Types Of Geopolymers Research Articles

Adsorption behaviour of simulant radionuclide cations and anions in metakaolin-based geopolymer

Geopolymers are a class of alkaline-activated materials that have been considered as promising materials for radioactive waste disposal. Currently, metakaolin-based geopolymers (MK-GPs) are attracting interest for the immobilisation of radionuclides in contaminated water from the Fukushima Daiichi Nuclear Power Station. However, the associated chemical interaction mechanisms and the theoretical prediction of the adsorption behaviour of MK-GP in response to cationic radionuclides have not been thoroughly studied or fully understood. In addition, there is a lack of studies on the adsorption capacity of MK-GP for anionic radionuclides. In this study, two types of metakaolin-based (Metastar501 and Sobueclay) geopolymers were synthesised at a K2O:SiO2:H2O ratio of 1:1:13. The binding capacity and interaction mechanism of MK-GP with Cs+, Sr2+, Co2+, I-, IO3-, SeO32-, and SeO42- were evaluated based on the zeta potential, radionuclide binding, and alkali leaching. The results showed that MK-GP does not have the ability to incorporate anionic radionuclides irrespective of the metakaolin source used, but both types of geopolymers have a high capacity to immobilise cationic radionuclides. The uptake of Cs+ was observed as a one-to-one exchange between Cs+ and K+ whereas both one–two and one–one ion exchanges are possible in the case of Sr2+ and Co2+ with K+. The formation of cobalt blue (CoAl2O4) also contributed to the binding of Co2+. Thermodynamic modelling was conducted according to the ion exchange mechanism which predicts the binding of Cs+ and Sr2+ at low concentrations.

PROPERTIES MEASUREMENT AND APPLICATIONS OF SOME GEOPOLYMERS IN DRY AND WET SAND

The interest in reducing carbon emissions due to the large number of industrial wastes led to the civil engineering sector’s interest in using these products for easy access and for their unique advantages in improving raw materials after mixing them and determining their optimal use ratios. Through experiments and continuous studies, three types of geopolymers were used for this study based on poor sandy soil and mixing it in certain proportions with geopolymers, recording and analysing the results and using it in the practical experiment by using a special model to shed the loads on a square footing and drawing the load - settlement curve that showed the improvement of the sandy soil’s ability to resist shear by increasing the loads and reducing the settlement in the foundations. the laboratory test proved improvement in the shear strength parameters in sandy soil after blending with geopolymers.

XRD and TG-DTA Study of New Phosphate-Based Geopolymers with Coal Ash or Metakaolin as Aluminosilicate Source and Mine Tailings Addition.

Coal ash-based geopolymers with mine tailings addition activated with phosphate acid were synthesized for the first time at room temperature. In addition, three types of aluminosilicate sources were used as single raw materials or in a 1/1 wt. ratio to obtain five types of geopolymers activated with H3PO4. The thermal behaviour of the obtained geopolymers was studied between room temperature and 600 °C by Thermogravimetry-Differential Thermal Analysis (TG-DTA) and the phase composition after 28 days of curing at room temperature was analysed by X-ray diffraction (XRD). During heating, the acid-activated geopolymers exhibited similar behaviour to alkali-activated geopolymers. All of the samples showed endothermic peaks up to 300 °C due to water evaporation, while the samples with mine tailings showed two significant exothermic peaks above 400 °C due to oxidation reactions. The phase analysis confirmed the dissolution of the aluminosilicate sources in the presence of H3PO4 by significant changes in the XRD patterns of the raw materials and by the broadening of the peaks because of typically amorphous silicophosphate (Si–P), aluminophosphate (Al–P) or silico-alumino-phosphate (Si–Al–P) formation. The phases resulted from geopolymerisation are berlinite (AlPO4), brushite (CaHPO4∙2H2O), anhydrite (CaSO4) or ettringite as AFt and AFm phases.

Basic Properties of fly Ash/Slag -Concrete Slurry Waste Geopolymer Activated by Sodium Carbonate and Different Silicon Sources

As a kind of granular waste with complex composition and alkali corrosiveness, concrete slurry waste (CSW) has severe recycling limitations in the ordinary Portland cement (OPC). Considering this, a new type of geopolymer, prepared by granulated blast furnace slag/fly ash, concrete slurry waste, and powdered activators (sodium carbonate and different silicon sources including sodium metasilicate pentahydrate and silica fume), was adopted to conduct a comparative study with the OPC counterpart. In this study, the homogenized CSW was mixed in the OPC and geopolymer with a constant ratio of 50 wt%, respectively. Then the properties were studied in terms of the flowability, setting times, mechanical strengths, and microstructures. The results showed that better flowability (200 mm) could be achieved in the obtained geopolymer than in the OPC reference group (95 mm) by increasing the powdered activators. The setting time of the OPC was significantly shortened due to the addition of CSW. The strengths of geopolymer were supported by the produced C-A-S-H and carbonates, with less chemically bonded water than the hydration products in the reference group. The dominant size of pores in the hardened geopolymer was much smaller than that in the OPC group which was 80 nm. Silica fume could be the alternate of the sodium metasilicate pentahydrate and had an insignificant negative impact on the fresh and hardened properties and microstructures of the geopolymer when the incorporation rate was within 5%.

Mechanical performance and durability of geopolymer lightweight rubber concrete

This research focuses on producing and testing a type of geopolymer concrete as an alternative to the conventional Portland cement concrete. The proposed concrete incorporates lightweight expanded clay aggregate (LECA) and rubber from car tyre waste which results in the production of a new concrete: “geopolymer LECA-Rubcrete”. A total of ten geopolymer concrete mixes were produced using rubber and LECA as partial replacements of fine and coarse aggregates, respectively. Variables such as the ratio of geopolymer binders, LECA pre-treatment, concrete curing method, and mixing procedures were examined. Physical, mechanical, and durability tests were conducted including workability, compressive strength, drying shrinkage, water absorption, surface abrasion, and carbonation. This research aimed to provide the necessary information needed to develop lightweight geopolymer Rubcrete structures to reduce carbon emissions and move a step closer towards a greener future. The results indicated that lightweight geopolymer Rubcrete is a suitable alternative to lightweight conventional concrete with similar or better durability properties. The workability increased by 9% and 20% when using rubber and LECA, respectively; however, the compressive strength decreased by 32% and 67%, respectively. Using 25% slag to 75% fly-ash decreased the workability by 44% and increased the strength by 47%. Specimens cured in the ambient condition showed less strength compared to those cured in water. Heat + water curing showed less strength in all mixes, except in mixes with no lightweight materials and with high fly-ash content, which showed 16–21% strength increase. Of the tested mixes, geopolymer LECA-Rubcrete mix that has high slag content showed comparable or better performance than that showed by Portland cement LECA-Rubcrete mix in all measured characteristics.

Characteristics of Waste Iron Powder as a Fine Filler in a High-Calcium Fly Ash Geopolymer.

Geopolymer (GP) has been applied as an environmentally-friendly construction material in recent years. Many pozzolanic wastes, such as fly ash (FA) and bottom ash, are commonly used as source materials for synthesizing geopolymer. Nonetheless, many non-pozzolanic wastes are often applied in the field of civil engineering, including waste iron powder (WIP). WIPs are massively produced as by-products from iron and steel industries, and the production rate increases every year. As an iron-based material, WIP has properties of heat induction and restoration, which can enhance the heat curing process of GP. Therefore, this study aimed to utilize WIP in high-calcium FA geopolymer to develop a new type of geopolymer and examine its properties compared to the conventional geopolymer. Scanning electron microscopy and X-ray diffraction were performed on the geopolymers. Mechanical properties, including compressive strength and flexural strength, were also determined. In addition, setting time and temperature monitoring during the heat curing process were carried out. The results indicated that the addition of WIP in FA geopolymer decreased the compressive strength, owing to the formation of tetrahydroxoferrate (II) sodium or Na2[Fe(OH)4]. However, a significant increase in the flexural strength of GP with WIP addition was detected. A flexural strength of 8.5 MPa was achieved by a 28-day sample with 20% of WIP addition, nearly three times higher than that of control.

Elaboration of geopolymer binder from pharmaceutical glass waste and optimization of its synthesis parameters

The objective of this study is to manufacture a new geopolymer binder from pharmaceutical glass waste as a main raw material. The geopolymer synthesis followed a chemical procedure whereby the effect of several parameters, namely, the glass particle size, the concentration of the alkaline solution and the cure temperature were optimized. Several techniques were used to characterize the raw material and the obtained geopolymers: X-ray diffraction, X-ray fluorescence, Fourier-transform infrared, scanning electron microscopy and thermo-gravimetric analysis. The compressive strength of the produced geopolymers was determined by mechanical tests. The results show that the pharmaceutical glass waste produces geopolymer binder of high mechanical performance. Contrary to metakaolin-based geopolymers, no sodium silicate is required for the setting and hardening of this geopolymer type. The thermal activation by increasing the cure temperature improves the geopolymerization kinetics and leads to a high compressive strength, which exceeds 60 MPa for 60 °C and NaOH alkaline solution molarity of 8 M.

Application of low-cost mesoporous geopolymer for dye waste removal

AbstrakEnvironmental pollution causes a significant reduction in water quality. Sustainable development and industrial waste pollution are the supporting factors for the amount of water that is not suitable for consumption. Contaminants in wastewater that pollute water sources include phenolic compounds, substituted compounds, various types of pesticides, and dyes. This study focuses on developing geopolymers as a low-cost alternative adsorbent for adsorbing harmful dyes. Geopolymers can rapidly absorb dyes due to their supportive surface properties to absorb dyes. The porous structure is derived from alumino-silicate materials such as kaolin, metakaolin, dolomite, fly ash, and slag which have been activated with alkaline or alkaline silicate solution. Geopolymers are readily stored adsorbents. Geopolymers have shown good adsorption capacity of the dyes of Methylene blue, Rhodamine B, Congo Red, Methyl Orange, Methyl Violet. This study aims to provide an overview of the types of geopolymer forming materials, geopolymer characterization, application of geopolymers as dye adsorbents, and comparison with other adsorbents. The adsorption isotherm model and adsorption kinetics are also summarized in this overview.

Influence of Microparticles on Setting Time and Micromorphology of Coal Ash Geopolymers

Geopolymers are inorganic materials with zeolites-like microstructure and mechanical properties similar to those of Ordinary Portland cement materials [1]. However, their properties are highly depending on the constituents (raw material and activator) characteristics, as well as, on the activation particularities (mixing parameters, curing time and temperature etc.). In order to explore the influence of partial replacement of coal ash with two types of fine aggregates (glass and sand microparticles) on micromorphology and setting time, four types of geopolymers were developed. The evaluations were performed by means of electronic microscopy and Vicat method. According to this study, the coal ash replacement with glass microparticles results in an increase in the initial and the final setting time, while the replacement of coal ash with sand particles show a significant decrease. Moreover, the microstructural analysis shows different behaviour, during activation, of the studied microparticles. The surface of the glass microparticles reacts in the alkaline environment, while the sand particles did not. Therefore, the increase of initial and final setting time can be correlated with the dissolution of Si-O from the glass particles, during geopolymerisation.

Synthesis and sintering at low temperature of a new nanostructured beta-Eucryptite dense compact by spark plasma sintering

The solid state reaction between kaolin and Li2CO3 with a 1:1 M composition has been studied in the temperature range 380°C-550 °C. The role played by Li2CO3 (basic medium) in the thermal transformation of the kaolin has been investigated by X-Ray diffraction, FESEM, TEM, MAS-NMR and XPS techniques. For the first time, a nanostructured high density β- Eucryptite (<10 nm) has been obtained by Spark Plasma Sintering (SPS) at 550 °C in high vacuum. The atmosphere used in sintering treatments has a determinant role in lithium migration and crystallization of β- Eucryptite. In the case of low vacuum treatments, an amorphous LiAlSiO4 geopolymer type material was obtained. Due to exclusive properties and performances of β- Eucryptite based materials, the results reported in the present investigation open new perspectives for new nanostructured and amorphous functional materials with null thermal expansion, ionic conduction and remarkable mechanical properties.

Experimental Investigations and Prediction of Thermal Behaviour of Ferrosialate-Based Geopolymer Mortars

This paper studies the thermal behaviour of ferrosialate geopolymer mortars. This is done by monitoring various factors influencing the strength gain/loss, weight loss, enthalpy changes, physical and chemical transformations in the ferrosialate geopolymer structure using TG/DT analysis. This study proposed a novel predictive equation for estimating this parameter with the help of gene expression programming (GEP). Fly ash is used as a raw feed for sialate geopolymer, and red mud along with fly ash is used for ferrosialate geopolymer. Till 200 °C, oven-cured samples showed maximum strength results. Whereas in later stages, i.e. after exposure to 400 °C, ambient cured samples surpassed the former by 4.14%. Development of broad amorphous hump in the XRD patterns, presence of thicker geopolymer structure in the SEM images for 400 °C samples, an exothermic peak in the DTA curves at 400 °C and increment in the compressive strength up to 400 °C exposure, all pointing to a conclusion that elevated temperature-favoured ferrosialate geopolymer formation till 400 °C. After exposure to 800 °C, maximum strength loss of 68.57% and 30.3% is observed for sialate and ferrosialate samples dehydroxylation, recrystallization, and melting of unreacted particles are the reasons for diminishing the strength at elevated temperatures. An equation using GEP model (r2 = 0.913) having nine genes is proposed that can predict the residual compressive strength of ferrosialate geopolymer mortars. Though this model is for ferrosialate geopolymer, a similar technique can be easily adapted to other types of geopolymers.

A critical review of slag and fly-ash based geopolymer concrete

Today, concrete remains the most important, durable, and reliable material that has been used in the construction sector, making it the most commonly used material after water. However, cement continues to exert many negative effects on the environment, including the production of carbon dioxide (CO2), which pollutes the atmosphere. Cement production is costly, and it also consumes energy and natural non- renewable resources, which are critical for sustainability. These factors represent the motivation for researchers to examine the various alternatives that can reduce the effects on the environment, natural resources, and energy consumption and enhance the mechanical properties of concrete. Geopolymer is one alternative that has been investigated; this can be produced using aluminosilicate materials such as low calcium (class F) FA, Ultra-Fine GGBS, and high calcium FA (class C, which are available worldwide as industrial, agricultural byproducts.). It has a high percentage of silica and alumina, which react with alkaline solution (activators). Aluminosilicate gel, which forms as a result of this reaction, is an effective binding material for the concrete. This paper presents an up-to-date review regarding the important engineering properties of geopolymer formed by FA and slag binders; the findings demonstrate that this type of geopolymer could be an adequate alternative to ordinary Portland cement (OPC). Due to the significant positive mechanical properties of slag-FA geopolymer cements and their positive effects on the environment, it represents a material that could potentially be used in the construction industry.

Mechanical properties and microstructures of hypergolic and calcined coal gangue based geopolymer recycled concrete

The geopolymer recycled concrete specimens were produced by using hypergolic or calcined coal gangue, slag, fly ash and recycled aggregate as the raw materials. Five different ratios of recycled coarse aggregate to total coarse aggregate and two types of geopolymer recycled concrete schemes (hypergolic coal gangue and calcined coal gangue respectively) were designed for specimen preparation. The compressive strength and splitting tensile strength of the specimens were studied, and the microstructure of the specimens was analyzed by scanning electron microscopy. It is demonstrated by the mechanical property test that the compressive and splitting tensile strength first drop and then grow with the increased mixing ratio of recycled coarse aggregate when the turning point occurs at the mixing ratio of about 30–50%. The microstructure analysis shows that the key factors affecting the mechanical properties of the recycled concrete include the internal porous structure, micro-cracks and the interface bonding ability between geopolymer and recycled coarse aggregate.

Inorganic polymers synthesized using biomass ashes-red mud as precursors based on clay-kaolinite system

Geopolymers are a new class of non-Portland cements produced using an alumino-silicate material (natural minerals, waste and/or industrial by-products) and an alkaline activator to be subsequently cured at relatively low temperatures. The aim of this work is to produce a new type of geopolymer using metakaolin (MK), rice husk ash (RHA) and red mud (RM) by alkaline activation containing sodium silicate and sodium hydroxide (NaOH). Four different geopolymer compositions were prepared at various Si/Al molar ratios (3.85, 4.30, 4.45 and 5.30). A metakaolin based geopolymers were synthesized as a reference. Specimens were characterized by XRD, ATR-FTIR and SEM/EDS. The study revealed that geopolymerization products exhibit an amorphous homogeneous structure with acceptable mechanical properties. RMRHA1 geopolymers shows the best mechanical characteristics (30 MPa) after 60 curing days. MK-RHA-RM based geopolymers obtained seem to offer a feasible alternative to conventional Portland cement contributing to the valorization of the wastes.

Effect of nano-silica on the chemical durability and mechanical performance of fly ash based geopolymer concrete

In this study, the effect of nano silica on the short term severe durability performance of fly ash based geopolymer concrete (GPC) specimens was investigated. Four types of GPC were produced with two types of low calcium fly ashes (FAI and FAII) with and without nano silica, and ordinary Portland cement concrete (OPC) concrete was also cast for reference. For the geopolymerization process, the alkaline activator has selected a mixture of sodium silicate solution (Na2SiO3) and sodium hydroxide solution (NaOH) with a ratio (Na2SiO3/ NaOH) of 2.5. Main objectives of the study were to investigate the effect of usability or replaceability of nano silica-based low calcium fly ash based geopolymer concretes instead of OPC concrete in structural applications and make a contribution to standardization process of the fly ash based geopolymer concrete. To achieve the goals, four types of geopolymer and OPC concretes were subjected to sulfuric acid (H2SO4), magnesium sulfate (MgSO4) and seawater (NaCl) solutions with concentrations of 5%, 5%, and 3.5%, respectively. Visual appearances and weight changes of the concretes under chemical environments were utilized for durability aspects. Compressive, splitting tensile and flexural strength tests were also performed on specimens to evaluate the mechanical performance under chemical environments. Results indicated that FAGPC concretes showed superior performance than OPC concrete under chemical attacks due to low calcium content. Amongst the chemical environments, sulfuric acid (H2SO4) was found to be the most dangerous environment for all concrete types. In addition, nano silica (NS) addition to FAGPC specimens improved both durability and residual mechanical strength due to the lower porosity and more dense structure. The FAIIGPC specimens including nano silica showed the superior mechanical performance under chemical environment.

Stress-strain behavior of geopolymer under uniaxial compression

The various types of structural materials that are available in the construction industry nowadays make it necessary to predict their stress-strain behavior. Geopolymer are alternatives for ordinary Portland cement concrete that are made from pozzolans activation. Due to relatively new material, many mechanical specifications of geopolymer are still not yet discovered. In this study, stress-strain behavior has been provided from experiments for unconfined geopolymers. Modulus of Elasticity and stress-strain behavior are critical requirements at analysis process and knowing complete stress-strain curve facilitates structural behavior assessment at nonlinear analysis for structures that have built with geopolymers. This study intends to investigate stress–strain behavior and modulus of elasticity from experimental data that belongs for geopolymers varying in fineness and mix design and curing method. For the sake of behavior determination, 54 types of geopolymer are used. Similar mix proportions are used for samples productions that have different fineness and curing approach. The results indicated that the compressive strength ranges between 7.7 MPa and 43.9 MPa at the age of 28 days curing.

Bond strength between concrete substrate and metakaolin geopolymer repair mortar: Effect of curing regime and PVA fiber reinforcement

The suitability of repairing Portland cement concrete with geopolymer mortars is explored as a viable way to replace Portland cement in concrete repairs and reduce their carbon footprint. Bond tests are performed through non-standard slant shear tests with variable bond plane inclination to assess concrete-geopolymer shear bond strength under different combinations of normal and shear stresses at the concrete-geopolymer interface. Interfacial cohesion and friction coefficients, two inherent mechanical properties of the substrate-repair interface, are extrapolated from experimental data and compared among different types of geopolymer repairs. The adoption of different curing temperatures for the geopolymer repair mortar (20°C and 45°C) and its reinforcement with various contents of Polyvinyl Alcohol fibers (volume fractions Vf = 0%, 0.5%, and 1%) are investigated to optimize the substrate-repair bond. Mechanical tests are supported by statistical analysis and microscope observation.

Phosphate-based geopolymer: Formation mechanism and thermal stability

Chemosynthetic phosphate-based geopolymer is a new type of low carbon and eco-friendly construction material. This article aims to investigate the formation mechanism and thermal stability of this new type of geopolymer. In this study, three mixes of the phosphate-based geopolymer were designed and synthesized at ambient temperature with different molar ratios of Si, Al and P, which were supplied by the raw materials of silica fume, metakaolin and monoaluminum phosphate. No accelerating setting condition (e.g., metal oxides addition or high temperature curing) was applied. The experimental results showed that the 28-day compressive strength of the hardened geopolymer paste arrived at about 31MPa when the Al/P molar ratio is equal to 1.0, which was ensured by the formation of an amorphous structure of SiO2·Al2O3·P2O5·nH2O and a crystalline phase, aluminum hydrogen phosphate (AlH3(PO4)2·3H2O). At elevated temperatures, a phase transition of the phosphate-based geopolymer was activated from aluminum hydrogen phosphate to berlinite (AlPO4) and the silicon-containing phase was rearranged.

A novel geopolymer application: Coatings to protect reinforced concrete against corrosion

This study evaluates the performance of two hybrid type geopolymer mortars composed of alkaline-activated fly ash (FA) and metakaolin (MK) as protective coatings against chloride-induced corrosion in reinforced concrete. In both cases, the coated, Portland cement (OPC)-based concretes (substrates) were subjected to accelerated techniques such as impressed voltage and wetting/drying (w/d) cycles in the presence of a 3.5% NaCl solution. The corrosion was also monitored by applying techniques involving linear polarization resistance and open circuit potential. The results allowed for the conclusion that the MK-based geopolymer coating exhibited the best performance, reducing the corrosion rate compared to concrete without coating (reference) by 4cycles of w/d. After cycle 5, the corrosion rate was similar for the specimens with or without coating. The application of geopolymer type coatings (mortars) is suggested as a method of protecting structures exposed to marine environments.

“Fly ash and GGBFS based powder-activated geopolymer binders: A viable sustainable alternative of portland cement in concrete industry”

Geopolymer is a new binding material, synthesized by alkali activation of aluminosilicate compounds. Previous researches around the world postulated that concrete from geopolymer binder exhibited superior engineering, thermal and durability properties than ordinary Portland cement (OPC) concrete, such as higher mechanical strengths, higher resistivity to sulphate and acid attacks and higher thermal resistivity.Geopolymers are generally made from activation of aluminosilicate powders by highly concentrated sodium hydroxide and or sodium silicate solutions, known as liquid-activated geopolymer. Recently, some cement and concrete companies around the world have commenced the production of liquid activator based geopolymer binders. However, this type of geopolymer does not appear as a viable replacement of Portland cement in concrete industry despite its substantial environmental benefits because of its limitation in mixing and handling process. Powder-activated geopolymer contains alkali activators in powder form which are blended together with source material. This geopolymer binder is physically similar to OPC and mixing and handling process are also similar to conventional process. Experimental results showed that concrete from this binder can set and harden in ambient temperature with significant early age strength.Two types of powder-activated geopolymer binders having different proportions of fly ash and slag were used in this study. Engineering properties of geopolymer concrete of four different strength grades (40, 50, 65 and 80MPa) were investigated in detail at ambient curing condition and compared with OPC concrete of same grade.