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Polycarboxylate superplasticizer (PCE) is one of the most widely-used chemical admixture in concrete, which is generally added during the mixing stage of concrete. However, part or major of the PCEs would be consumed during the initial rapid hydration resulting in the reduce of efficiency. Encapsulation of PCEs is an effective strategy to inhibit the undesired effects. However, due to retarding effect, low loading rate (high dosage required), and large capsule size (∼101-102 μm), most of the polymer and inorganic shell materials are not beneficial for the mechanical strength of concrete. Herein a type of silica matrix-microcapsule containing PCE were synthesized by the hydrolytic condensation of silane in an water/oil (W/O) emulsion. The loading rate could achieve ∼70 wt% based on the total weight of capsule. The size, specific surface area of the capsule could be well-regulated, which enabled the tunning of the release process within hours in simulated pore solution. Microcapsules containing PCE can significantly enhance the fluidity retention property of cement paste. The capsules also promote hydration due to silica, which could react with Ca(OH) 2 and yield calcium silicate hydrate gel. The strength of mortar showed that capsule improved the mechanical properties of mortar. [Display omitted] • Microcapsules containing PCE were prepared by the hydrolytic condensation. • The release process of microcapsules can be adjusted within hours. • Microcapsules enhance the fluidity retention property of cement paste. • Microcapsules improved the mechanical properties of mortar. [ABSTRACT FROM AUTHOR]

Agro-waste geopolymers are being significantly researched as sustainable substitutes to traditional construction materials for structural performance. However, a thorough assessment of their energy, environment, and economic (E3) performance is still questioned to facilitate in-situ building applications. This study first opts for a novel method of pressure catalysis for rice husk ash (RHA)-based geopolymers to enhance physico-mechanical performance with a low alkali activator dose. Afterward, the thermal conductivity of the optimized specimen was evaluated experimentally. Then, to assess its practical application, an E3 performance investigation was conducted on masonry brick/blocks as a pioneering approach for geopolymers. Distinct wall scenarios were simulated using Building Information Modeling (BIM) in a digital residential building. The experimental results showed that geopolymers with 50 % RHA, catalyzed under 20 MPa pressure, achieved 26.8 MPa compressive strength, lower density (1510 kg/m3), reduced water absorption (6.8 %), and 0.552 W/(m·K) thermal conductivity, outperforming traditional fired-clay brick and concrete block. The BIM analysis revealed that walls with RHA material had 53 % lower energy consumption and 30 − 41 % lesser CO 2 emissions, respectively. Despite the higher cost, the RHA block has advantages as a masonry unit due to a high economic index. The significant energy and environmental gains suggest the potential for optimizing the production process of RHA-based geopolymer to enhance cost-effectiveness and amplify benefits. • Development of rice husk ash (RHA) based structural block for masonry. • Optimizing physico-mechanical and thermal conductivity of block. • Evaluating Energy Environment and Economic (E3) performance of the residential unit in BIM. • Developing different wall scenarios and Evaluating E3 performance. • Comparison with conventional fired-clay and concrete block masonry. [ABSTRACT FROM AUTHOR]

In present work, effect of admixed NaCl (NC), NaCl + Na 2 SO 4 (NS), and NaCl + MgSO 4 (MS) on ionic concentration (Na+, Ca2+, K + , sulphate, and chloride) of aqueous pore solution of geopolymer concrete (GepC) made with fly ash (FA), and FA plus ground granulated blast furnace slag (GBFS) was evaluated and correlated with microstructure. Results showed admixed salts led to reduction in compressive strength than control mix. These findings are in line with variations in concentrations of Na+ and Ca2+ ions of pore solution. Fly ash based GepC with 14 M NaOH solution and admixed with NaCl + MgSO 4 salt showed higher strength loss of 61.58 %. Addition of salt led to increase in ionic concentration than control mix, where the concentration range of Na+ ion increased from 127.12–244.11 mmol/l to 133.73–541.3 mmol/l, and that of Ca2+ ion increased from 44.61–65.87 mmol/l to 46.71–143.72 mmol/l. GepC admixed with 3.5 % NC + 5 % MS showed lower sulphate concentration than 3.5 % NC + 5 % NS. The addition of GBFS resulted in decrease in free chloride content i.e., the range of free chloride content in fly ash based GepC was 0.71–0.89 % whereas that in case of fly ash-GBFS based GepC mix was 0.38–0.76 %. Further, the bound chloride content was higher in fly ash-GBFS based GepC (0.11–0.5 %) than fly ash based GepC (0.02–0.2 %). More formation of albite and CSH with GBFS content, and that of albite and nepheline with NaOH solution molarity as indicated by peak intensity from XRD analysis are in line with variations in compressive strength, and Na+ and Ca2+ concentrations of aqueous pore solution. Decalcification of CSH in magnesium sulphate environment as indicated by shifting of peak of Si–O–T bond to higher wavenumber is supported by variations of Ca2+ ion concentration, CSH peak intensity from XRD spectra, and compressive strength. • Chloride-sulphate salts reduced geopolymer concrete strength, aligning with changes in concentration of Na+ and Ca2+ ions. • Sulphate ion concentration reduced with increase in GBFS content and molarity of NaOH solution. • Bound chloride content increased with GBFS content and molarity of NaOH solution. • The Mg2+ ion associated with sulphate salt led to decalcification of CSH gel, resulting in deterioration of geopolymer concrete microstructure. [ABSTRACT FROM AUTHOR]

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

Reusing of iron ore tailings (IOT), particularly as recycled aggregate to prepare concrete, plays an important role in reducing dependence on natural resources and solving the problem of waste accumulation. In this paper, the effects of IOT as aggregate on the flowability, compressive strength of ultra-high performance geopolymer concrete (UHPGC) were studied, and the enhancement mechanism of IOT on compressive strength was elucidated through microscopic characterizations. The results show that with the increase of IOT content, the flowability of UHPGC decreases, and the compressive strength increases first and then decreases. 25 % IOT replacement yielded the best compressive strength, and 50 % substitution of IOT was comparable to the without IOT regarding compressive strength. The microstructure analysis shows that the crystalline components in the IOT do not participate in the hydration reaction and have the effect of micro-aggregate filling. The amorphous components on the IOT dissolve rapidly in the early stage, participate in geological polymerization reaction, and produce synergistic effect with slag to promote the formation of hydration products. However, excessive IOT incorporation will inhibit the dissolution of slag active ions and hinder the formation of hydration products. In addition, the enhanced interfacial transition zone (ITZ) and mechanical interlocking effect formed by IOT can effectively inhibit the crack development of UHPGC. • Proper use of IOT as aggregate can increase compressive strength of UHPGC. • The enhancement mechanism of IOT was elucidated through microscopic characterizations. • This study provided a new route to improving the comprehensive utilization of IOT. [ABSTRACT FROM AUTHOR]

Coal gangue (CG) represents a solid byproduct arising from coal mining activities, resulting in notable concerns related to land occupation and environmental pollution. In this study, a novel phosphoric acid-activated CG geopolymer (PCBG) was developed. At the macroscale, the effects of phosphoric acid concentration and water to solid ratio (W/S) on the strength development, optimal mix of PCBG, setting time, fluidity, and durability were systemically explored. At the microscale, microstructure and polymerization mechanism were unraveled by a serious of tests. Furthermore, the nine nanoscale hydration product models of PCBG were firstly developed by molecular simulation and test results. In addition, the Gibbs free energy, optimize structure, charge, electrostatic distribution, bond length, and elastic modulus of nine models were investigated to further understand and predict PCBG properties. The results show that the optimal calcination temperature, holding time, concentration and W/S ratio were 750 °C, 3 h, 7 mol/L and 0.25, and the peak compressive strength of 36.2 MPa was reached after curing for 28 days, and the concentration should be less than 11 mol/L to ensure the stability and integrity of the samples in water and sulfuric acid. The amorphous hydration products were composed of -Si-O-Al-O-P, -Al-O-P-, -Si-O-P- chains, meanwhile, six-coordination of Al and Q4 (3AlVI-O-P) were the main mode in hydration products. The charge and bond length of models were positively correlated with Al coordination number. The hydration product mode of Q4(3AlVI-O-P) could be used to predict the performance and structural changes of PCBG, whose elastic modulus was closely matched the experimental results (29.9 VS 30.2 GPa). This study presents a novel approach for the large-scale utilization of CG resources and offers a theoretical basis for phosphoric acid activation-based geopolymers. • A novel high-strength phosphoric acid-activated calcined coal gangue based geopolymer (PCBG) was developed. • The strength development mechanism, optimal mix, durability, and engineering performances were analyzed. • The nano-scale hydration structure modes of PCBG were firstly developed. • The Gibbs free energy, optimize structure, charge, bond length and elastic modulus of modes were calculated. [ABSTRACT FROM AUTHOR]

As a form of solid waste, electrolytic manganese residue (EMR) exhibits low reactivity, high sulfate content, and exceeds the standards for heavy metals. To address these drawbacks, a high-temperature thermal activation method was employed to enhance its reactivity and remove pollutants. The study investigated the physicochemical properties and leaching toxicity of EMR under different thermal activation conditions. Additionally, the thermally activated EMR was utilized in the preparation of geopolymer material, and the influence of EMR activation temperature, EMR content, sodium silicate content, and molar ratio on the mechanical properties, hydration mechanism, microstructure, and leaching toxicity of the EMR geopolymers was analyzed. The results indicated that after activation in the temperature range of 0–1200°C, the active content of silica-alumina in EMR increased, sulfate decomposition occurred, and the leaching of Mn2+ and NH 4 +-N decreased to 21.24 and 0.576 mg/L, respectively. When the activation temperature reached 1200°C, the compressive strength of the geopolymer, prepared with 50 % EMR, 50 % granulated blast furnace slag (GBFS), 30 % sodium silicate, and a molar ratio of 1.2, could reach 53.2 MPa at 28-day. Under activation in the range of 0–800°C, ettringite was abundant in the geopolymers, providing strength support. With activation in the range of 800–1200°C, the geopolymers became denser, exhibiting flaky and agglomerate gels. A diffraction peak appeared at 20°-40°(2θ) corresponding to C-(A)-S-H and N-S-A-H gels. Due to the slow depolymerization-polymerization kinetics of the EMR geopolymer and high sulfate content, the heat release rate and cumulative heat were significantly lower than ordinary portland cement (OPC). In the structure of EMR geopolymer, Mn2+ replaced Na+ and Ca2+ in the silicoaluminate structure or chemically bonded with anionic groups to the geopolymer. Simultaneously, Mn2+ participated in the formation of the EMR geopolymer gel, encapsulating within the gel. Therefore, the leaching of pollutants from EMR geopolymers met the standards of GB8978–1996. • The phase transformation process of thermally activated EMR was studied. • Prepared EMR high-strength geopolymer with compressive strength up to 53.2 MPa. • Studied the hydration mechanism and microstructure of EMR geopolymers. • Detailed analysis of EMR and geopolymer leaching toxicity was conducted. [ABSTRACT FROM AUTHOR]

Geopolymer cement, especially silicoaluminophosphate (SAP) geopolymer, is a sustainable binder that exhibits unique properties and has the potential to decrease carbon emissions in the construction industry. The SAP geopolymer was prepared using Ecuadorian zeolite tuff and phosphoric acid. Various experiments were conducted to determine the effects of several experimental factors, including phosphoric acid concentration, temperature, and acid-to-zeolite ratio, on the compressive strength of the SAP geopolymers. The results revealed that the SAP geopolymer with the highest compressive strength, GPA-R3, reached approximately 5 MPa after 14 days of aging. Characterization of the geopolymer samples, including X-ray diffraction, Fourier-transform infrared spectroscopy, and thermogravimetric analysis, revealed microcracks and pores in the materials, which correlated with the obtained values of compressive strength. A life cycle assessment showed a low environmental impact of geopolymers, particularly when using low acid concentrations. The GPA-R3 sample, which exhibited the best compressive strength, had a promising global warming potential of 535 kg of CO 2 -eq, outperforming other geopolymer and cement alternatives. • The zeolite based-silicoaluminophosphate (SAP) geopolymer has been prepared for the first time. • The effect of various variables on compressive strength of the SAP samples has been evaluated. • A compressive strength of ∼5 MPa was reached for the samples aged for 14 days. • Some SAP samples were characterized by XRD, FTIR, TGA-DSC and SEM techniques. • The environmental impact of SAP geopolymer has been evaluated through a life cycle analysis. [ABSTRACT FROM AUTHOR]

This study explores developing and characterizing a one-part geopolymer, an innovative and sustainable construction material. The effects of incorporating polyvinyl alcohol (PVA), polyethylene (PE), and glass fibers (GF) on the toughness of slag and fly ash-based one-part geopolymer mortars were investigated through compressive, three-point flexural, and four-point bending tests. The findings demonstrate that fiber incorporation reduces fluidity and compressive strength due to increased porosity, lower elastic modulus of fibers, and weak interfacial bonding. However, fibers significantly enhance damage resistance and toughness via crack bridging and load transfer mechanisms. Formulations with 2 % PVA fibers and combinations of 1 % PVA with 1 % PE fibers and 1 % PVA mixed with 0.5 % PE and 0.5 % GF demonstrate excellent toughness. Notably, the latter two fiber blends achieve 14 % and 10 % cost reductions, respectively, compared to using only PVA fibers, making them economically viable for large-scale applications. Scanning electron microscopy and X-ray diffraction provided insights into the toughening mechanisms, including crack bridging, fiber pull-out, and enhanced stress distribution within the geopolymer matrix. Digital image correlation techniques further elucidated the fibers' role in improving the post-cracking behavior and structural resilience under load. • Comprehensive investigation of PVA, PE, and glass fiber reinforcement in one-part geopolymer mortars, focusing on toughness optimization and cost-effectiveness. • Fiber incorporation significantly enhances damage resistance and toughness through crack bridging and load transfer mechanisms, despite minor reductions in fluidity and compressive strength. • Economically viable fiber blends (1 % PVA + 1 % PE; 1 % PVA + 0.5 % PE + 0.5 % GF) achieve excellent toughness with 14 % and 10 % cost reductions, respectively, compared to using only PVA fibers, making them suitable for large-scale applications. • SEM and XRD provide insights into the toughening mechanisms, including crack bridging, fiber pull-out, and enhanced stress distribution within the geopolymer matrix. DIC techniques elucidate the fibers' role in improving the post-cracking behavior and structural resilience under load, further validating the effectiveness of fiber reinforcement in one-part geopolymers. [ABSTRACT FROM AUTHOR]

Ultra-high-performance geopolymer concrete (UHPGC) is a new category of traditional UHPC developed to meet the desire for ultra-high-strength and green building materials. In the current study, random forest (RF), support vector regression (SVR), and extreme gradient boosting (XGB) are used to forecast the compressive strength (CS) of UHPGC. Firstly, the findings of the 113 CS tests available in the previous studies were extracted. Twelve feature variables, including GGBS, silica fume, fly ash, and rice husk ash contents as precursors, the Na 2 SiO 3 , NaOH, KOH, and extra water content, polypropylene fiber, steel fiber, liquid-to-binder (L/B) ratio, and curing temperature, were investigated. After analyzing the extracted data, it was found that there were more mixtures of steel fiber-based UHPGCs and synthetic fibers compared to mixtures without fibers. This may reduce the accuracy and comprehensiveness of the predictive models used. To address this issue, several experiments were designed, performed, and tested. Overall, the dataset of 128 CS results was used to develop the machine learning (ML) models. The findings validate the effectiveness of the RF, SVR, and XGB models in accurately predicting the strength of the UHPGC, as constructed by their excellent predictive accuracy (R2 > 0.84). The XGB model performance is superior to the RF and SVR models. The feature importance analysis determined that the steel fiber content and L/B ratio were the top two elements that might profoundly impact the CS. Additionally, NaOH and silica fume also have a positive correlation with CS. Conversely, the extra water and percentage of GGBS exhibit a low correlation with the CS. Through the application of ML models, this study not only ascertains the significance of algorithms including RF, SVR, and XGB in precisely forecasting the CS of UHPGC, but also reveals essential understandings regarding the importance of steel fiber content, L/B ratio, and various other pivotal variables, consequently facilitating the development of refined formulations and improved functionalities in eco-friendly construction materials. • Machine learning algorithms designed to predict the compressive strength of UHPGC. • An analysis of feature importance was conducted to investigate the impact of inputs on the compressive strength. • Ensemble Learning Algorithms outperformed support vector regression. • Steel fiber was found to be the most influential parameter controlling compressive strength. [ABSTRACT FROM AUTHOR]

During coal preparation, a substantial volume of coal gangue (CG) is generated, leading to severe environmental and health concerns stemming from its massive accumulation. Comprehensive research has been conducted on the utilization of CG in various engineering applications. Transforming it into supplementary cementitious material (SCM), geopolymer, and concrete aggregate holds pivotal significance in engineering applications, aligning with the imperatives of sustainable development. However, there are notable deficiencies in current research related to the grading, categorization, and standardization of CG for its optimal utilization based on its basic properties, which need to be addressed for further study and development. This paper takes the mineral composition of CG as a starting point, delving into an analysis of physical and chemical characteristics determined by the composition. Based on these characteristics, the effects of five main activation methods including mechanical, chemical, thermal, microwave, and composite treatments are comprehensively reviewed with a focus on their interaction mechanisms with CG. Subsequently, the fresh properties, mechanical properties, and durability of cementitious materials and aggregates prepared by CG were summarized and analyzed. Research suggests that contingent upon the degree and purpose of treatment (activation), CG can be applied in SCM (partially replacing cement), geopolymer (completely replacing cement), and concrete aggregate, with distinct treatment conditions influencing its engineering characteristics. This paper offers a systematic perspective and insights into the high-capacity utilization and value-added applications of CG. It highlights the issues encountered in the utilization of CG while further providing novel perspectives for its scaled utilization in engineering. [Display omitted] • Utilization of coal gangue in engineering is an ecological and sustainable way. • The pretreatment intensity varies across different utilization methods. • Progressed coal gangue exhibits excellent engineering utilization effect. • Numerous issues were identified, and some suggestions were proposed. [ABSTRACT FROM AUTHOR]

Lithium slag (LS) exhibits potential as a silica-alumina precursor for geopolymer synthesis, yet its limited reactivity poses challenges for widespread application in one-part geopolymers. This study employs alkali fusion activation to enhance LS reactivity and investigates the underlying mechanisms using XRD, FTIR, and ICP techniques. Results reveal that post-alkali fusion treatment transforms spodumene and quartz within LS into amorphous phases, significantly increasing the amorphous content from 15.9% to 53.1%. However, excessive inclusion of sodium hydroxide (NaOH) during alkali fusion reduces the amorphous phase content. Alkali fusion also enhances LS leaching concentration in an alkaline solution, but an overly abundant incorporation of NaOH adversely affects Si and Al leaching. Within specific parameters, increasing the alkali solution concentration and dissolution temperature enhances Si and Al leaching from LS. Subsequently, alkali-fused LS, along with slag and fly ash, is utilized to fabricate a one-part geopolymer that exhibits outstanding compressive strength. Results indicate that the compressive strength of alkali-fused LS geopolymer consistently surpasses that of the initial LS geopolymer during the curing period, reaching 50.6 MPa after 28 days. Alkali fusion effectively raises the pH of the geopolymer pore solution, promoting the formation of N(C)-A-S-H gel. The overall structure of the geopolymer prepared from alkali-fused LS is dense, with unreacted particles covered by a flocculent gel. However, excessive NaOH incorporation during alkali fusion reduces LS reactivity, diminishing the formation of N(C)-A-S-H gel. Simultaneously, the alkaline environment resulting from excessive NaOH facilitates carbonation reactions in geopolymer samples, thereby reducing compressive strength. • Alkali fusion altered the phase composition and crystalline structure of lithium slag. • Alkali fusion facilitated the leaching of Si4+ and Al3+ from lithium slag. • One-part geopolymer was prepared using alkali-fused lithium slag. [ABSTRACT FROM AUTHOR]

Reinforced concrete structures exposed to chemical attacks require special repair mortar with specific features to work in a corrosive environment and interact effectively with the damaged substrate concrete. In this study, various geopolymer mixtures containing nano-SiO 2 (0%, 1.0%, and 2.0% binder weight replacement) and polypropylene (PP) fibers (0%, 0.3%, and 0.6% volume fractions) were tested to evaluate bonding properties when exposed to 5% concentration of sulfate attack. The research analyzed diverse bond tests, such as the shear bond strength and tensile bond strength. The substrate layer chosen for the study was normal concrete, on which the geopolymer mixtures were used for repairing. These mixtures were then cured in an environment containing sodium sulfate. A comparison was made between the bond specimens cured in sulfate solutions and a reference mixture cured in a water tank. Although the mortar samples subjected to sulfate attack showed more shrinkage than samples cured in water, the normalized results revealed that sulfate solutions curing for geopolymer mixtures containing 1.0% nano-SiO 2 causes a higher bond strength (both tensile and shear) as compared to the reference mixture in water curing. • Experimental tests on the bonding of geopolymer repair materials in aggressive sodium sulfate environments. • Effects of NS and PP fiber on geopolymer repair mortar's fresh and hardened properties. • Effects of NS and PP on the shear and bond properties between geopolymer and normal concrete substrate. • The shrinkage of the samples cured in a sodium sulfate solution is more significant than in water. • The addition of 0.6% PP fibers and 2.0% NS nanomaterials improved the tensile bond strength. [ABSTRACT FROM AUTHOR]

Weak interlayer bonding, especially induced by a long period of printing interruption, is one of the major concerns for 3D printing concrete. The effect of CaCO 3 whiskers suspension (CWS) spray and printing time interval on the interlayer bonding of 3D printing fly ash-granulated blast furnace slag-steel slag based geopolymer was investigated with splitting tensile strength and direct shear strength tests. The underlying mechanisms were explored based on the characterization of micromorphology, porosity, surface roughness and reaction kinetics of interlayer area. It was revealed that the CWS spray at appropriate concentrations can significantly improve the interlayer bonding of geopolymer printed at extended printing intervals, with 0.05 g/mL of CWS increasing the shear strength up to 71% at 60 min and 0.10 g/mL of CWS increasing the splitting tensile strength by 40% at 40 min. The CWS at proper concentrations could replenish the interlayer moisture, fill the interlayer voids and provide nucleation sites for geopolymerization and hydration products, i.e., N(C)-A-S-H and C-S-H gels. However, excessive CaCO 3 whiskers or water content was harmful to the interlayer bonding. As the reaction process and microstructure of 3D printed ternary geopolymer were synergistically impacted by the printing time interval, residual water content, compensated moisture and CaCO 3 whisker reinforcement, the mix of CWS spray should be carefully designed to optimize its effectiveness on the interlayer strengthening. • CaCO 3 whiskers suspension spray strengthened interlayer of 3D printed geopolymer. • Interlayer printed at longer interval was improved more by CaCO 3 whiskers spray. • Water in suspension was beneficial for continuous geopolymerization at interlayer. • CaCO 3 whiskers suspension filled pores and densified interlayer microstructure. • CaCO 3 whiskers promoted the nucleation of reaction products at interlayer. [ABSTRACT FROM AUTHOR]

This study investigated the synergistic effects of ordinary Portland cement (OPC) and silica fume (SF) in fly ash-based geopolymer mortar (FA-GPM). The research comprehensively evaluated the impact of replacing fly ash (FA) with varying proportions of OPC and SF on the flowability and mechanical properties of the geopolymer mortar (GPM). Furthermore, this study analyzed the interaction mechanisms of these effects by examining the microstructure and hydration products. The results showed that increasing amounts of SF initially enhanced but subsequently reduced flowability, while the inclusion of OPC consistently decreased it. The combination of SF and OPC significantly improved the mechanical performance and microstructure of the GPM. Optimal mechanical performance, with compressive strengths of 37.66 MPa at 7 days and 50.52 MPa at 28 days, was achieved by adding 10% SF and 20% OPC. Microstructural analysis revealed that using OPC and SF together enhanced the dissolution of alumino-silicate materials in the alkaline activating solution, leading to increased polymerization reactions in the GPM. This process resulted in the formation of calcium-alumino-silicate-hydrate (C-A-S-H) gel, sodium-alumino-silicate-hydrate (N-A-S-H) gel, and calcium-silicate-hydrate (C-S-H) gel, creating a denser structure with reduced porosity and enhanced mechanical properties. This study highlights the advantages of incorporating SF and OPC into FA-GPM, providing valuable insights for further research and practical applications of geopolymer materials. • This study employs the synergistic action of OPC and SF to enhance the flowability and mechanical properties of FA-GPM. • To explore the effects of OPC and SF on GPM performance, combinations were designed with varying dosages of both materials. • Under conditions that meet workability, the synergistic effect of OPC and SF will yield superior mechanical properties. • The impact on GPM's flow and mechanical properties depends on the dosage of OPC and SF. • The synergy between OPC and SF leads to highly densified structures. The optimal mechanical performance was achieved with 20% OPC and 10% SF. [ABSTRACT FROM AUTHOR]

The cement industry's carbon emissions and resource-intensive production significantly contribute to climate change, necessitating a sustainable alternative like Geopolymer (GP), known for its superior strength. However, the processing of GP poses challenges owing to the absence of established standardized guidelines and the multitude of variables affecting its performance. Hence, the current study is an effort to develop the mix design of GP composites, considering the hybrid Taguchi-based Grey relational analysis (GRA) integrated with the principal component analysis (PCA) that optimizes GP's hardened and fresh state properties simultaneously. A series of nine experiments were executed following the L9 array recommended by the Taguchi method, considering the molarity of sodium hydroxide (NaOH), Ground granulated blast furnace slag (GGBS) content, alkaline solution to binder ratio (AL/B), and sodium silicate to sodium hydroxide ratio (Na 2 SiO 3 /NaOH) at three distinct levels. The mix design was evaluated employing Analysis of variance (ANOVA), with the assessment criteria focused on compressive strength, flowability, and setting time. Further, the enhanced performance of the optimized combination (14 M NaOH, 75% GGBS, AL/B=0.5, and Na 2 SiO 3 /NaOH=2) was validated through confirmatory experiments. Additionally, microstructural analyses conducted on the best and least performed samples of the L9 array and optimized samples using X-ray diffraction (XRD), Fourier transform infrared (FTIR), Thermo-gravimetric analysis (TGA)/Derivative thermogravimetry (DTG), and Scanning electron microscopy (SEM) analyses confirmed higher degree of geopolymerization (GPZ) and enhanced gel products, including C-S-H and N-(C)-A-S-H gel phases in optimized samples. These outcomes highlight the potential for sustainable GP composites with enhanced properties and performance. In summary, the effectiveness of the Taguchi-GRA-PCA technique is dependent on careful assessment of the type, number, and level of design parameters addressed. • The production of cement raises significant sustainability concerns. • Geopolymer is optimized via the Taguchi-GRA-PCA method to minimize the energy, materials, and time during testing. • PCA and equal-weight-based approaches yielded identical optimized combinations. • The optimized mix outperformed all L-9 arrays of Taguchi-tested combinations. • Microstructural differences exert a direct influence on Geopolymer compressive strength. [ABSTRACT FROM AUTHOR]

Portland cement is widely used in the construction industry. Its production contributes to carbon dioxide emissions, urging the need for sustainable alternatives. The present study aims to evaluate the strength, durability, microstructural properties, and cost-effectivity of geopolymer (GP) concrete containing polyethylene (PE) fibers, with fly ash (FA), ground-granulated blast furnace slag (GGBFS), and calcium magnesium carbonate (CaMg (C O 3) 2 known as dolomite) as binders. PE fiber used has an ultra-high molecular weight. Six different mixtures were produced with FA, GGBFS, dolomite, and/or PE fiber. The control mix used only FA as a binder without PE fiber. Fresh and mechanical properties, including slump value, compressive strength, and split tensile strength, were determined, and non-destructive tests, such as electrical resistivity and ultrasonic pulse velocity, were conducted. The durability of GP was evaluated through initial surface absorption and capillary suction absorption tests at different curing ages. Microstructural and mineralogical characteristics were analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR). The results revealed that the addition of PE fibers and CaMg (C O 3) 2 reduced the workability of GP by 30.22% in comparison with that of PE fiber along with GGBFS. Compared to the reference mix at 28 days, incorporating 20% GGBFS resulted in the highest improvement of 76.89% and 104.86% in compressive and split tensile strength, respectively. GP sample with 20% GGBFS replacement of FA presented the highest reduction of 44.4–41.63% for initial and secondary rate of absorption. SEM analysis showed that the addition of GGBFS and CaMg (C O 3) 2 to fiber-reinforced FA-based geopolymer mixes developed a denser and more homogenous matrix with improved mechanical behavior due to the co-existence of C − S − H and aluminosilicate gel. PE fibers improve the toughness properties by helping to absorb energy and bridging cracks. The development of a stronger matrix was characterized by C − S − H , calcium aluminate oxide (carbonate) hydroxide ( C 4 A H x ) and quartz. A one-way ANOVA analysis and cost analysis demonstrate the cost-effectiveness of partially replacing FA with CaMg (C O 3) 2 and GGBFS in PE fiber-reinforced GP concrete. • Different geopolymers were produced using polyethylene fiber, FA, GGBFS, and CaMg(CO 3) 2. • Evaluating strength, durability, microstructural properties, and cost-effectivity of geopolymer. • Microstructural and mineralogical characteristics were analyzed using SEM, XRD, and FTIR. • Cost analysis demonstrates the cost-effectiveness of partially replacing FA with CaMg(CO 3) 2. [ABSTRACT FROM AUTHOR]

Biomass is burned to generate heat and electricity. The use of biomass fuel has acquired great importance in the last years owing to its carbon-neutral nature. As a result, there is a massive build-up of biomass ash that will keep growing for decades to come. This study uses biomass ash waste to fabricate cements for construction and it presents a "zero fossil energy consumption and zero waste generation" approach to cement production. We measure the reactivity of crop biomass ash (CBA) from a power plant and the properties of one-part, CBA-slag geopolymer cements made with it. CBA has pozzolanic reactivity and potential as precursor for geopolymer fabrication. Up to 30% of CBA can be blended with ground granulated blast furnace slag (GGBS) to produce sound, one-part geopolymers activated with sodium carbonate and/or sodium silicate. Beyond this ash threshold, the geopolymer matrix experiences a strength reduction due to insufficient cement content. A one-part geopolymer consisting of 30% CBA and 70% GGBS activated with 10% sodium carbonate achieved a compressive strength of 30.70 MPa at 28 days of curing at ambient temperature. However, it exhibited a prolonged setting, taking up to 5 hours to initially set and 8 hours to finally set. Adding a sodium silicate activator significantly improved mechanical performance and accelerated setting. A formulation activated with 20% sodium silicate and 5% sodium carbonate reached a compressive strength of 46.09 MPa at 28 days, with setting times reduced to 57 minutes for the initial setting and 1 hour 15 minutes for the final setting. The sodium silicate activator enhanced hydrate formation and facilitated polymerization thereby accelerating the set and enhancing mechanical performance. Owing to the low carbon emission factor of CBA, the one-part CBA-GGBS has a low carbon footprint, which can reduce carbon emission by 80% in comparison to PC-GGBS (CEM II) mortar with a similar compressive strength. The CBA-GGBS geopolymer is economically feasible, applicable, and market attractive due to its low cost compared with equivalent PC products. [Display omitted] • A Crop Biomass Ash (CBA) from a power plant, with high Si and Al contents is investigated. • The highly crystalline mineral assemblage results in low pozzolanic reactivity. • The CBA is used to produce one-part geopolymer with compressive strength up to 46 MPa. • A "zero fossil energy consumption and zero waste generation" method is provided to recycle the CBA. • The one-part, CBA-slag geopolymer reduces carbon emissions by 86% compared to equivalent PC-based materials. [ABSTRACT FROM AUTHOR]

Silica fume (SF) is widely used in the developing of high-performance geopolymer systems. Previous studies have shown that using different types of SF may have different influences on the performance of geopolymers. What are the key factors (affecting the properties of geopolymers) still need to be clarified? This paper investigated the effects of three types of silica fume (SF1− SF3) with various silica contents (98.0%, 94.7% and 53.1%) and particle sizes (D 50 : 3.3 μm, 3.1 μm and 11.8 μm) on the rheology and compressive strength of alkali-activated calcium alumina cement (CAC)/fly ash mortar. The incorporation of SF can significantly increase the plastic viscosity. The increase in plastic viscosity was due to the ball-bearing action of the spherical SF particles, which reduced the friction between the particles under shearing. Replacing 20% of the fly ash with SF1 and SF2 improved the compressive strength of geopolymer mortars while the incorporation of SF3 decreased the compressive strength at the same replacement ratio. Inductively coupled plasma (ICP) spectrometry results indicated that the amorphous silica in the SFs was dissolved in an alkali solution. Activators with high concentrations of monomer and dimmer silicon groups may promote the reaction between precursors and activators. The formation of additional aluminosilicate gels reduced the amount of large capillary pores (500 nm to 1000 nm), leading to improved strength. The incorporation of coarse SF3 introduced extra voids in the mixture, as suggested by calculations of packing density, leading to reduced strength. • From a chemical perspective, SF effect is governed by Si dissolution rate. • From a physical perspective, SF effect is governed by its PSD. • Low SiO 2 content SF increases strength of geopolymers at low dosage. • CPM can optimize mix composition of SF-geopolymer systems. [ABSTRACT FROM AUTHOR]

This paper aims to develop an environmentally friendly and low-carbon geopolymer for 3D printing, which has excellent mechanical and rheological performance. The effect of ground granulated blast furnace slag (GGBS), NaOH and sand on mechanical strengths, 3D printing performance and rheological behavior was investigated to determine the optimum mix proportion for 3D-printed geopolymer. Moreover, polyethylene (PE) fibers were introduced to reinforce the performance of 3D-printed geopolymer. Results show that when the ratio of GGBS, NaOH and sand is 1:0.13:2.67, geopolymer exhibits superior mechanical, 3D printing and rheological properties. Increasing the dosage of GGBS and sand leads to an overall increase in the yield stress but a decrease in the consistency coefficient, indicating that it benefits the stacking and fluidity performance of 3D-printed geopolymer. However, with an increase of NaOH content, the stacking performance increases while the fluidity decreases. Although increasing NaOH and sand content benefits the viscosity recovery performance, an increase in GGBS content has an opposite effect. Incorporating PE fibers significantly increases the flexural strength with an increase of up to 27.8 % and 21.3 % in 7-d and 28-d flexural strength, respectively, given a PE fiber volume of 0.6 %. Increasing the volume of PE fibers leads to a significant rise in the stacking performance but a reduction in the fluidity. Furthermore, adding PE fibers negatively affects the geopolymerization but benefits the hydration process given an increase of Si/Al and Si/Ca ratio identified in PE fiber reinforced 3D-printed geopolymer. • Increasing GGBS and sand content benefited the 3D printing performance of geopolymer. • Increasing NaOH and sand content benefited the viscosity recovery performance of geopolymer. • PE fibers enhanced the stacking performance of the 3D-printed geopolymer paste. [ABSTRACT FROM AUTHOR]

The pursuit of sustainable development is an essential aspect of modern society's progress, aiming to achieve goals without causing waste, pollution, harm, or environmental degradation. The study focused on developing environmentally friendly binders by utilizing two industrial solid wastes: electric arc furnace slag (EAFS) and dealuminated kaolin (DK). The investigation aimed to assess the physio-mechanical, chemical properties, and durability of the binders against elevated temperatures and exposure to seawater, thereby contributing to sustainable practices. The eco-friendly geopolymer binders, EAFS and DK were blended in various proportions and mixed with alkaline activators. The resulting binders were cured at 40°C and a relative humidity of 98±2% for 180 days. Some of the binders were subjected to temperature increments in the order of 200, 400, 600, 800, and 1000°C, while the other geopolymer binders were immersed in seawater for upto 180 days. Setting times, compressive strength tests, evaluation of free slag and combined water contents, and analysis of the effects of elevated temperatures and seawater exposure on the phase composition of the geopolymer binders were conducted using XRD, TGA/DTG, and SEM/EDX. The finding showed the replacement of 10–20% of EAFS with DK resulted in a reduction in both the initial and final setting times. Increasing the amount of alkali activation content of EAFS upto (1.00 mol/Kg Na 2 O) (ES3 mix) leads to an increase in the values of compressive strength. Further increase in the alkali content (1.50 mol/Kg Na 2 O) reduces the compressive strength. The incorporation of DK enhanced the compressive strength value upto 30% DK (ES-DK3 mix). The increase in DK content beyond 30% resulted in reduced compressive strength values. ES-DK3 mix improved the thermal stability of the geopolymer matrix as well as demonstrated higher relative compressive strength values, especially at 1000°C. In addition to the mix, ES-DK3 showed superior durability against the attack of seawater. The compressive strength showed a sharp increase for specimens submerged in seawater for upto 180-days, this is attributed to the high reactivity of DK which acts as a nucleating agent that fills the open matrix preventing the penetration of SO 4 2- and Cl- ions to inhibit the formation of nonbinding material. [Display omitted] • Replacement of 10–20% of EAFS with DK resulted in a reduction in both the initial and final setting times. • Incorporation of DK enhanced the compressive strength value up to 30% DK (ES-DK3 mix). • The increase in DK content beyond 30% resulted in reduced compressive strength values. • The addition of 30% DK (ES-DK3 mix) improved the thermal stability to the geopolymer matrix. • The compressive strength of ES-DK3 showed a sharp increase in the values of up to 180-days. [ABSTRACT FROM AUTHOR]

3D printing concrete (3DPC) is an emerging technology that produces concrete using digital method and has revolutionized the traditional labor-intensive construction mode. However, the free formwork printing and layer-by-layer production of 3DPC induce severe shrinkage and plastic cracking during the early ages, especially for the geopolymer based materials. This research utilizes the nano-fibrillated cellulose (NFC) with the combination of magnesium oxides expansive agent (MEA) to mitigate the plastic and drying shrinkage of 3D printing geopolymer concrete (3DPGC), while optimizing its rheological behavior. The results show that after modification with proper dosages of NFC and MEA, 3DPGC showed reduced plastic and drying shrinkage at early ages, with improved printability, buildability, and mechanical strength. The underlying role of NFC and MEA on the performance of 3DPGC was thoroughly analyzed with rheometry, calorimetry, scanning electron microscopy, and internal humidity test. The water retention ability of nanocellulose can provide more moisture at early ages, thus mitigating cracking, while MEA can compromise the drying shrinkage at later ages. The contribution of the study shed light on the application of nanocellulose and MgO to increase the volume stability and mechanical performance of 3D printing geopolymer concrete. • The open time of 3D printing geopolymer prolongs by modification with nanocellulose. • Nanocellulose and MgO increase the thixotropy and printing performance of 3DGC. • The water retention ability of nanocellulose mitigate plastic and drying shrinkage of 3DPGC. • The designed 3DPGCs using nanocellulose and MgO exhibit higher strength at all directions. [ABSTRACT FROM AUTHOR]

By considering the current global challenges such as greenhouse gas emission and waste disposal management, the exploration of geopolymer concrete is highly focused now-a-days. On the other hand, the use of costlier commercial activators acted as the major drawback for the practical existence. Although the recent geopolymer researchers suggested the use of alternative activators from various resources such as palm oil ash, olive ash etc, the application of which are not appreciably promoted due to the complex derivation process. To overcome these effects, in this paper, first time, an attempt is initiated to develop a cost-effective geopolymer concrete by using textile mercerizing water as an alternate activator system. The viability of using mercerizing water instead of commercial sodium hydroxide activator was studied initially. By conducting the pH electrode test and Infrared Analysis, the alkalinity and the presence of sodium metal cations responsible for the reaction kinematics were confirmed. Also, the molar concentration of sodium cations in the mercerizing water was quantified using chemical titration analysis. The feasibility of using mercerizing water in the preparation of geopolymer was assessed using workability, mechanical strength and sustainability. From the results, it was inferred that the developed geopolymer concrete with 100 % textile mercerizing water exhibited the maximum strength of 46.9 MPa, 5.16 MPa and 5.81 MPa respectively under compression, tension and flexure which are almost equivalent and slightly better than the control geopolymer concrete. Also, the developed geopolymer concrete using 100 % textile mercerizing water and the combined flyash-GGBS binder system showcases the highest post-fire residual strength and 48 % reduced water absorption. The cost of construction of geopolymer concrete was significantly reduced by 58.43 % and showed 10.28 % reduced carbon footprint due to the complete replacement of sodium hydroxide solution using textile mercerizing water. The findings of this research work will lead to the development of equivalent molar sustainable activator from the textile mercerizing water and the exploration of eco-friendly and durable geopolymer concrete in an affordable price. [Display omitted] • TMW waste as a 100 % alternative to commercial hydroxide activator. • Alkalinity and reactive metal ions of TMW induced the maximum strength of 46.9 MPa. • GF-TM100 % offered 48 % reduced rate of water absorption and better fire resistance. • Consumption of TMW showed 10.28 % lower carbon footprint than commercial activator. • 58.43 % reduced construction cost in GF-TM100 % geopolymer. [ABSTRACT FROM AUTHOR]

Alkali-activated aluminosilicate minerals for the production of geopolymer building materials provide low-carbon and low-energy advantages compared to OPC. Pisha sandstone (PS) is a mudstone/sandstone rich in silica and aluminium, but it cannot be used directly as an engineering material due to the expansion of soggy clay minerals. In this study, the PS was modified via water and alkali leaching pretreatments, and the modified PS was used to investigate the feasibility of eliminating or attenuating the swelling of montmorillonite, and the alkali activation behavior of the PS system, respectively. The stirring frequency, dosage and types of leaching agent, and leaching time were considered as the variables. The ion concentration of the leachate was characterized using an inductively coupled plasma mass spectrometer (ICP-MS). The modified and untreated PS were characterized using a range of analytical techniques, including particle size analysis, powder XRD, SEM/EDX, TGA, and its free swelling volume in water, as well as the mechanical properties of the specimens prepared as cylinders. The results show that water leaching reduces the particle size of PS, diminishes the span of its particle size distribution, and decreases the relative amount of montmorillonite in PS. Montmorillonite undergoes dissolution/ion exchange under alkali leaching. With increasing alkali concentration and leaching time, the phase changes from Ca-montmorillonite to Na-montmorillonite to glassy phase silica-aluminate. The amorphous N-A-S-H and C-A-S-H coexist in the system, N-A-S-H is the major hydration product. PS is still classified as a material with low pozzolanic activity, as the amount of geopolymer produced in the system is very low. The degree of water-absorption swelling and cracks on the specimen surface induced by the ASR gel deepened with increasing alkali concentration. The involvement of reactive Al and reactive Ca converted the ASR gels into (N,C)-A-S-H gels or C-(A)-S-H gels, which depended on the atomic ratios of these reactive ions, and significantly improved the strength and water resistance of the specimens. • A new mean of water/alkali leaching modification was demonstrated. • The alkali-activation mechanism of Pisha sandstone was investigated. • Sodium aluminosilicate hydrated gel is major hydration product. • Alkali silica reaction in Pisha sandstone geopolymer was studied for the first time. [ABSTRACT FROM AUTHOR]

This study explores the potential of developing novel high performance geopolymer composite (GPC) materials utilizing mining waste (MW) as an aluminosilicate precursor for the geopolymer matrix and reinforcing it with leaf date palm fibers (LDPFs). Specifically, we examined the effects of incorporating varying amounts of LDPF fibers on the mechanical, physical, and morphological properties of the formulated GPC. The explored range of the incorporated fibers was from 0% to 4% (wt/wt). Mechanical properties were evaluated using modulus of rupture (MOR) and modulus of elasticity (MOE), while physical properties were assessed through water absorption (WA) and thickness swelling (TS). Additionally, X-ray diffraction (XRD), FTIR spectroscopy, scanning electron microscopy (SEM), and energy dispersive X-ray (EDX) were employed to visualize matrix phases and analyze the composition, elucidate changes in the structure, and examine the interfacial failure morphology, respectively. The results revealed that the MOR and MOE nearly doubled in the formulation reinforced with 2% (wt/wt) LDPF fibers compared to the geopolymer matrix, confirming the efficacy of these fibers as reinforcing element enhancing the strength and stiffness of the geopolymer matrix. The physical properties exhibited an increase with higher fiber loading, though they remained lower compared to those of other composites found in literature, confirming the suitability of LDPF fibers for geopolymer composite formulations. The structural and morphological analyses of the geopolymer composites indicated an acceptable degree of geopolymerisation and the fibers displayed good interfacial bonding with the geopolymer matrix, respectively. The research findings suggest that leaf date palm fibers are well-suited for reinforcing geopolymer matrix derived from mining waste, presenting a cost-effective option for construction materials. • The potential of mining waste as an innovative aluminosilicate raw material for geopolymers composites was studied. • Leaf date palm fiber has proven to be an effective reinforcing component for geopolymer composites. • Geopolymer composites with excellent mechanical properties and good durability was formulated. • The developed geopolymer composite offers a sustainable and cost-effective option for construction materials. [ABSTRACT FROM AUTHOR]

This paper presents an innovative application of a one-part geopolymer for microwave absorption. The influences of frequency, ageing time and mixing formulations on the mechanical, dielectric, and microwave-absorbing performance of the one-part binary geopolymer using fly ash and ladle furnace slag were investigated. The mixing formulations included alkali activators-to-aluminosilicate sources, sodium metasilicate-to-sodium hydroxide, and water-to-binder ratios. The results demonstrated that the dielectric constant decreased while the dielectric loss and loss tangent increased and remained constant with increasing frequency. The geopolymers have the highest dielectric values at an early age and diminish with ageing time. These resulted in the geopolymers having excellent microwave absorption (50 – 80%) at high-frequency levels and later ages. A higher water content resulted in higher porosity, reducing mechanical strength but enhancing microwave absorption. An optimal water content must be attained to achieve dual mechanical strength and microwave absorption performance. • One-part binary geopolymer based on FA and LFS was synthesized. • Geopolymers show excellent microwave absorbing performance at higher frequency. • Microwave absorption of the geopolymers improved at later age. • Porosity creates path to attenuate the microwave energy. [ABSTRACT FROM AUTHOR]

In order to realize the resource utilization of coal gasification fine ash (CGFA) in cement fields, a key is to solve the problem of low activity of CGFA. This paper studied the performance of CGFA as supplementary cementitious materials in cement. Furthermore, to enhance the activity of CGFA, targeted chemical activators were employed, with triethanolamine (TEA) and simulated high salinity wastewater (SHSW) chosen as representatives of organic and inorganic agents, respectively. It was found that CGFA had a synergistic effect with cement at a low dosage, while the inhibition effect on cement hydration was dominant at a high dosage. TEA promotes the strength development of the CGFA-cement system by promoting early hydration of cement and dissolution of active minerals in CGFA. However, the promoting effect of TEA on cement hydration will change to an inhibiting effect with the development of time, which will have an adverse effect on the development of strength. In general, the optimal dosage of TEA is 0.03 %, which can increase the 28-day activity index of CGFA from 69.1 % to 75.6 %. SHSW accelerates the strength development of the CGFA-cement system by promoting the hydration of cement and facilitating the dissolution and hydration of active minerals in CGFA. In addition, X-ray diffraction results show that a new hydration product, Friedel's salt, is formed under the excitation of SHSW. But this new hydration product will gradually dissolve as the pH decreases. The 28-day activity index of CGFA can be increased to a maximum of 83.3 % under the excitation of 2 % SHSW. [Display omitted] • The direct use of CGFA has adverse effects on the properties of cement. • Activity index of CGFA can be increased to a maximum of 83.3 % by chemical activators. • Activators promote the dissolution and hydration of active minerals in CGFA. [ABSTRACT FROM AUTHOR]

Construction and demolition waste (CDW) has been recently identified as a potential aluminosilicate source for geopolymers. However, the available research has mainly focused on developing CDW-based geopolymer pastes and mortars, while studies on geopolymer concretes sourced from CDW have been very limited. Thus, the current study aimed at experimentally identifying different CDW materials suitable for producing geopolymer concretes. Additionally, the study analysed the mechanical, microstructural, and environmental properties of CDW- based geopolymer concrete produced. In this regard, the effect of relevant parameters on the compressive strength development of CDW-based geopolymer concretes was comprehensively investigated, including those related to precursor types/fineness, alkali activator solution, aggregate type/size and curing regimes. Microstructural analyses were also conducted on the selected samples (100% brick waste, 100% tile waste, 100% concrete waste and 75% brick waste + 25% GGBS). Finally, the environmental impact of geopolymer concrete was assessed and compared with similar traditional concrete. Results showed that employing CDWs alone is not suitable to achieve sufficient strengths under all curing regimes. However, the inclusion of 25% GGBS significantly improved the strength performance of CDW-based geopolymer concrete, in comparison to other supplementary cementitious materials (SCMs) such as Class-C fly ash and calcium hydroxide. The particle size of CDWs and concentration of alkaline activators highly affect the performance of CDW-based geopolymer concretes. Utilization of CDWs with particles finer than 75 μm and high concentrations of NaOH (12 M) is recommended to achieve good performance. The results also indicate that almost similar energy is needed for producing CDW-based geopolymer and OPC-based traditional concrete, whereas a huge reduction in CO 2 emission (∼40%) was estimated in the case of geopolymers. The outcomes of the current study are expected to contribute to the advancement of geopolymer concrete derived from CDW in addition to providing valuable insights into this type of concrete for practitioners and academics. • Comprehensive assessment of various CDW materials for producing geopolymer concrete was performed. • Mechanical and microstructural properties of CDW-based geopolymer concrete were discussed. • Effects of relevant parameters on the performance of CDW-based geopolymer concretes were comprehensively investigated. • Environmental impacts of the developed geopolymer concrete were assessed. [ABSTRACT FROM AUTHOR]

Geopolymer concrete (GPC) has a tendency to spall and lose its strength at high temperatures, rendering it brittle. This research incorporates graphene nanoplatelets (GNPs) to enhance the fire resistance of GPC. A comprehensive experimental framework, comprising 20 distinct mix designs, was developed. Crumb rubber (CR) was substituted for natural sand in the mixture proportions, ranging from 10% to 30% by volume, while GNPs were incorporated in quantities ranging from 0.1% to 0.4% by weight of fly ash. The objective of this study is to assess the mechanical properties of these mixtures after exposure to 30, 60, and 90 min of ISO 834 standard fire. The properties of GPC were analyzed both before and after exposure to fire. The attributes and properties investigated include spalling, mass loss, stress-strain behavior under compression, compressive strength, compressive toughness, modulus of elasticity, and porosity. Furthermore, the study examined the interfacial interaction between the aggregates and the geopolymer matrix, as well as microstructural and morphological changes due to fire exposure, utilizing field emission scanning electron microscopy (FESEM). The results indicated that GNPs significantly mitigated the loss of post-fire compressive strengths of GPC. The Response Surface Methodology (RSM) was employed to develop statistical models and optimize the mixture proportions of CR and GNPs, aiming to maximize the compressive strength and the modulus of elasticity while minimizing the mass loss of GPC after exposure to fire. The optimization outcomes suggested that a mixture containing 10% CR and 0.3% GNPs represented the optimal composition for enhancing the fire resistance of GNP modified rubberized GPC. • Graphene nanoplatelets (GNPs) helped control thermal cracking in geopolymer concrete (GPC). • GPC containing 20–30% crumb rubber (CR) showed less spalling after 90 min of exposure to fire. • Adding GNPs enhanced the residual compressive strength of GPC after 30 and 60 min of exposure to fire. • Using 10% CR + 0.3% GNPs produced the highest post-fire residual compressive strength of GPC. [ABSTRACT FROM AUTHOR]

To enable effective raw coal gangue use, the effects of various alkali activators on coal gangue-slag-fly ash geopolymer grouting material (CSFGM) were investigated. Results showed that for sodium silicate modulus at 1.4, sodium silicate content at 12% and Na 2 O content at 6%, CSFGM showed the highest compressive. The compressive strength of CSFGM was related to the porosity and the proportion of 0.01–1 μm pores, and the main reaction product was C-(N)-A-S-H gel. The sodium silicate modulus had no significant effect on the reaction products. An increased sodium silicate content caused ordering of the C-(A)-S-H gel, but the consumption of Na 2 O reduced muscovite depolymerization. The higher Na 2 O content increased the C-(N)-A-S-H gel, leading to a further refined microstructure with reduced porosity. At 4% sodium silicate incorporating, the increase of Na 2 O content mainly promotes the depolymerization and polycondensation reaction of precursors. At 12% of sodium silicate incorporating, the increase of Na 2 O content promotes the better participation of sodium silicate in the polycondensation reaction of precursors. • CG can be used as a precursor to prepare geopolymer grouting materials. • The main reaction product of CSFGM is C-(N)-A-S-H gel. • Adapting the alkali activator enhances kaolinite and muscovite reactions in CG. • High sodium silicate system requires increased alkalinity for polycondensation. [ABSTRACT FROM AUTHOR]

Municipal solid waste incineration fly ash (MSWI FA) is categorized as a hazardous waste with significant implications on environmental safety and human health. This study tailored three types of alkali-activated materials (AAMs) by using ground granulated blast-furnace slag (GGBS) and metakaolin (MK) for the low-carbon stabilization/solidification (S/S) of MSWI FA. The intricate interactions between MSWI FA and AAMs synthesized from Al-rich precursors and Ca-rich precursors were investigated to elucidate the microstructural alterations of AAM-MSWI FA systems. Comprehensive characterization techniques were conducted, including isothermal calorimeter, thermal gravimetric analysis, Fourier-transform infrared (FTIR), X-ray diffraction (XRD), and 27Al and 29Si nuclear magnetic resonance (NMR). The results revealed that the incorporation of MSWI FA significantly delayed alkali activation reactions, hindering the formation of aluminosilicate gel due to high contents of Cl and potentially toxic elements (PTEs) in the MSWI FA. High volume of dissolved Cl from MSWI FA would react with available Ca from MSWI FA and GGBS as well as Al from GGBS and MK to form Friedel's salt, and this reaction was found to be more dominant in the Al-rich environment. Meanwhile, the C-(N-)A-S-H gel exhibited longer chain length in the Al-rich environment than in the Ca-rich environment. Overall, this study delivers microstructural insights into AAM-MSWI FA systems utilizing GGBS and MK as precursors. The results provide scientific groundwork for diverse practical applications of AAM-MSWI FA materials, thereby supporting the development of resource-efficient and low-carbon hazardous waste treatment strategies. [Display omitted] • GGBS-derived AAMs demonstrated good compatibility with MSWI FA. • MSWI FA delayed alkali activation reactions, hindering aluminosilicate gel generation. • MSWI FA impeded long-chain C-A-S-H and highly cross-linked N-A-S-(H) formation. • Cl from MSWI FA would react with the Ca and Al to form Friedel's salt. • C-(N-)A-S-H gels exhibited longer chain length in the Al-rich environment. [ABSTRACT FROM AUTHOR]

Large volumes of municipal solid waste incineration bottom ash (MSWIBA) are produced annually in China; however, their improper disposal causes serious ecological and environmental problems. This study investigated the feasibility of using MSWIBA and volcanic tuff to produce geopolymers. The effects of the MSWIBA content, silicon–sodium molar ratio, and alkali equivalent on the uniaxial compressive strength (UCS) and bulk density of the geopolymer samples were examined using single-factor and optimization tests. The test results showed that the UCS and bulk density of the geopolymer decreased as the MSWIBA content increased, whereas they increased as the alkali equivalent increased. As the silicon–sodium molar ratio increased, the UCS first increased and then decreased, and the change in bulk density was limited. In the final geopolymer preparation, the MSWIBA content was 17.85%, the silicon–sodium molar ratio was 1.71, and the alkali equivalent was 9.49%. According to X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, energy-dispersive spectrometry, and nuclear magnetic resonance analyses, the main phases of the geopolymer under the final preparation parameters were quartz, sanidine, calcite, orthoclase, gismondine, and illite. During the geological polymerization process, a large amount of CNASH gel was generated and attached to the surface of the particles or filled the pores between the particles, resulting in a pore size of 0.01–1 μm. The heavy metals in the geopolymers exhibited a good stabilization effect owing to the CNASH gel. Except for Cd, which posed a medium risk, the remaining heavy metals posed low or no risk. • Municipal solid waste incineration bottom ash and volcanic tuff were used as raw materials to prepare geopolymer. • Effect of municipal solid waste incineration bottom ash content, silicon-sodium molar ratio, and alkali equivalent. • Uniaxial compressive strength, bulk density and microstructure are analyzed. • Single factor experiment and optimization experiment. [ABSTRACT FROM AUTHOR]

Anthropogenic climate change is one of the main reasons for mainstreaming sustainability in all sectors. Reducing the carbon footprint of the built environment is one of the sustainability goals which is universally accepted. Reducing the carbon emissions from buildings entails cutting back operational and embodied carbon. Geopolymers are one of these materials that have been under focus recently for their capacity to reduce these two sources' emissions in buildings. In this study, the authors added to their previous work on understanding aerated geopolymers' performance as building materials. This article presents the effect of Na/Al ratio and curing moisture on the moisture storage, transfer, and moisture buffering capacity (MBC) of aerated geopolymers. The impact of vapor gradient and exposure to variable environmental conditions (temperature and relative humidity(%RH)) are also surveyed. Generally, the results show correlations between hydric performance and the tested experimental parameters. This stems from the influence of Na/Al and curing relative humidity on the degree of geopolymerization, rate of reaction, porosity, and phase composition of metakaolin-based geopolymers. Vapor permeability and moisture diffusivity increased with rising alkali oxide content because of the higher degree decomposition of porogen and pore stabilization effect of rapid polycondensation. Moisture permeability and diffusivity also showed direct relationships with curing relative humidity. Low relative humidity results in the rapid loss of inter-layer water and leads to densification of the matrix, while high %RH curing is suitable for pore formation and stability. The MBC of the samples increases with increasing Na/Al because of increased porosity leading to access to more gel pores. However, at high values, the sub-carbonation (internal carbonation) and carbonation lead to the formation of sodium carbonate, which is highly hydrophilic and influences the material's moisture exchange capacity negatively. This justifies the lower MBC at Na/Al=1. A similar observation was made when curing moisture content was increased. The influence of the Na/Al and curing moisture on the pore statistics of the geopolymer matrix are observed by their adsorption isotherms. At lower curing humidity and Na/Al, the samples tend to be less macroporous, dominated mainly by micropores. This is evidenced by the onset of capillary condensation at low %RH because of raid pore filling. The results also demonstrate the critical role Na/Al plays in determining the resulting matrix's microstructural integrity. This is evidenced by the low durability of the sample with Na/Al equal to 1.2. The samples' loss of structural integrity is because of carbonation-triggered retardation of strength development and stress put on micropores because of sub-carbonation-driven crystallization. • The effects of Na/Al and curing %RH on the hydric properties of aerated geopolymers were studied. • The vapor permeability and diffusivity of the samples showed a linear relationship with Na/Al and curing %RH. • Carbonation has a key impact on the moisture buffer capacity (MBC). • Carbonation also affects the durability of the aerated geopolymers. • MBC and moisture capacity showed a nonlinear relationship with curing %RH and Na/Al. [ABSTRACT FROM AUTHOR]

This paper investigates the thermal stability of lithium slag geopolymer (LSG) containing fly ash (FA) and silica fume (SF) exposed up to 900˚C. The effects of elevated temperatures on the microstructural evolution were investigated by thermogravimetric analysis (TGA), X-ray Diffraction (XRD), mineral analysis, surface porosity, and compressive strength of LSG modified by optimum incorporation of fly ash and silica fume. The results indicated that elevated temperature exposure significantly affects compressive strength, surface porosity, void size, weight loss, and phase transformation of fly ash incorporated lithium slag geopolymer (LSG FA) and silica fume incorporated geopolymer (LSG SF). The maximum loss in compressive strength of 44.07% was observed in LSG FA compared to 31.50% loss in LSG SF after exposure at 900˚C. The weight loss of LSG SF was higher than that of LSG FA between 500 and 800˚C and 800–1000˚C indicating a higher degree of dehydroxylation, crystal phase transformation, and viscous sintering observed in the former mix. A larger shrinkage cracking was observed in LSG SF by self-desiccation of the aluminosilicate paste matrix by dehydroxylation of mordenite molecules. Therefore, the degradation of compressive strength is governed by the combination of the crystallization of aluminosilicate gel and the formation of voids. • Sintering of LSG attributed the phase transformation, pore formation, and strength variation. • LSG FA has higher thermal stability and resistance to dehydroxylation than LSG SF. • LSG containing silica fume shows less shrinkage and more residual strength post fire exposure at 900°C by silica sintering. • High temperature LSG sintering forms aegirine-augite and plagioclase from mordenite and anorthite. [ABSTRACT FROM AUTHOR]

The engineering problems caused by dispersive soil are of worldwide concern. Traditional high carbon emission soil amendments such as cement and lime cause several environmental problems, including pollution and soil alkalization. Inorganic polymers are considered to be an economical, effective, and environmentally friendly soil amendment. Therefore, this paper proposes the use of the polymeric coagulant polyaluminum chloride (PAC) to improve soil dispersivity. PAC was added to the dispersive soils at different dry mass ratios of 0%, 0.5%, 1%, 1.5%, 2.5%, 4%, 5%, 6%, 7%, 8%, and 10%. The soil samples were then cured for 1, 4, 7, 14, and 28 days. Soil dispersivity was determined by crumb tests, pinhole tests, and exchangeable sodium ion percentage tests. Soil mechanical strength was assessed through unconfined compressive strength tests and unconsolidated undrained triaxial tests. Particle size distribution, pH, resistivity, X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy tests were conducted to investigate soil improvement mechanisms. Experimental results indicate that 1.5% PAC can transform highly dispersive soil into non-dispersive soil after 1 day of curing. When the PAC content increases from 0% to 7%, the unconfined compressive strength of the soil increases by 110.1%, and the internal friction angle and cohesion increase by 61.1% and 24.2%, respectively. The changes in the physicochemical properties and microstructure of the soil indicate the high-valence cations produced by PAC hydrolysis can effectively replace Na+ in the soil, while significantly reducing the pH value of the soil. Simultaneously, the coagulation effect generated markedly reduces soil porosity, resulting in a more compact soil structure. In summary, PAC demonstrates excellent potential in improving soil dispersivity and mechanical properties. Compared to traditional high carbon emission amendments such as cement and lime, PAC can effectively reduce soil alkalinity, mitigate environmental issues associated with these materials, and offer new possibilities for improving dispersive soils. • 1.5% polyaluminum chloride transform dispersive soil into non-dispersive soil. • Polyaluminum chloride increase the strength of the soil by up to 113.19%. • 1.5% polyaluminum chloride reduces exchangeable sodium content in soils. • Intergranular cementation is different for different contents. [ABSTRACT FROM AUTHOR]

Geopolymer presents a promising alternative to Portland cement for shotcrete, offering reduced environmental impacts, favorable mechanical performance, and improved durability. At present, small-scale applications have been implemented, but the fresh performances of spayed geopolymer are still rarely studied, restricting its further large application. This research investigates the rheological properties and shootability of sprayable fly ash/slag/silica fume based geopolymers considering the effects of different mix parameters. The water to binder (W/B) ratio has the greatest effect on the yield stress, and the dynamic yield stress is increased from 64.47 Pa to 388.64 Pa as the W/B ratio is reduced from 0.32 to 0.28. The change in dynamic yield stress is mainly related to either the formation of hydration products or the solid volume fraction. Mixtures with the highest thixotropic indexes are ideal for achieving both pumpability and shootability, while also exhibiting relatively low characteristic time. A modified equation for pumpability assessment is presented, which is more reasonable and consistent with the experimental results. The static yield stress is recommended for evaluating the build-up thickness of the designed fresh mixture, as there is a recognized strong correlation between them. In addition, the build-up thickness decreases with the increase of flowability, which could be used as a potential indicator. With the increasing sand to binder ratio, the mechanical strength exhibits a valley, which could be linked to the critical volume fraction of aggregate that corresponds to an effective interacting network, below which the sand-induced defects cause damage to strength and above which the interacting skeleton could contribute to strengthening. The strong environment savings of the current material are demonstrated, with the reduction in carbon emissions more than 50%. This study provides valuable information towards regulating and controlling the shootability of sprayable geopolymer and expands its broader application. • Rheological properties and shootability of sprayed geopolymer are examined. • Yield stress is most influenced by the water to binder ratio. • A modified equation for pumpability assessment is presented. • Static yield stress is recommended for evaluating the build-up thickness. • Sprayed geopolymer shows a more than 50% reduction in carbon emission. [ABSTRACT FROM AUTHOR]

This review paper presents a comparative evaluation of polymer, bacterial-based, alkali-activated, and geopolymer binders in regard to their production methods, mechanical properties, their environmental/life cycle assessment (LCA), and durability when exposed to deteriorating cycles (such as sulfates, acids, and high temperatures). The significance of this study is to compare the results of over 400 journal papers, which present an in-depth analysis of fresh and hardened state properties of various binders that are advocated in the literature. Historically, Portland cement is generally considered a binder that plays a major role in any cementitious composites because of its high availability, and relatively inexpensive cost. Despite its significant benefits, it is known that the manufacturing process of Portland cement is energy and carbon intensive, and the resulted material often has shortcomings when exposed to deteriorating causes such as sulfates, acids, and high temperatures. However, recent movement toward net-zero as well as ultra-high-performance practices has increased the need for a more sustainable and durable binding system. Based on the result of this paper, each binder presents specific advantages when compared to Portland cement for specific applications that can be a better choice for their ultra-high capabilities and ecological properties. This includes the significantly better performance of alkali-activated binders (specifically geopolymers), under high temperatures, or very rapid strength gain of polymer (e.g., epoxy, polyester, and vinyl ester) binders, making them great alternatives to Portland cement, for rapid repair and rehabilitation purposes. Similarly, bacterial concrete also have certain capabilities such as long term durability and the potential for a continued self-repair or self-healing. In terms of environmental impacts, however, polymer binders are heavily depedant on their source of energy (e.g., petroleum vs. bio-based resins) while alkali-activated concretes and geopolymers have activators' large contributions to overall LCA impact categories. For bacterial binders, the used urea and nutrition can play a key role in their LCA results. Finally, based on the highlighted capabilities of each binder, recommendations on performance-based or hybrid design methods and specifications for an optimized system are also provided. Novel areas in polymer, bacterial-based, alkali-activated, and geopolymer binders are also included. • A comparative analysis of various binding systems are provided. • Mechanical, Durability, and Ecological Properties vary significantly across binders. • Concentration, surface area, temp., and catalysts play key role in each binder. • Unique advantages and shortcomings of each binder is discussed. [ABSTRACT FROM AUTHOR]

Mining and beneficiation processes are accompanied by the discharge of large quantities of tailings, which occupy large areas of land and cause environmental pollution, which is a significant concern. This study prepared an environmentally friendly geopolymer using sulfur tailings and granulated blast furnace slag (GBFS) and characterized its performance and mechanism analysis. A low-cost and efficient CaO-Na 2 SiO 3 composite activator and comprehensive utilization method for sulfur tailings have been proposed. The experimental results showed that the CaO-Na 2 SiO 3 composite activator can improve the strength of STBG, especially the early strength. The highest 28d compressive strength of STBG can reach 32.2 MPa when the CaO content in the composite activators was 10%. However, when the CaO content in the activators was greater than 10%, the cumulative pore volume and harmful pore volumes of the STBG increased to 0.17 mg/L and 0.07 mg/L respectively, and the compressive strength developed slowly in the later period. In addition, the highest immobilization efficiency of STBG for Cu, Pb, and Mn can reach 99.9%, 93.9%, 91.6% respectively. The STBG can effectively immobilize heavy metals. • CaO-Na 2 SiO 3 composite activator can improve the early strength of sulfur-tailings-based geopolymer (STBG). • The maximum 28 d compressive strength of STBG can reach 32.2 MPa. • The addition of hybrid solid activator calcium oxide can promote the formation of C-A-S-H/N-A-S-H gel. • STBG can effectively solidify heavy metal elements such as Cu, Pb, and Mn. [ABSTRACT FROM AUTHOR]

How to simply and effectively improve the mechanical properties and UV resistance of polymer-modified cement-based coatings is the key to expand its application field. In this study, a novel type of polyacrylate (M-PA) emulsion modified by polydimethylsiloxane (PDMS), colloidal nano-silica (CNS), and 3-Glycidyloxypropyltrimethoxysilane (KH-560) was prepared based on the response surface methodology (RSM) to achieve composition optimization. In addition, the effect of M-PA emulsion on the mechanical properties, impermeability, microstructure, and UV resistance was comprehensively studied. The research results demonstrated that the tensile strength and hydrophobicity of M-PA emulsion film were the best when the content of CNS, PDMS and KH560 was 16–17%, 6–7% and 0.075–0.12%. The reason can be attributed to the chemical combination of modifier and the formation of 'Si-O-Si' of three-dimensional network structure in M-PA emulsion. In comparison with a coating containing unmodified PA emulsion, the bond and tensile strength of M-PA modified samples were increased by 29% and 43%, respectively, while the water absorption was reduced by 28% due to the refinement of microstructure. As a result, the hydrophobic film of the modified coating was still intact after UV-aging for 1000 h. • The optimal ratio of M-PA emulsion was determined by RSM. • Organic-inorganic cross-linked 'Si-O-Si' network improved mechanical properties of the coating. • PDMS enhances the UV resistance of the coating. [ABSTRACT FROM AUTHOR]

This study employs geopolymer as a complete replacement for the cement to solidify the shield muck discharged from tunneling in the silty clay layer, thereby creating an innovative synchronous grouting material. This novel grouting material not only utilizes geopolymer as its primary cementitious component but also incorporates shield muck, promoting the efficient utilization of the shield muck. The cementitious process of the grout is initiated by the principles of geopolymerization. Through a series of laboratory tests assessing grout performance, the new grouting material was developed by further optimizing the grout proportion using the response surface method (RSM). This involves a comprehensive analysis of the impacts of various factors such as muck moisture content, foam injection ratio, ground granulated blast furnace slag (GGBS) content, and sand content, along with their interactions on the key response variables, including consistency, fluidity, 2 h bleeding rate, setting time, and 3 d unconfined compressive strength (UCS). The optimal proportion of the new grouting material is found to be 140% muck moisture, 100% GGBS, and 230% sand. Experimental results reveal that the GGBS content has the most significant effect on various properties of the grout, while the interaction between these factors has distinct effects on different grout properties. This novel synchronous grouting material was subsequently employed in the Nanjing Metro Line 6 project, and it was found that both surface settlement and segment uplift meet the specified requirements. • Shield muck was used to create a novel synchronous grouting material via geopolymerization. • The effect of muck moisture content, foam injection ratio, and GGBS content on grouting performance is analyzed by RSM. • The impact of foams presented in the shield muck on the new synchronous grouting material was investigated. • A new synchronous grouting material was field-tested and its efficacy was validated. [ABSTRACT FROM AUTHOR]

The demand for sustainable binders has been globally encouraged owing to the alarming carbon emission levels associated with conventional cement production. Geopolymer binders are the most cost-effective, and sustainable engineered alternatives that provides the scope for the development of several binder systems made out of aluminosilicate wastes thereby contributing toward a clean environment. Next to fly ash, the second most widely used source material for geopolymerization is ground granulated blast furnace slag (GGBS) which offers several benefits such as high early age strength and excellent durability properties under low curing temperatures. In this context, this review article firstly describes the significance of different chemical oxide compositions namely: SiO 2 , Al 2 O 3 , CaO, Fe 2 O 3 , and MgO, present in GGBS during geopolymerization. Thereafter, the article discusses the compressive and microstructure properties of various GGBS-based geopolymer binder systems (paste, mortar and concrete) made with fly ash (FA), red mud (RM), and ferrochrome ash (FCA) – as some of the contemporary industrial wastes. The microstructure properties, such as x-ray diffraction (XRD), scanning electron microscope (SEM), and fourier transform infrared spectroscopy (FTIR) are taken into consideration to validate the reaction products, morphology, and bond arrangements, respectively. From this study, it is revealed that blending GGBS with aforementioned aluminosilicate wastes in suitable proportion delivers the viable sustainable option for potential applications in the construction industry thus reducing the dependence on conventional cement. [Display omitted] • GGBS-based geopolymer binder systems provide an eco-friendly alternative to traditional cement-based systems. • The chemical oxides present in GGBS govern the formation of geopolymer network inside the matrix. • Compressive strength development is mainly dependent on the effectiveness and quantity of C-A-S-H gels. • CaO in GGBBS provides the matrix stability by generation of calcium-based geopolymer gels. • Microstructure aspects are controlled by the curing conditions, choice of source materials, and type of aluminosilicate gels. [ABSTRACT FROM AUTHOR]

This study aims to study the feasibility of using additives to prolong the setting times of high-calcium fly ash-based geopolymer. Moreover, the effect of sodium silicate and sodium hydroxide ratios (S/N) on the compressive strength was observed by varying ratio at 1.0–2.5 by weight (wt%). For solid to alkaline activator (F/L) ratio investigation, the mixing proportions were varied at 0.5–3.3 wt%. The proper S/N and F/L ratios in this study were 1.0 and 2.0, respectively. The ratio was chosen to study the effect of additives on geopolymers. Thirteen additives were mixed in geopolymer pastes in two different mixing methods, wet and dry mixing. The results showed that both initial and final setting times of the pastes with sugars addition increased in the ranges of 133.6%− 135.3% and 125.3%− 148.7%, respectively, by wet mixing. Additionally, the percentage of sugars addition at 1–5 wt% and the dissolving time at 15–1440 min were also investigated. The results depicted that the initial and final setting times were prolonged in the range of 78%− 204% and 55%− 280% with 3 wt% of glucose addition. Moreover, the investigation of heat release, drying shrinkage, phase analysis and microstructural analysis were also reported. However, the compressive strength of geopolymer specimens with sugar addition at 90 curing days were slightly degraded. Hence, the results from this study could be guidance for practical application in which strength is not severely demanded. [Display omitted] • High calcium fly ash-based geopolymer were successfully synthesized. • Two different mixing methods were used to investigate the setting times. • Thirteen additives were added to prolong the setting times. • 3 wt% of glucose could delay the setting times more than 100% by wet mixing method. • Mechanical properties, durability, phase, and microstructure are also discussed. [ABSTRACT FROM AUTHOR]

The mechanistic insights into silico-aluminophosphate (SAP) geopolymer formation remain an enigma. Here, we aim to elucidate this process and improve the early-age performance of SAP geopolymers by utilizing incinerated sewage sludge ash (ISSA). Interestingly, phosphoric acid-ISSA interaction released Ca2+ and Al3+ ions from ISSA faster than the dealumination of metakaolin. These ions agglutinated with the active soluble (PO 4)3- units, evidenced by transmission electron microscopy (TEM), enhancing the early-age compressive strength of ISSA-incorporated SAP geopolymer binders. In contrast, the later strengths were relatively similar to the reference. Such binders had primary silico-alumino-phosphate (S-A-P) gels, possibly intimate with calcium-phosphate (C-P) and alumino-phosphate (A-P) gels, improving the micromechanical properties of the binder. The elastic moduli of these gels lay between 23–25 GPa, higher than conventional N-A-S-H gels. Furthermore, ISSA switched the chemistry of reaction products by favoring Al IV -OP units over Al VI -OP units in SAP geopolymers, even though the Si environment remained unchanged, as confirmed by NMR. • Formation mechanism of SAP geopolymer with and without ISSA is reported. • ISSA addition enhanced the early-age compressive strength of SAP geopolymer. • ISSA reduced the phosphoric acid in the SAP geopolymers by up to 28% by weight. • The mechanisms that govern such observations are discussed in detail. [ABSTRACT FROM AUTHOR]

Granite waste powder (GWP) is a solid waste produced during stone processing, and its accumulation has brought serious environmental and ecological problems. Due to its rich Si and Al components, GWP is a potential raw material for the preparation of geopolymers, but its low reactivity limits its utilization. This study aimed to enhance the reactivity of GWP toward geopolymer preparation by mechanical activation. During mechanical activation, the particle size of GWP decreased rapidly, and its internal pore volume gradually increased, which made its specific surface area continuously increase. The relative crystallinity of the main mineral phases in GWP decreases continuously with mechanical activation, and the aluminosilicate minerals (including albite, microcline, and biotite) are more easily amorphized than quartz. Leaching tests show that activated GWP can dissolve higher percentages of silicon and aluminum components in alkaline solutions. After 120 min of activation, the dissolution percentage of Si increased from 1.55% to 6.25%, and that of Al increased from 4.83% to 20.86%. The reaction heat result shows that the early geopolymerization involving activated GWP releases higher cumulative heat, which reflects a higher degree of reaction. Also, geopolymer incorporated with activated GWP, its compressive strength increased from 50.83 MPa to 78.94 MPa, and its flexural strength increased from 7.2 MPa to 10.0 MPa. These results confirmed that the reactivity of GWP can be significantly enhanced by mechanical activation. This technology may provide an efficient and promising method to improve the reactivity of GWP and promote its utilization in the preparation of geopolymers. • Mechanical activation was used to enhance the reactivity of GWP. • Aluminosilicate minerals are more likely to be amorphized than quartz during activation. • Activated GWP releases more Si and Al components in an alkaline solution. • Activated GWP promotes geopolymerization, enhancing the mechanical properties of geopolymer. [ABSTRACT FROM AUTHOR]

The low carbon footprint and superior properties of geopolymer make it a potentially suitable alternative to ordinary Portland cement, which has been one of the dominating research focuses in the last decades. However, the mechanisms of geopolymeric reactions and the nanostructure of geopolymer are still questionable. Besides, some undesired properties in geopolymer synthesis limit the field application of geopolymers. This paper focused on the current knowledge of the reaction chemistry and nanostructure of geopolymer and factors affecting metakaolin-based geopolymer synthesis. A systematic summary of the reaction process, chemical bonds in geopolymer, and models of geopolymer were provided to better understand the reaction mechanisms of geopolymerization. Various factors important to geopolymer's properties, including Si/Al ratio, Na/Al ratio, type of alkaline activator and alkali cation, water/solid ratio, and curing condition, were comprehensively reviewed to guide the geopolymer synthesis. Through this review, we hope to promote this field's continued growth and development and encourage the wider adoption of geopolymers as a sustainable alternative to traditional construction materials. • The mechanisms of geopolymeric reactions and the nanostructure of geopolymer were reviewed. • The reaction process, chemical bonds in geopolymer, and models of geopolymer were provided. • The factors affecting geopolymer synthesis were summarized. [ABSTRACT FROM AUTHOR]

This study delved into the utilization of waste glass powder (WGP) and ground granulated blast-furnace slag (GGBFS) as a binder and waste glass cullet (WGC) fine aggregate in fly ash (FA) based geopolymer concrete. The inherent characteristics of WGP, WGC, FA and GGBFS can be significantly altered by multiple factors such as sources, combustion temperatures, particle size, and impurity level. To offset the inconsistent characteristics of listed waste materials, this study provides a universal index to quantify and evaluate its reactivity to be used as aluminosilicate precursor and aggregate feedstock Ten distinct groups were examined: in five groups WG replaced fly ash at varying percentages (0, 10, 20, 30, 40%), and in five groups WG was used as a sand substitute with different fly ash and slag ratios (20, 40, 60, 80%). Alkali leaching tests were conducted on WGP, WGC, FA and GGBFS to determine the dissolubility and dissolution rate of reactive silica (Si) and calcium (Ca) within 3 h. The dissolubility and dissolution efficiency demonstrated decent correlations with the mechanical and durability properties of the resultant FA-based geopolymer. Leaching tests demonstrate that Ca from WGP, WGC, FA and GGBFS readily leaches out and reacts in both ambient and oven curing, while Si only exhibits activity primarily in high-temperature environments. Overall, the reactivity of Ca from GGBFS and WG improved by up to 50% and 30% in compressive strength and water absorption, respectively. Moreover, based on alkali leaching test, the most effective molar ratios (Si/Al=3.5–4) demonstrated the highest compressive strength (60–70 MPa), and verified intensively using scanning electron microscopy–energy-dispersive spectroscopy (SEM-EDS). Lastly, this study revealed that WGC as fine aggregate with the size of 20 µm also leached out a significant amount of Ca to the geopolymerization process. [Display omitted] • The feasibility of using waste glass as a substitute for fly ash in geopolymer mortar mixture. • Investigate the leaching behaviour of various industrial waste in geopolymer. • Emphasize the effect of leached calcium from industrial waste on properties of geopolymer in different curing methods. • Influence of Si/Al molar ratio on the performance of waste glass utilization in fly ash/ash-based geopolymer. [ABSTRACT FROM AUTHOR]

This study investigated the interfacial bond performances between ordinary Portland cement concrete (OPCC) and self-compacting geopolymer concrete (SCGC). The studied factors include nano-SiO 2 , repair material type, curing time, casting direction, and interface pretreatment method. The interfacial bond performances were assessed by Bi-surface shear and drying shrinkage tests. The evolutions in elemental compositions, hydration products, and microstructure in the matrix and interface were verified by BSE/EDS, XRD, and FTIR tests, respectively. ANOVA analysis was conducted to quantitatively analyze the influences of each factor from a statistical approach. The results demonstrated that the bond strength of SCGC increased by 24.5% to 31.7% compared to conventional OPCC. Meanwhile, geopolymers exhibited more compact microstructures but higher drying shrinkage (ε sh,u =891 µε). While nanofillers significantly amplified the cracking potential of geopolymers, which was attributed to the higher early-stage autogenous shrinkage instead of drying shrinkage. The SCGC showed a high enrichment degree of calcium at the interface, indicating that more calcium-rich products were formed. In contrast, the use of nano-SiO 2 in SCGC caused the enrichment of Na, Al, and Si at the interfacial regions, which provided extra nucleation sites for the polymerization of (C, N)-A-S-H gels. The nano-SiO 2 enhanced the intensity of the hydroxide ion and Si-O-T band and promoted the formation of (C, N)-A-S-H gels. The ANOVA analysis proved that the repair material, nano-SiO 2 , and interface treatment were significant factors to affect the interfacial bond strength. In addition, geopolymer-based repair materials were less sensitive to the casting direction, which differed from the conventional self-compacting OPCC. [Display omitted] • Geopolymer concrete at the same strength grade has 25-30% higher bond strength than conventional OPCC. • Nanofillers amplified the cracking potential of geopolymers due to higher early-stage autogenous shrinkage. • nano-SiO 2 in SCGC caused the enrichment of Na, Al, and Si at the interfacial regions. • geopolymer-based repair materials were less sensitive to the casting direction. [ABSTRACT FROM AUTHOR]

Geopolymerization has become a potential competitor to cement over the last 10 years due to its lower carbon impact. However, the development of geopolymerized applications on an industrial scale still faces numerous limits. As an answer, the valorisation of local sources of materials such as dredged sediment as precursors has been identified in the literature of high interest as it could solves sediment management problems as well as reducing geopolymerization environmental and economic cost. Therefore, this study evaluates, through a Life Cycle Analysis (LCA), the impact of mortars developed from untreated dredged sediments mixed with cement or alkalis. The solutions developed in the laboratory were transposed to a hypothetical industrial scale around the Port of Bordeaux area. Four mortars were compared with equivalent mechanical resistance: a classic Ordinary Portland Cement (OPC) mortar and three geopolymer mortars with NaOH and Na 2 SiO 3 alkalis. Results showed that, compared to the use of cement, in this specific case, geopolymerization effectively reduces the impact on climate change by 66% when sediment beneficial recovery was taken into account. This article is a first step in the industrial development adoption of waste geopolymer based mortar for public works as several conclusions were found to justify their implementation on a larger scale. Among them the use of alternative local precursors is effective in order to reduce the environmental cost of geopolymer. However, the market potential of geopolymer mortars will also highly depend on alternatives to silicate as an alkaline reagent. • Using locally available precursor such as dredged sediment could reduce the impact of geopolymerization. • Geopolymerization allowed a reduction of 66% of kg.CO 2.eq compared to the use of cement for treating sediment. • Geopolymer sediment-based had a better score than Cement sediment-based mortar for five of the seven impact categories. [ABSTRACT FROM AUTHOR]

Coal gasification slag is an industrial by-product obtained after valuable gas production from coal gasification. There is little research concentrating on geopolymer synthesis using coal gasification slag. In this study, the suitability of mechanical activation for coal gasification slag-based one-part geopolymer synthesis has been investigated by alkali fusion and component additive method. The results showed that coal gasification slag ground at 20 min (S-20) presented the finest particle size, and the corresponding geopolymer (G-20) had the highest compressive strength. The reaction degree test proved that mechanical activation improved the reaction degree of geopolymers. However, different mechanical activation times had little influence on the reaction degree of geopolymers. It can be concluded that the particle size of the coal gasification slag was the primary reason for the compressive strength in geopolymers, and finer coal gasification slag led to higher compressive strength. Fine coal gasification slag additive particles could fill the pores of the geopolymer or be connected by the newly formed hydration products. This helped to form a dense, uniform, and compact matrix and increased the compressive strength of the geopolymers. As the mechanical activation time went up, the coal gasification slag particles got bigger, and the coal gasification slag additive's filling effect got weaker, which decreased the compressive strength of geopolymers. Furthermore, this study gave a new explanation of the role of the coal gasification slag additive in one-part geopolymer, which improved the feasibility of the other materials for one-part geopolymer synthesis by the alkali fusion and component additive method. [Display omitted] • The effect of mechanical activation on CGS-based one-part geopolymer was studied. • Finer particle size increased the compressive strength of geopolymers. • MIP results confirmed the small pore size in the geopolymer matrix. • CGS additive filled in pores of geopolymer matrix played the role of filler. [ABSTRACT FROM AUTHOR]