Showing papers on "Geopolymer published in 2005"

Development and properties of low-calcium fly ash-based geopolymer concrete

Abstract: This Research Report describes the first part of the work carried out by the geopolymer research group at Curtin University of Technology. It describes the development and properties of heat-cured low-calcium fly ash-based geopolymer concrete. This Report will be followed by two other Reports describing the long-term properties of geopolymer concrete, and the behaviour of reinforced geopolymer concrete beams and columns.

29Si NMR study of structural ordering in aluminosilicate geopolymer gels.

Abstract: A systematic series of aluminosilicate geopolymer gels was synthesized and then analyzed using 29Si magic-angle spinning nuclear magnetic resonance (MAS NMR) in combination with Gaussian peak decon...

The composition range of aluminosilicate geopolymers

Abstract: Aluminosilicate geopolymers with SiO2/Al2O3 ratios ranging from 0.5 to 300 have been prepared from mixtures of dehydroxylated kaolinite with either ρ-Al2O3 or fine Aerosil SiO2, with the ratios Na2O/SiO2 and H2O/SiO2 kept constant throughout the series. All the compositions hardened at ambient temperature, but the high-alumina compositions were of low strength and did not display typical XRD and NMR geopolymer characteristics, by contrast with the compositions of S/A between 2 and 300 which showed typical amorphous geopolymer XRD traces and 27Al, 29Si and 23Na NMR spectra. The samples with increasing SiO2 content (S/A > 24) showed increasingly elastic behaviour, deforming rather than crushing in brittle fashion, and upon heating at 100–250 °C, their hydration water was expelled as bubbles, forming stable foamed materials at about 300 °C.

Geopolymer formation processes at room temperature studied by 29Si and 27Al MAS-NMR

Abstract: A systematic study of 29 Si and 27 Al MAS-NMR has been carried out in an attempt to understand the reaction mechanism of the geopolymer formation at room temperature. For selected compositions, reactions were followed at selected times after the initial mixing of the reactants until the final products formed. The reactants were silicate anions, metakaolin and aqueous alkali. Silicate anions from various sources, such as sodium orthosilicate (Na 4 SiO 4 ) and two types of sodium silicate solutions (2SiO 2 ·Na 2 O and 4SiO 2 ·Na 2 O) were investigated. Further, silicate anions formed from the reaction of colloidal silica and aqueous alkali was also studied as a source for silicate anions. Interaction of silicate anions with Al sites of metakaolin soon after the mixing was obvious as 29 Si MAS-NMR resonance lines of silicate anions were shifted to less shielded values. As the reaction progressed, the coordination of Al (IV, V, VI) in metakaolin changed almost completely to IV. It was indicated by NMR observation that polymeric silicate anions of high cross-linked densities were better than monomeric silicate anion in the geopolymerisation process.

The Role of Mathematical Modelling and Gel Chemistry in Advancing Geopolymer Technology

Abstract: Inorganic alkali aluminosilicate polymers, commonly referred to as geopolymers, have been studied for several decades due to their excellent mechanical and thermal properties, as well as chemical and fire resistance. Such properties make geopolymers suitable for use in a wide range of areas, including construction, building products, and refractory applications. Geopolymers are synthesized via reaction of aluminosilicate materials, such as metakaolin, fly ash (a coal combustion waste) and/or blast furnace slag, with alkaline silicate solutions at ambient or slightly elevated temperatures. Despite the increasing body of research on these advanced materials, little is understood about the underlying gel chemistry, surface phenomena, reaction kinetics or microstructure. It is shown here how reaction kinetic modelling coupled with an analysis of the gel chemistry has led to advances that make the wider acceptance of this technology possible. The ability to model the kinetics of the system allows the design of mixtures for specific applications, and allows better quality control during production. A system of differential equations describing chemical reaction kinetics is formulated and solved, providing a simulated heat flow signal. Validation of the model is undertaken by comparison of this signal with experimental calorimetric data. The process of development of this model is ongoing, but has already provided valuable insights into the reaction processes which, when coupled with understanding obtained from gel chemistry, provides a framework by which the behaviour of geopolymer-forming systems may be analysed. This is a critical step in the wider commercial acceptance of these materials, and in the development of specific geopolymer formulations tailored to particular applications.

Effects of aluminates on the formation of geopolymers

Abstract: The mechanisms of Al speciation and hydrolysis in geopolymer systems are investigated based on the partial charge model together with preliminary experimental validation. Calculation of the partial charges of species discloses that the positive partial charge of the Al atom is always higher than that of Si atom under conditions of similar pH values, suggesting greater tendency of [Al(OH)4]− tetrahedra to attract negatively charged groups from other species. Given Al atom with four hydroxyl groups under alkaline conditions and the potential to expand its coordination number with greater ease, condensation reactions involving aluminate species appear to occur much more readily. Thus, the model essentially predicts that aluminate species promote condensations reaction owing to factors such as their partial charge and the number of hydroxyl groups, implying that the solubility of aluminate sources (i.e. metakaolin) and the distribution of [Al(OH)4]− ions have an important influence on the mechanical properties of inorganic polymers. Corresponding experimental data on aluminate dissolution obtained from progressive milling of metakaolin particles demonstrated that varying particle sizes and different degrees of aggregation of metakaolin can have an important influence on inorganic polymer properties such as setting time, microstructure and compressive strength. The results indicate that milled metakaolin powders with high specific surface area have faster setting characteristics, higher compressive strength, and possess a more homogeneous microstructure, attributable to Al availability as predicted by the partial charge model.

Geopolymer materials based on fly ash

Abstract: Owing to their high strength and predominantly amorphous microstructure the materials on the basis of latent hydraulic active substances activated by alkalis (fly ash, slag) represent a transition between traditional inorganic binders and ceramics and, therefore, they are included into the group of so-called "chemically bonded ceramics". The products being formed during the alkaline activation of fly ashes exhibit their amorphous character with minority crystalline phases. The materials prepared on the basis of fly ashes activated by alkalis exhibit an excellent resistance to the corrosive action of salt solutions, they possess high values of strength and a good frost resistance; furthermore, they can withstand the exposure to temperatures of up to about 600°C. There is a substantial difference in the corrosion of geopolymer by sulfate solutions and that of the materials on the basis of Portland cement.

Structural studies of geopolymers by 29Si and 27Al MAS-NMR

Abstract: A systematic study of geopolymers by 29Si and 27Al MAS NMR has been carried out in an attempt to understand polymer structural details. 27Al MAS NMR data shows that transient aluminium species are formed during the reaction of metakaolin with NaOH. Interaction of silicate anions with the aluminium sites of metakaolin was evident during the synthesis of geopolymers as observed from low field shift of 29Si MAS NMR resonance lines of silicate centres. As the reaction progresses, the coordination of aluminium (IV, V and VI) in metakaolin changes almost completely to IV. 29Si MAS NMR of selected compositions of the ternary system of sodium silicate, metakaolin and aqueous alkali reveals that geopolymerisation occurs in a distinct compositional region. At high alkalinity [> 30% (mol/mol) overall Na2O content], connectivity of silicate anions is reduced, consistent with poor polymerisation. At low alkalinity [<10% (mol/mol) overall Na2O content], a clear 29Si NMR resonance line due to unconverted metakaolin is observed. NMR spectra were recorded from a series of samples with a fixed Na2O content (20 mol%) and varied SiO2/Al2O3 ratio to observe aluminium substitution in the cross-linked silicon tetrahedra of polymer network. Aluminium insertion into the silicate network is confirmed from the observed 29Si NMR shift as a function of Si/Al ratio. The identification of the presence or absence of metakaolin in the cured geopolymer product is not possible even by 29Si NMR as the signal from metakaolin is indistinguishable from a broad 29Si NMR peak consisting of many resonance lines from the network of cross-linked silicon/aluminium tetrahedra. In an attempt to identify metakaolin signal, we prepared geopolymers with higher SiO2/Al2O3 molar ratios. Since aluminium substitutions in the silicate tetrahedral network are decreased, this results in better-resolved 29Si NMR lines. The 29Si NMR signal due to metakaolin is then distinguishable in the spectra of cured products in a series of samples with 3 to 11 mol% metakaolin. These results indicate that a geopolymer structure is a network of silicon/aluminium tetrahedra with some presence of unreacted metakaolin. The silicon/aluminium tetrahedra might have connectivity ranging from 1 to 4.

Short Fiber Reinforced Geopolymer Composites Manufactured by Extrusion

Abstract: Geopolymer composites reinforced with short polyvinyl alcohol (PVA) fibers have been manufactured using the extrusion technique. The extruded products were thin plates with 6 mm thickness. It was demonstrated that short fiber reinforced geopolymer composites (SFRGCs) could be extruded without additional rheological modifier. Bending tests have been conducted with the extruded samples to investigate their mechanical properties. The fiber failure patterns in SFRGCs with various formulations were examined by scanning electron microscope and energy dispersive x-ray analysis techniques. The experimental results showed that the addition of PVA fiber could largely increase the ductility of SFRGCs, resulting in fiber failure modes changing from brittle to ductile. The effects of varying the amount of fly ash on the flexural behavior of various SFRGCs were also investigated. The SFRGCs incorporating small percentage of fly ash showed higher flexural strengths but smaller defections, while the SFRGCs incorporating a large percentage of fly ash had lower flexural strengths, but larger deflections. This could be attributed to the change of the bonding between fiber and matrix that led the change of failure mode from fiber fracture to fiber pullout.

Immobilization of Pb in a Geopolymer Matrix

Abstract: In a geopolymer matrix prepared by mixing a metakaolinite precursor with a solution of potassium hydroxide and silicate, 1 wt% Pb as the nitrate has been immobilized. Under the United States Environmental Protection Agency test protocol the Pb release was less than 5 ppm, the acceptable limit for landfills in the U.S.A. Electron microscopy showed Pb was present in the major amorphous phase and a minor (∼1 vol%) Ca-rich potassium silicate phase. Heating cured samples to several hundred degrees Centigrade was not significantly advantageous for immobilizing Pb.

Synthesis and thermal behavior of inorganic–organic hybrid geopolymer composites

Abstract: Inorganic geopolymer potassium aluminosilicate was prepared at room temperature by the reaction of kaolin, potassium silicate, and potassium hydroxide solution and was dispersed in situ into an epoxy matrix by various proportions to fabricate novel inorganic–organic hybrid geopolymer composites. The formation of inorganic geopolymer with respect to time was monitored by X-ray diffraction and FT-IR analysis and confirmed that 30 min is required to complete the geopolymerization. When geopolymers were properly mixed at different ratios with organic polymers such as epoxy and cured, these hybrid polymers exhibit significant thermal stability. Pure kaolin was also incorporated into the epoxy matrix to compare the change in chemical and thermal properties. Cone calorimetry results showed about 27% decreased in rate of heat release (RHR) on addition of 20% pure kaolin. However, about 57% of RHR was decreased on addition of only 20% geopolymer. Evaluation of CO2 and CO were found to be minimum 2.0 and 0.7 kg/kg, respectively, for hybrid geopolymer composites compared to very high yield for epoxy at 3.5 kg/kg after 200 s of ignition. The current study shows that due to the high thermal stability of hybrid geopolymer composites, the novel hybrid geopolymer composites have the ability to be potential candidates to use in practical application where fire is of great concern. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 112–121, 2005

Sulfate and Acid Resistance of Fly Ash-based Geopolymer Concrete

Abstract: Geopolymer concrete is emerging as a new material that offers the benefit of an environmentally friendly construction material for sustainable development. It utilises waste materials such as fly ash and has a low rate of greenhouse gas emission compared to Ordinary Portland Cement (OPC) concrete. The term 'geopolymer' was first introduced by Davidovits (1987) to describe a family of mineral binders based on alumino-silicates. This inorganic polymer has a wide range of applications in civil engineering. In geopolymer concrete, the silica and the alumina present in the source materials are induced by alkaline activators to form a gel. This geopolymer gel binds the loose aggregates and other unreacted materials in the mixture to form the geopolymer concrete. The chemical process involved in the formation of geopolymer binders is very different to that of OPC concrete. This paper presents the study of the resistance of fly ash-based geopolymer concrete to sulfate and acid attack. Test specimens were soaked in sodium sulfate solution and sulfuric acid solution for certain periods of time, and the resistance of geopolymer concrete was studied by evaluating the amount of expansion, the change in mass, and the residual compressive strength of test specimens after exposure. Test variables included exposure period and the concentration of the acid solution.

Hydration process of potassium polysialate (K-PSDS) geopolymer cement

Abstract: Environmental scanning electron microscope (ESEM) was used to quantitatively study in situ the hydration process of potassium polysialate (K-PSDS) geopolymer cement under an 80% relative humidity environment. An energy dispersion X-ray analysis (EDXA) was also employed to distinguish the chemical composition of the hydration products. The ESEM micrographs showed that metakaolin particles were packed loosely at 10 min after mixing, with many large voids. As hydration proceeded, gels were seen and these precipitated on the surfaces of the particles. At a later stage, the particles were wrapped by thick gel layers, and their interspaces were almost completely engulfed. The corresponding EDXA results showed that the molar ratios of K/Al and Si/Al gradually decreased with the development of hydration. As a result, the molar ratios of K/Al and Si/Al of hydration products after 9 h were 1·28 and 6·54, respectively, and these were close to the theoretical values (K/Al = 1·0, Si/Al = 6·0 for K-PSDS geopolymer ceme...

High reactivity metakaolin

Abstract: Metakaolin was prepared with kaolin by heat-treated technique that contained a great deal of amorphous SiO_2 and Al_2O_3.Affecting factors for the activity of metakaolin,burning temperature,burning time and contents of SiO_2 and Al_2O_3,were discussed through orthogonal tests.Activity index of Metakaolin was 114 that was larger by 11.8% than that of silica fume.Metakaolin with high pozzolanic activity,a new kind of mineral admixture,can be used to prepare high strength concrete.The compressive strength of MK concrete with water-cementitious materials ratio equal to 0.375 was 73.9 MPa which contained 10% MK.Geopolymer with amorphous to semi-crystalline structure was prepared with metakaolin activated by alkali activators.Its compressive strengths in early time were high reaching 55.8MPa cured at 60°Cfor 3 hours and 58.5 MPa cured at room temperature for 1 day.

Preparation of geopolymeric materials from fly ash filler by steam curing with special reference to binder products

Abstract: In order to prepare geopolymeric materials, sodium disilicate solution (1.48 mol/L) added with caustic soda solution (15 N) in 3 : 1 proportion and fly ash were used as geopolymer liquor (W) and filler (S), respectively, and were mechanically mixed with ratio W/S 0.45. The mixtures were cast into molds and steam-cured at 80°C up to 16 h under variable humidity, 40%RH, 60%RH, 80%RH and 100% RH, to make monolithic materials. As a result, relatively higher strength was obtained under 40%RH and 100%RH curings, while relatively lower strength under 60%RH and 80%RH curings. On the contrary, relatively larger shrinkage was noted, when cured under 40%RH, while relatively larger expansion, when cured under 100%RH. Monoliths cured under 60%RH and 80%RH showed little expansion and shrinkage in the entire range of curing time. On the other hand, monoliths cured under 40%RH showed relatively lower bulk density despite the shrinkage, while monoliths cured under 100%RH showed relatively higher bulk density despite the expansion. Monoliths cured under 60% RH and 80%RH showed intermediate bulk densities. These two extreme phenomena were discussed in terms of hydration-polycondensation process of silica complexes of the geopolymer liquor containing foreign metallic ions leached out of the fly ash filler. SEM-EDX analysis showed that binder portions were zeolitic gels in amorphous state consisting of Na 2 O, Al 2 O 3 and SiO 2 as main components associated with K 2 O, MgO, CaO and Fe 2 O 3 as well as free C. In hollow type of fly ash particulates so called cenospheres, needle-like or blade-like crystallites were encountered, which were composed of chemical components similar to the binder portions and zeolite Y (faujasite) formation was suggested. Furthermore, the CaO component was concentrated both in zeolitic gels and in zeolitic crystallites.

Behavior of Geopolymer Concrete Columns under Equal Load Eccentricities

Abstract: In geopolymer concrete, a by-product material rich in silicon and aluminum (low calcium fly ash) is chemically activated by a high alkaline solution to form a paste that binds the loose coarse and fine aggregates, as well as other un-reacted materials in the mixture. This paper presents the results of an experimental study on the behavior and the strength of twelve geopolymer concrete slender columns under equal load eccentricities. The primary variables of the test series were concrete compressive strength, longitudinal reinforcement ratio, and load eccentricity. The test results gathered included the deflection and the load capacity of the columns. The test failure loads were compared with the values calculated by the methods currently available for Ordinary Portland Cement (OPC) concrete. Excellent correlation between experimental and analytical results is found.

Composition and Structure of Hardened Geopolymer Products Using Infrared Ray Analysis Methods

Abstract: The structure,bonding state and ambient atmosphere of Si and Al of three types of geopolymers were investigated by using infrared ray(IR) analysis.The relationship between geopolymers and the corresponding zeolite crystals with the similar chemical composition was also discussed.The infrared evidence showed that SiO_4 tetrahedral chain was bonded by AlO_4 during the process of geopolymerisation reaction,and the two types of tetrahedral jointly form the three dimensional framework structure of geopolymers.The mutual transformation between geopolymers and zeolite crystals can be realized under suitable condition,which revealed that geopolymers may be the precursors of the corresponding zeolite crystals.

Structure characterization for the geopolymer of sodium silicate and metakaolin

Abstract: Geopolymers of metakaolin and sodium silicate were synthesized respectively with the ratios of the amount of SiO2 in the sodium silica solution to that of Al2O3 in metakaolinite equal to 1.0, and 0.66. The geopolymeric structures of the products were investigated by 27Al and 29Si solid-state nuclear magnetic resonances with magic-angle spinning (MAS NMR), Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), differential scanning colorimetry (DSC) and scanning electron microscopy (SEM). The reaction of the Al-O sheet in meakaolinite with low-order polymerized Si-O tetrahedral units such as monomer of SiO4 yields three-dimensional structures with the Q3 Si-O tetrahedral structure and the coordination of Al(IV) in the Al-O tetrahedral structure. The geopolymers are essentially X-ray amorphous. The assays by 27Al and 29Si NMR, FTIR confirm that the active structure in the metakaolinite is the sheet of Al-O with three coordination states.

Hybrid thermoplastic composites using ceramic reinforcements

Abstract: Polyethylene-based and polypropylene-based composites, incorporating silica nanoparticles and geopolymers, were prepared by melt compounding. Scanning electron microscope (SEM) images indicate that the silica nanoparticles do not distribute uniformly as fine particles in the matrix, but are unevenly distributed as clusters. As a result, the tensile properties of those composites are inferior to those of the matrix polymer. A novel concept of in situ formation of a reinforcing phase has been investigated as a method of resolving that problem. The reinforcing elements are microcrystalline phases developed during melt processing of mixtures of geopolymer precursors with polyethylene or polypropylene. Preliminary tensile test data on injection moulded specimens show some improvement in mechanical properties of both geopolymer–polyethylene and geopolymer–polypropylene composites relative to the matrix polymers. Scanning electron micrographs clearly show the presence in the composites of a nanoscale aci...

Research on direct shear test and pullout test between clay and geotextile

Abstract: In geopolymer reinforced soil structure, the behavior between the soil and geopolymer is very important to inner stabilization of reinforced soil structure, so the index between the soil and geopolymer is a crucial index. In this paper, systematic directtests and pullout tests were carried out between high liquid limit clay and two kinds of geopolymers. Based on the test result, stress-strain relationship is studied. Some useful conclusions and opinions which can be used to supervise the research and design are also presented. That is, the shear stress between the clay and the geopolymer increases with the normal stress increase, but the increase is not unlimited, and the increase ratio of shear stress will decreases. So the high-point of shear stress exists between clay and geopolymer. Due to sample preparation for pullout test, the scraggy interface between clay and geopolymer will generate anchor effect which leads to the friction coefficient and cohesion gained from pullout test more larger than that gained from direct shear test. But in practical engineering, the pullout test can better reflect the truth.