Hydration of fly ash cement

It is necessary to establish the material design system for the utilization of large amounts of fly ash as blended cement instead of disposing of it as a waste. Cement blended with fly ash is also required as a countermeasure to reduce the amount of CO₂ generation. In this study, the influences of the glass content and the basicity of glass phase on the hydration of fly ash cement were clarified and hydration over a long curing time was characterized. Two kinds of fly ash with different glass content, one with 38.2% and another with 76.6%, were used. The hydration ratio of fly ash was increased by increasing the glass content in fly ash in the specimens cured for 270 days. When the glass content of fly ash is low, the basicity of glass phase tends to decrease. Reactivity of fly ash is controlled by the basicity of the glass phase in fly ash during a period from 28 to 270 days. However, at an age of 360 days, the reaction ratios of fly ash show almost identical values with different glass contents. Fly ash also affected the hydration of cement clinker minerals in fly ash cement. While the hydration of alite was accelerated, that of belite was retarded at a late stage.     

不同养护条件对大掺量粉煤灰混凝土抗碳化性能试验研究

通过加速碳化试验,系统研究了不同养护条件和粉煤灰掺量的大掺量粉煤灰混凝土碳化规律.并利用扫描电镜和压汞法研究了大掺量粉煤灰混凝土碳化前后的微观形貌和孔结构变化.结果表明:经标准养护后的粉煤灰混凝土的抗碳化能力大于经自然养护后的粉煤灰混凝土的抗碳化能力;随着粉煤灰掺量的增加,混凝土抗碳化能力减小;标准养护下粉煤灰混凝土孔隙率相比于其在自然养护下的孔隙率降低了19.6％;碳化后浆体密实度增加,孔径细化,孔隙率降低31.4％.     

粉煤灰掺量对再生混凝土力学性能和抗冻性的影响研究

研究粉煤灰掺量、再生粗骨料取代率对再生混凝土抗压强度和抗折强度的影响,并对再生混凝土在不同冻融循环次数下的抗压强度和质量损失率进行了研究.结果表明:随着粉煤灰掺量的增加,再生混凝土抗压强度呈先增大后降低的趋势,当粉煤灰掺量为15%,再生粗骨料取代率为30%时,再生混凝土的抗压强度达到最大;粉煤灰掺量对抗折强度提高幅度较小;在冻融循环低于50次时,试块抗压强度下降速度较缓,此后下降速度加快,当冻融循环达到150次时,强度损失最大;再生粗骨料取代率对试块的抗冻性影响高于粉煤灰掺量.建立了考虑再生粗骨料取代率、粉煤灰掺量因素的冻融循环作用下再生混凝土抗压强度指数衰减规律预测模型.     

Effect of steam curing on class C high-volume fly ash concrete mixtures

The effect of steam curing on concrete incorporating ASTM Class C fly ash (FA), which is widely available in Turkey, was investigated. Cement was replaced with up to 70% fly ash, and concrete mixtures with 360 kg/m³ cementitious content and a constant water/binder ratio of 0.4 were made. Compressive strength of concrete, volume stability of mortar bar specimens, and setting times of pastes were investigated. Test results indicate that, under standard curing conditions, only 1-day strength of fly ash concrete was low. At later ages, the strength values of even 50% and 60% fly ash concretes were satisfactory. Steam curing accelerated the 1-day strength but the long-term strength was greatly reduced. Setting time of fly ash-cement pastes and volume stability of mortars with 50% or less fly ash content were found to be satisfactory for standard specimens. In addition, for steam curing, this properties were acceptable for all replacement ratios.     

粉煤灰对深井煤矿巷道隔热材料性能的影响

通过粉煤灰对隔热材料流动性、力学性能、热性能及耐久性的研究 ,指出低活性粉煤灰降低了隔热材料的流动性、强度及耐久性 ,却提高了材料的隔热性能 .对材料强度的测试结果表明 ,低活性粉煤灰的加入不会影响隔热材料的长期强度达到所要求的指标     

Fly‐ash particles and precipitated silica as fillers in rubbers. II. Effects of silica content and Si69‐treatment in natural rubber/styrene–butadiene rubber vulcanizates

This article explored the possibility of using silica from fly‐ash particles as reinforcement in natural rubber/styrene–butadiene rubber (NR/SBR) vulcanizates. For a given silica content, the NR : SBR blend ratio of 1 : 1 (or 50 : 50 phr) exhibited the optimum mechanical properties for fly‐ash filled NR/SBR blend system. When using untreated silica from fly‐ash, the cure time and mechanical properties of the NR/SBR vulcanizates decreased with increasing silica content. The improvement of the mechanical properties was achieved by addition of Si69, the recommended dosage being 2.0 wt % of silica content. The optimum tensile strength of the silica filled NR/SBR vulcanizates was peaked at 10–20 phr silica contents. Most mechanical properties increased with thermal ageing. The addition of silica from fly‐ash in the NR/SBR vulcanizates was found to improve the elastic behavior, including compression set and resilience, as compared with that of commercial precipitated silica. Taking mechanical properties into account, the recommended dosage for the silica (FASi) content was 20 phr. For more effective reinforcement, the silica from fly‐ash particles had to be chemically treated with 2.0 wt % Si69. It was convincing that silica from fly‐ash particles could be used to replace commercial silica as reinforcement in NR/SBR vulcanizates for cost‐saving and environment benefits. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

含镍废水处理中的助凝助沉工艺研究

将粉煤灰等几种物质应用于含镍废水处理中作为助凝助沉剂。试验研究了各自的最优加入量,对比了彼此的助凝助沉效果,结果表明,对试验的含镍废水,首选助凝助沉剂为粉煤灰,在100mL含镍废水中加入0.3g粉煤灰,可加速沉降,沉降在5min内基本完成,污泥的体积由原来的33.6%减少到14.1%,滤饼的含水量由88.27%降低到81.48%,并进行了工业试验。     

Effects of Ageing and Seeding on the Formation of Zeolite Y from Coal Fly Ash

Zeolite Y was selectively synthesised by treating Tarong fly ash in a hydrothermal system. The effects of ageing and seeding on the formation of the resultant phases, crystallisation kinetics, and gel chemistry of Si and Al were investigated. Most of the Si and Al components in the Tarong fly ash could be effectively transformed into zeolite Y in the presence of seeds but not the mineral phase, like mullite. The maximum crystallinity of zeolite Y obtained was 72%. The cation-exchange capacity (CEC) of the fly ash was 0.08 mmol/g but increased to 3.2 mmol/g after a proper treatment. Crystallisation of zeolite materials from fly ash is quite different from that of normal zeolite synthesis because the sources of Si and Al are relatively less reactive and other cation ions (e.g., K⁺, Mg²⁺) are present in fly ash. Zeolite P is a competitive phase present in the resulting products that could be eliminated by employing the seeding method. NMR study demonstrated that ageing plays an important role in enhancing the hydrothermal condition during which both Si and Al in fly ash dissolved into a basic solution and reacted to form ring-like structures, and further to zeolite materials. Seeding can selectively induce the formation of zeolite Y and eliminate the processes of induction and nucleation.     

不同粉煤灰掺量混凝土的碳化特性

采用加速碳化和自然碳化2种试验方法,研究了在同强度等级条件下,养护不同时间、含有不同比例粉煤灰混凝土的碳化特性.研究表明:除了粉煤灰掺量为65%的试验组在养护不充分时抗碳化性能下降很多外,自然环境中,尤其在养护充分的情况下,粉煤灰含量不同的混凝土的抗碳化性能并未显示出明显的差异.加速试验环境与自然环境中混凝土的碳化表现...     

MXene和纳米SiO2对粉煤灰水泥水化性能的影响

本文利用差热分析、X射线衍射、扫描电镜等手段研究了纳米Si O_2和MXene对粉煤灰水泥水化性能的影响。结果表明,单掺纳米Si O_2能够促进粉煤灰水泥早期水化,提高水化开始时的放热速率,并使粉煤灰水泥浆体更加密实;而单掺MXene、复掺纳米Si O_2和MXene对粉煤灰水泥后期水化的促进作用比较明显,能够促进水泥中期强度增长。     

Effect of fly ash on the kinetics of Portland cement hydration at different curing temperatures

This paper describes the effect of fly ash on the hydration kinetics of cement in low water to binder (w/b) fly ash-cement at different curing temperatures. The modified shrinking-core model was used to quantify the kinetic coefficients of the various hydration processes. The results show that the effect of fly ash on the hydration kinetics of cement depends on fly ash replacement ratios and curing temperatures. It was found that, at 20 °C and 35 °C, the fly ash retards the hydration of cement in the early period and accelerates the hydration of cement in the later period. Higher the fly ash replacement ratios lead to stronger effects. However, at 50 °C, the fly ash retards the hydration of the cement at later ages when it is used at high replacement ratios. This is because the pozzolanic reaction of the large volumes of fly ash is strongly accelerated from early in the aging, impeding the hydration of the cement.     

粉煤灰喷射混凝土力学性能及其在露天煤矿边坡中的应用

本研究制备粉煤灰喷射混凝土试件,测试了粉煤灰喷射混凝土的基本力学特性,得到了喷射混凝土的最佳粉煤灰掺量;提出了露天煤矿边坡的"挂网+粉煤灰喷射混凝土"加固处理方法;模拟分析了暴雨条件下粉煤灰喷射混凝土加固前后边坡稳定性。研究结果表明:粉煤灰喷射混凝土的最佳粉煤灰掺量为20%;采用"挂网+粉煤灰喷射混凝土"对露天煤矿边坡进行加固后,其在暴雨条件下的整体稳定系数由0.98增大至1.48,满足安全开采要求。     

粉煤灰对桥梁混凝土抗渗性能的影响规律研究

为研究粉煤灰对桥梁混凝土抗渗性能的影响,制备了不同粉煤灰掺量的混凝土样品,测试分析了桥梁混凝土抗压强度、孔隙结构、渗透高度和抗氯离子渗透性能随粉煤灰掺量和养护龄期的变化规律。研究结果表明:(1)当桥梁混凝土养护龄期为7d时,桥梁混凝土的抗压强度随着粉煤灰掺量的增多而逐渐降低;当混凝土龄期大于28d时,桥梁混凝土的抗压强度在粉煤灰掺量为30%左右时最大。(2)粉煤灰掺量为30%时,桥梁混凝土密实度达到最大,此时其内部小孔隙增大而大孔隙减小。(3)桥梁混凝土抗氯离子渗透系数随着粉煤灰掺量的增大先减小后增大,在粉煤灰掺量为30%时取得最小值。     

高掺量粉煤灰混凝土强度发展潜力

测定了粉煤灰火山灰的反应率;估算了粉煤灰火山灰反应所需的最小水泥用量[或Ca(OH)2量];研究了高掺量粉煤灰混凝土的长期强度增长趋势。试验结果表明:粉煤灰的火山灰反应程度极其有限,极限火山灰反应率不大于20%;高掺量粉煤灰混凝土不会存在所谓“贫钙”问题;与普通混凝土相比,高掺量粉煤灰混凝土具有更强的后期强度增长趋势。     

Analysis and design of a stabilized fly ash as pavement base material

The main objective of this study is to utilize a class F fly ash as base material in road pavements. Since class F fly ashes do not manifest desirable engineering properties for this purpose, it was decided to stabilize the material with cement. Fly ash may be utilized with or without aggregate as a pavement layer. It should be noted that, in this research only aggregate free stabilized mixtures (fly ash and cement only) were used since the aim was to utilize high volumes of this waste material. Cement content in the stabilized, laboratory prepared samples were between 2%, 4%, 8%, and 10% by total weight. Initially, Texas triaxial test was carried out to justify the suitability of the fly ash as pavement material. Then, mechanical tests were performed to obtain the fundamental properties of the cement stabilized material in order to analyze the pavement structure. Under repeated wheel loading, fatigue cracking is the primary mode of failure of stabilized materials in which cracks initiate due to the repeated tensile stresses. Utilizing an accelerated full scale road test data for the fatigue performance of cement stabilized fly ash and performing a mechanistic-empirical design procedure, required layer thickness for different lives were obtained for different amount of cement content.     

不同C_3S含量阿利特-硫铝酸盐水泥熟料与粉煤灰混合材的适应性研究

研究了不同C3S含量的阿利特-硫铝酸盐水泥熟料与粉煤灰混合材的适应性。结果表明：C3S含量一定时,随粉煤灰掺量增加,水泥的凝结时间延长,抗压强度降低;粉煤灰掺量一定时,随C3S含量的增加,水泥的凝结时间延长,抗压强度增大;C3S含量增大时,随着粉煤灰掺量增多,水泥各龄期抗压强度降幅减小;掺加粉煤灰后水泥的早期抗压强度降低幅度较大,后期抗压强度降幅较小。熟料中C3S含量低时,对高粉煤灰掺量的适应性差;C3S含量高时,其适应性好。     

Pozzolanic activity of various siliceous materials

The accelerated pozzolanic activity of various siliceous materials, like silica fume, fly ash (as received and fine ground), quartz, precipitated silica, metakaolin and rice husk ash (RHA; various fineness and carbon content), has been determined. The compressive strength of accelerated tests has been compared with cubes cured in water at 7 and 28 days. Maximum activity has been observed in case of RHA (<45 μ), followed by quartz and silica fume. The 10% replacement of cement by sand has shown accelerated pozzolanic index of 92% compared with 85% required in ASTM for silica fume as mineral admixture.     

利用活化粉煤灰制备高掺量粉煤灰烧结砖

研究了分别经机械和化学活化后的粉煤灰对高掺量粉煤灰烧结砖性能和显微结构的影响。结果表明:用磨细粉煤灰代替原灰配料,可以改善烧结砖的力学性能,尤其是砖的抗压强度能显著提高。当用掺量质量分数为60%的磨细灰制砖时,烧结砖的抗压强度提高至原灰烧结砖的2倍,并且有更为致密的微结构。在粉煤灰砖中加入质量分数为2%的外加剂D进行化学活化后,可明显改善干坯强度,并提高烧结砖的抗压强度。     

原状粉煤灰对超高性能混凝土性能的影响

为提高粉煤灰的综合利用率,降低原料成本,采用未经磨细和分选的原状粉煤灰等质量替代硅灰来制备超高性能混凝土(UHPC),并研究了不同掺量的原状粉煤灰对UHPC力学性能及微观结构的影响。结果表明:原状粉煤灰的掺入可使UHPC中胶凝材料的粒度呈梯度分布,形成良好的微级配;并且使新拌混凝土的流动度增大,影响了钢纤维在UHPC基体中的分布;当原状粉煤灰掺重不超过30%时,UHPC抗折强度随着原状粉煤灰掺量的增加呈现不同程度的增长,30%原状粉煤灰掺量的UHPC抗折强度与不掺粉煤灰的空白样相比提高了34%;由于原状粉煤灰水化缓慢,当原状粉煤灰掺量在0%~40%时,UHPC抗压强度随着原状粉煤灰掺量的增加有所下降。孔结构分析表明:UHPC的平均孔径以及总孔体积均随着原状粉煤灰的掺入而减小,基体更加密实;当原状粉煤灰掺量为30%时,SEM照片显示钢纤维与UHPC基体结合紧密,界面黏结增强。     

Classification of carbon in Canadian fly ashes and their implications in the capture of mercury

Fly ashes produced from Canadian power plants using pulverized coal and fluidized bed combustors were examined for their carbon content to determine their ability to capture mercury. The feed coal used in these power plants were lignite, subbituminous, high and medium volatile bituminous, their blends, and also blends of coal with petroleum coke (Petcoke). The carbon and mercury content of the coals and fly ashes were determined using the ASTM standard method and by the cold vapour atomic absorption spectrometry method. The carbon content of the fly ash was concentrated by strong acid digestion using HCl and HF. The quantitative and qualitative analyses of the carbon concentrate were made by using a reflected light microscope. The results show that the carbon content of fly ash appears to be partially related to depositional environment during coalification and to the rank of the coal. The Hg captured by the fly ash depends on the rank and blend of the feed coals and the type of carbon in the fly ash. The isotropic vitrinitic char is mostly responsible for the capture of most Hg in fly ash. The inadvertent increase in carbon content due to the blending of coal with petroleum coke did not increase the amount Hg captured by the fly ash. The fly ash collected by the hot side electrostatic precipitator has a low Hg content and no relation between the Hg and carbon content of the ash was observed. These results indicate that the quantity of carbon in the fly ash alone does not determine the amount Hg captured. The types of carbon present (isotropic and anisotropic vitrinitic, isotropic inertinitic and anisotropic Petcoke), the halogen content, the types of fly ash control devices, and the temperatures of the fly ash control devices all play major roles in the capture of Hg.