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首页> 外文会议>25th conference on cement microscopy >ASSESSMENT OF POZZOLANIC REACTIVITY OF CLASS-F FLY ASHES THROUGH MINERALOGICAL MICROSTRUCTURAL CHARACTERIZATION
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ASSESSMENT OF POZZOLANIC REACTIVITY OF CLASS-F FLY ASHES THROUGH MINERALOGICAL MICROSTRUCTURAL CHARACTERIZATION

机译：通过矿物学和微结构表征对F类粉煤灰的火山灰反应性进行评估

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The effectiveness of low lime fly ash used in cement is determined to a largernextent by three parameters viz. fineness, carbon content (Loss on Ignition) and the glassy phaserncontent of the fly ash. In this work, typical Indian class-F fly ashes have been characterized forrntheir physico- chemical and mineralogical properties. While the particle size distribution varyrnwidely among the samples, the chemical and mineralogical characteristics vary with in arnnarrow range. The reactive silica content of the fly ash was determined following chemicalrntreatment as per EN-196-2 method. The microscopic examination of the residue left after thernchemical treatment reveals that this treatment attacks preferentially the glassy portion of thernspherical particles of the fly ash. This observation was supported by the XRD analysis carriedrnout on the fly ash before and after the chemical treatment. The XRD of the residue shows totalrndisappearance of the amorphous hump and enhancement of crystalline quartz and mulliternpeaks. The SEM examination of classified fly ash fractions reveals that these glassy, sphericalrnparticles are predominantly present in the -45μm fractions. This is further confirmed by higherrnreactive silica content obtained in this fraction. Also, the mortars containing -45μm fraction ofrnthe fly ash show superior flow property as compared to the one with +45μm fraction, due tornthe ‘ball bearing effect’ of the small spherical particles.rnIn order to determine the pozzolanic reactivity of the Class-F fly ash in cementrnand concrete, the samples of fly ash were aged up to 28 days in different solutions viz., 1 NrnNaOH, saturated solutions of Ca(OH)2, and CaSO4.2H2O corresponding to the pH of aroundrn13.5, 12, and 6.5 respectively. The treatment was aimed at simulating the pH of the pore fluidrnnormally encountered in concrete/ cement paste matrix at different ages. Information fromrnanalyses for various elemental oxides in the solution suggests that the fly ash reacts with in 7rndays in 1 N NaOH, at 28 days in case of Ca(OH)2 and very little reaction is observed forrnCaSO4.2H2O solution. The SEM examination of the treated fly ash reveals that these reactionsrnpreferentially occur on the surface of the spherical glassy particles, which corroborates thernearlier result that the spherical particles are indeed more reactive and contributes to thernpozzolanic reactions of the fly ash. The above characterization studies on fly ash have beenrnfound useful in evolving directions for optimizing its use in blended cement and concrete.
机译：水泥中使用的低石灰粉煤灰的有效性通过三个参数确定为更大。粉尘的细度，碳含量（着火损失）和玻璃态相含量。在这项工作中，典型的印度F级粉煤灰具有其理化和矿物学特性。虽然样品之间的粒度分布变化很大，但化学和矿物学特征随窄范围变化。根据EN-196-2方法对化学处理后的粉煤灰中的反应性二氧化硅含量进行了测定。在化学处理后留下的残留物的显微检查表明，该处理优先侵蚀了飞灰的球形颗粒的玻璃部分。在化学处理之前和之后对粉煤灰进行的XRD分析支持了这一观察结果。残留物的XRD显示出无定形驼峰的完全消失以及晶体石英和多峰的增强。 SEM对分类的粉煤灰馏分的检查表明，这些玻璃状球形颗粒主要存在于-45μm馏分中。在该级分中获得的更高反应性二氧化硅含量进一步证实了这一点。此外，由于小球形颗粒的``滚珠效应''，含有-45μm的粉煤灰的砂浆比具有+45μm的灰浆的砂浆表现出优异的流动性.rn为了确定F级的火山灰反应性水泥和混凝土中的粉煤灰，粉煤灰样品在不同的溶液中老化28天，这些溶液包括1 NrnNaOH，Ca（OH）2饱和溶液和CaSO4.2H2O，对应的pH值约为13.5、12。和6.5。该处理旨在模拟不同年龄的混凝土/水泥浆基质中通常遇到的孔隙的pH。来自溶液中各种元素氧化物的分析信息表明，在Ca（OH）2的情况下，粉煤灰在1 N NaOH中在7天的时间内反应了28天，而对于CaSO4.2H2O溶液观察到的反应极少。 SEM检查处理后的粉煤灰表明，这些反应优先发生在球形玻璃状颗粒的表面，这证实了较早的结果，即球形颗粒确实更具反应性，并有助于粉煤灰的火山灰反应。已经发现上述粉煤灰的表征研究在不断发展的方向上对优化其在水泥和混凝土混合料中的使用很有用。

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