Dry Mix Slag—High-Calcium Fly Ash Binder. Part Two: Durability

This work investigates durability of cement-free mortars with a binder comprised of ground granulated blast furnace slag (GGBFS) activated by high-calcium fly ash (HCFA) and sodium carbonate (Na2CO3): the soundness, sulfate resistance, alkali-silica reactivity and efflorescence factors are considered. Results of tests show that such mortars are resistant to alkali-silica expansion. Mortars are also sulfate-resistant when the amount of HCFA in the complex binder is within a limit of 10 wt%. The fineness of fly ash determines its’ ability to activate GGBFS hydration, and influence soundness of the binder, early strength development, sulfate resistance and efflorescence behavior. The present article is a continuation of authors’ work, previously published in MSA, Vol. 14, 240-254.

Dry Mix Slag—High-Calcium Fly Ash Binder. Part One: Hydration and Mechanical Properties

High-calcium fly ash (HCFA)—a residue of high-temperature coal combustion at thermal power plants, in combination with sodium carbonate presents an effective hardening activator of ground granulated blast-furnace slag (GGBFS). Substitution of 10% - 30% of GGBFS by HCFA and premixing of 1% - 3% Na2CO3 to this dry binary binder was discovered to give mortar compression strength of 10 - 30 to 30 - 45 MPa at 7 and 28 days when moist cured at ambient temperature. High-calcium fly ash produced from low-temperature combustion of fuel, like in circulating fluidized bed technology, reacts with water readily and is itself a good hardening activator for GGBFS, so introduction of Na2CO3 into such mix has no noticeable effect on the mortar strength. However, low-temperature HCFA has higher water demand, and the strength of mortar is compromised by this factor. As of today, our research is still ongoing, and we expect to publish more data on different aspects of durability of proposed GGBFS-HCFA binder later.

木质素纤维-高钙粉煤灰复合改良膨胀土试验研究

为改进单一方法改良膨胀土存在的不足,选用木质素纤维和粉煤灰复合改良膨胀土,提升改良土强度和破坏韧性,抑制膨胀变形。分别开展了自由膨胀率、有荷膨胀率(50 kPa)、无侧限抗压强度试验、低应力直剪试验获得单掺粉煤灰时的最优掺量,再掺入木质素纤维进行力学强度试验、水稳试验和微观试验,以力学特性变化结合微观结构特征分析复合改良效果。结果表明:单掺粉煤灰能够抑制膨胀土的膨胀特性,提升改良土强度,最佳粉煤灰掺量为20%;加入木质素纤维进行复合改良能够进一步提升土体强度,增强破坏韧性,水稳性也大大增强,20%粉煤灰和1.0%木质素纤维复合改良效果最好;复合改良能够很好地改善孔隙分布,抑制土体裂缝延伸,增强土体密实度。

微波活化粉煤灰的微观结构及粉煤灰-水泥浆体的早期性能

微波辐照是激发粉煤灰活性的一种高效低碳的活化方式,高活性粉煤灰有利于早强混凝土的制备。本工作首先研究了微波辐照温度(600℃、700℃、800℃)对粉煤灰物理化学性能的影响,采用X射线衍射仪(XRD)、扫描电子显微镜(SEM)对其物相组成和微观形貌进行表征,然后研究了活性粉煤灰-水泥浆体的早期性能。研究结果表明:微波辐照促使粉煤灰中的石英相和莫来石相向非晶相转化,极大地提高了粉煤灰的活性。当微波辐照温度为800℃时,与未活化粉煤灰相比,活性粉煤灰非晶相含量从49.13%增加到了58.71%,且28 d活性指数高达94.13%,提高了33.06%。与未活化粉煤灰-水泥浆体相比,800℃微波辐照的粉煤灰-水泥浆体的早期力学性能提升非常显著,其中1 d的抗压强度增加了41.36%。因此,微波辐照活化粉煤灰的合适温度为800℃。

煤矿采动影响体微生物采残煤与CO_(2)-粉煤灰协同充填关键技术

煤矿采空区是我国实现“双碳”目标的重要突破口,煤炭开采形成的、能够富集煤层气、为后期微生物活动和矿化充填提供底物和空间的地质体定义为采动影响体。以采动影响体为研究对象,提出了采动影响体微生物采残煤与CO_(2)-粉煤灰协同矿化充填关键技术,并从必要性和可行性2个方面阐述了该技术在采动影响体资源二次开发、CO_(2)安全封存以及燃煤电厂粉煤灰固废高效处置等的广阔前景。其总体思路是将采动影响体作为一个厌氧发酵“工厂”,高产高效产甲烷菌群作为“劳动者”对“工厂”已有的原材料——残煤、薄煤层和分散有机质以及注入的CO_(2)进行加工,其“产品”是甲烷,进而实现微生物采残煤和CO_(2)资源化。同时,CO_(2)与碱性的粉煤灰结合,在实现了CO_(2)矿化封存的同时,也实现了采动影响体的充填。该技术涉及的关键科学问题包括采动影响体类型划分与有机质特征、采动影响体原位条件下厌氧发酵产甲烷机制、微生物-CO_(2)-粉煤灰协同矿化/固化机制以及微生物采残煤与充填关键技术示范工程建设。实验室物理模拟采动影响体原位条件实验表明其中残煤和富含有机质的泥页岩能够在微生物作用下生成生物甲烷,且添加少量的粉煤灰能够进一步强化甲烷的产出。物理模拟地下水补给的动态实验表明营养物质的补给对厌氧发酵系统的影响尤为重要,补给循环周期为14 d的厌氧发酵系统恰与产甲烷菌群繁殖的周期一致,能够保证厌氧发酵系统的持续高效运行。高钙粉煤灰-CO_(2)-矿井水协同胶结的试件经过28 d的养护后抗压强度为12.31 MPa,其矿化封存潜力约为21.99 m3 CO_(2)/t(粉煤灰),说明粉煤灰在实现采空区固化的同时能够实现CO_(2)减排。此外,基于微生物采残煤与粉煤灰充填目的对工程试验靶区进行优选,地下水滞留区是CO_(2)矿化和粉煤灰充填的最佳场所,因采掘活动自然形成的自然圈闭和人工充填形成的圈闭是较有利的工程试验靶区之一。针对这些靶区提出了微生物采残煤与CO_(2)-粉煤灰协同充填关键技术,旨在为中国碳减排和采空区生态环境治理提供一条新的技术路径。

黄原胶-粉煤灰联合处理酸污染土试验研究

绿色环保型生物聚合物黄原胶应用于岩土工程,可提高土体强度及抗风蚀、水蚀能力。鉴于黄原胶分子中的丙酮酸基团和糖苷键在酸性土壤条件下易水解,导致凝胶黏性减小、固土效果减弱,拟采用碱性材料粉煤灰协同黄原胶固化酸污染土,并开展液塑限、击实及无侧限抗压强度试验。结果表明:粉煤灰有助于提高固化土的塑限、最优含水率及最大干密度。酸性土壤条件下,粉煤灰能明显改善黄原胶固土效果,联合法固化酸污染土强度甚至超过联合法固化未污染土。另外,粉煤灰可提高土壤的pH值,缓解黄原胶水解,使其发挥增黏及胶结土颗粒的作用。基于试验结果,建议采用联合法固化酸污染土(FA=9%,XG=3%),可比酸污染上海黏土强度提高310%;在未污染土中采用黄原胶即可(XG=4%),可比未污染天然上海黏土强度提高90%。研究成果有助于绿色环保型生物聚合物的推广与应用。

电解锰渣-赤泥-粉煤灰路面砖的力学性能及浸出毒性研究

针对大宗工业固废回收利用难的问题,实现多种固废减量化、无害化、资源化的目标,通过利用取自中国西南地区企业的石膏类、碱性及硅铝质三类典型大宗固废中的电解锰渣、赤泥、粉煤灰协同处理的无害化渣制备环保型透水混凝土路面砖(permeable concrete paving bricks,PCB),研究了水洗、掺渣量对所制备PCB的力学性能与浸出毒性的影响,并通过X射线衍射(XRD)和扫描电子显微镜(SEM)对最佳性能PCB的物相组成与微观形貌结构进行分析.结果表明:①随着无害化渣与水洗无害化渣掺入量的提升,路面砖的劈裂抗拉强度、线性破坏荷载发生明显变化,总体呈下降趋势.当无害化渣掺入量为6%、水洗无害化渣掺入量为14%时,经28 d养护,所制备砖体的劈裂抗拉强度分别为4.09和3.46 MPa,达到了《透水路面砖和透水路面板》(GB/T 25993-2010)中规定的f_(ts)4.0与f_(ts)3.0等级.②路面砖的重金属与NH_(4)^(+)-N的浸出毒性均低于《水泥窑协同处置固体废物技术规范》(GB 30760-2014)的要求.路面砖的主要物相中方解石、石英与钙矾石是主要支撑性物质.研究显示,电解锰渣、赤泥、粉煤灰协同处理的无害化渣可替代部分原材料制备透水混凝土路面砖,满足力学性能与浸出毒性相关标准,能有效促进固体废弃物的减量化与资源化,建议进一步开展砖体在实际应用场景中的环境风险试验,以期为电解锰渣、赤泥、粉煤灰的综合利用技术发展提供更明确的支撑.

粉煤灰 - 锂渣基发泡陶瓷的制备及性能研究

为制备低成本兼具高孔隙率与高压缩强度的发泡陶瓷,以粉煤灰、锂渣、长石、滑石和碳化硅为原料,经1180、1200、1220、1240℃分别保温10、20、40、60 min烧结制备发泡陶瓷试样。主要研究了锂渣的掺量(质量分数分别为0、10%、20%、30%)对试样物相组成、显微结构、孔隙率及压缩强度的影响。结果表明:1)随锂渣掺量的增加,发泡陶瓷的孔隙率增加,体积密度降低,压缩强度波动;2)锂渣中丰富的钙、硫成分,可发挥助熔剂和发泡剂作用,降低烧结温度,提高发泡陶瓷的孔隙率,改善气孔圆整度,提高压缩强度;3)当锂渣掺量为20%(w)时,经1220℃保温20~40 min烧结所得发泡陶瓷的体积密度为0.32~0.40 g·cm^(-3),孔隙率为84.4%~87.6%,压缩强度为1.51~2.35 MPa。

固体NaOH/Na_(2)SiO_(3)激发矿粉/粉煤灰-炉渣基注浆材料性能研究

以矿粉和粉煤灰-炉渣作为前驱体,其中粉煤灰、炉渣以质量比4:1共同粉磨制备前驱体之一,以NaOH和Na_(2)SiO_(3)配制模数为1.2的固体激发剂,制备碱激发注浆材料。研究粉煤灰-炉渣的掺量、激发剂的掺量(以Na_(2)O计)对注浆材料工作性能和力学性能的影响,并通过扫描电镜(SEM)和能谱分析(EDS)对水化产物进行物理化学表征,使用核磁共振分析注浆材料孔结构特征。研究结果表明:粉煤灰-炉渣掺量为50%的注浆材料的28 d最大抗压强度达31.25 MPa。水化产物主要为C-A-S-H凝胶,浆液结石体内部孔隙主要为胶凝孔(孔径<10 nm)和过渡孔(孔径为[10~100) nm),占比超过90%。

水泥-粉煤灰基矸石胶结充填体破坏特征及强度形成机制

在煤矿结构充填开采中,不同充填率条件下对矸石胶结充填体强度的需求不同,拟通过改变粉煤灰在水泥–粉煤灰二元胶凝材料用量中的占比(下称“粉煤灰占比”)调控矸石胶结充填体强度,对不同粉煤灰占比(0~90%)矸石胶结充填体进行单轴压缩试验,探明矸石胶结充填体的强度调控范围,结合数字图像相关技术对试样破坏形态进行分析,结合声发射事件对试样脆延性破坏模式进行分析。采用承压筒法和单轴压缩试验分别测定了煤矸石的强度和不同粉煤灰占比水泥–粉煤灰二元胶凝材料的强度,并根据煤矸石的强度与水泥–粉煤灰二元胶凝材料的强度关系揭示矸石胶结充填体的强度形成机制。研究结果表明:矸石胶结充填体强度随着粉煤灰占比的增加而减少,实现了较大的矸石胶结充填体强度调控范围:1.77~30.04 MPa。不同强度范围的矸石胶结充填体试样对应的破坏形态和脆延性破坏模式也不同,材料性质发生了质的变化。随着粉煤灰占比的增加,在破坏形态方面,矸石胶结充填体试样由剪切破坏(0~50%粉煤灰占比)向拉剪复合破坏(60%~80%粉煤灰占比)再向拉伸破坏(90%粉煤灰占比)转变,对应的强度范围分别为20.8~30.04 MPa,5.63~12.35 MPa和1.77 MPa;在脆延性破坏模式方面,试样由脆–延性破坏(0~40%粉煤灰占比)转变为延性破坏(50%~90%粉煤灰占比),对应的强度范围分别为24.64~30.04 MPa和1.77~20.8 MPa。矸石胶结充填体的强度由水泥–粉煤灰二元胶凝材料的强度(1.43~55.5 MPa)和煤矸石的强度(平均强度为4.43 MPa)共同决定。水泥–粉煤灰二元胶凝材料对矸石胶结充填体的强度贡献较大,煤矸石使矸石胶结充填体的强度受限。所得试验结果为结构充填中充填材料的强度选择提供参考。

粉煤灰-矿渣再生混凝土抗压强度及尺寸效应研究

以粉煤灰和矿渣掺入方式和掺量为变量,设计24组C30再生粗骨料混凝土,对再生混凝土的抗压强度进行了研究。试验结果表明,粉煤灰或矿渣单掺时,再生混凝土的抗压强度随矿物掺料的掺量增加呈现先上升后下降趋势,同等掺量下矿渣单掺优于粉煤灰单掺;双掺时保持粉煤灰或矿渣掺量20%不变,再生混凝土立方体和轴心抗压强度随另一种微细矿物掺量的增加同样呈现先上升后下降趋势,双掺较单掺方式对再生混凝土抗压强度的提升效果更佳,且再生混凝土的抗压强度存在明显的尺寸效应。单掺粉煤灰或矿渣时再生混凝土轴心抗压强度和立方体抗压强度换算系数随其掺量增加而增大,双掺则稳定保持在0.85±0.02。此外,论文还建立了不同微细矿物掺料条件下再生混凝土抗压强度换算系数的修正公式,验证结果表明公式预测误差较小。建议实际工程再生混凝土配制采用粉煤灰和矿渣双掺方式,且掺量控制在25%以内。

Preparation and sintering properties of zirconia-mullite-corundum composites using fly ash and zircon

Zirconia-mullite-corundum composites were successfully prepared from fly ash,zircon and alumina powder by a reaction sintering process.The phase and microstructure evolutions of the composite synthesized at desired temperatures of 1 400,1 500 and 1 600°C for 4 h were characterized by X-ray diffractometry and scanning electronic microscopy,respectively.The influences of sintering temperature on shrinkage ratio,apparent porosity and bulk density of the synthesized composite were investigated.The formation process of the composites was discussed in detail.The results show that the zirconia-mullite-corundum composites with good sintering properties can be prepared at 1 600°C for 4 h.Zirconia particles can be homogeneously distributed in mullite matrix,and the zirconia particles are around 5μm.The formation process of zirconia-mullite-corundum composites consists of decomposition of zircon and mullitization process.

Hydration mechanism of low quality fly ash in cement-based materials

The hydration mechanism of low quality fly ash in cement-based materials was investigated. The hydration heat of the composite cementitious materials was determined by isothermal calorimetry, and the hydration products, quantity, pore structure and morphology were measured by X-ray diffraction(XRD), thermalgravity-differential thermal analysis(TG-DTA), mercury intrusion porosimetry(MIP) and scanning electron microscopy(SEM), respectively. The results indicate that grinding could not only improve the physical properties of the low quality fly ash on particle effect, but also improve hydration properties of the cementitious system from various aspects compared with raw low quality fly ash(RLFA). At the early stage of hydration, the low quanlity fly ash acts as almost inert material; but then at the later stage, high chemical activity, especially for ground low quality fly ash(GLFA), could be observed. It can accelerate the formation of hydration products containing more chemical bonded water, resulting in higher degree of cement hydration, thus denser microstructure and more reasonable pore size distribution, but the hydration heat in total is reduced. It can also delay the induction period, but the accelerating period is shortened and there is little influence on the second exothermic peak.

Degradation of n-butyl xanthate using fly ash as heterogeneous Fenton-like catalyst

Heterogeneous Fenton-like process using fly ash as a catalyst was studied to degrade n-butyl xanthate form aqueous solution. The different reaction parameters on the degradation efficiency of the process were investigated. The fly ash/H2O2 catalyst possesses a high oxidation activity for n-butyl xanthate degradation in aqueous solution. It is found that both the dosage of catalyst and initial solution pH significantly affect the n-butyl xanthate conversion efficient. The results indicate that by using 1.176 mmol/L H2O2 and 1.0 g/L fly ash catalyst with mass fraction of 4.14% Fe(III) oxide at pH 3.0, almost 96.90% n-butyl xanthate conversion and over 96.66% COD removal can be achieved within 120 min with heterogeneous catalysis by fly ash. CS2 as an intermediate of n-butyl xanthate oxidation. Finally, it is demonstrated that the fly ash/H2O2 catalytic oxidation process can be an efficient method for the treatment of n-butyl xanthate containing wastewater.

Preparation and mechanical properties of polypropylene fiber reinforced calcined kaolin-fly ash based geopolymer

To improve the environmental benefits and solve the problems of large shrinkage and high brittleness, the partial replacement of calcined kaolin by fly ash as a raw material for geopolymer synthesis and the influences of polypropylene (PP) fiber on the mechanical properties and volume stability were investigated. The results show that compressive strength of the geopolymer containing 33.3%(mass fraction) fly ash by steam curing at 80 ℃ for 6 d is improved by 35.5%. The 3-day compressive strength, flexural strength and impacting energy of geopolymers containing 0.05%PP fiber increase by 67.8%, 36.1% and 6.25%, while the shrinkage and modulus of compressibility decrease by 38.6% and 31.3%, respectively. The results of scanning electron microscopy (SEM) and the appearances of crack growths confirm that PP fiber can offer a bridging effect over the harmful pores and defects and change the expanding ways of cracks, resulting in a great improvement of strength and toughness.

Alkali desilicated coal fly ash as substitute of bauxite in lime-soda sintering process for aluminum production

By desilication treatment,the Al2O3/SiO2 molar ratio of coal fly ash could be improved to the range of 1.63-2.0.The desilicated coal fly ash(DSCFA)was enriched in alumina extraction.A processing technology was developed for alumina extraction from the DSCFA with the lime sintering process.Ca/(SiO2+TiO2)molar ratio,and NaO/Al2O3 molar ratio,sintering time,and temperature were the most significant parameters impacting on the aluminum extraction efficiency.The optima aluminum extraction efficiency was obtained under conditions of Ca/(SiO2+TiO2)molar ratio of 2.0,NaO/Al2O3 molar ratio of 0.98,and sintering at 1 200 ℃for 60 min.Astandard industrial dissolution method was used under conditions of caustic ratio(αk=n(NaO)/n(Al2O3)of 2.0,Al2O3 concentration of 50 g/L,sodium hydroxide concentration(Nk)of 60.78 g/L,Na2CO3 concentration of 10 g/L,temperature of 85℃, and dissolution duration of 10 min.The final aluminum extraction efficiency was 90%.

Investigation of the medium calcium based non-burnt brick made by red mud and fly ash: durability and hydration characteristics

Red mud is a type of highly alkaline waste residue produced in the process of alumina smelting by the Bayer process.Based on the idea of medium calcium content,solid wastes such as red mud and fly ash were used to prepare non-burnt bricks;and the mass ratio of CaO/SiO2 was selected in the range of 0.88–1.42.Mechanical properties and durability were investigated with a compressive strength test.X-ray diffractometry(XRD),scanning electron microscope(SEM),and Fourier transform infrared spectroscopy(FTIR)techniques were used to characterize the hydration characteristic.The environmental performance was analyzed by Inductively Coupled Plasma Mass Spectrometry(ICP).The results indicated that the mechanical properties and the durability were optimal when the mass ratio of CaO/SiO2 was 1.23.The hydration products were mostly C–S–H gel,ettringite,Na4Ca(Si10All6)O32·12H2O and Ca3Al2(SiO4)(OH)8.They were responsible for the strength development,and the CaO/SiO2 mass ratio of 1.23 had the best polymerized structure.The results of an environmental performance test showed that the heavy metals in the raw materials were well-solidified in the brick.Therefore,this paper provides an effective solution for use of solid wastes in building material.

Compressive Strength, Pore Size Distribution and Chloride-ion Penetration of Recycled Aggregate Concrete Incorporating Class-F Fly Ash

The effects of fly ash on the compressive strength, pore size distribution and chloride-ion penetration of recycled aggregate concrete were investigated. Two series of concrete mb：tures were prepared. The concrete mixtures in series I had a water-to-binder ratio and a cement content of 0.55 and 410 kg/ m^3 , respectively. The concrete rnixtures in series II had a water-to-binder ratio and a cement content of 0.45 and 400 kg/ ml respectively. Recycled aggregate was ased as 20% , 50% , and 100% replacements of natural coarse aggregate in the concrete mixtures in both series. In cutdition, fly ash was used as 0% , 25% and 35% by weight replacements of cement. The results show that the compressive strengths of the concrete decreased as the recycled aggregate and the fly ash contents increased. The total porosity and average porosity diameter of the concrete increased us the recycled aggregate content increased. Furtherrruore , an increase in the recycled aggregate content decreased the resistance to chloride ion penetration. Nevertheless, the replacement of cement by 25% fly ush improved the resistance to chloride ion penetration and pore diameters and reduced the total porosity of the recycled aggregate concrete.

矿渣和粉煤灰对微生物-氧化镁协同固化钻屑性能的改良机理

钻屑作为一种固废,其主要处理方式为水泥固化,但加工水泥易产生大量二氧化碳,不利于环境保护。基于上述问题,提出了一种改良后微生物-氧化镁协同固化钻屑新方法。通过强度测试,研究了高炉矿渣和粉煤灰对微生物-氧化镁协同固化钻屑的改良,获得了钻屑固化体强度随高炉矿渣掺量增加而升高,随粉煤灰掺量增加而逐渐降低的规律,最高强度为5.4MPa。采用FTIR、XRD和SEM等测试手段,对固化体中产物类型和结构进行了分析,结果表明:产物由连续的水菱镁石(矿化产物)、云雾状水化硅酸镁和层状水滑石(水化产物)组成。钻屑颗粒由矿化产物和少量水化产物固化,揭示了矿渣和粉煤灰在微生物-氧化镁协同固化钻屑的作用机理。

Utilization of fly ash from coal-fired power plants in China

The rapidly increasing demand for energy in China leads to the construction of new power plants all over the country. Coal, as the main fuel resource of those power plants, results in increasing problems with the disposal of solid residues from combustion and off gas cleaning. This investigation describes chances for the utilization of fly ash from coal-fired power plants in China. After briefly comparing the situation in China and Germany, the status of aluminum recycling from fly ash and the ad- vantages for using fly ash in concrete products are introduced. Chemical and physical analyses of Chinese fly ash samples, e.g., X-ray diffraction (XRD), ICP (Inductive Coupled Plasma) and particle size analysis, water requirement, etc. are presented. Rea- sonable amounts of aluminum were detected in the samples under investigation, but for recovery only sophisticated procedures are available up to now. Therefore, simpler techniques are suggested for the first steps in the utilization of Chinese fly ash.