Ash Slurry Research Articles

Properties and Microstructure of Low-Strength Recycled Concrete Aggregate Treated Using Cement–Fly Ash Slurry with Various Concentrations and Soaking Durations

Properties and Microstructure of Low-Strength Recycled Concrete Aggregate Treated Using Cement–Fly Ash Slurry with Various Concentrations and Soaking Durations

The novel inorganic solidified foam prepared by direct foaming and its characteristics for preventing spontaneous combustion of coal

ABSTRACT To mitigate coal spontaneous combustion disasters caused due to air leakage in coal mines, inorganic solidified foam is widely employed to seal these areas. This study proposes a simplified method for preparing such foam by directly foaming a mixture of water, cement, fly ash, and foaming agent. This new inorganic solidified foam plugging material aims to enhance sealing effectiveness. The research investigates the foaming ability and stability characteristics of different types of surfactants, analyzing their compatibility with cement and fly ash. It identifies that lauramidopropyl surfactant (LX) exhibits the lowest viscosity in the cement-fly ash slurry mix, resulting in superior foaming performance. By studying effects of water-cement ratio and foaming agent concentration on the foaming performance of cement-fly ash slurry mix, it is found that when the water-cement ratio is 0.6 and the foaming agent concentration is 0.5%, the foaming performance of inorganic solidified foam is optimal, yield the highest foaming efficiency with a multiple of 4.33 times and compressive strength of 0.13 MPa, effectively bonding and reinforcing fractured coal bodies to sealing air leakage cracks efficiently. This study contributes to simplifying the preparation equipment and the application processes of inorganic solidified foam, making it more suitable for widespread application in the confined spaces of coal mines, providing a new technical approach for preventing and controlling coal spontaneous combustion in mines.

Study on the improvement of grouting stone properties in coal mine goafs using combined denitrifying bacteria.

Grouting can effectively reduce residual deformation of coal mine goafs, but fly ash grouting materials suffer from poor flowability and slow early strength development. Microbially -induced calcite precipitation (MICP), with its high environmental compatibility and minimal disturbance to geotechnical bodies, effectively improves the injectability of grouting slurry in goafs. This study combined Castellaniella denitrificans and Sporosarcina pasteurii to induce calcite precipitation, preparing cement-fly ash slurry with varying water-solid ratios, solid ratios and denitrifying bacteria concentrations. The physical properties of the slurry and the mechanical properties of the grouted stone bodies under sealed curing conditions were measured. Results show that the dual-bacteria MICP improves stone body performance by enhancing cohesive, frictional and interlocking forces, so that the strength of the stone bodies cured by MICP increased rapidly within 7 days, and the strength reached the standard 2.03 MPa at 28 days under conditions of low solid ratio and high water-solid ratio, with the best compressive strength at a denitrifying bacteria concentration with an optical density of 0.8 at 600 nm wavelength. At a water-solid ratio of 1 : 1.2 and a solid ratio of 15%, initial and final setting times were 67.2 and 96 h, respectively, which prolonged the initial setting time and final setting time by nearly 70% and 110% compared with that of the slurry without MICP treatment, indicating that MICP enhances slurry fluidity, providing more time for grouting construction in goafs.

Plant and Soil Effects of Alternative Sources of Phosphorous over Three Years of Application

Plant growth and food security depend heavily on phosphorous (P). Recovering and recycling P from animal, municipal, and food waste streams can significantly reduce dependency on traditional mineral P. This is particularly pertinent in the EU regions with limited native P supplies. The agronomic performance of including P-based recycling-derived fertilisers (two struvite and two ashes) or cattle slurry was compared to a conventional mineral P fertilisation programme along with no P and no fertiliser controls over three years. A field-scale experiment was set up to evaluate the perennial ryegrass dry matter yield (DMY), P uptake, and soil test P effects. Struvite, ash, and cattle slurry proved effective in replacing P mineral fertiliser and produced yields similar to those of the mineral fertiliser programme. Differences were observed in plant P recovery, with struvite-based programmes achieving a significantly higher P recovery than ash-based programmes, which had the lowest plant P recovery. Differences in Morgan’s soil test P were also noted, with potato waste struvite (PWS) and poultry litter ash (PLA) showing significantly higher soil test P values. The findings strongly indicate that a range of recycled bio-based fertilisers from the bioeconomy can be used to reduce reliance on conventional imported mineral P fertiliser, with some programmes based on recycled fertilisers even surpassing the performance of conventional linear economy mineral fertilisers.

Experimental analyses of CO2 sequestration potential in mineralized fly ash and its efficacy in mitigating coal spontaneous ignition risks in underground mine goafs

To effectively utilize fly ash solid waste and realize fly ash resource utilization, carbon sequestration and emission reduction, as well as mine fire prevention and suppression, this paper analyses the components of fly ash by X-ray fluorescence spectrometer (XRF), rheological experiments, the CO2 sequestration experiments by the mineralization of fly ash, thermogravimetric analysis experiments, and flame-retardant property experiments. Additionally, the changes in the physical structure and morphology of fly ash before and after mineralization were analyzed by X-ray diffraction (XRD) and scanning electron microscope (SEM). The carbon sequestration capacity and fluidity of fly ash slurry, as well as the ability of mineralized fly ash slurry to inhibit spontaneous coal combustion are comprehensively investigated. The research results indicate that CO2 is sequestered as calcite on the fly ash surface after mineralization. The optimal CO2 sequestration capacity of fly ash is 65.12 kg/t when 0.5 mol/L NaHCO3 is used as an additive. The fluidity of mineralized fly ash slurry is greater than that of fly ash slurry, and the lower the water-cement ratio is, the worse the fluidity. Mineralized fly ash slurry with a water-cement ratio of 3:1 has a strong carbon sequestration capacity and high fluidity, making it suitable for preventing coal spontaneous ignition in mine goafs. Mineralized fly ash slurry exhibits a regular trend where the better the mineralization effect, the lower the CO release during the low-temperature oxidation stage of coal, and the higher the cross-point temperature. Mineralized fly ash slurry has a stronger ability to inhibit spontaneous coal combustion than does ordinary fly ash slurry.

Internal Erosion Induced Instability of Coal Ash Ponds: Forensic Analysis using Smoothed Particle Hydrodynamics (SPH)

Coal-based power generation will continue to be the backbone of energy supply until renewable energy sources become mainstream. Hence, management of large quantities of coal ash generated as a by-product is a global concern. Coal ash is commonly disposed in ash ponds and is prone to internal erosion because of low specific gravity. The consequent breach of an ash pond may result in severe socioeconomic impacts. Thus, design and analysis techniques incorporating internal erosion are essential for constructing resilient ash ponds. This study investigates the effect of internal erosion on the stability of ash ponds using a five-phase SPH model. The approach is utilised for analysing an operational ash pond from India, where instability due to internal erosion was observed. The results indicate that the amount of erodible fly ash significantly influences the initiation of instability and the subsequent mass flow, with close to 100 % reduction in mass flow as the fly ash content is reduced from 80 % to 20 % by weight. The study also highlights the significance of appropriate coal ash slurry disposal practices and field monitoring for averting such failures. Further, replacing the erodible coal ash with a non-erodible material is validated as a feasible failure mitigation measure.

Dynamic characterization of water hammer in gangue fly ash slurry pipelines during valve closure

In the process of coal-filling mining, the gangue fly-ash slurry (GFS) needs to be transported over a long distance to reach the gobs. The abrupt closure of the valve during the transportation of GFS can result in a water hammer that significantly endangers the stability and safety of the pipeline transport system. To study the fluctuations in pressure induced by abrupt closure of the valve, experiments on the rheological parameters of gangue-coal ash slurry were conducted. Transient numerical simulations were carried out using the computational fluid dynamics method for various valve closing times. The results indicate that, with the increase of slurry concentration, the yield stress of the slurry significantly increases. When the concentration exceeds 76%, the increase in yield stress reaches 38.4% and 35.1%, respectively. Upon valve closure, the internal pressure of the slurry in the pipeline exhibits periodic dynamic oscillations. As the duration of valve closure increases, the frequency of periodic water hammer events decreases. The maximum water hammer pressure caused by valve closure decreases with the increasing distance between the valve and the closure point. At the same time, the intensity of maximum water hammer pressure fluctuations increases with the increase in slurry concentration and flow velocity in the pipeline. The results can provide references for water hammer protection and pipeline selection during the transportation of backfill slurry in mining.

Improvement of the mechanical properties of beta-hemihydrate phosphogypsum by incorporating wet-ground low-calcium fly ash slurries

Beta-hemihydrate phosphogypsum (β-HPG) is a low-carbon cementitious material used in construction. Nevertheless, the poor water resistance and low mechanical strength of β-HPG limit its utilization. In this study, two low-calcium fly ash (FA) slurries with median particle sizes of 1.83 μm and 1.14 μm were prepared using a wet-grinding process for the improvement of β-HPG, and the mechanical strength and softening coefficient were tested to assess the effect. The results show that wet-ground low-calcium FA can significantly enhance the mechanical strength and softening coefficient of β-HPG. Compared with specimens without wet-ground low-calcium FA, the dry compressive strength and softening coefficient of specimens with 30% wet-ground low-calcium FA (D50=1.14 μm) increased by 104.9% and 71.8%, respectively. It is worth noting that the 1 d compressive strength also increased by 11.9%. Specifically, wet-ground low-calcium can increase the pH value and conductivity of the FA slurry, further accelerate the hydration process of FA in β-HPG, forming more ettringite and gels to fill in the pores between dihydrate gypsum (DH) crystal, and reducing the larger pores in the hardened paste. This study can develop a high-performance cementitious material that will enable the effective use of β-HPG.

Effect of rubberized concrete integrating uncoated and coated crumb rubber on the flexural behavior of the RC beams reinforced with steel and GFRP bars

In this investigation, crumb rubber (CR) was a viable substitute for concrete's conventional natural fine aggregate (FNA). This approach carries dual advantages: the conservation of natural resources and the environmentally conscious recycling of rubber waste, diverting it from traditional disposal methods. The study incorporated varying proportions of CR (5%, 10%, and 20%) by volume of the sand used in the mixtures. The primary study objective is to enhance the bond between CR particles and the surrounding concrete components by coating the CR with cement or fly ash slurry (CTR and FATR). For the limitation of the previous research discussed the CR effect on the beam’s behavior, fourteen beams were poured with different rubberized concrete (RuC) and tested in flexure. This comprehensive approach sought to assess the influence of diverse factors, including rubber content, treatment materials, and the nature of internal reinforcement, on the overall performance and characteristics of the beams. The results assumed that the compressive strength was raised by 6.0–11.0% and 13.0–22.0% for the mixes cast with CTR and FATR, respectively, compared to the corresponding mixes cast with UR. Consequently, the tensile strength of the RuC-integrated CTR and FATR was raised by 5.9–11.0% and 14.0–22.0%, respectively, compared to the mixes integrating uncoating CR. Moreover, the beams cast with FATR concrete experienced the highest flexural capacities among all the steel RC beams. Furthermore, using the carbon fiber reinforced polymer (CFRP) bars as internal reinforcement for the RC beams showed the highest load capacities.

Tribo-Erosion Analysis of HVOF Colmonoy-88-Coated Pump Impeller Steel in Coal Ash Particle Slurries

Abstract Coal ash slurries hold paramount importance in the service life of the coal and mining industries, significantly impacting their operational efficiency and durability. The literature reveals that the prominent dominating parameters such as rotational speed, concentration, time duration, and particle shape and size have a major impact on erosion wear. This research aims to explore the effects of coal ash slurries on Colmonoy-88-coated pump impeller steel, employing a combination of design of experiments (DOE) and digital image analysis (DIA). Through slurry experiments, it is observed that erosion wear increases non-linearly with an increase in influencing parameters. The particle size emerges as the most significant factor, followed by concentration, speed, and time. Additionally, DIA is leveraged to validate the influence of various erodent particle sizes on the erosion wear of the pump impeller steel. Results indicate that coal particles possess irregular shapes and sizes compared to fly ash and bottom ash, consequently resulting in larger erosion wear due to their lowest circularity factor (0.72). Furthermore, smaller particles exhibit lower erosion wear-rates compared to larger ones. This study sheds light on the intricate dynamics of erosion wear in the context of coal ash slurries, offering insights crucial for optimizing pump impeller steel durability in similar operational environments.

Review of Treatment Methods for Enhancing Recycled Concrete Aggregates Properties

Abstract: The use of recycled concrete aggregates (RCA) as a potential substitute for natural aggregates in concrete production has been recommended by many research studies due to the environmental and cost benefits associated with it. However, due to RCA’s high-water absorption, its engineering properties are lower than natural aggregates (NA). Therefore, researchers have also suggested various pretreatment methods to enhance RCA's mechanical and durability properties, including thermal, mechanical, and chemical treatment. In this study, an attempt has been made to investigate the combined effect of heat, abrasion, and fly ash slurry pretreated RCA on the workability and compressive strength of recycled aggregate concrete (RAC) using superplasticizer for 0.4, 0.5, and 0.6 w/c ratio. The study results show that pretreatment of RCA along with the addition of superplasticizer can lead to higher workability and compressive strength of recycled aggregate concrete (RAC) compared to untreated RCA.

Formulation determination and performance study of high-volume fly ash-based grouting fire extinguishing materials

Considering the continued advancement of China's industrial sector, a substantial quantity of circulating fluidized bed fly ash (CFBFA) and calcium carbide slag (CS) is generated throughout the production process. Considering the rich calcium content inherent in CFBFA (circulating fluidized bed fly ash) and the inherently alkaline nature of CS(carbide slag), the amalgamation of these two constituents leads to a multitude of hydration reactions, culminating in the synthesis of polymeric grouting materials. This study undertaked a comprehensive examination and regulation of three factors within the binary system: water-cement ratio, CS content, and CS particle size. Through the utilization of scanning electron microscopy (SEM), X-ray diffraction (XRD), and (TG) thermogravimetric analysis, the investigation aims to elucidate the influence mechanism of the composite gelling system comprising fly ash and calcium carbide slag on the compressive strength, setting time, and other pertinent indicators of grouting materials. The data reveals that when the water-cement ratio is set at 0.85, CS content at 30%, and CS ball milling time at 1 h, the resulting grouting material exhibits a fluidity of 279 mm, a water separation ratio of 3.13%, and achieves a strength of 15.6 MPa at 28 days. It boasts a stable and easily transportable slurry, which possesses a certain degree of cementitious performance, effectively sealing off any air leakage channels. Moreover, by subjecting CS to appropriate pre-treatment measures, a suitable quantity of active silicon and aluminum elements can be thoroughly dissolved within the CFBFA (circulating fluidized bed fly ash) slurry system, giving rise to a staggered distribution and dense hydration product structure. Considering the requirements for gangue mountain fire extinguishing slurry, a CFBFA-CS based grouting material formula has been carefully selected. Additionally, simulation grouting fire extinguishing experiments have demonstrated that the injection of the slurry is highly effective in reducing the temperature of the combustion test block, isolating oxygen, and lowering the temperature within the combustion zone. After 5 h, the temperature drops to below 100 °C, and no re-ignition phenomena are observed. The outcomes of this research can provide valuable scientific guidance for the development of high-performance fire extinguishing grouting materials utilizing fly ash and carbide slag.

Optimization of specific energy consumption in the high concentration slurry disposal pipelines for coal ash in thermal power plants

ABSTRACT In thermal power plants, the disposal of coal fly ash is one of the major challenges requiring energy input for its safe disposal, so optimization is needed to minimize the required energy input at maximum fly ash transportation. Present work is focussed on high concentration optimized transportation of ash slurry in thermal power plants using Computational Fluid Dynamics (CFD) which behaves as a Bingham plastic fluid, modeled using Herschel-Bulkley model. Specific Energy Consumption (SEC) is the measure of the energy required for the slurry transportation. Therefore, a parametric investigation to establish the effect of concentration of slurry (Cw), pipe diameter (D), no. of pipes (N), particle size (d) over SEC is conducted. Therefore, these operational parameters need to be carefully selected, as even a minor variation from the desired optimum values may result in huge SEC consumption thereby causing financial consequences. It is found in the current study that the SEC substantially depends on all of the above-mentioned parameters. Mathematical models for prediction of SEC based on the study are also developed for the future designers of such systems.

Laboratory mechanical properties and frost resistance of vibration-compacted cement–fly ash slurry and cement–fly ash-treated macadam mixtures

The objectives of this study were to characterize the compaction and mechanical characteristics and frost resistance of vibration-compacted cement–fly ash slurry (CFAS) and cement–fly ash-treated macadam (CFATM) mixtures and recommend the optimal ratio and dosage of cement–fly ash (CFA) based on laboratory compaction experiments, unconfined compressive testing, indirect tensile testing, and frost resistance testing. The effects of the CFA ratio and dosage, curing age, and gradation type on the mechanical strength and frost resistance were analyzed, and strength prediction equations were presented. Then, the optimal CFA ratio and dosage are recommended. The results show that the mechanical strength of CFAS and CFATM mixtures increased nonlinearly with increasing curing age. Gradation type, CFA ratio, and CFA dosage affected the conventional, initial, and ultimate mechanical strengths of these mixtures. A CFATM mixture cured for a longer duration with self-developed skeleton-dense gradation and the addition of less fly ash exhibited better frost resistance. To maximize the mechanical strength of CFAS and CFATM mixtures, the CFA ratio should not exceed 1:1 and 1:1–1:1.5, respectively. In addition, 3.5%–4.0% cement and 4.0%–7.0% fly ash should be used in the CFATM base or subbase to obtain optimal results. This paper provides a new option for the design of CFAS and CFATM mixes.

Study on Resistance Loss of Fly Ash Slurry Multistage High‐Pressure Grouting Pipeline Based on Fluent

In order to understand the resistance loss along the way during multistage high‐pressure slurry transportation, the flow state of fly ash slurry in the pipeline was simulated by Fluent software in this paper, and the effects of pipe diameter D, pipe transportation flow rate Q, and fly ash mass concentration Cw on the resistance loss along the pipeline were studied. The fly ash slurry is a non‐Newtonian Bingham fluid that moves in a turbulent state in a pipeline. When simulating the flow of fly ash slurry using Fluent software, the mesh type is a mixed mesh of hexahedron and wedge shapes, and the viscous model is selected as realizable k‐ε Turbulence Model, with Enhanced‐Wall Function (EWF) selected as the wall function, combined with a four‐layer boundary layer mesh, which can more accurately capture the details of velocity changes at the wall, thereby improving the accuracy of the model. The inlet of the model is the velocity inlet, and the outlet is the pressure outlet. The coupled algorithm is chosen as the solution method. Under these conditions, the model converges quickly and the calculation accuracy is high. The results show that the resistance loss along the pipeline decreases as a power function with the increase of pipeline diameter, and there is a polynomial relationship between the pipeline flow and the resistance loss along the pipeline, while the mass concentration of fly ash slurry changes linearly with the resistance loss along the pipeline. In addition, three friction coefficient models, namely Blasius formula, Colebrook–White equation, and Wilson–Thomas model, were selected according to the flow characteristics of fly ash slurry. Based on the Blasius formula with the smallest relative calculation error, the Blasius formula was modified by multiple linear regression analysis to improve the accuracy of the frictional resistance coefficient model and to provide help for the design and use of separate layer grouting conveying system.

Effect of the strength grade of parent concrete on the performance of recycled aggregate treated by cement-fly ash slurry under prolonged soaking duration

The detrimental effects of quarrying natural resources have contributed to large-scale environmental pollution. Utilizing recycled concrete aggregate (RCA) obtained from construction and demolition waste as a replacement for natural aggregates has become an effective solution for environmental sustainability. However, the inevitably diminished characteristics of the adhered mortar and the existence of an additional interfacial transition zone (ITZ) have negatively suppressed the widespread use of these materials in production lines. The present study aims to comprehensively investigate the effects of a cement-fly ash slurry with a mass ratio of 50% of the total weight of RCA on the microstructure and engineering properties of RCA derived from three different parent concretes with strength grades of 20, 30, and 60 MPa. The RCAs were soaked for 24 h, 48 h, and 72 h to evaluate the long-term effects of the pozzolanic slurry. A sequence of laboratory tests was conducted, including mercury intrusion porosimetry (MIP) test, thermal gravimetric–differential thermal analysis (TG-DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses, and measurements of water absorption and crushing value. The MIP results demonstrated a significant increase in medium capillary and gel pores, and a reduction in large capillary pores in the RCA with an increase in soaking time. TG-DTA results indicated an increase in Ca(OH)2 content during the first 24 h and 48 h of treatment. However, after 72 h of treatment, the Ca(OH)2 content of the treated RCA decreased in all cases. XRD analysis revealed the appearance of a few additional ettringite peaks among the treated RCAs in all cases. SEM images demonstrated the presence of additional hydration products after treatment, which filled the pores and improved the surface texture. Furthermore, after treatment, the crushing value of all treated RCA decreased by 6.0–27.1%, whereas the water absorption decreased by 12.0–30.9% compared to the untreated RCA. Based on several experimental results, the formation of hydration products and the improvement mechanism of RCA from three different parent concretes by slurry treatment with different soaking durations were discussed. In conclusion, a prolonged impregnation time of 72 h yielded a dominant performance, effectively intensifying their inferior properties, regardless of the initial strength grade of parent concrete.

Measurement of Yield Stress and Flow Potential of Fly Ash Slurries Using a Rheometer

Measurement of Yield Stress and Flow Potential of Fly Ash Slurries Using a Rheometer

CFD Analysis of Fly Ash Slurry Flow Across Horizontal Pipe

Fly ash is a significant consequences of coal-fired power stations. Fly ash slurry transportation via long pipelines is a challenge for thermal plants and other industries. In the current investigation, numerical simulation has been performed to analyse the flow pattern of fly ash slurry via horizontal pipe. It has been discovered that pressure loss over horizontal pipe increases with velocity and solid concentration. Study of rheological flow properties of fly ash slurry is crucial for the development of its transportation system. The current work may help develop slurry pneumatic conveying systems for thermal plants.

Workability, autogenous shrinkage and microstructure of alkali-activated slag/fly ash slurries: Effect of precursor composition and sodium silicate modulus

The alkali-activated slag/fly ash system is used as a cementitious material to instead of ordinary Portland cement and has good application prospects for recycling various solid wastes and low carbonization in the construction field. In this work, we aim to reveal the effects of changes in precursor composition and sodium silicate modulus in alkali-activated slag/fly ash slurry on strength and autogenous shrinkage, and make a comparative study about workability, autogenous shrinkage and microstructure. The test results showed that the engineering performance of alkali-activated cementitious materials mainly depended on the constituent materials and their ratios. With the increase of fly ash content, the slump was enhanced, the setting time was extended, the strength was slightly reduced, and the autogenous shrinkage was significantly mitigated. For the reference slurry (n = 1.2), the 28 d autogenous shrinkage value of S10F0 was 6064.28 μm/m, the 28 d autogenous shrinkage value of S9F1 was 1516.67 μm/m, and the shrinkage value was reduced by 75%. And with the increase of sodium silicate modulus, the slump was enhanced, the setting time was increased, the early strength was reduced, the later strength developed faster, and the influence on the sample autogenous shrinkage was smaller. The reaction products were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). With the increase of fly ash content, the calcite phase was observed in the reacted products, the flocculent components and many unreacted fly ash spheres in diameter were observed, and there were many micro-pores in the hardened solid particles. Combined with autogenous shrinkage and mercury intrusion porosimetry analysis, it could be discovered that when the modulus of sodium silicate increased, the capillary pore volume increased, and the total porosity and pore size decreased significantly, when the modulus of the activator increased from 1.2 to 2.0, the porosity decreased by 44.36%. making the autogenous shrinkage and strength increase. When the activator modulus was 1.2 and the content of fly ash was more than 30%, the content of NaOH in the solution was higher, which accelerated the early reaction rate, resulting in more pores inside the slurry, larger pore size, smaller capillary pore volume, and expansion of alkali-activated material slurry volume. This study may shed valuable insights to the improvement of autogenous shrinkage by adjusting precursor composition and sodium silicate modulus.

Enhancing Recycled Aggregate Concrete Using a Three-Stage Mixed Coal Bottom Ash Slurry Coating

Enhancing Recycled Aggregate Concrete Using a Three-Stage Mixed Coal Bottom Ash Slurry Coating