, the durability of the newly designed alkali-activated slag concrete is assessed. Results show the designed concretemeets the requirements for fresh and hardened concrete. The results of the other mechanical properties are similar or better to the concrete mixes used nowadays to produce sleepers. However, not all requirements on durability are met. Due to the unavailability of certain test conditions, a direct result cannot be given. Therefore, the three durability properties are assessed by comparing the results of this research with results from the literature. The comparison for electrical resistivity shows an excellent behaviour, better compared to similar OPC concretes and on par with CEM III/B concrete types. The alkali-activated binder demonstrates less damage under a freeze-thaw attack with de-icing salts than other alkali-activated concretes but still fails to meet the requirement set by ProRail. The accelerated carbonation test indicates a similar carbonation resistance compared to other alkali-activated concrete types but a lower resistance compared to similar concrete. More research is necessary to investigate these properties further. The environmental impact of the concrete used to produce a sleeper is reduced by 34 to 68%compared to a CEM III/B or OPC binder, respectively. Taking into account the global warming potential only, these numbers increase to 75 to 90% respectively. The total environmental impact of a complete sleeper, including steel and plastic components, is lowered by 12 to 35%. This is explained by the fact that the steel and plastic components contribute 75% to the environmental cost, and improving the cost of these components is beyond this research’s scope. This research shows a significant potential to improve the sustainability of concrete structural elements by replacing the cement binder with an alkali-activated binder. This binder is capable of meeting the mechanical requirements, shows good workability. The compressive strength values are comparable to high strength concrete. Further research has to be conducted in the fields of behaviour under carbonation and freeze-thaw attacks. With these results and conclusions, this research has attributes to realizing more sustainable railway sleepers using an alkali-activated binder.