Search

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]

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]

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.

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]

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]

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]

Copyright of Experimental Technology & Management is the property of Experimental Technology & Management Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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.

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.

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]

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]

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]

To date, carbon utilization within the concrete industry is predominantly revolved around gaseous and liquid carbon dioxide (CO2), with relatively limited research dedicated to the application of solid CO2. This study was the first to use solid CO2 (dry ice) as an additive in alkali-activated slag and fly ash (AASF) to investigate its influences on the alkali-activation process and various property improvements. Two study systems were designed: one with alkali-activated slag (AAS) as the control group and fly ash (FA) added at substitution rates of 10%, 30%, and 50%; and the other with 50% FA alkali-activated materials (AAM) as the control group and dry ice added at substitution rates of 4%, 8%, and 12%. Several tests were conducted on AASF, encompassing assessments of setting time, compressive strength, and durability (electrical resistivity and chloride ion diffusion coefficient). Furthermore, a comprehensive analysis of its microstructure was undertaken, employing analytical techniques, such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). The results showed that FA substitution effectively mitigated the short setting time of AAS; however, the mechanical properties and durability decreased by approximately 50%. When dry ice was added to AAM concrete, it induced a series of physical and chemical effects that altered the kinetics of the hydration reaction of AAM. Specifically, adding dry ice significantly prolonged the setting time of AAMs. Moreover, this addition did not damage the mechanical properties or durability of AAS(F). [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]

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]

Conventional geopolymers are proven to be eco-friendly compared to Portland cement-based concrete (PC). However, the used alkali activator, i.e. sodium silicate is associated with high carbon emission and cost, making the geopolymers not really a sustainable alternative to PC. This experimental investigation was carried out to understand the potential of rice husk ash (RHA)-based alkali activator in the synthesis of fly ash-blast furnace slag (FA-GGBFS)-based geopolymers at ambient temperature. Three different concentrations of sodium hydroxide (by wt. %) solutions, i.e. 20%, 24%, and 27%, were used to synthesize an RHA-based alkali activator. A commercial-grade sodium silicate solution was used to compare the results of geopolymer mortars (GPM) with the prepared RHA-based alkali activator. Fresh, mechanical, and microstructural investigations were carried out for both the RHA and commercial-grade alkali activator-based FA-GGBFS GPM specimens. The compressive strength of RHA-based optimum GPM was found to be 41 MPa at 28 days of the curing period, which was close to the control sample made with the commercial activator; similar observations were found for the flow table test. Microstructural investigation (XRD and SEM) confirmed that the GPM prepared with the RHA-based alkali activator has a similar microstructure as the GPM with the commercial-grade alkali activator. [ABSTRACT FROM AUTHOR]

Significant environmental issues are raised by the phosphogypsum (PG) waste that is being produced. In Lithuania, about 1,500,000 tons of PG waste is generated yearly, and about 300 Mt is generated yearly worldwide. A by-product of burning wood biomass in thermal power plants is biomass fly ash (BFA). By 2035, compared to 2008 levels, industrial biomass incineration for combined heat and power and, as a consequence, BFA, is expected to triple. This study revealed the possibility of using these difficult-to-utilise waste products, such as BFA and PG, in efficient alkali-activated materials (AAM). As the alkaline activator solution (AAS), less alkaline Na2CO3 solution and Na2SiO3 solution were used. The study compared the physical–mechanical properties of BFA-PG specimens mixed with water and the AAS. After 28 days of curing, the compressive strength of the BFA-PG-based, water-mixed samples increased from 3.02 to 6.38 MPa when the PG content was increased from 0 to 30 wt.%. In contrast, the compressive strength of the BFA-PG-based samples with AAS increased from 8.03 to 16.67 MPa when the PG content was increased from 0 to 30 wt.%. According to XRD analysis, gypsum crystallisation increased when the PG content in the BFA-PG-based samples with water increased. The presence of AAS in the BFA-PG-based samples significantly reduced gypsum crystallisation, but increased the crystallisation of the new phases kottenheimite and sodium aluminium silicate hydrate, which, due to the sodium ions' participation in the reactions, created denser reaction products and improved the mechanical properties. The outcome of this investigation aids in producing sustainable AAM and applying high volume of hardly usable waste materials, such as BFA and PG. [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]

In this study, an inorganic retarder and a synthesized dispersant (based on PCE) were used to improve the retention and workability of alkali-activated ground granulated blast furnace slag (GGBFS), with NaOH as the sole activator. The objective of the study was to formulate pumpable concrete mixtures with workable time of more than 90 min. The prolonged retention in slump was attained by the addition of the retarder. The effect of the dispersants, synthesized with different monomer to macromonomer ratios, on the workability of the paste was investigated by analyzing the fundamental rheological parameters. The addition of dispersant reduced the initial storage modulus and improved the workability of the alkali-activated paste mixtures. The interaction between the dispersant and NaOH-activated GGBFS systems was investigated by means of adsorption studies and zeta potential measurements. The dispersing ability and the amount adsorbed on GGBFS increased with an increase in the anionic charge of the dispersant. Zeta potential measurements suggested that the dispersion mechanism is primarily due to steric hindrance. Concrete mixtures of compressive strength in the range of ordinary concrete with pumpable workability for 90 and 120 min were achieved with the addition of both retarder and dispersant. The study concludes that a retarder is necessary to prolong the workable times, whereas a dispersant with a higher anionic charge is required to improve the workability of sodium hydroxide-activated GGBFS mixtures.

To improve the sustainable utilization of alkali-activated steel slag material, experiments were conducted to systematically investigate effects of sodium silicate modulus and GBFS content on the setting time, workability, mechanical properties and pore structure of alkali-activated steel slag cementitious material. Results show that the setting time is prolonged and workability is reduced as silicate modulus increases. The setting time is first shortened and then prolonged and workability is slightly reduced as GBFS content increases. Increasing silicate modulus and adding GBFS have positive effects on the development of elastic modulus, compressive and splitting tensile strength of alkali-activated steel slag material due to more refined pore structure. The highest compressive strength at 28 d can reach C35 strength level. Manufacturing alkali-activated steel slag material can achieve low energy consumption and carbon emission. If chemical activators can be replaced by some industrial wastes, cost, energy consumption and carbon footprint will be further decreased.

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.

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.

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.

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.

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.

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.