Large Amount Of Fly Ash Research Articles

Strength prediction of concrete with large amount of fly ash based on improved random forest

Strength prediction of concrete with large amount of fly ash based on improved random forest

Analysis of the Performances and Optimization of Polyurethane Concrete with a Large Percentage of Fly Ash

The properties of polyurethane concrete containing a large amount of fly ash are investigated, and accordingly, a model is introduced to account for the influence of fly ash fineness, water ratio, and loss of ignition (LOI) on its mechanical performances. This research shows that, after optimization, the concrete has a compressive strength of 20.8 MPa, a flexural strength of 3.4 MPa, and a compressive modulus of elasticity of 19.2 GPa. The main factor influencing 28 and 90 d compressive strength is fly ash content, water-binder ratio, and early strength agent content.

Strength prediction of concrete with large amount of fly ash based on improved random forest

Strength prediction of concrete with large amount of fly ash based on improved random forest

Evaluation of fly ash concrete in salt environment

Indonesia is an archipelagic country with many buildings located in the coastal area. Seawater contains 3.5% salt, which can eat away at the strength and durability of concrete. Sodium salts can be dangerous when combined with reactive alkaline aggregates, and the crystallization of salts in concrete cavities can destroy them due to crystallization pressure. Concrete porosity is important to study, especially in beachfront buildings and buildings that intersect with the ground. In Riau Province, several companies operate AMP (Asphalt Mixing Plant) or paved mixture production units, which produce a large amount of fly ash or AMP waste. Research suggests that using only alkaline cement, using only alkaline cement, a mixture of 15% and 20% fly ash, can be more durable than concrete. This study used fly ash additives with seawater curing to determine the compressive strength of concrete with a curing life of 7, 14, and 28 days. This research was conducted because there was limited compressive strength research on concrete using a mixture of fly ash with seawater curing.

Central composite design-based development of eco-efficient high-volume fly ash mortar

High-volume fly ash (HVFA) mixtures that contain a large amount of fly ash have been widely investigated as sustainable materials with desirable mechanical properties and durability performances at mature ages. However, the low strength at early ages is the main obstacle that limits their wider applications in the practice. This work presents the development of the HVFA mortar with high early-age strength as well as low environmental impact with the help of central composite design-based statistical model. Besides, the effects of fly ash, limestone powder, asphalt emulsion content and water-to-cementitious material ratio (w/cm) as four main variables of HVFA mortar on the compressive strength and splitting tensile strength at curing ages ranging from 7 days to 28 days as the responses of this environmentally friendly material were investigated. Moreover, the multi-objective optimization was conducted to achieve the eco-efficiency of HVFA mortar. In this study, HVFA mortar with fly ash content of 67%, limestone powder content of 5%, no asphalt emulsion and w/cm of 0.25 exhibited 28-d compressive strength of 39.2 MPa and 28-d splitting tensile strength of 3.3 MPa. The optimized mix design of HVFA mortar can ensure the equivalent strength while noticeably reducing the CO2 intensity (CO2 emission per compressive strength) by 17.57%.

Laboratory and Field Evaluation of Stabilized Fly Ash as an Alternative Material for Sustainable Pavements

Thermal power plants in India produce a large quantity of fly ash, which is harmful to the environment. Underutilization of fly ash and the scarcity of natural minerals have created the need for an unusual construction strategy to prevent huge waste dumps on valuable land and to preserve fast-depleting resources. A study was conducted to determine the efficacy of lime-stabilized fly ash blended with quarry fines as flexible pavement subbase materials. The laboratory investigations were conducted to determine compaction characteristics, unconfined compressive strength, California bearing ratio (CBR), and durability to obtain the optimal quarry fines, fly ash, and lime (QFL) mix. The durability of QFL mixes was studied using 12 wetting–drying cycles. Using the strength and durability criteria specified by the Indian Road Congress, the optimum mix proportion of 40Q:60F+3L was determined. Pavement analyses were performed using the IITPAVE program. The QFL mix was observed to be superior to conventional granular subbase (GSB) layer material in terms of service life and cost-effectiveness. A field investigation was carried out on trial test sections constructed using the optimum QFL mix and GSB in the subbase layer of pavement. Field dry density and dynamic cone penetrometer (DCP) tests were performed on the compacted subgrade and subbase layers to assess the desired quality assurance in the construction of test sections. The early structural performance assessment of pavement sections using a falling weight deflectometer (FWD) test indicated that QFL could effectively replace conventional GSB.

Strength Evaluation of High Strength Concrete by Using Fly Ash and Silica Fume as A Partial Replacement of Cement

Abstract: Presently large amounts of fly ash are generated in thermal industries with an important impact on environment as well as humans. In recent years, many researchers have established that the use of supplementary cementitious materials like fly ash (FA), GGBS, blast furnace slag, silica fume, metakaolin, and rice husk ash, hypo sludge etc. can, not only improve the various properties of concrete, but also can contribute to economy in construction costs. This research work describes the feasibility of using Fly ash and Silica Fume as partial replacement of cement. The cement has been replaced by fly ash accordingly in the range of 0%, 10%, 20%, 30%, 40%, 50%, and 60% by weight of cement and 10% of silica fume in common for M30 grade of Concrete. Concrete mixtures produced, tested and compared in terms of compressive strength and split tensile strength with the conventional concrete for 7, and 28 days. It is found that, 30% of fly ash and 10% of silica fume can be replaced and good strength obtained is comparable to the conventional concrete mix.

Preparation, properties and applications of fly ash-based porous geopolymers: A review

A very large amount of fly ash is generated from coal combustion , and the high value-added and efficient utilization conversion of this solid waste into a resource remains an issue to be solved. Among the many methods of waste resource utilization, the preparation of porous geopolymers is an effective way to improve the added value of fly ash. In this review, the processes for obtaining fly ash-based porous geopolymers are divided into two categories: bulk-type (direct foaming, sacrificial template, additive manufacturing , and fast microwave foaming method) and sphere-type (suspension solidification, direct molding, and calcium chloride solution gel method). The synthesis routes, main characteristics (pore structure, porosity), and performance (mechanical and thermal properties as well as adsorption etc.) of fly ash-based porous geopolymers are reviewed, and examples of applications such as heat insulation , filtration, sound absorption, and pH buffering are presented. Moreover, the future development prospects of this field are discussed.

Effects of fly ash on MgO-based shrinkage-compensating cement: Microstructure and properties

The application of MgO expansive additive (MEA) in cement-based materials is one of the effective measures to compensate for shrinkage. However, related to the delayed excessive expansion, the incorporation of MEA has a potential risk of crack formation and decline of mechanical properties. To address the latter issue, an innovative approach using a large amount of fly ash with pozzolanic activity to coordinate the expansion stress of MEA and the resistance response of cement matrix is proposed in this paper. The effects of fly ash on MgO-based shrinkage-compensating cement are systematically investigated from the aspects of macroscopic properties and microstructural characteristics. The addition of 20% fly ash magnifies the effect of MEA compensation for early shrinkage and inhibits the later excessive volume expansion. In this way, the problem of mechanical properties decrease has been well resolved, and compared with 28 days, the compressive and flexural strengths with 20% fly ash at 90 days are increased by 23.3% and 18.4%, respectively. XRD and TG/DSC confirm fly ash slows down the early hydration process of MgO-based shrinkage-compensating cement and forms a stronger cement matrix through secondary reaction to offset the later reduced delayed expansion of MEA. NAD demonstrates fly ash stabilizes the positive effect of MEA on increasing microstructure compactness through expansion. SEM and EDS illustrate fly ash improves distribution of Mg(OH)2, avoiding the deterioration of microstructure caused by local excessive expansion.

Damage mechanism of engineered cementitious composites after exposed to elevated temperatures: Experimental and molecular dynamics study

Replacing cement with large amounts of fly ash in engineered cementitious composites (ECC) is one of the win-win measures to enhance matrix ductility and effectively reduce carbon emissions. However, the high content of fly ash undoubtedly makes the mechanical properties of ECC lower, resulting in its performance at high temperature to be questioned. To solve this problem, this paper combines experiments and molecular dynamics study to fully explore and innovatively explain the performance of ECC exposed to different temperatures (20 °C, 200 °C, 400 °C, 600 °C and 800 °C) from the aspects of macroscopic mechanical properties, microstructural characteristics and molecular-scale interfaces. From 20 °C to 800 °C, the mechanical properties first increase and then decrease significantly. SEM shows the changes in the microscopic morphology at elevated temperatures, such as the increase of cracks and pores in the matrix, and the melting of the PVA fibers. TG/DSC and XRD illustrate the phase transformation at different temperatures. 29Si NMR demonstrates the decomposition of hydration products and the depolymerization of silicate chains at higher temperatures. Additionally, molecular dynamics study is carried out to characterize the interaction between PVA fibers and C–S–H gel at a molecular scale as a function of temperature. With the increase of temperature, the morphology of C–S–H gradually changes from layered structure to spherical structure, the water molecules between the C–S–H layers gradually diffuse to the C–S–H channel, and PVA chains are present by disordered distribution. The simulated results have a good agreement with experimental results and further explain the damage mechanism of ECC at elevated temperatures on the nano-scale level.

Chemical stabilization of heavy metals in municipal solid waste incineration fly ash: a review

Sufficient attention should be attached to the large amount of fly ash containing high levels of toxic heavy metals generated after municipal solid waste incineration. Because heavy metals could be leached out of the fly ash under specific conditions, it is necessary to stabilize the heavy metals in fly ash before landfill disposal. Processing technologies of incineration fly ash include solidification/stabilization technology, thermal treatments, and separation processes. This study reviewed the current treatment technologies of municipal solid waste incineration (MSWI) fly ash, with the main focus on the treatment of heavy metals in fly ash with chemical stabilization. Chemical stabilization processes involve chemical precipitation of heavy metal and chelation of heavy metals. In multiple studies, chemical stabilization technology has shown practical feasibility in terms of technology, economy, and effect. In addition, the combination of two or more stabilization agents broadens the general applicability of the agents to heavy metals and reduces the cost. The application of joint processing technology realizes the remove of soluble salt from fly ash. To minimize pollutants while increase their usable value, effective use of waste and co-disposal of several kinds of wastes have gradually become the research hotspots. New developments in chemical stabilization are progressively moving towards the sustainable direction of harmlessness and resource utilization of MSWI fly ash.

Acidic corrosion-abrasion resistance of concrete containing fly ash and silica fume for use as concrete floors in pig farm

The objective of this study is to investigate the resistance of concretes to organic acid corrosion and abrasive corrosion, which occurs in typical pig farms. For the concrete mixtures, cement was replaced by fly ash and silica fume with different weight percentages up to 30%. The cubic mortar and concrete specimens were prepared and tested for compressive strength and mass loss due to organic acid corrosion. The test results indicated that fly ash and silica fume mixed together significantly enhance the compressive strength of the concrete, especially at long-term curing periods. The resistance of the concrete and mortar against organic acid corrosion was greatly improved by the substitution of fly ash and silica fume. Moreover, two testing machines were developed to simulate the abrasion-corrosion attack on concrete floors in pig farms (one for organic acid corrosion tests in wet-dried conditions and the other one for an abrasion testing machine with steel brushes). The concrete slab was cast and tested with a wet-dry switching system in an organic acid solution cooperating with an abrasion test. The test results demonstrated that applying a large amount of fly ash and silica fume is not effective for increasing the resistance of the concrete against organic acid corrosion and abrasive corrosion. The concrete mixture with 5 wt% of silica fume shows the highest resistance to organic acid corrosion together with abrasive corrosion with a mass loss reduction for 7.14% compared to the reference mixture.

Effect of Equal Volume Replacement of Fine Aggregate with Fly Ash on Carbonation Resistance of Concrete.

Concrete is prepared by substituting an equal volume of fly ash for fine aggregate, and the effect of substitution rate on its carbonation resistance is studied. Using a rapid carbonation test, the distribution law of the internal pH value of concrete with fly ash as fine aggregate (CFA) along the carbonation depth under different substitution rates (10%, 20%, 30%, and 40%) after carbonation is studied and compared with the test results of phenolphthalein solution. Then, to further clarify the damage mechanism of fly ash replacing fine aggregate on concrete carbonation, the changes in the pore structure and micromorphology of CFA after carbonation are studied by means of mercury intrusion pressure and electron microscope scanning tests. The results indicate that the carbonation depth of CFA increases gradually with increasing carbonation time. In particular, in the later stage of carbonation, the carbonation rate of concrete decreases significantly with an increase in the substitution rate. The carbonation depth XC of CFA measured by phenolphthalein solution is approximately 0.24–0.39 times of the complete noncarbonation depth measured by the pH method. The pH value test is a reliable test method that can reveal the carbonation mechanism of CFA. Carbonation can significantly reduce the proportion of more harmful holes in concrete with a large amount of fly ash, but it can also increase the proportion of less harmful and harmful holes. In general, the pore size distribution and micromorphology of concrete can be improved by replacing fine aggregates with fly ash.

Effect of fine aggregate type on early-age performance, cracking analysis and engineering applications of C50 concrete

Due to the increasing resource shortage and environmental problems caused by the over-mining of river sand, manufactured sand has been adopted as an alternative to river sand as an important component of modern concrete in some engineering construction processes. However, the uncertain stone dust content of manufactured sand has the potential to cause a reduction in the crack resistance of concrete, especially in practical engineering applications. This paper compares and analyses the effect of river sand and manufactured sand on the basic properties of C50 concrete and explores the law of fine aggregate type on the cracking resistance of concrete. The results of the study show that the tensile strength of manufactured sand concrete (MSC) is not as good as that of river sand concrete (RSC) in the case of large amounts of fly ash and slag, and the working properties of both are relatively close. The effect of different fine aggregate types on the adiabatic temperature rise of concrete is not significant and remains largely consistent. However, in the engineering application of large volume thick base slab concrete, the internal generation of heat of hydration is greater, the temperature rise is higher and the difference between internal and external temperature and cooling shrinkage is prone to the risk of temperature cracks due to temperature stresses. Therefore, with a small difference in adiabatic temperature rise between RSC and MSC, the magnitude of temperature stresses generated is close, but since the use of manufactured sand leads to a decrease in the tensile strength of the concrete itself, the risk of cracking is greater in MSC compared to RSC. Finally, the RSC mix proportion obtained from the laboratory were successfully applied to the foundation slab of a 500 m tall building, which is of great practical engineering importance.

Geotechnical Behaviour of Fly Ash–Bentonite Used in Layers

Increasing infrastructure growth has forced the construction industry to look for wasteful, cheap, and suitable materials for construction. An investigation into the geotechnical utilization of fly ash was carried out in the present study. Practical applications normally involve the use of large quantities of fly ash, so proper mixing of the fly ash with other materials may not be significantly achieved. Therefore, the present paper investigates the behaviour of a fly ash–bentonite layered system with different ratios. The physical properties and chemical composition of fly ash and bentonite were determined. SEM and energy dispersive X-ray experiments were also used to investigate the morphology and phase compositions of fly ash and bentonite. A series of consolidated undrained (CU) triaxial tests on fly ash–bentonite were carried out to investigate shear strength characteristics. Fly ash (F) and bentonite (B) were used in the following ratios: 1:1 (50% F:50% B), 2:1 (67% F:33% B), 3:1 (75% F:25% B), and 4:1 (80% F:20% B), with different numbers of interfaces (N), i.e., 1, 2, and 3 for each ratio. The deviator stress and cohesion value were found to increase with the number of interfaces for each ratio. The angle of shear resistance changed marginally with the increase in the fly ash–bentonite ratios and varying interfaces.

Hydration and Microstructure of Ternary High-Ferrite Portland Cement Blends Incorporating A Large Amount of Fly Ash and Limestone Powder

Hydration and Microstructure of Ternary High-Ferrite Portland Cement Blends Incorporating A Large Amount of Fly Ash and Limestone Powder

Hydration and Microstructure of Ternary High-Ferrite Portland Cement Blends Incorporating a Large Amount of Fly Ash and Limestone Powder

Hydration and Microstructure of Ternary High-Ferrite Portland Cement Blends Incorporating a Large Amount of Fly Ash and Limestone Powder

Effect of Curing Time on the Surface Permeability of Concrete with a Large Amount of Mineral Admixtures

In order to explore the influence of curing time on the surface permeability of concrete, 10 groups of high content fly ash and slag concrete with two kinds of water‐binder ratio were designed. There were cured under five curing methods, respectively. The influence of curing time on the surface permeability of concrete was studied. The mechanism was explained by hydration heat and mercury intrusion porosimetry. The results show that inadequate curing time leads to insufficient hydration of cementitious materials in concrete with large amount of mineral admixtures and significant increase in the diffusion of chloride ions on the surface of concrete. Standard curing for 14 days can basically ensure the chloride ion penetration resistance of concrete with large amount of mineral admixture. When the standard curing time is less than 7 days, the chloride ion penetration resistance deteriorates seriously. Under the condition of insufficient standard curing time, adding a small amount of limestone powder can effectively enhance the chloride ion permeability of concrete with a large amount of fly ash and slag.

Experimental analysis on alkali activated fly ash (AAFG) and GGBS based coarse aggregate in cement concrete

Many applications of fly ash have been studied and employed in various fields. Thermal power stations use pulverized coal as fuel. Thus produce large amounts of fly ash as a by-product of combustion. The present analyses investigates the manufacturing process of Alkali Activated Fly Ash (AAFG) and Ground Granulated Blast Furnace Slag (GGBS) Based Coarse Aggregate using an ordinary concrete mixer and its properties are analyzed. The flexural capacity of the Reinforce Concrete (RC) beam with AAFG increases by increasing the diameter of reinforcement and decreases in the replacement AAFG beam, and the crack width decreases as an increase in the replacement of the fly ash aggregate up to 50% in concrete. The durability property of concrete blended with AAFG shows similar results to conventional concrete. From the Rapid Chloride Permeability Test (RCPT) results, it shows that AAFG concrete and conventional concrete are both in the moderate zone only.

Numerical analysis of an 80,000 Nm3/h fly ash entrained-flow gasifier at various burner inclination angles.

The raw syngas effluent from a fluidized bed gasifier typically contains a large amount of fly ash having a high concentration of carbon, which is undesirable. The present work examined the newly developed entrained-flow gasification technology intended to gasify raw syngas. Simulation of gas-solid flow and reaction behavior in an industrial-scale entrained-flow gasifier applying this new technology was first performed to obtain a better understanding of the particle flow and gasification characteristics. In addition, the devolatilization and heterogeneous reactions of fly ash particles were characterized by thermogravimetric analysis and user-defined function. The predictions from the simulation showed good agreement with the results of in situ experimental measurements. The combustion reaction for raw syngas occurred in the burner jet zone. As the hot gaseous products diffused, gasification reactions dominated the other zones. When burner inclination angle was 0°, 8.5°, and 25.5°, the temperature at the bottom outlet of the gasifier was lower than the ash flow temperature with the value of 1360°C. Solid slag formed and blocked the outlet. By comparison, this gasifier with the burner inclination angle of 17° could discharge the liquid slag and function as a continuous operation. In this way, the carbon conversion in fly ash reached the maximum value of 87%.