Metakaolin-based Geopolymer Research Articles

Metakaolin-based geopolymer formation and properties: The influence of the maturation period and environment (air, demineralized and sea water)

Preparation and application parameters are decisive for the use of any construction or repair material. For this reason, the effect of the maturation period and the influence of the surrounding environment (air, demineralized and sea water) on geopolymer properties has been studied. Geopolymer samples prepared with the maturation period of 2 and 28 days have been exposed to air, demineralized or sea water. The solids were then investigated in terms of their mechanical properties, the formation of geopolymer netting, and their stability in aqueous media. The presented results have proven that shortening the maturation period has a marginal effect on the final properties of geopolymer solids. Infrared spectroscopy has revealed that neither the length of the maturation period nor the ambient environment investigated has an effect on the formation of geopolymer bonds. No undesirable crystalline phases have been formed, which also concerns sea water. The submersion in aqueous media as early as 2 days after preparation, even in sea water, has no significant adverse effects on geopolymer bond formation or properties. These findings can facilitate the potential public acceptance and wider application of geopolymers in practice.

Characteristics of metakaolin-based geopolymers using bemban fiber additives

<p>The aim of this study was to investigate the chemical composition and thermal properties of kaolin, the physical properties of metakaolin, and the mechanical properties of metakaolin-based geopolymers using bemban fiber. Kaolin was calcinated to become metakaolin at 600 ℃ for 2 h for optimum conditions. The chemical composition of kaolin mostly consisted of 59.30% SiO<sub>2</sub>, 34.30% Al<sub>2</sub>O<sub>3</sub>, and 3.06% Fe<sub>2</sub>O<sub>3</sub>. The transformation of kaolin into metakaolin with temperature was determined through thermal stability tests and analyzed using thermogravimetric analysis (TGA) and differential thermal analysis (DTA). Regarding the thermal properties of kaolin, predehydroxylation occurred at 31.07–92.69 ℃, dihydroxylation occurred at 400–600 ℃, and the endothermic peak in the DTA curve was recorded at 505.63 ℃. This research also analyzed the physical and mechanical characteristics of metakaolin-based geopolymers, with the additional variation percentages of bemban fiber alloys resulting from a 3% NaOH alkalization treatment for 2 h. The test results indicate that the bemban fiber improves the physical and mechanical characteristics of geopolymers. This improvement is related to the enhanced geopolymer characteristics, including a water absorption capacity of 1.10%, porosity of 2.32%, compressive strength of 35.33 MPa, and splitting tensile strength of 11.29 MPa with the addition of 1.5% bemban fiber. Although the split tensile strength increases as the fiber content increases, adding 1.5% of bemban fiber is optimum because a higher content decreases the workability of mixtures.</p>

Estudo preliminar do efeito da cura por carbonatação em geopolímeros

Abstract Carbonation curing differs from weathering carbonation since it is performed intentionally at the early ages of cement hydration. This cure involves applying different levels of CO2 (5% to 99%) to concrete for a short period of time, usually followed by conventional hydration. The objective of this article was to evaluate the carbonation curing in metakaolin-based geopolymer concretes, activated with NaOH and Na2SiO3, and compare them with Portland cement (PC) concrete. The following tests were applied: determination of pH, carbonation depth, water absorption by immersion, void index, and compressive strength. The results showed that after the carbonation curing, the geopolymer concrete had compressive strength and carbonation depth equivalent to the concrete with PC, but with a lower absorbed CO2 content. Although this type of cement absorbs less CO2 but is more sensitive to carbonation. The effect on the void ratio was not remarkable. Furthermore, the alkalinity of concretes can be partially recovered after subsequent curing by water immersion.

Rapid fabrication of porous metakaolin-based geopolymer via microwave foaming

Microwave foaming was used for the first time to rapidly fabricate the metakaolin-based porous geopolymers. Mechanical, thermal, and microstructural (optical and scanning electron microscope) investigations coupled with X-ray diffraction, Fourier-transform infrared spectroscopy, and nuclear magnetic resonance techniques were conducted to characterize the obtained foams. High porosity metakaolin-based porous geopolymers could be obtained at 4 min of foaming/curing. The effect of the sodium silicate solution content on the total porosity as well as the mechanical and thermal properties was investigated. The total porosity decreased firstly and then increased in the range of ∼74 to ∼84 vol% with the increase of Na2SiO3 content. The foams with 47.7 wt% Na2SiO3 exhibited the lowest thermal conductivity (0.104 W/mK) and the highest total porosity (83.2 vol%). The fabrication time, mechanical, and thermal properties were compared with those of foams obtained by the conventional direct foaming method. With this approach, the preparation time can be greatly reduced, and the compressive strength (1.89–2.04 MPa) and thermal conductivity (0.104–0.155 W/mK) of the materials obtained were not inferior to similar components obtained by other foaming routes. The rapidly obtained porous geopolymers with high porosity and high strength as well as low thermal conductivity can be employed as thermal insulation materials and ceramic precursors.

Impact of interatomic structural characteristics of aluminosilicate hydrate on the mechanical properties of metakaolin-based geopolymer

This study explores the influence of the interatomic structure of sodium aluminosilicate hydrate (N-A-S-H) with varying silica contents on the mechanical properties of metakaolin-based geopolymer. Geopolymer pastes comprising Si/Al ratios between 2.0 and 3.0 were synthesized. A larger number of Si-O-Si linkages compared to Si-O-Al linkages and a higher atomic number density were found in the geopolymers with higher silica contents, which enhanced the compressive strength of the geopolymer pastes up to the optimal Si/Al ratio of 2.5. The paste with a Si/Al = 2.5 exhibited a greater portion of Q4(1Al and 2Al) and denser morphology compared to the other geopolymer pastes. Furthermore, in-situ high-energy synchrotron X-ray scattering experiments were conducted to assess the elastic modulus of the aluminosilicate structure at a local atomic scale. The modulus value in real space decreases with increasing silica contents up to Si/Al = 2.5 and increases with the presence of excessive unreacted silica fume. The modulus value in reciprocal space for the axial and lateral directions both presented a positive value at the geopolymer comprising a Si/Al ratio higher than 2.5, indicating that the load-bearing property of N-A-S-H changed at higher Si/Al ratios. Moreover, the smallest difference between the strains along the axial and lateral directions was detected for the geopolymer with Si/Al = 2.5 in both the real and reciprocal space, owing to the most interconnected and flexible nanostructure, which led to the highest mechanical strength.

Drying shrinkage inhibition effect and mechanism of polyol shrinkagex reducing admixture on the metakaolin-based geopolymer

Geopolymers, environmentally friendly materials, face application limitations due to their high drying shrinkage and propensity for cracking. The shrinkage reducing admixture (SRA) has shown promise in mitigating drying shrinkage in cement-based materials, yet its impact and mechanism in geopolymers remain uncertain. This study examines the influence of the small molecule polyol SRA-2-methyl-2,4-pentanediol on metakaolin-based geopolymer (MKG) properties and its multiscale structural development, aiming to understand the drying shrinkage behavior. The findings reveal that SRA significantly curbs the drying shrinkage of MKG while also reducing its mechanical properties. Analyses of macroscopic and microscopic properties indicate that while SRA does not alter the hydration products of MKG, it can impede the hydration process, particularly in the early stages. Specifically, SRA inhibits the formation of N-A-S-H gel, thereby reducing shrinkage caused by late-stage polycondensation. Furthermore, the alkaline environment in MKG aids SRA in lowering pore solution surface tension and increasing its contact angle, reducing drying shrinkage forces. Additionally, SRA modifies MKG's micro-structure, decreasing pore volume, particularly in the 10–50 nm range, further mitigating shrinkage due to surface tension.

Performance of Metakaolin-Based Geopolymer Incorporating Recycled Plastic Aggregate

Recently, research has been devoted to producing a more sustainable and environmentally friendly composite for substituting conventional cement concrete. This supports the global effort toward limiting the environmental impact of cement production. Geopolymer composites or alkali-activated materials have gained more attention within the research community due to the wide availability of waste (e.g., fly ash, slag) or natural (metakaolin, pozzolans) source materials suitable for geopolymer production. The present study investigates the potential of producing metakaolin-based geopolymer mortars with partial substitution of natural sand by recycled plastic fine aggregate (RPFA) to enhance composite sustainability. The primary variables of the experimental program include the percentage replacement of fine natural aggregate by RPFA (0, 10, 20, and 30% by volume). Tests comprising flowability, compressive strength, Flexural strength and unit weight of the various mixes were evaluated. The results indicated that replacing 10%, 20%, and 30% of sand with RPFA caused a reduction in the compressive strength by 10.6%, 21.8%, and 33.9% relative to the control mix. The flexural strength also decreased by 17.5%, 22.4%, and 30.4% compared to the control mix. Although substituting natural aggregate with RPFA reduced the mechanical properties, it improved the mix flowability by up to 20% relative to the control mix. Additionally, a reduction in the unit weight by up to 16.2% relative to the control mix was obtained, which offer a viable mean of producing lightweight mortar.

Development of sulfhydryl grafted hierarchical porous geopolymer for highly effective removal of Pb (II) from water

Geopolymers have captured increasing attention in the adsorption of lead ions due to their zeolite-like three-dimensional network structure, and several advantages such as low cost and environmental friendliness. However, their adsorption performance is limited by a small specific surface area and fewer adsorption sites. In this study, a metakaolin-based geopolymer was first pretreated with different concentrations of nitric acid to increase the porosity and surface area. Subsequently, the sulfhydryl functional group was grafted onto the above hierarchical porous geopolymer, which is a inorganic material with multistage pore structure. The result of N2 adsorption and desorption results demonstrated that an increase in specific surface area and number of grafting sites for sulfhydryl groups with increasing acid concentration when the highest nitric acid concentration used is 5 mol/L and acid treatment time is for 5 h. The specific surface area of the fabricated geopolymers was as high as 343.87 m2/g and the concentration of silanol groups reached 4.46 mmol/g at 3 mol/L acid concentration. The maximum Pb2+ adsorption quantities for SH-1HGeo, SH-2HGeo, and SH-3HGeo samples were 173.2 mg/g, 239.8 mg/g, and 386.3 mg/g, respectively. The adsorption processes were in accordance with the pseudo-second-order kinetic model and the Langmuir models, indicating that the Pb2+ adsorption on the sulfhydryl grafted hierarchical porous geopolymer was mainly chemisorption and monolayer adsorption. The contribution of different Pb2+ adsorption mechanism on geopolymer was ion-exchange, while that on SH-3HGeo was functional group complexation.

Influence of Curing Temperature on the Strength of a Metakaolin-Based Geopolymer

The present work focuses on the further development of a new family of geopolymers obtained by the alkaline activation of a binder. The aim is to find a viable alternative to concrete that can be used in civil construction. Regarding the influence of the curing temperature on this type of mixture, the recommendations in the existing literature are different for fly ash, ground granulated blast-furnace slag, and metakaolin-based geopolymers. While for fly ash and slag, increasing the curing temperature above 60 °C is reported to be advantageous, for metakaolin geopolymers, the opposite is reported. In this context, the objective of this work is to evaluate the mechanical strength of several metakaolin-based geopolymer specimens subjected to different curing temperatures (10, 15, 20, 30, 40 and 50 °C). Furthermore, several stress-strain diagrams are also shown. Based on the results, we recommend using curing temperatures below 30 °C in order to avoid reducing the strength of metakaolin-based geopolymers. Curing at 50 °C, relative to room temperature, results in a reduction of more than 35% in flexural strength and a reduction of more than 60% in compressive strength. Regarding the behavior of the geopolymers, it was found that the strain, at the ultimate stress, is about 2 to 2.5 times the strain of an equivalent cement mortar.

Mn-doped geopolymers photocatalysts with sustained-release OH− for highly efficient degradation of malachite green and tetracycline

Hydroxyl radicals (•OH) are the primary reactive groups in photocatalytic reactions. However, the stability and long-term effectiveness of photocatalysis in degrading dye wastewater and antibiotic contaminants remains a major challenge. In this study, the sustained-release microspheres containing OH− were prepared by Mn-doped metakaolin-based geopolymers (Mn-MGPs), and a strategy combining defect engineering and OH− sustained-release was presented. A large number of oxygen vacancies (O), which can enhance the light absorption properties, can generate superoxide radicals (O2•-) on the catalyst surface and promote the formation of (•OH) to fabricate efficient heterojunction photocatalysts. The photocatalysts were systematically characterized for photocatalytic activity and long-term effectiveness in the degradation of malachite green (MG) and tetracycline (TC). The mechanism of the enhanced photocatalytic performance of the catalysts was investigated by characterization and DFT theoretical calculations, and the pollutant degradation pathway was proposed. This study provides an innovative approach to the controlled design of valence heterostructures.

Mechanical properties prediction of geopolymer concrete subjected to high temperature by BP neural network

High temperatures can deteriorate the mechanical properties of geopolymer buildings. Rapid prediction of the residual mechanical properties and failure mode of geopolymer concrete (GPC) after thermal treatment is important to ensure the safety of buildings. In this study, a method combining BP neural network with numerical simulation is proposed to predict the residual mechanical properties and failure mode of GPC subjected to high temperature simultaneously. 15 GPC specimens with 65 % aggregate content were prepared by mixing metakaolin-based geopolymer and limestone aggregates. These GPC specimens were divided into 5 groups and heated at 25 °C, 200 °C, 400 °C, 600 °C and 800 °C, respectively. The uniaxial compression tests were conducted on the GPC after thermal treatment. The variation in the peak stress, peak strain and elastic modulus of GPC with temperature was further analyzed. The prediction method by combining the BP neural network with numerical simulation was constructed to predict the mechanical properties and failure mode of GPC subjected to high temperature. The reliability of the prediction method was verified by comparing the predicted results and the experimental results. The results show that as the temperature increases, the peak stress and elastic modulus decrease and the peak strain increases, showing a deterioration of the mechanical properties of GPC after thermal treatment. The prediction method combining the artificial neural networks and numerical simulation has high accuracy, with prediction errors of less than 10 % for peak stress and less than 20 % for peak strain and elastic modulus. The results also show that under uniaxial compression load, the predicted failure mode of GPC after thermal treatment is consistent with the experiment results. The method proposed in this study can simultaneously predict the mechanical properties and failure mode of GPC with low error, which have potential application prospects in building safety assessment.

Pollutants abatement in aqueous solutions with geopolymer catalysts: A photo fenton case

Environmental pollution is a serious threat to human health and the natural environment, and it has aroused widespread concern. One of the most effective processes in the removal of pollutants from wastewater is the Fenton reaction. This process is based on the production of highly reactive •OH radicals due to the rapid reaction between Iron ions and hydrogen peroxide under acidic conditions.The hydroxyl radical has a high oxidation potential of E°(•OH/H2O) = 2.8 V/SHE at acidic pH, so they are extremely reactive and non-selective oxidizing agent towards organic contaminants in wastewater.In order to avoid the drawbacks of a standard Fenton reaction, a photo Fenton reaction has been tested working at neutral pH in water in the removal of refractory pollutants. For the first time, a heterogeneous system was experimented, impregnating porous metakaolin-based geopolymers, obtained by using hydrogen peroxide and vegetable oil in different ratios, as foaming agents, with iron working as photocatalyst. The dirty wastewater as scrubber water (SCRW) and liquid fraction of digestate (LFD) were tested obtaining 40–90% abatement of Total Carbon Content.

Metakaolin-based geopolymer as an alternative binder in semi-insulating refractories

Semi-insulating refractories are recognized for their capability to minimize thermal losses and potentially save energy. Encouraging the advancement of cement-free compositions, cold-setting binders like geopolymers have emerged as captivating alternatives. This study focused on evaluating the incorporation of a metakaolin-based geopolymer binder in semi-insulating fused silica-containing castables. As reference materials, calcium aluminate cement (CAC)-bonded compositions with and without polymeric microspheres were also investigated. Three refractory castables were processed, and the prepared samples underwent characterization, including mechanical strength, apparent density and porosity, thermal shock resistance, thermal conductivity measurements, and SEM analysis. The geopolymer-bonded castable presented improved performance, exhibiting a thermal conductivity of 0.735 W/m.K at 800 °C, flexural strength of 6.24 MPa and apparent density of 1.68 g/cm3 after firing at 815 °C. The results underscore that utilizing geopolymer as a replacement for CAC enabled the design of a semi-insulating castable with enhanced properties and without the need for using porogenic agents.

Design optimization and performance evaluation of metakaolin-based geopolymer filled porous (semi-flexible) asphalt mixture

This study was conducted to enhance the mixture design proportions and performance of metakaolin based geopolymer (MKG) filled porous asphalt concrete (MKGAC) mixture. The optimum dosage contents of various admixtures, namely fly ash, fine sand, expansion agent, and coupling agent, were determined based on the laboratory evaluation of the mechanical, shrinkage, and fluidity properties of the modified MKG. Additionally, scanning electron microscope (SEM), energy spectra, X-ray diffraction (XRD), and surface free energy measurements were also conducted to characterize the morphological structure and interfacial bonding of the basic (unmodified) and modified MKGAC. In the study, the solid content of the basic MKG was varied within a range of 26%–32%, with 30% determined as the optimum content for maximizing workability and performance characteristics, namely fluidity, shrinkage resistance, low-temperature cracking resistance, moisture resistance, high-temperature stability, and fatigue-crack resistance potential. Based on the high-temperature stability, fatigue, low-temperature cracking, and moisture resistance evaluations, 30% fly ash, 40% fine sand, 6% HCSA expansive agent, and 1.25% KH550 coupling agent were recommended as the optimum admixture contents for modifying and maximizing the performance of MKGAC. The SEM, energy spectra, and XRD analyses, on the other hand, showed that the microstructure and morphological compositions of the geopolymer (MKG) were uniformly consistent after modification with the admixtures. Lastly, it was also quantitatively observed that the interfacial energy between the geopolymer and asphalt-binder matrix increased after adding the admixtures, indicating an enhancement in the adhesive bond strength between the geopolymer (MKG) and the asphalt-binder matrix.

Thickness, Adhesion and Microscopic Analysis of the Surface Structure of Single-Layer and Multi-Layer Metakaolin-Based Geopolymer Coatings

This work is focused on creating coating layers made of a metakaolin-based geopolymer suspensions (GP)-formed Al matrix modified using H3PO4 acid with Al(OH)3 in isopropyl alcohol, named GP suspension I, and H3PO4 acid with nano Al2O3 in isopropyl alcohol, named GP suspension J. The selected GP suspensions were applied on aluminum and steel underlying substrates as single-layer coatings and multi-layer coatings, where multi-layer coatings included three and five layers that were polymerized by a curing process. Curing was divided into two types with every layer curing process and final layer curing process. For both GP suspensions I and J, the effect of the number of layers and the type of substrate on adhesion was investigated. The prepared samples on underlying substrates were characterized on the microscopy analysis including SEM for high-resolution images and 3D laser confocal microscopy (CLSM) for the 3D visualization of the coatings structure. Microscopy analysis showed structural defects such as porosity, cracks and peeling, which increase with a greater number of applied layers. However, these defects were only evident on a micro scale and did not seem to be fatal for the performance of the surface stability. The EDS mapping of the prepared layer showed inhomogeneity in the distribution of elements caused by the brush application. A grid test and thickness measurement were performed to complete the microscopy analysis. The grid test confirmed a very high adhesion of GP coatings on the aluminum substrate with a rating of one (only in one case was there a rating of two) and a lower adhesion on the steel substrate with the most frequent rating of three (in one case, there were ratings of two and one). The thickness measurement proved a noticeably thicker thickness of the prepared layer on the Fe substrate compared to the Al substrate by 20%–30% in the case of suspension I and by 70%–10% in the case of suspension J. The thickness of the layer also showed a dependence on the method of application and curing, as a thicker layer was always achieved when curing after the final layer of the GP suspension, compared to curing after each applied layer. The resulting single-layer and multi-layer thicknesses ranged from approx. 7 to 30 µm for suspension I and from approx. 3 to 11 µm for suspension J. A non-linear increase in thickness was also evident from the thickness measurement data.

Effect of aluminosilicate precursors and curing regime on physico-mechanical durability and microstructural characteristics of coral geopolymers (Cor-Geo): Cleaner production for coral islands

This study investigated the mechanical, durability, microstructure, carbon footprint and cost characteristics of new-generation metakaolin-based geopolymer composites. Instead of GBFS, 25 % metakaolin was used, and 25 % and 50 % coral fine aggregate (CFA) was used instead of coral filler (FC). The produced coral geopolymers were cured at 30 °C (24 h) and 80 °C (8 h). The apparent porosities of coral geopolymers cured in the ambient cured range from 7.3 to 9.2 %, and those heat cured vary between 3.8 and 6.2 %. The immersion water absorption of the ambient cured coral geopolymers exceeded 5 %, while the water absorption of the heat-cured specimens was much lower than 5 %. The dry unit weights of coral geopolymer are between 2100–2200 kg/m3. In ambient cured coral geopolymers, compression strength up to 40 MPa was obtained after 24 h, while compression strength of almost 100 MPa was obtained after 8 h of heat curing. The ambient cured capillary water absorption of the mix with 50 % CFA was 3.5 kg/m2, while the capillary water absorption of the specimen without CFA and heat cured was less than 0.5 kg/m2. Exposed to 750 °C, the compression strength of all coral geopolymers was more than 10 MPa. The compression strength of the samples exposed to MgSO4 decreased by 10–60 %. The CO2 emissions of coral geopolymers range between 328 and 340 kgCO2/kg, and their costs between 411 and 442 USD/m3. As a result, it has been determined that geopolymer composites can be used for both prefabricated and construction sites in coral islands with coral aggregates.

Influence of partial substitution of metakaolin by palm oil fuel ash and alumina waste ash on compressive strength and microstructure in metakaolin-based geopolymer mortar

Geopolymer is recognized as an alternate binder that compounds silica-rich and alumina-rich materials as raw materials and is produced by alkaline activation. In general, biomass ashes in particular for palm oil fuel ash (POFA) is an ideal starting material on the grounds of its high silica concentration, while industrial by-products, especially alumina waste (AW) is also employed as starting material due to its high alumina content. The objective of this research is to address the effects on the compressive strength and also the microstructure of metakaolin-based geopolymer mortar studied through the adaptability of the substitution of metakaolin (MK) by POFA and AW. In order to investigate the effects of POFA and AW substitution on the polymerization reaction and its outcomes, metakaolin-based geopolymers were produced. The most recent data suggests that POFA and AW probably serve as feedstocks for geopolymers with a little strength reduction. The partial substitution of MK by POFA reduces the polymerization reaction rate while maintaining the same water/binder ratio. However, because of the long-lasting polymerization reaction, it is still obtainable to reach a significant degree of polymerization reaction and also provides a comparable 28-day curing age compressive strength for 20 % replacement of MK by POFA. Considering 10 % substitution of POFA by AW, it results in 22.08 % improvement in the compressive strength after 28 curing days. On top of that, the compressive strength development of the geopolymer sample was investigated using scanning electron microscopy and energy dispersive x-ray spectroscopy (SEM/EDS), x-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR). It was discovered that the density and the compressive strength were induced by the particle morphologies, the surface area of POFA and AW, and the chemical composition as a result of the geopolymerization.

Comparative study of metakaolin-based geopolymer characteristics utilizing different dosages of water glass in the activator solution

Geopolymers gained attention from researchers due to their durability and potential to replace materials based on Portland cement. They offer a promising and eco-friendly alternative as binders in the construction industry. This study goal is to investigate the effects of varying dosages of sodium silicate (water glass) and sodium hydroxide in activator solutions, as well as the impact of different curing temperatures, on metakaolin-based geopolymer binder. Kaolin was heated to 750 °C for 3hr to produce metakaolin, and activator solutions were prepared with various amounts of water glass (0, 25, 50, 75, and 100) wt%. The fresh geopolymer binder was cured at two temperatures: 60 °C and 75 °C for one day. After a curing period of 28 days, various properties such as microstructural characteristics (examined through SEM), chemical bonding (analyzed using FTIR), chemical compositions (analyzed XRD), thermal conductivity and bulk density, volumetric shrinkage, and efflorescence were determined. Compressive measurements were conducted at early stages (7, 14, and 28 days) to assess mechanical properties, revealing a significant increase in mechanical strength. The geopolymer sample with 50 wt% of water glass cured at 60 °C exhibited optimal characteristics, including a higher compressive strength of 16.3 MPa and minimal efflorescence. This composition achieved an appropriate Si/Al ratio of 1.85, resulting from the formation of gel products through the reaction of compact structures. When the water glass content exceeded 50 wt%, the higher Si/Al ratio led to the deposition of the Al–Si phase, slowing down the interaction between the metakaolin powder and the alkaline activator. Regarding the influence of curing temperature, the average compressive strength of the geopolymer binder cured at 60 °C was greater as compared to the binder cured at 75 °C. Moisture loss and porosity increased with higher curing temperatures. The geopolymer binders exhibit a thermal conductivity value range (0.09–0.39)W/m.k.

An Investigation of the Strength Properties of Fly Ash and Metakaolin-Based Geopolymer Mortars Containing Multi-Wall Carbon Nanotube, Nano Silica, and Nano Zinc

In this study, the mechanical properties of geopolymer mortar composites containing different nanomaterials were investigated. Metakaolin (MK) and fly ash (FA) were used as binders in geopolymer mortar samples. Sodium silicate (Na2SiO3) and sodium hydroxide (NaOH) solution (12 M) were used as alkali activators. Multi-walled carbon nanotube (MW-CNT), nano-SiO2 (NS), and nano-ZnO (NZ) were used in the study. Geopolymer mortar samples without nanomaterials were determined as control samples, and geopolymer mortar samples containing 0.5% by weight of MW-CNT, NS, and NZ were prepared. All prepared samples were cured at 20±2 °C laboratory conditions for 7 days and 28 days. The curing geopolymer mortar samples were carried out with compressive strength and flexural strength tests. As a result of this study, the mechanical strength of all geopolymer mortar samples containing nanomaterials increased compared to the control samples. The highest compressive strength and flexural strength were obtained from geopolymer mortar samples containing MW-CNT. These samples were followed by geopolymer mortar samples containing NS and NZ, respectively.

Effect of carbonation curing on the physical, mechanical, and microstructural properties of metakaolin-based geopolymer concrete

Carbonation curing can absorb CO2 and fix it as a carbonate mineral in cementitious materials. Carbonation curing in Portland cement-based materials has been widely discussed in the literature, unlike carbonation curing in geopolymers. Therefore, the objective of this article was to evaluate the effect of carbonation curing on the physical, mechanical, and microstructural properties of metakaolin-based geopolymer concrete. Changes in pH value, carbonation depth, CO2 absorption, compressive strength, and microstructure formation were determined before and after carbonation curing. The results showed that the carbonation depth of Portland cement concrete is similar to the carbonation depth of geopolymer concrete. Furthermore, compressive strength after post-conditioning was not affected by carbonation curing, remaining statistically equal to reference concrete. Also, the formation of carbonates (Na2CO3 and CaCO3) refined the pore structure and increased closed pores, reducing the void ratio and the water absorption (permeability properties). A hybrid system containing N-A-S-(H) gel and carbonate crystals was identified.