Submit to Materials Review for Materials Propose a Special Issue

Journal Browser

Current State of Coal Fly Ash Utilization: Characterization and Application

Print Special Issue Flyer
Special Issue Editors
Special Issue Information
Keywords
Published Papers

A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Construction and Building Materials".

Deadline for manuscript submissions: closed (10 November 2022) | Viewed by 25232

Share This Special Issue

Special Issue Editors

Dr. Alex Kondratiev

E-Mail Website
Guest Editor

College of Environmentally Sound Technologies & Engineering, National University of Science & Technology (MISIS), Moscow, Russia
Interests: coal ash slags; thermodynamics; phase equilibria; SiO₂-Al₂O₃-CaO-'FeO' system; slag viscosity; liquid metals; smelting processes; metallurgical waste utilization
Special Issues, Collections and Topics in MDPI journals

Dr. Dmitry Valeev

E-Mail Website
Guest Editor

Vernadsky Institute of Geochemistry and Analytical Chemistry of Russian Academу of Sciences, Moscow 119991, Russia
Interests: coal fly ash; high-silica bauxite; red mud; bauxite residue;aluminium dross; alumina production; coagulant polyaluminum chloride; high-pressure acid leaching (HPAL); flotation; magnetic separation; carbothermic reduction; mineral processing; non-ferrous metals extraction; waste utilization.
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Coal fly ash (CFA) is the main solid waste from coal-fired power plants. The world’s annual growth of this type of waste is about 700–800 million tons. CFA contains oxides of non-ferrous metals (SiO₂, Al₂O₃, Fe₂O₃, CaO), as well as unburned carbon and rare earth elements. So, CFA can be used as feedstock in metallurgy, chemical and construction industries. The novel science direction is the use of CFA to reduce CO₂ emissions by reacting a part of the carbon dioxide with calcium oxide and obtaining construction materials. An important direction is the zeolite production. This type of materials can be used for the purification of wastewater from heavy metals. It is promising to use СFA for the production of ceramics with high physical properties based on silicon carbide (SiC). In addition, new studies of an Al₂O₃-SiO₂-Fe₂O₃-CaO system are needed to simulate the coal combustion process to obtain CFA with a necessary chemical composition for further recycling. Using new methods of green chemistry (hydrometallurgy and/or pyrometallurgy), on the one hand, it is possible to reduce the negative impact of CFA on the environment and human health and, on the other hand, to obtain new materials with a lower cost.

Dr. Alex Kondratiev
Dr. Dmitry Valeev
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Materials is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

coal fly ash
magnetic separation
flotation
leaching
carbothermic reduction
alumina
silica
mullite
zeolites
concrete
geopolymer
solvent extraction
resin sorption
construction materials
ceramics materials
non-ferrous metals extraction

Published Papers (13 papers)

Download All Papers

Editorial

Jump to: Research

6 pages, 205 KiB

Open AccessEditorial

Current State of Coal Fly Ash Utilization: Characterization and Application

by Dmitry Valeev and Alex Kondratiev

Materials 2023, 16(1), 27; https://doi.org/10.3390/ma16010027 - 21 Dec 2022

Cited by 5 | Viewed by 1204

Abstract

This Special Issue of Materials is devoted to various aspects of coal fly ash (CFA) utilization [...] Full article

(This article belongs to the Special Issue Current State of Coal Fly Ash Utilization: Characterization and Application)

Research

Jump to: Editorial

16 pages, 2808 KiB

Open AccessArticle

Study of Forms of Compounds of Vanadium and Other Elements in Samples of Pyrometallurgical Enrichment of Ash from Burning Oil Combustion at Thermal Power Plants

by Anton Volkov, Ulyana Kologrieva and Pavel Stulov

Materials 2022, 15(23), 8596; https://doi.org/10.3390/ma15238596 - 2 Dec 2022

Cited by 5 | Viewed by 1294

Abstract

The results of the processing of ash from the combustion of fuel oil after roasting with the addition of Na₂CO₃ followed by aluminothermic melting are presented. As a result, metallic nickel and vanadium slag were obtained. Studies of slag, metal, and deposits on the electrode were carried out. The resulting metal contains about 90 wt% Ni. The main phases of scurf on the electrode are a solid solution based on periclase (Mg_{1–x–y–z}Ni_xFe_yV_zO), sodium-magnesium vanadate (NaMg₄(VO₄)₃), and substituted forsterite (Mg_2–x–yFe_xNi_ySiO₄). The processing of ash made it possible to significantly increase the concentration of vanadium and convert it into more soluble compounds. Vanadium amount increased from 16.2 in ash to 41.4–48.1 V₂O₅ wt% in slag. The solubility of vanadium was studied during aqueous leaching and in solutions of H₂SO₄ and Na₂CO₃. The highest solubility of vanadium was seen in H₂SO₄ solutions. The degree of extraction of vanadium into the solution during sulfuric acid leaching of ash was 18.9%. In slag, this figure increased to 72.3–96.2%. In the ash sample, vanadium was found in the form of V⁵⁺, V⁴⁺ compounds, vanadium oxides VO₂ (V⁴⁺), V₂O₅ (V⁵⁺), and V₆O₁₃, and nickel orthovanadate Ni₃(VO₄)₂ (V⁵⁺) was found in it. In the slag sample, vanadium was in the form of compounds V⁵⁺, V⁴⁺, V³⁺, and V^(0÷3)+; V⁵⁺ was presented in the form of compounds vanadate NaMg₄(VO₄)₃, NaVO₃, and Ca_xMg_yNa_z(VO₄)₆; V³⁺ was present in spinel (FeV₂O₄) and substituted karelianite (V_{2–x–y–z}Fe_xAl_yCr_zO₃). In the obtained slag samples, soluble forms of vanadium are due to the presence of sodium metavanadate (NaVO₃), a phase with the structure of granate Ca_xMg_yNa_z(VO₄)₆ and (possibly) substituted karelianite (V_{2–x–y–z}Fe_xAl_yCr_zO₃). In addition, spinel phases of the MgAl₂O₄ type beta-alumina (NaAl₁₁O₁₇), nepheline (Na_4–xK_xAl₄Si₄O₁₆), and lepidocrocite (FeOOH) were found in the slag samples. Full article

(This article belongs to the Special Issue Current State of Coal Fly Ash Utilization: Characterization and Application)

► Show Figures

Figure 1

15 pages, 5689 KiB

Open AccessArticle

The Discrepancy between Coal Ash from Muffle, Circulating Fluidized Bed (CFB), and Pulverized Coal (PC) Furnaces, with a Focus on the Recovery of Iron and Rare Earth Elements

by Jinhe Pan, Xin Long, Lei Zhang, Andrei Shoppert, Dmitry Valeev, Changchun Zhou and Xiao Liu

Materials 2022, 15(23), 8494; https://doi.org/10.3390/ma15238494 - 29 Nov 2022

Cited by 8 | Viewed by 1472

Abstract

Coal ash (CA) is not only one of the most solid wastes from combustion, easily resulting in a series of concerns, but it is also an artificial deposit with considerable metals, such as iron and rare earth. The variation in the coal ash characteristics due to the origins, combustion process, and even storage environment has been hindering the metal utilization from coal ash. In this study, three ash sample from lab muffle, circulating fluidized bed (CFB), and pulverized coal (PC) furnace was derived for the discrepancy study from the combustion furnace, including properties, iron, and rare earth recovery. The origins of the coal feed samples have more of an effect on their properties than combustion furnaces. Magnetic separation is suitable for coal ash from PC because of the magnetite product, and the iron content is 58% in the Mag-1 fraction, with a yield of 3%. The particles in CA from CFB appear irregular and fragmental, while those from PC appear spherical with a smooth surface. The results of sequential chemical extraction and observation both indicated that the aluminosilicate phase plays an essential role in rare earth occurrences. Rare earth in CA from muffling and CFB is facilely leached, with a recovery of approximately 50%, which is higher than that from PC ash. This paper aims to offer a reference to easily understand the difference in metal recovery from coal ash. Full article

(This article belongs to the Special Issue Current State of Coal Fly Ash Utilization: Characterization and Application)

► Show Figures

Figure 1

15 pages, 4560 KiB

Open AccessArticle

Feasibility Study of Grinding Circulating Fluidized Bed Ash as Cement Admixture

by Xingquan Du, Zhong Huang, Yi Ding, Wei Xu, Man Zhang, Lubin Wei and Hairui Yang

Materials 2022, 15(16), 5610; https://doi.org/10.3390/ma15165610 - 16 Aug 2022

Cited by 7 | Viewed by 1463

Abstract

With the widespread application of circulating fluidized bed (CFB) combustion technology, the popularity of CFB ash (CFBA) has increased dramatically and its production and large-scale utilization have become increasingly important. In the context of carbon neutrality peaking, using CFBA as a cement admixture as an effective method of resource utilization not only reduces the pressures caused by carbon emissions in the cement industry but also solves the environmental problems caused by CFBA depositing. However, the formation conditions of CFBA are worse than those of traditional pulverized coal boilers. CFB ash is the combustion product of coal at 850 °C–950 °C, and the characteristics of CFBA usually include a loose and porous structure with many amorphous substances. Furthermore, it has the disadvantages of large particle size, high water-demand ratio, and low activity index when it is directly used as a cement admixture. In this study, CFBA (including fly ash (CFBFA) and bottom ash (CFBBA)) produced by a CFB boiler without furnace desulfurization with limestone was used as a cement admixture material, and the effect of grinding on the fineness, water-demand ratio, and activity index of CFBA were studied. The experimental results showed that the grinding effect could significantly reduce the fineness and water-demand ratio of CFBA as a cement mixture and improve the activity index. With the increase in the grinding time, the water-demand ratio of CFBA first decreased and then increased. CFBBA ground for 10 min and CFBFA ground for 4 min can reduce the water-demand ratio of CFBA by up to 105% and increase the compressive strength of 28-day-old CFBA cement by 7.05%. The grinding process can ensure that CFBA meets the Chinese standards for a cement admixture and realize the resource utilization of CFBA. Full article

(This article belongs to the Special Issue Current State of Coal Fly Ash Utilization: Characterization and Application)

► Show Figures

Figure 1

18 pages, 5391 KiB

Open AccessArticle

The Triaxial Test of Polypropylene Fiber Reinforced Fly Ash Soil

by Lihua Li, Xin Zhang, Henglin Xiao, Jiang Zhang, Na Chen and Wentao Li

Materials 2022, 15(11), 3807; https://doi.org/10.3390/ma15113807 - 26 May 2022

Cited by 2 | Viewed by 1759

Abstract

Recently, soil reinforcement using arranged or randomly distributed fibers has attracted increasing attention in geotechnical engineering. In this study, polypropylene (PP) fibers with three lengths (6, 12, and 24 mm) and three mass percentages (0.5%, 1%, and 1.5%) were used to reinforce a coal fly ash soil (FAS) mixture. Unconsolidated, undrained triaxial tests were carried out in order to study the mechanical properties of the polypropylene fiber-reinforced FAS mixture and evaluate the impact of fiber on the shear strength of the FAS mixture. It is found that the fiber length of 12 mm could significantly improve the shear strength of the polypropylene fiber reinforced FAS mixture, and little effect is shown on the shear strength while using a fiber length of 24 mm. Additional fibers enhance the energy absorption capacity of the FAS specimens and therefore the highest energy absorption capacity occurs when the fiber content is 1% and the fiber length is 12 mm. The peak deviator stress enhances impressively with the addition of polypropylene fiber. The impact of fiber on the peak deviator stress is the largest when fiber content is within 1.0%. The fiber length has little effect on the peak deviator stress when it exceeds 12 mm. Full article

(This article belongs to the Special Issue Current State of Coal Fly Ash Utilization: Characterization and Application)

► Show Figures

Figure 1

15 pages, 4885 KiB

Open AccessArticle

A Study of Physicochemical Properties of Stockpile and Ponded Coal Ash

by Rostislav Šulc, Martina Šídlová, Petr Formáček, Roman Snop, František Škvára and Adéla Polonská

Materials 2022, 15(10), 3653; https://doi.org/10.3390/ma15103653 - 20 May 2022

Cited by 6 | Viewed by 1381

Abstract

The article describes chemical and also selected physical properties of ponded high temperature fly ash (FA) and bottom ash (BA) from a Mělník lignite power plant located in the Czech Republic. The research was carried out on samples obtained from drills with a depth of up to 54 m and the age of the samples retrieved from the lowest layers of the stockpile dating back to 1960. At the same time, a comparison was made with fresh fly ash and fresh bottom ash obtained from the identical power plant. The study analyzed a total of 98 stockpile samples. The properties selected were studied across the entire stockpile, namely moisture content, specific density, specific surface, carbon content, elemental and phase composition, pH, electrical conductivity and leachability. SEM analyses were also performed. The performed measurements of chemical properties proved the chemical stability of the material even after several decades of storage in the stockpile. The largest changes are evident in the results of the analyses related to the leachability of SO₃, Cl⁻ and F⁻. In contrast, the pH does not change significantly, and the composition is pH neutral or alkaline. Regarding ponded BA, particle disintegration was noted depending on the increasing core borehole depth. Full article

(This article belongs to the Special Issue Current State of Coal Fly Ash Utilization: Characterization and Application)

► Show Figures

Figure 1

13 pages, 4437 KiB

Open AccessArticle

Tensile Strength of Class F Fly Ash and Fly Ash with Bentonite Addition as a Material for Earth Structures

by Mariola Wasil and Katarzyna Zabielska-Adamska

Materials 2022, 15(8), 2887; https://doi.org/10.3390/ma15082887 - 14 Apr 2022

Cited by 3 | Viewed by 1467

Abstract

The behavior of soils under tensile stress is of interest to geotechnical engineers. Tensile strength of soils is often associated with tensile fractures that can generate a privileged flow path. The addition of bentonite improves the plastic properties of the soil, therefore the study was conducted for the compacted class F fly ash and fly ash with various bentonite additions. An amount of bentonite was: 5, 10 and 15%, calculated in weight relation to dry mass of samples. The tensile strength of compacted clay was also established, for comparison. Laboratory tests were carried out using the direct method (breaking) on cylindrical samples and the indirect method (the Brazilian test) on disc-shaped specimens. For this purpose, a universal testing machine with a frame load range of ±1 kN was used. It is stated that bentonite considerably influences the tensile strength of the fly ash evaluated with both methods. The tensile strength values obtained with the Brazilian method are comparable or higher than those obtained with the direct method. The achieved tensile strength values of compacted fly ash, improved by 10−15% of bentonite addition, are comparable with the results obtained for clay used in mineral sealing, while the strain at maximum tensile strength is similar in the direct test and lower in the indirect test. Full article

(This article belongs to the Special Issue Current State of Coal Fly Ash Utilization: Characterization and Application)

► Show Figures

Figure 1

14 pages, 4664 KiB

Open AccessArticle

Improving the Properties of Porous Geopolymers Based on TPP Ash and Slag Waste by Adjusting Their Chemical Composition

by Elena A. Yatsenko, Boris M. Goltsman, Sergei V. Trofimov, Viktor M. Kurdashov, Yuri V. Novikov, Victoria A. Smoliy, Anna V. Ryabova and Lyudmila V. Klimova

Materials 2022, 15(7), 2587; https://doi.org/10.3390/ma15072587 - 31 Mar 2022

Cited by 11 | Viewed by 1728

Abstract

The possibility of improving the properties of porous geopolymer materials based on ash and slag waste from thermal power plants by adjusting their chemical composition is considered. An X-ray phase analysis of ash and slag wastes was carried out, the geopolymers’ precursor compositions were calculated, and additives to correct their chemical composition were selected. The samples were synthesized and their physical and mechanical properties (density, porosity, compressive strength, thermal conductivity) were analyzed. The micro- and macro-structure of the samples and the pore distribution of the obtained geopolymers were studied and pore-distribution histograms were obtained. The influence of Si:Al ratio on structural changes was described. The geopolymers’ phase composition was studied, consisting of an amorphous phase and high quartz and mullite. A conclusion about the applicability of this method for obtaining high-quality porous geopolymers was made. Full article

(This article belongs to the Special Issue Current State of Coal Fly Ash Utilization: Characterization and Application)

► Show Figures

Figure 1

13 pages, 1166 KiB

Open AccessArticle

Fly Ash-Added, Seawater-Mixed Pervious Concrete: Compressive Strength, Permeability, and Phosphorus Removal

by Sangchul Hwang and Jung Heum Yeon

Materials 2022, 15(4), 1407; https://doi.org/10.3390/ma15041407 - 14 Feb 2022

Cited by 12 | Viewed by 1840

Abstract

A mix proportion of off-spec fly ash (FA)-added, seawater-mixed pervious concrete (SMPC) was optimized for compressive strength and permeability and then the optimized SMPC was tested for the rate and extent of aqueous phosphorus removal. An optimum mix proportion was obtained to attain the percentages (% wt.) of FA-to-binder at 15.0%, nano SiO₂ (NS)-to-FA at 3.0%, liquid-to-binder at 0.338, and water reducer-to-binder at 0.18% from which a 7-day compressive strength of 14.0 MPa and a permeability of 5.5 mm/s were predicted. A long-term maximum compressive strength was measured to be ~16 MPa for both the optimized SMPC and the control ordinary pervious concrete (Control PC). The phosphorus removal was favorable for both the optimized SMPC and the Control PC based on the dimensionless Freundlich parameter (1/n). Both the optimized SMPC and Control PC had a first-order phosphorus removal constant of ~0.03 h⁻¹. The optimized SMPC had a slightly lower capacity of phosphorus removal than the Control PC based on the Freundlich constant, K_f (mg^1−1/n kg⁻¹ L^1/n): 15.72 for the optimized SMPC vs. 16.63 for Control. This study demonstrates a cleaner production and application of off-spec FA-added, seawater-mixed pervious concrete to simultaneously attain water, waste, and concrete sustainability. Full article

(This article belongs to the Special Issue Current State of Coal Fly Ash Utilization: Characterization and Application)

► Show Figures

Figure 1

20 pages, 14109 KiB

Open AccessArticle

Kinetics Study of Al Extraction from Desilicated Coal Fly Ash by NaOH at Atmospheric Pressure

by Andrei Shoppert, Irina Loginova and Dmitry Valeev

Materials 2021, 14(24), 7700; https://doi.org/10.3390/ma14247700 - 13 Dec 2021

Cited by 15 | Viewed by 2797

Abstract

The most promising source of alumina in the 21st century is the coal fly ash (CFA) waste of coal-fired thermal plants. The methods of alumina extraction from CFA are often based on the pressure alkaline or acid leaching or preliminary roasting with different additives followed by water leaching. The efficiency of the alumina extraction from CFA under atmospheric pressure leaching is low due to the high content of acid-insoluble alumina phase mullite (3Al₂O₃·2SiO₂). This research for the first time shows the possibility of mullite leaching under atmospheric pressure after preliminary desilication using high liquid to solid ratios (L:S ratio) and Na₂O concentration. The analysis of the desilicated CFA (DCFA) chemical and phase composition before and after leaching has been carried out by inductively coupled plasma optical emission spectrometry (ICP-OES) and X-ray diffraction (XRD). The morphology and elemental composition of solid product particles has been carried out by scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX). An automated neural network and a shrinking core model (SCM) were used to evaluate experimental data. The Al extraction efficiency from DCFA has been more than 84% at T = 120 °C, leaching time 60 min, the L/S ratio > 20, and concentration of Na₂O—400 g L⁻¹. The kinetics analysis by SCM has shown that the surface chemical reaction controls the leaching process rate at T < 110 °C, and, at T > 110 °C after 15 min of leaching, the process is limited by diffusion through the product layer, which can be represented by titanium compounds. According to the SEM-EDX analysis of the solid residue, the magnetite spheres and mullite acicular particles were the main phases that remained after NaOH leaching. The spheric agglomerates of mullite particles with non-porous surface have also been found. Full article

(This article belongs to the Special Issue Current State of Coal Fly Ash Utilization: Characterization and Application)

► Show Figures

Graphical abstract

14 pages, 3451 KiB

Open AccessArticle

Effect of Electrolytic Manganese Residue in Fly Ash-Based Cementitious Material: Hydration Behavior and Microstructure

by Yaguang Wang, Na Zhang, Yongyu Ren, Yingtang Xu and Xiaoming Liu

Materials 2021, 14(22), 7047; https://doi.org/10.3390/ma14227047 - 20 Nov 2021

Cited by 9 | Viewed by 1851

Abstract

Electrolytic manganese residue (EMR) is a solid waste with a main mineralogical composition of gypsum. It is generated in the production of metal manganese by the electrolysis process. In this research, EMR, fly ash, and clinker were blended to make fly ash-based cementitious material (FAC) to investigate the effect of EMR on strength properties, hydration behavior, microstructure, and environmental performance of FAC. XRD, TG, and SEM studied the hydration behavior of FAC. The pore structure and [SiO₄] polymerization degree were characterized by MIP and ²⁹Si NMR, respectively. The experimental results indicate that FAC shows excellent mechanical properties when the EMR dosage is 10%. Moderate content of sulfate provided by EMR can promote hydration reaction of FAC, and it shows a denser pore structure and higher [SiO₄] polymerization degree in this case. Heavy metal ions derived from EMR can be adsorbed in the hydration products of FAC to obtain better environmental properties. This paper presents an AFt covering model for the case of excessive EMR in FAC, and it importantly provides theoretical support for the recycling of EMR in cementitious materials. Full article

(This article belongs to the Special Issue Current State of Coal Fly Ash Utilization: Characterization and Application)

► Show Figures

Graphical abstract

19 pages, 2900 KiB

Open AccessArticle

Mud-Based Construction Material: Promising Properties of French Gravel Wash Mud Mixed with Byproducts, Seashells and Fly Ash as a Binder

by Yassine El Mendili, Manal Bouasria, Mohammed-Hichem Benzaama, Fouzia Khadraoui, Malo Le Guern, Daniel Chateigner, Stéphanie Gascoin and Jean-François Bardeau

Materials 2021, 14(20), 6216; https://doi.org/10.3390/ma14206216 - 19 Oct 2021

Cited by 6 | Viewed by 2483

Abstract

The French gravel industry produces approximatively 6.5 million tons of gravel wash mud each year. This material offers very promising properties which require an in-depth characterization study before its use as a construction material, otherwise it is removed from value cycles by disposal in landfills. We examined the suitability of gravel wash mud and seashells, with fly ash as a binder, as an unfired earth construction material. Thermal and mechanical characterizations of the smart mixture composed of gravel wash mud, Crepidula fornicata shells and fly ash are performed. The new specimens exhibit high compressive strengths compared to usual earth construction materials, which appears as a good opportunity for a reduction in the thickness of walls. The use of fly ash and Crepidula shells in addition to gravel wash mud provides high silica and calcium contents, which both react with clay, leading to the formation of tobermorite and Al-tobermorite as a result of a pozzolanic reaction. Considering the reduction in porosity and improvements in strength, these new materials are good candidates to contribute significantly to the Sustainable Development Goals (SDGs) and reduce carbon emissions. Full article

(This article belongs to the Special Issue Current State of Coal Fly Ash Utilization: Characterization and Application)

► Show Figures

Figure 1

19 pages, 14788 KiB

Open AccessEditor’s ChoiceArticle

Circulating Fluidized Bed Fly Ash Mixed Functional Cementitious Materials: Shrinkage Compensation of f-CaO, Autoclaved Hydration Characteristics and Environmental Performance

by Wei Zhang, Xiaoming Liu, Zengqi Zhang, Yaguang Wang, Yang Xue, Xiansheng Hao and Yang Lu

Materials 2021, 14(20), 6004; https://doi.org/10.3390/ma14206004 - 12 Oct 2021

Cited by 16 | Viewed by 1976

Abstract

Circulating fluidized bed (CFB) fly ash is a by-product from CFB power generation, which is hard to utilize in cement because it contains f-CaO and SO₃. This work aims to explore the mechanism of the shrinkage compensation of free-CaO (f-CaO) and the autoclaved hydration characteristics and environmental performance of CFB fly ash mixed cementitious materials (CMM). In this work, long-term volume stability of CMM is improved with the addition of CFBFA. These findings suggest that the compressive strength of sample CMM0.5 is the highest under both standard condition (67.21 MPa) and autoclaved condition (89.56 MPa). Meanwhile, the expansion rate (0.0207%) of sample CMM0.5 is the lowest, which proves the shrinkage compensation effect of f-CaO in CFBFA. The main hydration products of CMM0.5 are Ca₂SiO₄•H₂O (C-S-H) gel, CaAl₂Si₂O₇(OH)₂•H₂O (C-A-S-H) gel and Ca(OH)₂. In addition, the high polymerization degree of [Si(Al)O₄] and the densified microstructure are presented at the sample CMM0.5. The leaching results indicates that the heavy metals in CMM0.5 satisfies the WHO standards for drinking water due to physical encapsulation and charge balance. Therefore, this investigation provides a novel method of using CFB fly ash in cement. Full article

(This article belongs to the Special Issue Current State of Coal Fly Ash Utilization: Characterization and Application)

► Show Figures