Ratio Of Geopolymer Research Articles

Influence of Rock Block Content on Mechanical Properties of Coarse-Grained Fillers Stabilized with Fiber and Geopolymer

This study employed fiber and geopolymer to enhance the engineering performance of coarse-grained fillers. By conducting a series of comparative mechanical tests, the ideal mass mixing ratio design of geopolymer and fiber was investigated first. Then, the influence of rock block content on the mechanical properties of coarse-grained fillers stabilized with fiber and geopolymer was explored. The deformation damage characteristics of fiber- and geopolymer-stabilized coarse-grained fillers with different rock block contents were also discussed in the final test. The results show that the ideal mass mixing ratio of geopolymer for coarse-grained filler stabilization was 15% of dry fine-grained soil in weight and the ideal dosage and length of fiber was 0.4% of dry fine-grained soil in weight and 1.2 × 10−2 m. The compressive strength of fiber- and geopolymer-stabilized coarse-grained fillers shows a tendency to increase first, then decrease, and then re-increase with the increase in rock block contents. The best compressive strength and resistance to deformation were achieved when the rock block content was 30%. The failure mode of fiber- and geopolymer-stabilized coarse-grained fillers translated from shearing slip to vertical splitting as the rock block content increased. This study can provide a reference and support for the engineering application of coarse-grained fillers stabilized with fiber and geopolymer.

Optimization of solidification/stabilization materials based on solid waste geopolymer

With the development of mining economy and human society, heavy metal pollution incidents have gradually increased while a large amount of mine solid waste has been produced.Red mud (RM) and blast furnace slag (BFS) are common solid wastes in mines with excellent heavy metal adsorption properties. Optimization of geopolymer solidification/stabilization(S/S) materials based on these waste materials is a good way to reduce solid waste and cure heavy metal contaminated soil, and has outstanding environmental protection significance.In this study, RM and BFS were used as geopolymer raw materials, and sodium hydroxide was used as alkali activator to prepare lead nitrate contaminated soil with Pb content of 0.5%. Laboratory tests were conducted to explore the effects of alkali-solid ratio, BFS content on the mechanical strength, toxic leaching characteristics and pH of geopolymer S/S lead contaminated soil. The optimal ratio of geopolymer is obtained. The results show that the S/S soil cured with RM and BFS geopolymer has good mechanical properties and heavy metal adsorption properties, and it has certain scientific research value and utilization prospect for the remediation of Pb contaminated soil.

Identification and characterization of tephra for geopolymer precursor

Abstract Volcanic ash and pumice are products of volcanic eruptions characterized by a high amount of amorphous silica and alumina. They can potentially serve as a source of raw materials for the production of geopolymers. Geopolymers are more environmentally friendly compared to conventional cement. However, there is a requirement for aluminosilicate for creating geopolymers. This study aims to identify the mineralogical composition and chemical properties of the volcanic ashes and pumices that are potentially used as geopolymers precursor materials. Tephra and pumice samples were collected from several volcanoes in Indonesia. The samples include two tephras from recently erupted volcanoes in Java and one pumice material from West Sumatra. Tephras were collected one week after the eruptions of Mt. Tangkuban Perahu (26th July 2019). Another source of tephra was collected from Mt. Kelud, which erupted on 13th February 2014. Pumice samples of Mt. Maninjau were collected at Sungai Limau district, 30 km from the Maninjau caldera, a product of the Holocene (52K) volcanic eruption of Mt. Maninjau. Mineralogy of the tephra and pumice samples was identified with XRF and XRD. Chemical properties characterized include pH, exchangeable cations, cation exchange capacity (CEC), potential-P, and available-P. Results showed that crystalline feldspar minerals and amorphous volcanic glass dominated volcanic ash and pumice. The SiO2 content is higher in pumice, followed by tephras from Mt. Tangkuban Perahu and Mt. Kelud (74.97%-60.28%). But the Al2O3 content is higher in Mt. Kelud compared to pumice and Mt. Tangkuban Perahu (23.57%-4.03%). The pH is very acidic to slightly acidic (2.35–6.1). Mg is higher than Ca, Na, and K. The potential-P and available-P were considered very low. Among the samples, Mt. Kelud volcanic ash has the highest available P compared to Tangkuban Perahu volcanic ash and pumice. The SiO2/Al2O3 ratio are 4.35, 8.00, and 26.38 for samples of Mt. Kelud, Mt. Maninjau pumice, and Mt. Tangkuban Perahu, respectively. The optimum ratio of geopolymer is between 2.5–5; thus, volcanic ash Mt. Kelud is the most suitable option. Nevertheless, the exchangeable basic cations of volcanic ash and pumice indicated that they are more suitable for plant nutrition.

Transport mechanism of uranyl nitrate in nanopore of geopolymer with different Si/Al ratios: Molecular dynamics simulation

Geopolymer is an amorphous cementitious material produced by geopolymerization using minerals or industrial waste as the main raw material under the action of activators. It can be used for safe treatment of heavy metal and radioactive pollution. This study applied molecular dynamics simulation to investigate the transport behaviour of uranyl nitrate in nanochannel of geopolymer, and focused on the influence of changes in the Si/Al ratio of geopolymer on the adsorption and diffusion of ions and water molecules. The simulation results described by density distribution, radial distribution function (RDF), hydrogen bonding network structure, mean square displacement (MSD) and diffusion coefficient. The density distribution shows that geopolymer has the strongest adsorption capacity for UO22+, followed by NO3−, and finally H2O. The results also indicate that the changes in molecular composition of geopolymer have a significant impact on kinetic characteristics of UO22+, NO3− and H2O. As the Si/Al ratio decreases, the adsorption capacity of geopolymer shows an upward trend, with the most significant improvement in the adsorption of UO22+. In addition, when the Si/Al ratio reduces, the migration rate of UO22+ and NO3− slows down. It could hinder the diffusion of ions in nanopores of geopolymer. The work could optimize the preparation of geopolymer adsorbent, and reveal the transport mechanism of uranyl nitrate in nanopore of geopolymer with different Si/Al ratios at the atomic scale.

29Si and 27Al NMR study of the structural transformation of calcined kaolin residue-based geopolymer using low alkali activator content for sustainable construction materials

Geopolymer commercialization efforts in parallel with unconventional research are the only pathway to achieve the large-scale deployment of geopolymer technology. Geopolymers with a low quantity of alkali activator produced by the compression process are one way to bring this technology to industry because of the higher strength and lower efflorescence of the product. In this work, calcined kaolin residue-based geopolymers with a low alkali activator content were synthesized by various Si/Al mole ratios with soluble silicate from Na2SiO3 to adjust the Si ratio. The effects of Si/Al mole ratios on the structural transformation, microstructure, and compressive strength of geopolymers containing low alkali activator content were studied. The structural transformation and microstructure of geopolymers were characterized by NMR, SEM, and BET, and the compressive strength was assessed using a mechanical testing machine. The results present that geopolymer synthesized with various Si/Al mole ratios of precursor materials impacted the change in polymerization degree of silicate species (Qn(mAl)) and aluminate species. The Q4(4Al) and Q4(3Al) structures were transformed into the Q4(2Al) structure, and the content of the AlIV structure decreased when the Si/Al mole ratio of geopolymer was increased to 1.58. However, the contents of Q4(4Al) and AlIV structures increased again when the geopolymer had a Si/Al mole ratio of 1.62. SEM/EDX and BET results of geopolymers presented denser matrices, more amorphous aluminosilicate gels, and higher Si/Al ratios in aluminosilicate gels, while the pore size and pore volume were quite small when the Si/Al mole ratio of precursor materials was increased. In contrast, the highest Si/Al mole ratio of 1.62 showed different properties. The compressive strength of geopolymer was maximized at a Si/Al mole ratio of 1.58, and the decline in compressive strength of geopolymer with higher Si/Al mole ratio was related to the contents of Si–O–Si, Si–O–Al, and Al–O–Al bonds, content of aluminosilicate gels, and properties of the microstructure. The geopolymer synthesis using calcined kaolin residue and low alkali activator content is considered an eco–friendly process, which uses waste materials and less chemicals, and obtains high-strength products.

Effect of Silica Fume on the Volume Expansion of Metakaolin-Based Geopolymer Considering the Silicon-to-Aluminum Molar Ratio

This paper investigates the effect of silica fume on the mechanical properties of metakaolin-based geopolymers with different silicon-to-aluminum molar (S/A) ratios. Geopolymer has been extensively studied as an alternative to traditional cementitious material because of its low CO2 emissions. Previous studies revealed that the application of silica fume can improve the compressive strength of geopolymer, however, the optimum dosages are different. To examine the reason for the different optimum dosages of silica fume, this study prepares geopolymer specimens of which variables are the S/A ratio and silica fume dosage, and conducts compressive strength and initial setting time tests. To examine whether the strength degradation is caused by the expansion due to the added silica fume in geopolymer, the volume and dynamic modulus are also measured. The results show that a part of silica fume dissolves and changes the S/A ratio of geopolymer, and that a part of silica fume remains in the geopolymer matrix. These combined effects of silica fume result in an irregular compressive strength trend, and, thus, an optimum dosage of silica fume can vary depending on the S/A ratio. Furthermore, the volume expansion of geopolymer with silica fume is observed, however, no sign of damage on the compressive strength is found.

Characteristics of hybrid alkaline cement composites with high cement content: flash set and high compressive strength

This paper explores hybrid alkaline cement composites with high cement content over 50%. Calcium (Ca) accelerates the strength development and improves the compressive strength of geopolymer. However, the mixing proportion of Ca in geopolymer has been limited because Ca significantly decreases the flow of fresh geopolymer. This study resolves the flow decline issue by mixing a part of the initial mixing water with cement before adding it into a metakaolin-based geopolymer, which is named hybrid alkaline cement composites (HACC) in this study. The cement/(metakaolin + cement) ratio investigated is up to 85%. Based on the initial setting time and compressive strength results, some unique characteristics of the HACC are observed: i) the material is set within 10 min and the 28-day compressive strength is over 80 MPa with 1:1 mixing ratio of geopolymer and cement paste, and ii) the compressive strength of HACC is not always higher with a lower w/c ratio of cement paste.

Understanding geopolymer binder-aggregate interfacial characteristics at molecular level

The interfacial characteristics of geopolymer binder to aggregate composites are poorly understood, especially at molecular level. Herein, molecular models are developed to study, for the first time, the geopolymer-aggregate interface. Chemically, various forms of interfacial bonding are characterized, including Al-O-Si bonding through condensation reactions, NaO and H-bonding. An atomic-level interfacial transition zone (ITZ) is identified, attributed to the concentration of –OH groups. Increasing the Si/Al ratio of geopolymer is found to decrease the ITZ density, but have limited effect on the ITZ width. A heterogeneous diffusion characteristic occurs in geopolymer, due to the weak interfacial interaction. Mechanically, lowering the Si/Al ratio promotes the interfacial strength due to the stronger interfacial interaction and higher cross-linking degree in geopolymer. Under loading the interfacial fracture undergoes three stages: crack propagation, chain bridging (including aluminosilicate and ionic bridging) and breakage. The above atomic-level findings may facilitate a better design of geopolymer concrete in engineering.

Effect of Si/Al molar ratio on the immobilization of selenium and arsenic oxyanions in geopolymer.

The effect of Si/Al molar ratio of geopolymer on the immobilization of Se and As oxyanions was studied through leaching test and solid characterizations including XRD, FTIR, TG, NMR, XAFS, and N2 adsorption-desorption isotherm. As a whole, the leaching percentages of Se and As oxyanions increased with the increase of the Si/Al molar ratio of geopolymer. Linear combination fitting confirmed that most of selenite, selenate and arsenate ions existed in geopolymers through electrostatic interaction. Thus, Al tetrahedrons in geopolymer structure control the charge stability for these oxyanions to a large extent. Differently, as for arsenate ions, they were recrystallized into an arsenate compound (Na3.25(OH)0.25(H2O)12)(AsO4) in geopolymers. The additive of these pollutants has an adverse effect on the compactness of geopolymer, then influencing the leaching performance in turn. However, the changes in leaching results did not follow the variation trend of specific surface areas and pore volumes of geopolymers with different Si/Al ratios. The number and distribution of Al tetrahedron and compactness of geopolymer have a synergistic effect on the immobilization of these oxyanions. Besides, the compressive strengths of geopolymer samples are always higher than 20MPa, which meets the requirement of safe disposal of hazardous waste.

Synthesis of high-porosity hybrid geopolymer/alginate adsorbent for effective removal of methylene blue and optimization of parameters using RSM

In this work, high-porosity geopolymer/sodium alginate (GSA) adsorbent was successfully prepared by entrapping fly ash-based geopolymer into sodium alginate (SA) using a simple method. The geopolymer slurry was firstly prepared which involved the utilization of sodium hydroxide (NaOH) as the alkaline activator followed by the addition of SA and albumen into the slurry. Natural albumen was used as the foaming agent. The effect of mass ratio of geopolymer to SA, albumen content (wt%), NaOH concentration and curing temperature (°C) on the removal of methylene blue (MB) was investigated using one factor at time (OFAT) method and optimized by response surface methodology (RSM), which achieved by 30 run of experiments using central composite design (CCD). A quadratic model was employed to correlate all the independent variables for maximizing the MB removal through the analysis of variances (ANOVA). The model suggested that the optimum condition for the preparation of GSA adsorbent for the efficient MB removal of 84.94% was achieved with mass ratio of geopolymer to SA was 1:0.13, albumen content of 25 wt%, NaOH concentration of 7 M and curing temperature of 60 °C. The albumen content was the most effective factor in the preparation of GSA adsorbent that increased the MB removal, followed by the curing temperature and mass ratio of geopolymer to SA.

Compressive Strength of Fly Ash Geopolymer Concrete by Varying Sodium Hydroxide Molarity and Aggregate to Binder Ratio

The concentration of sodium hydroxide solution increased the reaction rate during geopolymerisation process and thus enhanced the development of early strength of concrete. While the percentage volume of aggregates played a vital role in the strength development due to the better durability then paste alone and also filling and packing ability. The aim of the study is to determine the optimum molarity of sodium hydroxide and aggregate to binder ratio of geopolymer concrete towards high strength performance concrete based on compressive strength. The variable samples investigated include the sodium hydroxide (NaOH) concentration and aggregate to binder ratio at room temperature curing; the ratio of alkali activator solution and solid to liquid ratio remained constant. This resulted the presents work on the development of fly ash based geopolymer concrete having increment on the rate of compressive strength development from 7 to 28 days was found between 61 MPa and 82 MPa, respectively.

Influence of Calcium Bentonite Addition on the Compressive Strength, Efflorescence Extent and Drying Shrinkage of Fly-Ash Based Geopolymer Mortar

ABSTRACT The influence of calcium bentonite addition on the compressive strength, efflorescence extent and drying shrinkage of fly-ash based geopolymer mortar was investigated. The results showed that appropriate amount (e.g. 15 wt%) of calcium bentonite addition favoured the enhancement of compressive strength mainly because its addition allowed the geopolymer to tolerate more water glass addition and therefore increased the Si/Al ratio of geopolymer. The maximum 28 d compressive strength of the geopolymer mortar with calcium bentonite addition reached 47.8 MPa, which was evidently larger than the maximum value of the specimen without calcium bentonite addition. Calcium bentonite addition was also beneficial for the reduction of drying shrinkage percentage of geopolymer mortar due to water adsorption and volume expansion properties of calcium bentonite. Moreover, calcium bentonite addition could reduce, even eliminate the efflorescence mainly due to Na+ adsorption by calcium bentonite through ion exchange.

Hydrothermal synthesis of pollucite from metakaolin-based geopolymer for hazardous wastes storage

In this contribution, a low-temperature (∼200 °C) hydrothermal route is developed to fabricate pollucite from metakaolin-based geopolymer for the immobilization of Cs. The macroscopic immobilization performance upon hydrothermal treatment has been correlated with the microscopic structural evolution and process parameters for the first time. Upon hydrothermal treatments, analcime and pollucite first crystallize from Na-rich and Cs-rich amorphous geopolymer at 170 °C, respectively, and further grow with the increasing hydrothermal temperature. By probing the interplay between hydrothermal temperature, hydrothermal time and initial Na/Cs ratio of geopolymer in the immobilization performance of Cs using orthogonal experimental design, the optimal procedure has been screened as treating (0.2Na, 0.8Cs)-GP at 230 °C for 6 h. Moreover, the results demonstrate the role of Cs-contained hydrothermal medium in enhancing the immobilization performance of Cs and mechanical properties of the encapsulation matrix due to the accelerated nucleation of pollucite. The converted dominant leaching mechanism, i.e., from diffusion for the untreated geopolymer to surface wash off for the hydrothermal product, further emphasizes the superiority of trapping Cs in pollucite structures due to their stronger blocking effect.

Effects of Si/Al ratio on the efflorescence and properties of fly ash based geopolymer

Abstract Efflorescence seriously affects the practical application of geopolymer. In this study, fly ash based geopolymer was prepared by raw materials containing different Si/Al ratios. A test method of the efflorescence degree of geopolymer was proposed and applied. The effects of the Si/Al ratio on products, microstructure, pore structures, compressive strength, water loss rate and efflorescence of geopolymer were systematically investigated. The reaction products and structures of geopolymer were tested by XRD, FTIR, TG-DTA, SEM-EDS and BET. The results showed that the efflorescence degree of different samples can be compared by the test method simply, effectively and quantitatively. The products of geopolymer were mainly amorphous gels N(C)-A-S-H containing large amounts of Si and Al components. The structures, properties and efflorescence degree of the geopolymer were different due to the different Si/Al ratio. When the Si/Al ratio of geopolymer was 1.5, the content of [AlO4]- structures was highest, while the volume and size of pore were relatively small. The dense matrix and [AlO4]- structures of geopolymer can reduce the efflorescence degree significantly. This study can provide a reference for future investigation about efflorescence inhibition and efflorescence test methods of geopolymer.

Immobilization of cesium in fly ash-silica fume based geopolymers with different Si/Al molar ratios

Geopolymers are considered as promising matrixes for waste solidification. However, the effects of the Si/Al molar ratio of geopolymer on the immobilization efficiencies for metal ions have not been fully studied and understood. In the present study, geopolymers with different Si/Al ratios were synthesized from coal fly ash and silica fume. Adsorption tests were conducted to evaluate their immobilization efficiencies for Cs+. The results indicated that geopolymer with low Si/Al ratio could have a better immobilization performance for Cs+ than that with high Si/Al ratio. High Si/Al ratio could contribute to a more compact structure of geopolymer. Each sorption process fitted better with the pseudo-second-order model, and all of them were governed by film diffusion. However, the diffusion mode was gradually closed to particle diffusion with the increase in the Si/Al ratio. Both Langmuir and Freundlich models could well fit the sorption data, and the free energy of each sorption process decreased with the increase in the Si/Al ratio according to D-R equation. The distribution of AlO4 tetrahedron in the geopolymer structure plays a significant role in the immobilization of Cs+. Low Si/Al ratio could result in that more AlO4 tetrahedrons distribute in the small rings (<eight-member), which has stronger locking effects on Cs+. However, high Si/Al ratio leads to the distribution of AlO4 tetrahedrons mainly in larger rings (≥eight-member), and this could contribute to the high leaching amount of Cs+. In addition, high-temperature treatment could contribute to the formation of nepheline or pollucite in geopolymer matrix. These minerals locked Cs+ in their structures, and the leaching amount of Cs+ was reduced correspondingly from high levels (26.36%, 27.26%, and 66.92%) to very low levels (0.67%, 0.53%, and 0.95%).

Effect of sodium polyacrylate on mechanical properties and microstructure of metakaolin-based geopolymer with different SiO2/Al2O3 ratio

The mechanical properties and microstructure of geopolymer are affected by the molar ratio of SiO2/Al2O3. Meanwhile, organic polymer has the effect of improving the toughness of geopolymer, which depends on the SiO2/Al2O3 ratio of geopolymer inevitably. Therefore, it is important to investigate the effect of the organic polymer on the mechanical properties and microstructure of geopolymer with varying SiO2/Al2O3 ratio for using organic polymer to modify geopolymer. In this work, the SiO2/Al2O3 ratios of metakaolin-based geopolymers are adjusted to 2.0, 2.5, 3.0, 3.5 and 4.0 by adding silica fume and β-Al2O3, with Na2O/SiO2, H2O/SiO2 being maintained at 0.2, 4.0, respectively. The geopolymers with each SiO2/Al2O3 ratios are modified by addition of 0, 0.4, 0.8, 1.2 and 1.6 wt% of sodium polyacrylate (PAAS).The mechanical properties of these samples are measured and the rate of change is used to characterize the effect of PAAS on the metakalin-based geopolymers. The mechanism is also shown by 29Si NMR, XPS and FTIR. The results show that the effects of polymer on the mechanical properties of metakaolin-based geopolymer are affected by SiO2/Al2O3 ratio and the effect becomes less obvious with SiO2/Al2O3 ratio increasing from 2.0 to 4.0. Incorporation of PAAS can reduce the degree of polymerization of [SiO]4 or [AlO]4 in geopolymer and form the Si‒O‒C bond, which are two main reasons for polymer improving the toughness of geopolymer. But these effects decrease when the SiO2/Al2O3 ratio of geopolymer increases from 2.0 to 4.0, which is corresponding to the effect on the mechanical properties. The toughening effect of organic polymer on geopolymer depends on the SiO2/Al2O3 ratio of geopolymer, and only the geopolymer with lower SiO2/Al2O3 ratio (no more than 2.5 in this work) can be significantly toughening modified by organic polymer. Therefore, it is necessary to consider the SiO2/Al2O3 ratio of the geopolymer when geopolymer modified by organic polymer is designed.

Property and microstructure of aluminosilicate inorganic coating for concrete: Role of water to solid ratio

As a potential matrix of inorganic coating, aluminosilicate geopolymer has excellent properties of low Volatile Organic Compounds (VOC) emission, anticorrosion and long life. However, little concern has been devoted to basic parameters of the aluminosilicate geopolymer coating. The present paper investigated the influence of water to solid ratio on the property and microstructure of the coating. Results showed that as the water to solid ratio of geopolymer coating increased from 0.8 to 1.0, the hardening process was delayed significantly. The variation of autogenous shrinkage differed from that of drying shrinkage. The overall porosity measured by Mercury Intrusion Porosimetry (MIP) decreased, while a dramatic increased volume of pores with the size of 30–50nm was detected. Besides, the Fourier Transform Infrared Spectroscopy (FTIR) results indicated that polycondensation degree was affected in an inverse manner at early and late ages of geopolymer hardening.

Facile fabrication of green geopolymer/alginate hybrid spheres for efficient removal of Cu(II) in water: Batch and column studies

The growing environmental awareness and the demand for high efficiency of natural resource encourage industry to look for alternative environmentally benign materials. In this work, a new geopolymer/alginate hybrid spheres (GAS) was fabricated from the green geopolymer and sodium alginate by a feasible one-pot method. The effect of mass ratio of geopolymer and sodium alginate (Geo/SA) on the properties of GAS was investigated. The results demonstrated that the GAS-4 (Geo/SA=1: 0.16) had a good sphericity with an inner honeycomb structure. The GAS-4 was used as an adsorbent for the removal of Cu(II) in water. Batch-wise adsorption indicated GAS-4 possessed an excellent Cu(II) removal efficiency (99±3.4%) from a 50mg/L solution with a dosage of 0.15g/100mL. The adsorption kinetic was fitted well by the pseudo-second-order model, indicating the chemical interaction of GAS-4 and Cu(II). The adsorption isotherm followed the Langmuir model indicating a monolayer adsorption of Cu(II) on GAS-4. Moreover, application of GAS-4 in a column mode for the continuous treatment of Cu(II) effluents exhibited optimum breakthrough curves by adjusting the bed heights. The experimental breakthrough curves were correlated with the Thomas, Adams-Bohart and Yoon-Nelson models. The overall results strongly suggested that the GAS-4 hybrid sphere was not only environmentally friendly, cost-effective but also could be applied for the continuous treatment of heavy metals containing water.

Experimental Study on Utilization of Quartz Mill Tailings as a Filler to Prepare Geopolymer

ABSTRACTQuartz mill tailings are produced in a huge amount per year in China. Therefore, now there is an urgent demand for utilization of the quartz mill. In the present research, the quartz mill tailings were used as a filler for metakaolin-based geopolymer to restraint the shrinkage and improve mechanical property. This work studied the influence of quartz mill tailings on the properties of geopolymer prepared by alkali-activated metakaolin. Performance of geopolymer incorporated with quartz mill tailings were addressed in terms of workability, compressive and flexural strength, and drying shrinkage at different ages. Further, X-ray Diffraction, Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR) and Mercury Intrusion Porosimetry (MIP) were applied to investigate the relevant microstructure. The results indicated that addition of quartz mill tailings increased the viscosity of the paste, and meanwhile decreased the flowability of geopolymer. Up to 20% of the tailings can replaces metakaolin to prepare geopolymer without a negative effect on the mechanical property. Up to 30% of quartz mill tailings had a role to decrease the drying shrinkage. Besides, weight loss ratio of geopolymer decreased gradually with increasing dosage of the quartz mill tailings. Addition of the quartz mill tailings did not change the mineral composition of alkali-activated metakaolin, and meanwhile the amorphous or semi-crystalline phase has been found. MIP and FTIR results showed that moderate addition of quartz mill tailings optimized the microstructure of geopolymer. Therefore, quartz mill tailings can replace metakaolin up to 20% to prepare geopolymer.

Metakaolin-, fly ash- and calcium hydroxide-based geopolymers: effects of calcium on performance

Effects of calcium on the performance of geopolymers prepared from metakaolin, class C fly ash (CFA) and calcium hydroxide are studied, including setting times and compressive strength testing. Leaching concentrations of calcium from prepared geopolymers are investigated by inductively coupled plasma atomic emission spectrometry. Relative contents of geopolymeric products and hydration products are studied by acid dissolving testing. The mineral composition, morphology and chemical groups of geopolymeric products and hydration products are analysed by X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy. Geopolymer setting time is much faster when calcium content increases. Calcium has a positive effect on compressive strength of geopolymers. By acid dissolving testing, the ratio of geopolymer value/ordinary hydration product value in metakaolin-based geopolymer was 4·4 : 1, whereas in CFA-based and CFA + 6% calcium hydroxide-based geopolymers the values were 1 : 1·7 and 1 : 1·5, respectively. Thus, the main product in metakaolin-based geopolymer is geopolymeric products, whereas in CFA-based geopolymer, hydration products also occur. In the alkali-activated condition, CFA-based geopolymer is a composite system with geopolymeric gel and calcium–silicate–hydrate gel co-existing.