Alkaline Activation Of Fly Ash Research Articles

Rapid and inexpensive method for bisphenol a detection in water samples based on alkaline activated fly ash modified carbon paste electrode

Rapid and inexpensive method for bisphenol a detection in water samples based on alkaline activated fly ash modified carbon paste electrode

Mechanical Behavior of a Mine Tailing Stabilized with a Sustainable Binder

Mining is a primary sector for the national economy of many countries, but exploiting these natural resources causes negative impacts on the environment. Tailings produced during mining, called mine tailings, have to be disposed of, and for that purpose, they are often mixed with Portland cement to control environmental toxicity and improve their mechanical properties. However, the high environmental impacts of producing Portland cement are well known. In this sense, sustainable binders based on the alkaline activation of industrial wastes have been studied as an alternative to using Portland cement. This study focused on applying a sustainable binder based on the alkaline activation of fly ash to improve the mechanical performance of a mine tailing from a mine located in Portugal. Geotechnical tests and chemical analysis were conducted to characterize the mine tailing and fly ash used in the alkaline activation process. In addition, triaxial tests were performed to evaluate the mechanical performance of the specimens, with both natural and stabilized tailings. The developed study proved that stabilized tailing with activated fly ash shows promising mechanical performance showing that this approach can be an excellent alternative to using Portland cement.

Heat flow modelling of the alkaline activation of fly ash with sodium hydroxide in the presence of portlandite

Alkali-activated cement is a promising alternative to replace totally or partially Portland cement. The heat flow and the degree of reaction are widely analyzed variables on the alkali-activation process. In this paper, a phenomenological-based semi-physical model of the alkali-activation process was developed. The model predicts the heat flow and the degree of reaction, by correlating the composition of the fly ash, the NaOH concentration (alkaline activator), the concentration of portlandite and curing temperature. The model considers balanced chemical reaction and the process diffusive phenomena. For validation microcalorimetric measurements at 25 °C and 35 °C was made, and secondly Freisleben-Hansen model was fitted with the experimental data. The results indicate a reaction acceleration for concentration of NaOH in (6–10) M and a reaction deceleration due to portlandite. The fly ash particle size and diffusivity-associated factors have an incidence of more than 5 % on the heat flow and degree of reaction.

Novel Foaming-Agent Free Insulating Geopolymer Based on Industrial Fly Ash and Rice Husk.

This study highlights the synthesis of a new thermal insulating geopolymer based on the alkaline activation of fly ashes. A porous geopolymer material can be prepared without the addition of a foaming agent, using high ratio solution/ashes (activating solutions used are water, sodium or potassium hydroxide). In order to increase the porosity of the material and to make it more ecological, rice husks are incorporated into the formulation. The geopolymer materials were prepared at room temperature and dried at moderate temperature (105 °C) by a simple procedure. The microstructural characteristics of these new porous geopolymers were assessed by optical microscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA) and X-ray fluorescence (XRF). Infrared spectroscopy (FTIR) was used to confirm the geopolymerisation. The effect of the ratio solution/ashes and the percentage of the rice husk addition on thermal and mechanical analysis was evaluated. An insulating material for a solution/ashes ratio of 0.9 and a rice husk content of 15% having a λ value of 0.087 W/(m·K), a porosity of 61.4% and an Rc value of 0.1 MPa was successfully prepared.

Heat Flow Modelling of the Alkaline Activation of Fly Ash with Sodium Hydroxide in the Presence of Portlandite

Heat Flow Modelling of the Alkaline Activation of Fly Ash with Sodium Hydroxide in the Presence of Portlandite

Identification and characterization of faujasite zeolite phase in alkali activated class F fly ash

This paper concerns the identification and characterization of the Faujasite-Zeolite phase resulting from the alkaline activation of Fly Ash (FA) by sodium hydroxide (NaOH). FA was chemically analyzed and used to prepare the zeolitic material. Alkali activated materials are described as materials obtained by the reaction between precursors and activators. Two key process parameters have been taken into account for the synthesis of this material: the liquid/solid ratio, the concentration of the alkaline solution. For this purpose, Alkali activated FA (AAFA) was prepared by combining Moroccan FA (ASTM class F) and sodium hydroxide (purity, 99%). The FA mixture (100 g) was heated to 80–90 °C in aqueous NaOH (5 mol / L, 300 mL) with magnetic stirring and kept at reflux for 6 h. The synthesized zeolite are characterized using various techniques including X-ray diffraction (XRD),Fourier-transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) were conducted to evaluate the characteristics of the resulting products. The thermogravimetric results reveal the presence of new products such as Faujasite.

2021 Frank Newman Speller Award:Corrosion Mechanisms of Steel and Copper in Engineering Applications

The main research lines of the scientific career of the author are herein, exemplified including corrosion and protection mechanisms of steel in different environments, and copper corrosion in climate systems. Stainless steel (SS) due to its high corrosion resistance is a material widely used for many engineering applications. Impedance measurements were performed on polarized specimens at the pitting region of Type 304 SS in environment containing chloride at 25°C and 60°C. The transfer function was analyzed, indicating instability system, corroborating results obtained using the Kramers-Kronig transforms. Steel reinforcement has been studied for structural applications in civil engineering and architecture using cementitious materials, alkaline-activated fly ash (AAFA), an alternative to the ordinary Portland cement (OPC). The main compounds used as corrosion inhibitors in concrete were included. Carbon steel embedded in OPC mortar was tested in the presence of phosphates as corrosion inhibitors. An organic lacquer was applied to tinplate with titanium-passivation treatment and, in general, acceptable and comparable behavior was obtained to conventional chromium-passivated lacquered tinplate. Copper is also a material used in many engineering applications. Ant-nest corrosion of copper tubing in air-conditioning systems has been reported. The copper corrosion rates occasioned by carboxylic acids, formic, acetic, propionic, and butyric, were included.

The development of technology for production of zeolites from fly-ash from Troitskaya power plant

The study examines the technology of processing fly ash from Troitskaya power plant for the production of zeolite. The paper presents the results of laboratory studies evaluating the suitability of fly ash from Troitskaya power plant for the production of zeolites and the development of the zeolite production process. Fly ash contains a small amount of heavy metals that can complicate processing, but contains a large amount of silicon oxide. The technology consists of high-temperature alkaline activation of fly ash and hydrochemical synthesis. The resulting powder has a specific surface area of 89.7 m2/g, determined by the BET method, and an average pore diameter of 0.345 μm. The static exchange capacity was 220 mg/g.

Fracture toughness of fly ash-based geopolymer gels: Evaluations using nanoindentation experiment and molecular dynamics simulation

This paper presents the fracture toughness of sodium aluminosilicate hydrate (N-A-S-H) gel formed through alkaline activation of fly ash. While the fracture toughness of N-A-S-H is obtained experimentally from nanoindentation experiment implementing the principle of conservation of energy, the numerical investigation is performed via reactive force field molecular dynamics. A statistically significant number of indentations are performed on geopolymer paste yielding frequency distribution of Young’s modulus. Four distinct peaks are observed in the frequency distribution plot from which the peak corresponding to N-A-S-H was separated using statistical deconvolution technique. The young’s modulus of N-A-S-H, thus obtained from statistical deconvolution shows excellent match with the values reported in the literature, thus confirming successful identification of indentations corresponding to N-A-S-H. From the load-penetration depth responses of N-A-S-H, fracture toughness was obtained following the principle of conservation of energy. The experimental fracture toughness shows good correlation with the simulated fracture toughness of N-A-S-H, obtained from reactive force field molecular dynamics. The fracture toughness of N-A-S-H presented in this paper paves the way for multiscale simulation-based design of tougher geopolymer binders.

Experimental Study on the Flexural Behavior of Alkali Activated Fly Ash Mortar Beams

This work aims to study the possibility of using alkaline activated fly ash in structural members. The work, of an experimental nature, focuses on the evaluation of the behavior of simply supported beams under two symmetrical loads (four-point tests). For such study, 10 beams were built, of which, five using fly ash and the remaining five using traditional Portland cement. The test results are compared. Conclusions on the practical application of fly ash in structures were explained and, as mention later in this document, there is room for improvement. This is one of very few works on fly ash alkali activated structures and further studies are necessary in the future. Some aspects, such as shrinkage and deformability are presented as some of the negative points concerning the potential use of fly ash. These are two aspects that need more attention in future investigations.

Effect of various commercial of Na2SiO3 on compressive strength of Fly ash-based alkaline activated mortar

This study aimed to assesses the effect of various commercial Na2SiO3 on the compressive strength (CS) of alkaline activated fly ash mortar (AAFM). The three mixture of alkaline activated mortar (AAM) C1, C2 and C3 were prepared from the source material of fly ash and alkaline activator solution (AAS). The initial AAS was comprised of NaOH (10M) and various grade of Na2SiO3. The various grades of Na2SiO3 were characterized by their SiO2/Na2O molar ratio of 2.0, 2.2, and 3.3, respectively. The sample from each mixture was characterized based on the CS and microstructure changes using useful tools of XRD and FTIR analysis. The results obtained indicated that the highest CS achieved among the three mixtures were 48.23MPa of mixture C2 prepared with SiO2/Na2O molar ratio of 2.2. This was mainly due to higher binder formation (N-A-S-H gel type) and a higher rate of reaction of the main source material. This result is in line with XRD and FTIR analysis results finding.

Fracture toughness of sodium aluminosilicate hydrate (NASH) gels: Insights from molecular dynamics simulations

This paper evaluates the fracture toughness of sodium aluminosilicate hydrate (N-A-S-H) gel formed through alkaline activation of fly ash via molecular dynamics (MD) simulations. The short- and medium-range order of the constructed N-A-S-H structures shows good correlation with the experimental observations, signifying the viability of the N-A-S-H structures. The simulated fracture toughness values of N-A-S-H (0.4–0.45 MPa m0.5) appear to be of the same order as the available experimental values for fly ash-based geopolymer mortars and concretes. These results suggest the efficacy of the MD simulation toward obtaining a realistic fracture toughness of N-A-S-H, which is otherwise very challenging to obtain experimentally, and no direct experimental fracture toughness values are yet available. To further assess the fracture behavior of N-A-S-H, the number of chemical bonds formed/broken during elongation and their relative sensitivity to crack growth are evaluated. Overall, the fracture toughness of N-A-S-H presented in this paper paves the way for a multiscale simulation-based design of tougher geopolymers.

Effect of incorporating multifilament polypropylene fibers into alkaline activated fly ash soil mixtures

Soil stabilization is a well-known methods for the treatment problematic soils. Its advantages over soil replacement include low cost and fast implementation. The alkaline activation of soft soils is a new technique that has been proposed recently to stabilize soft soils. However, its strengthening mechanism and the final product in terms of stiffness and brittleness resemble those observed in cemented soils. In other words, the residual strength which emerges when approaching failure is very low, and this results in immediate damage to building structures. These shortcomings need to be overcome, particularly in places where seismic loading can be expected. In the case of cemented columns under heavy embankments, horizontal displacement is likely to occur under seismic loading. This will result in the failure of stabilized material due to frail bending moments, making greater residual strengths more important than higher peak strengths. To address this problem, a fix fly ash content of 40% and polypropylene fibers in the range of 0.5%, 0.75%, 1%, and 1.25% were considered. Compressive, flexural and indirect tensile strength test results revealed the feasibility of polypropylene fibers to improve post-peak behavior, thus allowing for higher residual strength after failure.

Synthesis of alkaline cements based on fly ash and metallurgic slag: Optimisation of the SiO2/Al2O3 and Na2O/SiO2 molar ratios using the response surface methodology

Abstract During the present work, different binders were synthetized by alkaline activation of fly ash (FA) and a mixture of 75% fly ash and 25% metallurgical slag (FASLG). Two different curing periods, of 7 and 28 days, were considered. A Variance Analysis (ANOVA), conducted to assess the effectiveness of the Response Surface Methodology that was used to structure the study, revealed that this was capable to predict, with satisfactory precision, the maximum compression strength values of the pastes considered. By optimising the independent variables, defined as the SiO2/Al2O3 and Na2O/SiO2 molar ratios, 28-day uniaxial compression strength (UCS) values of 44.3 MPa and 28.5 MPa were predicted, for the FA28 and FASLG28, respectively. The experimental results showed UCS values of FA28 = 41.5 MPa and FASLG28 = 22.1 MPa, confirming the validity of each model. R-square values of 85.76% (FA28) and 85.48% (FASLG28) are an effective measure of the experimental variability associated with the estimation of new observations, which can be further reduced if more variables are controlled and included in the model.

Sustainable alkaline activation of fly ash, aluminium anodising sludge and glass powder blends with a recycled alkaline cleaning solution

Introduction of new residues and wastes in the development of alkaline activated materials is a major concern regarding the spreading and dissemination of this technique. Such increase in the spectrum of available raw materials will decrease the need for long-distance transportation of the more traditional precursors that have been tirelessly used in the past two decades (e.g. fly ash, blast furnace slag). Additionally, the use of commercial activators severely hinders its environmental and financial performance, promoting the need to develop waste-based activators. In this paper, wastes from the aluminium anodising and extrusion processes and from the production of optical lenses were combined with low-calcium fly ash, to produce binders exclusively made from wastes and residues. The performance was assessed through uniaxial compression strength tests, which were accompanied by the monitorisation of several physical properties, including temperature, pH and weight; and by a thorough microscopic analysis, including scanning electron microscopy, coupled with energy dispersive spectroscopy, and x-ray diffraction, for mineralogy characterisation. Results show that the addition of glass powder and aluminium anodising sludge to class-F fly ash optimised the final precursor, which was then successfully activated with a disposed solution, originally used to clean the aluminium extrusion steel dies. The inclusion of soluble silicon and aluminium in the precursor raised the compression strength after short-term curing, compared with pastes prepared only with fly ash.

Radiological characterisation of alkali-activated construction materials containing red mud, fly ash and ground granulated blast-furnace slag

Poor storage of industrial wastes has been a cause of land contamination issues. These wastes or by-products have the potential to be used as secondary raw materials in construction, promoting the concept of a circular economy that will avoid land contamination. Here we evaluate radiological environmental impacts when wastes that contain elevated levels of naturally occurring radionuclides (NORs) such as red mud, fly ash and ground granulated blast furnace slag are made into ‘green cements’ such as geopolymers or alkali-activated materials (AAMs). During the study, three AAM concrete and mortar series with various mixing ratios were prepared and investigated. The NOR content, I-Index, radon emanation and exhalation of the precursor waste materials and their cement products were measured and calculated and the strength of the cement products was compared. The emanation and the exhalation properties were calculated for the final products, weighing the data of the components as a function of their mixing ratio. The I-index alone suggested that the AAMs would be suitable products. AAMs containing ground granulated blast furnace slag exhibited the lowest radon exhalation and higher compressive strength, while the fly ash and red mud AAMs had increased final radon exhalation. In the case of fly ash, alkaline activation of fly ash dramatically increased the radon exhalation; the highest measured fly ash exhalation was 1.49 times of the theoretically calculated exhalation value. This highlights the increased risk of using fly ash as a component in AAMs and the need to carry out testing on the final products as well as individual secondary raw materials.

Synthesis and characterisation of a binder cement replacement based on alkali activation of fly ash waste

Abstract This study considers the valorisation of an important amount of fly ash generated as waste in the process of coal burning in a thermal power plant of Iasi municipality (Romania). The waste valorisation is related to the development of a new building material by using the alkaline activated fly ash based on the fact that inorganic polymers with similar properties to ordinary Portland cement may be obtained by alkaline treatment. Three main operating parameters were considered for the synthesis of this material: the liquid/solid ratio, the concentration of alkaline solution and the activation temperature. By minimizing the activation temperature and recycling the hydroxide solution, the synthesis of low-cost materials for partial cement replacement in concrete was possible. The synthesized materials were thoroughly characterised for analysis of chemical composition, morphology, physical and mechanical properties by XRD, SEM, EDX, TGA, FTIR, density and compressive strength. According to experimental results, the synthesized materials have a bigger specific surface area as compared to that determined for fly ash. The XRD and FTIR analysis proved that fly ash waste contains: quartz, mullite, iron oxide and a vitreous phase, while the synthesized materials after the fly ash alkaline treatment contain: quartz, sodalite, chabazite, geopolymer gel.

Parameters Affecting the Mechanical Properties of Fly Ash-Based Geopolymer Binders – Experimental Results

As the demand for concrete and the needs to satisfy development of infrastructure facilities increase, it is essential to find alternatives to create environment-friendly concrete. The particular procedure of alkaline activation of fly ash - in which ash resulting from a power plant is combined with a specific alkaline activator in order to create a solid material, then dried at a certain temperature - opened new opportunities for this new material to get attention worldwide. In order to obtain a material with similar properties of ordinary Portland cement concrete and to obtain desirable compressive strengths, the parameters that affect this type of binders should be fully understood. The aim of this paper is to study the main parameters affecting the mechanical strength of the fly ash-based geopolymer paste and their interactions. Parameters such as molarity of sodium hydroxide (from 8M to 12M) and alkaline activators ratio (from 0,5 to 2,5) were analysed to observe how they affect the mechanical properties of the geopolymer paste. Experimental results show that the compressive strength of the fly ash-based geopolymer paste produced using Romanian local raw materials increases with the increase of the concentration of sodium hydroxide and higher ratios of Na2SiO3/NaOH solution.

Alkali-Activated Fly Ashes: Influence of Curing Conditions on Mechanical Strength

Alkaline activation of fly ashes is a procedure that enables an alternative binder which has been receiving much interest by several research groups particularly on the manufacturing of mortars and concretes. The properties of the materials that are developed during the alkaline activation are influenced by the curing conditions (temperature and relative humidity). Another relevant facet related to the curing procedures is the possibility of carbonation occur, which may have an impact on the mechanical strength of the alkaline cements. In this research, several sets of curing conditions were tested to understand which one results in a higher strength and reveals carbonation. Uniaxial compressive strength tests were conducted to assess mechanical behavior. The outcome suggests that higher temperature and low relative humidity yields higher mechanical strength.

The Effect of Alkaline Activator Ratio on the Compressive Strength of Fly Ash-Based Geopolymer Paste

Alkaline activation of fly ash is a particular procedure in which ash resulting from a power plant combined with a specific alkaline activator creates a solid material when dried at a certain temperature. In order to obtain desirable compressive strengths, the mix design of fly ash based geopolymer pastes should be explored comprehensively. To determine the preliminary compressive strength for fly ash based geopolymer paste using Romanian material source, various ratios of Na2SiO3 solution/ NaOH solution were produced, keeping the fly ash/alkaline activator ratio constant. All the mixes were then cured at 70 °C for 24 hours and tested at 2 and 7 days, respectively. The aim of this paper is to present the preliminary compressive strength results for producing fly ash based geopolymer paste using Romanian material sources, the effect of alkaline activators ratio on the compressive strength and studying the directions for future research.