Mechanical and chemical properties of metakaolin-based geopolymer exposed to elevated temperature

A method is presented to fabricate metakaolin-based geopolymers that are structurally and mechanically stable up to 600°C. The chemical environment of the geopolymers is characterized using thermogravimetric analysis and Fourier-transform infrared spectroscopy. Residual free water turned into steam and caused damage to the geopolymer when exposed to elevated temperatures. The curing temperature was increased from 80 to 120°C to remove water during the curing process. A correlation was drawn between the amount of Si-O-Al linkage formed and the position of fingerprint peaks in infrared spectra, providing a tool to evaluate the level of geopolymerization. Flexural and tensile properties of geopolymers fabricated using the optimized method were measured for no heat treatment and for exposure to elevated temperatures of 200, 400, and 600°C. The flexural strength was measured to be 10.80 ± 2.99 MPa at room temperature, 10.36 ± 0.64 MPa at 400°C, and 8.04 ± 1.60 MPa at 600°C. The flexural modulus is reported to be 13.09 ± 3.40 GPa at room temperature and 11.03 ± 0.53 GPa at 600°C. The flexural toughness decreased with increasing temperature. The tensile properties of the geopolymer were measured with direct tensile tests paired with an extensometer. The tensile strength decreased from 4.16 ± 2.08 MPa at room temperature to 3.13 ± 0.97 MPa at 400°C, and 2.75 ± 0.86 MPa at 600°C. The Young's modulus decreased from 45.38 ± 30.30 GPa at room temperature to 26.88 ± 6.65 GPa at 600°C. Both flexural and tensile tests have shown that the metakaolin-based geopolymers cured at 120°C is mechanically stable at temperatures up to 600°C.     

Properties of Geopolymer Composites Reinforced with Basalt Chopped Strand Mat or Woven Fabric

Geopolymers or polysialates are inorganic polymeric, ceramic‐like materials composed of alumina, silica, and alkali metal oxides that can be made without any thermal treatment. Additions of reinforcing phases vastly improve the mechanical properties and high‐temperature stability of the geopolymer. The processing and mechanical properties of both chopped strand mat as well as 2‐D woven fabric‐reinforced potassium geopolymer composites have been evaluated. Hand lay‐up and hydraulic press processing methods were used to produce composite panels. The room‐temperature tensile and flexural strength of chopped strand mat composites was 21.0 ± 3.1 and 31.7 ± 4.4 MPa, respectively, while those of basalt weave‐reinforced geopolymer composites reached 40.0 ± 5.9 and 45.2 ± 9.3 MPa, respectively. Composite microstructures were examined using optical microscopy as well as scanning electron microscopy (SEM). Mass, volume, and porosity fractions were also determined. The effect of high‐temperature treatments at 25°C, 300°C, 600°C, and 800°C were analyzed. Finally, Weibull statistical analysis was performed, which showed an increase in reliability when a reinforcement phase was added to K‐geopolymer.     

Assessment of recycling use of GFRP powder as replacement of fly ash in geopolymer paste and concrete at ambient and high temperatures

Environmental issues caused by glass fiber reinforced polymer (GFRP) waste have attracted much attention. The development of cost-effective recycling and reuse methods for GFRP composite wastes is therefore essential. In this study, the formulation of the GFRP waste powder replacement was set at 20–40 wt%. The geopolymer was formed by mixing GFRP powder, fly ash (FA), steel slag (SS) and ordinary Portland cement (OPC) with a sodium-based alkali activator. The effects of GFRP powder content, activator concentration, liquid to solid (L/S) ratio, and activator solution modulus on the physico-mechanical properties of geopolymer mixtures were identified. Based on the 28-day compressive strength, the optimal combination of the geopolymer mixture was determined to be 30 wt% GFRP powder content, an activator concentration of 85%, L/S of 0.65, and an activator solution modulus of 1.3. The ratios of compressive strength to flexural strength of the GFRP powder/FA-based geopolymers were considerably lower than those of the FA/steel slag-based geopolymers, which indicates that the incorporation of GFRP powder improved the geopolymer brittleness. The incorporation of 30% GFRP powder in geopolymer concrete to replace FA can enhance the compressive and flexural strengths of geopolymer concrete by 28%. After exposure to 600 °C, the flexural strength loss for geopolymer concretes containing 30 wt% GFRP powder was less than that of specimens without GFRP powder. After exposure to 900 °C, the compressive strength and flexural strength losses of geopolymer concretes containing 30 wt% GFRP powder were similar to those of specimens without GFRP powder. The developed GFRP powder/FA-based geopolymers exhibited comparable or superior physico-mechanical properties to those of the FA-based geopolymers, and thus offer a high application potential as building construction material.     

Potassium‐Based Geopolymer Composites Reinforced with Chopped Bamboo Fibers

Bamboo is a fast‐growing, readily available natural material with tensile specific strength equivalent to that of steel (250–625 MPa/g/cm³). In the pursuit of sustainable construction materials, a composite was made with potassium polysialate siloxo geopolymer as the matrix and randomly oriented chopped bamboo fibers (Guadua angustifolia) from the Amazon region as the reinforcement. Four‐point flexural strength testing of the geopolymer composite reinforced with bamboo fibers was carried out according to ASTM standard C78/C78M‐10^e1. Potassium‐based metakaolin geopolymer reinforced with 5 wt% (8 vol%) untreated bamboo fibers yielded 7.5 MPa four‐point flexural strength. Scanning electron microscopy and optical microscopy were used to investigate the microstructure. In addition, X‐ray diffraction was used to confirm the formation of geopolymer.     

Effect of nano silica and fine silica sand on compressive strength of sodium and potassium activators synthesised fly ash geopolymer at elevated temperatures

Environment friendly geopolymer is a new binder which gained increased popularity due to its better mechanical properties, durability, chemical resistance, and fire resistance. This paper presents the effect of nano silica and fine silica sand on residual compressive strength of sodium and potassium based activators synthesised fly ash geopolymer at elevated temperatures. Six different series of both sodium and potassium activators synthesised geopolymer were cast using partial replacement of fly ash with 1%, 2%, and 4% nano silica and 5%, 10%, and 20% fine silica sand. The samples were heated at 200°C, 400°C, 600°C, and 800°C at a heating rate 5°C per minute, and the residual compressive strength, volumetric shrinkage, mass loss, and cracking behaviour of each series of samples are also measured in this paper. Results show that, among 3 different NS contents, the 2% nano silica by wt. exhibited the highest residual compressive strength at all temperatures in both sodium and potassium‐based activators synthetised geopolymer. The measured mass loss and volumetric shrinkage are also lowest in both geopolymers containing 2% nano silica among all nano silica contents. Results also show that although the unexposed compressive strength of potassium‐based geopolymer containing nano silica is lower than its sodium‐based counterpart, the rate of increase of residual compressive strength exposed to elevated temperatures up to 400°C of potassium‐based geopolymer containing nano silica is much higher. It is also observed that the measured residual compressive strengths of potassium based geopolymer containing nano silica exposed at all temperatures up to 800°C are higher than unexposed compressive strength, which was not the case in its sodium‐based counterpart. However, in the case of geopolymer containing fine silica sand, an opposite phenomenon is observed, and 10% fine silica sand is found to be the optimum content with some deviations. Quantitative X‐ray diffraction analysis also shows higher amorphous content in both geopolymers containing nano silica at elevated temperatures than those containing fine silica sand.     

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%.     

The influence of alkaline treatment on the mechanical performance of geopolymer composites reinforced with Brazilian malva and curaua fibers

Lignocellulosic fibers obtained from the curaua (Ananas erectifolius) and malva (Malva sylvestris) plants in Brazil can be used as suitable reinforcements for geopolymers (GPs) owing to their high strength, ready regional availability, and low cost. In this work, the tensile and flexural strengths of untreated and NaOH alkali-treated curaua and malva fiber-reinforced GP composites were measured according to ASTM standards. Curaua reinforced GP composites had an average tensile strength of 25.7 (±) 7.1 MPa and flexural strength of 18.9 (±) 4.72 MPa. Malva GP composites withstood 19.18 (±) 9.0 MPa in tension and 31.5 (±) 7.6 MPa in flexure. Additionally, pullout tests were performed to investigate the debonding mechanisms for both fibers, with and without alkaline treatment, finding increases in chemical bonding for the treated samples due to roughness enhancements through fiber surface modifications with alkali treatment. Thermogravimetric analysis and X-ray diffraction were used to characterize the physical fiber modifications after alkali treatment, evidencing lignin and hemicellulose removals. Scanning electron microscopy and energy-dispersive X-ray spectroscopy were used to further examine the fiber–matrix interaction, with proofs of interfacial tailoring.     

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.     

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-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.     

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.     

Sustainable activation of pumice with partially variable substitutions of metakaolin and/or fumed silica

Sustainable alkali activation of pumice from Turkish origin was studied by a partial replacement of metakaolin and/or fumed silica additives. Following the characterization of as-received pumice by X-ray fluorescence spectroscopy, x-ray diffraction, and nuclear magnetic resonance spectroscopy, a series of powder mixtures were prepared by introducing metakaolin and/or fumed silica (8, 14, and 20 M) into 1 M of the pumice. The mixtures were then dissolved in 11 M NaOH or sodium silicate solutions. The slurries were poured into polyacetal molds to obtain geopolymer samples for mechanical testing and cured in a constant 50°C temperature in a humidity oven for 48 h and then left for 1 week to undergo additional curing at ambient temperature. The microstructural, mechanical, and thermal properties of the final geopolymer samples were determined by XRD, scanning electron microscopy, Weibull analysis of 3-point flexural and compressive tests and thermal conductivity measurements. Results showed that all the Weibull values were best for 14 M of metakaolin and/or fumed silica. The metakaolin-added pumice yielded higher compressive strengths of (53.78 ± 33.30 MPa) than fumed silica (10.87 ± 4.04 MPa) and fumed silica plus metakaolin (41.22 ± 5.16 MPa). Thermal conductivities (0.19–0.46 Wm^–1K^–1) were also comparable to the thermal conductivity of metakaolin-based geopolymers.     

Synthesis and characterization of melt‐processable polyimides derived from 1,4‐bis(4‐amino‐2‐trifluoromethylphenoxy)benzene

A series of molecular‐weight‐controlled imide resins end‐capped with phenylethynyl groups were prepared through the polycondensation of a mixture of 1,4‐bis(4‐amino‐2‐trifluoromethylphenoxy)benzene and 1,3‐bis(4‐aminophenoxy)benzene with 4,4′‐oxydiphthalic anhydride in the presence of 4‐phenylethynylphthalic anhydride as an end‐capping agent. The effects of the resin chemical structures and molecular weights on their melt processability and thermal properties were systematically investigated. The experimental results demonstrated that the molecular‐weight‐controlled imide resins exhibited not only meltability and melt stability but also low melt viscosity and high fluidability at temperatures lower than 280°C. The molecular‐weight‐controlled imide resins could be thermally cured at 371°C to yield thermoset polyimides by polymer chain extension and crosslinking. The neat thermoset polyimides showed excellent thermal stability, with an initial thermal decomposition temperature of more than 500°C and high glass‐transition temperatures greater than 290°C, and good mechanical properties, with flexural strengths in the range of 140.1–163.6 MPa, flexural moduli of 3.0–3.6 GPa, tensile strengths of 60.7–93.8 MPa, and elongations at break as high as 14.7%. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Experimental Investigation of Mechanical and Morphological Properties of Flax-Glass Fiber Reinforced Hybrid Composite using Finite Element Analysis

The use of cellulosic fibers as reinforcing materials in polymer composites has gained popularity due to an increasing trend for developing sustainable materials. In the present experimental study, flax and glass fiber reinforced partially eco-friendly hybrid composites are fabricated with two different fiber orientations of 0° and 90°. The mechanical properties of these composites such as tensile, flexural and impact strengths have been evaluated. From the experiments, it has been observed that the composites with the 0° fiber orientation can hold the maximum tensile strength of 82.71 MPa, flexural strength of 143.99 MPa, and impact strength of 4 kJ/m². Whereas the composites with 90° fiber orientation can withstand the maximum tensile strength of 75.64 MPa, flexural strength of 134.86 MPa, and impact strength of 3.99 kJ/m². Morphological analysis is carried out to analyze fiber matrix interfaces and the structure of the fractured surfaces by using scanning electron microscopy (SEM). The finite element analysis (FEA) has been carried out to predict the resulting important mechanical properties by using ANSYS 12.0. From the results it is found that the experimental results are very close to the results predicted from FEA model values. It is suggested that these hybrid composites can be used as alternate materials for pure synthetic fiber reinforced polymer composite materials.     

Thin fly ash/ ladle furnace slag geopolymer: Effect of elevated temperature exposure on flexural properties and morphological characteristics

The flexural properties and thermal performance of 10 mm-thin geopolymers made from fly ash and ladle furnace slag were evaluated before and after exposure to elevated temperatures (300 °C, 600 °C, 900 °C, 1100 °C and 1150 °C). Class F fly ash was mixed with liquid sodium silicate (Na₂SiO₃) and 12 M sodium hydroxide (NaOH) solution using aluminosilicate/activator ratio of 1:2.5 and Na₂SiO₃/NaOH ratio of 1:4 to synthesise thin fly ash (FA) geopolymers. 40 wt% of ladle furnace slag was partially replacing fly ash to produce fly ash/slag-based (FAS) geopolymers. Thermal treatment enhanced the flexural strength of thin geopolymers. In comparison to the unexposed specimen, the flexural strength of FA geopolymers at 1150 °C and FAS geopolymers 1100 °C was increased by 161.3% to 16.2 MPa and 208.9% to 24.1 MPa, respectively. A more uniform heating was achieved in thin geopolymers which favoured the phase transformation at high temperatures and contributed to the substantial increase in flexural strength. The joint effect of elevated temperature exposure and the incorporation of ladle furnace slag further improved the flexural strength of thin geopolymers. The calcium-rich slag refined the pore structure and increased the crystallinity of thin geopolymers which aided in high strength development.     

Mechanical and microstructural evolutions of fly ash/slag-based geopolymer at high temperatures: Effect of curing conditions

Designing a building material with excellent heat resistance is crucial for protection against catastrophic fires. Geopolymer materials have been investigated as they offer better heat resistance than traditional cement owing to their ceramic-like properties. Curing temperature and conditions are crucial factors that determine the properties of geopolymers, but their impacts on the heat resistance of geopolymers remain unclear. This study produced geopolymers from fly ash and ground granulated blast furnace slag by using sodium silicate and sodium hydroxide solutions as alkaline solutions. To examine the effect of curing conditions on the high-temperature performance of geopolymer, four different curing conditions, namely, heat curing (70 °C for 24 h), ambient curing (20 °C), water curing, and the combination of heat and water curing (70 °C for 24 h followed by water curing), were applied. At 28 d, the specimens were subjected to high temperatures (500 °C, 750 °C, and 950 °C), and their mechanical and microstructural evolutions were studied. The results revealed that the curing condition significantly affects the properties of the unexposed geopolymer; the effect on its high-temperature performance is insignificant. Furthermore, all the specimens could maintain adequate compressive strength after exposure to the maximum temperature of 950 °C, promising the use of geopolymer for structural applications.     

Study of poly(trimethylene terephthalate) as an engineering thermoplastics material

Poly(trimethylene terephthalate) (PTT) was systematically studied as an engineering thermoplastics material. Crystallization rates, crystalline degrees, and mechanical properties of two commercial PTT polymers and one glass fiber–reinforced PTT compound were investigated and compared with those of poly(butylene terephthalate) (PBT). PTT raw polymers have crystallization temperature (T_c) values around 152°C, and their kneaded polymers show T_c values of about 177°C, about 15°C lower than the values of PBT polymers used in this study. From the exothermic heat values of DSC measurements, both PTT and PBT show the crystalline degree order greater than 30%. Injection‐molded PTT specimens and PBT specimens exhibit crystalline degrees from 18 to 32% and 23.8 to 30%, respectively. PTT polymers show higher tensile and flexural strengths, but lower impact strengths and elongations than those of PBT polymers. The low elongation behavior of PTT does not change with the intrinsic viscosity and the molder temperature. PTT‐GF30 promotes better mechanical properties than those of PBT‐GF30, close to those of PET‐GF30. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1657–1666, 2004     

Strength of single-phase high-entropy carbide ceramics up to 2300°C

The mechanical properties of single-phase (Hf,Zr,Ti,Ta,Nb)C high-entropy carbide (HEC) ceramics were investigated. Ceramics with relative density >99% and an average grain size of 0.9 ± 0.3 µm were produced by a two-step process that involved carbothermal reduction at 1600°C and hot pressing at 1900°C. At room temperature, Vickers hardness was 25.0 ± 1.0 GPa at a load of 4.9 N, Young's modulus was 450 GPa, chevron notch fracture toughness was 3.5 ± 0.3 MPa·m^1/2, and four-point flexural strength was 421 ± 27 MPa. With increasing temperature, flexural strength stayed above ~400 MPa up to 1800°C, then decreased nearly linearly to 318 ± 21 MPa at 2000°C and to 93 ± 10 MPa at 2300°C. No significant changes in relative density or average grain size were noted after testing at elevated temperatures. The degradation of flexural strength above 1800°C was attributed to a decrease in dislocation density that was accompanied by an increase in dislocation motion. These are the first reported flexural strengths of HEC ceramics at elevated temperatures.     

Mechanical properties of natural fiber hybrid composites based on renewable thermoset resins derived from soybean oil,for use in technical applications

Natural fiber composites are known to have lower mechanical properties than glass or carbon fiber reinforced composites. The hybrid natural fiber composites prepared in this study have relatively good mechanical properties. Different combinations of woven and non‐woven flax fibers were used. The stacking sequence of the fibers was in different orientations, such as 0°, +45°, and 90°. The composites manufactured had good mechanical properties. A tensile strength of about 119 MPa and Young's modulus of about 14 GPa was achieved, with flexural strength and modulus of about 201 MPa and 24 GPa, respectively. For the purposes of comparison, composites were made with a combination of woven fabrics and glass fibers. One ply of a glass fiber mat was sandwiched in the mid‐plane and this increased the tensile strength considerably to 168 MPa. Dynamic mechanical analysis was performed in order to determine the storage and loss modulus and the glass transition temperature of the composites. Microstructural analysis was done with scanning electron microscopy. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

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.