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By reutilizing industrial byproducts, inorganic cementitious alkali-activated materials (AAMs) contribute to reduced energy consumption and carbon dioxide (CO2) emissions. In this study, coal gangue (CG) blended with ground granulated blast furnace slag (GGBFS) was used to prepare AAMs. The research focused on analyzing the effects of the GGBFS content and alkali activator (i.e., Na2O mass ratio and alkali modulus [SiO2/Na2O]) on the mechanical properties and microstructures of the AAMs. Through a series of spectroscopic and microscopic tests, the results showed that the GGBFS content had a significant influence on AAM compressive strength and paste fluidity; the optimal replacement of CG by GGBFS was 40–50%, and the optimal Na2O mass ratio and alkali modulus were 7% and 1.3, respectively. AAMs with a 50% GGBFS content exhibited a compact microstructure with a 28 d compressive strength of 54.59 MPa. Increasing the Na2O mass ratio from 6% to 8% promoted the hardening process and facilitated the formation of AAM gels; however, a 9% Na2O mass ratio inhibited the condensation of SiO4 and AlO4 ions, which decreased the compressive strength. Increasing the alkali modulus facilitated geopolymerization, which increased the compressive strength. Microscopic analysis showed that pore size and volume increased due to lower Na2O concentrations or alkali modulus. The results provide an experimental and theoretical basis for the large-scale utilization of AAMs in construction. [ABSTRACT FROM AUTHOR]

This study prepared modified alkali-activated slag repair materials by incorporating an ethylene-vinyl acetate copolymer emulsion (EVA). Sulfate attack tests, shrinkage tests, scanning electron microscopy, and mercury intrusion porosimetry tests were conducted to examine the durability and microstructural features of the alkali-activated slag repair materials. The experimental results demonstrated that adding EVA can enhance the shrinkage and strength of alkali-activated slag mortar, but that the materials exhibit poor resistance to sulfate attack. Optimizing the ratio design can yield alkali-activated cementitious materials with high strength, good durability, high bonding strength, and low shrinkage. This can reduce brittleness and increase the shrinkage rate of the material's defects, which has significant implications for subsequent fracture repair. The image of the microstructure showed that the section of alkali-activated slag paste is smooth and exhibits polymer emulsion filling gaps in the amorphous cementitious material. A connection between fibrous filaments on the cross section of the matrix crack enhances the strength of the material. The proportion of microcracks is increased and material strength is decreased after sulfate attack. [ABSTRACT FROM AUTHOR]

Removal of dissolved zinc (Zn) from water by a novel alkali-activated material (AAM) prepared from steel industry slags in a fixed-bed column was investigated. Design of experiments was used to find the optimum operation parameters [flow rate $\lpar Q\rpar$ (Q) , adsorbent mass, ($m_{{\rm ads}}$ m ads ), and initial Zn concentration ($C_0$ C 0 )] for the removal of Zn2+ from a ZnCl2 solution. Regression models for the breakthrough ($q_{\rm b}$ q b ), and saturation ($q_{{\rm sat}}$ q sat ) capacities of the bed and three other response parameters as functions of $Q$ Q , $m_{{\rm ads}}$ m ads and $C_0$ C 0 were fitted with coefficients of determination ($R^2$ R 2 ) ranging from 0.48 to 0.99. Experimental values of $q_{\rm b}$ q b and $q_{{\rm sat}}$ q sat varied within 1.42–7.03 mg Zn/g and 10.57–17.25 mg Zn/g, respectively. The optimum operation parameters were determined to be $Q =$ Q = 1.64 ml/min and $m_{{\rm ads}} =$ m ads = 4.5 g, whereas $C_0$ C 0 had negligible effect on the response parameters in the range 73–107 mg Zn/l. Finally, three empirical breakthrough curve (BTC) models were employed to describe the individual BTCs of which the modified dose – response model was found to give the best fit (0.960 $\le$ ≤ $R^2$ R 2 $\le$ ≤ 0.998). The results of the present work demonstrate that the novel AAM has considerable potential to be utilized in water purification applications. [ABSTRACT FROM AUTHOR]

This study aims to explore the effects of temperature cycling on the performance of alkaliactivated fly ash-slag cementitious materials (AAFS) under various slag contents, alkali concentrations, and alkali modulus conditions. Through analyses using XRD, SEM, and FT-IR, the research examines the evolution of mass loss, drying shrinkage characteristics, and compressive strength of AAFS subjected to 60°C temperature cycles. The findings reveal that temperature cycling significantly promotes the hydration reaction of AAFS, enhancing its compressive strength, particularly after 60 cycles of temperature exposure. The hydration products C-S-H and C-A-S-H contribute positively to compressive strength, with notable effects observed from 0 to 60 cycles. Increasing slag content magnifies its impact on AAFS performance, reducing mass loss and increasing both shrinkage rate and compressive strength. When the slag content reaches 100%, the rate of mass loss during temperature cycling is minimized, and both drying shrinkage and compressive strength are significantly improved. However, the effect becomes less pronounced when the slag content exceeds 50%. Higher alkali concentration and modulus lead to an increased matrix density, yet the compressive strength of AAFS peaks at an alkali concentration of 6% and a modulus of 1.0, due to a reduction in [SiO4]4- ions and a shift from dual to single activation. Considering both economic and practical aspects, it is recommended to use AAFS combinations with no more than 50% slag content, an alkali concentration of 6%, and an alkali modulus of 1.0. These discoveries provide theoretical support for the application of AAFS in specific environmental conditions. [ABSTRACT FROM AUTHOR]

Highlights: What are the main findings? Copper slag can be upcycled in alkali-activated carbon fabric-based composites; A 20 wt.% metakaolinite substitution of copper slag increases reaction heat and mechanical properties; What is the implication of the main finding? Low reactivity at 20 °C, but instantaneous at 80 °C with K-solution SiO2/K2O of 2.25; Composites with an elastic modulus of 19 GPa and flexural strength of 88 MPa. Copper slag is an industrial residue with a large unutilized fraction. This study presents the development of alkali-activated composites from a copper slag named Koranel®. The effects of metakaolinite, ordinary Portland cement (OPC) and surfactants were investigated. The reactivity of Koranel with potassium silicate solutions with molar ratio R = SiO2/K2O varying from 1 to 2.75, with 0.25 intervals, was investigated using isothermal calorimetry. The reactivity was relatively low at 20 °C; the reaction started after a few hours with a low silica modulus, to several weeks with the highest silica modulus. The substitution of Koranel by OPC (5 wt.%) or by metakaolinite (10–20 wt.%), both led to higher reaction heat and rate; meanwhile, the addition of 2 wt.% polyethylene glycol/2-methyl 2,4 pentanediol delayed the reaction time in the system containing metakaolinite. Raising the curing temperature from 20 °C to 80 °C shortened the setting time of the low reactive systems, from several days to almost instantaneous, opening perspectives for their application in the production of prepreg composite materials. The use of carbon fabric as reinforcement in the alkali-activated matrix led to composite materials with flexural strength reaching 88 MPa and elastic modulus of about 19 GPa—interesting for engineering applications such as high-strength lightweight panels. [ABSTRACT FROM AUTHOR]

Alkali-activated slag and fly ash (FA)-blended seawater sea sand concrete (AASC) is a new type of concrete produced without Portland cement or river sand. The advantages of utilising industrial waste and marine resources are that they are not only eco-friendly but cost-saving. This study aimed to investigate the properties of AASC exposed to elevated temperatures. Slag and FA were activated using NaOH and water glass solutions for mixing AASC. Heating and compressive tests were conducted to analyse the thermal and compressive properties of the AASC. The results showed that the AASC with higher FA content (Type II) had fewer flaky structures and more integral interfacial transition zones than the other type of AASC (Type I) after exposure to 600 °C. Type I AASC had better mechanical performance at temperatures below 400 °C but was inferior to Type II AASC beyond 600 °C. A compressive constitutive model was proposed for AASC. [ABSTRACT FROM AUTHOR]

The use of solid activators to prepare alkali-activated materials (AAM) holds great potential for on-site applications, as it eliminates the need to transport and store large quantities of concentrated alkaline solutions. This study compared the early-age properties and efflorescence between alkali-activated slag/fly ash (AASF) using solid and liquid sodium silicates as activators. The results revealed that AASF with solid sodium silicates exhibited comparable mechanical strength while possessing reduced initial setting time and flowability. All AASF mixtures were susceptible to efflorescence and carbonation, resulting in varying mineralogical compositions of carbonation products: Vaterite was detected in AASF with solid activators, while aragonite and pirssonite were identified in AASF with liquid activators containing 4 and 6 wt.% Na2O, respectively. The efflorescence of AASF exposed to bottom water was more severe than those exposed to natural conditions, as evidenced by the decalcification of reaction products, migration of alkalis, and formation of crystalline carbonates. [ABSTRACT FROM AUTHOR]

To improve solid waste resource utilization and environmental sustainability, an alkali-activated material (AAM) was prepared using steel slag (SS), fly ash, blast furnace slag and alkali activators in this work. The evolutions of SS content (10–50%) and alkali equivalent (4.0–8.0%) on workability, mechanical strength and environmental indicators of the AAM were investigated. Furthermore, scanning electron microscopy, X-ray diffraction and nuclear magnetic resonance techniques were adopted to characterize micromorphology, reaction products and pore structure, and the reaction mechanism was summarized. Results showed that the paste fluidity and setting time gradually increased with the increase in SS content. The highest compressive strength was obtained for the paste at 8.0% alkali equivalent due to the improved reaction rate and process, but it also increased the risk of cracking. However, SS was able to exert a microaggregate filling effect, where SS particles filling the pores increased the structural compactness and hindered crack development. Based on the optimal compressive strength, global warming, abiotic resource depletion, acidification and eutrophication potential of the paste are reduced by 76.7%, 53.0%, 51.6%, and 48.9%, respectively, compared with cement. This work is beneficial to further improve the utilization of solid waste resources and expand the application of environmentally friendly AAMs in the field of construction engineering. [ABSTRACT FROM AUTHOR]

Light metal die casting is usually performed using steel molds. However, these lead to a reduced quality of the casting due to the occurrence of metal corrosion on the surface and the incorporation of hydrogen into the casting as a result of required process chemistry. Ultra‐high performance concrete based on alkali‐activated slag can be used to produce mineral molds for aluminum casting. The use of reusable mineral molds not only enables the production of various thin‐walled geometries. The risk of metal corrosion is eliminated and the concrete molds can withstand multiple cycles due to their thermal stability and high strength, making them potentially superior to the already common lost mineral molds. [ABSTRACT FROM AUTHOR]

The requirements related to reducing the carbon footprint of cement production have directed the attention of researchers to the use of waste materials such as blast-furnace slag or fly ashes, either as a partial replacement for cement clinker or in the form of new alternative binders. This paper presents alkali-activated materials (AAMs) based on blast-furnace slag partially replaced with fly ash, metakaolin, or zeolite, activated with water glass or water glass with a small amount of water, and doped with zinc oxide. The mortars were tested for flow, hydration heat, mechanical strength, microstructure, and antimicrobial activity. The obtained test results indicate the benefits of adding water, affecting the fluidity and generating a less porous microstructure; however, the tested hydration heat, strength, and antibacterial properties are related to more favorable properties in AAMs produced on water glass alone. [ABSTRACT FROM AUTHOR]

Alkali-activated slag (AAS) is emerging as a possible and more sustainable alternative to Ordinary Portland Cement (OPC) in the construction industry, thanks to its good mechanical and chemical properties. Conversely, the effects of its high drying shrinkage are still a concern for its long-term durability. This study aims to investigate the drying shrinkage behaviour of six AAS/sodium hydroxide mortar compositions and the main phenomena affecting their drying shrinkage behaviour. Specifically, the molarity, solution-to-binder ratio (s/b), autogenous shrinkage, creep compliance, microcracking, and carbonation are considered as possible causes of the differences between AAS and OPC. The results show that it is not possible to correlate the shrinkage magnitude with the molarity of the activating solution, while an increase in the s/b increases the drying shrinkage. Concerning the other factors, autogenous deformation remains significant even after a period of 112 days, while the creep compliance is definitely affected by the drying process but does not seem to affect the shrinkage magnitude. Furthermore, the presence of microcracks caused by the drying process definitely influences the drying shrinkage. Finally, carbonation depends on the molarity of the activating solution, even though its effects on the material are still unclear. [ABSTRACT FROM AUTHOR]

This study aims to develop a material-saving performance prediction model for fast-hardening alkali-activated slag/silica fume blended pastes. The hydration process in the early stage and the microstructural properties after 24 h were analyzed using design of experiments (DoE). The experimental results show that the curing time and the FTIR wavenumber of the Si-O-T (T = Al, Si) bond in the band range of 900–1000 cm−1 after 24 h can be predicted accurately. In detailed investigations, low wavenumbers from FTIR analysis were found to correlate with reduced shrinkage. The activator exerts a quadratic and not a silica modulus-related conditioned linear influence on the performance properties. Consequently, the prediction model based on FTIR measurements proved to be suitable in evaluation tests for predicting the material properties of those binders in the building chemistry sector. [ABSTRACT FROM AUTHOR]

Alkali-activated (or geopolymer) membranes have emerged recently as an alternative for conventional ceramic membranes. Their main benefit is the simple and low-energy manufacturing not requiring sintering, and thus potential for clearly lower costs, while having largely similar performance as conventional ceramic materials. In this work, metakaolin, blast furnace slag, and their mixture (representing typical low, high, and medium Ca-content raw materials, respectively) were compared as aluminosilicate precursors for the preparation of self-supporting membrane disks (diameter 75 mm, height 3 mm). A thorough material characterization was performed to evaluate mechanical strength, shrinkage, microstructure, chemical composition, pore size distribution, specific surface area, zeta potential, and water flux at different temperatures (20–60 °C) and pressures (200–1000 kPa). Based on this screening, metakaolin-based membrane (i.e., the low-calcium system) indicated overall better performance than the two others based on blast furnace slag or their mixture. As a final part of the study, ammonium-containing model effluent ([NH 4 +] = 50 mg L−1) was distributed through the membrane (using 200 kPa pressure at 25 °C) to evaluate the potential for nitrogen removal and recovery. The mass balance examination indicated that ammonium was retained in the membrane matrix (i.e., not concentrated in the retentate fraction), and thus the likely removal mechanism was via ion-exchange. The obtained results provide interesting insights for the further development of alkali-activated membranes for applications requiring ammonium nitrogen removal, such as membrane bioreactors in municipal wastewater treatment. [ABSTRACT FROM AUTHOR]

This paper studied the influence of the modulus and dosage of sodium silicate on the hydration of alkali-activated copper-nickel slag (CNS) materials. CNS was used as the main raw material, and ground granulated blast furnace slag (GBFS) powder was selected as the mineral additive. The hydration and hardening mechanisms were discussed. The experimental results showed that [SiO4]4− and [AlO4]5− with a high degree of polymerization in the CNS glassy phase more easily underwent depolymerization-condensation and produced more C-S-H gels when the modulus was small and the sodium silicate dosage was high. When the content of sodium silicate was 7.0% and the modulus of sodium silicate solution was 1.0, the 28-day compressive strength of the material reached 125 MPa. This alkali-activated copper-nickel slag material can be used for mine filling, which has certain economic and ecological benefits. [ABSTRACT FROM AUTHOR]

This paper presents a new method for predicting the final products of red mud-slag-based alkali-activated materials (RM-AAMs) using comprehensive phase analysis. As the first step, a quantitative method by X-ray diffraction (XRD) was used to analyze six different types of red mud and ground-granulated blast-furnace slag (GGBS). Secondly, X-ray fluorescence (XRF) was employed to determine the bulk elemental oxide contents of the precursors. A procedure combining XRD and XRF was then used to quantify both the crystalline and amorphous components of the precursors. In addition to investigating precursors, soluble silica from sodium silicate has been considered in calculating reactive silica. The research includes forty sets of alkali-activated samples using various activators with different concentrations. The XRD results of hardened paste samples revealed that the method could successfully predict the final products of RM-AAMs. By predicting the final products of the alkali-activation process, the optimization of raw material types and contents will be more efficient. For example, in the case of having C-S-H as the final product, adding substances with high reactive alumina would be unnecessary. [ABSTRACT FROM AUTHOR]

The mechanical interactions of C-(N-)A-S-H (Calcium-sodium-aluminum-silicate-hydrate) gel with slag and fly ash inclusions in alkali-activated materials (AAM) are quantified through image-supported grid nanoindentation. Nonuniform distributions of indent-specific indentation properties reveal that the elasticity-related domain is up to 130 times the contact indentation depth, while the hardness-related domain, in turn, is by a factor of two to three smaller. These rather large domains are consistent with the slag/fly-ash inclusions being much stiffer and harder than the surrounding C-(N-)A-S-H gel. Corresponding Hashin-Shtirkman bounds for the overall AAM stiffness consistently frame ultrasonic data characterizing this homogenized material scale. This confirms our new testing protocol. [ABSTRACT FROM AUTHOR]

For rational disposal of solid wastes, low-cost cemented paste backfills (CPB) were prepared with iron tailings, ground granulated blast-furnace slag (GGBS), and calcium carbide slag (CS). To ensure that CPB can be effectively utilized in mine backfill projects, the effects of solid contents, GGBS content, CS/GGBS ratio, and mixing water on the workability and mechanical properties of CPB were investigated. The results indicated that when the solid content was 70%, the GGBS content was 14%, the CS/GGBS ratio was 0.4, the mixing water was tap water, the fluidity of fresh CPB slurry was 167 mm, and 28d unconfined compressive strength (UCS) of CPB reached 2.89 MPa, at which time the effect of the activation of the GGBS with CS was optimal. The analysis of X-ray diffraction (XRD), scanning electron microscopic imaging (SEM), thermogravimetric analysis (TG-DTG), and Fourier transform infrared spectroscopy (FTIR) demonstrated that the hydration products are mainly C-S-H gels, C-A-S-H, hemicarbonate, and hydrotalcite in CS-GGBS cementitious material. The C-S-H gel content gradually increased with increasing curing time and CS content (15%–35%). When the CS content was increased to 25%, the C-S-H gel content significantly increased, which improved the overall structural compactness and increased the UCS of CPB. [ABSTRACT FROM AUTHOR]

Steel slag (SS) is a secondary material from steelmaking production with little commercial value. Its volumetric expansion and low reactivity limit the use of SS in Portland cement (PC)-based materials. This study investigated the potential use of basic oxygen furnace (BOF) slag as a single precursor in alkali-activated matrices (AAMs). Six AAM pastes were assessed by changing the silica modulus (0.75, 1.50 and 2.22) and the sodium concentration (4% or 6% Na2O—wt. SS). The early hydration was assessed using isothermal calorimetry (IC), followed by the assessment of the mechanical performance (compressive strength), apparent porosity, and structure and microstructure characterization (X-ray diffraction, thermogravimetric analysis and scanning electron microscopy). The results indicated that although the BOF slag may be considered a low-reactivity material, the alkaline environment effectively dissolved important crystalline phases to produce hydrates (reaction products). An optimized combination of activator sources was achieved with 4% Na2O and a silica modulus of 1.50–2.22, with a compressive strength up to 20 MPa, a significant amount of reaction products (C-S-H/C-A-S-H gels), and low initial and cumulative heat release. Those properties will help to promote SS recycling use in future engineering projects that do not require high-strength materials. [ABSTRACT FROM AUTHOR]

The influence of different testing methods on alkali-silica reaction (ASR) behavior is a result of the difference in the effect of exposure conditions on it. This study investigated the impact of temperature and the addition of alkali on ASR behavior in an alkali-activated material (AAM) system and compared it with an ordinary Portland cement (OPC) system. The results showed that the ASR in the AAM system was more independent of the exposure conditions than that in the OPC system because of its inherently high alkalinity and dense microstructure. More ASR products with higher Na:Si ratios were evident in the alkali-activated slag (AAS) mortars than in the OPC mortars. The accelerated test conditions developed for OPC systems could be applied to AAM systems. However, owing to the difference in the acceleration effect, comparing the ASR-induced expansion in OPC and AAM systems using the accelerated test method was misleading to some extent. This study contributes to the understanding of the ASR in AAM systems and is of considerable importance for the industrial application of AAMs. • The ASR in AAMs system is more independent of exposure conditions than the OPC system. • The acceleration effect of temperature and extra alkalis on ASR in AAMs and OPC system is different. • Comparing the ASR-induced expansion in OPC and AAMs system through the accelerated test method is misleading to some extent. • The OPC-system accelerated test conditions could be applied to AAM systems. • This study is of importance for the industrial application of alkali-activated materials. [ABSTRACT FROM AUTHOR]

Nano-silica (NS) is one of the most commonly used nanomaterials in alkali-activated materials (AAMs). Differing from other inactive nanoparticles, as an active Si source, the pozzolanic activity of NS has a significant effect on the hydration reaction and properties of alkali-activated materials. In this study, activated Si in the activator was replaced by NS to prepare alkali-activated slag/fly ash cementitious materials. The effects of different dispersion methods (dry-mix (MD), water dispersion (WD), and activator dispersion (AD)) of NS on the fluidity, rheological properties, and setting time of fresh pastes were investigated. Effects of NS and reactive Si in the activator on the hydration process of alkali-activated slag/fly ash paste were investigated using isothermal calorimetry and the Krstulović-Dabić hydration model. ICP-OES was utilized to study the changing behavior of the composition of the fresh paste pore solution during the hydration reaction. The results show that ions in the pore solution change continuously with the hydration time and eventually stabilize. The stabilized pore solution is mainly composed of OH- and Na+. Different NS dispersion methods have significant effects on paste workability, rheology, and setting time. Activator dispersion can elevate the content of active Si in the activator, causing changes in the hydration process of the paste, especially for the initial hydration period. NS has the most significant effect on the hydration process due to its pozzolanic activity compared to nucleation and filling effects. The Krstulovic-Dabic model can roughly simulate the hydration kinetics possessed of alkali-activated NS/slag/fly ash after entering the accelerated period. • Dispersion methods have significant effects on paste workability, rheology, and setting time. • Activator dispersion NS increases the active Si content in the activator. • NS has the most significant effect on the hydration process due to its pozzolanic activity. • The stabilized pore solution consists mainly of OH- and Na+. [ABSTRACT FROM AUTHOR]

High-calcium alkali-activated materials (AAMs) can somewhat replace ordinary Portland cement (OPC) to reduce its environment impact, but these materials suffer from deleterious expansion due to the alkali-silica reaction (ASR). Here, the role of volcanic glass powder (VGP) addition in mitigating the ASR in alkali-activated slag (AAS) mortars was investigated for the first time and compared the performance with that of fly ash (FA). Optimal additions of VGP can effectively mitigate the expansion of AAS mortars, which is a combination of ASR- and zeolite-induced expansion. With increasing replacement level of VGP or FA, the ASR-induced expansion decreased and the zeolite crystallization-induced expansion increased. AAS mortars containing VGP exhibited higher overall expansion than those containing FA. The slightly lower ASR mitigation performance of VGP than FA in AAS mortars is due to the different roles of alumina and silica in suppressing the ASR in AAM systems. • The influence of volcanic glass powder on ASR in alkali-activated slag mortars is investigated for the first time. • Volcanic glass powder can effectively mitigate the expansion in AAS mortars. • The expansion in AAS mortars incorporating VGP or FA is combination of ASR- and zeolite-induced expansion. • With an increase in VGP or FA, the ASR-induced expansion decreases and zeolite crystallization-induced expansion increases. • AAS mortars containing VGP exhibited higher overall expansion than those containing FA. [ABSTRACT FROM AUTHOR]

With the rapid development of alkali-activated concrete (AAC) as a promising sustainable concrete, it is vital to thoroughly understand the microstructural characteristics and micromechanical properties, which determine the macroscopic mechanical properties and structural performance of AAC. This paper presents a critical review on the multiscale microstructure and micromechanical properties of AAC with both single and blend precursor systems, including alkali-activated fly ash (AAF), alkali-activated metakaolin (AAMK), alkali-activated slag (AAS), and alkali-activated fly ash-slag (AAFS). These types of AAC are systematically studied from nano-scale to macro-scale, covering solid gel particles (N-A-S-H, C-A-S-H and N-C-A-S-H), gel matrix (solid gel particles + gel pores), paste (unreacted particles + reaction products + pores), mortar and concrete (paste + interfacial transition zone + aggregates). The recent advances in microstructure and micromechanical properties of AAC are discussed, with special focus on microstructure-mechanical property relationships. The remaining challenges and opportunities for future research are also provided. [ABSTRACT FROM AUTHOR]

The requirements related to reducing the carbon footprint of cement production have directed the attention of researchers to the use of waste materials such as blast-furnace slag or fly ashes, either as a partial replacement for cement clinker or in the form of new alternative binders. This paper presents alkali-activated materials (AAMs) based on blast-furnace slag partially replaced with fly ash, metakaolin, or zeolite, activated with water glass or water glass with a small amount of water, and doped with zinc oxide. The mortars were tested for flow, hydration heat, mechanical strength, microstructure, and antimicrobial activity. The obtained test results indicate the benefits of adding water, affecting the fluidity and generating a less porous microstructure; however, the tested hydration heat, strength, and antibacterial properties are related to more favorable properties in AAMs produced on water glass alone.

The effects of chemical oxides and the surface area (SA) of slags on the initial reactivity of alkali-activated materials (AAMs) are coupled. It is well known that the reactivity of slag in AAMs is impacted by the SA, however, a quantitative measure of this effect was not provided in previous studies. For a proper understanding of the effect of slag chemistry on the reaction kinetics of AAMs, a quantitative description of the slags SA's effect is required. The reaction kinetics in the activated slags were monitored using isothermal calorimetry. The SAs of the pulverised slags were linked to the time-to-reach-the-main-peak (TTRP) of the reaction, the slope of the acceleration part of the main peak, and the total heat at one, three, and seven days. A 100% relative increase in SA caused a ~51%-75% relative decrease in TTRP. The slope of the acceleration stage also considerably increased with the SA of the slags. However, the effect of the SAs on the total heat was only distinct up to three days and then considerably reduced at seven days. The result of this study indicates that the effect of SA on the initial reactivity of AAMs cannot be simply considered using the proportional contribution. The outcome of this study can provide a promising measure to decouple the effects of SAs and the chemical compositions of slags on the reaction kinetics of AAMs by providing quantitative results for the effect SAs.

Even though the demand for utilizing geopolymers is growing, the need for current standard guidelines to regulate compliance to address the complexity of the mix design could be one of the major hurdles of utilizing geopolymers vastly in construction. There is no straightforward standard that addresses the complexity of the mix design of geopolymers. Thus, this work addresses main factors affecting the compressive strength of slag based geopolymers and provide a tool for predicting it. This article includes experimental work to evaluate the properties of slag-based geopolymer binders and the development of a model using Artificial Neural Network (ANN) algorithms for predicting the performance of these slag-based geopolymer binders. In this paper, we have utilized and developed ANN models for optimizing slag-based geopolymer mixes based on precursor materials' physiochemical properties and activation solutions constituents that can enhance performance compressive strength prediction in construction applications. • A high-accuracy DOE model was developed and used to characterize the Geopolymeric paste. • A developed ANN model was superior in forecasting the compressive strength of AAS systems. • The choice of the alkali activator has minimal impact on the compressive strength. • The optimal water-to-slag ratio is approximately 0.28. • The optimal alkali oxide concentration is 6 %. [ABSTRACT FROM AUTHOR]

In alkali-activated slag/fly ash systems, autogenous shrinkage represents the dominant type of shrinkage. Increasing contents of added water and fly ash contents both reduce the importance of autogenous shrinkage. For a constant added water content (AW/B = 0.14), increasing the fly ash content from 20 to 40% resulted in an autogenous shrinkage reduction on paste specimens (from 5644 to 2168 μm/m at 28 days). The autogenous shrinkage of control ordinary portland cement (OPC) paste (water-cement ratio [w/cm] of 0.50) reached 505 μm/m. Alkali-activated slag/fly ash mixtures of this study had average pore radius values ranging between 3.40 and 3.55 nm, compared to 8.25 nm for the OPC paste control specimen. Smaller pores and high sodium concentrations result in higher internal pressure during the process of selfdesiccation and could be the main causes for the very high autogenous shrinkage values recorded. [ABSTRACT FROM AUTHOR]

In this study, ground granulated blast furnace slag was activated with a wide variety of sodium salts to compare the effects of their pH and anion size on the hydration progress and compressive strength development of GGBFS pastes. Research was carried out on samples activated with twelve different sodium salts and cured for one year. Changes in their phase composition (XRD), loss on ignition at different temperatures, expansion and microstructure (SEM + EDS) were examined over the entire curing period. The results showed that the presence of sodium ions is more important than the pH of the system, as activation took place even in the case of compounds whose solutions are characterized by a low pH, such as sodium tartrate or phosphate. The compressive strength of the pastes ranged from approximately 8 to 65 MPa after one year of curing. [ABSTRACT FROM AUTHOR]

In this study, coralline-activated materials were prepared using ball-milled coral powder as cementitious material and coral sand as fine aggregate. XRF (X-ray fluorescence) and chemical dissolution tests were carried out to determine the content and reactivity of various elements in coral powder. The compressive strength of the developed composites was evaluated at different ages, and the formation and transformation of mineral crystals in coralline-activated samples were further analyzed by XRD (X-ray diffractometer). The results show that the calcium content in coral powder was as high as 89.5% (loss on ignition). However, only 56% of the active calcium could participate in the polymerization reaction. The silicon and aluminum content was too low, and the slag addition could improve the deficiency of silicon and aluminum in coral powder. With the increase in slag content (from 0% to 50%), the compressive strength of the composites increases significantly. Nevertheless, the enhancement is not pronounced when the slag content exceeds 50%. The increase in slag amount can stimulate the transformation of calcium minerals, e.g., aragonite and calcite, into hydrated calcium silicate and calcium aluminosilicate gels, which significantly enhances the resulting compressive strength. [ABSTRACT FROM AUTHOR]

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Purpose: Adsorbent amendment to contaminated sediments is one in situ remediation method to decrease the bioaccessibility of pollutants from the sediments. In this work, alkali-activated blast furnace slag (BFS) granules were used in a field experiment at Lake Kivijärvi (Finland). The lake was heavily affected by a mining accident in 2012, which released a significant peak load of metals and sulfate. The purpose of this work was to evaluate the performance of the novel amendment material for in situ remediation in real conditions with a preliminary cost estimation. Methods: Alkali-activated BFS granules were prepared and characterized for composition, microstructure, and surface properties. Two mesocosms were placed in the lake: one with granule dosing and another without. Sediment and pore water samples were collected after a two-week period. Similar small-scale experiment was performed in laboratory with a three-month duration. Bioaccessibility of metals from sediments was assessed with a three-stage leaching procedure. Results: The granules were effective in decreasing the mobility of Fe, Zn, Ni, and Cr in all leaching stages by approximately 50–90% in comparison with unamended sediment in the mesocosm experiment. Laboratory-scale incubation experiments also indicated decreased release of Ba, Co, Ni, Al, Fe, Mg, Mn and S. The estimated material costs were lower than the removal of the contaminated sediments with dredging and off-site treatment. Conclusion: The results showed preliminarily the effectiveness of alkaline-activated BFS in the remediation of metal-contaminated sediments in a field experiment. However, topics requiring further study are the leaching of trace elements from the material and impact on the sediment pH. [ABSTRACT FROM AUTHOR]

The use of electric arc furnace slag (EAFS) as sole precursor to produce alkali-activated mortars has been experimentally investigated. EAFS, a by-product of the steel recycling industry, is a coarse material with unevenly distributed and size-extensive particles. Milling of EAFS was required to achieve a cement-like sized powder before it could be used as precursor. Different combinations of sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) were used, by varying the Na2O/binder concentration (4%, 6%, 8%, 10%, 12%) and SiO2/Na2O ratio (0, 0.5, 1.0, 1.5, 2.0, 2.5) to maximize the mechanical performance. The alkaline solutions were prepared 24 h prior to mixing to unify temperatures for all mixes. The results showed that the SiO2/Na2O ratio and strength development are directly proportional. The maximum 28-day compressive strength obtained, after being subjected to an initial 24 h thermal curing at 80 °C, was 9.1 MPa in mixes with 4% Na2O/binder and 2.5 SiO2/Na2O. However, after an additional 28 days of accelerated carbonation, the maximum compressive strength (i.e., 31 MPa compared to 3.9 MPa in uncarbonated mixes, corresponding to an 800% increase) was obtained in mixes with 12% and 1.0 for Na2O/binder and SiO2/Na2O, respectively, thus showing an alteration in the optimal alkaline activator contents. [ABSTRACT FROM AUTHOR]

The use of sodium carbonate as an alkali activator for slag to produce alkali-activated slag is promising due to its sustainable, economic and user-friendly properties. However, the lower early age performance of composites made with such binder has limited its use especially in applications where higher early age is required. Hence, in order to propel the application of this sustainable binder, it is imperative to find ways in which the early age performance can be enhanced without having a detrimental effect on later age performance. One of the effective and sustainable ways to enhance the early age strength of sodium carbonate activated slag is by incorporation of various additives as partial replacement of sodium carbonate on/and slag. In order to propel more application of sodium carbonate slag for various applications, this current study was undertaken. In this paper, an overview of the types of various additives that can be used to enhance the early age compressive strength of sodium carbonate activated slag composites was discussed. The mechanism and dosage of each of the additives were briefly discussed alongside the limitation and advantages of the additives. Findings from this overview showed that the early age compressive strength of sodium carbonate activated slag can be enhanced with the use of additives such as calcium oxide, calcium hydroxide, Portland cement, sodium hydroxide and sodium silicate.

In this study we compare the leaching behavior and the antibacterial and cytotoxic properties of 100% slag or stone wool derived alkali activated materials. The antibacterial activity was measured as the inhibiting capacity against two Gram-negative bacterial strains, Escherichia coli and Pseudomonas aeruginosa and one Gram-positive bacterial strain: Enterococcus faecalis. The cytotoxicity properties were tested on mouse embryonic fibroblast NIH-3T3 cell-line. It was proved that the high quality of the 3D aluminosilicate network of the consolidated materials obtained from powders of CaO or MgO-rich slags or stone wool, opportunely activated with NaO and/or Na-silicate, was capable of stabilizing heavy metal cations. The concentrations of leachate heavy cations were lower than the European law limit when tested in water. The effect of additives in the composites, basal fibers or nanocellulose, did not reduce the chemical stability and slightly influenced the compressive strength. Weight loss in water increased by 20% with basalt fibers addition, while it remained almost constant when nanocellulose was added. All the consolidated materials, cement-like in appearance, exhibited limited antibacterial properties (viability from 50 to 80% depending on the bacterial colony and the amount of sample) and absence of cytotoxicity, envisaging good acceptance from part of the final consumer and zero ecological impact. CaO-rich formulations can replace ordinary Portland cement (showing bacterial viability at 100%) with a certain capability for preventing the reproduction of the E. coli and S. aureus bacteria with health and environmental protection results.

The production of alkali-activated materials (AAMs) is known for its environmentally friendly processing method, where several amorphous-rich aluminosilicate material sources combine with an alkali media solution to form solid, ceramic-like materials. In terms of the Si:Al, Na(K):Al, and Na(K):H2O ratios, the theory of AAM formation is quite well developed, but some open questions in the technology process remain, especially with regards to the means of curing, where the generation of defects can be persistent. Knowing that deformation is extremely high in the early ages, this study investigates the effects of temperature and moisture on shrinkage behavior within the first 72 h of AA pastes made from ladle (LS) and electric arc furnace (EAF) slag and activated by sodium silicate (Na2SiO3). The method to determine the deformation of alkali-activated slag-based materials, in terms of both autogenous and drying shrinkage, was based on the modified ASTM C1698-19 standard for the measurement of autogenous shrinkage in cement pastes. Autogenous deformation and strain were measured in four samples, using the standard procedure at room temperature, 40 and 60°C. Furthermore, using an adjusted method, nine samples were characterized for strain and partial surface pressure, while drying at room temperature, 40, or 60°C at a relative humidity of 30 or 90%. The results show that the highest rate of autogenous shrinkage occurred at a temperature of 60°C, followed by drying shrinkage at 60°C and 30% relative humidity, owing to the fact that the rate of evaporation was highest at this moisture content. The study aimed to provide guidance regarding selection of the optimal curing set in order to minimize deformations in slag-based alkali-activated materials. In the present case, curing at a temperature of around 40°C under lower moisture conditions for the first 24 h provided optimal mechanical properties for the slags investigated. The methodology might also be of use for other aluminosilicate sources such as metakaolin, fly ash, and mineral wool–based alkali-activated materials.

The production of Portland cement (PC) which is the main binder in conventional cementitious materials contributes about 7% to the world’s anthropogenic carbon dioxide emission. As the demand for PC is expected to increase significantly in the coming years, it is imperative to find other environmentally friendly alternatives. Alkali-activated binders (AABs) obtained by alkali activation of aluminosilicate precursors are viable alternatives for PC as they possess lower embodied carbon and energy compared to PC. However, the conventional activators (i.e. sodium silicate and sodium hydroxide) are corrosive, expensive and have a high environmental footprint. These limitations have resulted in impractical and expensive applications of such binders on a large scale. On the other hand, sodium carbonate, which is less corrosive, cheaper and available naturally in the environment can be used as a sustainable alternative to sodium silicate and sodium hydroxide. In a quest to propel the application of sustainable binders, this study was undertaken to explore the properties of slag activated with sodium carbonate at ambient temperature. The effect of sodium carbonate dosage on the fresh, mechanical and durability properties are discussed. A simplified sustainability assessment of concrete made with different binders was also carried out and the results showed that the sodium carbonate activated slag concretes are a sustainable alternative to PC concrete to achieve a cleaner environment.

The production of alkali-activated materials with excellent mechanical performance requires the use of water glass, which has a significant carbon footprint. Such materials can have a lower carbon footprint if we replace water glass with alternative activators sourced from waste. In this study, we assessed the suitability of locally available amorphous waste materials (stone wool, glass wool, bottle glass and cathode-ray tube glass) as a source for the preparation of alternative alkali activators. We quantified the amount of silicon and aluminium dissolved in the activator solutions via inductively coupled plasma-optical emission spectrometry. The alternative activators were then used to produce alkali-activated fly ash and slag. The compressive strength values of alkali-activated fly ash specimens upon the addition of NaOH, water glass and the most promising alternative activator were 38.98 MPa, 31.34 MPa and 40.37 MPa, respectively. The compressive strength of slag specimens activated with alternative activators with the highest concentration of dissolved silicon (21 g/L) was, however, 70% higher than the compressive strength of slag specimens activated with only 10 M sodium hydroxide. The compressive strength of slag specimens with the addition of the most promising alternative activator was significantly lower (3.5 MPa) than the compressive strength of those that had been activated by commercial water glass (34.3 MPa). [ABSTRACT FROM AUTHOR]

• The phase composition of an IGCC slag was analyzed at the particle level. • The IGCC slag comprised 98% amorphous calcium-rich aluminosilicate. • The IGCC slag did not contain free CaO which can cause volumetric expansion. • Considering amorphous composition, the IGCC slag was closest to Class C fly ash. • The IGCC slag has the potential to be a feedstock for AAM or glass-ceramics. Integrated gasification combined cycle (IGCC) is a highly efficient method for producing electricity but discharges a byproduct in the form of a glassy slag, similar to other electricity generation operations. Several technologies for recycling IGCC slag have been developed thus far, although the results obtained are not promising or universally applicable. We quantitatively characterized an IGCC slag by using various testing methods, including an automated scanning electron microscopy-energy dispersive spectrometry (SEM-EDS) system, to recognize its potential for recycling. The IGCC slag did not contain free CaO, and the absence of free lime would address a concern of volumetric expansion during hydration. Automated SEM-EDS analysis revealed that approximately 98% of the IGCC slag particles consisted of calcium-rich aluminosilicate materials. Obvious differences in the concentrations of Si, Al, and Ca between the amorphous phases and the average chemical bulk were recognized. The chemical composition of the amorphous Si-Al-Ca phases was similar to that of Class C fly ash, while the average bulk composition of the IGCC slag was in between that of Class C and Class F fly ashes. Considering this discrepancy, understanding the dissolution mechanism of the reactive amorphous fraction as well as an exact assessment of the reaction products based on the role of Ca in alkali-activated materials provides a new approach for the valorization of IGCC slag. [ABSTRACT FROM AUTHOR]

Fabric-reinforced cementitious composites are a recent family of commercial products devoted to the external retrofitting and strengthening of masonry and concrete structures. In the present work, the authors investigate the possibility of using, as matrix, a mortar based on alkali-activated materials. Basalt textile was selected as reinforcement because it is an effective, low-cost and environmentally friendly reinforcement. The matrix was prepared using by-products of industrial processes. Mortar was characterized by measuring its drying shrinkage, capillary water absorption, compressive and flexural strengths and analyzed using X-Ray diffractometry, Fourier-transform infrared spectroscopy, and thermogravimetric analysis. The mechanical behavior of the composites was investigated through tensile and direct shear tests. The basalt fabric-reinforced alkali-activated matrix composite showed, under tension, a tri-linear response curve, mainly governed by cracks development and widening. The measured ultimate stress, ultimate strain and tensile modulus of elasticity in region III were 434 MPa (CoV 14.2%), 2.192% (CoV 4.1%) and 39 GPa (CoV 11.3%), respectively. The load–global slip response curves of the composite show an average peak load around 1148 N (CoV 23.0%) and an exploitation ratio versus the textile and the tensile of 0.40 and 0.86, respectively. Even if the preliminary results are encouraging, the performance of FRAAM composites would be positively affected by an increase of the dimensional stability of the matrix. [ABSTRACT FROM AUTHOR]

Aiming to reduce the carbon dioxide emissions associated with cement production, alternative binders such as inorganic polymers currently receive substantial attention and slags from the non‐ferrous metallurgy are promising precursors. However, studies that correlate their chemistry and crystallinity with the newly formed binder remain limited. In this work, the effect of three different solidification methods on glass formation and reactivity of FeOx–SiO2 slags, as well as on the molecular structure of the resultant Fe‐rich inorganic polymers, was investigated. The inorganic polymers were synthesized by mixing the slags (approximate molar ratio FeO/SiO2 = 1.6) with an alkali silicate solution (molar ratios SiO2/Na2O = 1.6 and H2O/Na2O = 25). Results demonstrated that higher cooling rates promoted higher glass formation and faster reaction kinetics when the slags were activated. 57Fe Mössbauer spectroscopy indicated that all the slags consisted predominantly of Fe2+ ions with a minor amount of Fe3+ ions, regardless of the variability in glass content. The binder phase of all inorganic polymers consisted of iron in both Fe2+ and Fe3+ states, after 28 days of curing. After pulverizing the inorganic polymer pastes and exposing the powder to air for 28 additional days, the Fe2+ state in the binder transformed to Fe3+. The compressive strength evolution of the three slags showed that the 2‐day strength was higher for the samples with a higher amorphous fraction, while after 28 days, this influence was less pronounced. [ABSTRACT FROM AUTHOR]

• Sodium carbonate fails in extending the pot life of the investigated systems. • Low alkali content reduces the degree of reaction without improving the pot-life. • Amorphous calcium carbonate and vaterite were found in low reacted systems. • Very high alkali content negatively affects the mechanical properties at longer age. The paper investigates the effect of tri-blend solid alkaline activators, based on sodium metasilicate pentahydrate, potassium hydroxide and sodium carbonate, on the physico-chemical features, the fresh and hardened performances of activated slag pastes prepared with the one-part methodology. Specifically, the alkali to slag ratio (Ac) and the total amount of the selected activators were varied at a fixed water/binder ratio, molar silica modulus (Ms) and relative mass activators ratio. Microstructures and reaction products were analyzed by means of X-ray diffraction, thermogravimetry, scanning electron microscopy and FT-IR. Fresh and elasto-mechanical properties of pastes were also evaluated. Amorphous calcium carbonate (ACC) as well as metastable vaterite were found in low reacted systems, produced by the preferential early-age reaction between dissolved carbonate ions present in the pore solution and the calcium ions released by the partial dissolution of the slag and stabilized by a sufficient high concentration of magnesium in the pore solution, not consumed to the form hydrotalcite. Sodium carbonate failed in extending the pot life of the investigated systems. The optimal alkali content was found to be close to 0.075 as it determines the development of compact and dense microstructure (2025 kg/m3), the maximum elasto-mechanical properties (elastic modulus of 26.1 GPa and compressive strength of 102.8 MPa at 28 days) and it allows to produce flowable mixtures (200 mm). [ABSTRACT FROM AUTHOR]

• Using a database of 676 points with 15 inputs, ANN, KNN, and DT methods predicted the CS of AAMs. • RreliefF and interaction analysis assessed input factors' significance and interaction. • Based on statistical performance indicators, ANN was more accurate than KNN and DT. • NaOH, Na 2 SiO 3 , fine aggregate, w/b, specimen age, and slag were crucial inputs according to RreliefF analysis. Alkali-activated materials (AAMs) have recently gained attention as potentially useful alternative binders that can reduce carbon dioxide emissions initiated by the production of Portland cement (PC) and decarbonize concrete production. Plenty of research has been conducted to explore the numerous characteristics of AAMs. However, when utilizing typical empirical and statistical methods, it is still difficult to accurately estimate the mechanical features of AAMs due to inaccuracy and uncertainty. This research presents machine learning (ML) models intending to estimate AAM's compressive strength (CS) based on their mixture's proportions. Literature records were mined to compile a comprehensive dataset with 676 mixture designs. Three ML models were employed to assess AAM's CS prediction capabilities. These models included an artificial neural network (ANN), a K-nearest neighbor (KNN), and a decision tree (DT). In addition, RreliefF and interaction analysis were conducted to examine the significance and interaction of various factors used in the database. Statistical assessments of results showed that ANN's prediction accuracy was higher than that of KNN and DT. The correlation coefficient (R2) values of 0.91 for ANN, 0.79 for KNN, and 0.78 for DT confirm the applicability of ANN for determining the CS of AAMs. RreliefF analysis showed that the most important variables were the amounts of sodium hydroxide (NaOH) and sodium silicate (Na 2 SiO 3), followed by the fine aggregate, water/binder ratio, specimen age, and slag. The remaining variables moderately affected the results (i.e., CS of AAM). ML approaches can evaluate AAM CS across different input parameter values to optimize resource allocation and streamline future testing. The RreliefF analysis and interaction study indicated how input components affect AAM CS. These findings may help researchers and industry professionals determine the best raw material quantity, composition, and other factors for AAM development. [ABSTRACT FROM AUTHOR]

This study focuses to discuss the performance of alkali-activated mortar (AAM) reinforced by Polyvinyl Alcohol (PVA) fiber as a replacement of fine aggregate. Drying shrinkage is a major problem of alkali-activated mortar (AAM). Therefore, in order to reduce shrinkage and improve the performance of the mortar; the Polyvinyl Alcohol (PVA) fiber was introduced to replace the fine aggregate. An experimental test, including flow rate, compressive strength, modulus elasticity, poison's ratio, flexural strength and rate of drying shrinkage, was performed to investigate the performance of AAM with various percentage of PVA fiber. Based on the test, it was obtained that the utilization of PVA fiber as a fine aggregate replacement shows a slight decrease in the flow rate compared to plain AAM. The density of PVA AAM reinforced-fiber of five mixtures is almost similar to plain AAM with the differences lower than 2%. The use of PVA at levels ranging from 0% to 2%, with a level increment of 0.5% by volume, as fine aggregate replacement increased compressive strength, but decreased flexural strength. The replacement of fine aggregate with a certain value of PVA, which are 0.5% by volume, reduces the drying shrinkage of mortar. However, adding PVA more 0.5% by volume to the mortar increases the drying shrinkage. [ABSTRACT FROM AUTHOR]

Alkali-activated materials or geopolymer technology is one of the material innovations that can provide several benefits by reducing the use of Portland cement. The source of precursor materials come from industrial by-products. This study investigated the reliability failure of seven-variation of alkali-activated fly ash/slag/micro-silica mortar (AAM) and one-type of Portland Cement (PC) mortar. Compressive strength test accompanied by acoustic emission is used to characterize cylindrical mortar specimens. Examination of fracture distribution according to stress level until final failure was then performed. The compressive strength of four-type of alkali-activated mortar AAM (AAM-IV, V, VI, and VII) at 14 and 28 days shows a slight strength increase, 61.9 to 63.6 MPa, 62.3 to 65.6 MPa, 64.8 to 68.3 MPa and 63.1 to 63.6 MPa, respectively. The slight increase of AAM compressive strength is caused by high early strength achieved due to the replacement of more than 40 % of fly ash with GGBFS. The presence of more CaO in the AAM mixture accelerates the reaction in early age. By contrast, PC mortar shows significantly strength increases from 55.2 MPa to 69.5 MPa during the same period. Amplitude filters greater than (50dB, 60dB, 70dB and 80 dB) is utilized to investigate the reliability of compressive strength of the mortar by acoustic emission. It was found that filter greater than 60dB is the most suitable filter. Alkali-activated mortars which contain raw material of 42.5% fly ash, 42.5% GGBFS, and 15% micro-silica has the lowest reliability of failure than those of other mortars whereas Portland cement mortar shows the highest reliability of failure than other alkali-activated mortars. [ABSTRACT FROM AUTHOR]

Abstract This paper investigates the effect of using different admixtures on the one-part ambient-cured alkali activated pastes. Na 2 SiO 3 -Anhydrous powder was used as solid activator along with three superplasticizers including naphthalene, melamine and polycarboxylate with different water/precursor ratios. The flowability, setting time and compressive strength development were evaluated for all AAMs mixes. ATR-FTIR test was used to check the admixtures stability in high alkali media. All types of admixtures significantly improved the flowability of the Na 2 SiO 3 -anhydrous one-part AAMs and marginally affected the compressive strength. The results showed that polycarboxylate was effective for high water/precursor (≥0.36) while naphthalene performed better in case of low water/precursor (≤0.36) for Na 2 SiO 3 -anhydrous one-part AAMs. However, lowering the water/precursor ratio in the Na 2 SiO 3 -anhydrous one-part AAMs using superplasticizers showed no improvement or modest improvement in the compressive strength. The ATR-FTIR results revealed the relatively high stability of admixtures in Na 2 SiO 3 alkali medium of one-part AAMs (for w/b = 0.4). Highlights • The effectiveness of different admixtures in Na 2 SiO 3 -Anhydrous one-part AAMs was evaluated. • The most effective types for Na 2 SiO 3 AAMs were naphthalene when w/b ≤ 0.36 and polycarboxylate when w/b ≥ 0.36. • Minimizing the water/precursor ratio using admixtures marginally affected the compressive strength of Na 2 SiO 3 AAMs. [ABSTRACT FROM AUTHOR]

The potential for using secondary carbon fiber, recovered from aviation carbon fiber wastes, for reinforcing composite materials based on blast-furnace slag activated by a sodium silicate solution is evaluated. The influence of the concentration and length of the secondary carbon fiber on the structure, physicomechanical properties, and nature of the fracture of dispersion-reinforced composites was investigated. [ABSTRACT FROM AUTHOR]

Automation through 3D printing can be a possible technological breakthrough in construction. However, the carbon footprint is not necessarily reduced as the print formulations consist of more ordinary Portland cement (OPC) compared to conventional high-performance mortar. In this study, a hybrid mortar with minor amount of OPC and mainly Fe-rich, low-Ca slag is used for printing several structures, followed by a profound study on the durability properties of the printed material. The hybrid mortar outperformed the benchmark with respect to its compressive strength (80.5 ± 4.3 MPa versus 52.4 ± 1.7 MPa) and drying shrinkage (0.8 mm/m versus 1.3 mm/m). The capillary pores present in the printed hybrid resulted in a lower freeze-thaw resistance. Leaching tests showed that the hybrid binder immobilized heavy metals. The hybrid mortar has a CO 2 impact between 164 kg CO 2 /m3 and 548 kg CO 2 /m3, and costs range from 129 to 193 euro/m3. This study showed that the hybrid mortar can offer a suitable alternative to 3D-printable OPC-mortars. [Display omitted] • Higher objects could be printed with Fe-rich slag hybrid mortar compared to reference OPC-mortar. • CT-images identified difference in porosity between the printed layers due to compaction. • The freeze-thaw resistance poor during first cycles and improved with increasing cycles. • The release of heavy metals is below legislative criteria, due to the binder type and slag treatment. • Cost and CO 2 footprint of hybrid mortars are potentially favourable compared to OPC counterparts, depending on used slag. [ABSTRACT FROM AUTHOR]