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The recent COVID-19 emergency has led to an impressive increase in the production of pharmaceutical vials. This has led to a parallel increase in the amounts of waste glass; manufacturers typically recover material from faulty containers by crushing, giving origin to an unrecyclable fraction. Coarse fragments are effectively reused as feedstock for glass melting; on the contrary, fine powders (<100 microns), contaminated by metal and ceramic particles due to the same crushing operations, are landfilled. Landfilling is also suggested for pharmaceutical containers after medical use. This study aims at proposing new opportunities for the recycling of fine glass particles, according to recent findings concerning alkali activation of pharmaceutical glass, combined with novel processing, i.e., binder jetting printing. It has already been shown that pharmaceutical glass, immersed in low-molarity alkaline solution (not exceeding 2.5 M NaOH), undergoes surface dissolution and hydration; cold consolidation is later achieved, upon drying at 40–60 °C, by a condensation reaction occurring at hydrated layers of adjacent particles. Binder jetting printing does not realize a full liquid immersion of the glass powders, as the attacking solution is selectively sprayed on a powder bed. Here, we discuss the tuning of key parameters, such as the molarity of the attacking solution (from 2.5 to 10 M) and the granulometry of the waste glass, to obtain stable printed blocks. In particular, the stability depends on the formation of bridges between adjacent particles consisting of strong T-O bonds (Si-O-Si, Al-O-Si, B-O-Si), while degradation products (concentrating Na ions) remain as a secondary phase, solubilized by immersion in boiling water. Such stability is achieved by operating at 5 M NaOH. [ABSTRACT FROM AUTHOR]

The utilization of calcium carbide residue (CCR) to activate solid wastes can effectively promote sustainable development. This paper explores adding sodium carbonate (Na2CO3) to CCR activators to improve the early reactivity of alkali-activated materials (AAMs) made from sewage sludge ash (SSA). The research focuses on the effects of Na2CO3 on setting, hardening, mechanical strength, and environmental benefits. The findings indicate that Na2CO3 can shorten the paste' hardening time and significantly enhance the early mechanical properties. The introduction of Na2CO3 accelerates the consumption of CCR during the early phases and facilitates the formation of C-(N)-A-S-H gels. Meanwhile, it can significantly reduce the porosity and refine the pore structure. When the dosage reaches 8%, the total intruded pore volume of the sample decreases to 0.15 mL/g. This activation method reduces energy consumption, CO2 emissions, and costs by 69%, 50%, and over 90%, respectively, making it an efficient, eco-friendly approach to AAM production. [ABSTRACT FROM AUTHOR]

Alkali-activated materials (AAMs) are regarded as a substitute for Portland cement. They have high chloride resistance and a low carbon dioxide footprint. The aim of this review is to provide a multi-scale perspective to understand material–product–microstructure–property relationships in terms of the chloride binding behaviour of AAMs. The physical and chemical chloride stability of different reaction products is summarised from nanostructure, to microstructure to macro properties. An analysis of studies in the literature gives an overview of recent progress in chloride transport in AAMs influenced by different reaction products. Results show that a higher calcium/silicon, aluminium/silicon molar ratios and alkali content increase the formation of amorphous phases, leading to a denser microstructure and lower chloride penetration in AAMs. Higher magnesium oxide and aluminium oxide contents result in increased formation of hydrotalcite. The enhanced physical and chemical absorption of chloride by hydrotalcite leads to higher resistance of chloride penetration in AAMs. Investigation of increasing chloride resistance could potentially focus on increasing gel and hydrotalcite formation. [ABSTRACT FROM AUTHOR]

This paper aimed to investigate the durability of ambient-cured fly ash-phosphogypsum blended geopolymer mortar (GPM) when exposed to a water and sulfate environment at different durations. Water absorption, porosity, and sulfate resistance tests were conducted to determine the durability. The GPM was prepared at 0 wt%, 30 wt%, and 40 wt% PG replacement of fly ash content in the mixture. The mix proportions were determined experimentally at 10 M sodium hydroxide, alkaline liquid/precursor of 0.4, sodium silicate/sodium hydroxide of 1.5, and binder/aggregate of 1.0. The samples were immersed in potable water and magnesium sulfate solution. The changes in weight, length, and compressive strength were monitored. Scanning electron microscopy-energy dispersive X-ray spectroscopy was used to analyze the structure and composition. The findings showed that GPM with 30 wt% phosphogypsum added had lower water absorption, porosity, and sulfate attack than GPM with 0 wt% phosphogypsum attributed to the formation of hydrated gels leading to a dense microstructure and improved strength. The changes in weight, length, and strength variations trend for GPM were within optimal performance standards. This has implications for the practical application of GPM in construction where it can be used as an alternative to Portland cement mortar in sulfate-rich environments. [ABSTRACT FROM AUTHOR]

Alkali activated materials (AAMs) offer significant advantages over traditional materials like Portland cement, but require the use of strong alkaline solutions, which can have negative environmental impacts. This study investigates the synthesis of AAMs using metakaolin and wollastonite, aiming to reduce environmental impact by eliminating sodium silicate and using only sodium hydroxide as an activator. The hypothesis is that wollastonite can provide the necessary silicon for the reaction, with calcium from wollastonite potentially balancing the negative charges usually countered by sodium in the alkaline solution. This study compares raw and carbonated wollastonite (AAM-W and AAM-CW) systems, with raw materials carefully characterized and binding networks analyzed using TGA, FT-IR, and XRD. The results show that while wollastonite can reduce the amount of sodium hydroxide needed, this reduction cannot exceed 50%, as higher substitution levels lead to an insufficiently alkaline environment for the reactions. The carbonation of wollastonite enhances the availability of silicon and calcium, promoting the formation of both N-A-S-H and C-A-S-H gels. [ABSTRACT FROM AUTHOR]

Understanding the strength development of alkali-activated materials (AAMs) with fly ash (FA) and granulated blast furnace slag (GBFS) is crucial for designing high-performance AAMs. This study investigates the strength development mechanism of AAMs using machine learning. A total of 616 uniaxial compressive strength (UCS) data points from FA-GBFS-based AAM mixtures were collected from published literature to train four tree-based machine learning models. Among these models, Gradient Boosting Regression (GBR) demonstrated the highest prediction accuracy, with a correlation coefficient (R-value) of 0.970 and a root mean square error (RMSE) of 4.110 MPa on the test dataset. The SHapley Additive exPlanations (SHAP) analysis revealed that water content is the most influential variable in strength development, followed by curing periods. The study recommends a calcium-to-silicon ratio of around 1.3, a sodium-to-aluminum ratio slightly below 1, and a silicon-to-aluminum ratio slightly above 3 for optimal AAM performance. The proposed design model was validated through laboratory experiments with FA-GBFS-based AAM mixtures, confirming the model's reliability. This research provides novel insights into the strength development mechanism of AAMs and offers a practical guide for elemental design, potentially leading to more sustainable construction materials. [ABSTRACT FROM AUTHOR]

The production of municipal solid waste incineration fly ash (MSWI-FA) and municipal sludge (MS) has been increasing annually, raising concerns about proper disposal. In this study, a thermal treatment method with attributes of energy efficiency and complete detoxification was applied to synergistically convert MSWI-FA and MS into precursors for the synthesis of high-strength alkali-activated materials (AAMs). The impact of mass ratios of MSWI-FA and MS on the mineralogy, microstructure, and reactivity of obtained precursors were investigated. The mechanism of alkali activation was deeply studied by characterizing the evolution of reaction products. The strength development of synthesized AAMs was characterized in a one-year time scale, as well as the environmental compatibility. The results revealed that strength, with values ranging from 12.8–33.0 MPa at 3 d, 29.5–44.1 MPa at 28 d and 39.3–54.8 MPa at 365 d. Furthermore, after one year of curing, the release of Ni, Cr, Cu, Pb, Zn, Mn, and Ba from synthesized AAMs into both deionized water and acetic acid were far below the regulatory limits in China. All these contribute to promoting the safe disposal and effective valorization of MSWI-FA and MS. [ABSTRACT FROM AUTHOR]

Alkali-activated materials (AAMs), which are prepared by using various solid wastes as precursors and reacting with alkaline solutions, are gradually applied in the construction industry. However, not all solid waste precursors can exhibit good performance in the preparation of AAMs. To realize the effective utilization of phosphorus slag (PS) solid waste, alkali-activated PS-GBFS-FA (AAPGF) was prepared by using PS and GBFS/FA. Using different contents of GBFS/FA to replace PS, the workability performance, mechanical properties and hydration products of AAPGF were investigated. The incorporation of GBFS/FA improves the fluidity of AAPGF, but leads to slurry flash setting. When containing 30% GBFS/FA, the 28 days compressive strength of AAPGF can reach the highest 72.65 MPa. GBFS/FA increased the number of C-(A)-S-H gels, accompanied by the formation of hydrotalcite gels. In addition, GBFS/FA also transforms AAPGF hydration products from C-S-H gel to C-(N)-A-S-H and N-A-S-H gel with high degree of polymerization, and SiO4 tetrahedron is Q2 unit. GBFS/FA will significantly reduce unhydrated particles, but it will lead to uneven distribution of hydration products and produce large pores. The results of this study can provide reference value for the effective use of PS. [ABSTRACT FROM AUTHOR]

Abstract This paper aimed to investigate the durability of ambient-cured fly ash-phosphogypsum blended geopolymer mortar (GPM) when exposed to a water and sulfate environment at different durations. Water absorption, porosity, and sulfate resistance tests were conducted to determine the durability. The GPM was prepared at 0 wt%, 30 wt%, and 40 wt% PG replacement of fly ash content in the mixture. The mix proportions were determined experimentally at 10 M sodium hydroxide, alkaline liquid/precursor of 0.4, sodium silicate/sodium hydroxide of 1.5, and binder/aggregate of 1.0. The samples were immersed in potable water and magnesium sulfate solution. The changes in weight, length, and compressive strength were monitored. Scanning electron microscopy-energy dispersive X-ray spectroscopy was used to analyze the structure and composition. The findings showed that GPM with 30 wt% phosphogypsum added had lower water absorption, porosity, and sulfate attack than GPM with 0 wt% phosphogypsum attributed to the formation of hydrated gels leading to a dense microstructure and improved strength. The changes in weight, length, and strength variations trend for GPM were within optimal performance standards. This has implications for the practical application of GPM in construction where it can be used as an alternative to Portland cement mortar in sulfate-rich environments.

The safe and secure encapsulation or immobilization of nuclear waste, particularly low to intermediate‐level waste (accounting for ∼97% of the total volume of nuclear waste), has been a significant concern. Consequently, numerous studies have been conducted on various materials such as ordinary Portland cement‐based, bitumen, and ceramics for the purpose of waste encapsulation/immobilization. However, these studies generally offer a broad overview of materials performance without focusing on specific radioisotopes of concern. Cesium (Cs) and strontium (Sr) are important radioactive nuclides to consider for encapsulation, but the existing studies on immobilizing these elements are fragmented and lack a comprehensive understanding. This critical review article offers a thorough qualitative and quantitative analysis to uncover the primary trends/knowledge gaps within the field. It comprehensively delves into waste classifications/management and leaching assessments, followed by an exploration of the immobilization performance and durability issues of various traditional and advanced cementitious materials including low‐temperature chemically bonded ceramics such as alkali‐activated matrices and Mg‒K phosphates for the immobilization of Cs and Sr. Furthermore, the review article provides fresh insights and perspectives, including recommendations for improvements, novel technologies, and future trends in this domain. [ABSTRACT FROM AUTHOR]

Alkali-activated materials (AAMs) are promising alternatives to ordinary Portland cement (OPC), but standardized mix design approaches are limited. This study introduces a machine learning-based framework for inverse mix design of AAMs, predicting optimal mixes based on target properties and sustainability. The model considers eight key factors, including precursor reactivity, activator properties, and liquid-to-binder ratio. It operates in four steps: (i) constructing forward prediction models, (ii) generating new mix designs, (iii) evaluating workability and strength, and (iv) filtering for performance and sustainability. Experiments validated the model, targeting fluidity >100% and compressive strengths of 40 MPa (A40) and 50 MPa (A50). The A40 and A50 mixes achieved fluidities of 147.7% and 170.0%, and 28-day compressive strengths of 41.5 and 57.5 MPa. Both had lower environmental impacts (GWP, AP, and EP) compared to OPC-based mortars. This framework enhances AAM design efficiency and sustainability for broader applications. [ABSTRACT FROM AUTHOR]

The application of nanotechnologies in alkali-activated materials can significantly improve their performance. In this study, the effects of nano-TiO₂ on the hydration process, hydration products, and microstructure of alkali-activated steel slag - slag materials were analysed using techniques such as hydration heat analysis, infrared spectroscopy and SEM. The results show that the addition of nano-TiO₂ significantly enhances the mechanical properties of alkali-activated steel slag - slag materials at different curing ages. The improvement in the early-stage strength can be mainly attributed to the pronounced nucleation-inducing effect of nano-TiO₂, which accelerates the hydration reaction. The enhancement in the later-stage strength is attributed to the filling effect of nano-TiO₂, as well as the induction of the formation of more gel products, optimising the pore structure and increasing the compactness of the matrix.

Abstract These days, the construction industry is facing sustainability issues, leading to the selection of greener, low-carbon, alkali-activated materials. This study examines a low calcium alkali activated system composed of three constituents (ceramic brick, metakaolin waste, and phosphogypsum). The AAB compositions consist of the primary precursor, waste ceramic brick, which is increasingly (20–100 wt%) replaced with waste metakaolin. The alkaline solution was made of sodium hydroxide and water; dosage depended on the Na2O/Al2O3 ratio (1.00–1.36). The AAB specimens were inspected by using XRD (X-ray diffraction) and FT-IR (Fourier transform infrared spectroscopy) methods for the evaluation of mineral composition, accompanied by SEM–EDS (scanning electron microscopy & energy dispersive X-ray spectroscopy) for the analysis of the microstructure. The compressive strength after 7, 28 and 90 days, along with water absorption and softening coefficient were determined. Also, mixture calorimetry was established. The results have shown that the initial materials are suitable for producing medium-strength alkali-activated binder under ambient temperature. The maximum compressive strength was reached by using the combination of 80% CBW and 20% MKW (13.9 and 21.2 MPa after 28 and 90 days respectively). The compressive strength development was linked with the formation N–A–S–H gel and faujasite type zeolite. A higher level of geopolymerization in composition with metakaolin waste led to lower compressive strength. Consequently, binding materials with low demand of high final and especially early compressive strength could be produced under ambient temperature curing, making them more sustainable.

In the realm of sustainable construction materials, the quest for low-environmental-impact binders has gained momentum. Addressing the global demand for concrete, several alternatives have been proposed to mitigate the carbon footprint associated with traditional Portland cement production. Despite technological advancements, property inconsistencies and cost considerations, the wholesale replacement of Portland cement remains a challenge. This study investigates the feasibility of using alkali-activated slag (AAS)-based binders for two specific applications: structural plaster and pervious concrete. The research aims to develop an M10-grade AAS plaster with a 28-day compressive strength of at least 10 MPa for the retrofitting of masonry buildings. The plaster achieved suitable levels of workability and applicability by trowel as well as a 28-day compressive strength of 10.8 MPa, and the level shrinkage was reduced by up to 45% through the inclusion of shrinkage-reducing admixtures. Additionally, this study explores the use of tunnel muck as a recycled aggregate in AAS pervious concrete, achieving a compressive strength up to 20 MPa and a permeability rate from 500 to 3000 mm/min. The relationship between aggregate size and the physical and mechanical properties of no-fines concretes usually used for cement-based pervious concrete was also confirmed. Furthermore, the environmental impacts of these materials, including their global warming potential (GWP) and gross energy requirement (GER), are compared to those of conventional mortars and concretes. The findings highlight that AAS materials reduce the GWP from 50 to 75% and the GER by about 10–30% compared to their traditional counterparts. [ABSTRACT FROM AUTHOR]

This study focuses on the use of alkali-activated materials and geopolymer grouts in deep soilmixing. Three types of grouts, incorporating metakaolin and/or slag and activated with sodium silicate solution, were characterized at different scales to understand the development of their local structure and macroscopic properties. The performance of the soilmix was assessed by using combinations of the grouts and model soils with different clay contents. Feret's approach was used to understand the development of compressive strength at different water-to-solid ratios ranging from 0.65 to 1. The results suggested that incorporating calcium reduced the water sensitivity of the materials, which is crucial in soilmixing. Adding soils to grouts resulted in improved mechanical properties, due to the influence of the granular skeleton. Based on strength results, binary soilmix mixtures containing 75% of metakaolin and 25% of slag, with H2O/Na2O ratios ranging from 28 to 42 demonstrated potential use for soilmixing due to the synergistic reactivity of metakaolin and slag. The optimization of compositions is necessary for achieving the desired properties of soil mixtures with higher H2O/Na2O ratios. [ABSTRACT FROM AUTHOR]

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]

The environment is currently confronted with challenges arising from the substantial accumulation of challenging-to-recycle waste glass. To address this issue, the utilization of alkali-activated waste glass (AAWG) emerges as a promising solution for generating potential low-carbon materials. AAWG, serving as a novel binder, is characterized by a lack of Al/Ca, diverging from both geopolymer and calcium silicate hydrate gels. Consequently, variations in gel properties necessitate corresponding adjustments in AAWG preparation methods. However, to date, there has been limited comprehensive exploration by researchers into the effects of curing conditions (humidity, temperature, and duration) on the compressive strengths of AAWG. The interaction among these factors in influencing AAWG compressive strengths remains unclear. Furthermore, the feasibility of employing AAWG as a standalone binder in concrete, along with the performance of the interfacial transition zone around the aggregates, remains uncertain. Considering these unresolved issues, this study investigates the impact of curing conditions (humidity, temperature, and time) on AAWG compressive strengths. Concrete incorporating AAWG as the binder, granite as coarse aggregates, quartz sand as fine aggregates, and silica sand/flour as inert fillers exhibited compressive strengths surpassing 75 MPa. This research contributes to advancing the upcycling of waste glass to produce high-strength concrete. [ABSTRACT FROM AUTHOR]

Alkali-activated materials (AAMs) are favoured for their low carbon emissions, excellent mechanical properties, and excellent chemical resistance. In this paper, ternary alkali-activated cementitious materials were prepared from slag, steel slag, and lithium slag to investigate their strength and resistance to sulphate attack. A series of experiments were conducted using a variety of material combinations, alkali activator combinations, water–binder ratios, and exposure environments. These experiments employed both macro and micro comparative analyses. The hydration reaction products, physical phase composition, and microstructure of the ground granulated furnace slag, lithium slag, and steel slag (GLS) ternary AAMs were analysed using x-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). It was experimentally demonstrated that the GLS ternary AAMs had excellent compressive strength, good resistance to sodium sulphate erosion, and that resistance to magnesium sulphate erosion decreased with time. This study contributes to the advancement of knowledge regarding the utilisation of lithium slag and steel slag, and offers new insights into the field of alkali-activated cementitious materials and their resistance to sulphate erosion. [ABSTRACT FROM AUTHOR]

The feasibility and performance of using calcined coal gangue (CCG) to substitute metakaolin (MK) as the precursor to prepare alkali-activated materials (AAMs) were thoroughly evaluated by conducting combined experiments of flowability test, mechanical measurement, calorimetry and microstructure analysis, etc. It was found that the increased substitution ratio of CCG to MK can increase the flowability of the prepared paste by up to 28.1% and decrease its viscosity by up to 55.8%. In addition, a prolonged setting time of up to 31.8% was found with the increased substitution amount of CCG to MK, which can be attributed to the low reactivity of CCG compared to that of MK. Lastly, even though the presence of CCG can lead to a decrease in the early compressive strength of the hardened paste, a highly recovered long-term mechanical property can be found due to the continuous reaction of CCG. All of these results prove the feasibility of using CCG as one co-blended precursor with MK to prepare alkali-activated materials. [ABSTRACT FROM AUTHOR]

Fly ash–slag-based alkali-activated materials have excellent mechanical performance and a low carbon footprint, and they have emerged as a promising alternative to Portland cement. Therefore, replacing traditional Portland cement with slag–desulfurization gypsum-based alkali-activated materials will help to make better use of the waste, protect the environment, and improve the materials' performance. In order to better understand it and thus better use it in engineering, it needs to be characterized for performance and compositional design. This study developed a novel framework for performance characterization and composition design by combining Categorical Gradient Boosting (CatBoost), simplicial homology global optimization (SHGO), and laboratory tests. The CatBoost characterization model was evaluated and discussed based on SHapley Additive exPlanations (SHAPs) and a partial dependence plot (PDP). Through the proposed framework, the optimal composition of the slag–desulfurization gypsum-based alkali-activated materials with the maximum flexural strength and compressive strength at 1, 3, and 7 days is Ca(OH)2: 3.1%, fly ash: 2.6%, DG: 0.53%, alkali: 4.3%, modulus: 1.18, and W/G: 0.49. Compared with the material composition obtained from the traditional experiment, the actual flexural strength and compressive strength at 1, 3, and 7 days increased by 26.67%, 6.45%, 9.64%, 41.89%, 9.77%, and 7.18%, respectively. In addition, the results of the optimal composition obtained by laboratory tests are very close to the predictions of the developed framework, which shows that CatBoost characterizes the performance well based on test data. The developed framework provides a reasonable, scientific, and helpful way to characterize the performance and determine the optimal composition for civil materials. [ABSTRACT FROM AUTHOR]

As the world becomes increasingly aware of the devastating effects of climate change, the need for sustainable building materials that are both durable and environmentally friendly increases. Geopolymer and alkali-activated materials formed by a chemical reaction between an alkaline activator solution and an aluminosilicate source have gained popularity in recent years. The alkaline activator solution dissolves the aluminosilicate source, which then undergoes a polycondensation reaction to form a three-dimensional geopolymeric gel network. The development of this network ensures the strength and durability of the material. Today, this phenomenon of durability has been studied in detail to enable the development of superior construction materials, taking into account degradation mechanisms such as carbonation, leaching, shrinkage, fire, freezing and thawing, and exposure to aggressive environments (chlorides, acids, and sulphates). Although there are many unsolved problems in their engineering applications, slag-based alkali-activated materials appear to be more advantageous and are promising as alternative materials to ordinary Portland cement. First of all, it should not be ignored that the cure sensitivity is high in these systems due to compressive strength losses of up to 69%. Loss of strength of alkali-activated materials is considered an important indicator of degradation. In binary precursors, the presence of fly ash in slag can result in an improvement of over 10% in compressive strength of the binary-based alkali-activated materials after undergoing carbonation. The binary systems can provide superior resistance to many degradation mechanisms, especially exposure to high-temperature. The partial presence of class F fly ash in the slag-based precursor can overcome the poor ability of alkali-activated materials to withstand high temperatures. Due to the desired pore structure, alkali-activated materials may not be damaged even after 300 freeze–thaw cycles. Their superior permeability compared to cementitious counterparts can extend service life against chloride corrosion by more than 20 times. While traditional (ordinary Portland cement-based) concrete remains the most widely used material in construction, geopolymer concrete's superior performance makes it an increasingly emerging option for sustainable and long-lasting infrastructure. [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]

Currently, the hazardous potential of spent fluorescent lamps due to their mercury content, which usually exceeds the limit allowed by standards, it is well known. When these are taken out from use, mercury is distributed between all the components of the lamp; in particular, it can be found in the phosphorescent powder called "phosphor" which is attached as a thin layer on the walls of the lamps. Although many efforts have been made to develop technologies for recovery of mercury, in many cases their effectiveness is very hard to be proved from both technical and economic points of view. Therefore, this work is focused on evaluating the feasibility of valorizing this type of waste glass as an active precursor for the synthesis of fly ash-based alkali-activated materials. In this respect, the potential of synthesized alkali-activated materials to immobilize mercury from waste glass added to the synthesis mixture was experimentally proved through compliance leaching tests. Important microstructural changes that appear with the increasing addition of waste glass to the synthesis mixture were highlighted by SEM and N2-BET analysis. Sharp increase in the SiO2/Al2O3 molar ratio of the synthesis mixture with the increasing addition of waste glass leads to an increase in the unreacted glassy fraction that acts as defect sites in the structure of the alkali-activated material, having a negative effect on its mechanical properties. However, the compressive strength tests showed that an addition of waste glass up to 5% of the total mass of the synthesis mixture has a beneficial effect on the compressive strength of alkali-activated materials. [ABSTRACT FROM AUTHOR]

Novel ceramic membranes present unquestionable potential in wastewater treatment among the emerging technologies, while a few challenges such as cost, energy consumption, durability, and resistance in harsh mediums still limit their commercialization. Here, we review the capability of available industrial aluminosilicate waste materials in the fabrication of novel ceramic membranes using green and economical alkali‐activation synthesis method. The different sources of alkali‐activated aluminosilicate wastes including ashes, mining wastes, glass and ceramic wastes, slags, construction wastes, industrial byproducts, and agricultural wastes are introduced and the chemistry of geopolymers is reviewed. In this review, the major points are the following. 1) The alkali‐activated structures present reasonable chemical, frost, carbonation, and mechanical resistance as well as the ability to immobilize the toxic materials. 2) The synthesis aspects of porous and nonporous alkali‐activated ceramic membranes are explored by characterization methods. Furthermore, the durability analysis in harsh environments reveals that alkali‐activated ceramic membranes possess high resistance against acidic, alkaline, and other antifouling chemical washing methods. In summary, it is demonstrated that the studied membranes have an undeniable capability in the separation of organic solvents in the pervaporation process as well as toxic material removal from water with high ion‐exchange capacity. [ABSTRACT FROM AUTHOR]

The utilization of waste rubber as aggregates shows both environmentally friendly features and high cost-efficiency in construction, but may cause poor workability such as rubber flotation and agglomeration. To address the above issues, the pelletization method was adopted to produce rubberized artificial geopolymer aggregates (R-GPA), and the effects of different rubber modification methods and rubber contents were investigated through pelletization technologies, mechanical tests, X-ray computed tomography (XCT) and backscattered electron with energy-dispersive spectroscopy (BSE-EDS). Results showed that the combined modification with NaOH solution and silane coupling agent presented the most effective surface modification efficiency. According to microscopic analysis, rubber modification could effectively enhance the rubber-matrix interface. The produced R-GPA could thus possess an oven-dried particle density within 1500–1800 kg/m³, a water absorption of 7%–10.5%, and a pelletization efficiency over 98%, which provided a new insight into the value-added utilization of waste rubber and the promotion of artificial aggregate technologies.

The utilization of waste and by-products as precursors in alkali-activated materials has great importance in the reduction of environmental pollution on slopes, landfills, and highways. Properties studies of alkali-activated mixtures using red ceramic waste (RCW) and blast furnace slag (BFS) have been scarcely investigated in the literature. This paper aims to evaluate the properties and behavior of alkali-activated pastes based on RCW and BFS. The influence of the following parameters was evaluated: silica modulus (Ms) between 1.0 and 1.3 and RCW content (25, 50, and 75 %). The compressive strength, workability, and reaction kinetics were analyzed. In addition, embodied environmental impacts and FTIR microstructural analyses were performed. Flow diameters in the range of 147.3 mm to 163 mm (Ms = 1.3) and 142.4 mm to 154.1 mm (Ms = 1.0) were observed and the RCW incorporation slightly reduced mixtures workability. An optimum RCW content in the range of 25 %-50 % was identified, which provided excellent mechanical and microstructural properties reaching values up to 68.68 MPa for the best mixture and values above 50 MPa for systems with 50 % RCW. Higher RCW contents also led to reaction delays according to the isothermal calorimetry test. The increase in Ms generated higher band intensities of the Si-O-T chemical bonds. The mixtures evaluated had significantly lower CO2 emissions and equivalent energy consumption than OPC-based binders, with reductions of up to 65.6 % (CO2 emission) and 75.2 % (energy consumption), indicating the environmental benefit provided by this type of mixture.

This study evaluated the effects of various Mg-based admixtures, including magnesium oxide (MgO), layered double hydroxides (LDH), and calcined layered double hydroxides (CLDH), on the chloride resistance of alkali-activated fly ash-slag (AAFS) mortars. To this end, chloride diffusion tests were conducted on AAFS mortars containing 5 wt% MgO, Mg-Al-CO3 LDH, and CLDH. The results revealed that all Mg-based admixtures investigated in this study enhanced the chloride resistance of AAFS mortars. The inclusion of MgO led to a finer pore structure and promoted the formation of more Friedel's salt, thereby enhancing the chloride resistance performance. Although the inclusion of Mg-Al-CO3 LDH and CLDH resulted in more lager pores in the matrix, leading to slightly lower compressive strength, the overall content of Mg-Al LDH and Friedel's salt formed in the system increased, which led to an improved chloride binding capacity and enhanced chloride resistance.

Eco-friendly and cheap treatments based on the use of mildly alkaline solutions have been recently investigated to modify natural fibers, altering their surface and improving their compatibility mainly with polymer matrices. A challenge for the researchers is nowadays represented by the assessment of this kind of treatments as a viable approach also for geopolymer based composites. In such a context, this study presents a novel and sustainable approach for enhancing sisal fibers for geopolymer composites using a sodium bicarbonate (NaHCO3) treatment. While the treatment offers a greener alternative to conventional methods, its key advantage lies in achieving a balance between fiber properties. Although it slightly reduces raw fiber strength, the NaHCO3 treatment effectively removes impurities, promoting improved crystallinity and, more importantly, significantly enhances fiber surface roughness and homogeneity. This tailored surface modification fosters superior interfacial bonding with the geopolymer matrix, resulting in composites with significantly enhanced flexural toughness (82 %) – a critical property for construction materials – compared to those reinforced with untreated fibers. Flexural strength is also improved by (53 %). This work not only demonstrates the effectiveness of NaHCO3 treatment but also highlights its potential for developing high-performing, eco-friendly construction materials. A comprehensive evaluation, including three-point bending tests to assess toughness, validates this promising approach.

Geopolymers are binder materials that are produced by a chemical reaction between silica or aluminum compounds with an alkaline activating solution. Foamed geopolymer materials are increasingly being cited as a viable alternative to popular organic insulation materials. Since the foaming process of geopolymers is difficult to control, and any achievements in improving the performance of such materials are extremely beneficial, this paper presents the effect of the addition of basalt powder on the properties of foamed geopolymers. This paper presents the results of physicochemical studies of fly ash and basalt, as well as mechanical properties, thermal properties, and structure analysis of the finished foams. The scope of the tests included density tests, compressive strength tests, tests of the thermal conductivity coefficient using a plating apparatus, as well as microstructure tests through observations using light and scanning microscopy. Ground basalt was introduced in amounts ranging from 0 to 20% by mass. It was observed that the addition of basalt powder contributes to a reduction in and spheroidization of pores, which directly affect the density and pore morphology of the materials tested. The highest density of 357.3 kg/m3 was characterized by samples with a 5 wt.% basalt powder addition. Their density was 14% higher than the reference sample without basalt powder addition. Samples with 20 wt.% basalt addition had the lowest density, and the density averaged 307.4 kg/m3. Additionally, for the sample containing 5 wt.% basalt powder, the compressive strength exceeded 1.4 MPa, and the thermal conductivity coefficient was 0.1108 W/m × K. The effect of basalt powder in geopolymer foams can vary depending on many factors, such as its chemical composition, grain size, content, and physical properties. The addition of basalt above 10% causes a decrease in the significant properties of the geopolymer. [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]

Alkali-activated materials are gaining much interest due to their outstanding performance, including their great resistance to chemical corrosion, good thermal characteristics, and ability to valorise industrial waste materials. Reusing waste glasses in creating alkali-activated materials appears to be a viable option for more effective solid waste utilisation and lower-cost products. However, very little research has been conducted on the suitability of waste glass as a prime precursor for alkali activation. This study examines the reuse of seven different types of waste glasses in the creation of geopolymeric and cementitious concretes as sustainable building materials, focusing in particular on how using waste glasses as the raw material in alkali-activated materials affects the durability, microstructures, hydration products, and fresh and hardened properties in comparison with using traditional raw materials. The impacts of several vital parameters, including the employment of a chemical activator, gel formation, post-fabrication curing procedures, and the distribution of source materials, are carefully considered. This review will offer insight into an in-depth understanding of the manufacturing and performance in promising applications of alkali-activated waste glass in light of future uses. The current study aims to provide a contemporary review of the chemical and structural properties of glasses and the state of research on the utilisation of waste glasses in the creation of alkali-activated materials. [ABSTRACT FROM AUTHOR]

A new era has dawned in the manufacturing of cement-free binders with appropriate mechanical strengths and durability to combat CO2 emissions. However, the assessment of their performance in extreme conditions is ongoing. Here, we attempted to use incinerated sewage sludge ash (ISSA), a waste product of sewage sludge incineration that contains limited amounts of heavy metals, along with waste glass powder (GP) and ground granulated blast furnace slag (GGBS), as precursors to produce cement-free binders through alkali-activation. The alkali-activated materials (AAMs) were then subjected to an intensified sewage corrosion test for 6 months. The aim was to utilize the heavy metals in the ISSA as biocides to resist the biogenic acid attack on the AAMs. The experimental results indicated that superior performance was achieved by using a ternary binder prepared with ISSA, GP, and GGBS under biogenic acid simulation. Such enhanced durability can be attributed to the low Ca content in the resulting alkali-activated gels, which also reduced the grain size of gypsum formed and prevented expansion deterioration. Furthermore, the slow release of heavy metals from the AAMs prepared with the ISSA, evidenced by the leaching test results, was able to inhibit microbial growth. [ABSTRACT FROM AUTHOR]

Chloride binding by the hydrate phases of cementitious materials influences the rate of chloride ingress into these materials and, thus, the time at which chloride reaches the steel reinforcement in concrete structures. Chloride binding isotherms of individual hydrate phases would be required to model chloride ingress but are only scarcely available and partly conflicting. The present study by RILEM TC 283-CAM 'Chloride transport in alkali-activated materials' significantly extends the available database and resolves some of the apparent contradictions by determining the chloride binding isotherms of layered double hydroxides (LDH), including AFm phases (monosulfate, strätlingite, hydrotalcite, and meixnerite), and of alkali-activated slags (AAS) produced with four different activators (Na2SiO3, Na2O·1.87SiO2, Na2CO3, and Na2SO4), in NaOH/NaCl solutions at various liquid/solid ratios. Selected solids after chloride binding were analysed by X-ray diffraction, and thermodynamic modelling was applied to simulate the phase changes occurring during chloride binding by the AFm phases. The results of the present study show that the chloride binding isotherms of LDH/AFm phases depend strongly on the liquid/solid ratio during the experiments. This is attributed to kinetic restrictions, which are, however, currently poorly understood. Chloride binding by AAS pastes is only moderately influenced by the employed activator. A steep increase of the chloride binding by AAS occurs at free chloride concentrations above approx. 1.0 M, which is possibly related to chloride binding by the C–(N–)A–S–H gel in the AAS. [ABSTRACT FROM AUTHOR]

AbstractTo realize the safe disposal of solid waste containing heavy metals, sewage sludge jointly with slag and metakaolin was used to prepare alkali-activated materials (AAMs), and the effect mechanism of polycarboxylate acid superplasticizer (PCE), naphthalene superplasticizer (NS) and aliphatic superplasticizer (AS) in AAMs were studied. The results showed that both the fluidity and strength of AAMs decreased with the addition of sludge. For the NaOH + Na2SiO3 activated mortar specimen, the incorporation of sludge can reduce their fluidity and strength from 206 mm and 80.25 MPa to 193 mm and 42.43 MPa, respectively. However, the addition of superplasticizers into sludge-containing AAMs leads to a reduction of 3–9% of the fluidity. Interestingly, it can enhance the strength of the AAMs, especially the NS and AS, which increase the strength by approximately 25%. This is attributed to the increase of particle dispersion by superplasticizers. However, the free water released in the process is reabsorbed by the sludge, which increases the local alkali concentration and promotes the activation of the activity. The dispersed sludge particles can play the role of physical filling, making the structure denser. HIGHLIGHTSSludge is adverse effects on both the fluidity and strength of alkali-activated materials (AAMs).The addition of superplasticizers (SPs) increases the strength of AAM with sludge.SPs do not affect improving the fluidity of AAMs with sludge, even slightly bad.The dispersion effect of SPs on the sludge is beneficial to promote its activity in AAMs.Sludge is adverse effects on both the fluidity and strength of alkali-activated materials (AAMs).The addition of superplasticizers (SPs) increases the strength of AAM with sludge.SPs do not affect improving the fluidity of AAMs with sludge, even slightly bad.The dispersion effect of SPs on the sludge is beneficial to promote its activity in AAMs. [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]

Environmental and economic problems arising from cement production have made it necessary to find alternative binders. At this point, geopolymer mortars have come to the fore as an alternative construction material. In this study, 40% metakaolin + mineral additives (20% fly ash + 20% granulated blast furnace slag + 20% red mud) were used as binding material. NaOH (12M) and Na2SiO3 solutions were used. Recycling concrete aggregate and marble powder (MP) were used in equal proportions as aggregate. Different types of fibers (steel fiber (SF), polyamide fiber (PAF), and polypropylene fiber (PPF)) were used with different ratios (0.25, 0.50, 0.75, and 1%). In addition to mechanical properties (7, 28, and 56 days) such as compressive strength (CS), flexural strength (FS), and ultrasonic pulse velocity, high temperature, freezing–thawing, and sulfate resistances were performed. Results indicated that the series with 1% vol. SF had the highest unit weight and low water absorption, with the highest CS 38.5 MPa and FS 27.88% higher than the reference. However, considering the durability resistance, the best performance was observed in the series with 1% PPF by volume. The residual CS of this series after freezing–thawing was 32.95 MPa, the FS was 4.90 MPa, the CSs after Na2SO4 and Mg2SO4 were 38.32 MPa and 41.40 MPa, and FSs were 5.05 MPa and 4.41 MPa, respectively. Considering the abrasion resistance loss, the sequence of the series was as follows: 0.5% by volume PPF > 0.75% by volume PAF = 0.25% by volume SF. [ABSTRACT FROM AUTHOR]

The increasing scarcity of virgin natural resources and the need for sustainable waste management in densely populated urban areas have heightened the importance of developing new recycling technologies. One promising approach involves recycling agricultural waste in construction applications and transforming it into secondary products. This is anticipated to reduce the demand for new resources and lower the environmental impact, aligning with industrial ecology principles. Combined with a low carbon emission binder (i.e., alkali-activated), utilizing agro-waste to produce zero-cement particle boards is a promising method for green construction. Traditionally, particle boards are engineered from wood or agricultural waste products that are pressed and bonded with a binder, such as cement or synthetic resins. However, alternative binders replace cement in zero-cement particle boards to address environmental concerns, such as the carbon dioxide emissions associated with cement production. This study investigated the effects of accelerated aging on the performance of alkali-activated agro-waste particle boards. Accelerated aging conditions simulate natural aging phenomena. Repeated wetting–drying and freezing–thawing cycles increased water absorption and thickness swelling and reduced flexural strength. The thermal performance of the alkali-activated particle boards did not exhibit significant changes. Hence, it was confirmed that agro-waste has a high potential for utilization in producing particle boards provided that the working environment is carefully selected to optimize performance. [ABSTRACT FROM AUTHOR]

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Adsorption is a promising method to remove dyes, such as methylene blue, from wastewater. In this study, a dynamic adsorption set-up was used to treat synthetic wastewater containing methylene blue by using alkali-activated blast furnace slag and lignin composite foam. The structure of the foam without lignin was frst optimized by comparing cationic and non-ionic surfactants in the preparation of the foam via the direct foaming method. The selection of the surfactant afects the porosity and pore structure of the foam through diferent abilities to stabilize the gas–liquid interface and changes in the viscosity of the fresh-state paste. The foam prepared with non-ionic Triton X-114 surfactant had the highest adsorption performance and was selected for the optimization of adsorption conditions. The optimized conditions were 5 mg/L infuent concentration of methylene blue, pH of 7, and fow rate of 1.0 L/h (corresponding to ~ 9 min empty bed contact time). To further enhance the methylene blue adsorption performance, a composite containing lignin was prepared. The optimum lignin amount in the foam was 0.8 wt% and it resulted a ~ 93% higher adsorption amount compared to the foam without lignin. The highest cumulative adsorption capacity in this dynamic adsorption setup was 39.5 mg/g, which is among the highest reported values for methylene blue removal by monolithic adsorbents. The present study provides a proof of concept for the enhancement of adsorption performance of alkali-activated materials by introduction of lignin into the structure. [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]

Cement-based coral aggregate concrete (CAC) and its structures reinforced with fiber-reinforced polymer (FRP) bars suffer from low strength, poor anti-permeability resistance, and insufficient durability. To overcome these drawbacks, this study employs well-durable slag-based alkali-activated materials as alternatives to ordinary Portland cement to develop FRP bars reinforced alkali-activated coral aggregate concrete (AACAC) beams. The effects of the type of FRP bars (GFRP, BFRP, and CFRP bars), the longitudinal reinforcement ratio (0.48–1.12%), and the diameter of FRP bars (8 and 10 mm) on the flexural behavior of CAC and AACAC beams were evaluated. The results revealed that with the increased reinforcement ratio, the number of cracks in AACAC beams increased, and their crack height and crack spacing gradually lowered. Furthermore, the cracking load, ultimate load, and slope of load–deflection curves at the ascending stage (i.e., flexural stiffness) exerted a significant improvement with increasing reinforcement ratio, but the mid-span deflection and the strength utilization of internal FRP bars decreased. When the reinforcement ratio increased from 0.48 to 1.12%, the ultimate load capacity for BFRP bars reinforced AACAC beam was enhanced by about 47.8%, but the strength utilization of internal FRP bars reduced from 66.8 to 55.1%. Compared with cement-based CAC beams, AACAC beams exhibited a smaller crack width under the same concrete strength and load value, but contained a lower ultimate loading capacity and mid-span deflection, demonstrating that AACAC beams had a bigger brittleness than CAC beams. [ABSTRACT FROM AUTHOR]

Porous alkali-activated materials are synthetic aluminosilicates that should be often produced as granules for practical applications. In the present study, municipal solid waste incineration fly ash with ~1.2 wt% of metallic aluminium was used as a novel blowing agent for metakaolin (their ratio ranged from 0% to 100%) with an aqueous sodium silicate solution as the alkali-activator and granulation fluid in high-shear granulation. The compressive strength of all granules was sufficient (≥2 MPa). Water absorption indicated an increase in porosity as the fly ash content increased. However, X-ray microtomography imaging showed no clear correlation between the fly ash content and porosity. The granules exceeded the leaching limits for earth construction materials for antimony, vanadium, chloride and sulphate. Of those, antimony, chloride and sulphate could be controlled by decreasing the ash content, but the source of vanadium was identified as metakaolin. The increase in the fly ash content decreased the cation exchange capacity of the granules. In conclusion, the recommended fly ash content is equivalent to 0.3 wt% of Al0 and the developed granules could be best suited as light-weight artificial aggregates in concrete where the additional binder would provide stabilization to decrease the leaching.

Thermal energy storage (TES) system has been widely employed in concentrated solar power (CSP) plants to ensure the system efficiency. With excellent thermal characteristics, electrolytic copper powder (ECP), graphene oxide (GO) and lead-smelter slag (LSS) aggregate – a mining waste material, have been utilised in this study, aiming to fabricate metallurgical geopolymer material as a storage medium in the TES system. This paper investigated the effect of ECP contents (0, 5%, 10%, 15%, 20%) on the strength, specific heat, thermal conductivity and thermal stability of GO-engineered geopolymer mixes incorporating LSS aggregate. With 10% ECP inclusion, the flow rate and compressive strength improved significantly. Increasing ECP content improved the thermal conductivity but reduce specific heat of geopolymers. The results revealed that ECP was a promising component to be incorporated into geopolymer to enhance its physio-mechanical characteristics and thermal stability. The combination of ECP, GO and LSS to produce geopolymer materials for TES system can provide an eco-friendly solution to the CSP plants and the industry waste recovery.

In place of Portland cement concrete, alkali-activated materials (AAMs) are becoming more popular because of their widespread use and low environmental effects. Unfortunately, reliable property predictions have been impeded by the restrictions of conventional materials science methods and the large compositional variability of AAMs. A support vector machine (SVM), a bagging regressor (BR), and a random forest regressor (RFR) were among the machine learning models developed in this study to assess the compressive strength (CS) of AAMs in an effort to gain an answer to this topic. Improving predictions in this crucial area was the goal of this study, which used a large dataset with 381 points and eight input factors. Also, the relevance of contributing components was assessed using a shapley additive explanations (SHAP) approach. In terms of predicting AAMs CS, RFR outperformed BR and SVM. Compared to the RFR model’s 0.96 R 2, the SVM and BR models’ R 2-values were 0.89 and 0.93, respectively. In addition, the RFR model’s greater accuracy was indicated by an average absolute error value of 4.08 MPa compared to the SVM’s 6.80 MPa and the BR’s 5.83 MPa, which provided further proof of their validity. According to the outcomes of the SHAP research, the two factors that contributed the most beneficially to the strength were aggregate volumetric ratio and reactivity. The factors that contributed the most negatively were specific surface area, silicate modulus, and sodium hydroxide concentration. Using the produced models to find the CS of AAMs for various input parameter values can help cut down on costly and time-consuming laboratory testing. In order to find the best amounts of raw materials for AAMs, academics and industries could find this SHAP study useful.