Geopolymer Samples Research Articles

Characterization and performance evaluation of laterite based geopolymer binder cured at different temperatures

This paper presents the results of experimental evaluation of curing conditions on the microstructure and performance of geopolymer binders developed from iron-rich laterite soils. Two calcined iron-rich laterites namely LB600 and LY600 were used as solid precursors in the preparation of geopolymer binders. The geopolymer samples were cured at 20, 60 and 80 °C. FTIR, XRD, EDS and DTA/TG were used to evaluate the microstructural properties of the prepared products. The performance of the binder was evaluated in terms of the compressive strengths, water absorption, porosity, bulk density and thermal conductivity. The findings from this study showed that the dissolution of the calcined laterites in 8 M NaOH increased the dissolution of Al, Si and Fe elements with increasing temperature from 20 to 80 °C. This higher dissolution of the monomers further resulted to an increase in the compressive strength of the binders at 7 and 28 days. It was also found out that curing the geopolymer in the dry state resulted in higher compressive strength at all ages compared to those cured in the wet and wet-dry state. Drying shrinkage evaluation of the geopolymer samples cured between 60 and 80 °C exhibited a lower linear shrinkage due to a high degree of geopolymerization. Microstructural investigation of the geopolymer samples cured at 80 °C showed a heterogeneous compact and dense structure resulting from high polycondensation. This densified microstructure also induced an increase in the thermal conductivity from 0.65 to 0.90 W/mK and 0.75 to 0.91 W/mK for LB600 and LY600, respectively. Nonetheless, both geopolymer binders made of LB600 and LY600 laterite powders performed well in dry, wet and wet-dry conditions, and can be used for various construction applications especially in the precast industry.

Microstructure and Composition of Red Mud-Fly Ash-Based Geopolymers Incorporating Carbide Slag

In order to solve the problem of the recycling utilization about an industry waste solid-red mud, a kind of geopolymer material system based on red mud-fly ash-carbide slag has been developed. The microstructure and composition of the geopolymer material system at the age of 28 days was tested by the scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). It was showed that the compressive strength of the geopolymer sample was 15.1 MPa when the liquid solid ratio (L/S) was 0.7, sand-binder ratio was 3:1, alkaline activator used carbide slag, and the fly ash, red mud and carbide slag were prepared as the proportion of 4:3:3. Through SEM-EDS and XRD results, the spherical beads in fly ash were dissolved in the alkaline environment to form silicon and aluminum monomers. Carbide slag played the roles of calcium component support in C-A-S-H, C-S-H gels and alkaline activator.

Resistance of fiber-reinforced fly ash-steel slag based geopolymer mortar to sulfate attack and drying-wetting cycles

Fly ash-steel slag based geopolymer mortar was studied for recycling solid wastes and developing a sustainable alternative to Ordinary Portland Cement (OPC). The fiber-reinforced geopolymer mortar was prepared from the main raw materials of fly ash, steel slag, and fibers. This paper studies the mechanical properties, mass loss rates and appearance of fiber-reinforced geopolymer under double-factor coupling, i.e. sulfate corrosion and drying-wetting cycle process on the geopolymer samples. The results show that the compressive strength and flexural strength of each sample gradually increase and tend to be stable under double-factor coupling. After 15 cycles, the compressive strength of the SF-4 (mixed with 0.4 vol% steel fiber) is still the highest, which is 67.9 MPa, and the compressive strength of the BF-3 (mixed with 0.3 vol% basalt fiber) increases the most, whose growth rate is 96.6%. Due to the evaporation of water and diffusion of sodium sulfate between samples and solution, the change of mass loss rate of samples was unstable. The white precipitate was observed on the surface of samples, and it was sodium sulfate by X-ray diffraction (XRD) analysis. Both stable and dense structures of samples and fiber-bridged matrix function make fiber-reinforced geopolymer mortar present excellent performance in resistance to double-factor coupling corrosion.

Effect of kaolin and argillite mixtures on the dielectric properties of geopolymers

The use of geopolymer in radiofrequency applications and more precisely in antenna is innovative. The objective of this study is to highlight the impact of mixtures of kaolin and argillite on the structure and dielectric properties of geopolymers for antenna application. For this, six geopolymer formulations based on mixtures of kaolin and argillite with different proportions (33, 50 and 67%) and calcined at 600 and 750 ​°C were studied using mercury intrusion porosimetry, dielectric measurements and NMR spectroscopy. Low porosity values were obtained whatever the mixture. At 600 ​°C, the porosity increases with the increase of argillite content from 18 to 23%. At 750 ​°C, no impact of argillite content on the porosity (16%) was detected. However, the pore size increases with increasing the argillite content regardless of the calcination temperatures due to the unreacted secondary phases present in argillite. MAS-NMR experiments on geopolymer samples and calcined mixtures have evidenced a strong correlation between reactive aluminum resulting from dehydroxylation of kaolin and clay minerals of argillite and the geopolymerization rate. These structural variations influence the dielectric properties. Indeed, ε and tan ​δ values increase with the increase of argillite content and calcination temperature due to the increase in the number of moles of free alkali earth cations (Ca2+ and Mg2+).

Rottenstone as a basis for obtaining geopolymer material

The possibility of obtaining perspective geopolymer materials for use in the building industry was shown. Geopolymer materials are used with such advantages as high strength, density, water resistance, heat and heat resistance, environmental friendliness, durability, and high corrosion resistance. The raw material is rottenstone, a rock with a high silica content, which is widespread in Ukraine. Rottenstone is characterized by a ratio of SiО2:Al2O3 equal to 16… 20, which provides a high strength of the final material. It was indicated that physico-chemical processes that take place during polymerization are similar to those that take place in thin pellicles of the released SiO2 gel, cements the particles, and thus promotes hardening. As a result of the treatment of raw materials with alkali solution at temperatures of 80-120 °С, a monolithic solid material of olive color with a density of 1200-1700 kg/m3, humidity of 30-45% was formed. Precipitations were observed on the surface of the material due to the presence of non-chemically bound sodium and potassium cations in the pores of the geopolymer. When dried, they diffuse to the surface of the geopolymer and are subjected to atmospheric carbonization. It was indicated that in order to obtain a high-strength geopolymer material, it is necessary to carry out final heat treatment at temperatures close to 100 °С. The behavior of geopolymer samples aged over time at room temperature during their heating was investigated. The samples of the material are melted due to the presence of Na2O×SiО2×8Н2O and Na2O×SiО2×5Н2O crystal hydrates, which melt at relatively low temperatures at 48°С and 72°С, respectively. The formation of building geopolymer materials should take into account this melting by placing it in molds was concluded. Indicators of moisture loss at a temperature of about 100°С depending on the heat treatment time were obtained.

Influence of various factors on properties of geopolymer paste: A comparative study

AbstractA comprehensive experimental study was conducted to investigate effect of different production parameters such as activator type, activator concentration and curing temperature on fresh and hardened properties of volcanic tuff based geopolymer paste (GP) samples. Volcanic tuff obtained from Nevşehir (Central Anatolia, Turkey) was ground to particle size less than 45 μm, after that alkali activation process was provided with two type of alkali activators such as NaOH and NaOH+Na2SiO3 (SH and SH + SS) solutions. Produced geopolymer samples were cured at different temperatures ranging from 23 to 150°C. Compressive strength, setting time, hydration heat of GP samples were investigated. Additionally, microstructural investigations were performed with SEM and XRD analyzes. As a result of modification of experimental parameters, compressive strength development reached to 41.43 MPa was obtained from GP samples, which did not harden in laboratory conditions. It was also determined that the alkali activation of volcanic tuff with SH exhibited better mechanical and microstructural properties than alkali activation with SH + SS.

Use of fly and bottom ashes from a thermoelectrical plant in the synthesis of geopolymers: Evaluation of reaction efficiency

The use of by-products as raw materials in the manufacturing of industrial products has risen in the last years because of environmental considerations. One example is the use of coal ashes from thermal-electrical plants in the production of geopolymer -- a green cement made by mixing aluminosilicate with alkaline activator. In this study, fly and bottom ashes from a thermal-electrical unit were used as sources of aluminosilicate in the synthesis of geopolymers. A mixture of sodium hydroxide (10 mol/L) and sodium silicate (SiO2/Na2O ratio of 2.2) was used as the alkaline activator. The type (fly or bottom ash) and content of the ash were the variables in the synthesis. The ashes were characterized by X-ray fluorescence (XRF), X-ray diffraction (DRX), particle size distribution (PSD), specific surface area (BET), and thermal analysis (DTA/TGA). The ash-based geopolymer samples were measured to obtain their compressive strength after curing. The evolution of the geopolymerization process was also assessed based on final alkali concentration measurements. The results show that it is possible to obtain geopolymers using coal ashes as raw materials with high solid content. The compressive strength for the bottom ash geopolymer after 90 days of curing is 35 MPa. The low concentration of unreacted alkalis after curing (1.5× 10-3 – 3.5 × 10-3 M) corresponds to high efficiency of the geopolymerization reaction.

Laterite clay-based geopolymer as a potential adsorbent for the heavy metals removal from aqueous solutions

This study is focused on the investigation of low iron lateritic clay-based geopolymer as a potential adsorbent for the higher uptake of Ni(II) and Co(II) ions from aqueous solutions. BET analysis revealed that the sieved geopolymer sample (SGS) was characterized by 17.441 m2/g of surface area, 0.005 cm3/g of pore volume, and 13.549 Å of pore diameter. SEM investigation confirmed the presence of pores and cavities onto the surface of SGS. XRD analysis showed that the geopolymer is semi-crystalline in nature. It was found that the adsorption ability of SGS remained 520 mg/g for Ni(II) ions and 500 mg/g for Co(II) ions when 0.5 M solutions were stirred with SGS for 60 min. The temperature and pH of the solution were maintained at 60 °C and 7.0, respectively. The adsorption data of both heavy metal (HM) ions fitted best in the pseudo-second-order kinetic model. The low activation energy value i.e. 2.507 kJ/mol for Ni(II) ions and 2.286 kJ/mol for Co(II) ions confirmed adsorption is physisorption. Adsorption data were tested with Langmuir and Freundlich models, the data showed comparatively better fitting in the Freundlich model. The greater value of monolayer adsorption capacity (Xm) for Ni(II) ions was found 1.77 × 10−2 mol/g while for Co(II) ions it remained 1.69 × 10−2 mol/g confirming the better interaction of metal ions with the adsorbent surface. Negative values of ΔG° confirmed the spontaneity of the process while the positive value of ΔS° showed the randomness of adsorbate particles. The positive value of ΔH° showed that the adsorption process remained endothermic for both HM ions. The experimental results confirmed the ability of laterite clay-based geopolymer for better removal of HM ions and hence can be employed for the wastewater treatment processes at low-cost adsorbent.

EPS İle İkame Edilmiş Uçucu Küllü Geopolimer Hafif Harcın Fiziksel, Mekanik ve Isıl Geçirimlilik Özelliklerinin İncelenmesi

Bu çalışmada genleştirilmiş polistiren (EPS) kullanılarak uçucu kül tabanlı geopolimer hafif harçlar imal edilmiştir. EPS hacimce %20, %40, %60, %80, %100 oranlarında ırmak kumu ile yer değiştirerek, EPS agregalı geopolimer harçların üretimi gerçekleştirilmiştir. EPS’li geopolimer harçlar, F sınıfı uçucu külün sabit oranda NaOH ile aktive edilmesiyle, 75 °C’de 24 ve 48 saat sıcaklık kürüne tabii tutulmuştur. Sıcaklık kürü sonrası geopolimer hafif harç numunelerin fiziksel özellikleri, mekanik özellikleri ve ısıl geçirimlilik özellikleri araştırılmıştır. Ayrıca 300 °C, 600 °C, 900 °C’de yüksek sıcaklık sonrası geopolimer harçların eğilme, basınç dayanımları ve geopolimer hamurların mikro yapısı incelenmiştir. Elde edilen sonuçlara göre 24 saat sıcaklık kürüne tabii tutulan hafif geopolimer harçların birim ağırlıkları 1,93 ile 0,61 g/cm3 arasında, 48 saat sıcaklık kürüne tabii tutulan hafif geopolimer harçların birim ağırlıkları 1,87 ile 0,66 g/cm3 arasında olduğu görülmüştür. Yüksek sıcaklık sonrası %20 ve %40 EPS ikameli (EUK 20, EUK40) geopolimer harçların basınç dayanımındaki kayıp oranları, referans geopolimer numuneye göre daha az olduğu belirlenmiştir. FESEM görüntülerinde yüksek sıcaklık sonrası dayanım kaybına yol açan gözenekli yapı ve mevcut dayanımı devam ettiren NASH jeli yapısı görüntülenmiştir. Birim ağırlık ile basınç dayanımı (R2=0,9008), ısı geçirgenlik katsayısı (R2=0,9787), ultrasonik geçiş hızı (R2=0,9082), ve yarmada çekme dayanımı (R2=0,9191) arasında yüksek oranda doğrusal ilişki olduğu sonucuna ulaşılmıştır.

Online measurement of the atmosphere around geopolymers under gamma irradiation

ABSTRACT The gas production of wasteforms is a major safety concern for encapsulating active nuclear wastes. For geopolymers and cements, the H2 produced by radiolytic processes is a key factor because of the large amount of water present in their porous structure. Herein, the gas composition evolution around geopolymers was monitored online under 60Co gamma irradiation. The transient evolution of the hydrogen release yield was measured for samples with different formulations. Its evolution and the final values are consistent with the presence of a pseudo-first-order chemical reaction consuming hydrogen in the samples. The results show that this phenomenon can significantly reduce the hydrogen source term of geopolymer wasteform provided their diffusion coefficient remains low. Lower hydrogen production rates and faster kinetics were observed with geopolymer formulations in which pore water pH was higher. Besides hydrogen release, a steady oxygen consumption was observed for all geopolymer samples. The oxygen consumption rates are proportional to the diffusion coefficients estimated in the modelization of hydrogen recombination by a pseudo-first-order reaction.

Microstructural characteristics of geopolymer materials with twenty eight days of curing and after eight years stored at room temperature

The main purpose of this study was to perform a microstructural evaluation in geopolymer samples with 28 days of curing (GP28D) and after 8 years of storage (GP8Y). The knowledge on the microstructure of geopolymers in the long run is crucial for the use of these materials, given their great potential applicability. Equally important is the use of industrial waste as raw materials for the manufacture of new materials. In this perspective, this study employed two industrial wastes to produce the samples: bottom ash from mineral coal (BA) and residues from white paper recycling industries. The latter was treated to use the kaolin present in composition. The treatment of the paper waste was carried out by burning the cellulose. Then, the resulting material was subjected to chemical reaction in hydrochloric acid (HCl) to separate the CaCO3 from kaolin. In addition to kaolin, calcium chloride (CaCl2) and water were also obtained as reaction products. The kaolin obtained from the paper residue was dehydroxylated at a temperature of approximately 850 °C for 2 h to obtain processed metakaolin (PMK). To obtain the geopolymer samples, BA/PMK proportions of 2:1 were activated with NaOH solutions of 5, 10 and 15 M mixed with sodium silicate. After the synthesis, the samples were cured for 28 days and subjected to analysis. Then they were stored for more eight years and again underwent microstructural analysis. The results of the analyzes showed significant changes in the microstructure of the materials with 28 days of cure and after eight years. The micrographs obtained in SEM showed a denser structure and the micrographs obtained in TEM showed that the amorphous structure was partially replaced by a crystalline structure. The samples aged for eight years did not show significantly higher mechanical resistance in relation to the samples analyzed with 28 days of cure. It is important to highlight that the results did not show microstructural degradation after eight years.

The influence of activator type and quantity on the transport properties of class F fly ash geopolymer

It is known that transport properties of porous materials were important in terms of its durability aspect. In this paper, the effect of activator type, Na amount on the transport properties of geopolymer mortar made with class F fly ash were explored. Two different class F fly ash were employed in producing geopolymer that activated alkaline solutions. As alkali activator, sodium hydroxide solution, and combination of sodium silicate with sodium hydroxide were used. Activator contained 6%, 9%, 12% and 15% of fly ash weight as Na amount. Heat curing regimes were imposed to specimens at 100 °C temperature for 24 h duration. Tests were carried out on the geopolymer samples including water absorption, volume of permeable voids, sorptivity, depth of penetration of water under pressure, chloride ion penetration and accelerated corrosion. It is found that the transport properties of geopolymer samples are improved by increasing the Na amounts of mortar mixtures from 6% to 15%. In general, better results were obtained with 15% Na ratio. The mortars produced with only sodium hydroxide have shown better transport properties than mortars made with combination of sodium hydroxide-sodium silicate mixture.

The effect of temperature, time of curing and Na2O/SiO2 molar ratio on mechanical and chemical properties of geopolymer cement

The geopolymer cement is a suitable alternative material for Portland cement due to their environmental compatibility, low curing temperature, and high strength. In this research, Kaolin was used as a raw material for the construction of a geopolymer cement, while sodium hydroxide was an alkali hydroxide. Kaolin is calcined at 750 °C to obtain meta-kaolin. Geopolymer samples were prepared at various curing temperatures (25, 50, and 75 °C), different curing times (3, 7, 21, 28, and 60 days) and with different activator ratios (0.6-0.9). The thermal analysis of kaolin was done via DTA/TGA. Investigation on the geopolymer cement structure and phases were performed using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and magic angle spinning nuclear magnetic resonance (MAS-NMR). Also, the effects of temperature and time of curing and Na2O/SiO2 molar ratio were studied. The results showed that the maximum compressive strength was 115MPa, which obtained at a molar ratio of Na2O/SiO2=0.9, a curing time of 60 days, and a curing temperature of 75°C. The microstructure of cement was studied using scanning electron microscopy (SEM).

A survey on one year strength performance of reinforced geopolymer composites

Heat curing is a widely used method in geopolymer mortar production. While the heat curing shows an increase in strength values, the effect of this situation in the long term has not been examined sufficiently. In this study, the short-term and long-term effects of the curing conditions were examined together and a geopolymer sample with 90% metakaolin and 10% colemanite waste (by weight) was used. Also, polyolefin and polyamide fibers were used as 0.5%, 1.0%, and 1.5%, by volume. A wetting–drying method was applied for curing with heat curing. The Si-O-Al bonds were established to be stronger with wetting–drying curing. 14, 56, 90, and 365 days’ flexural and compressive strengths results were determined. Also, the high-temperature test was applied after 365 days. SEM, TGA-DTA, and FTIR analyses were carried out pre and post the high-temperature test. When a comparison was done between the 14-day and the 90-day results, the 90-day results showed a reduction of strength according to 14-days. At the end of 365 days, these reductions fell and results were obtained close to 90 days of strength. The use of high-temperatures for curing was thought to contribute to the development of early-age strength by supporting the dissolution of solid binding materials and the formation of reaction products. On the other hand, due to the adverse effects on the quality and microstructure of the rapidly developing reaction products, strength decreases have been observed. Despite all these effects, the structure of the geopolymer has been preserved.

Comparison of mechanical behaviour of geopolymer and OPC-based well cement cured in saline water

Well cement plays a vital role in maintaining wellbore integrity in a carbon capture and storage project. To date, ordinary Portland cement (OPC)-based well cement has been used and there are contrasting research findings on its suitability as well cement. This research aims to use geopolymer as well cement, and major aim of this work is to analyse the mechanical behaviour of both geopolymer and OPC subjected to various down-hole conditions including different salinity (0–30% NaCl) and confinements (0–15 MPa). This research comprises experimental and numerical works. Under the experimental work, series of unconfined compressive strength (UCS) test were conducted for geopolymer and OPC samples cured in saline water with 0–30% NaCl salinity for a period of 45 days. COMSOL multiphysics software was used for the numerical study, and first, laboratory scale uniaxial stress–strain behaviour of both geopolymer and OPC was validated numerically. The model was then extended to study the triaxial mechanical behaviour under different salinity (0–30% NaCl) and confining pressures (0–15 MPa) conditions. Based on the results, it was noticed that UCS of geopolymer increases with salinity due to the high resistance against alkali leaching in saline water compared to fresh water. The UCS of OPC increases with salinity up to 10% NaCl, and then it reduces with any further increase in salinity. The UCS of geopolymer is 6% to 66% higher than that of OPC depending on the salinity conditions and geopolymer possesses higher UCS than OPC for any given salinity condition. COMSOL multiphysics numerical software predicted the stress–strain behaviour of geopolymer and OPC accurately up to yield point. Failure strength of geopolymer in saline water is 3% to 61% higher than that of OPC for a given confining pressure. Findings of this research indicate that geopolymer can be a good alternative for OPC based well cement under deep down-hole conditions.

Chemical, physical and radiological evaluation of raw materials and geopolymers for building applications

The main goal of this study was the evaluation of physical–chemical, as well as radiological properties of residual materials used for geopolymer synthesis and those final products as a possible application as new materials in a civil engineering industry. Concentration of 40K and radionuclides from the 238U and 232Th decay series in waste precursors, their metaphases and geopolymer samples synthetized by alkali activation were determined together with corresponding absorbed dose rate ( $$\dot{D}$$ ) and the annual effective dose rate. Natural activity concentrations in the alkali-activated material (geopolymer) were found to be lower than that of both residual materials and calcined ones.

Influence of the thermal treatment on the characteristics of porous geopolymers as potential biomaterials.

Highly porous sodium geopolymer structures were successfully produced through the chemical direct foaming approach at ambient temperature. The impact of the thermal treatment, as well as the influence of various additions of hydrogen peroxide, as a foaming agent, on the porosity, microstructure and mechanical characteristics of the produced geopolymers was investigated. The evaluation of bioactivity was carried out by assessing the formation of an apatite layer on the samples' surface, using scanning electronic microscopy and inductively coupled plasma spectrometry for the simulated body fluid solution, in which the geopolymer samples were kept up to 28days. In addition, the biodegradability was estimated through the weight change of the samples and pH-measurements. The results demonstrated that the geopolymer foams, produced using 4.5vol% H2O2 and heat-treated at 500°C for 1h, possessed a high open porosity (71 vol %), excellent compressive strength (3.56±0.27MPa), and suitable chemical stability. The pH value of SBF solutions, in which these geopolymers were immersed for 28days, remained close to the physiological one. The in vitro study indicated that the developed geopolymer foams possessed bioactivity, as demonstrated by the formation of apatite particles on their surface after immersion in the simulated body fluid solution for 28days.

Durability analysis of eggshell powder–flyash geopolymer composite subjected to wetting–drying cycles

PurposeThe purpose of this study is to investigate the effect of various heat conditions on the durability of eggshell powder (ESP)–flyash (FA) geopolymer subjected to wetting–drying cycles.Design/methodology/approachIn this study, two waste materials, ESP and FA, which are destined for landfills, were used as precursors to produce geopolymers in a sustainable manner. The mixture of Na2SiO3and NaOH was used as a liquid alkaline activator in geopolymerization. The ESP and FA content were varied as 30, 50 and 70% and Na2SiO3/NaOH ratios were varied as 0.5, 1 and 2. Geopolymer samples were cured at three heat conditions: 25°C (ambient temperature), 50°C and 80°C for seven days prior to durability tests.FindingsThe results of this study revealed that the strength loss of the geopolymer decreases with an increase in curing temperature up to 50°C and then increases for higher temperature up to 80°C. Further, the strength loss of the geopolymer decreases with an increase in FA replacement and Na2SiO3/NaOH ratio. Geopolymer composites exhibited early strength development because of the inclusion of calcium-rich ESP. The weight loss of the ESP–FA geopolymer follows a similar pattern of strength loss. Geopolymer samples previously cured at optimum heat condition of 50°C for seven days exhibited higher durability.Originality/valueThe inclusion of calcium-rich ESP in FA-based geopolymer is novel research. As ESP–FA geopolymer composites show higher mechanical strength and higher durability compared to Indian standards, the potential use of this geopolymer can be in road subbases/subgrades.

Characteristics of a Fly Ash-Based Geopolymer Cured in Microwave Oven

Geopolymer is known as an alkaline alumino-silicate material that has many potential advantages to replace for cement-based materials. Geopolymer is a green material with low or non-CO2 emission technology, high strength and heat resistance, high chemical resistance, and low energy production. Geopolymer has synthesized from activated alumino-silicate resources in high alkaline conditions. After formed, the geopolymer samples are cured in different conditions such as room temperature, drying oven temperature (from 40°C to 150°C), high pressure and temperature conditions of autoclave equipment. In this study, the paper would like to introduce a new technique for curing the specimens. The geopolymer samples were cured in a microwave oven set by various regimes of curing time. After cured in microwave conditions, the samples were tested for engineering properties such as compressive strength (MPa), volumetric weight (kg/m3), and water absorption (kg/m3). This technology is a useful solution because of saving time for curing the geopolymer specimens in comparison with others (normally, it takes time for curing in 28 days). Microstructural characteristics of the fly ash-based geopolymer were analyzed and evaluated using scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR).

Produção de geopolímeros utilizando cinza da casca de arroz como fonte complementar de sílica

Resumo O silicato de sódio é a fonte complementar utilizada na reação de geopolimerização. Entretanto, esse reagente é produzido em alta temperatura ou em autoclave a alta pressão, o que gera muito impacto ambiental. Visando a produção de geopolímeros mais ecológicos, produziu-se um silicato de sódio alternativo (ASW) a partir da dissolução da sílica presente na cinza de casca de arroz (CCA). Foram preparados geopolímeros nas razões molares SiO2/Al2O3 de 3,0, 3,5 e 4,0 e com concentrações de NaOH de 8 e 10 M. Os corpos de prova foram submetidos a ensaios de resistência à compressão (7 e 28 dias), FTIR e DRX. O desempenho mecânico dos geopolímeros produzidos com ASW foi semelhante aos produzidos com silicato de sódio comercial. A análise do comportamento mecânico e dos espectros de infravermelho sugeriu que ocorreu maior dissolução da CCA com o aumento da relação molar SiO2/Al2O3 e da concentração do álcali.