Fly Ash Research Articles

Rheology, shrinkage, mechanical properties and microstructure of ultra-light-weight concrete with fly ash cenospheres

Cenospheres are low-density and hollow microspheres derived from coal-fired power plant fly ash waste. This study aims to prepare ultra-light-weight (<1000 kg/m3 wet density) concrete using fly ash cenospheres (FAC). To begin with, FAC’s shell thickness and the water absorption and desorption were characterized. A mixing procedure was designed to avoid the segregation between the FAC and cement slurry. FAC can affect the rheological properties of fresh mixture over time through absorption and desorption of free water. The presented ultra-light-weight concrete has several advantages compared to the ones prepared using foaming methods. First, shrinkage is significantly reduced due to FAC’s internal restraint and curing effects. Secondly, it has good mechanical performance, especially in bending and is more environmentally friendly due to use of less cement. X-ray computed tomography illustrates that FAC ultra-light-weight concrete has smaller pores of more uniform size compared with those prepared using foaming methods. X-Ray diffraction, thermal gravimetry-derivative thermal gravimetry, fourier-transform infrared spectroscopy and scanning electron microscopy are employed for the hydration products and microstructure characterization. Outcomes prove that FAC can combine well with the cement matrix, and react with calcium hydroxide to produce C-A-S-H through pozzolanic reaction.

Dynamic characterization of the flow field of air classifier disturbed structures and application to efficient separation of fly ash

Classification is crucial for the resource utilization of fly ash, impacting both utilization rates and product quality. This study introduces an enhanced flow field structure in a perturbed rotating centrifugal air classifier by optimizing toothed and tail blade designs for efficient fly ash classification. Using numerical simulations and experiments, we examine the flow field performance and separation efficacy at various speeds, and employ Dynamic Mode Decomposition (DMD) for modal analysis. Results show the toothed blade, angled at 35°, produces small-scale turbulence with high pressure and velocity, while the tail blade’s rightward bend induces large-scale vortices, aiding flow control. Modal analysis highlights that both Drs-types 1 and 2 predominantly exhibit weakly attenuated modes. Optimal classification occurs at Rs = 950rpm and fv = 0.3kg/s, with both Drs-types surpassing the original structure in effectiveness and pressure. These findings provide new directions for industrial applications and the design of cyclone air classifiers.

Effects of Na2SiO3/NaOH ratio in alkali activator on the microstructure, strength and chloride ingress in fly ash and GGBS based alkali activated concrete

In this study, the impact of alkaline solutions composed of various Na2SiO3/NaOH ratio and NaOH molarity on the strength, chloride ingress and chloride binding capacity of fly ash (FA) and ground granulated blast furnace slag (GGBS) based alkali activated concrete (AAC) was investigated. The microstructural properties of alkali activated binders (AAB) composites was also studied to understand its influence on the chloride permeability of AAC. Chloride permeability of concrete was tested by using the rapid chloride penetration test (RCPT) and by immersing concrete in NaCl solution (ASTM C1556). The compressive strength, chloride ingress and chloride binding capacity of AAC was compared with Portland cement-based concrete (OPC). Results showed that higher Na2O/SiO2 ratio in alkaline solutions resulted in a weak microstructure with, low strength and high chloride ingress. Concrete activated by alkaline solutions with Na2O/SiO2 molar ratio =1 (+3), exhibited greater compressive strength and resistance to chloride ion penetration. The increase of SiO2 concentration in alkaline solution greatly reduces the binding capacity of AAC while the bound chlorides increased with the NaOH molarity. No chemical chloride binding was observed in AAC but for OPC concrete, calcium salts formed in the microstructure after immersion in NaCl solution. Compared to OPC concrete, AAC showed superior performance in terms of strength and chloride diffusion making it a potential candidate for application in marine structures.

Immobilization mechanism of heavy metals by crystals and liquid phase during melting treatment of MSWI fly ash

Melting treatment has emerged as a promising technology for managing municipal solid waste incineration (MSWI) fly ash owing to its advantageous features of effective detoxification and volume reduction. The melting treatment of MSWI fly ash involves the immobilization of heavy metals by crystals and liquid phase. Herein, the immobilization mechanism of heavy metals (Cu, Pb and Cd) by the crystals and the liquid phase was investigated using melting experiments, thermodynamic calculations and density functional theory (DFT) calculations. Results demonstrate that the immobilization of heavy metals is influenced by a combination of factors: the reaction of heavy metals, physical encapsulation ability of the liquid phase and chemical fixation ability of both the crystals and the liquid phase. An increase in the content of SiO2 and Al2O3 promotes the conversion of heavy metals oxides into heavy metals chlorides. Furthermore, an increase in the content and polymerization degree of the liquid phase facilitates the physical encapsulation of heavy metals chlorides. The chemical fixation ability of the crystals and the liquid phase differs for Cu and Pb, while Cd cannot be immobilized through chemical fixation. To enhance the immobilization of heavy metals during melting treatment, the chemical composition of MSWI fly ash should be adjusted within the anorthite region of the ternary phase diagram. This study provides valuable insights into the immobilization mechanism of heavy metals by the crystals and the liquid phase during the melting treatment of MSWI fly ash.

Tensile strength and durability performances-based evaluation of 3D-printed and mold-cast fibrous geopolymer composites produced at various alkaline activator combinations

This study aimed to investigate the effects of the sodium silicate-to-sodium hydroxide ratio, SH molarity, and carbon fiber volume fraction on the tensile strength and durability properties of mold-cast and 3D-printed geopolymer composites, including flexural and splitting tensile strengths, ultrasonic pulse velocity, water absorption, sorptivity index, and chloride penetration properties. For that purpose, the ground-granulated blast furnace slag and fly ash were employed as alumino-silicate-rich raw material. In order to activate the alumino-silicate-rich raw material, two sodium silicate/sodium hydroxide ratios of 1 and 2 and three sodium hydroxide molarities of 8M, 10M, and 12M were designated. Furthermore, carbon fiber was incorporated into the geopolymer composites at three volume fractions: 0%, 0.3%, and 0.6%. In total, 18 nonfibrous and fibrous geopolymer composites were manufactured in two different ways: mold-cast and 3D-printed. The findings demonstrated that the strength and durability characteristics of 3D-printed specimens were inferior to those of mold-cast specimens, attributed to the presence of weak interfacial bonds between layers. It has been observed that the incorporation of carbon fiber has the effect of improving tensile strength performance. Nevertheless, the addition of carbon fiber led to a slight decrease in UPV values, and an increase in water absorption and sorptivity index values. Also, it adversely influenced the chloride penetration of geopolymer composites. The findings of the study also indicated that increasing the sodium hydroxide molarity had a positive impact on the strength and durability properties of the composites. Nevertheless, it was observed that increasing the sodium silicate-to-sodium hydroxide ratio led to a decrease in both tensile strength and durability performances. Additionally, the microstructure of the geopolymer composites was analyzed using scanning electron microscope (SEM) images.

Sustainable enhancement of fly ash/steel slag composite cement: The role of TriDiethanolamine Citrate in promoting hydration and microstructure

The development of sustainable cementitious materials is critical for reducing the environmental impact of the cement industry. This study examined the feasibility of using the new amide-alcohol organic hydration promoter, TriDiethanolamine Citrate (TriDECA), in fly ash or steel slag (FA/SS) composite cement. The effects of TriDECA on the hydration process, hydration products, microstructure and compressive strength of FA/SS composite cement, as well as its impact on the dissolution of FA and SS, were systematically investigated. Results demonstrated that TriDECA significantly accelerated the dissolution of FA and SS, promoted the formation of hydration products (C-S-H, AFm), and refined the pore structure. Additionally, TriDECA increased the concentration of critical ions in the pore solution, promoted hydration and enhanced overall performance. At 28 days, FA-TriDECA and SS-TriDECA showed 8.1 % and 14.2 % higher strength than FA-TEA and FA-Ref, respectively. For SS-TriDECA, the increase was 13.2 % and 11.2 % compared to SS-TEA and SS-Ref, respectively. These findings suggest that TriDECA is a promising additive for enhancing the sustainability and performance of FA/SS composite cements, offering advantages in hydration promotion and microstructure improvement over traditional alkanolamines.

Optimizing the content of Li2CO3, Na2SO4 and TEA in fly ash–cement system by response surface methodology

With an optimized dosage, hardening accelerators become a vital means of modifying fly ash-cement system (FAC). This study comprehensively investigated the mechanical properties of FAC modified by Li2CO3, Na2SO4, and triethanolamine (TEA) under different dosages, and optimized the dosage of accelerators through the response surface method (RSM). The synergistic effect of accelerators on the hydration of FAC was characterized by thermogravimetric differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The results demonstrated that the factors and response value followed a quadratic polynomial model. The regression coefficients R2 of the model were all greater than 0.9, indicating good agreement with the experimental data. The content of Li2CO3 and Na2SO4 had an extremely significant effect on the compressive strength of 1d and 3d, followed by TEA. The optimal mix ratio predicted by RSM was 0.12% Li2CO3, 0.47% Na2SO4, and 0.40% TEA. Early hydration stages revealed that the combined action of these accelerators increased the formation of CH, CaCO3, and amorphous C-(A)-S-H gel. Microscopically, the surface of fly ash exhibited alkali-induced corrosion, thereby enhancing its pozzolanic reactivity.

Limestone calcined clay-based engineered cementitious composites (LC3-ECC) with recycled sand: Macro performance and micro mechanism

Limestone calcined clay cement (LC3) contributes to the development of sustainable cement-based materials. In this study, LC3 was combined with fly ash (FA) and recycled sands (RS) to develop engineered cementitious composites (ECC). Three FA/LC3 ratios (1, 1.5, and 2) and three RS particle sizes (0.15–1.18 mm, 0.15–2.36 mm, and 0.15–4.75 mm) were studied. Compared to ordinary Portland cement (OPC)-based paste, the LC3 substitution resulted in higher hydration heat and hydration degree, forming more hydration products. Although LC3 substitution produced a slightly lower compressive strength, a more robust tensile strain-hardening behavior than OPC-based ECC was achieved. The increasing FA/LC3 ratios gradually reduced compressive strength, tensile strength, and crack width. The multiple cracking behavior with controlled widths of LC3-based ECC was found to be more stable, which could be traced to the superior properties of fiber/matrix interfacial transition zone. In addition, utilizing RS as fine aggregates with various particle sizes could achieve an ultra-high tensile strain capacity exceeding 8 % for LC3-based ECC, thereby enhancing its utilization efficiency. Furthermore, the utilization of LC3 resulted in 28.6–47.1 % and 6.6–22.0 % reductions in carbon emission and embodied energy, respectively. The combination of LC3 and RS holds a promising approach to developing sustainable ECC with desirable mechanical performance.

Effect of sludge-based additive on particulate matter emission during the combustion of agricultural biomass pellet

In this study, the effects of a sludge-based additive on particulate matter emission during the cornstalk pellet combustion were investigated using a vertical fixed bed reactor combined with a Dekati low pressure impactor (DLPI). It was found that the PM1 and total PM10 yields from the cornstalk pellet combustion were much higher than those from the individual combustion of sludge-based additive. With the addition of sludge-based additive, the alkali and alkaline earth metals (AAEMs) in biomass would react with the Al/Si-containing and P-containing inorganic minerals in sludge-based additive to form various aluminosilicates, silicates, and K-Ca-P compounds, which could enhance the potassium fixation and retain it in the coarse particles, such as fly ash and residual ash. The PM1 and total PM10 yields from the composite pellet combustion could be effectively reduced by 62%, with the mixing ratio of sludge-based additive increasing to 75%. The mixing ratio of sludge-based additive showed a positive synergistic effect in reducing the emission of PM and a mixing ratio of <30% was recommended based on comprehensive considerations to produce relatively high-quality pellet fuel with respect to good heating value and low ash content and PM emission in later combustion application.

Utilization of waste phosphogypsum in high-strength geopolymer concrete: Performance optimization and mechanistic exploration

Phosphogypsum (PG) is an industrial waste produced during the manufacture of phosphoric acid. In this study, dihydrate phosphogypsum (DPG), ground granulated blast furnace slag (GGBFS), fly ash (FA), Portland cement clinker (PCC), sulfate alumina cement clinker (SACC), water reducer, sand, and stone were combined to create a phosphogypsum-based geopolymer (PBG) concrete. Concrete mix design was carried out based on the principle of maximum packing density, and the effects of water reducer type, sand ratio, water-to-binder ratio, and DPG content on PBG concrete properties were investigated. Results indicated that compared to SiKa ViscoCrete 540P (SVC 540P) water reducer, Melflux PLUS 1087L (MP1087L) significantly enhanced the performance of PBG concrete. With a water-to-binder ratio of 0.34, a sand ratio of 32.2 %, and a PG:GGBFS:FA ratio of 5:4:1, the 28-day unconfined compressive strength (UCS) of the concrete exceeded 60 MPa. The concrete primarily consisted of phases such as dihydrate gypsum (CaSO4·2H2O), ettringite (Ca6(Al(OH)6)2(SO4)3(H2O)26), polymer (-Si-O-Al-), quartz (SiO2), albite (Na(AlSi3O8)) and Muscovite ((K,Na)Al2(Si,Al)4O10(OH)2). Using two mild alkalis as activators, PBG concrete can avoid the efflorescence often associated with geopolymer preparation and can cure at 20 °C. PBG concrete offers high strength, ease of preparation, and environmental benefits, providing a new avenue for the reuse of PG.

High-performance superhydrophobic fly ash based geopolymers with graphene oxide reinforcement for enhanced durability and repellency

While high-performance fly ash geopolymers offer a demonstrably reduced carbon footprint in the construction industry, their inherent affinity for water (hydrophilicity) can facilitate the accumulation of moisture within the material matrix, potentially leading to the initiation and propagation of internal corrosion. The implementation of hydrophobic functionalization strategies on fly ash geopolymers demonstrably enhances their resistance to corrosive degradation. Nevertheless, a crucial challenge persists in the form of mitigating potential declines in mechanical strength. This investigation endeavors to attenuate the deleterious effects exerted by the hydrophobic aluminosilicate hydrate phase on the material's mechanical properties, while concurrently preserving its superhydrophobic character. Our approach involved the incorporation of a novel composite modifier, wherein polymethylhydrosiloxane (PMHS) served as the principal hydrophobic component. Graphene oxide (GO) was strategically introduced to achieve efficient pore filling, owing to its exceptional dispersibility. Furthermore, the presence of GO reinforces the mechanical performance of the composite due to its inherent superior mechanical properties. Additionally, the well-dispersed GO portion forms nano hydrophobic particles by covalently grafting hydrophobic groups, further enhancing the overall hydrophobicity of the composite. This synergistic interplay between PMHS and GO facilitated the successful development of a high-performance fly ash geopolymer composite characterized by exceptional mechanical strength, three-dimensional superhydrophobicity, and enhanced chemical stability. The graphene oxide reinforced high-performance three-dimensional superhydrophobic hybrid hydrogel geopolymer composites maintained high compressive strength while achieving a water contact angle of 153 ° and a water absorption rate of only 1.7 %. Remarkably, the geopolymer retains its high hydrophobicity even after 24 hours in an acid-base solution, with a contact angle exceeding 140° and water absorption rates lower than 4 %.

Effect of ionic soil stabilizer on the properties of lime and fly ash stabilized iron tailings as pavement base

The large use of iron tailings is in urgent need given its huge emissions and pollution to environment. This paper sought to utilize a large quantity of iron tailings with fly ash and lime to prepare road base materials, and use ionic soil stabilizer (ISS) to improve its pavement performance. Different dosage ISS content of was added to the lime-fly ash stabilized iron tailing materials to improve the mechanical strength, frost resistance properties and decrease the dry shrinkage. The results show that the UCS of the specimen with 0.67 % ISS represents enhancement of 195.5 % compared to the control sample at 7 d. After undergoing 15 freeze-thaw cycles, the residual UCS ratio remains at 76.6 %, whereas the control sample exhibits signs of failure. Additionally, the dry shrinkage strain at 30 d was 66.3 % lower than that of the control sample without ISS. The mechanisms underlie that the adsorbed ISS onto iron tailings can reduce the repulsion between total fine particles by lowering the general zeta potential, thus decreasing the porosity of the road base materials. Besides, the ISS can hinder the phase transformation from ettringite (AFt) to monosulfoaluminate (AFm) and its hydrophobic groups can prevent the infiltration and migration of water. The findings reveal that ISS significantly enhances the pavement performance of the stabilized iron tailings, thereby presenting a novel approach for the incorporation of iron tailings in road construction endeavors.

Developing ultra-high performance concrete with different strength grade based on mix proportion sensitivity factor analysis

Abstract Owing to the excellent strength and durability, ultra-high-performance concrete (UHPC) has been used for fabricating large-scale and important infrastructures. However, mix proportion of UHPC is still the core factor influencing its workability, strength, cost and energy resource consumption. Based on this, the amount of cementitious materials, water-binder ratio, and the content of steel fibers were matched to obtain UHPC with required workability and strength according to three-factor five-level orthogonal range analysis considering the interaction of these three parameters. Experimental results show that the water-binder ratio and steel fiber content is the primary factor to guarantee the fluidity/compressive and flexural strength of UHPC, respectively. For developing UHPC with compressive strength grade of 150 MPa and flexural strength higher than 50 MPa, the amount of cementitious materials (including cement, silica fume, cenosphere, and fly ash) and the content of steel fibers should be higher than 1000 kg m−3 and 2.5 vol.%, and the corresponding water-binder ratio is equal to 0.16. When the aim is to fabricate UHPC with compressive strength grade of 120 MPa and flexural strength higher than 40 MPa, the water-binder ratio can be increased but should be lower than 0.20 with the increasing amount of cementitious material, and the volume fraction of steel fibers should be higher than 1.5 vol.%. High steel fiber content and water-binder ratio all easily coarsens the microstructure and pore structure of UHPC, and this phenomenon cannot be compensated by using high amount of cementitious materials. It should be adjusting the matching degree of amount of cementitious materials and water-binder ratio to obtain a slurry with appropriate fluidity and cohesiveness, and then content of steel fibers can be selected to perform without adverse effects.

Unlocking the potential of environmentally friendly adsorbent derived from industrial wastes: A review.

With increasing urbanization and industrialization, growing amounts of industrial waste, such as red mud (RM), fly ash (FA), blast furnace slag (BFS), steel slag (SS), and sludge, are being produced, exposing substantial threats to the environment and human health. Given that numerous researchers associate with conventional adsorbents, developing and utilizing industrial wastes derived from adsorption technology still has received limited attention. Utilizing this waste contributes to developing alternative materials with superior performance and significantly reduces the volume of solid waste. The excellent physical and chemical characteristics of these wastes are also investigated in this paper. This review attempts to demonstrate a comprehensive overview of the application of industrial waste-based adsorbent in the adsorption process for removing organic pollutants, dyes, metallic ions, non-metallic ions, and radioactive substances. In addition, industrial waste-based adsorbents are among the most promising and applicable techniques for pollutant removal, offering remarkable adsorption efficiency, rich surface chemistries, reasonable cost, simple operation, and low energy consumption. This review summarizes state-of-the-art advancements in engineered adsorbents (including physical and chemical modifications). It provides a holistic view regarding a comprehensive understanding of the mechanism involved in adsorption for water remediation. The challenges and the prospects for future research in applying these adsorbents are also elucidated, contributing to sustainable waste management and environmental sustainability.

Temperature-Dependent Compressive Strength Modeling of Geopolymer Blocks Utilizing Glass Powder and Steel Slag

This article investigates the development of geopolymers as a modern, environmentally sustainable binder with ceramic-like properties, offering exceptional thermal and fire-resistant characteristics. The study primarily utilized fly ash (FA) in combination with glass powder (GP) and steel slag (SS). The SS content varied between 30% and 40%, while the molarity of NaOH was set at 10M, 12M, and 14M. Based on these variables, a total of 18 mixes incorporating GP and SS were formulated. The samples were subjected to elevated temperatures of 200 °C, 400 °C, 600 °C, and 800 °C, after which their compressive strength was measured. To better understand the material formation, scanning electron microscopy and energy dispersive X-ray spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and thermogravimetry differential thermal analysis analyses were conducted. The study aimed to examine the influence of oxide ratios (Na/Si, Si/Al, H2O/Na2O, and Na/Al) on compressive strength at elevated temperatures. Additionally, the research sought to develop a predictive model, elucidating the relationship between these oxide ratios and compressive strength of geopolymers. To achieve this, ten machine learning techniques were applied, revealing the complex connection between oxide ratios and the strength properties of geopolymers. The support vector regressor (SVR) model outperformed other regression and boosting models, achieving a high coefficient of determination (R2) value of 0.95, indicating superior predictive accuracy. The reduced error levels and high R2 values highlighted the enhanced performance of the SVR model. A sensitivity analysis was done to understand the contributions of each parameter to the outcome predictions further. Employing machine learning techniques to forecast compressive strength of geopolymer blocks under various elevated temperature conditions improves predictive accuracy and optimizes resource utilization, leading to significant time savings.

Prediction of the R3 Test-Based Reactivity of Supplementary Cementitious Materials: A Machine Learning Approach Utilizing Physical and Chemical Properties

This study utilized machine learning (ML) models to investigate the effect of physical and chemical properties on the reactivity of various supplementary cementitious materials (SCMs). Six SCMs, including ground granulated blast furnace slag (GGBFS), pulverized coal fly ash (FA), and ground bottom ash (BA), underwent thorough material characterization and reactivity tests, incorporating the modified strength activity index (ASTM C311) and the R3 (ASTM C1897) tests. A data set comprising 46 entries, derived from both experimental results and literature sources, was employed to train ML models, specifically artificial neural network (ANN), support vector machine (SVM), and random forest (RF). The results demonstrated the robustness of the ANN model, achieving superior prediction accuracy with a testing mean absolute error (MAE) of 9.6%, outperforming SVM and RF models. The study classified SCMs into reactivity classes based on correlation analysis, establishes a comprehensive database linking material properties to reactivity, and identifies key input parameters for predictive modeling. While most SCMs exhibited consistent predictions across types, GGBFS displayed significant variations, prompting a recommendation for the inclusion of additional input parameters, such as fineness, to enhance predictive accuracy. This research provided valuable insights into predicting SCM reactivity, emphasizing the potential of ML models for informed material selection and optimization in concrete applications.

Eco and user–friendly curcumin based nanocomposite forensic powder from coal fly ash for latent fingerprint detection in crime scenes

Eco and user–friendly curcumin based nanocomposite forensic powder from coal fly ash for latent fingerprint detection in crime scenes

Revolutionizing Dye Sensitized Solar Cells – Impact of Silicon Dioxide Purity Derived from Coal Fly Ash for Enhanced Photoelectric Performance

Revolutionizing Dye Sensitized Solar Cells – Impact of Silicon Dioxide Purity Derived from Coal Fly Ash for Enhanced Photoelectric Performance

High-temperature behaviour of geopolymer composites containing carbon fibre and nano-silica: Mechanical, microstructure, and air-void characteristics

The fly ash–ground granulated blast-furnace slag-based geopolymer (FSG) represents a groundbreaking material, offering a sustainable and environmentally friendly alternative to conventional construction materials. This paper presents a systematic experimental study on FSG reinforced with carbon fibre (CF, 0%–1.0%) and nano-silica (NS, 1%–3%) at high temperatures (20, 200, 400, 600, 800, and 900 °C). Various tests concerning appearance, residual strength, uniaxial tension, XRD, FTIR, TGA, SEM, and air-void characteristics were conducted to analyse thermal effects. The findings show that as temperature increases, the colour of the geopolymer transitions from dark grey to yellow grey. Enhanced geopolymerisation during thermal solidification from 20 to 400 °C significantly increases the compressive, flexural, and tensile strengths of the geopolymer. The addition of CF and NS improves the residual strength of geopolymers at high temperatures, with optimal concentrations found to be 0.6% for CF and 2% for NS. CF maintains its bridging effect at high temperatures, enhancing fibre–matrix bonding, while NS promotes the formation of additional hydration products on CF surfaces, thereby strengthening the material further. After exposure to 800 °C, despite a weakening of the fibre–matrix interface, the modified geopolymers (FSGC0.6 and FSGC0.6N2) exhibit finer air bubble chord lengths and superior air-void characteristics than the control group. This supports the theory that the synergistic action of CF and NS not only enhances geopolymerisation but also fills pores, thus limiting crack propagation and densifying the pore structure.

Multiscale Prediction Model for Autogenous Shrinkage of early-age Concrete Incorporating High Volume Fly Ash

Multiscale Prediction Model for Autogenous Shrinkage of early-age Concrete Incorporating High Volume Fly Ash