Fully reacted high strength geopolymer made with diatomite as a fumed silica alternative

Geopolymers are formed by mixing of aluminosilicate sources with alkaline meta-silicate solution at room temperature. In the current study, diatomite of Turkish origin was fully utilized as a fumed silica alternative for the preparation of geopolymer, having a typical formula of K₂O•Al₂O₃•4SiO₂•11H₂O. From XRD of this sample, a broad peak centered at 28° 2θ indicated the well-known formation of amorphous geopolymer, as well as a fully reacted microstructure of geopolymer as seen by scanning electron microscopy. Additionally, geopolymer having the same formula was made by using fumed silica, in order to compare with geopolymers prepared from diatomite. The Weibull modulus was calculated from four-point bending and compressive strength testing of both geopolymer composites. The use of diatomite as a fumed silica substitute in geopolymer production resulted in a very close flexure strength 9.2 (± 4.2 MPa) when compared to geopolymer made from fumed silica 10.2 (± 3.3 MPa). There was a significantly higher compressive strength 71 (± 13.9 MPa) and Weibull modulus (5.4), than comparable properties of geopolymer made from fumed silica, which had a compressive strength 54 (± 25.8 MPa) and Weibull modulus of 2.0. The discrepancy was attributed to some self-reinforcement of the geopolymer matrix due to unreacted diatomite.     

Bone ash reinforced geopolymer composites

Potassium-based, geopolymer composites were made with BASF^® metakaolin and Mymensingh clay-derived metakaolin from Bangladesh. Since the natural Mymensingh clay contained 40 wt.% quartz, this same amount of quartz particulates was added to the BASF^® metakaolin to make a synthetic analog of the natural calcined clay. By analogy with bone china, bone ash or calcined hydroxyapatite (5CaO•3P₂O₅ or “HA”) particles, having a Ca: P ratio of 3.3:1, were added to make the three types of geopolymer-based composites described above. For less refractory particulate additions, dicalcium phosphate (DCP) (2CaO•P₂O₅ or “DCP”) particles, having a Ca: P ratio of 2:1, were also added to another set of geopolymers. The ambient temperature compressive and flexural strengths were measured for all of the geopolymer composites. The HA or DCP reinforced geopolymer composites were fabricated and heat-treated to 1150°C/1 h, after which they were converted to their mineralogical analogs. Their mechanical properties of compressive and 3-point flexural strengths were again measured. Flexural strengths of 22.42 ± 11.0 MPa and 31.97 ± 8.3 MPa were measured in 1 × 1 × 10 cm³ heat-treated geopolymer bars reinforced with 10 wt.% of DCP and in geopolymer reinforced with 10 wt.% DCP +40 wt.% quartz additions, respectively. Significant improvements to ambient temperature properties were observed due to the self-healing effect of the flowing amorphous DCP, whose presence was verified by SEM. The geopolymer samples exhibited reduced water absorption (WA) (on a percentage dry weight basis) of within 0.03-0.5% after being heated at 1100℃/1 h and 1125℃/1 h, as compared with those at room temperature, which varied between 2.56% and 7.89%.     

Preparation of one-part geopolymeric precursors using vanadium tailing by thermal activation

The main purpose of this study is to develop a user-friendly one-part geopolymer using vanadium tailing (VT). Geopolymeric precursor consists of activated VT and metakaolin that can react directly with water to form geopolymers. The roasting temperature plays an important role in the VT activation, which affects the compressive strength of the final geopolymer. The geopolymer with accepted compressive strength, that is 29.0 MPa after 7 days curing in ambient condition, can be prepared using VT after thermal activation at appropriate temperature (400-600°C). As the roasting temperature is increased to 700°C, the VT is molten and sintered and the ability of providing alkaline and Si⁴⁺ is drastically weakened, which results in a poor compressive strength geopolymer.     

Sodium silicate activated slag‐fly ash binders: Part I – Processing,microstructure, and mechanical properties

Alkali silicate activated slag and class F fly ash‐based binders are ambient curing, structural materials that are feasible replacements for ordinary Portland cement (OPC). They exhibit advantageous mechanical properties and less environmental impact than OPC. In this work, five sodium silicate activated slag‐fly ash binder mixtures were developed and their compressive and flexural strengths were studied as a function of curing temperature and time. It was found that the strongest mixture sets at ambient temperature and had a Weibull average flexural strength of 5.7 ± 1.5 MPa and Weibull average compressive strength of 60 ± 8 MPa at 28 days. While increasing the slag/fly ash ratio accelerated the strength development, the cure time was decreased due to the formation of calcium silicate hydrate (C–S–H), calcium aluminum silicate hydrate (C–A–S–H), and (Ca,Na) based geopolymer. The density, microstructure, and phase evolution of ambient‐cured, heat‐cured, and heat‐treated binders were studied using pycnometry, scanning electron microscopy, energy dispersive X‐ray spectroscopy (SEM‐EDS), and X‐ray diffraction (XRD). Heat‐cured binders were more dense than ambient‐cured binder. No new crystalline phases evolved through 28 days in ambient‐ or heat‐cured binders.     

Amorphous self-glazed,chopped basalt fiber reinforced,geopolymer-based composites

Geopolymer composites reinforced with refractory, chopped basalt fibers, and low melting glass were fabricated and heat treated at higher temperatures. K₂O·Al₂O₃·4SiO₂·11H₂O was the stoichiometric composition of the potassium-based geopolymer which was produced from water glass (fumed silica, deionized water, potassium hydroxide), and metakaolin. Addition of low melting glass (T_m ~815°C) increased the flexure strength of the composites to ~5 MPa after heat treatment above 1000°C to 1200°C. A Weibull statistical analysis was performed exhibiting how the amorphous self-healing and self-glazing effect of the glass frit significantly improved the flexure strength of the geopolymer and ceramic composites after exposure for 1 hour to high temperatures. At 950-1000°C, the K-based geopolymer converted to primarily a crystalline leucite ceramic, but the basalt fiber remained intact, and the melted glass frit flowed out of the surface cracks and sealed them. 1150℃ was determined to be the optimum heat treatment temperature, as at ≤1200°C, the basalt fibers melt and the strength of the reinforcement in the composites is significantly reduced. The amorphous self-healing and amorphous self-glazing effects of the glass frit significantly improved the room temperature flexure strength of the heat-treated geopolymer and ceramic composites.     

Synthesis of volcanic ash-based geopolymer mortars by fusion method: Effects of adding metakaolin to fused volcanic ash

The present study aimed at improving the properties of geopolymer mortars obtained from volcanic ash as a source material. An alkali fusion process was used to promote the dissolution of Si and Al species from the volcanic ash and thus to enhance the reactivity of volcanic ash. Various amount of metakaolin (30%, 40%, 50% and 60% MK by weight) was used to consume the excess alkali needed for the fusion. The amount of amorphous phase was determined both in the volcanic ash and the fused volcanic ash and X-ray diffraction analysis was used to evaluate effect of the alkaline fusion method. Geopolymers were prepared by alkali activation of mixtures of powders of fused volcanic ash, various amount of metakaolin and river sand using a sodium silicate solution as activator. The geopolymer mortars were characterized by determination of setting time, linear shrinkage, scanning electron microscopy and compressive strength. The results of this study indicate that geopolymer mortars synthesized by the fusion method exhibit low setting time (7–15 min), low shrinkage (0–0.42%) and high compressive strength (41.5–68.8 MPa). This study showed that, by enhancing the reactivity of volcanic ash by alkali fusion and balancing the Na/Al ratio through the addition of metakaolin, all volcanic ashes can be recycled as an alternative source material for the production of geopolymers.     

Facile synthesis of phenolic-reinforced silica aerogel composites for thermal insulation under thermal-force coupling conditions

The objective of this research was to develop a reinforced silica aerogel composites with enhanced thermal insulation performance under thermal-force coupling conditions. Phenolic-reinforced silica aerogel composites (RAs) were synthesized via a sol-immersion-gel process based on the in-situ polymerization of resorcinol (R), formaldehyde (F), and triaminopropyltriethoxysilane (APTES). Ambient pressure drying (APD) was used to dry the gels. Samples with different carbon/silica ratios, RA12, RA13, and RA14, were synthesized by controlling the R/APTES molar ratio at 1/2, 1/3, and 1/4. The densities of the RA12, RA13 and RA14 samples were 0.32 ± 0.005, 0.34 ± 0.006, and 0.37 ± 0.003 g/cm³. The thermal conductivity of the RA12, RA13, and RA14 samples were 0.024, 0.026, and 0.027 W/(m·K). The existence of the phenolic network favored the mechanical strength of the RAs, RA14 showed compressive strength, tensile strength, and three-point bending strength of 4.3 MPa at 20% strain, 2.4 MPa, and 8.4 MPa at 1.45% strain. The RAs showed excellent thermal insulation performance on a customized apparatus, the back temperature was as low as 219.82 °C and 330.67 °C within 60 min in the environments of 600 °C −0.01 MPa and 600 °C −0.9 MPa. The excellent thermal-shock performance of RAs was also demonstrated under flame exposure from a butane torch, with a temperature difference of 878 °C within 30 min being reported. The excellent thermal insulation performance of RAs under thermal-force coupling conditions reveals a widespread application perspective in the field of new energy vehicles power battery thermal protection.     

Mechanical characterization of lightweight engineered geopolymer composites exposed to elevated temperatures

In this study, the effect of different factors, such as PVA fibers (2% by total volume) and precursor type (slag, fly ash, or a combination of both), on the behavior of green lightweight engineered geopolymer composites (LEGC) and lightweight engineered cementitious composites (LECC) after exposure to temperatures up to 800 °C for 1 h is investigated. Expanded glass granules were used as lightweight aggregate instead of silica sand to reduce the spalling tendency and density of the composite. The flowability, density, color change, mass loss, spalling resistance, residual mechanical properties (compressive strength, stress-strain diagram, tensile stress-strain diagram, load-deflection response, failure mode), and microstructural analysis (by scanning electron microscopy) were investigated before and after exposure to thermal deterioration. The findings pointed out that the dry density, compressive strength, fiber bridging stress, strain capacity, maximum load, and maximum deflection of the developed mixtures before exposure to fire deterioration were in the range of 1703–1883 kg/m³, 16.66–64.11 MPa, 2.66–4.97 MPa, 2.40–3.33%, 1573–4824 N, and 2.92–5.53 mm respectively. It's worth mentioning that the substitution of 50% slag in the lightweight EGC mixture demonstrated the optimal tensile strain capacity and deformation capacity and further enhanced both ultimate tensile strength and flexural strength of fly ash-based EGC (FA-EGC) mixtures. After heat exposure, both LEGC and LECC composites demonstrated strain hardening behavior and deflection hardening behavior up to 300 °C of heat treatment, while after exposure to a temperature of 300 °C and above, both deflection hardening behavior and strain hardening behavior are dramatically damaged. This is attributable to the melting of the PVA fibers. Also, the microstructural analysis showed that incorporating fly ash into lightweight EGC mixtures can effectively reduce the melting point of PVA fibers and further improve the fire resistance of EGC mixtures.     

Mechanical and microstructural analysis of geopolymer composites based on metakaolin and recycled silica

This paper evaluated mechanical and thermal stability of alkali-activated materials obtained from metakaolin and alternative silica sources, such as rice husk ash (RHA) and silica fume (SF), and were reinforced with recycled ceramic particles (RP) obtained by grinding bricks. Specimens were produced, and after 7 days of curing, they were exposed to temperatures between 300 and 1200°C to determine the influence that different percentages of RP had on the mechanical behavior and microstructure of the produced composites. The results showed a reduction in the linear contraction by 10.22% with 20 wt% RP and that the reinforcing materials improved the mechanical performance of the geopolymers after exposure to high temperatures; the compressive strengths reached 137.7 (±11.4)  MPa after being exposed to 1200°C for the matrix based on RHA and 180.6 (±19.15) MPa after being reinforced with 20 wt% RP. The improvement was mainly due to densification and the formation of crystalline products such as leucite, kalsilite, and mullite.     

Mechanical and acoustic absorption properties of lightweight fly ash/slag-based geopolymer concrete with various aggregates

Acoustic absorption and thermal insulation play a key role in modern buildings to make living comfortable and energy-saving. This paper aims to study the workability, physical and mechanical properties, thermal conductivity, and acoustic absorption of modified geopolymer concrete (GPC) with various types of lightweight aggregates (LWA) such as extruded polystyrene foam beads waste (EPS), vermiculite, or lightweight expanded clay aggregate (LECA). The mixtures of geopolymer concrete have been modified by substituting for the ordinary aggregates (dolomite) by volume with various ratios of 0, 25, 50, 75, and 100% for each type of LWA. Besides, the mechanisms of specimens were examined by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and mapping. The results illustrated that the compressive strength values range between 8.5 and 47.50 MPa. The hardened density of concrete was between 1500 and 2450 kg/m³, and thermal conductivity was between 0.45 and 1.16 W/m.K. Geopolymer concrete was considered an acoustic absorption and thermally insulating material. Geopolymer concrete was considered an acoustic absorption and thermally insulating material. EPS, vermiculite, and LECA will be beneficial for applications in lightweight geopolymer concrete due to their capability to reduce weight and excellent thermal conductivity, and the property of improving acoustic absorption. The mechanical results indicated that 25% LECA was the best compared with the ratios of other LWA and gained 35.0, 2.7, and 4.3 MPa of compressive, splitting tensile and flexural strength, respectively. It had positive workability; the thermal conductivity was 1.1 W/m.K, and hardened density was decreased to 10% compared to the control. In addition, LECA is considered the superior and suitable material for acoustic absorption compared with other aggregates.     

Production of nepheline/quartz ceramics from geopolymer mortars

This research has investigated the mechanical properties and microstructure of metakaolin derived geopolymer mortars containing 50% by weight of silica sand, after exposure to temperatures up to 1200 °C. The compressive strength, porosity and microstructure of the geopolymer mortar samples were not significantly affected by temperatures up to 800 °C. Nepheline (NaAlSiO₄) and carnegieite (NaAlSiO₄) form at 900 °C in the geopolymer phase and after exposure to 1000 °C the mortar samples were transformed into polycrystalline nepheline/quartz ceramics with relatively high compressive strength (～275 MPa) and high Vickers hardness (～350 HV). Between 1000 and 1200 °C the samples soften with gas evolution causing the formation of closed porosity that reduced sample density and limited the mechanical properties.     

Immobilization of strontium-loaded zeolite A by metakaolin based-geopolymer

Zeolites are the preferred inorganic ion exchange materials for purifying radioactive waste liquid. Radionuclide-loaded zeolites, which are considered to be radioactive waste, are strictly required to be encapsulated within a solid matrix. In this paper, we investigate the feasibility of immobilizing exhausted zeolite A, loaded with ⁹⁰Sr radionuclide, in metakaolin based-geopolymer. The geopolymer solidification blocks had better mechanical performance and leaching resistance in deionized water, sulfuric acid, magnesium sulfuric and acetic acid buffer solutions than the cemented blocks. While the compressive strength of the geopolymer solidification product was 37.62 MPa after curing for 28 days, the equivalent value for the cement block was only 11.32 MPa. The geopolymer solidification blocks also exhibited even lower compressive strength loss after high-temperature and freeze-thaw cycles tests. XRD and EDS analysis indicated that most of the strontium radionuclide in the geopolymer solidification blocks was incorporated in the zeolite structure as the charge balancing cation. The microscopic analysis revealed that geopolymer matrix appeared more compact and dense, and encapsulated the Sr-loaded zeolite A more tightly than did the cement. Therefore, it could be concluded that metakaolin based-geopolymer are more compatible with exhausted zeolite A and present a remarkable advantage for radioactive waste immobilization.     

Lightweight porous silica ceramics with ultra-low thermal conductivity and enhanced compressive strength

In recent years, the need for robust thermal protection for reusable spacecraft and vehicles has spurred strong demand for high-performance lightweight thermal insulation materials that exhibit high strength. Herein, we report silica porous ceramics prepared via the direct foaming technique with lightweight, ultra-low thermal conductivity and enhanced compressive strength. Silica particles (particle size: 500 nm and 2 μm) were used as the raw materials. The nano-sized silica particles were easily sintered, thereby improving the compressive strength of the ceramics, whereas the micro-sized silica particles maintained the pore structure integrity without deformation. The addition of nano-silica enhanced the compressive strength by 764% (from 0.039 to 0.337 MPa). In addition, the thermal conductivity of the ceramics was as low as 0.039 W m^?1 K^?1. Owing to these outstanding characteristics, these porous silica ceramics are expected to be employed as thermal insulation material in diverse fields, especially aerospace and space where weight is an important constraint.     

Reaction kinetics and mechanical properties of a mineral-micropowder/metakaolin-based geopolymer

In this study, metakaolin was partially replaced with mineral micropowder to prepare a mineral-micropowder/metakaolin-based geopolymer was prepared under alkali activation, and the compressive and flexural strengths of various geopolymer specimens were determined. Geopolymer reaction kinetics were examined using the Johnson-Mehl-Avrami-Kolmogrov model, and the effects of the mineral-micropowder content on the properties and structure of the metakaolin-based geopolymer were investigated. Results revealed that micropowder addition significantly influenced the mechanical properties, microstructure, and reaction heat of the geopolymer. At a powder content of 30 wt%, the polymer exhibited superior mechanical properties; furthermore, the compressive and flexural strengths of the specimens cured for 28 d were 58.3 MPa and 12.6 MPa, which were 24.1% and 40% higher than those of the control group, respectively. Meanwhile, the geopolymer setting time was significantly reduced because the presence of calcium in mineral micropowder promoted the geopolymerisation reaction. Therefore, the formation of a multi-gel phase considerably enhanced the geopolymer structure.     

Developing a hollow glass microsphere/geopolymer thermal insulation composite for hot metal surface coating

Manufacturing inorganic thermal insulation materials with superior properties such as low thermal conductivity (k < 0.1 W/mK) and high mechanical properties in terms of adhesion strength is critical for energy efficiency in energy-intense industries. Geopolymer-based composites composing of hollow glass microspheres (HGMs), waste fly ash (FA), and metakaolin (MK) were successfully applied on hot (T～300 °C) metal surfaces via spray deposition technique. The effect of Si/Al and Na/Al mole ratios and HGM loading on geopolymer composites' physical, microstructural, thermal, and adhesion strength properties were explored. The best composite composition was obtained when Si/Al mole ratio, Na/Al mole ratio, and HGM loading were 2.5, 1.0, and 10 wt %, respectively. This composition achieved an HGM/geopolymer composite material with low thermal conductivity (k ～ 0.05 W/mK), high adhesion strength (～5.0 MPa), and high stability under immersion in water and vibration environments (particularly exposed to water). The results showed that HGM/geopolymer composites could be used as a thermal insulation material in energy-intense industries.     

Novel thermal insulating and lightweight composites from metakaolin geopolymer and polystyrene particles

In this work, new foamed thermal insulation geopolymer composite based on polystyrene particles (PP) and metakaolin was developed. Compressive strength, flexural strength, high temperature resistance and microstructure were evaluated. The experimental results show that compressivestrengthand flexural strength of the thermal insulation geopolymer composite decrease with increasing polystyrene particle content. However, it still exhibits considerable and sufficient strength. The dry density and thermal conductivityalso decrease as polystyrene particle content increases due to the contribution of polystyrene particles with low density. The floatation of the thermal insulation geopolymer composite on water surface indicates the relatively low density and a good quadratic function relationship can be found between thermal conductivity and dry density. Furthermore, the dense interfacial transition zone indicates the high compressive strength and flexural strength of thermal insulation geopolymer composites. The cumulative intrusion volume corresponding to the porosity decreases and the critical pore diametersshift to lower values with addition of polystyrene particles. Geopolymer composites gain strength after exposure around 400 °C, and it suffers dramatic strength loss after 800 °C temperature exposure especially for the 100% polystyrene particles addition specimen.     

Relative importance of Al(V) and reinforcement to the flexural strength of geopolymer composites

We prepared 1 cm × 1 cm × 10 cm geopolymer bars from sodium silicate and six commercial metakaolins, both unreinforced and reinforced with 20 wt% of 55-μm wollastonite (CaO·SiO₂) needles, to evaluate the relative contributions of five-coordinated aluminum in the metakaolin and the presence of a reinforcing phase to the flexural strength of geopolymers. Two metakaolins, with about 20 at% and lower of five-coordinated aluminum content, did not react sufficiently with our processing method and could not be tested. The flexural strengths of the other four geopolymers were similar at about 11–14 MPa unreinforced and 22–29 MPa reinforced. The effect of reinforcement on flexure strength is more significant than the choice of metakaolin provided that the metakaolin is reactive. The geopolymerization reaction depends on the amount of five-coordinated aluminum present in the metakaolin and is the primary difference between the samples that reacted and those that did not react.     

Amorphous self-healed,chopped basalt fiber-reinforced,geopolymer composites

Geopolymer composites containing refractory, chopped basalt fibers and low-melting glass were made and systematically heat-treated at higher temperatures. Potassium-based geopolymer of stoichiometric composition K₂O·Al₂O₃·4SiO₂·11H₂O was produced by high shear mixing from fumed silica, deionized water, potassium hydroxide, (i.e., water glass) and metakaolin. With the addition of low-melting glass (T_m ~815°C) the flexure strengths of the composites increased to ~6 MPa after heat treatment above 900°C to 1100°C. A Weibull statistical analysis was performed showing how the amorphous self-healing effect of the glass frit significantly improved the flexure strength of the geopolymer and ceramic composites after high-temperature exposure. At temperatures up to 900°C, the geopolymer-basalt composite remained amorphous and the low-melting glass frit flowed into the dehydration cracks in the geopolymer matrix. This type of composite could be described as amorphous self-healed geopolymer (ASH-G). At ~1000°C, the geopolymer converted to primarily a crystalline leucite ceramic, but the basalt fiber remained intact, and the melted glass frit flowed and sealed the cracks developed at that temperature. This type of composite could then be described as amorphous self-healed ceramic (ASH-C). A temperature of 1150°C was determined to be optimum as at 1200°C the basalt fibers melted and the strength of the reinforcement was lost in the composites. The amorphous self-healing effect of the glass frit significantly improved the room temperature flexure strength of the heat-treated geopolymer-based composites.     

Conductivity modification of proton conducting polymer gel electrolytes containing a weak acid (<Emphasis Type="Italic">ortho</Emphasis>-hydroxy benzoic acid) with the addition of PMMA and fumed silica

Polymer gel electrolytes synthesized by dispersing nano size fumed silica in polymer gel electrolytes containing polymethylmethacrylate (PMMA), ortho-hydroxy benzoic acid (o-OHBA) and dimethylacetamide (DMA) have been studied by complex impedance spectroscopy, viscosity and pH measurements. The addition of acid, polymer and fumed silica has been found to result in an increase in conductivity and viscosity of gel electrolytes and gels with conductivity higher than the corresponding liquid electrolytes have been obtained. Nano dispersed polymer gel electrolytes show conductivity 2.95 × 10⁻⁴ S cm⁻¹ and viscosity 1.74 × 10⁴ cP at 25 °C. Two maxima observed in the variation of conductivity of nano dispersed gels with fumed silica concentration have been assigned to the enhanced dissociation of weak acid and the formation of a high conducting interfacial region between fumed silica and gel electrolyte, respectively, which has also been supported by pH and viscosity studies. The small increase in conductivity of nano dispersed gels over the 20–100 °C temperature range and its constant value with time is suitable for devices.     

Geopolymer reinforced with E‐glass leno weaves

This study explores the viability of fiberglass‐geopolymer composites as an intermediate temperature structural ceramic composite. E‐glass fibers are cheap, readily available, resistant to heat, electricity and chemical attack. Geopolymers are refractory and can be processed at room temperature. However, pure geopolymers have low tensile strength and fracture toughness, as is typical of ceramics. In this work, tensile and flexure properties of metakaolin‐based sodium and potassium geopolymers reinforced with E‐glass leno weaves were measured and the data was analyzed by Weibull statistics. The average tensile and flexural strengths for sodium geopolymer reinforced with E‐glass leno weaves were 39.3 ± 7.2 MPa and 25.6 ± 4.8 MPa, respectively. For potassium geopolymer reinforced with E‐glass leno weaves, the average tensile and flexural strengths were 40.7 ± 9.9 MPa and 15.9 ± 4.0 MPa, respectively. The composites were heat treated for one hour at two temperatures, 300°C and 550°C and their flexure properties were studied at room temperatures. The average flexural strengths for sodium geopolymer reinforced with E‐glass leno weaves were reduced to 6.6 ± 1.0 MPa after heat treatment at 300°C, and 1.2 ± 0.3 MPa after heat treatment at 550°C, respectively. For potassium geopolymer reinforced with E‐glass leno weaves, the average flexural strengths were 6.1 ± 1.5 MPa and 1.3 ± 0.3 MPa after heat treatment at 300°C and 550°C, respectively. SEM and EDS were performed to observe the fiber‐matrix interface. XRD was done to check if the geopolymer was amorphous as expected.