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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.

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.

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]

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

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

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]

Alkali-activated materials, sometimes called geopolymers, can be used as alternative cementitious materials to conventional Portland cement. Currently, there is a significant interest in these materials due to their low CO2 footprint. The typical applications of alkali-activated materials are within civil engineering; however, potential applications as well cementing material within the oil and gas industry are also receiving emerging interest. This paper presents a systematic study of the compressive strength development from 1 to 28 days for metakaolin-based alkali-activated cement. The results show that the compressive strength is highly dependent upon the initial Si/Al ratio in the mix design, as well as the concentration of the activator solution. Furthermore, due to the relatively low initial reactivity of the metakaolin material used, different types of co-binders were included in the slurry composition to improve early strength development. The two different co-binders tested were another, more reactive metakaolin material and Blast Furnace Slag (GGBFS). It was found that both these co-binders performed as intended, by ensuring early strength development via precipitation of K-A-S-H and C-A-S-H gels, respectively, and also by enabling subsequent strength development due to improved dissolution of the low-reactive metakaolin. [ABSTRACT FROM AUTHOR]

In the present study, porous inorganic polymers were synthetized by alkaline activation of volcanic ash and ' ghiara' paleosoil using Al swarf and Al commercial powder as pore inducing agent. The Alkali Activated Foams (AAFs) were characterized in terms of mineralogy, macro- and microstructure, by synchrotron X-ray diffraction, electron microscopy, infrared spectroscopy, and X-ray computed microtomography. The obtained porous matrices show different microstructures; the size and extent of the pores vary according to the type, size and amount of the foaming agent and to the viscosity of the pastes. Addition of Al swarf to the volcanic ash based slurry generates expansion of the paste, whereas ghiara based one do not expand due to a lower viscosity of the slurry. Moreover, results indicate that the Al addition procedure during the synthesis affects the pore characteristics: Al powder added directly to the volcanic ash-based slurry triggers an incipient pore nucleation, whereas AAFs prepared adding Al powder to the solid mix do not develop an extended pore network. Results of this research show that porosity can be efficiently tailored in volcanic based AAFs by regulating the amount and type of Al. [ABSTRACT FROM AUTHOR]

The demand for resource saving and recycling of waste materials to achieve a circular economy is increasing. In Europe, nearly all blast furnace slag and fly ash are used as supplementary cementitious material. Furthermore, there is urgent need to reduce the CO2 emissions of building materials industry. Like in OPC‐based concretes, the reduction in the binder content by the use of fillers can be a way to reduce the CO2 emissions of alkali‐activated binders even further. Therefore, this study aims at the use of industrial residues as a filler in alkali‐activated materials to reduce the CO2 emissions of alkali‐activated binders. In this study, three industrial residues including municipal solid waste incineration ash (MSWIA), steel slag (SS) and ash formed by the thermal treatment of tar‐containing asphalt (EcoF) are used as fillers for alkali‐activated binders and are compared with fine quartz powder as an inert reference filler. The binder is ground granulated synthetic slag, which is replaced with the four filler materials at a 32 vol.% replacement level. The samples are reacted with 15 and 25 wt.% NaOH solution. The results show a potential advantage of using SS and EcoF as a filler in concrete as they exhibited a slightly higher compressive strength at all tested ages compared to quartz powder. [ABSTRACT FROM AUTHOR]

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

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.

Popular and eco-friendly alkali-activated materials (AAMs) replace Portland cement concrete. Due to the considerable compositional variability of AAMs and the inability of established materials science methods to understand composition–performance relationships, accurate property forecasts have proved impossible. This study set out to develop AAM compressive strength (CS) evaluation machine learning (ML) models using techniques including extreme gradient boosting (XGB), bagging regressor (BR), and multi-layer perceptron neural network (MLPNN). Ten input variables were used with a large dataset of 676 points. Statistical and K-fold studies were also used to evaluate the developed models’ correctness. XGB predicted the CS of AAM the best, followed by BR and MLPNN. The MLPNN and BR models had R 2 values of 0.80 and 0.90, respectively, whereas the XGB model had 0.94. Results from statistical analyses and k-fold cross-validation of the used ML models further attest to their validity. The built models can potentially compute the CS of AAMs for a variety of input parameter values, reducing the requirement for costly and time-consuming laboratory testing. Researchers and businesses may find this study useful in determining the necessary quantities of AAMs’ raw components.

This study explores the potential of waste brick and geo-cement aggregates as substitutes for natural sand in alkali-activated materials (AAMs) for mortar production. With a focus on achieving net-zero construction and mitigating environmental impact, the study replaces Portland Cement (OPC) and virgin aggregates with waste materials and by-products. The investigation evaluates the substitution of sand (up to 100 % by weight) in AAMs with waste brick aggregates (WBA) and waste geo-cement aggregates (WGA) obtained from demolished construction and research lab waste, respectively. The research methodology involves assessing mechanical, durability, and microstructure properties to assess the performance of the developed AAMs with waste aggregates. Notably, AAM composites containing waste brick and geo-cement aggregates surpass natural aggregate composites in terms of mechanical strength, water absorption, freeze-thaw resistance, acid ingress, and chloride attack. The 7-day 50 % waste brick mixture achieved a maximum compressive strength of 61 MPa, while a 70 % waste geo-cement mortar mixture attained a maximum flexural strength of 12 MPa. Combinations, whether comprising waste brick or geo-cement mortar aggregates, demonstrate compressive strengths well over 40 MPa, rendering them suitable for heavy load-bearing structures. The 50 % waste geo-cement mortar mixture stands out with the lowest water absorption rate of 6 % and the least compressive strength loss of 13 % after the freeze-thaw test, with reductions of 6 % and 18 %, respectively, compared to the control. Additionally, 100 % waste brick AAMs exhibit the lowest compressive strength loss after chloride and acid attack tests, with reductions of 13 % and 2.5 %, respectively. When compared to all other mixtures, the 50 % waste brick aggregates mortar mixture obtained the best overall performance. The composites developed in this study affirm their suitability for use in heavy-load structural components, showcasing favourable mechanical and durable properties. These findings underscore the need for additional exploration in this direction to advance sustainable construction practices.

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.

Alkali-activated materials are environmentally friendly gelling agents that have been intensively studied in soil solidification over a long period of time. Currently, there is little research on the deformation and damage laws of solidified soils during compression failure. This study investigates the energy dissipation mechanism and plastic damage model of Weibull distribution to explore solidified soil under different curing ages, moduli, and cement, ground granulated blast furnace slag (GGBS), and alkali-activator contents to further explore the damage evolution law and elastic-plastic state of alkali-activated slag soil. The destruction of solidified soil is accompanied by energy dissipation, and the damage to a specimen under load can be expressed as the amount of dissipated energy. In this paper, the change rules of the damage variable (D), total dissipation energy (U), elastic strain energy (Ue), and dissipation energy (Ud) of solidified soil during compression are described in detail, and the damage to the solidified soil is characterized using the dissipation energy ratio (Ud/U) and damage variable. Based on the energy dissipation mechanism, a brittleness index (BI) is established considering the pre-peak elastic-plastic state and post-peak load-bearing capacity loss states. The U, Ue, and BI increase with a decrease in the modulus and increase in the curing age and cement, GGBS, and alkali-activator contents, whereas Ud/U and D decrease. D is linearly proportional to Ud/U. The BI and Ud/U demonstrated an exponential correlation. Finally, the influence of the cement, GGBS, and alkali-activator contents are shown to increase through X-ray diffraction (XRD), thermogravimetry (TG/DTG) and nuclear magnetic resonance (NMR) tests. Additionally, the effects of the cement, GGBS, and alkali-activator contents and alkali-activator modulus on the damage variable and brittleness index are explained from a microscopic point of view. The relationships between porosity and Ud/U, D, and BI are established. This study provides a reference value for the characterization of mechanical properties of solidified soil and the relationship between the pore structure and mechanical indexes.

The purpose of the paper was to analyze trends in the formation of alkali-activated materials (AAMs) produced from alternative starting materials to blast furnace slags and fly ash. The research was reviewed on the basis of literature data from the past few years, which shows that the researchers are increasingly paying attention to the possibility of synthesis of AAM from such waste materials as industrial slags and ashes, concrete and demolition waste, red brick waste and glass waste. This is driven by the need to find competitive solutions to the commonly used blast furnace slags and fly ashes in the cement industry, which are also a source for obtaining traditional AAM. Analysis of material solutions has shown that these materials are being successfully used to produce new AAMs, with most of them being only a partial replacement for slags and fly ash. The article also points out that silicon- and aluminum-rich waste materials such as red mud, rice husks, and waste glass can be successfully used to activate AAMs materials, in place of typical activators in the form of sodium silicates or hydroxides, which in turn contributes to lowering the carbon footprint of AAMs. However, the future of this type of solution depends on several factors, the most important of which seems to be the understanding of the polymerization mechanisms of the more complex aluminosilicate systems and the achievement of reproducible physical and chemical parameters of AAM, resulting in strong and durable binders and, ultimately, construction materials made from them.

This research used gene expression programming (GEP) and multi expression programming (MEP) to determine the compressive strength (CS) of alkali-activated material (AAM) to compare and develop more reliable genetic algorithm-based prediction models. To learn more about how raw ingredients affect and interact with the CS of AAM, a SHapley Additive exPlanations (SHAP) analysis was conducted. A comprehensive dataset containing 676 points with fifteen influential parameters was formulated from the previously published literature. According to this study, considering the impact of 15 input variables, both genetic algorithms produced results close to the experimental CS (retrieved from the literature). When the performance of the GEP and MEP models were compared, it was found that the MEP model, with an R2 of 0.86, performed better than the GEP model, with an R2 of 0.82. The assessment of the statistical parameters of generated models revealed that the MEP model was more effective. Additionally, SHAP analysis revealed that slag content, followed by the specimen's age, sodium silicate, and curing temperature, showed a positive correlation with CS of AAM, which were the most important parameters. The results also revealed the importance of chemical contents, i.e., CaO, SiO2, Al2O3, of FA and slag on the CS of AAM. The built models might be used to compute the CS of AAMs with varying input parameter values, minimizing the effort, time, and cost of unnecessary lab tests. Furthermore, the outcomes of the SHAP study might help researchers and the industry determine the quantity or composition of raw ingredients when producing AAMs.

Life Cycle Assessment (LCA) quantifies the environmental impacts associated with products throughout their life cycle. LCA also assists in the interpretation of impact assessment results, enabling improvements in a product or process. This paper applied the LCA methodology to quantify and compare the greenhouse gas emissions associated with different types of concrete: with a traditional binder (Portland cement) and with alkali-activated materials (Metakaolin, Lateritic Soil, and Lateritic Concretion) as precursors. The environmental impact was evaluated using greenhouse gas emissions (kg CO2-eq/m³), considering 1 m³ of each binder and resistance of approximately 30 MPa, obtained by a recommended mix ratio. The main objective is to evaluate whether alkali-activated binders present lower emissions than Portland cement. The results demonstrated that Portland cement is responsible for over 92% of the emissions associated with traditional concrete production. The use of alternative materials in civil construction, such as laterite soil, reduces carbon dioxide emissions by 79% compared to traditional concrete.

This study investigates the development of elastic and creep properties of sodium hydroxide-activated blast furnace slag mortar, utilizing three different molarities of the activator solution and two solution-to-binder ratio and a reference OPC-based mixture, since the earliest age. The experimental phase involves a series of hourly-repeated 5-min long creep tests on the aging material. This approach enables continuous monitoring, facilitating the characterization of early-age elastic stiffness and creep properties. Linear regression is employed to calculate the tangent unloading (elastic) modulus and Poisson's ratio. To model short-term creep behaviour, a power-law creep function is utilized. The integration of these findings with calorimetry-derived evolutions of cumulative heat release establishes linear correlation between (compressive) strength and heat release, along with a power function relationship between unloading (elastic) modulus and heat release. An optimal alkali dosage (Na2O content) appears to be vital for long-term strength development. Additionally, the creep parameters, namely amplitude (A) and kinetic (K), demonstrate a gradual decrease, although they maintain values higher than those of the corresponding OPC mixture, as the heat release progresses.

Marl soils with different carbonate contents usually show more unpredictable behavior than other problematic soils. In some marl soil groups, freezing–thawing (F-T) cycles can result in slaking and detrimental effects on the soil mechanical properties. However, up to now, studies on the performance of stabilized marl with alkali-activated materials under F-T cycles have been noticed to be quite limited. Moreover, the filled pores in the marl layered matrix and cementing materials bonded particles during the formation mechanism have not been clearly explored yet. This study investigated the improvement of slaking marl soil with a geopolymer based on recycled glass powder (RGP) activated with sodium hydroxide (NaOH) for complete replacement of industrial cement. The study evaluated the effects of the changes of the curing times (7, 28, and 90 days), RGP content (5%, 10%, and 15%), alkali concentration (2, 4, and 6M), curing temperatures as close to research conditions as possible (20°C and 50°C), volumetric strain, and 12 cycles of F-T for the unconfined compression strength (UCS) and consolidation test results. The control sets, comprising natural and cement-stabilized samples, were prepared and examined to provide a reference baseline. The mineralogical and microstructural characteristics were determined through X-ray diffractometer (XRD) and scanning electron microscopy (SEM) techniques. The results revealed that the cyclic F-T actions damaged the bonding between marl layers and made an irreversible structure with a lower UCS value. The results indicated that after conducting F-T cycles, the UCS of stabilized samples (15% RGP content, 2 M NaOH, 90 days curing) diminished from 3,667 to 2,668 kPa (27% reduction) after 12 F-T cycles. The one-dimensional consolidation test results confirmed a considerable reduction (92% for 90-day cured samples) in the settlement. [ABSTRACT FROM AUTHOR]

Alkali-activated grouts (AAGs) are increasingly used to replace ordinary portland cement owing to their several advantages. The mechanical properties and environmental aspects of AAGs are affected by the type of activator. In this study, the effects of sunflower stalk ash (SSA) and commercial alkaline reagents on the mechanical properties, microstructures, and CO 2 emissions of geopolymer grouts were investigated for the first time using blast furnace slag and black rice husk ash as precursors. The results indicated that the potassium and calcium salts in the SSA promoted the formation of C(K)-A-S-H and C–S–H. The compressive strength of the SSA-activated grouts was higher than that of the slurry prepared using commercial products (24.88 vs. 11.59 MPa). Using SSA instead of commercial reagents can reduce kg CO 2 -eq/t powder by 84.4 %. [ABSTRACT FROM AUTHOR]

In this study, the fluidity, setting time, and compressive strength for 40%/60% ground granulated blast furnace slag (GGBFS)/metakaolin (MK) based geopolymer synthesis were experimentally investigated. By conducting 120 groups of tests, the effects of three design parameters of the alkaline activator, including the alkaline activator concentration, modulus, and liquid–solid ratio, were systematically analyzed. The test results show that the compressive strength of the GGBFS–MK geopolymer synthesis reaches a maximum value for a modulus of 1.2 or 1.4. Furthermore, according to the experimental results obtained, a series of contour plots for the relationship between the influencing parameters and the workability and mechanical properties for GGBFS–MK geopolymer synthesis are summarized. Then, a mix design method is proposed. Appropriate combinations of the concentration and modulus that can be used to generate a target compressive strength and fluidity are identified from the contour plots for different liquid–solid ratios. This method can be used to determine the mix proportion design for GGBFS–MK geopolymer synthesis that shows a specified compressive strength and working performance. [ABSTRACT FROM AUTHOR]

The effectiveness of textile-reinforced mortars (TRM) utilized as jacketing overlays that are applied to short, shear-critical reinforced concrete (RC) columns was investigated experimentally and verified analytically in this study. Moreover, the possibility of replacing the standard ordinary portland cement (OPC) matrix with an alternative alkali-activated material (AAM) in the TRM retrofitting technique was explored. Seven rectangular-shaped RC columns were constructed with a shear span-to-height ratio of 1.5. Four of the seven specimens were constructed to be more ductile with closely spaced shear reinforcement, and the rest had their stirrups positioned at larger spacings. Both series of columns were retrofitted with two and four layers of TRM jacket overlays, which were made from uncoated carbon textiles and AAM or OPC-based mortar. They were subjected to cyclic loading combined with a constant vertical load. The control (unretrofitted) specimens exhibited brittle failure, and the retrofitted specimens performed significantly better for deformation capacity, with a clear shift in the failure mode toward shear–flexure. The load capacity of the jacketed columns was governed by yielding in the longitudinal reinforcement. An important result is that AAM-based TRM jacketing is not inferior to its OPC-based counterpart. [ABSTRACT FROM AUTHOR]

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

This study aimed to investigate the impact of as-received biomass fly ashes (BFA) and green liquor dregs obtained from a pulp and paper plant in Brazil as substitutes for metakaolin in geopolymeric formulations. The properties of this type of waste material vary widely between different industrial plants. This study refrains from subjecting the waste materials to any form of pretreatment, taking into account their organic matter and particle size heterogeneity, requiring extensive characterization to evaluate their influence on the compressive strength, apparent open porosity, and water absorption of the geopolymeric samples. The objective was to assess their potential for upcycling purposes as an alternative to energy-intensive materials, such as ordinary Portland cement (OPC) and advanced ceramics. This potential arises from the ability of alkali-activated materials (AAM) to undergo curing at ambient temperatures, coupled with the possibility of compositions primarily derived from waste materials. To improve the sustainability of the products, the amorphous content of the raw material, which is more reactive than crystalline phases, was quantified and used as the base for mixture ratios. This approach aimed to reduce the requirement for alkaline activators, which have significant environmental impacts, while also increasing the waste content in the formulation. The incorporation of waste materials into the geopolymer matrix generally led to a reduction in the compressive strength compared to the benchmark metakaolin sample (19.4 MPa) but did not present a trend. The dregs led to values of 4.1 MPa at 25 wt% and 7.1 MPa at 50 wt%, a behavior that is somewhat counterintuitive, and BFA at 10 wt% presented 5.7 MPa. Nevertheless, the apparent open porosity remained at high levels for all the samples, close to 50%, and the compressive strength of most of them was over the values obtained for the metakaolin-only samples with mixture ratios calculated from the total composition instead of the amorphous composition. The decrease in strength and the increase in porosity were attributed to the specific characteristics of the waste materials, such as their high crystallinity, presence of organic matter, heterogeneous particle composition, and size. Overall, this study provides insight into the variations in geopolymerization based on the bulk and amorphous content of the aluminosilicate sources and how the characteristics of the waste materials influence the geopolymer matrix. It also highlights how calculating mixture ratios based on the amorphous composition improves the possibility of waste valorization through alkali activation. Additionally, it suggests that BFA and dregs might be effectively utilized in applications other than OPC substitution, such as adsorption, filtration, and catalysis. [ABSTRACT FROM AUTHOR]

There is an increasing trend in research projects and case studies to demonstrate the potential of Additive Manufacturing (AM) with concrete, better known as 3D concrete printing. Like ordinary construction, the latest upgrades on this topic are strongly focused towards improving eco-sustainability in terms of low-carbon materials. Low-carbon binders’ alternative to Portland cement and the utilisation of selected waste materials in place to virgin aggregates has high potential in fulfilling the sustainable development goals. In this paper, an experimental study was performed by incorporating ground waste tire rubber aggregates of different size gradation (0–1 mm and 1–3 mm) and replacement levels (50 v/v% and 100 v/v%) in a “greener” alkali-activated mix designed for 3D printing applications. First, the experimental program involved the optimization of mix design rheology and printing parameters to successfully integrate rubber aggregates into the printable alkali-activated mixtures. Then, a comprehensive characterization, including static mechanical testing, dynamic thermo-mechanical analysis, thermal conductivity testing, and acoustic insulation measurements was conducted. Comparison with identical Portland-based rubberized formulations designed for AM revealed better mechanical isotropy, flexural strength, thermo-mechanical behaviour, heat insulation, and high-frequency acoustic insulation for alkali-activated composites. The influence of rubber aggregate size on the fresh and hardened state behaviour of the mixes was also studied and discussed. Keeping the losses in mechanical strength restrained, the rubberized composites designed in this study have demonstrated significant thermal and acoustic insulation properties that are desired for energy-saving applications in buildings. The research verified the practicability of using waste aggregates in low-carbon binders for sustainable lightweight and thermo-acoustically effective applications, establishing an attractive starting point to address future research on material optimization for practical purposes.

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.

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.

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.

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.

This study uses the Weibull analysis to predict the robustness of various mortars based on a fracture process analysis through a flexural test recorded by an acoustic emission sensor. Alkali-activated materials (AAMs) are an alternative to Portland cement that can decrease the amount of emitted CO2. This study aimed to characterise and compare the properties of AAM cement mortars to those of the commonly used ordinary Portland cement (OPC) mortars using the Weibull distribution to clarify the reliability and robustness of the prepared AAM cements; four different AAM cement mortar compositions—with fly ash (F), ground-granulated blast-furnace slag (G), and microsilica (M) alkali activation (sodium hydroxide (NaOH) and sodium silicate (Na2SiO3))—were considered in this study. The fracture process under a flexural loading of AAMs was based on four combinations of F/G/M activated by the alkaline solution—AAM-IV, AAM-V, AAM-VI, and AAM-VII, with OPC as control. The Weibull analysis showed that AAMs were more robust than the OPC mortar and possessed minor fractures compared to the OPC mortar.