Fly Ash Research Articles

Enhancing Mid-Term Strength and Microstructure of Fly Ash–Cement Paste Backfill with Silica Fume for Continuous Mining and Backfilling Operations

Fly ash–cement composite backfill slurry, prepared by partially replacing cement with fly ash, has been demonstrated to effectively reduce the mine backfill costs and carbon emissions associated with cement production. However, the use of fly ash often results in insufficient early and medium-term strength of the backfill material. To address the demand for high medium-term strength in backfill materials under continuous mining and backfilling conditions, this study developed a silica fume–fly ash–cement composite backfill slurry. The effects of varying silica fume contents on the slurry’s flowability, uniaxial compressive strength, microstructure, and pore characteristics were systematically investigated. The results showed that increasing the silica fume content significantly reduced the slurry’s flowability. However, at a silica fume content of 5%, the slurry achieved optimal medium-term strength, with a 14-day uniaxial compressive strength of 3.98 MPa, representing a 25% improvement compared to the control group. A microstructural analysis revealed that a moderate silica fume content promoted the formation of calcium silicate hydrate gel, filled micropores, and optimized the pore structure, thereby enhancing the overall strength and durability of the material. Conversely, an excessive silica fume content above 5% led to a marked decrease in both flowability and strength. Based on a comprehensive evaluation of silica fume’s effects on the flowability, strength, and microstructure, the optimal silica fume content was determined to be 5%. This study provides a theoretical basis and practical guidance for improving the efficiency of continuous mining and backfilling operations, and for designing high-performance backfill materials suitable for continuous mining and filling conditions.

Study on mechanical properties and mechanism of soda residue-fly ash stabilised marine clay based on orthogonal matrix method

Improving the engineering and mechanical properties of marine clay (MC) by modifying it with soda residue (SR) and fly ash (FA), and stabilising with cement and /or lime to create Soda residue-Fly ash stabilised soil (SRFSS). Using the orthogonal design, the mechanical properties of SRFSS were analyzed, recommending a basic proportion of 70% SR + 20% FA + 10% MC. Results showed SR significantly impacted optimum water content (OWC), unconfined compressive strength (UCS), and water absorption quality. FA influenced the maximum dry density (MDD), while cohesion (c) was mainly affected by lime and cement. Cement had a higher unit contribution rate to mechanical indices than lime, except for MDD and OWC. The excellent properties of SRFSS were derived from good gradation and the cementation action of the materials. This research provides a solution for improving MC properties and promoting solid waste reutilisation.

Analysis of engineering performance of concrete comprising recycled crushed plastic waste and fly ash

This study investigated the attributes of blending of recycled crushed polypropylene plastic coarse aggregates (PPCA) and fly ash (FA) towards the fresh and hardened properties of concrete. Natural coarse aggregate was partially replaced with PPCA at volumetric replacement levels up to 30% and cement was replaced with FA up to 20%. Initially, the performance of PPCA and FA in concrete was investigated distinctly. The incorporation of 30% of PPCA in concrete rather impaired the workability (from 95 mm – 50 mm: 47%) and the compressive strength (from 44.6 MPa to 31.4 MPa: 29.7%). By appropriate using of a superplasticizer, the loss in the workability could be recovered. Microstructural investigation was conducted employing scanning electron microscope analysis; it showed that the formation of a weak interfacial transition zone between PPCA and cement paste to be the reason for strength reduction in PPCA concrete. In contrast, the addition of 10 – 20% of FA in concrete improved the workability by 63.2% – 100%, but yet again, the 28-day compressive strength reduced by 15.8 – 35.6%. Meanwhile, thermal conductivity results and constitutive relationships proved that the use of PPCA enhanced the thermal insulation property and ductility of PPCA concrete, respectively. Eventually, a total of six concrete batches with binary blended PPCA and FA were cast to find the optimum replacement levels. The optimum binary combination with reasonable strength and workability at a minimal cost was achieved to be 10% PPCA and 20% FA.

Fire performance and characterization of geopolymer foams using fly ash and coal gangue

The paper introduces foamed geopolymers as effective thermal insulation materials for buildings, with the ability to withstand high temperatures. The production methods for achieving a porous microstructure in geopolymers are discussed, emphasizing the use of foaming agents like aluminium powder. The presented research focuses on developing geopolymer foams from industrial waste materials [fly ash and coal gangue] with enhanced thermal and fire resistance while maintaining robust mechanical properties. The novelty lies in evaluating these foams at a medium-sized panel scale [750 mm x 750 mm x thickness] and assessing their fire resistance through comprehensive tests, differentiating it from existing literature that primarily explores smaller-scale materials. Class F fly ash from Skawina power plant, Poland and waste rock from coal mining KWK Wieczorek, Katowice, Poland were used for preparation of geopolymer foam. The research aims to contribute insights into the fire performance of geopolymer foams under ISO 834-1 fire scenario, paving the way for potential applications as thermal insulation panels in building facilities. Results from fire exposure tests, post-fire mechanical property assessments, SEM observations, EDS analyses, XRD analyses, as well as ageing effects are presented and discussed. While foamed geopolymers demonstrate resilience and fire resistance, variations in their mechanical properties and microstructure due to fire exposure are highlighted. The research underlines the potential of employing geopolymer foams as a sustainable solution for thermal insulation in construction, opening up further exploration and application in the construction industry.

Increasing the strength of alkali activated mortars prepared without cement by adding lime and crushed brick

Alkali-activated concretes, which aim to reduce cement, have received the most attention in recent years. By activating cementless geopolymer mortar samples with lime, blast furnace slag [BFS], fly ash [FA], crushed brick, sodium hydroxide, and sodium silicate, the study aims to produce more affordable and environmentally materials. Hydrated lime and crushed brick mortars, which have been utilized in ancient structures for thousands of years, have endured to the present day because of their toughness and appropriate construction techniques. However, the biggest disadvantage of ancient mortars is that their setting time is long due to the lime they contain and therefore their strength properties cannot be developed at an early age. In order to improve these properties of the mortars, 7.5 mole NaOH was used in fixed ratios and Na2SiO3 in variable ratios. On the mortar’s characteristics, the impacts of lime, crushed brick, BFA, and FA were examined. Tests on the generated samples included flow-table, setting-time, density, water absorption, porosity, flexural and compressive strength tests, as well as SEM, XRD, and FTIR studies. The reference ancient mortar sample has the lowest compressive strength value at 1.47 MPa, while the Y4 sample, which has a high BFS content at 22.5 MPa, has the highest compressive strength value. The YS4 sample comprising BFS, NaOH, and Na2SiO3 had the fastest setting time, at 20 minutes. In comparison to the reference samples, the samples’ workability was also enhanced. The reference sample had the highest water absorption value, 26.8%, while the other samples’ values stayed below 2%. In this case, activators contributed to the improvement of the mechanical qualities of traditional lime mortars.

Impact of Microwave Pre-Curing on Pore Structure and Environmental Performance of Metakaolin- and Fly Ash-Based Geopolymers

Microwave technology in geopolymer synthesis offers a transformative, sustainable alternative to traditional methods, enhancing material properties and production efficiency. However, the effects of microwave-induced changes on pore structure and their relationship with mechanical strength and environmental performance, such as heavy metal leachability, are not fully understood. This study investigates the impact of microwave pre-curing on geopolymers, focusing on how microwave power and duration influence their pore structure and environmental performance. A total of 48 mixtures were prepared using sodium silicate and sodium hydroxide as alkali activators, with metakaolin and fly ash as raw materials. The modulus was adjusted to 1.5, and the liquid-to-solid ratio was set at 1.6 for metakaolin and 0.7 for fly ash. Microwave irradiation power settings of 100 W, 300 W, 440 W, 600 W, and 800 W were tested. The heating times ranged from 30 s to 90 s at intervals of 15 s. Our findings reveal that optimal microwave settings (100 watts for 45 s) can significantly enhance mechanical properties, with compressive strengths reaching 15.9 MPa for fly ash-based and 9.094 MPa for metakaolin-based geopolymers. However, excessive microwave energy leads to increased porosity, with adverse effects on structural integrity. Moreover, microwave pre-curing effectively reduces heavy metal leachability. Chromium (III) was used in leaching tests and it was demonstrated that ion concentrations as low as 0.097 mg/L enhance environmental safety. Advanced techniques like Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and X-ray CT were applied for the analysis of the atomic bonding, phases and pore structure of the studied geopolymers along with their ability to withstand compression (MPa). Chromium (III) was encapsulated and its leached concentration was measured by ICP-MS to evaluate the performance of the synthesized geopolymers. These results underscore the need for precise control over microwave irradiation parameters to maximize the benefits while mitigating negative impacts. This study provides valuable insights into the controlled use of microwave technology for geopolymer synthesis, recommending optimal irradiation conditions for improved performance and sustainability and advancing sustainable construction materials. The developed geopolymers show promise for applications in construction, waste stabilization, and heavy metal immobilization, contributing to more sustainable and environmentally friendly materials in these industries.

Utilizing Agricultural Residues from Hot and Cold Climates as Sustainable SCMs for Low-Carbon Concrete

Supplementary cementitious materials (SCMs), such as fly ash, slag, and silica fume, predominantly derived from industrial waste, are widely utilized in concrete due to their proven ability to enhance both its mechanical and durability properties. Moreover, these SCMs play a crucial role in mitigating the carbon footprint of concrete by reducing its cement content, which is responsible for approximately 8% of global CO2 emissions. However, the sustainability and long-term availability of conventional SCMs are increasingly under scrutiny, particularly in light of the impending shutdown of coal-fired power plants, which threatens the future supply of fly ash. As a result, the concrete industry faces an urgent need to identify alternative SCMs to maintain and advance eco-friendly practices. This article stands out from previous reviews by employing a bibliometric analysis to comprehensively explore the use of commonly utilized agricultural ashes (rice husk, palm oil, and sugarcane bagasse), prevalent in tropical and subtropical regions as SCMs. Additionally, it provides valuable insights into the potential of cold-weather crops (e.g., barley, canola, and oat) that demonstrate promising pozzolanic reactivity. The study critically evaluates and compares the physical and chemical characteristics of agricultural ashes from both hot and cold climates, assessing their influence on the fresh, mechanical, and durability properties of concrete. It also addresses the challenges and limitations associated with their use. Furthermore, in line with the United Nations and Environmental Protection Agency (EPA) sustainability goals, the review evaluates the environmental benefits of using agricultural ashes, emphasizing waste reduction, resource conservation, and energy savings. This comprehensive review paper should deepen the understanding of agricultural ashes as sustainable SCMs, providing a strategic direction for the construction industry to adopt low-carbon concrete solutions across various climates while promoting advancements in production methods, performance standards, and emerging technologies such as hybrid materials and 3D printing.

Ensemble Bagging Model for Predicting Flexural Strength of Geopolymer Concrete

Waste materials, such as fly ash and lime mortar, are used in the concrete industry to create an environmentally friendly environment. However, since the experimental studies will take time, it is necessary to predict the flexural strength (FS) and properties of Geopolymer concrete (GPC) using ensemble Learning (EL) algorithms in order to shorten the experimental work process and save money and time. In this study, a new ensemble the Bagging prediction model using gradient boosting regressor estimator is proposed to predict the FS of GPC using lime mortar. The performance of the proposed model was evaluated using the performance metrics [Formula: see text], RMSE, MSE, MAE, and MAPE. The proposed model was compared using the individual learning algorithms and validated using [Formula: see text]-fold cross-validation technique. From the SHAP plot obtained using the best proposed EL model BGR, ICE, and PDP analysis, it is seen that the blast furnace slag content has the most significant effect on the FS of GPC.

Research Possibilities for Efficient Capitalization in Construction Eco-Products, of Mineral Additions Generated by the Local Romanian Industries as Wastes or By-Products

The current paper intends to present the directory lines and paths for the development and implementing construction eco-products, with advanced functionality (materials, elements and structures, models and technologies), considering the efficient and customized valorization of by-products and generated waste of local industries, in the context of National Strategy for Research, Innovation and Smart Specialization 2022-2027 regarding the transition to Circular Economy (EC). This represents one of the two main axes of the research project Nucleu Programme of the National Research Development and Innovation Plan 2022-2027, supported by MCID, "ECODIGICONS" project no. PN 23 35 04 01: “Fundamental-applied research into the sustainable development of construction products (materials, elements, and structures, as well as methods and technologies) that utilizes current national resources to enhance the eco-innovative and durable aspects of Romania's civil and transport infrastructure”, financed by the Romanian Government starting with the beginning of 2023. One of the novelties of the proposed approach of the project is considering the entrepreneurial environment of construction industry or complementary branches as essential stakeholders for the future results of the current scientific research. This dramatically changes the dynamic of the project, in terms of specific objectives, namely their focus on solving the current wastes’ problem by innovatively integrating them into competitive construction products with fast applicability and in accordance with support market requests. By the use of strategic management specific methods (e.g., External Environment (EE) and Internal Environment (IE) evaluation, SWOT analysis and derived specific strategies, etc.), four research directions have been identified for the valorization, at regional or even national level, of mineral additions (inert/hydraulically latent/pozzolanic, etc., derived from waste and industrial by-products (metallurgy, processing industry, construction/demolition, etc.)) by development of eco-smart materials and products for construction. The three directions are related to the considered mineral additions: Power plant ashes (fly ash and/or bottom ash), Steel slag and Garnet type residue Hence, the paper is willing to present the identification and the preliminary analyses of the specified research axes, plotted as necessary steps for achieving an intelligent and sustainable transition of the Romanian construction infrastructure. This approach implicitly ensures in the short and medium term, the increase of the degree of implementation of the principles of the Circular Economy (EC) in Romania, in the existing context which includes relevant factors like: geo-political, industrial and economic, urban and demographic, scientific, socio-cultural and environmental, in accordance with the imperatives of National, European and World Sustainable Development strategies.

Methane Adsorption Energy Variation Affected by Industrial Components in Deep and Thick Coal Reservoirs

The relevant literature indicates that coal facies have a significant impact on the pore structure and adsorption properties of deep coal reservoirs. The content of submicroscopic components is used to calculate the parameters of coal facies. Based on traditional coal phase parameters and ash content, the coal phases of the coal samples in the study area were divided. Based on the adsorption potential theory, the differences in methane adsorption energy changes between different coal phases were compared. The results are as follows. The wet herbaceous swamp facies (type A) could be divided into two subtypes by using the ash yield: subtype A-1 (with an ash yield lower than 20% and a gel index (GI) lower than 5), and subtype A-2 (with an ash yield larger than 20% and a GI lower than 5). With the increase in micro-pore volume shown in A-1 samples, cumulative surface free energy increases linearly and the maximum rate of decline decreases linearly. Coal facies have an important effect on adsorption parameters: VL increases and PL decreases with higher structural preservation index (TPI). The effect of a low ash yield and different Ro,max on methane adsorption energy parameters is stronger.

Innovative Super Steel Belt Technology and its Application in the Drying and Treatment of Iron-bearing Waste Ash in Baosteel Zhanjiang lron & Steel Co., Ltd

During the ironmaking, steelmaking and steel rolling processes, steel enterprises generate a large amount of solid waste including iron, zinc, dust (ash) and mud, accounting for about 10% of the total steel production [1]. These solid wastes mainly include fly ash or sludge of blast furnace and rotary hearth furnace and some steel rolling sludge. The traditional way is to recycle these sediment (ash) as ingredients and return them to sintering, achieving internal recycling and utilization within the enterprise. However, some of the ash contains high levels of harmful elements such as zinc and lead. Directly returning to the batching process will cause zinc and lead to continuous circulation and enrichment in the system, resulting in excessive loads of zinc and lead in blast furnaces, which seriously affects the safety, stable production, and equipment life of steelmaking enterprises.

Calcium Hydroxide–Phosphate-Modified Fly Ash Enhances the Adsorption and Stabilization of Soil Lead and Cadmium

Calcium Hydroxide–Phosphate-Modified Fly Ash Enhances the Adsorption and Stabilization of Soil Lead and Cadmium

Innovative Super Steel Belt Technology and its Application in the Drying and Treatment of Iron-bearing Waste Ash in Baosteel Zhanjiang lron & Steel Co., Ltd

During the ironmaking, steelmaking and steel rolling processes, steel enterprises generate a large amount of solid waste including iron, zinc, dust (ash) and mud, accounting for about 10% of the total steel production [1]. These solid wastes mainly include fly ash or sludge of blast furnace and rotary hearth furnace and some steel rolling sludge. The traditional way is to recycle these sediment (ash) as ingredients and return them to sintering, achieving internal recycling and utilization within the enterprise. However, some of the ash contains high levels of harmful elements such as zinc and lead. Directly returning to the batching process will cause zinc and lead to continuous circulation and enrichment in the system, resulting in excessive loads of zinc and lead in blast furnaces, which seriously affects the safety, stable production, and equipment life of steelmaking enterprises.

Optimization and characterization of lime and GGBS treated fly ash for sustainable road pavement applications

Optimization and characterization of lime and GGBS treated fly ash for sustainable road pavement applications

Influence of fly ash and waste tire rubber particles on mechanical and tribological properties of composite brake linings

AbstractTo investigate the influence of waste tire rubber (WTR) and fly ash (FA) on mechanical and tribological properties of composite brake linings, 8 different formulations of 8–40 wt% FA and 10–12 wt% WTR were selected. The mechanical tests showed that high amounts of resin and FA result in the highest hardness. The inclusion of WTR, decreased hardness and internal shear strength; however, increased the acetone extraction and resistance to coefficient of friction (COF) fluctuations. With the use of WTR, steady COF fluctuations with the temperature changes are achieved. The tribological properties were evaluated with both a drum‐type and disc‐type dynamometer by the SAE‐J661 standard. Reduced COF fluctuations were observed in <15 wt% FA and 10 wt% WTR containing samples. The highest COF was obtained for the 14 wt% FA and the lowest wear rate for the samples containing 8 wt% FA. The brake composites exhibited consistent COF in the range of 0.34–0.52, and wear rates lower than 7 wt%. Two compositions containing 40 and 25 wt% FA (no WTR), and one containing 10 wt% WTR and 8 wt% FA provided the best results. Finally, four best compositions were selected and worn surfaces were analyzed with SEM after full‐scale dynamometer tests.Highlights Three composites with high waste percentage were successfully manufactured Fly ash and waste rubber are used without any post‐processing to cut costs Waste rubber increased resistance to COF fluctuations with temperature change Full‐scale dynamometer tests are performed for friction and wear properties Worn surfaces were analyzed with SEM method

Sustainable Use of Recycled Plastic and Coal Bottom Ash in the Development of Construction Material

Mineral coal bottom ash (CBA) is a by-product of coal combustion in power plants. Its potential use in building materials has attracted interest due to its beneficial properties and environmental implications. The aim of this study is to assess the feasibility of using mineral coal slag from the Anou Araren coal company in Niger (Sonichar), in combination with plastic waste, in various construction applications. In this case, the focus is on compressive strength and slip potential for floor coverings. Following a technical characterization of the various elements involved in the production of the proposed material, 02 firing methods are described, with the advantages and disadvantages of each. Mixtures with varying proportions of plastic waste and bottom ash (30%/70%, 40%/70% and 50%/50%) were studied. For the mix selected, the results show that the CBA/plastic waste material has good compressive strength and low slip potential, making it suitable for use in a variety of construction applications.

Waste materials utilization in 3D printable concrete for sustainable construction applications: a review

AbstractThree dimensionally printed concrete (3DPC) is an interesting topic that has attracted increasing attention during the last few years. This paper offers a comprehensive review of the utilization of waste materials in 3DPC. The literature on the different waste materials that have been utilized in 3DPC, such as silica fume, fly ash, recycled sand, waste glass, municipal incineration ash, ground granulated blast furnace slag, and steel slag, are reviewed. The influence of these waste materials on the main parameters of 3D printing of concrete such as the buildability, extrudability, and open time are discussed. In addition, the paper addressed the effect of these wastes on the mechanical strengths of the printed concrete. This paper finds that merging the technology of 3D printing of concrete with the usage waste materials will revolutionize the construction industry by addressing the challenges in meeting the required strength parameters of concrete using 3D printing technology and at the same time making construction process more economically and environmentally viable. Finally, to improve the efficiency of this emerging construction technique, authors recommend using combination of different waste materials together, taking into consideration using some additives to balance out the negative effects of waste materials on other parameters.

Investigation of nanomaterial and hazardous emissions at coal-fired power stations in Mpumalanga, South Africa

Coal-fired power stations remain the main source of electricity generation in South Africa. The combustion of coal creates fly ash and slag, and increases emissions of particulate matter, which is composed of nano-sized materials. In this study, we investigated nanoparticle emissions from coal-fired power stations. Soil samples were collected at 500 m and 1 km radii from Matla and Kriel power stations. The soil samples were examined using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray fluorescence (XRF) spectrometry. SEM images confirmed polydisperse particles in the form of semi-spherical, semi-oval, irregular-shaped and amorphous particles in dust and soil samples. The particle size range was 4–150 nm. Carbon sheet–metal oxide composites of As, Zn, Cu, Cr, Ni and V were observed. We found that coal-fired power stations are a potential source of nano-pollution, pointing to elevated human and environmental exposure around such sites. Currently, there are no environmental limits for nanomaterials due to the lack of robust risk assessment; however, this study suggests that coal-fired power stations may be hotspots that could be used as priority cases to examine the environmental implications of nano-pollution.

The Impact of Exogenous Organic Matter on the Properties of Humus Compounds of Soils Developing on a Reclaimed Fly Ash Landfill

Fly ash does not contain organic matter to initiate soil-forming processes and the proper development of plant cover. Therefore, in the reclamation of fly ash landfills, an integrated approach is required, including the introduction of exogenous organic matter into the top layer of ash. This study assessed changes in the content and quality of organic matter in soils developing on a reclaimed fly ash landfill. This study included reclaimed areas without the introduction of EOM (RV_1—the direct introduction of plants) and with the introduction of EOM (RV_2—surface humus and RV_3—sewage sludge). In samples taken 15 years after reclamation, the contents of total organic carbon (TOC) and total nitrogen (TN), the fractional composition of organic matter, the susceptibility of organic matter to oxidation, and soil carbon management indices (carbon pool index (CPI), C lability (L), lability index (LI), and carbon management index (CMI)) were determined. The study results showed that the use of EOM in the reclamation of the ash dump significantly increased the content and improved the quality parameters of organic matter and thus influenced the initiation of the process of organic matter accumulation. In RV_1 soil, the accumulation of carbon resources was only found in the topsoil. An increase in carbon resources in the 15–40 cm layer was only noted in the variants in which EOM was introduced (RV_2 and RV_3). Carbon management indices showed that organic matter transformations covered only the top layers of these soils and were closely related to the EOM inflow. The interdependence of the CPI and L was most beneficial in the soil reclaimed with sewage sludge. In the soil of this reclaiming variant, the CMI had a value above 100, which indicates the initiation of the soil-forming process. Significant differences between the assessed reclamation variants were confirmed by means of PCA based on organic matter quality indicators. The organic matter content and quality indicators were the most favorable in the soil of variant RV_3. The obtained results confirmed that the introduction of EOM into the top layer of fly ash has a beneficial effect on the accumulation and quality indicators of organic matter and thus on the development of the soil-forming process in Technosols developing on a reclaimed fly ash landfill.

Mechanical properties of discarded shield residue improved by calcium carbide slag and fly ash as subgrade filling.

To utilize discarded shield residue and alleviate the shortage of subgrade filling, industrial wastes such as calcium carbide slag (CCS) and fly ash (FA) were considered to enhance the mechanical properties of the shield residue. A series of laboratory tests, including California Bearing Ratio (CBR) tests, unconfined compressive strength (UCS) tests, moisture content tests, pH tests, water stability tests, and dry-wet cycles tests were performed on discarded shield residue with additive contents. The results show that the UCS and CBR values enhanced significantly with the increase in curing time. However, the moisture content and pH of the stabilized soil exhibited a decreasing trend. The early UCS of CCS-FA stabilized soil is slightly lower than that of QL-FA stabilized soil. After 60 curing days, all stabilized soil exhibited a UCS value exceeding 1.9 MPa. In addition, the CBR values of CCS-FA stabilized soil were more than 8 times higher than those of the original shield residue. Furthermore, the water stability of CCS-FA stabilized soil is slightly better than QL-FA stabilized soil, especially at 7 days and 14 days. As for dry-wet cycles test, after the fifth cycle, the CCS-FA stabilized soil maintained overall integrity. The CCS can effectively replace QL to enhance the mechanical properties of shield residue as subgrade filling.