Geopolymer Matrix Research Articles

Study on the Compressive Strength and Reaction Mechanism of Alkali-Activated Geopolymer Materials Using Coal Gangue and Ground Granulated Blast Furnace Slag.

By reutilizing industrial byproducts, inorganic cementitious alkali-activated materials (AAMs) contribute to reduced energy consumption and carbon dioxide (CO2) emissions. In this study, coal gangue (CG) blended with ground granulated blast furnace slag (GGBFS) was used to prepare AAMs. The research focused on analyzing the effects of the GGBFS content and alkali activator (i.e., Na2O mass ratio and alkali modulus [SiO2/Na2O]) on the mechanical properties and microstructures of the AAMs. Through a series of spectroscopic and microscopic tests, the results showed that the GGBFS content had a significant influence on AAM compressive strength and paste fluidity; the optimal replacement of CG by GGBFS was 40-50%, and the optimal Na2O mass ratio and alkali modulus were 7% and 1.3, respectively. AAMs with a 50% GGBFS content exhibited a compact microstructure with a 28 d compressive strength of 54.59 MPa. Increasing the Na2O mass ratio from 6% to 8% promoted the hardening process and facilitated the formation of AAM gels; however, a 9% Na2O mass ratio inhibited the condensation of SiO4 and AlO4 ions, which decreased the compressive strength. Increasing the alkali modulus facilitated geopolymerization, which increased the compressive strength. Microscopic analysis showed that pore size and volume increased due to lower Na2O concentrations or alkali modulus. The results provide an experimental and theoretical basis for the large-scale utilization of AAMs in construction.

Enhancing geopolymer performance with silane-functionalized graphene oxide: Efflorescence reduction, pore refinement, and improved high-temperature properties

Geopolymer materials offer environmental benefits and strong mechanical properties but face limitations such as efflorescence, shrinkage, thermal stability and poor mechanical performance at high temperatures. This study introduces a novel solution using silane-functionalized graphene oxide nanocomposites (GO-APTS) to address these challenges. Experiments on metakaolin-based geopolymers demonstrate that incorporating GO-APTS improves dispersion, enhances mechanical strength, refines pore structures, and boosts resilience to high temperatures while reducing shrinkage and efflorescence, without compromising the workability of the mixes. Although the structural integrity of the material at nanoscale degrades beyond certain temperatures, the overall thermal resistance is significantly increased, with treated geopolymers displaying a ∼6 % improvement in porosity, ∼20 % higher residual compressive strength and ∼15 % reduction in shrinkage compared to control samples after exposure to heat. Our work reveals the promising potential of silanized graphene oxide nanocomposites in crafting cementitious materials suitable for high-temperature applications, paving the way for their broader use in innovative construction and industry solutions.

Geopolymer Materials from Fly Ash-A Sustainable Approach to Hazardous Waste Management.

This study explores the utilisation challenges of fly ash from municipal waste incineration, specifically focusing on ash from a dry desulphurisation plant (DDS), which is categorised as hazardous due to its high heavy metal content. The ash's low silicon and calcium contents restrict its standalone utility. Laboratory investigations initially revealed that geopolymers derived solely from fly ash after flue gas treatment (FGT), in combination with coal combustion fly ash, exhibited low compressive strength (below 0.6 MPa). However, the study demonstrated significant improvements by modifying the FGT ash through water leaching. This process enhanced its performance when mixed with high-silica and -aluminium fly ash, resulting in geopolymers achieving compressive strengths of up to 18 MPa. Comparable strength outcomes were observed when the modified ash was blended with commercial cement. Leachability tests conducted for heavy metals (HMs) such as copper, zinc, lead, cadmium, and nickel indicated that their concentrations fell below the regulatory limits for landfill disposal: 2, 4, 0.5, 0.04, and 0.4 mg/kg, respectively. These results underscore the effectiveness of water-washing FGT ash in conjunction with other materials for producing geopolymers, contributing to sustainable waste management practices.

Preparation of lightweight porous slag-based geopolymer highly hydrophobic materials for efficient oil-water separation

Surface hydrophobic modification is a critical technology for enhancing the application properties of materials, crucial for the development of geopolymer materials in oil-water separation. in this study, a lightweight porous slag-based geopolymer highly hydrophobic materials (PSGHHMs) were successfully prepared in-situ using slag and liquid water glass by varying different influencing factors, such as the amount of water/foaming agent/polymethylhydrosiloxane (PMHS) and the curing temperature. The PSGHHMs exhibited high strength, large flux and excellent highly hydrophobic properties, with contact angle reaching 156.14° and a sliding angle of less than 2°. SEM-EDS, TG-DSC and FT-IR analysis reveal that the in-situ modification mechanism of PSGHHMs involves the hydrolysis of Si-H in PMHS under alkaline conditions to form Si-OH. This subsequently reacts with Ca-OH in C-S-H gel to produce Ca-O-Si. Consequently, the PSGHHMs retained their excellent highly hydrophobicity even after calcination at 450℃ for 2.5 h. The PSGHHMs demonstrated robust resistance to acid/alkali/salt corrosion, as well as to friction, with the ability to quickly restore damaged highly hydrophobic properties. Additionally, the PSGHHMs could quickly absorb light/heavy oils, and achieving a desorption efficiency of over 99 %. They were also capable of continuously separation of oil-in-water emulsions and oil-water mixtures. Given these properties, the PSGHHMs have broad potential applications in antifreezing, antifogging, drag reduction and oil-water separation.

Thermo-mechanical performance assessment of geopolymer synthesized with steel slag and glass powder at elevated temperatures

This study utilizes glass powder (GP) and steel slag (SS) as a solid precursor material along with Fly Ash (FA) as a key ingredient to produce geopolymer composite (GPC). The developed geopolymer materials were subjected to elevated temperatures up to 800 °C to simulate intense fire conditions. Thermo-mechanical testing was conducted to evaluate the performance and microstructural characteristics of the exposed geopolymers. Results demonstrated that the GPC incorporating GP exhibited exceptional resistance to high temperatures, significantly retaining compressive strength. Conversely, the SS-based geopolymer showed a 52–54% reduction in strength, indicating improved thermal resistance. Both SS and GP-based GPC demonstrated resilience to high-temperature exposure, with SS addition providing the benefit of preserving structural integrity. However, the noted reduction in compressive strength highlights potential challenges for the application of geopolymer materials in areas exposed to high temperatures or fire.

Geopolymer composites reinforced with silverskin fibers from the coffee industry waste

This paper aims to develop sustainable geopolymer composites reinforced with silverskin fibers derived from coffee industry waste. Geopolymer and geopolymer composites were synthesized from blast furnace slags (BFS) with a solid/liquid (alkaline solution) ratio of 1.4. A sodium metasilicate/sodium hydroxide (Na2SiO3/NaOH) mixture at a mass ratio of 2.5 served as the alkaline activator in the geopolymerization process. The composites were evaluated by incorporating 2%, 3%, and 5% by weight of silverskin fibers, which were used in their natural form (SGCn), after treatment with sodium hydroxide (SGCNaOH), and after treatment with sodium hydroxide followed by a steam explosion process (SGCSE).Characterizations of the geopolymer composites included X-ray fluorescence analysis (XRF) for elemental oxide identification, Fourier transform infrared spectroscopy (FTIR) for functional group detection, and thermogravimetric analysis (TGA) for thermal stability assessment. The influence of fibers on the hardness of the geopolymer materials was evaluated using hardness scale measurements. Morphologies, microstructures, and elemental compositions were analyzed through field emission gun scanning electron microscopy with energy dispersive X-ray spectroscopy (FEG-SEM/EDS).The results demonstrate that the incorporation of silverskin fibers, especially those treated with NaOH and subjected to steam explosion, significantly enhances the thermal stability of geopolymer composites. The 5% NaOH-treated fiber composite exhibited the highest Tmax and Tend, indicating superior thermal stability. Additionally, the 5% SGCNaOH composite showed the highest residual mass, further supporting the enhanced thermal stability of these composites.Unlike other fibers, which showed a decrease in hardness, the addition of SGCSE fibers maintains a relatively high hardness in the geopolymer composites. The 2% SGCSE composite exhibited an average hardness equal to that of the pure geopolymer at 66 Shore D.These findings underscore the potential of using treated silverskin fibers to develop more thermally stable, cost-effective, and sustainable geopolymer materials. By utilizing industrial residues and waste, these advanced materials can be applied in the production of construction and building materials, contributing to both environmental sustainability and economic efficiency.

Properties of Fiber-Reinforced Geopolymer Mortar Using Coal Gangue and Aeolian Sand.

Geopolymers, as a novel cementitious material, exhibit typical brittle failure characteristics under stress. To mitigate this brittleness, fibers can be incorporated to enhance toughness. This study investigates the effects of varying polypropylene fiber (PPF) content and fiber length on the flowability, mechanical properties, and flexural toughness of coal gangue-based geopolymers. Microstructural changes and porosity variations within the Fiber-Reinforced Geopolymer Mortar(GMPF) matrix were observed using scanning electron microscope (SEM) and Low field NMR(LF-NMR) to elucidate the toughening mechanism of PPF-reinforced geopolymers. The introduction of fibers into the geopolymer matrix demonstrated an initial bridging effect in the viscous geopolymer slurry, with a 3.0 vol% fiber content reducing fluidity by 5.6%. Early mechanical properties of GMPF were enhanced with fiber addition; at 1.5 vol% fiber content and 15 mm length, the 3-day flexural and compressive strengths increased by 30.81% and 17.4%, respectively. Furthermore, polypropylene fibers significantly improved the matrix's flexural toughness, which showed an increasing trend with higher fiber content. At a 3.0 vol% fiber content, the flexural toughness index increased by 198.35%. The data indicated that a fiber length of 12 mm yielded the best toughening effect, with an 84.03% increase in the flexural toughness index. SEM observations revealed a strong interfacial bond between fibers and the matrix, with noticeable damage on the fiber surface due to frictional forces, and fiber pull-out being the predominant failure mode. Porosity testing results indicated that fiber incorporation substantially improved the internal pore structure of the matrix, reducing the median pore diameter of mesopores and converting mesopores to micropores. Additionally, the number of harmless and less harmful pores increased by 23.01%, while the number of more harmful pores decreased by 30.43%.

Assessing viability and leachability in fly ash geopolymers incorporated with rubber sludge

This study explores the innovative use of rubber sludge (RS) from glove manufacturing as a partial replacement for fly ash (FA) in geopolymer production. The research investigates the physical properties, functional group analysis, microstructural analysis, phase analysis and compressive strength. The partial replacement of different types of RS, such as activated sludge (AS), pre-leaching sludge (PLS) and coagulant sludge (CS), will affect differently on the geopolymer integrity and performance. CS enriched with high calcium content, facilitated the formation of a denser geopolymer matrix with C(N)-A-S-H gel in conjunction with C-S-H, C-A-S-H and N-A-S-H gels, enhancing the compressive strength of FA/CS geopolymers up to 70.4 MPa, surpassing FA/AS and FA/PLS geopolymers. The fly ash/rubber sludge geopolymers exhibited compressive strengths ranging from 20.5 to 70.4 MPa, not only meeting ASTM standards for construction but also effectively immobilizing hazardous metals, particularly Zn (>98.4 %), the Zn leaching in geopolymers was reduced by more than 87.4 % compared to the rubber sludge itself, thereby mitigating environmental toxicity. This utilization addresses significant industrial waste management issues, providing a cost-effective and environmentally friendly alternative for construction. The findings contribute to advancing sustainable building materials and advocate for equitable utilization of industrial waste resources.

Experimental studies on behavior of one-part geopolymer composite slabs subjected to blast loading

Over the past two decades, geopolymer has emerged as a noteworthy alternative to traditional cementitious materials in construction, offering comparable performance with reduced carbon dioxide emissions. The recent development of one-part geopolymer composites, which transform the alkaline activating solution into a solid powder form, has significantly enhanced the scalability and applicability of geopolymer in construction contexts. This study investigates the mechanical behavior of one-part geopolymer composite slabs when subjected to blast loading. Four slab specimens were constructed using the one-part geopolymer composite. Two of these specimens were reinforced with steel wire mesh, while the other two used PVA fibers for reinforcement. These slabs were tested under various blast loading induced by a shock tube. Employing three-dimensional digital image correlation techniques, the dynamic responses and damage mechanisms exhibited by these slabs were analyzed and discussed. The experimental results reveal that the fiber-reinforced geopolymer composite (FRGC) slabs demonstrate superior blast resistance compared to those reinforced with steel wire mesh. In particular, the one-part geopolymer matrix combined with PVA fibers exhibited a synergistic effect, indicating an enhanced capacity for energy dissipation. The findings suggest that one-part geopolymer concrete reinforced with PVA fibers holds significant potential for applications in the field of protective engineering, marking a step forward in the development of sustainable and resilient construction materials.

Improved carbon fibers dispersion in geopolymer composites

Carbon fibers (CFs) reinforced alkali-activated (AA) ground granulated blast furnace slag (GGBFS) geopolymer composites have excellent mechanical and thermoelectrical properties, as well as low energy consumption and low CO2 emissions during their production. However, the dispersion of CFs in the geopolymer matrix is always a technical issue in the preparation of the green composite material. Therefore, this study comparatively investigated various dispersion methods, including, mixing sequence (pre-mixing and after-mixing methods), dispersing agent (nano silicon dioxide [nSiO2]), and ultrasonic treatment time (0, 15, 30, and 45 min), as well as CFs content (0.5, 1.0, and 1.5 wt% of GGBFS). The distribution of CFs was then qualitatively and quantitatively evaluated by a series of tests, such as flowability, electrical resistivity, flexural strength, scanning electron microscope (SEM) analysis, and X-ray computed tomography (CT). The experimental results showed that the proposed pre-mixing method provided excellent dispersion characteristics for CFs compared with the after-mixing method. The introduction of nSiO2 can enhance the dispersion of CFs and the mechanical and electrical properties of AA GGBFS geopolymer composites. At a carbon fiber content of 1.5 %, the pre-mixing method and the addition of nSiO2 dispersant reduced the resistivity of the 28-day geopolymer composites by 17.0 % and 38 %, respectively, compared with the after-mixing method. It is feasible to use X-ray CT scanning with the gray-scale frequency map to analyze the dispersion effect of CFs in AA GGBFS geopolymer composites. However, the results were not intuitive when less agglomeration of CFs occurred for the low content of CFs. The scanning method is more applicable to the sample with over 1.0 wt% CFs. The average pixel areas of uniformly dispersed CF bundles in the 2D images of the pre-mixing method and the addition of nSiO2 dispersant specimens were 3.32 % and 6.55 % higher than those of the after-mixing method, respectively. The 2D and 3D scanning results from the dispersion characteristics of CFs were consistent. 2D scanning could provide a time-consuming option for the measurement of CFs dispersion characteristics.

High performance illitic clay-based geopolymer: Influence of thermal/mechanical activation on strength development

The scientific community's interest in geopolymers keeps on growing under environmental and climate change pressures. Although most studies concern metakaolin or industrial by-products as aluminosilicate precursors, few are those concerning clay cuttings characterized by little or no kaolinite content. This study proposes a method to activate illitic clay in order to obtain a geopolymer with high mechanical performances. The tested illitic material contained 53 wt% of illite/muscovite, 22 wt% quartz, 7 wt% feldspars and low content of calcite. The innovation consists in coupling thermal and mechanical activations favoring both the clay dehydroxylation and the destruction of the clay crystalline structure. Such increase of amorphous rate in the precursor is required to make the material reactive. The evolution of the precursor material after activation was followed by ThermoGravimetric Analysis (TGA/DTG), X-Ray Diffraction (XRD), Fourier-Transform InfraRed spectroscopy (FTIR) and Scanning Electron Microscopy coupled to Energy Dispersive X-ray spectrometry (SEM-EDX). The impact of the variations of the mechanical activation duration and ball:powder mass ratio (b:p) were mainly explored, as well as the Liquid:Solid mass ratio (L:S) which is a key parameter of the geopolymerization. Finally, an optimized geopolymer with a mechanical compressive strength reaching 126 MPa after 28 days has been manufactured with a grinding duration of 240 min, a b:p = 15 and a L:S = 0.5. The demonstration was done that a geopolymer can be manufactured from 100% illitic clay precursor, in addition to a relatively low amount of alkaline solution (L:S mass ratio of 0.5) then lowering the cost and the environment impact of the final geopolymer material. The resulting illitic clay based geopolymers can display very high mechanical resistance (compressive strength up to 126 MPa after 28 days), fully competitive with conventional building materials.

Study on the microscopic characteristics and hydration mechanism of thermo-alkali activated electrolytic manganese residue geopolymers

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 NH4+-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.

Enhancing Geopolymeric Material Properties: A Comparative Study of Compaction Effects via Alkaline and Acidic Routes

Enhancing Geopolymeric Material Properties: A Comparative Study of Compaction Effects via Alkaline and Acidic Routes

Influence of ground granulated blast furnace slag on recycled concrete powder-based geopolymer cured at ambient temperature: Rheology, mechanical properties, reaction kinetics and air-void characteristics

In this paper, ground granulated blast-furnace slag was used to enhance the properties of recycled concrete powder based geopolymer cured at ambient conditions. The rheology, workability, strength, hydration reaction kinetics, microstructure, and air-void characteristics of the geopolymer were investigated. The results showed that adding the slag accelerated the setting process and reduced the water absorption and porosity of the geopolymer mixtures. Excellent mechanical properties were achieved when the slag content exceeds 30 %. The 28-d compressive and flexural strength of the geopolymer with 50 % slag addition reached 61.2 and 5.17 MPa, respectively. The yield stress and plastic viscosity of the geopolymer increased as the slag content increased. A quantitative model between the slag content, resting time, and rheological parameters was established, with high accuracy, realistically reflecting the rheological properties of the geopolymer. The addition of the slag provided nucleation sites for the C-S-H gel, which promoted the hydration reaction, increased the hydration products and the total heat release, and formed a denser and more uniform microstructure, thereby increasing the strength of the geopolymer. The slag addition was also found to reduce the air content, spacing factor, and average chord length of the geopolymer matrix. As the slag content increased, the air bubbles became smaller and more stable, and exhibited a more uniform distribution.

Enhancing the mechanical and thermal properties of geopolymers prepared by refractory brick dust: An investigation into optimal mix ratios and curing conditions

This study proposes the development of a novel geopolymer by investigating the feasibility of using refractory brick dust (RBD), a waste product from brick manufacturing. The focus was on exploring the trade-off between waste incorporation and high-temperature resistance in geopolymer pastes. Throughout the experiments, the NaOH solution concentration was consistently maintained at 10 M. The primary goal was to examine how varying the ratios of Na2SiO3/NaOH (NS/NH) and RBD/alkaline activator (AS) on the geopolymers’ characteristics. A series of meticulous tests were conducted using various curing methods, ranging from room temperature to high temperatures between 100 °C and 140 °C, with curing times extending up to 72 h. It was observed that geopolymers exhibit the highest compressive strength after being precured at 100 °C for 72 h, achieving a maximum compressive strength of 15.40 MPa. SEM microstructure analysis revealed a correlation between the curing regime, material density and porosity. Specifically, at 140 °C, the data indicated that more porous structures have lower compressive strength. Geopolymers exhibited good mechanical properties at low curing temperatures, but exposure to temperatures above 1200 °C resulted in significant deterioration. For example, Mix 3.0RBD2.0, with a higher RBD/AS and NS/NH ratio, experienced the greatest compressive strength loss of 61.3% and a mass loss of 15.5% at these elevated temperatures. Interestingly, a geopolymer composition of 2.0RBD0.5 showed high-temperature-induced physical changes that might alter its strength and stability, yet it retained its overall structure. This study provides an in-depth explanation of the importance of optimising waste utilization to develop resilient geopolymer materials. It demonstrates how the composition – specifically, a Si/Al ratio of approximately 2.26, which is preferred based on EDS results – along with the curing methods, significantly influences the performance and high-temperature resistance of geopolymers.

Influence of Residue Soil on the Properties of Fly Ash-Slag-Based Geopolymer Materials for 3D Printing.

This study investigates the impact of residue soil (RS) powder on the 3D printability of geopolymer composites based on fly ash and ground granulated blast furnace slag. RS is incorporated into the geopolymer mixture, with its inclusion ranging from 0% to 110% of the combined mass of fly ash and finely ground blast furnace slag. Seven groups of geopolymers were designed and tested for their flowability, setting time, rheology, open time, extrudability, shape retention, buildability, and mechanical properties. The results showed that with the increase in RS content, the fluidity of geopolymer mortar decreases, and the setting time increases first and then decreases. The static yield stress, dynamic yield stress, and apparent viscosity of geopolymer mortar increase with the increase in RS content. For an RS content between 10% and 90%, the corresponding fluidity is above 145 mm, and the yield stress is controlled within the range of 2800 Pa, which meets the requirements of extrusion molding. Except for RS-110, geopolymer mortars with other RS contents showed good extrudability and shape retention. The compressive strength of 3D printing samples of geopolymer mortar containing RS has obvious anisotropy.

Evaluation of Porous Geopolymer Materials Prepared Using Water Glass Synthesized from Rice Husk Ash ‐ Influence of Alkali Concentration and Heat-treatment on Physical Properties of The Porous Geopolymer -

Evaluation of Porous Geopolymer Materials Prepared Using Water Glass Synthesized from Rice Husk Ash ‐ Influence of Alkali Concentration and Heat-treatment on Physical Properties of The Porous Geopolymer -

Waste valorization: Sustainable geopolymer production using recycled glass and fly ash at ambient temperature

This research explores the reutilization of waste glass powder (GP) and class F fly ash (FA) in the development of an advanced geopolymer, focusing on reducing natural resource consumption to serve as a green alternative for conventional concrete material. Investigating mix ratios of GP-to-FA (0-to-1), activated with 2–12 M NaOH, followed by ambient temperature curing, this study mainly assesses strength (compressive, and flexural) and durability at different ages. Mechanical properties concerning reaction kinetics and Al/Si ratio, reveal that GP initially acts as an inert filler with slow reaction kinetics, while significant strength improvement at later ages is attributed to the reaction between GP and FA. Optimal performance is achieved with a geopolymer mixture featuring a GP-to-FA ratio of 1:3 (Al/Si ratio of 0.51) and an 8 M NaOH solution, resulting in the highest compressive strength of 40 MPa and superior durability. Microstructural analysis (SEM-EDS, and 29Si MAS NMR) identifies the reacting product as calcium/sodium aluminate silicate hydrate (C/N-(A)-S-H) gel within the geopolymer matrix. Leaching tests further underscore potential environmental concerns related to excessive alkali leaching, necessitating meticulous mix design management. Embodied energy and carbon footprint assessments confirm the environmental friendliness of the GP-FA-based geopolymer. Overall, this research demonstrates the feasibility of producing effective geopolymers from dry waste at ambient temperature, emphasizing the potential synergy between waste glass recycling and the concrete industry towards sustainable construction practices.

Effect of Zr-glass fibers waste on the mechanical, structural, and durability of eco-friendly geopolymers based on natural pozzolan: A Box-Behnken design approach

Geopolymer (GP) materials are attracting increasing interest as a promising alternative to conventional cement-based materials, due to their beneficial characteristics. This article presents the preparation of two series of GP composites based on natural pozzolan (Pz), reinforced with varying percentages (0, 0.5, 1, 1.5, and 2 %) of short fiberglass waste rich in zirconia (Zr-GFW). Two alkaline activation solutions were used with a 1:1 ratio: NaOH (10 M): Na2SiO3 for the first series, and NaOH (12 M): Na2SiO3 for the second series. The effect of Zr-GFW incorporation on the structural, physical, mechanical, and chemical properties was investigated. Besides, a comparison between the two series with the different concentrations of alkaline solutions was also discussed. XRD analysis shows that no significant reaction occurred between zirconia and Pz-based GP matrix. The results show that a 1 % Zr-GFW is sufficient for excellent mechanical strength, up to 65 MPa, and good physical properties. Furthermore, based on the Box-Behnken design statistical method, the developed response surface methodology model shows a strong fit to the experimental data, with high values of R² (0.9998). In this model, the compressive strength studied is 64.28 MPa. After exposure to an 80 % solution of acetic acid for 60 days, the evaluation of chemical durability showed that the dense structure of the studied GP composites resisted the acid attack tests, as confirmed by SEM analysis. The percentage weight loss (%WL) of the GP composites ranges from 14.66 % to 16.15 %, resulting in a decrease in compressive strength of up to 55 %. However, this reduction is better than several previous works. The findings suggest that these GP composites not only contribute to waste management but also enhance the energy performance of buildings.

Fresh and hardened properties for a wide range of geopolymer binders – An optimization process

The objective of this study was to identify the optimal geopolymer binder compositions produced from local industrial by-products and compare them with commercially available materials. The first part investigated the optimal binder composition by studying 27 mixtures. In this part of the research, three series of binders were created: the first series of 18 mixtures was Na-based fly ash-slag, the second series consisted of 8 mixtures of K-based fly ash-slag, and the third series were a mixture of metakaolin-slag based geopolymer. The compressive strengths of the mixtures at the age of seven days ranged from 2.18 to 96.23 MPa. The strength development is clearly defined by the components and proportions of the blends. Geopolymers reach about 80% of their 28-day strength in seven days. The 25% water content was optimal for slag-fly ash geopolymers. The strength of the material increased from 68.08 to 96.23 MPa when the Blaine surface area of the slag increased from 3500 to 4500 cm2/g. The optimal proportions of the alkali solution were the intermediate ratios: SiO2/Na2O = 2.0 and SiO2/K2O = 1.5. In the case where Visonta fly ash is prepared for blending, the fly ash content can be maximized by 30%–50% in addition to the blast-furnace slag. In the second part of the research, mortars were prepared from the selected binders: 4 mixtures were prepared with two different binders. In one of these mortars, the solid part of the binder consisted of local raw materials originating from Hungary. This mixture was prepared with 43 m% fine aggregates. The optimal composition of the tested 27 binders tested was selected as the geopolymer matrix for the production of three further mortar mixtures. In these geopolymer mortars, 55, 65, and 75 m% of aggregate applied. The flowtable values of fresh mortars decreased when the proportion of sand increased. The lower the additive content was, the higher the strength of the geopolymer mortar. The 28-day compressive strengths of filtered fly ash-slag mortar sample with 55%, 65%, and 75% of fine aggregate (F–S-a55, F–S-a65, and F–S-a75) made with the selected optimised filtered fly ash-slag geopolymer binder of group A-I.3 (F–S-A-I.3) varied between 11.39 and 40.15 MPa, whereas the Visont fly ash-slag mortar sample with 43% of fine aggregate (V–S-a43) has been 25.05 MPa. For 28 days, the density ranged between 1870 and 2204 kg/m3. The V–S-a43 is found to be the lowest-density blend. The chloride migration test revealed that geopolymer mortars with higher slag content have higher resistance to Cl− ions.