不同助磨剂对粉煤灰火山灰活性影响的研究

探讨不同助磨剂对粉煤灰不同时期火山灰活性的影响。结果表明:单掺适量的不同助磨剂可以不同程度地提高粉煤灰早期、中期与后期的火山灰活性,其中早期的激发作用效果最大,后期的激发作用效果最小。且随着粉磨时间的延长,各水泥试样的3d、7d及28d抗压强度比值均有明显的提高但增幅下降。其中,当三乙醇胺掺量为0.03%时其对粉煤灰早期火山灰活性的激发作用效果最大;当乙二醇掺量为0.06%时其对粉煤灰中期火山灰活性的激发作用效果最大;当丙三醇掺量为0.09%时其对粉煤灰后期火山灰活性的激发作用效果最大。     

生物质灰对水泥硬化浆体抗压强度影响的试验研究

对比研究了生物质灰与普通粉煤灰在粒度分布、颗粒形态、化学组成、活性指数等方面的不同,并开展了不同掺量生物质灰对水泥硬化浆体抗压强度的影响研究.结果表明:生物质灰颗粒形状不规则、平均粒径及粒径分布范围较大,具有特有的细长纤维状颗粒,且其活性组分Al2O3不足普通粉煤灰的三分之一;生物质灰的火山灰活性小于普通粉煤灰;相同掺量下,生物质灰-水泥复合胶砂各龄期的抗压强度均小于普通粉煤灰-水泥复合胶砂,生物质灰掺量越大,复合胶砂的强度相比纯水泥组下降程度越大;与普通粉煤灰相比,掺加生物质灰的硬化水泥浆体微观结构更为疏松多孔,特别是其特有的细长纤维状颗粒的存在.     

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.     

矿物掺合料对蒸养水泥净浆性能的影响

研究了蒸养条件下粉煤灰、矿渣的掺量对水泥净浆化学结合水量和抗压强度的影响,揭示了矿物掺合料对蒸养水泥净浆水化性能和力学性能的影响。试验结果表明,与标准养护相比,蒸汽养护更有利于激发粉煤灰和矿渣的火山灰活性,促进水泥的早期水化,提高水泥浆体的早期强度;但无论是蒸汽养护还是标准养护,随着矿物掺合料掺量的增加,复合胶凝材料的水化性能和力学性能明显减弱,因此矿物掺合料掺量不宜太大。     

Use of recycled copper slag for blended cements

Copper slag is a by‐product generated during smelting to extract copper metal from the ore. The copper slag obtained may exhibit pozzolanic activity and may therefore be used in the manufacture of addition‐containing cements. In this paper the effect of the incorporation of the copper slag in cement is measured. Blends of copper slag with Portland cement generally possess properties equivalent to Portland cement containing fly ash, but very different to the silica fume incorporation. Copper slag and fly ash reduce the heat of hydration more effectively than silica fume in mortars. The replacement of 30% cement by copper slag reduces the flexural and compressive strength in a similar way to fly ash; however, after 28 days, the reduction is less than the percentage of substitution. Hydrated calcium aluminate phases were analysed using scanning electron microscopy (SEM) and X‐ray diffraction (XRD) techniques. The pozzolanic activity of copper slag is similar to that of fly ash and higher than silica fume. In the presence of low water/cement ratios, certain pozzolanic materials produce a very compact cement paste that limits the space available for hydration products, a determining factor in the formation of hydrated calcium aluminates. SEM was found to be a useful analytical technique when aluminates are formed and can be clearly detected by XRD. Copyright © 2008 Society of Chemical Industry     

Hydration of fly ash-portland cements

Hydration products of fly ash-portland cements were studied with x-ray diffraction (XRD), differential thermal analysis (DTA) and scanning electron microscopy (SEM) as part of a continuing research effort to understand the pozzolanic activity of fly ashes. It was found that the amount of calcium hydroxide crystals in the cement pastes is diminished due to the addition of fly ash to the cement. Ettringite was produced in the early age, and the consumption of sulfate by the formation of ettringite was accelerated by the addition of fly ash. A partial conversion of ettringite to monosulfate within the first 7 days of hydration in the fly ash-portland cement pastes, but the formation of ettringite continued to form up to at least 28 days of hydration in the pastes without fly ash. Examination of the fly ash bearing pastes showed, in all cases, varying amounts of calcium hydroxide and unreacted portland cement, with minor quartz and gehlenite hydrate. It appears that hydration reactions actually occur in the fly ash cement pastes more or less on a particle-by-particle basis.     

Packing effect and pozzolanic reaction of fly ash in mortar

This research is to study the effect of particle size of fly ash on packing effect and pozzolanic reaction of mortar when 20% of fly ash is used to replace Portland cement type I. Both effects can be determined by using fly ash and insoluble material which have almost the same particle size to replace Portland cement type I. Normally, the compressive strength of fly ash mortar is contributed from hydration reaction, packing effect, and pozzolanic reaction. For mortar mixed with insoluble material, the compressive strength is due to hydration reaction and packing effect. Thus, compressive strength due to pozzolanic reaction can be determined from the difference in compressive strength between fly ash mortar and insoluble material mortar. The results show that the strength activity index of fly ash mortar depends on the median particle size of fly ash and curing ages of mortar samples. At early ages, the strength activity index of fly ash mortar due to packing effect is higher than that due to pozzolanic reaction. At the ages of 3 to 90 days, the difference in strength activity index due to packing effect of fly ashes with median particle size of 2.7 and 160 μm is almost constant about 22% of the strength of standard mortar (STD). The differences in strength activity index due to pozzolanic reaction of fly ashes with median particle size of 2.7 and 160 μm are 3%, 20%, and 27%, respectively, at the ages of 3, 28, and 90 days.     

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。     

粉煤灰水泥的水化动力学

研究了粉煤灰水泥中粉灰和水泥熟料的水化过程动力学；讨论了这两种反应的动力学常数对系统性质的影响。提出了为改善粉煤灰水泥的性质，必须同时促进粉煤灰的火山灰反庆和水泥熟料的水化反应。     

循环流化床高硫高钙固硫灰在水泥和混凝土中的应用研究(一)

对云南省的高硫高钙褐煤CFB固硫灰的化学组成、物理性状以及掺加该种固硫灰的水泥水化机理、微观矿相和物理性能进行了试验研究。确认了经碱激发后,该固硫灰活性系数高于一般的粉煤灰和火山灰质混合材;与其他材料进行复合,用作水泥活性混合材料及水泥缓凝剂,可以代替部分水泥熟料和石膏,降低水泥生产成本和粉磨能耗。还可用于制造微膨胀水泥和混凝土膨胀剂。但使用时,必须根据该固硫灰的化学成分严格控制其掺加量。     

氯化钠与三乙醇胺复合对粉煤灰水泥水化程度影响的研究

探讨氯化钠与三乙醇胺复合对粉煤灰水泥不同水化阶段水化程度的影响。结果表明:将一定掺量的氯化钠与三乙醇胺复合掺入可以不同程度地提高粉煤灰水泥不同龄期的水化程度,其水化3d的水化程度的增幅最大,水化28d的水化程度的增幅最小;且随着粉磨时间的延长,粉煤灰水泥不同龄期的水化程度均有不同程度的提高但增幅下降。将一定掺量的氯化钠与三乙醇胺复合掺入后粉煤灰水泥不同龄期的水化程度均高于单掺氯化钠或三乙醇胺,其中氯化钠对早期水化程度的提高效果优于三乙醇胺;而三乙醇胺对后期水化程度的提高效果优于氯化钠;当氯化钠掺量为2%,三乙醇胺掺量为0.06%进行复掺且粉磨时间为15min时粉煤灰水泥不同龄期的水化程度均达到最大值。     

Study on the pozzolanic properties of rice husk ash by hydrochloric acid pretreatment

The pozzolanic properties of rice husk ash by hydrochloric acid pretreatment are reported in the paper. Three methods have been used to estimate the pozzolanic activity of rice husk ash. The heat evolution and the hydration heat of cement, the Ca(OH)₂ content in the mortar and the pore size distribution of mortar are determined. It is shown that compare with the rice husk ash heated untreated rice husk, the sensitivity of pozzolanic activity of the rice husk ash heated hydrochloric acid pretreatment rice husk to burning conditions is reduced. The pozzolanic activity of rice husk ash by pretreatment is not only stabilized but also enhanced obviously. The kinetics of reaction of rice husk ash with lime is consistent with diffusion control and can be represented by the Jander diffusion equation. A significant increase in the strength of the rice husk ash (pretreated) specimen is observed. The results of heat evolution indicate that the rice husk ash by pretreatment shows the behavior in the increase of hydration of cement. The cement mortar added with the rice husk ash by pretreatment has lower Ca(OH)₂ content after 7 days and the pore size distribution of the mortar with the rice husk ash with pretreatment shows a tendency to shift towards the smaller pore size.     

海水环境下矿物掺合料对硫铝酸盐水泥的水化影响

研究了海水环境下掺入硅灰、粉煤灰、矿渣对硫铝酸盐水泥抗压强度、化学收缩和水化产物的影响规律.结果表明:当硅灰的掺量为2.5%时,水泥浆体的抗压强度比空白组高.矿渣掺量为10%的水泥浆体28 d抗压强度明显超过掺入硅灰和粉煤灰时的强度,60 d强度高于空白组.掺入2.5%硅灰后,水泥浆体的化学收缩增大;在水化早期,粉煤灰和矿渣的火山灰活性很低,导致水泥浆体的化学收缩降低.掺入10%硅灰加快了硫铝酸盐水泥3 d水化反应,钙矾石生成量增多,水泥浆体早期强度比掺其它掺合料有所提高,但体积过快膨胀会破坏其内部结构,对水泥浆体的强度发展不利.     

粉煤灰和矿渣粒度分布对混凝土微观结构和抗氯离子渗透性的影响

针对胶凝材料比表面积和粒度分布等物理性质存在的差异,将P·Ⅱ水泥,Ⅰ级、Ⅱ级粉煤灰和S95级、S105级矿渣进行互掺,固定水泥用量,设计了4种粉煤灰和矿渣的组合方式,通过流动度试验分析了组合方式对净浆流动性的影响,并将粒度分布曲线与Fuller分布曲线进行了比较。在净浆配合比的基础上,对不同组合方式的混凝土进行了工作性、力学性能及自由氯离子浓度测试,探讨了粉煤灰和矿渣的粒度分布对混凝土强度和抗氯离子渗透性的影响,并对硬化浆体水化产物的微观形貌和化学组成进行了分析,揭示了影响机理。研究结果表明,矿物掺合料的粒度分布是决定颗粒级配优劣的重要因素。Ⅰ级粉煤灰具有更强的滚珠效应,在提高流动性方面起了关键性作用。粉煤灰和矿渣的水化及火山灰反应程度影响着混凝土的力学性能和耐久性能,由于Ⅰ级粉煤灰有更大的比表面积,火山灰活性也较高,因此Ⅰ级粉煤灰和S95/S105级矿渣组合的净浆流动度,混凝土的工作性、抗压强度和抗氯离子渗透性均明显高于Ⅱ级粉煤灰和S95/S105级矿渣组合。其中Ⅰ级粉煤灰和S95级矿渣组合的胶凝材料粒度分布曲线与Fuller曲线最为接近,粒度分布最优,水化浆体中Ca(OH)₂含量最低,火山灰反应最为充分,对应的混凝土微观结构致密,抗氯离子渗透性最好。     

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.     

Activation of fly ash cementitious systems in the presence of quicklime: Part I. Compressive strength and pozzolanic reaction rate

In the first part of this study, the effect of industrially produced quicklime on the strength development and pozzolanic reaction rates of different fly ash/cement (FC) systems was investigated. Two high calcium fly ashes, diversified on their active silica and calcium oxide contents, and one with moderate calcium content were used. Strength development, hydration evolution, and pozzolanic reaction rates of the quicklime-fly ash-cement (QFC) systems were monitored and presented. Moreover, new efficiency factors were calculated for the activated systems in an attempt to optimize the quicklime addition in each case, whilst correlations were attempted between the nonevaporable water contents (W_n) and the cementitious efficiency factor (k values) of the activated systems. The addition of quicklime increased both the early and later strengths of the high-calcium fly ash specimens. For the two high-lime ashes tested, a 3% addition of quicklime was found to be the optimum dosage both for short and longer curing periods. It is possible that such an offer of lime fully employed the available silica from the ashes to form additional cementitious compounds, principally pozzolanic C-S-H. In the case of lower-lime fly ash, a small quantity of added lime (5%) was found to be effective only during the initial stages of the hardening process. When quicklime additions increased, no accelerating effect was detected, as a result of the diminished proportion of soluble silica in the pore solution. Identification of the generated hydration products, porosity of the activated mixtures and examination of their microstructure will be presented in Part II of the study.     

Fire resistance of fired clay bricks-fly ash composite cement pastes

This work aims to study the effect of substitution of fly ash for homra on the hydration properties of composite cement pastes. The composite cements are composed of constant proportion of OPC (80%) with variable amounts of fly ash and homra. The addition of fly ash accelerates the initial and final sitting time, whereas the free lime and combined water contents decrease with fly ash content. The fly ash acts as nucleation sites which may accelerate the rate of formation of hydration products which fill some of the pores of the cement pastes. The fire resistance of composite cement pastes was evaluated after firing at 250, 450, 600, 800 °C with rate of firing 5 °C/min with soaking time for 2 h. The physico-mechanical properties such as bulk density and compressive strength were determined at each firing temperature. Moreover, the phase composition, free lime and microstructure for some selected samples were investigated. It can be concluded that the pozzolanic cement with 20 wt% fly ash can be used as fire resisting cement.     

粉煤灰与矿渣的早期火山灰反应放热行为及其机理

针对大体积混凝土绝热温升计算中粉煤灰与矿渣的火山灰反应放热问题,利用微量热仪法测试了不同掺量粉煤灰和矿渣对水泥水化热及放热速率的影响规律,分析了粉煤灰和矿渣水化3d以前的火山灰反应放热行为,采用X射线衍射与差示扫描量热–热重法研究了粉煤灰与矿渣对水泥早期水化及其火山灰放热行为的影响机理。结果表明：粉煤灰与矿渣水化3d时火山灰反应热分别约为3～5J/g和15～16J/g。粉煤灰对水泥水化的阻碍作用在水化24h前最为明显,其火山灰效应主要发生于水化24h之后;矿渣对水泥水化有促进作用,自加水开始即表现出一定的火山灰效应。粉煤灰与矿渣掺入后有助于水泥水化产物中钙矾石的稳定,钙矾石抑制了水泥水化,Ca（OH）2生成量减少,因而粉煤灰与矿渣的火山灰反应也受到影响。     

基于Ca(OH)2含量的复合胶凝材料中水泥水化程度的评定方法

对粉煤灰反应程度和Ca(OH)2含量进行测定,并结合水泥水化平衡计算理论,建立了基于Ca(OHh含量的复合胶凝材料中水泥水化程度的评定方法.结果表明:随着粉煤灰掺帚的增加,复合胶凝材料浆体中粉煤灰的反应程度和Ca(OH)2含量逐渐降低,而其中水泥的水化程度却由此增大,90d龄期时含有大比例(超过35%)粉煤灰的复合胶凝材料中水泥水化程度高达80%以上,有的甚至接近完全水化.水胶比对复合胶凝材料中水泥水化程度的影响远不如粉煤灰掺量明显.与等效化学结合水量法相比,基于Ca(On)2含量的评定方法能更精确和直观地表征复合胶凝材料中水泥的水化程度.     

蒸养条件下复合胶凝材料水化过程(英文)

复合胶凝材料水化性能在蒸汽养护及标准养护下有很大差异。通过水化程度、水化产物分析,研究了养护条件及胶凝材料组成对大掺量粉煤灰和磨细矿渣粉矿物掺合料复合胶凝材料体系水化性能的影响。采用化学结合水法、氢氧化钙法及X射线衍射法对复合胶凝材料的水化程度和水化产物进行了表征。结果表明:蒸汽养护条件加速了复合胶凝材料的早期水化,在蒸养阶段更为明显;化学结合水法和氢氧化钙法均能表征胶凝材料的水化程度,当采用氢氧化钙法时,应考虑掺合料火山灰反应影响;蒸汽养护条件下,复合胶凝材料的水化产物种类不变,但水化产物含量增多。