Geopolymer Gel Research Articles

Improved interlayer bonding of 3D printed fiber reinforced geopolymer by healing agents: properties, mechanism, and environmental impacts

The weak interlayer bonding significantly impacts the mechanical properties of 3D printed fiber reinforced geopolymer (3DP-FRG). Three mineral-based and one polymer-based interlayer healing agents (IHAs) were used to enhance the interlayer self-healing properties. The effects of IHAs on interlayer bonding properties, self-healing mechanisms, and environmental impacts were investigated. The results showed that IHAs improved the 28 day interlayer tensile and shear bonding strength by 38.87% and 22.19%, and reduced 1, 3, and 7 days shrinkage by 43.61%, 22.17%, and 9.10%. The main interlayer self-healing products were geopolymer gel, calcite, and albite. Mineral-based IHAs and precursors dissolved rapidly, forming free [SiO4]4- and [AlO4]5- monomers. Polymer-based IHA prevented interlayer water evaporation and accelerated the migration rate of monomers. The lifecycle assessment from ‘cradle to gate’ indicates that 3DP-FRG has a minimal environmental impact. Carbon emissions and embodied energy of 1 m3 3DP-FRG could reach 313 kg and 900 MJ.

Ternary geopolymer with calcined halloysite: impact on mechanical properties and microstructure

Abstract As a natural clay mineral, halloysite (Hal) possesses a distinctive nanotubular morphology and surface reactivity. Hal calcined at 750°C (Hal750°C; 0.0, 1.0, 2.0, 4.0, 6.0, 8.0 wt.%) was used to replace ground granulated blast furnace slag (GGBFS; 50.0, 49.5, 49.0, 48.0, 47.0, 46.0 wt.%) and fly ash (FA; 50.0, 49.5, 49.0, 48.0, 47.0, 46.0 wt.%) for the preparation of geopolymer in this study. The effects of the replacement ratio of Hal750°C on setting time, compressive strength, flexural strength, chemical composition and microstructure of the geopolymer were investigated. The results indicated that Hal750°C did not significantly alter the setting time. The active SiO2 and Al2O3 generated from Hal750°C participated in the geopolymerization, forming additional geopolymer gel phases (calcium (aluminate) silica hydrate and sodium aluminosilicate hydrate), improving the 28 day compressive strength of the geopolymers. When the amount of Hal750°C was 2.0 wt.%, the 28 day compressive strength of the ternary (GGBFS-FA-Hal750°C-based) geopolymer was 72.9 MPa, 34.8% higher than that of the geopolymer without the addition of Hal750°C. The special nanotubular morphology of residual Hal750°C mainly acted like reinforcing fibres, supplementing the flexural strength of the geopolymer. However, excessive Hal750°C addition (>4.0 wt.%) reduced compressive and flexural strength values due to the low degrees of geopolymerization and the porous microstructure in the ternary geopolymer. These findings demonstrate that the appropriate addition of Hal750°C improved the compressive strength of geopolymers prepared using GGBFS/FA, which provides essential data for future research and supports the utilization of low-value Hal-containing clays in geopolymer preparation.

E-waste as a potential precursor for geopolymers

Abstract The rapid growth in electronics production and the shortening product lifespans have resulted in a growing problem of electronic waste (e-waste). E-waste is a complex mixture of organic and inorganic materials, making its recycling a challenge. This study explores the potential of powdered e-waste as a geopolymer precursor and investigates the geopolymerization of reactive phases in e-waste. Research techniques, including XRD, XRF, SEM/EDX, and FTIR, were used to characterize the e-waste and obtained geopolymers. Significant contents of reactive SiO2, Al2O3 and CaO components were detected in the e-waste which can participate in the formation of geopolymer gel. The present study elucidate the feasibility of utilizing e-waste as a geopolymer precursor, offering a potential for sustainable waste management and resource recovery in the electronics recycling industry.

Geopolymer/zeolite-P materials prepared from high-CaO fly ash, biomass ash, and metakaolin using geopolymerization with a hydrothermal process for environmental clean-up

This study aims to synthesize geopolymer/zeolite-P (GP-ZP) materials as a building material for environmental clean-up. High-CaO fly ash (FA), biomass ash (BMA), and metakaolin (MK) are designed as starting materials to generate geopolymeric and zeolitic materials simultaneously through geopolymerization and zeolitization using hydrothermal treatment at only 100 °C. This study explores that CaO can be quarantined in the geopolymeric structure using SiO2/Al2O3 molar ratios of 6.0 and 8.0 while at lower SiO2/Al2O3 molar ratios, CaO tends to precipitate various calcium compounds. Various SiO2/Al2O3, Na2O/Al2O3, CaO/Al2O3, and CaO/SiO2 molar ratios are investigated using different ratios of FA and BMA mixes to explore the geopolymeric binding characteristics and evaluate the types of zeolites formed. Unmilled and milled MK are also used to partly replace FA to improve the development of porous zeolite-P materials in geopolymeric matrix. Furthermore, the differences in the material characteristics obtained from the powdered and bulk materials are compared in terms of the mineralogical composition, surface morphology, specific surface area, and cation exchange capacity. The mechanical properties of the materials are also investigated to understand the relationship between the phase development and binding properties. Hydrothermal treatment improves the mechanical properties when the FA and BMA system is used with an SiO2/Al2O3 ratio of 8.0, or when the FA, BMA, and MK system is used with an SiO2/Al2O3 ratio of 6.0, showing the better development of geopolymeric gel composited with zeolite-P. The environmental clean-up capability is determined using powdered and bulk material dosages of 1.0 g and 10.0 g, respectively, to remove nearly 100 % of 20 mg/L methyl orange dye.

Recycling E-waste CRT glass in sustainable geopolymer concrete for radiation shielding applications

Waste cathode ray tube (CRT) glass, enriched with heavy metal of Pb, is classified as hazardous waste and needs to be disposed of harmlessly. This study recycles waste CRT glass as heavy aggregate in sustainable geopolymer concretes (GCs) to enhance its γ-ray shielding performance. It also comprehensively evaluates its macro-performances, microstructure, and environmental and economic impacts. The results demonstrate that the compressive strength of GCs decreases with the dosage of CRT glass. The generation of geopolymer gel is hindered by excessive CRT glass. Besides, the compatibility between CRT glass and the geopolymer matrix is poor. Both factors influence the strength development of CRT glass-incorporated GCs. The compressive strength of GCs with 50 % CRT glass aggregate exceeds 30 MPa, meeting the requirements for building materials. Due to the increase in the density and the introduction of heavy nuclei Pb, the γ-ray shielding performance of GCs is 9 % higher than that of normal concrete. In terms of economic and environmental benefits, this approach realizes the value-added recycling of CRT glass, avoiding the disposal cost of CRT glass. Besides, due to the utilization of sustainable geopolymer as cementitious materials, the carbon footprint of designed CRT glass-enhanced radiation shielding GCs is even 34 % lower than that of normal concrete. This study highlights the advantages of geopolymer and CRT glass in developing sustainable radiation shielding materials for nuclear technology and medicine fields.

Performance optimization and environmental assessment of novel alkali-activated binders containing carbonated recycled concrete powder

This study investigates the influence of carbonated recycled concrete powder (CRCP), alkali content (AC), and silicate modulus (SM) on the compressive strength, chemical composition, and environmental benefits of CRCP-blast furnace slag blended alkali-activated binders (AABs). The results show that increasing CRCP content reduces the compressive strength of AABs due to lower geopolymeric reactivity. Using response surface methodology, the optimal values for AC and SM in AABs containing 50 wt% CRCP were determined as 14.28% and 0.92, respectively, resulting in predicted and actual strengths of 49.9 MPa and 46.8 MPa. Chemical analyses reveal that calcite and vaterite are the predominant crystalline phases in AABs, while both Si-Al gels and calcite from CRCP participate in geopolymeric reactions. The effects of AC and SM on AAB strength are further elucidated through the combined analysis of precursor dissolution amount, geopolymeric gel formation amount, and calcium carbonate decomposition amount. Moreover, CRCP demonstrates negative carbon emissions, with a global warming potential of −0.16 kg CO2 eq/kg. The optimally proportioned AAB containing 50 wt% CRCP shows global warming potential and carbon intensity values significantly lower than those of Portland cement, at 54.4% and 50.8%, respectively. These findings emphasize that AABs containing 50 wt% CRCP not only meet the 43-grade strength classification but also offer notable environmental benefits. In summary, this study contributes to the development of a novel 43-graded low-carbon binder containing high-volume CRCP.

Innovative In-House Sodium Silicate Derived from Coal Bottom Ash and Its Impact on Geopolymer Mortar

Aluminosilicate precursors and alkaline solutions are combined to produce geopolymers. However, the high cost and energy demand of conventional alkaline activators limit the widespread use of alkali-activated materials (AAMs). Alkaline activators extracted from industrial wastes and by-products can address these challenges by reducing environmental impacts to a certain extent. Researchers have investigated the process for extracting alkali activators from waste materials that are high in silica, such as Waste Glass (WG) and Rice Husk Ash (RHA). However, there were limited studies on the extraction of sodium silicate from materials containing a moderate amount of silica. This study presents detailed findings on the production of alternate sodium silicates from Coal Bottom Ash (CBA) containing 43.7% SiO2 using a hydrothermal process, demonstrating the potential of CBA as an affordable and eco-environmental source of alkaline activators for geopolymers. The derived sodium silicate (DSS) was prepared using various sodium hydroxide (SH) molarities (3, 6, and 9 M) and stirred for 5 hrs at 80 °C. The solubility of silica from CBA was also examined and compared with that of COM-SS and RHA, which served as the control. CBA-SS performance in AAM mortar, flowability, hardened density, compressive strength, and ultrasonic pulse velocity (UPV) tests were performed. The results revealed that the silica dissolution increased with increasing SH concentration. In addition, the specimens activated by commercial sodium silicate (COM-SS), RHA-9M, and CBA-9M exhibited an increase in their compressive strengths at 56 days, which were 62.9, 93.52, and 59.08 MPa, respectively. The specimens activated with Coal Bottom Ash Sodium Silicate (CBA-SS) performed similarly to COM-SS. Therefore, geopolymer mortars can utilize CBA as a source of silica to derive sodium silicate. XRD and FESEM-EDX results confirmed the production of aluminosilicate hydrate (C-A-S-H) and calcium sodium aluminosilicate hydrate (N-A-S-H) as the primary components of the geopolymer gel.

Design of physical and functional properties of zeolitic porous monoliths by combining different foaming additives

Self-supporting zeolitic foams were synthesized by a geopolymer gel conversion process, employing silicon powder and hydrogen peroxide as foaming additives. The influence of silicon and hydrogen peroxide combination on the physical properties, mechanical characteristics, and pore distribution was studied. Correlations between these properties were drawn. This approach allows to manufacture porous monoliths tuned in terms of zeolite type and amount and characterized by bulk density ranging between 573 and 762 kg/m3 and thermal conductivity 0.33–0.53 W/mK. Pore structure, size, and distribution were dominated by the type of foaming agent: the foamed samples showed the presence of two classes of pores, the first of the order of magnitude of 1 μm, the second of the order of magnitude of 100 μm. The use of hydrogen peroxide enhanced the porosity in the meso-macropore range (0.1–5 μm). The hydrothermal treatment performed on the foamed geopolymer allowed to achieve the crystallization of zeolites within the solid geopolymer. Mainly FAU and LTA were the zeolitic phases present in the foams, whereas the use of silicon as foaming agent locally increased the Si/Al ratio on the geopolymer surface, promoting the nucleation of FAU.

The Influence of Particle Size and Calcium Content on Performance Characteristics of Metakaolin- and Fly-Ash-Based Geopolymer Gels.

This research systematically investigates the influence of raw material particle size and calcium content on the geopolymerization process to gain insight into the physical and mechanical properties of geopolymer gels, including setting time, fluidity, pore structure, compressive strength, and leaching characteristics of encapsulated Cr3+ heavy metal ions. Utilizing a diverse range of particle sizes of metakaolin (MK; 3.75, 7.5, and 12 µm) and fly ash (FA; 18, 45, and 75 µm), along with varied calcium levels, this study assesses the dual impact of these factors on the final properties of both metakaolin- and fly-ash-based geopolymers. Employing sophisticated analytical techniques such as Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), and Nuclear Magnetic Resonance (NMR), the research meticulously documents alterations in chemical bonding, micro-morphology, and pore structures. Key findings reveal that reducing the size of MK and FA particles to 3.75 and 18 µm, respectively, enhances the compressive strength of their matrices by 128.37 and 297.58%, respectively, compared to their original values (63.59 and 33.87 MPa, respectively) at larger particle sizes. While smaller particle sizes significantly bolster compressive strength, they adversely affect slurry flow and reduce the leaching rates of Cr3+ from MK- and FA-based matrices, reaching 0.42 and 0.75 mg/L at 3.75 and 18 µm, respectively. Conversely, increased calcium content markedly enhances setting times and contributes to the formation of dense microstructures through the production of calcium aluminate silicate hydrate (C-A-S-H) gels, thus improving the overall curing performance and durability of the materials. These insights underline the importance of fine-tuning particle size and calcium content to optimize geopolymer formulations, offering substantial benefits for varied engineering applications and promoting more sustainable construction practices.

Immobilization of radioactive borate liquid waste using calcined laterite–phosphoric acid–Fe3O4-based geopolymer waste forms

In this study, the feasibility of preparing a calcined laterite–phosphoric acid–Fe3O4-based geopolymer is investigated and its application for immobilizing radioactive borate liquid waste (RBLW) is explored. The addition of Fe3O4 enhances the compressive strength of the geopolymer and mitigates the retardation effects on the geopolymer caused by RBLW. Reactions between Fe3O4 and H3PO4 not only promote the geopolymerization process by generating heat and forming additional geopolymer gel, but also produce amorphous iron–phosphorus phases, contributing to higher compressive strength of the waste forms. Moreover, partial replacement of [AlO4] tetrahedra with [FeO6] octahedra creates stable –Fe–O–P–O–Al–O–Si– network structures. The geopolymer waste forms exhibit remarkable leaching resistance after Fe3O4 addition owing to the reduced open porosity, leading to radionuclide immobilization through physical encapsulation more efficiently. Furthermore, residual Fe3O4 may contribute to Co2+ immobilization through magnetic adsorption. Overall, the calcined laterite–phosphoric acid–Fe3O4-based geopolymer waste forms exhibit excellent performance in immobilizing RBLW, offering a new strategy for RBLW treatment.

PVA fiber reinforced red mud-based geopolymer for 3D printing: Printability, mechanical properties and microanalysis

Red mud-based geopolymers are an efficient alternative to resolve the high cement consumption in 3D printed concrete (3DPC). From a materials perspective, good printability and mechanical properties are critical to adopting red mud-based geopolymers in 3DPC. In this study, we selected bauxite tailings-red mud and blast furnace slag to prepare geopolymers. Polyvinyl alcohol (PVA) fibers with 0, 0.3 %, 0.6 %, 0.9 %, and 1.2 % volume fractions were used to reinforce 3D printed red mud-based geopolymers. To evaluate the influence of PVA fiber on the printability and mechanical properties of 3D printed red mud-based geopolymer. We tested the workability, extrudability, structural build-up ability, shape stability, and mechanical properties of the red mud-based geopolymer containing different volume fraction PVA fibers, and a microstructural analysis was performed to reveal the interface bond between the fibers and the geopolymer matrix. The results showed that adding PVA fibers impaired the workability of the red mud-based geopolymer mortar. The red mud-based geopolymer mortar showed a more than threefold increase in extrusion pressure compared to the control mixture (P0) when adding 1.2 % vol fiber. For all other mixtures, the increase was less than twice that of the control mixture. The PVA fiber had a significant positive impact on the structural build-up ability and shape stability of the 3D printable red mud-based geopolymer. In addition, PVA fibers promoted the bending strength of the hardened geopolymer specimens better than the compression strength, and the geopolymer gel on the fibers indicated the good interfacial bonding ability of the PVA fiber. This study demonstrates the feasibility of 3D printed red mud-based geopolymer and the reinforcement of 3D printed red mud-based geopolymer by PVA fibers, providing a material perspective to increase the range of red mud applications in 3D printed concrete.

Preparation of solid alkali activator for geopolymer synthesis using vanadium-bearing shale tailing

The vanadium-bearing shale tailing (VST) with large reserves pollutes the environment and urgently needs to be utilized as a resource. Due to its main component being silica, VST has great potential as a raw material for geopolymer. Therefore, this study uses VST to prepare the solid alkali activator (SAA) by thermochemical methods. Analysis show that the temperature and NaOH dosage of thermochemical reaction significantly affect the alkaline activation effect of SAA. Temperature affects the silicate content and the amount of NaOH affects the soluble silicate content in SAA. When the reaction temperature is high (such as above 900 ℃) and the amount of sodium hydroxide is low (such as the mass ratio of sodium hydroxide to VST is 0.6), quartz almost transforms into silicates, but the silicates have a stable cyclic chemical structure and are difficult to dissolve during the geopolymerization reaction. When the reaction temperature is low (such as less than 700 ℃) and the amount of sodium hydroxide is high (such as the mass ratio of sodium hydroxide to VST is 0.9), quartz in VST is difficult to fully convert into silicates, there are unreacted quartz and sodium hydroxide in SAA, and SAA has poor alkaline activation performance. The optimal synthesis process conditions for SAA are as follows: synthesis temperature is 900 °C and the mass ratio of sodium hydroxide to VST is 0.95. The main silicate components of SAA are Na2SiO3 and Na15.6Ca3.8Si12O36. During the synthesis of one-part geopolymer (OPG), Na2SiO3 dissolution generates a strong alkaline reaction environment and provides active silicon-oxygen tetrahedron monomers or oligomers, Na15.6Ca3.8Si12O36 is bonded with geopolymer gel structure by stable cyclic silicate structure, which makes OPG have a compact integrated structure. When the mass ratio of SAA to MK is 1:1.3, the 7-day compressive strength of the prepared OPG is about 49 MPa, SAA has the potential as a substitute for commercial sodium silicate to prepare geopolymers.

Efflorescence and mitigation of red mud–fly ash–phosphogypsum multicomponent geopolymer

In this study, the efflorescence formation of geopolymers synthesized from red mud (RM), fly ash (FA) and phosphogypsum (PG) was evaluated to investigate the influence of different proportions. The mechanical properties, leaching properties and microstructure of the geopolymers were studied through compressive strength test, visual observation of efflorescence, leach properties and a series of microscopic tests by changing PG content (0–25 %), reducing precursor alkali concentration (4–10 %) and changing FA content (0–300 g). The results show that PG rich in SO42- lead to the formation of a new efflorescence product Na2SO4, the presence of Aluminum (Al) in FA is beneficial to the polymerization degree and chemical stability of the geopolymer gel, and excessive or insufficient alkali content will affect the polymerization reaction and the efflorescence resistance of the geopolymer. The geopolymers are synthesized with 55 % RM, 25 % FA and 20 % PG as precursors and activated with 10 wt% Na2O, which shows good strength and resistance to efflorescence. Proper alkali content is conducive to the formation of geopolymer strength phase. The initial pH value required for the suitable effective strength and strength development of the multicomponent geopolymers in this study is about 10.5–11.3, which can provide a reference for the synergistic utilization of RM-FA-PG.

Surface modification of geopolymer coatings with polymethylhydrosiloxane-tetraethyl orthosilicate (PMHS-TEOS) for inhibiting efflorescence

Geopolymer coatings, as novel environmentally friendly inorganic coating, hold promising prospects in the field of concrete protection due to their characteristics such as corrosion resistance and fire resistance. However, its vulnerability to efflorescence can alter surface colouration and damage the structural integrity of the surface film, thereby diminishing its concrete protective efficacy. To inhibit efflorescence in geopolymer coatings, this study reports a surface modification method using polymethylhydrosiloxane-tetraethyl orthosilicate (PMHS-TEOS) for the first time. To explore the underlying mechanism, the effects of PMHS-TEOS on the geopolymer gel structure, mechanical properties, and ion leaching concentration were investigated. The experimental results indicate that PMHS-TEOS can penetrate the surface of geopolymer coatings and participate in the activation reaction, generating a new gel phase that effectively fills pore structure. Moreover, its hydrophobic groups facilitate the establishment of a waterproof structure, thereby inhibiting water infiltration and alkaline ion leaching. After PMHS-TEOS modification, the contact angle of the geopolymer coating reached 136.5°, demonstrating excellent wear resistance. The dissolution rate of alkaline cations in the modified geopolymer coatings was reduced by approximately 90 % and no efflorescence was observed in the long-term accelerated tests. This method is convenient for practical engineering of geopolymer coatings.

Experimental study on preparation of fly ash-based geopolymer blended with recycled calcium source

A large amount of waste eggshells raises environmental issues. This study uses eggshells as recycled calcium source to synthesize fly ash and eggshell geopolymer (FAEG). The effects of eggshell content, liquid-solid ratio, NaOH/Na2SiO3 ratio, and NaOH solution concentration on the strength of the FAEG were evaluated by unconfined compressive strength (UCS) test. The geopolymerization products and microstructure characteristics of the FAEG were analyzed by XRD, FTIR, TGA, and SEM test. The results show that eggshells acted as recycled calcium sources are capable of significantly enhancing the UCS of the FAEG. The optimal content of eggshells is 15%. The NaOH/Na2SiO3 ratio has a significant effect on the UCS of the FAEG, while the influence of liquid-solid ratio and NaOH concentration is slight. The optimal NaOH/Na2SiO3 ratio is 50:50 and the liquid-solid ratio is recommended to be 0.55. Eggshells take part in the geopolymerization by acting as a precipitating and seeding element in the reaction and favoring the generation of the geopolymeric gels in the FAEG.

Influence of foaming additives on the porous structure and properties of lightweight geopolymers based on ash–slag waste

Lightweight geopolymer is a promising thermal insulation material that conserves energy used for heating and cooling buildings. This study investigates foaming agents that influence the porous structure and properties of geopolymer foams based on ash–slag waste from thermal power plant using a 12 M sodium hydroxide solution, waterglass, and foaming agents (30 % hydrogen peroxide solution, aluminum, silicon, and zinc powders). The study demonstrates the feasibility of foaming geopolymers by water evaporation without foaming additives, where the best density of 949 kg/m3 and compressive strength of 4.2 MPa were achieved in samples foamed by microwave radiation, but such properties cannot attribute geopolymers as lightweight. Foaming with H2O2 is hard to synchronize with geopolymerization reactions. Aluminum and silicon powders lead to rapid reactions in alkaline conditions, resulting in uneven pore sizes. Zinc powder was the most effective foaming agent, producing materials with a density of 331 kg/m3 and compressive strength of 1.17 MPa, and it also integrates into the geopolymer gel structure. The foaming process should occur at room temperature. Elevated temperatures increase curing rates and result in incomplete geopolymerization, preventing uniform pore formation. Synthesized geopolymers are suitable for building insulation, basements, underground pipelines, and utility networks.

Effect of synthesis conditions on mechanical properties and microstructure of coal gasification slag-based geopolymer

Coal gasification slag (CGS) is an industrial solid waste produced during coal gasification, and it is mostly deposited on the land at present, resulting in serious environmental pollution. In order to promote its resource utilization, geopolymer was synthesized from CGS in this study. The influence of important factors containing the water-solid ratio, alkali activator dosage, activator modulus and curing temperature on the mechanical properties and microstructure of geopolymers were investigated. Micromorphology, chemical composition, mineralogy and chemical bonding of the geopolymer were assessed by scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR), respectively. Results indicate that the compressive strength of geopolymer can be improved by reducing the amount of initial water. The optimal mechanical properties of geopolymer are obtained when the alkali activator dosage is 25 % and the activator modulus is 1. The moderate temperature (e.g. 60 °C) is the most favorable to the compressive strength development of geopolymer. Under these optimal conditions, the 90 days compressive strength of the CGS-based geopolymer (CGSG) can reach 58.3 MPa. The Si/Al molar ratio of the geopolymer gels is between 2.0 and 3.1, and the Al/Na molar ratio is around 1.0. These results can provide a reference for recycling of the CGS and production of eco-friendly building materials.

Molecular Insights into Adhesion at Interface of Geopolymer Binder and Cement Mortar.

The degradation of concrete and reinforced concrete structures is a significant technical and economic challenge, requiring continuous repair and rehabilitation throughout their service life. Geopolymers (GPs), known for their high mechanical strength, low shrinkage, and durability, are being increasingly considered as alternatives to traditional repair materials. However, there is currently a lack of understanding regarding the interface bond properties between new geopolymer layers and old concrete substrates. In this paper, using advanced computational techniques, including quantum mechanical calculations and stochastic modeling, we explored the adsorption behavior and interaction mechanism of aluminosilicate oligomers with different Si/Al ratios forming the geopolymer gel structure and calcium silicate hydrate as the substrate at the interface bond region. We analyzed the electron density distributions of the highest occupied and lowest unoccupied molecular orbitals, examined the reactivity indices based on electron density functional theory, performed Mulliken charge population analysis, and evaluated global reactivity descriptors for the considered oligomers. The results elucidate the mechanisms of local and global reactivity of the oligomers, the equilibrium low-energy configurations of the oligomer structures adsorbed on the surface of C-(A)-S-H(I) (100), and their adsorption energies. These findings contribute to a better understanding of the adhesion properties of geopolymers and their potential as effective repair materials.

Synthesis of geopolymer mortar from biomass ashes and forecasting its compressive strength behaviour

The global warming dilemma raised an exigency toward sustainability in the construction industry and compelled scientists to hunt for alternative binders in construction materials. The, geopolymerization as a spectacular technology has arisen as a looming solution to this dilemma. This work assesses the features of geopolymer mortar developed with both industrial and agricultural wastes at ambient temperature curing. The geopolymer mix proportion was evolved in this study using main precursor material as fly ash, ground granulated blast furnace slag (GGBFS), sugarcane bagasse ash (SCBA) or rice husk ash (RHA). Workability and mechanical properties, including compressive strength, flexural strength, and split tensile strength of different mortar mixes with various percentages of RHA and SCBA for 365 days, were evaluated. Geopolymer mortar with 10 % SCBA and 5 % RHA achieved improvements of 25 % and 13.91 % in compressive strength, 10.6 % and 3.5 % in flexural strength, and 35 % and 16.8 % in split tensile strength, respectively. Good geopolymer gel formation is clearly evident from the SEM images of SCBA mortar. The main polymeric bonds Si–O–Al and Si-O-Si are also identified using FTIR. To assess the efficacious use of biomass ashes, resistance to chemical attack using H2SO4, HCl, Na2SiO3, and NaCl solutions for 365 days was studied. It was revealed that SCBA incorporated geopolymer mortar specimens achieved good resistance compared with RHA geopolymer mortar. The relation between the ambient temperature cured geopolymer specimen compressive strength at 28 days and 365 days chemical solution curried geopolymer specimen compressive strength find out using python and obtained R2 values more than 95 %. Also, this research proposed various machine learning techniques such as long short-term memory, support vector regression, random forest regression, XGBOOST, and AdaBOOST algorithms for the prediction of compressive strength of geopolymer using 724 mixture proportions with diverse curing temperatures and varying ages. The XGBOOST algorithm achieved the highest R² value of 0.92, demonstrating its effectiveness for the strength prediction.

Exploring mechanical and fracture properties in geopolymer concrete with ternary precursor waste materials through laboratory investigations and statistical analysis

The prevalent excessive utilization of cement concrete, characterized by energy-intensive processes and notable carbon dioxide emissions, necessitates a shift towards sustainable construction materials. This study addresses the environmental challenges posed by conventional cement concrete by investigating the potential of recycled precursor geopolymer concrete as an environmentally friendly alternative. The research delves into the mechanical and fracture characteristics of ternary blend geopolymer (TBG) concrete incorporating an industrial by-product, red mud (RM), through comprehensive laboratory testing and statistical analysis. The investigation focuses on assessing the impact of varying RM replacement levels (0 %, 8 %, 15 %, 23 %, and 30 %) on mechanical properties and fracture behaviour in both Mode I and Mode II, utilizing semi-circular bend (SCB) specimens for fracture tests. Statistical methodologies, including Weibull fracture failure probability modelling and analysis of variance (ANOVA), were employed to interpret the results derived from 180 SCB test specimens. Furthermore, microstructural analysis through FTIR, SEM, and EDX testing was conducted on the diverse mixes. The outcomes revealed that the incorporation of RM in geopolymer concrete consistently diminished the compressive strength and flexural strength of the geopolymer concrete as the incorporation levels increased. For instance, the compressive strength decreases from approximately 40 MPa in the RM-free sample to about 25 MPa in the sample with 30 % RM. However, statistical analysis revealed that up to 8 % RM inclusion does not significantly affect the compressive strength and, in some cases, may even slightly increase it, highlighting the subtle effect of RM dosage. Additionally, Weibull modelling revealed that the probability of failure for samples with 30 % RM is about five times higher than for samples without RM. The microstructural analysis also depicted that high RM content may lead to decreasing homogeneity and the formation of deep cracks, negatively impacting mechanical properties. Elevated Fe and Al concentrations with higher RM content suggest potential reactions forming stable geopolymer gels and the presence of minerals like katoite.