Geopolymer Samples Research Articles

Experimental research on the mechanical properties of graphene geopolymer

This research study used metakaolin as a raw material, a mixed solution of sodium hydroxide and sodium silicate as an alkali excitant, and a graphene dispersant as an additive to manufacture a graphene geopolymer sample. The compressive strength and bending strength of the sample were tested. The results showed that the geopolymer hydration products were observed to be more compact, and the internal porosity was reduced after the addition of the graphene. The geopolymer strengths had been obviously increased, and the compressive strength and bending strength reached 46.9MPa and 6.7MPa, respectively. However, the graphene’s role in improving the strength of the original geopolymer became gradually weakened when the addition amounts of the graphene were increased to a certain extent. Furthermore, the role of the graphene in improving the compressive strength of the geopolymer was determined to gradually decrease with the increase in the content of sodium hydroxide in the alkali excitant.

Durability of Fly Ash Based Geopolymer Concrete Infilled with Rubber Crumb in Seawater Exposure

Geopolymer is an alternative binder to replace Ordinary Portland Cement (OPC)in construction industry. Source materials that rich in silica (Si) and alumina (Al) were activated by using alkaline solution. Production of tires keep increasing every year and due to its non-biodegradable properties it causes problems for disposal process. In current scenario, waste materials should be used or recycled so that the existing natural resources can be saved and at the same times it can protected environment. In this paper, the effect of rubber crumb on fly ash based geopolymer concrete have been investigated by immersing the samples in seawater for 28 and 60 days. The rubber crumb was used to replace coarse aggregates from range 5% until 20%. The ratio of fly ash/alkaline activator and sodium silicate/sodium hydroxide(NaOH) ratio were fixed at 2.0 and 2.5. It has been shown that the compressive strength decreased when the content of rubber crumb increased. The highest compressive strength (39.6 MPa) was obtained at 5% replacement of rubber crumb when exposure to seawater for 28 days. The density of geopolymer samples also increased when immersed in seawater for all samples. The lack of bonding between rubber crumb and geoplymer paste cause increasing in porosity hence reduced the strength, increment in density and changes in weight of geopolymer samples.

Geopolymers as an Alternative for Oil Well Cementing Applications: A Review of Advantages and Concerns

Geopolymers, being inorganic polymers created from rock sources, were evaluated as an alternative to Portland cement. To evaluate their usability, some properties of a selected geopolymer were measured and compared with those from a neat class G Portland cement. The geopolymeric slurries showed a non-Newtonian viscosity behavior with a measurable, albeit low, yield stress. The pumpability measurements using atmospheric and pressurized consistometer showed an adequate set profile for both the geopolymer and cement sample. Static fluid loss test shows that the geopolymeric slurries experienced a lower fluid loss compared to that of the Portland cement. The shrinkage factor for the geopolymers was reduced (expanded) as the downhole temperature was ramped up. The shrinkage of the Portland cement sample proceeded only with a lower rate. Tensile strength of the geopolymers was approximately 5% of their compressive strength; however, this value for Portland cement was approximately 10% of its compressive strength. Finally, shear bond strength of geopolymers would benefit from improvement.

Methods of enhancing strength of geopolymer produced from powder-based 3D printing process

A previous study presented a method of formulating geopolymer for powder-based 3D concrete printing (3DCP) for construction applications. The highest strength achieved in using this method was 16 MPa. While this is sufficient for some special construction applications, a higher strength is necessary for the majority of the construction applications. The present study presents a number of curing methods to enhance the strength of 3D printed geopolymer parts. The effects of curing temperatures and curing mediums on the compressive strength of geopolymer samples produced via the 3DCP process have been evaluated. Curing of the printed samples has been carried out in tap water, three alkaline solutions and three fly ash-based geopolymer slurries at different temperatures (25 °C, 40 °C, 60 °C and 80 °C). Results showed that printed geopolymer samples cured in a combination solution of N Grade sodium silicate solution and sodium hydroxide solution (8.0 M) at 60 °C gained the highest compressive strength of 30 MPa. This strength is nearly double the strength achieved in the previous study. The higher strength achieved in this newly developed post-processing method opens up wider range of possible construction applications due to the significantly improved strengths.

Modulation of Inorganic Matrices for Functional Nanoarchitectures Fabrication: The Simultaneous Effect of Moisture and Temperature in the Preparation of Metakaolin Based Geopolymers

Abstract The concept of geopolymerization has usually been applied to develop structural materials endowed with mechanical properties and other characteristics of interest in building and related applications. With the aim to show the role of these inorganic polymers in the modulation of functional nanoarchitectures, this contribution introduces a study on the effect of simultaneously controlled humidity and temperature adopted in view to produce nanostructured geopolymers derived from metakaolin for functional applications. Geopolymer samples were prepared by dissolving high-quality metakaolin in water-glass solutions then cured and dried using well controlled humidity and temperature conditions for different aging times. Characterization of the resulting porous aluminosilicate materials was carried out by XRD, FTIR, NMR, thermal analyses (TG-DTA), FE-SEM and specific surface area (SBET) among other techniques. Chemical stability, mechanical properties and sorption ability have been investigated with the aim to further explore their potential functional applications. Incorporation of polymers, such as alginic acid, yields functional nanorachitectures that display ability for removal of heavy metal ions in solution (e.g. Cu2+).

Influence of different brine water salinity on mechanical properties of fly ash-based geopolymer cement

PurposeThe purpose of this paper is to investigate the mechanical properties changing of geopolymer cement under different brine salinity.Design/methodology/approachGeopolymer Cement of Class F Fly Ash and Class G Cement slurries were prepared according to API RP 10B. The optimum alkaline activator/cement and water/cement ratio of 0.44 was used for geopolymer and Class G cement samples, respectively. The alkaline activator was prepared by mixing the proportion of Sodium Hydroxide (NaOH) solutions of 8 M and Sodium Silicate (Na2SiO3) using ratio of 1:2.5 by weight. The slurries were cured for 24 hours at 130oC and 3,000 psi in HPHT Curing Chamber followed by coring process. Both cement sample were immersed in brine water salinity up to 28 days with different brine salinity up to 30 per cent of NaCl. The mechanical properties were investigated using OYO Sonic Viewer-SX and Uniaxial Compressive Strength. The surfaces of the cement samples were extracted for Scanning Electron Microscope (SEM) and EDS tests to evaluate the morphology and chemical compositions of the cured samples.FindingsThe paper shows that geopolymer samples experiences strength reduction in brine water but the reduction rate of geopolymer is about half of the Ordinary Portland cement based oil well cement. The finding was also verified by SEM and EDS result.Originality/valueThis paper investigates the mechanical property changes of emerging geopolymer cement due to different water salinity. The results provide potential application of geopolymer cement for oil well cementing.

Preparation, characterization, and determination of mechanical and thermal stability of natural zeolite-based foamed geopolymers

This study is the first attempt to evaluate the effect of two foaming agents, aluminum powder and hydrogen peroxide (30 wt% water solution) on zeolite-based geopolymers and their possible use as building material according to Ecuadorian technical standards. These foamed geopolymers were prepared by alkali activation of an Ecuadorian natural zeolitic tuff and by alkali activation using NaOH (10 M), Ca(OH)2 and Na4Si5O12, with the use of two different foaming agents mentioned. In the case of aluminum powder, the experimental range was between 0.05 and 0.25 wt%; on the other hand, the percentages of hydrogen peroxide ranged from 0.5 to 4.0%. For characterization of the foamed geopolymer samples, quantitative X-ray diffraction (QXRD), thermogravimetric (TGA), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) techniques were used. The results of both foaming agents in zeolite-based geopolymers met Ecuadorian technical standards NTE INEN 643 and NTE INEN 638; nevertheless, the use of aluminum powder as foaming agent exhibited a better pore size distribution, suggesting a better performance. On the basis of these results, foamed geopolymers are suitable construction materials for the application of manufactured for masonry wall in houses.

Recycling of phosphate mine tailings for the production of geopolymers

Abstract Phosphate sludge is a fine by-product produced with large quantities during ore phosphate beneficiation (washing and flotation), and deposited in surface impoundment without treatment, which create environmental issues. The main objective of this study was to investigate the potential reuse of phosphate sludge as a partial replacement of fly ash and metakaolin for the production of geopolymers. Geopolymers were prepared by mixing phosphate sludge with metakaolin or with fly ash in a proportion of 50 wt%. The effects of the main experimental factors (NaOH concentration, curing temperature and curing time) on the main physical characteristics (density, water absorption and compressive strength) were assessed using an experimental design of response surface methodology (DOE). The microstructure of geopolymer samples were investigated using X-ray diffraction, scanning electron microscopy and Fourier-transform infrared spectroscopy. Analysis of variance confirmed that the adopted DOE model described well the experimentally observed properties. The results of the microstructural analysis showed that the development of a gel-like phase was favored by the increase of sodium hydroxide concentration (from 8 to 14M) for the two kinds, fly ash and metakaolin-based geopolymers. The physical properties of the geopolymers indicated that an increase of temperature and NaOH concentration led to strengthen and dense materials, while the addition of phosphate sludge resulted in a reduction on the mechanical properties. However, substitution of fly ash by phosphate sludge resulted in strong specimens (62 MPa), which indicated that the use of phosphate mine tailings in geopolymers can be a viable technological solution for the sustainable management of these by-products.

Numerical simulation of mechanical properties tests of tungsten mud waste geopolymer

Abstract Geopolymers are believed to become in the future an environmental friendly alternative for the concrete. The low CO2 emission during the production process and the possibility of ecological management of the industrial wastes are mentioned as main advantages of geopolymers. The main drawback, causing problems with application of geopolymers as a building material is the lack of the theoretical material model. Indicated problem is being solved now by the group of scientists from the Silesian University of Technology. The series of laboratory tests are carried out within the European research project REMINE. The paper introduces the numerical analyses of tungsten mud waste geopolymer samples which have been performed in the Atena software on the basis of the laboratory tests. Numerical models of bended and compressed samples of different shapes are presented in the paper. The results obtained in Atena software were compared with results obtained in Abaqus and Mafem3D software.

An Assessment of Reuse of Light Ash from Bayer Process Fluidized Bed Boilers in Geopolymer Synthesis at Ambient Temperature

Sustainable civil construction in the future, besides having low energy consumption and greenhouse gas emissions, must also adopt the principle of reusing wastes generated in the production chain that impact the environment. The aluminum production chain includes refining using the Bayer process. One of the main wastes produced by the Bayer process that has an impact on the environment is fly ash. Geopolymers are cementitious materials with a three‐dimensional structure formed by the chemical activation of aluminosilicates. According to studies, some are proving to be appropriate sources of Al and Si in the geopolymerization reaction. The research reported here sought to assess the possibility of reusing fly ash characteristic of the operational temperature and pressure conditions of Bayer process boilers in geopolymer synthesis. Geopolymerization reaction was conducted at an ambient temperature of 30°C, and the activator used was sodium hydroxide (NaOH) 15 molar and sodium silicate (Na2SiO3) alkaline 10 molar. Fly ash and metakaolin were used as sources of Al and Si. XRD, XRF, and SEM Techniques were used for characterizing the raw materials and geopolymers. As a study parameter, the mole ratios utilized followed data from the literature described by Davidovits (year), so that the best results of the geopolymer samples were obtained in the 2.5 to 3.23 range. Resistance to mechanical compression reached 25 MPa in 24 hours of curing and 44 MPa after 28 days of curing at ambient temperature.

Primena alumosilikatnih polimera na bazi metakaolina u adsorpciji jona kadmijuma iz otpadnih voda

Alumosilicate polymers (geopolymers) based on metakaolin as precursor and alkaline activators of different concentrations (2M, 4M, 6M and 8M NaOH/Na2SiO3) were used to remove ions of cadmium from wastewater. Experiments were carried out in a batch process at room temperature (23 ± 1 ° C) for different operating parameters: adsorption time, pH value of solution, initial concentration of metal and mass of adsorbents. It was found that the optimum pH value for all adsorbents is above 6.0. The adsorption efficiency increases with increasing pH of the solution. With an increase in the initial concentration of cadmium, the adsorption capacity increases and reaches a value of over 200.0 mg/g. The experimental results have better agreement with Freundlich's adsorption isotherm (surface heterogeneity, hemisorption mechanism) and the pseudo-second order model (the principle of the chemisorption mechanism and adsorption rate depend on the adsorbent concentration). Alumosilicate geopolymer samples were characterized using X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Fourier-Transform Infrared Spectroscopy (FTIR).

Study of mechanical and microstructural properties of geopolymer concrete with GGBS and Metakaolin

Geopolymers are a new type of artificial polymer which is developed when an aluminosilicate source is triggered or activated by the application of alkaline hydroxide and silicate solution. They have shown good mechanical properties and shows good resistance to chemicals, lesser shrinkage, no damage to environment and shows formidable durability. Ground granulated blast furnace slag(GGBS) is a good aluminosilicate source as it contains high amounts of alumina and silica which are necessary for the geopolymerisation reaction to take place. In this paper, three variations in terms of weight percentages of GGBS and metakaolin clay have been taken with 80%-20%,50%-50%, and 20%-80% respectively. A 10M solution of sodium hydroxide with sodium silicate was used as alkaline activator solution. For practical purposes ambient curing of the geopolymer samples has been adopted. The Degree of reaction was evaluated for all the percentage variations of the geopolymer concrete at 7 days of curing. The mechanical properties of geopolymer concrete have been studied by compressive test, split tensile test and four-point loading test. To understand the structural integrity of the casting of the geopolymer specimens, ultrasonic pulse velocity test was performed. The study of micro-structure of geopolymer concrete was carried out by Fourier transform infrared spectroscopy (FTIR) technique.

Effects of Si/Al molar ratio on strength endurance and volume stability of metakaolin geopolymers subject to elevated temperature

Good structural performance in a fire scenario necessitates that the structural material possesses chemical stability, deformation resistance and strength endurance. Excellent chemical stability for geopolymers has been reported in literature at a microscale. However, their performance at macroscale has not yet been systematically explored and the underlying mechanisms remain unexplained. In current study, effect of variation in Si/Al molar ratio on the meso- and macro-scale thermal stability of metakaolin geopolymers has been comprehensively investigated to discover the underlying mechanisms governing the performance. Results show that all the geopolymer samples experienced reduction in compressive strengths after exposure to high temperature up to 900°C. Although, the geopolymer mixes exhibited good chemical stability at microscale, they possessed poor volume stability at mesoscale with very high thermal shrinkage. It was observed that thermal shrinkage induced crack formation dominates the residual strength for geopolymer mixes with Si/Al molar ratio ≤ 1.50, while densification of matrix is the governing factor of the residual strength for geopolymer mixes with Si/Al molar ratio > 1.50. Re-crystallization of nepheline at high temperature adversely affect the strength by inducing expansion and cracking of the geopolymer matrix. Geopolymer sample with Si/Al ratio 1.75 retained highest strength (6MPa) because viscous sintering of geopolymer mixes with high Si/Al ratio at temperature beyond 600°C enables localized healing of micro-cracks and densification of matrix which favored compressive strength gain after exposure to 900°C. At an even higher Si/Al of 2.0, foaming of unreacted silica upon heating can lead to expansion and cracking of the sample which reduce the strength. It was observed that due to high degree of cracking damage and low residual strength retention, it is essential to improve the macro-scale stability of metakaolin geopolymers for structural fire resistance applications.

Immobilization of toxic inorganic anions (Cr2O72-, MnO4- and Fe(CN)63-) in metakaolin based geopolymers: A preliminary study

Geopolymer (GP) consists of polymeric Al and Si tetrahedral network, with alkali metal cation (Na+ or K+) balancing the negative charge of Al tetrahedra. Although immobilization of heavy metal cations, that could balance the negatively charged Al tetrahedra in GP, was extensively studied, this is the first study that deals with immobilization of metal anions (dichromate, permanganate and hexacyanoferrate). GP samples were prepared from metakaolin (MK) as an aluminosilicate material and sodium silicate activator (Si/Al molar ratio 2) in the presence of the three anions. The efficiency of immobilization was studied in terms of % leaching of metal anions using atomic absorption spectrophotometry and in terms of leaching of total metal anions by conductivity measurements. The % leaching was less than 10% when 0.2% (w/w) of metal anion salts were incorporated in the GP. However, the % leaching increased from 10% to 20% with increasing loading of dichromate salt from 0.2% to 1.5% (w/w) which indicates that GP has limited capacity (limited number of pores) for immobilization of metal anions. When silica gel and alumina were employed as additives to MK (changing Si/Al ratio), the leaching of dichromate and total ions increased substantially and the surface of GP becomes more crystalline as indicated by SEM and EDS studies. The present work suggests that the mechanism of heavy metals immobilization by balancing the negatively charged Al tetrahedra of GP is not true.

Preparation and microstructural analysis of smelting waste non-ferrous metal slag geopolymer

The geopolymer samples were prepared with smelting waste slag of non-ferrous metal as the raw material and water glass as the activator. The effect of modulus of water glass and water binder ratio on the compressive strength was studied. The results show that the strength of the geopolymer activated by water glass with modulus of 1.1 and water binder ratio of 0.28 can maintain an increasing trend in the 90 curing days. Through the analyses with XRD, SEM (EDS), and FTIR, the main reaction products are found to be geopolymer gels, which bond the crystalline minerals to provide strength. The molecular chains of amorphous phase in slag become shorter after depolymerization-polycondensation.

Prediction of Torsional Strength for Very High Early Strength Geopolymer

Very early high strength geopolymers are gaining acceptance as alternative repair materials for highways and other infrastructure. In this study, a very rapid geopolymer binder based on Metakaolin (MK) and Parawood ash (PWA), developed by the authors, was experimentally tested and a prediction model for its torsional strength is proposed. The geopolymer samples were subjected to uniaxial compression, flexural beam, and torsion tests. The modulus of rupture and torsional strength in terms of compression strength were found to be well approximated by 0.7(f’c)1/2 and 1/7(x2y) (f’c)1/2, respectively. Also an interaction relation to describe combined bending and torsion was developed in this study. In addition, the effects of aspect ratio (y/x) were studied on both torsional strength and combined bending and torsion. It was found that an aspect ratio of y/x = 3 significantly reduced the torsional resistance, to about 50 % of the torsional strength of a square section.DOI: http://dx.doi.org/10.5755/j01.ms.23.4.17280

Mechanical and thermal properties of fly ash based geopolymers

The traditional cement industry consumes a large quantity of energy and emits greenhouse gas CO2. With the promotion of sustainable development, attentions have been drawn to how to develop a “green” material with similar or even better engineering properties than ordinary Portland cement (OPC), and geopolymer has been recognized as one of the most promising materials. In this study, an experimental investigation on the thermo-mechanical properties of geopolymers prepared using a class F fly ash, KOH and Na2SiO3 is presented. Based on the testing results, the effects of water/ash ratio, curing methods, cooling methods, and sealing degree on the compressive strength and thermal properties of the geopolymer products are studied. The tested results show that the geopolymer cured at appropriate conditions can reach a compressive strength of more than 100 MPa and a good residual strength (up to 96 MPa) after 500 °C heating. The geopolymer sample with a water/ash ratio of 0.2 shrinks 2.0% in the longitudinal direction after 500 °C heating, while expanses 9.4% after 800 °C heating. In addition, it is found that the studied geopolymer possesses good spallation resistance when cooled down in water after high temperature heating.

Split tensile strength of slag-based boroaluminosilicate geopolymer

In this study, split tensile strength of the slag-based boroaluminosilicate geopolymers was studied. The metallurgical slag obtained from the rockwool furnace was used as the aluminosilicate source. The mixture of sodium hydroxide and borax was used as the alkali activator. The experiments were designed using the Taguchi method. The four main factors that considered in four different levels are sodium hydroxide concentration, curing time, the weight ratio of the borax to sodium hydroxide solution, and the weight ratio of the alkali activator to slag. In total, 16 set of tests based on the L9 array was conducted. The ANOVA analysis results showed that the specimen with the curing time of 14 days, sodium hydroxide concentration of 8 M, the weight ratio of the borax to sodium hydroxide solution of 0.9, and the weight ratio of the alkali activator to slag of 0.7 possesses the highest strength of 8.48 ± 1.07 MPa. Also, the FT-IR results revealed that, the slag-based boroaluminosilicate geopolymer sample with the highest strength had a B–O bond; however, for the slag-based boroaluminosilicate geopolymer sample with the lowest strength, no B–O bond was detected.

Preparation of mesoporous geopolymer using metakaolin and rice husk ash as synthesis precursors and its use as potential adsorbent to remove organic dye from aqueous solutions

In this work, mesoporous geopolymer was synthesized using a novel and easy synthesis route employing metakaolin and rice husk ash as sources of silica and alumina, and soybean oil as a mesostructure-directing agent. For comparison purposes, a geopolymer sample was produced without the use of oil. The samples were characterized by Fourier transform infrared spectroscopy (FT–IR), X–ray diffraction (XRD), specific surface area, pore volume, average pore size, and pore size distribution (BET and BJH methods). The materials were tested to remove methyl violet 10B dye from aqueous solutions. The results showed that the mesoporous geopolymer presented adsorptive superior behavior compared to the geopolymer prepared without the use of oil, being attributed to its superior pore properties. The adsorption equilibrium was attained within 120min, and the maximum adsorption capacity of mesoporous geopolymer was 276.9mgg–1. Therefore, the mesoporous geopolymer prepared in this work comprises a potential adsorbent, presenting pore intrinsic properties that result in a high adsorption capacity.

Geopolymer with improved thermal stability by incorporating high-magnesium nickel slag

The present study investigates the thermal stability of binary geopolymers prepared with fly ash and high magnesium nickel slag (HMNS). TGA, XRD and SEM techniques are adopted to investigate the chemical composition and microstructure of the binder gel phase exposed to high temperatures. The results show that incorporating HMNS mitigates dehydration induced mass loss and volume shrinkage of the geopolymer samples between room temperature and 250°C, and increases their residual strengths when exposed to high temperatures between 600°C and 800°C. The key role that HMNS substitution of improving the thermal stability of geopolymers is associated with the formation of sodium-alumina(magnesia)-silica hydrate (N-A(M)-S-H) gel phase, which turns to be a less porous microstructure after thermal exposure when compared with the N-A-S-H gel phase, which is formed in the pure fly ash sample. The binary geopolymers exhibit higher residual strengths and better maintaining of volume stability in the range from 250°C to 550°C compared to Portland cements. However, both the geopolymer and Portland cement show severer volume shrinkage after exposure of 600°C, because of the viscous sintering of geopolymer gels and the decomposition of cement hydration products, respectively.