Geopolymer Samples Research Articles

Using coal fly ash-based geopolymer to immobilize Cd from lead fuming furnace slag

Lead fuming furnace slag (LFFS) is a by-product of lead metal production, which is a toxic solid waste according to toxicity characteristic leaching procedure (TCLP) test. It was investigated the feasibility of preparation of geopolymer using coal fly ash (CFA) and LFFS and the immobilization efficiency of Cd in geopolymer. The synthesized geopolymer samples were examined by compressive strength, Fourier transform transmission infrared spectroscopy (FTIR) spectra, X-ray diffraction (XRD) and backscattered electron (BSE) microscope. There is a certain mass ratio (2:3) of the LFFS to the CFA at which the compressive strength of the geopolymeric matrix is the highest. Leaching test shows that Cd in LFFS can be effectively immobilized in the geopolymer structure. Geopolymerization is not only a potential technological solution for reusing LFFS but also an effective immobilization method for LFFS treatment and disposal.

A comparative study on the durability of geopolymers produced with ground glass fiber, fly ash, and glass-powder in sodium sulfate solution

An experimental investigation was conducted to investigate the performance of geopolymers made with three different precursors consisting of fly ash, Ground Glass Fiber (GGF), and Glass-Powder (GLP) exposed to sodium sulfate solution. Precursors were activated using either sodium hydroxide solution or combinations of sodium hydroxide and sodium silicate solution with varying levels of sodium and silica content. Among the mixtures with each of the three precursors, mortar mixtures with the highest compressive strength were selected to test their resistance against exposure to a 5% sodium sulfate solution. Changes in the weight and compressive strength of the specimens were monitored up to 120days of exposure. In addition, change in the microstructure of geopolymer samples and mineral phases was investigated using SEM-EDX and XRD analyses, respectively. Further, techniques such as mercury intrusion porosimetry (MIP) spectrometry and inductively coupled plasma mass spectrometry (ICP-MS) were used to study the pore structure and the leachability of elements from geopolymers, respectively. Results of this study revealed that the GGF and fly ash-based geopolymers performed significantly better in comparison to the GLP-based geopolymer, when exposed to the sodium sulfate solution. The durability of GGF and Fly ash based geopolymer samples could be related to their stable alumino-silicate gel that develops upon geopolymerisation as well as the low amount of calcium oxide in the geopolymer systems. On the other hand, the poor performance of the GLP-based geopolymer could be related to the less stable geopolymerisation products which result in increased porosity, and the high amount of available alkalis present in the raw GLP.

Effect of vacuum dehydration on gel structure and properties of metakaolin-based geopolymers

Abstract In aluminosilicate mineral materials, water plays a significant role during the process of geopolymer reaction and is related closely to the development of the strength and structure. In this work, a geopolymer is synthesized via the reaction of metakaolin with alkaline silicate solutions, including water glass and a NaOH solution. This study investigated the effect of water on the gel structure and properties of metakaolin-based geopolymers. Geopolymer samples were found to fast release water under vacuum and allowed the development of low-defect porous materials. After 3 days of curing in suitable conditions, the samples were treated under vacuum, during which the compressive strength did not decrease. Under vacuum at 120 °C, the residual water of the sample produced using water glass was 8.31% and that of the sample produced using NaOH solution was only 1.08%. The results of XRD and FTIR demonstrated that the sample produced using NaOH solution consisted primarily of NaA zeolite. SEM analysis indicated that the pores in sample growed with increasing H 2 O/Na 2 O molar ratio. Additionally, vacuum dehydration can suppress the formation of micro cracks and reduce the shrinkage of the samples.

Durability of Geopolymer Mortar Based on Waste-Glass Powder and Calcium Aluminate Cement in Acid Solutions

The aim of this study is to investigate the durability of geopolymer mortars based on waste-glass powder (WGP) and calcium aluminate cement (CAC) exposed to acid attack. Geopolymer specimens were prepared by a combination of WGP and CAC activated by an aqueous solution of sodium hydroxide and sodium silicate and were cured under hydrothermal conditions. The prepared specimens were immersed in sulfuric and hydrochloric acid solutions (pH=1) for 6 months, and their residual compressive strength and several key durability parameters were assessed and compared to those of portland cement and high alumina cement mortars as control specimens. Microstructural and compositional changes in the geopolymer samples were studied using scanning electron microscopy, X-ray diffractometry (XRD), and Fourier transform infrared spectroscopy. The results showed that the acid resistance of geopolymer mortar against both acid solutions was comparable to the control mortars, as indicated by the relatively lower strength loss and lower mass change. The microstructure of the geopolymer after acid exposure, however, possessed significant microcracks in the near-surface region, leading to a higher porosity and a lower strength. XRD results revealed the formation of gypsum crystals due to the reaction between sulfuric acid and calcium from the geopolymer gel.

Effect of polyacrylic resin on mechanical properties of granulated blast furnace slag based geopolymer

The mechanical performances of alkali-activated granulated blast furnace slag (GBFS) based geopolymer modified with polyacrylic resin were investigated in this paper. The water-to-binder ratio, alkaline activator content (Na2O wt%) and SiO2/Na2O molar ratio in this experiment maintained at 0.5, 6% and 0.8, respectively. Geopolymer samples were synthesized by alkaline solution and GBFS with incorporating amount of 0.25, 0.5, 0.75, 1.0, 3.0 and 5.0wt% polyacrylic resin. The mechanical properties of samples were measured using compression tests, flexure tests and bending toughness tests. The results show that the compressive and flexural strength were both up to the maximum value while doping 1wt% polyacrylic resin, the ratio of flexural-compressive strength and bending toughness at curing 28days were increased by 36.3% and 104.6% respectively, compared with the control samples. The structural evolutions of specimen after incorporating polyacrylic resin were characterised by FTIR as well as 29Si NMR spectroscopy. It indicated that a new absorption peak namely SiOC bond at wavenumber of about 1180cm−1 in the FRIR spectra appeared while incorporating polyacrylic resin whatever 1wt% or 5wt%, the chemical shifts corresponding resonance peaks of siliceous species moved towards to low field, and the polymerization degree of Si transformed from Q3, Q4 to Q0, Q1, Q2.

Effect of Kaolinite Mass Ratio on Compressive Strength of Kaolinite-Calcite Based Geopolymer

This study focuses on the preparation of geopolymers using various proportions of kaolinite and calcite mixture, and the effects of kaolinite mass ratio to calcite on compressive strength of kaolinite/calcite-based geopolymer. Several geopolymer samples were formed using pure kaolinite, pure calcite, and various mass ratio of kaolinite to calcite to examine properties of the geopolymers. The impact of NaOH concentration on the compressive strength of the geopolymers was also examined. The results of the laboratory analyses indicate that the compressive strength of geopolymers did not increase steadily with increasing concentration of NaOH. The optimum workability of geopolymers was obtained at 10 M NaOH and 30 % kaolinite content in the mixture. Several sensitivity experiments were carried out using the parameters at cure temperatures of 22, 45, 65 and 85 o C. The best compressive strength of 12.68 MPa was obtained on the 28th day of curing process at 85 o C. The structural evolution of the geopolymers prepared was investigated using FTIR spectroscopy. They were also characterized by X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM).

An investigation of the effect of migratory type corrosion inhibitor on mechanical properties of zeolite-based novel geopolymers

The effects of migratory type corrosion inhibitor and curing time on the thermal stability and mechanical properties of Ecuadorian natural zeolite-based geopolymers were evaluated. Geopolymer samples were prepared by alkali activation of the natural zeolite by 8 M NaOH solution and calcium hydroxide Ca(OH)2 1–3 wt%, with an activator/binder ratio of 0.6. The geopolymer samples cured for 24 h at 40 °C and then for 6 days more at room temperature showed the compressive strength values in a range of 3–5,5 MPa. Mineralogical analysis of natural zeolite obtained by XRD is as follows: Mordenite (∼67%), quartz (∼27%) and amorphous (∼6%). SEM-EDS micrographs analysis of geopolymers revealed the presence of Na and Ca which proves the incorporation of the activators, NaOH and Ca(OH)2. The compressive strength values obtained indicate that the use of alkali activation of natural zeolites is an effective method for the synthesis of geopolymers. The mechanical properties of geopolymers were slightly but not adversely affected by the addition of the migratory corrosion inhibitor, MCI-2005 NS. These results will be used in future research on geopolymer concrete with embedded reinforcing steel.

The behaviour of iron in geopolymer under thermal shock

In this paper, alkali-activated fly ash (geopolymer) samples were microstructurally analysed after thermal shock. The prepared samples were heated at 1000°C, and then quenched in water to room temperature. X-ray diffraction (XRD), and energy dispersive spectroscopy (EDS) were used to analyse the samples. The colour of the interior and exterior section of samples were different, where the former was darker than the latter. XRD results showed that hematite forms in small quantities in both interior and exterior sections. EDS analyses showed the presence of iron-rich points in both sections; however, there were many accumulated iron points in the interior section. It was concluded that, to reduce free energy of the system, dissoluble iron during geopolymerisation diffuses through molten channels when geopolymer is being heated and forms accumulated iron regions.

Geopolymers based on calcined tunisian clays: Effects of alkaline solution on vibrational spectra and mechanical properties

The effects of alkaline solution and calcined clays on vibrational spectra and mechanical properties were studied on geopolymer samples prepared from two alkaline solutions, calcined clays and three metakaolins. Structural evolution of the prepared geopolymers was characterized using FTIR spectroscopy and compression tests. Our results indicated high positive correlation between reactivity and compressive strength of the studied samples. Commercial potassium silicate and laboratory prepared k-silicate solutions were used to assess their effects on the prepared geopolymers. It was also observed that various secondary phases appeared, causing a slight change in the species' reactivity. Finally, it was concluded that changing alkaline solution and calcined clays decreased the mechanical properties, but increased the FTIR shift values. However, further work is needed to study the effects of alkaline solutions and natural clays from Tunisia on the properties of the prepared geopolymer. This is compulsory for prospective application of those products in various industries.

Development of Green Geopolymer Using Agricultural and Industrial Waste Materials with High Water Absorbency

Geopolymer is a promising porous material that can be used for evaporative cooling applications. Developing a greener geopolymer using agricultural and industrial wastes is a promising research area. In this study, we utilize rice husk (RH), rice husk ash (RHA), metakaolin (MK), ground granulated blast furnace slag (GGBS), and palm oil fuel ash (POFA) to prepare geopolymer pastes, with alkali liquid as an activator. Many geopolymer samples have been prepared as per the Design of Experimental software (DOE), and its corresponding response surface mode and central composite design and later they were characterized. The samples were cured in an oven for 2 h at 80 °C, and thereafter stored at room temperature (~25–30 °C) prior to being tested for its water absorption and compressive strength. The effect of the different composition of precursors on water absorption, density, porosity, and the compressive strength of the prepared geopolymers have been investigated. The results showed that the compressive strength of geopolymers is directly proportional to the ratio of the alkali liquid. Post-optimization, the best geopolymer paste mixture was confirmed to contain 10% of RH, 15% RHA, 35% MK, 10% POFA and 30% of GGBS, with 72% desirability for maximum water absorption (~38%) and compressive strength (4.9 MPa). The results confirmed its applicability for evaporative cooling.

Investigation on the microstructure and mechanism of geopolymer with different proportion of quartz and K-feldspar

Geopolymer appears to be an alternative to ordinary Portland cement as a new sustainable material. The effect of the aggregate contents of quartz and K-feldspar on the microstructure and mechanical properties of Geopolymer samples was investigated in the present study. It was found that the aggregate contents influence the compressive strength and bending strength of geopolymeric bricks. Also, The K-feldspar/quartz mass ratio (F/Q) has a linear relation with the modulus of alkaline activator at the peak value of bending strength. This is due to the fact that the quartz reacts with the sodium hydroxide and forms [H2SiO4]2− which is the main component of sodium silicate, and that the K-feldspar has the ability to provide additional alkaline. The results of electron-microprobe analysis indicated that the matrix phase is composed of more amount of [SiOAlOSi]n polymerization monomer with increasing alkaline activator modulus ratio when K+ is not involved in the reaction. However, the polymerization monomer of [SiOAl]n was only favored despite of variation of alkaline activator modulus when the K+ exists.

The utilization of Şaphane alunite in geopolymer production

The aim of this work is to research the usage of alunite from the alunite deposits of Şaphane-Kutahya (Turkey) as a raw material in the production of a geopolymer material. Alunite samples were characterized and prepared to use in body recipes. Manufacturing of geopolymer was conducted by mixing alumina silicate sources, silica fume, and sodium silicate solution. The geopolymer samples were cured at 60 °C for 24 h. Chemical and microstructural characterization of materials prepared from representative samples was carried out using X-ray fluorescence (XRF), X-ray diffraction (XRD), 27Al-magic angle spinning nuclear magnetic resonance (27Al MAS-NMR), and scanning electron microscopy (SEM), techniques, respectively. The compressive strength of the geopolymer materials was obtained from the samples after 7 and 28 days. Compressive strength measurements show a maximum strength of almost 48 MPa after 28 days. As a result of this study, it has been shown that alunite minerals can be utilized as alternative raw materials for production of geopolymer mortars.

Structural and chemical properties of thermally treated geopolymer samples

This article presents the results of the compositional, structural and morphological study of geopolymers synthesized from metakaolin and an alkali activator. The study involved the investigation of the structural and chemical properties of the geopolymer, in addition to thermally treated geopolymers up to 600 and 900°C. The precursor of the geopolymer, and the geopolymer samples before and after the thermal treatment, were investigated by Fourier transformation infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and SEM analysis. The corrected average value of the ratio of silicon and aluminum in the geopolymer samples (SiGP:Al) is about 1.46, which suggests that the obtained geopolymer samples represent a mixture of roughly equal amounts of sialate and sialate-siloxo units. Annealing the geopolymer samples at 600°C decreases the amount of Si-ONa bonds and induces the cross-linking of polymer changes. At the same time, other sodium containing alumino-silicate phases are created. The thermal treatment at 900°C leads to a considerable reduction of oxygen and particularly sodium, followed by significant morphological changes i.e. formation of a complex porous structure. Additionally, a new semicrystaline phase appears. Both XRD and XPS results imply that this new phase may be nepheline and it is plausible that this phase begins to nucleate at temperatures below 900°C.

Properties of Alkali Activated Ground Granulated Blast Furnace Slag Based Geopolymers

Ground granulated blast furnace slag, red mud, wheat straw ash are secondary material which after alkaline activation can be used in the construction materials’ domain. Their disposal poses a threat to the environment, whereas by reusing them we would be able to reduce this negative impact. This paper describes the research carried out in order to synthesise some geopolymer recipes, which are based on ground granulated blast furnace slag, red mud and wheat straw ash, alkaline activated with sodium hydroxide or a solution made with sodium hydroxide and sodium silicate. Factors that influence the compression strength have been studied such as: the nature of the alkaline activator, the chemical composition of solid materials in the recipes and the curing time. The geopolymer samples have been dried at room temperature for 7 and 28 days, respectively, and after the compressive strength tests has been made. Following this research it has been found out that NaOH/Na2SiO3 activated geopolymer samples have shown a higher resistance in the compressive strength. From the SEM analysis it has been found out that the samples with a higher amount of ground granulated blast furnace slag in their composition had a more homogeneous and less porous design than those with a smaller amount of ground granulated blast furnace slag.

Correlation between Compressive Strength and Fire Resistant Performance of Rice Husk Ash-Based Geopolymer Binder for Panel Applications

Panel structures which are mainly used as insulation materials should possess high fire resistance characteristic. In addition, their mechanical requisites for walls and doors such as compressive strength must not be unduly compromised. Rice husk ash (RHA) was used as an aluminosilicate source and two factors namely RHA/AA ratio and NaOH concentration were analyzed using statistical tool to study the effect of both factors on the compressive strength. Surface morphology and fire resistant behavior of four selected samples based on their compressive strength (brittle, semi-brittle, ductile, and semi-ductile samples) were studied to determine the correlation between compressive strength and fire resistant performance of those selected samples. Results showed that RHA-based geopolymer sample recorded high compressive strength above 28 MPa when its RHA/AA ratio and NaOH concentration were high ranging from 0.7 to 0.8 and 12M to 14M, respectively. Brittle geopolymer sample (GS) with low Si/Al ratio shows high compressive strength together with high degree of geopolymerization. Ductile GS in comparison, shows low compressive strength irrespective of its degree of geopolymerization. Semi-ductile GS showed the best fire resistant properties with a maximum non-exposed surface temperature of only 50°C after 50 minutes (after it was exposed to a direct fire with temperature of 900°C) followed by semi-brittle and brittle GS.

A multiscale investigation of reaction kinetics, phase formation, and mechanical properties of metakaolin geopolymers

A multiscale study is presented of the reaction kinetics, phase formation, mechanical properties of metakaolin-based geopolymers by varying Si/Al ratios of 1.2–2.2 and Na/Al ratios of 0.6–1.2. Macro- and nano-mechanical properties of geopolymer samples were determined by unconfined compression testing and grid nanoindentation technique, respectively. The latter, in combination with statistical deconvolution, also enables the extraction of generally 4 distinct phases together with their nanomechanical properties and volumetric fraction within the synthesized geopolymers. Moreover, the reaction kinetics, phase formation (particularly geopolymer gel development), and mechanical property development were investigated by characterizing geopolymers cured at the final setting time, 7, and 28 days. Phase formation was characterized by Fourier transform infrared spectroscopy (FTIR) via monitoring the evolution of the Si-O-T (T: Si or Al) and Al-O bonds. Results illustrate that the fraction of geopolymer gels dominantly governs the mechanical behavior, both of which increase with the Si/Al and Na/Al molar ratios, while the final setting time increases with the Si/Al ratio, but decreases with the Na/Al ratio. The chemical composition for the best mechanical performance of the studied geopolymers is a Si/Al ratio of 1.7 and Na/Al ratio of 0.9. The relationships among geopolymer chemical compositions, geopolymer gel formation rate, and macromechanical properties are also discussed.

Resistance of geopolymer and Portland cement based systems to silage effluent attack

Traditional Portland cement (PC) concrete has been used for many years in the agricultural industry for the construction of silos and silage effluent storage facilities. However, the acidic nature of the silage effluent produced by silage has led to severe degradation of PC concrete which in turn has significant environmental and financial implications. This study compares the resistance of PC and geopolymer (GP) mortars and pastes to silage effluent over 12months. The GP samples displayed increased resistance to silage effluent in terms of mass and strength loss. Analysis of microstructure suggests that the increased stability of the reaction products is the main factor behind increased silage effluent resistance when compared with PC. It was also found that blends of pulverised fuel ash (PFA) and ground granulated blast furnace slag (GGBS) with a higher PFA content may offer increased long term silage effluent resistance due to the nature of the main binder gel produced in PFA dominant systems.

Performance and microstructure characteristics of the fly ash and residual rice husk ash‐based geopolymers prepared at various solid‐to‐liquid ratios and curing temperatures

This article presents the results of a study on the effects of solid‐to‐liquid (S/L) ratio and of curing temperature on strength development, phase composition, and microstructure in geopolymers that prepared using a mixture of class‐F fly ash (FA) and residual rice husk ash (RHA) and a solution of sodium hydroxide (NaOH) and sodium silicate (Na2SiO3). The samples were prepared at various S/L ratios (2.4–2.8) and then cured at various curing temperatures [room temperature (RT): 90°C] to investigate these effects. A compressive strength test was conducted on the samples after the curing process to determine the development of strength over time. Moreover, X‐ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) were used to examine the microstructural properties of the samples. Furthermore, scanning electron microscopy was used to characterize the surface morphologies of the samples. This study found that the S/L ratio and the curing temperature had significant effects on the properties of the geopolymer samples. The compressive strength of all the geopolymer samples increased with curing age. The highest strength was obtained from the samples that were prepared at an S/L ratio of 2.6 and a curing temperature of 60°C. XRD and FTIR analyses showed that the major crystalline phases presented in the resultant samples were quartz, mullite, and cristobalite with the additional presence of minor zeolite phases. The results of this study support the use of FA and RHA as solid waste materials in the preparation of geopolymers. © 2016 American Institute of Chemical Engineers Environ Prog, 36: 83–92, 2017

Response of alkali activated low calcium fly-ash based geopolymer concrete under compressive load at elevated temperatures

For geopolymer cement (GPC) concrete to become a viable building material in the main stream construction industry, reliable stress–strain curves need to be established. This paper presents the stress–strain curves for GPC concrete at ambient and elevated temperatures of up to 800 °C. Prediction models for capturing the stress–strain response of GPC concrete at ambient temperatures, based on widely accepted OPC models, are also presented here. At high temperatures testing only covered one type of temperature-load history; that is: samples were heated up to test temperatures then loaded to failure under displacement control. Between 20 and 200 °C all the tested samples underwent a decrease in strength. However, samples tested between 200 and 400 °C manifested a moderate to significant gain in strength. At 800 °C all samples underwent a decrease in strength. The initial loss of strength may be attributed to the loss of water from the GPC concrete samples, which is supported by thermogravimetric analysis of geopolymer samples. Between 200 and 400 °C, the increase in the compressive strength of all tested concrete mixtures is attributed to further geopolymerization, which has been proven by differential scanning calorimetry results. The loss of strength at 800 °C is attributed to possible disintegration of the geopolymer gel and formation of new phases within the geopolymer system.

Optimizing and Characterizing Geopolymers from Ternary Blend of Philippine Coal Fly Ash, Coal Bottom Ash and Rice Hull Ash.

Geopolymers are inorganic polymers formed from the alkaline activation of amorphous alumino-silicate materials resulting in a three-dimensional polymeric network. As a class of materials, it is seen to have the potential of replacing ordinary Portland cement (OPC), which for more than a hundred years has been the binder of choice for structural and building applications. Geopolymers have emerged as a sustainable option vis-à-vis OPC for three reasons: (1) their technical properties are comparable if not better; (2) they can be produced from industrial wastes; and (3) within reasonable constraints, their production requires less energy and emits significantly less CO2. In the Philippines, the use of coal ash, as the alumina- and silica- rich geopolymer precursor, is being considered as one of the options for sustainable management of coal ash generation from coal-fired power plants. However, most geopolymer mixes (and the prevalent blended OPC) use only coal fly ash. The coal bottom ash, having very few applications, remains relegated to dumpsites. Rice hull ash, from biomass-fired plants, is another silica-rich geopolymer precursor material from another significantly produced waste in the country with only minimal utilization. In this study, geopolymer samples were formed from the mixture of coal ash, using both coal fly ash (CFA) and coal bottom ash (CBA), and rice hull ash (RHA). The raw materials used for the geopolymerization process were characterized using X-ray fluorescence spectroscopy (XRF) for elemental and X-ray diffraction (XRD) for mineralogical composition. The raw materials’ thermal stability and loss on ignition (LOI) were determined using thermogravimetric analysis (TGA) and reactivity via dissolution tests and inductively-coupled plasma mass spectrometry (ICP) analysis. The mechanical, thermal and microstructural properties of the geopolymers formed were analyzed using compression tests, Fourier transform infra-red spectroscopy (FTIR), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). Using a Scheffé-based mixture design, targeting applications with low thermal conductivity, light weight and moderate strength and allowing for a maximum of five percent by mass of rice hull ash in consideration of the waste utilization of all three components, it has been determined that an 85-10-5 by weight ratio of CFA-CBA-RHA activated with 80-20 by mass ratio of 12 M NaOH and sodium silicate (55% H2O, modulus = 3) produced geopolymers with a compressive strength of 18.5 MPa, a volumetric weight of 1660 kg/m3 and a thermal conductivity of 0.457 W/m-°C at 28-day curing when pre-cured at 80 °C for 24 h. For this study, the estimates of embodied energy and CO2 were all below 1.7 MJ/kg and 0.12 kg CO2/kg, respectively.