Microstructure and properties of mullite-based porous ceramics produced from coal fly ash with added Al_2O_3

Using coal fly ash slurry samples supplemented with different amounts of Al2O3, we fabricated mullite-based porous ceramics via a dipping-polymer-replica approach, which is a popular method suitable for industrial application. The microstructure, phase composition, and compressive strength of the sintered samples were investigated. Mullite was identified in all of the prepared materials by X-ray diffraction analysis. The microstructure and compressive strength were strongly influenced by the content of Al2O3. As the Al/Si mole ratio in the starting materials was increased from 0.84 to 2.40, the amount of amorphous phases in the sintered microstructure decreased and the compressive strength of the sintered samples increased. A further increase in the Al2O3content resulted in a decrease in the compressive strength of the sintered samples. The mullite-based porous ceramic with an Al/Si molar ratio of 2.40 exhibited the highest compressive strength and the greatest shrinkage among the investigated samples prepared using coal fly ash as the main starting material. © 2017, University of Science and Technology Beijing and Springer-Verlag Berlin Heidelberg.

An artificial neural network approach for prediction of long-term strength properties of steel fiber reinforced concrete containing fly ash

In this study, an artificial neural network (ANN) model for studying the strength properties of steel fiber reinforced concrete (SFRC) containing fly ash was devised. The mixtures were prepared with 0 wt%, 15 wt%, and 30 wt% of fly ash, at 0 vol.%, 0.5 vol.%, 1.0 vol.% and 1.5 vol.% of fiber, respectively. After being cured under the standard conditions for 7, 28, 90 and 365 d, the specimens of each mixture were tested to determine the corresponding compressive and flexural strengths. The pa- rameters such as the amounts of cement, fly ash replacement, sand, gravel, steel fiber, and the age of samples were selected as input variables, while the compressive and flexural strengths of the concrete were chosen as the output variables. The back propagation learning algorithm with three different variants, namely the Levenberg-Marquardt (LM), scaled conjugate gradient (SCG) and Fletcher-Powell conjugate gradient (CGF) algorithms were used in the network so that the best approach can be found. The results obtained from the model and the experiments were compared, and it was found that the suitable algorithm is the LM algorithm. Furthermore, the analysis of variance (ANOVA) method was used to determine how importantly the experimental parameters affect the strength of these mixtures.

Investigation on high-volume fly ash pastes modified with micro-size metakaolin subjected to high temperatures

Portland cement(PC) containing high-volume fly ash(HVFA) is usually used to obtain economical and more sustainable merits, but these merits suffer from dramatically low compressive strength especially at early ages. In this work, the possibility of using micro-size metakaolin(MSK) particles to improve the compressive strength of HVFA paste before and after subjecting to high temperatures was studied. To produce HVFA paste, cement was partially substituted with 70% fly ash(FA), by weight. After that, FA was partially substituted with MSK at ratios fluctuating from 5% to 20% with an interval of 5%, by weight. The effect of MSK on the workability of HVFA mixture was measured. After curing, specimens were subjected to different high temperatures fluctuating from 400 to 1000 ℃ with an interval of 200 ℃ for 2 h. The results were analyzed by different techniques named X-ray diffraction(XRD), thermogravimetry(TGA) and scanning electron microscopy(SEM). The results showed that the incorporation of MSK particles into HVFA mixture exhibited a negative effect on the workability and a positive effect on the compressive strength before and after firing.

Influence of fly ash and sewage sludge application on wheat biomass production,nutrients availability,and soil properties

The influence of fly ash(FA)applied alone and/or with sewage sludge(SS)on wheat(Triticum vulgare)grain yield,biomass production and soil properties was studied in a field experiment.The results showed that both FA and SS significantly increased grain yield and plant biomass.FA applied alone increased significantly soil pH and EC while FA applied together with SS did not significantly affect them compared to mono FA treatment.Soil pH and EC values increased with time in FA and FA-SS treatments.SS increased soil organic matter and total N content and SS applied together with FA increased also available soil B.From the plant nutrients tested only tissue N concentration was increased significantly in all treatments compared to control.Copper,Zn,Mn,Ni,and Pb at both available and total concentrations are significantly affected.

Investigation of the Effect of Using Different Fly Ash on the Mechanical Properties in Cemented Paste Backfill

In the cemented paste backfill(CPB)method,which can also be used for fortification purposes in mines,different additive materials with pozzolanic properties can be employed as substitutes instead of cement that is the main binder.One of the most popular pozzolanic materials that can be employed instead of cement is fly ash,which is thermal power plant tailings.But the compositions of fly ash and tailings used in high amounts in the CPB method,as well as the chemical structures that these materials form by interacting with the cement binder,affect the mechanical properties of the material depending on time.In this study,fly ash with 4 different chemical compositions(TFA,SFA,YFA,and CFA)was used as a cement substitute in CPB.By substituting fly ash with different chemical compositions in different proportions,CPB samples were created and their strength was elucidated according to 28,56,and 90-day curing times.The results of the study revealed that TFA with the highest CaO/SiO_(2) and SO_(3) ratios remained stable at the strength values of 6 MPa(total 9% binder)and 10 MPa(total 11% binder)in the long term.However,CFA with the lowest CaO/SiO_(2),SO_(3),and the highest SiO_(2)+Al_(2)O_(3)+Fe_(2)O_(3) ratios resulted in the greatest strength increase at a 20%substitution rate(11% of the total binder).Nevertheless,it was found that the SFA,which is in Class F,increased its strength in the early period based on the CaO rate.

Removal of lead(Pb(Ⅱ))and zinc(Zn(Ⅱ))from aqueous solution using coal fly ash(CFA)as a dual-sites adsorbent

Coal fly ash(CFA)is composed of minerals containing some oxides in crystalline phase(i.e.,quartz and mullite),as well as unburned carbon as mesoporous material,thus enabling CFA to act as a dual-sites adsorbent with unique properties.This work focused on the adsorption of Pb(Ⅱ)and Zn(Ⅱ)from binary system,a mixture containing two metal ion solutions present simultaneously,onto NaOH-modified CFA(MCFA).Several adsorption tests were conducted to evaluate the effect of several parameters,including pH and contact times.The experiment results indicated that chemical treatment of CFA with NaOH increased pore volume from 0.021 to 0.223 cm^3·g^(-1).In addition,it could also enhance the availability of functional groups on both minerals and unburned carbon,resulting in almost 100%Pb(Ⅱ)and 97%Zn(Ⅱ)adsorbed.The optimum pH for adsorption system was pH=3 and quasi-equilibrium occurred in 240 minutes.Equilibrium data from the experimental results were analyzed using Modified Extended Langmuir(MEL)and Competitive Adsorption Langmuir-Langmuir(CALL)isotherm models.The analysis results showed that the CALL isotherm model could better describe the Pb(Ⅱ)and Zn(Ⅱ)adsorption process onto MCFA in binary system compared with MEL isotherm model.

Preparation and Properties of Eco-Friendly Aerated Concrete Utilizing High-Volume Fly Ash with MgO and CaO Activators

The associated MgO in limestone is believed to affect the volume stability of cementitious materials at room tem-perature,which limits the utilization of low grade limestone.In this study,MgO was used as an alkali activator instead of partial CaO to prepare the aerated concrete under hydrother mal conditions.The expansion process was studied to evaluate the influence of the raw materials on the gas forming stability of the slurry.The pore structure(porosity,pore size and its distribution)was analyzed by the image method.The physic mechanical properties(density,strength,thermal properties)of concrete with the addition of MgO were comprehensively investigated.Besides,the mineral compositions and morphology of the hydration products were analyzed to demonstrate the infuence mechanism of MgO on the mechanical properties.Experimental results show that the final expansion rate of the slurry decreases with MgO content.A reasonable MgO content,ie,MgO/(MgO+CaO)<20%,con-tributes to improve the compressive strength,attributing to an increased reaction rate to C-S-H gel and tobermor-ite.The addition of MgO causes the thermal conductivity and specific heat to increase.The pore structure is mainly related to the amount of air entraining agent.This study has a significance for the further utilization of magnesium-rich carbonates in the autoclaved building products.

Effective Utilization of Coal Fly Ash in Building Material Production

This paper is aimed at verifying utilization possibilities of alkaline modified coal fly ash as cement replacement in the concrete. The influence of alkaline activated coal fly ash originating from Slovakian power plant in Novsky （Si/Al = 3,1） as a partial cement replacement in concrete on compressive strength of hardened composites after 28 and 90 days was investigated. Alkaline activation of coal fly ash was realized in an autoclave at 130 ℃ and pressure of 160 kPa during 5 hours and in a reactor under normal conditions （equal temperature during 36 hours） at solid/liquid ratio of 0.5. Coal fly ash/cement mixtures were prepared with 25 % cement replacement by starting and modified coal fly ash and given in forms. Compressive strengths of composites after 28 and 90 days of hardening were compared to referential composite without coal fly ash and evaluated according to the standard of STN EN 450 by the value of relative strength KR （compressive strength of coal fly ash/cement composite to compressive strength of comparative concrete）. The final compressive strengths of hardened composites based on alkaline activated coal fly ash reached values in the range of 6 up to 50 MPa. In the set of experimental composites based on alkaline activated coal fly ashes, the highest value of relative strength after 28- and 90- days of hardening reached composite with cement replacement by coal fly ash zeolitized in autoclave （105% of compressive strength of referential sample）, what is connected with formation of zeolitic phases on surface of coal fly ash particles. The achieved results confirm that alkaline activation of coal fly ash in an autoclave under observed conditions can be successfully used as a partial cement replacement in concrete of C20/25 and C25/30 in accordance with requirements of standards （STN EN 450 and STN EN 206）.

Characterization of LDPE Reinforced with Calcium Carbonate—Fly Ash Hybrid Filler

The synergetic effect of calcium carbonate (CC)-fly ash (FA) hybrid filler particles on the mechanical and physical properties of low density polyethylene (LDPE) has been investigated. Low density polyethylene is filled with varying weight percentages of FA and CC using melt casting. Composites are characterized for mechanical, thermal, microstructural and physical properties. Results show that the flexural strength increases with increases in FA content of the hybrid filler. It is evident from the study that to achieve optimum density a certain combination of both fillers need to be used. The optimum combination of CC and FA for a higher density (1.78 g/cm3) is found to be at 20 wt% FA and 30 wt% CC. An increase of 7.27% in micro-hardness over virgin polyethylene is obtained in composites with 10 wt% FA and 40 wt% CC. The presence of higher amount of CC is seen to be detrimental to the crystallinity of composites. X-ray, FTIR and DSC results show that composite with 45 wt% CC and 5 wt% FA exhibits a typical triclinic polyethylene structure indicating that the composite is amorphous in nature. There was the synergy between FA and CC fillers on flexural strength and crystallinity of composite. However, the fillers show the antagonistic effect on energy at peak and micro-hardness.

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.

Effect of temperature on the hydration process and strength development in blends of Portland cement and activated coal gangue or fly ash

This paper describes the results of an investigation into the effect of the variation of curing temperatures between 0 and 60 °C on the hydration process,pore structure variation,and compressive strength development of activated coal gangue-cement blend(ACGC) . Hardened ACGC pastes cured for hydration periods from 1 to 360 d were examined using the non-evaporable water method,thermal analysis,mercury intrusion porosimetry,and mechanical testing. To evaluate the specific effect of activated coal gangue(ACG) as a supplementary cementing material(SCM) ,a fly ash-cement blend(FAC) was used as a control. Results show that raising the curing temperature accelerates pozzolanic reactions involving the SCMs,increasing the degree of hydration of the cement blends,and hence increasing the rate of improvement in strength. The effect of curing temperature on FAC is greater than that on ACGC. The pore structure of the hardened cement paste is improved by increasing the curing temperature up to 40 °C,but when the curing temperature reaches 60 °C,the changing nature of the pore structure leads to a decrease in strength. The correlation between compressive strength and the degree of hydration and porosity is linear in nature.

Physicochemical Properties of Coal Gasification Fly Ash from Circulating Fluidized Bed Gasifier

The coal gasification fly ash(CGFA) is an industrial solid waste from coal gasification process and needs to be effectively disposed for environmental protection and resource utilization.To further clarify the feasibility of CGFA to prepare porous carbon materials,the physicochemical properties of ten kinds of CGFA from circulating fluidized bed(CFB) gasifiers were analyzed in detail.The results of proximate and ultimate analysis show that the CGFA is characterized with the features of near zero moisture content,low volatile content as low as 0.90%-9.76%,high carbon content in the range of 37.89%-81.62%,and ultrafine particle size(d50=15.8-46.2 μm).The automatic specific surface area(SSA) and pore size analyzer were used to detect the pore structure,it is found that the pore structure of CGFA is relatively developed,and part of the CGFA has the basic conditions to be used directly as porous carbon materials.From SEM images,the microscopic morphology of the CGFA is significantly different,and they basically have the characteristics of loose and porous structure.XRD and Roman spectroscopy were used to characterize the carbon structure.The result shows that the CGFA contains abundant amorphous carbon structure,and thus the CGFA has a good reactivity and a potential to improve pore structure through further activation.Through thermal gravimetric analysis,it can be concluded that the order of reactivity of the CGFA under CO_(2) atmosphere has a good correlation with the degree of metamorphism of the raw coal.The gasification reactivity of the CGFA is generally consistent with the change trend of micropores combined with the pore structure.According to the physicochemical properties,the CGFA has a good application prospect in the preparation of porous carbon materials.

Physical and mechanical properties of municipal solid waste incineration residues with cement and coal fly ash using X-ray Computed Tomography scanners

A significant volume of Municipal Solid Waste incineration bottom ash and fly ash (i.e.,incineration residues) are commonly disposed as landfill.Meanwhile,reclamation of landfill sites to create a new land space after their closure becomes an important goal in the current fewer and fewer land availability scenario in many narrow countries.The objective of this study is to reclaim incineration residue materials in the landfill site by using cement and coal fly ash as stabilizers aiming at performing quality check as new developed materials before future construction.Indeed,physical and mechanical properties of these new materials should be initially examined at the micro scale,which is the primary fundamental for construction at larger scale.This research examines quantitative influences of using the combination of cement and coal fly ash at different ratio on the internal structure and ability of strength enhancement of incineration residues when suffering from loading.Couple of industrial and micro-focus X-ray computed tomography (CT) scanners combined with an image analysis technique were utilized to characterize and visualize the behavior and internal structure of the incineration residues-cement-coal fly ash mixture under the series of unconfined compression test and curing period effect.Nine types of cement solidified incineration residues in term of different curing period (i.e.,7,14,28 days) and coal fly ash addition content (i.e.,0%,9%,18%) were scanned before and after unconfined compression tests.It was shown that incineration residues solidified by cement and coal fly ash showed an increase in compression strength and deformation modulus with curing time and coal fly ash content.Three-dimension computed tomography images observation and analysis confirmed that solidified incineration residues including incineration bottom and fly ash as well as cement and coal fly ash have the deliquescent materials.Then,it was studied that stabilized parts play a more important role than spatial void distribution in increment or reduction of compression strength.

Characterization of Wollastonite Glass-ceramics Made from Waste Glass and Coal Fly Ash

The crystallization behavior of wollastonite glass-ceramics was investigated by means of X-ray diffraction （XRD） analysis and surface morphological observations, and the chemical compositions were evaluated by field emission-scanning electron microscopy （FE-SEM） and energy dispersive X-ray spectroscopy （EDS）. Various heat treatment temperatures （850, 900, 950, 1000 and 1050 ℃） were used to obtain glass-ceramics of the ideal wollastonite crystal phase as well as optimum mechanical properties and chemical durability. From XRD, FE-SEM and EDS, the crystallization of acicular crystal phase in the matrix was achieved at heat treatment temperature of 1000 and 1050 ℃, and wollastonite （CaSiO3） was found in the acicular type main crystal phase in the glass-ceramics. Various properties, such as density, compressive strength, bending strength and chemical durability were also examined. The mechanical properties of glass-ceramics obtained at the heat treatment temperature of 1000 and 1050 ℃ were superior to those obtained at the heat treatment temperature of 850 ℃.

早强型粉煤灰改性土力学特性及强度预测模型分析

由于硅酸盐水泥在生产过程中容易造成严重的资源消耗,因此粉煤灰常被用来部分替代水泥固化剂。但是粉煤灰由于自身的低活性,其改性土强度的形成,通常需要较长的养护周期。因此采用一种早强型粉煤灰基固化剂,通过一系列的无侧限抗压强度试验,探究了改性土无侧限抗压强度与固化剂掺量、养护龄期、改性土孔隙率等参数的变化规律。试验结果表明,早强型粉煤灰改性土7 d无侧限抗压强度可以达到28 d强度的80%~90%。基于试验结果,建立了基于孔隙率/掺量两个参数的强度预测公式,并进一步提出了预测公式的折减系数。

粉煤灰对煤矿充填膏体性能的影响

为探讨粉煤灰对煤矿充填膏体性能的影响,试验采用坍落度试验和流变试验综合评价膏体流变性,通过干缩变形研究其长期稳定性及对接顶性能的影响,研究了水泥、煤矸石用量及膏体浓度不变的情况下粉煤灰掺量64.2%-69.8%,膏体流变性、泌水率、抗压强度和干缩率的变化情况。结果表明：1随粉煤灰掺量的增加,膏体流变性减弱,黏聚性增强,泌水率减小。2随粉煤灰掺量的增大,不同龄期膏体抗压强度变化不同,3 d强度变化不大,在0.5 MPa左右;7 d强度呈先增后降的趋势,在66.7%掺量时最大达到2.5 MPa;14 d强度于67.8%掺量前在4 MPa上下变化,在68.9%掺量时达到6.9 MPa;28 d强度发展缓慢,与14 d变化趋势相似。7-14 d水化作用显著,强度增长量能达到28 d强度的40%-60%。3膏体的干缩量随粉煤灰用量增加而减小,与龄期近似满足对数关系。且膏体干缩量曲线160 d开始趋于平稳,干缩率不超过0.2%。

改性粉煤灰微粉高填料纸的增强技术研究

探讨了对改性粉煤灰高填料纸的增强技术。研究结果表明:改性的粉煤灰微粉适合于作为造纸填料,不仅留着率可以达到50%以上,而且不会引起严重的掉毛掉粉现象,纸张的白度和不透明度分别可以达到83%ISO以上和93%以上。实验试用了5种增干强剂,自制的一种增干强剂效果较好,其他几种增干强剂作用效果都不太显著。添加聚乙烯醇合成纤维对于提高高填料纸的强度作用明显。添加量为5%时抗张强度明显改善,添加量为10%时耐破强度明显改善。PVA合成纤维与增干强剂混合使用对高填料纸各项性能改善良好,PVA用量为10%,N64170增干强剂用量为2%时,高填料纸各项性能最好。

Mercury emission and adsorption characteristics of fly ash in PC and CFB boilers

The mercury emission was obtained by measuring the mercury contents in flue gas and solid samples in pulverized coal (PC) and circulating fluidized bed (CFB) utility boilers. The relationship was obtained between the mercury emission and adsorption characteristics of fly ash. The parameters included unburned carbon content, particle size, and pore structure of fly ash. The results showed that the majority of mercury released to the atmosphere with the flue gas in PC boiler, while the mercury was enriched in fly ash and captured by the precipitator in CFB boiler. The coal factor was proposed to characterize the impact of coal property on mercury emissions in this paper. As the coal factor increased, the mercury emission to the atmosphere decreased. It was also found that the mercury content of fly ash in the CFB boiler was ten times higher than that in the PC boiler. As the unburned carbon content increased, the mercury adsorbed increased. The capacity of adsorbing mercury by fly ash was directly related to the particle size. The particle size corresponding to the highest content of mercury, which was about 560 ng/g, appeared in the range from 77.5 to 106 µm. The content of mesoporous (4–6 nm) of the fly ash in the particle size of 77.5–106 µm was the highest, which was beneficial to adsorbing the mercury. The specific surface area played a more significant role than specific pore volume in the mercury adsorption process.