【作者】 吴传明；

【导师】 钱觉时；

【作者基本信息】 重庆大学 ， 材料科学与工程， 2009， 博士

【摘要】 水介质长期作用的低钙湿态粉煤灰是我国及世界范围内大量长期堆存于灰场、资源化利用严重滞后的燃煤固体废弃物,有关低钙湿灰资源化利用的研究结果较多,主要是将其用于道路路基稳定、建筑制品生产及活性激发,但对粉煤灰与水长期接触后基本性能变化研究奇缺。对湿灰性能变化的研究,有利于燃煤电厂可持续发展,更有利于环境保护。针对现有研究方法中,无法获得水介质作用前后同批次粉煤灰,从而难以反映水介质长期作用过程对粉煤灰性能影响的研究难点,本文通过实验室模拟制备低钙湿灰的方法,对比研究了粉煤灰性能随与水接触时间长短的变化规律。试验采用仪器分析及粉煤灰用做掺合料时性能测试方法,对长龄期(5年)与水介质作用粉煤灰的性能及其变化进行分析,并得出以下研究结果:1)低钙湿灰长期与水接触发生一定程度的自水化反应,颗粒被水化产物所覆盖而变得粗化,进而使粉煤灰早期矿物减水作用明显降低,需水量比降低约10%,但仍可满足作为一般混凝土掺合料时的需水性要求。粉煤灰与水接触后其体积稳定性得到改善,但自水化过程也导致了粉煤灰烧失量增加;2)低钙粉煤灰长时间与水接触后,其基本矿物组成及其晶体结晶度大小基本无变化;长时间(最长为3年)与水介质作用的低钙粉煤灰,大部分颗粒仍保持原有形态,但少数颗粒表面出现侵蚀现象,具体表现为粉煤灰颗粒内部晶态颗粒逐渐暴露,颗粒外部外形规则的晶体受水侵蚀后颗粒尺寸变小,氧化钙含量决定了粉煤灰与水作用过程中形态发生变化的大小;3)湿灰活性在与水作用前5个月内下降明显,降低值可达5%以上,但不超过10%,后期活性降幅较小。粉煤灰与水接触后,其早期水化速度降低,后期水化速度加快。湿灰体系呈碱性,在与水介质作用前几天碱性增加迅猛,随后呈现缓慢降低趋势,氧化钙含量越高,后期碱性降速越大;4)较高的环境温度(95℃)在加快粉煤灰自水化同时,又有激发粉煤灰活性的作用,但粉煤灰活性整体仍表现为降低的趋势;排灰介质成分、酸碱性、静态/动态浸泡方式对湿灰活性影响不明显。细度对粉煤灰与水作用早期的活性影响较小,但导致其后期活性下降明显;氧化钙含量越高,粉煤灰活性下降速度和幅度也越大; 5)虽然低钙湿灰用于混凝土时矿物减水作用同原状干灰相比,有明显降低,但混凝土坍落度经时损失得到改善。掺加长期与水介质作用的湿灰的新拌混凝土泌水性及其与外加剂的适应性同掺加原状干灰新拌混凝土无明显差异;6)用长期与水介质作用的粉煤灰拌制的混凝土强度早期明显降低,后期降幅趋缓:掺加与水介质作用5个月粉煤灰混凝土强度抗压强度比下降约5%,掺加30%的与水介质作用时间为36个月粉煤灰,其混凝土抗压强度比仍可达到75%;掺加与水介质作用时间为5年粉煤灰混凝土28d抗压强度比与掺加湿排36个月粉煤灰混凝土几近一致。长期湿排粉煤灰硬化混凝土耐久性试验结果表明,其耐久性发展趋势与原状干灰类似。本文研究结果说明长期与水介质作用的低钙湿排粉煤灰,虽然使得混凝土大部分性能降低,但仍可满足作为水泥混凝土掺合料时的性能要求。更多还原

【Abstract】 The long-term wetting fly ash of low-calcium is a kind of spreading industrial solid waste of coal power plants that is packed in stacks both at home and abroad, and they are slightly used. Researchs on low-calcium wetting fly ash were aboundent, which were generally focused on road pavement, building products and application after activation. But there is a bad shortage of investigation on its basic properties after long-term wetting. A well investigation on its property change will be helpful both for the sustanible development of power plants and the environment protection.To avoid the gererally-existed research threshold in determining the property changes--- obtaining the same batch of dry fly ash that has the same composition with the long-term wetting one, a simulative wetting process was carried out in lab. The rules of wetting age on its properties were expermentally performed. A five-year long time wettingg fly ash was analysed instrumentally and its performance when used as concrete mixture was also carried out. The results showed that:1) Due to the self-cementing process to some degree, low-calcium fly ash particles were coated with hydration production after a long-term contacting with water. Meanwhile, the particle size became coarser and its distribution became broader. Even though a 10% reduction in water requirement was occured due to its deduction in water-reducing effect after the early period of wetting, it could still fullfill the water requirement when used as a concrete mixture. Fly ash became much more sound after wetting, while its loss on ignition grew up which was attributed to its hydration process; 2) The distinction of the minerals and crystallizing degree of low-calcium fly ash before and after wetting was neglectable. After a long time wetting process( 3 years at most), major part of the low-calcium fly ash kept their original morphology while some others were erodened and their inner crystal particles became seen while the out part of regular crystals became smaller, all of which was directly influenced by its CaO content.3) A more than 5% but less than 10% activity loss occurred due to a first five-month of wetting, while the later period of activity loss became smaller. After a wetting process, the early hydration process was decelerated while the later hydration could be accelerated. The alkalinity of wetting fly ash was higher than 7, which surged up swiftly during the first serval days of wetting and declined slowly afterwards. It also showed that the higer content of CaO, the much swift of the declination of its alkalinity. The alkalinity peak of low-calcium was postponed when compared with high-calcium ash. 4) A high wetting temperature(95℃) quickened the self-cementing process, during which the fly ash was also activated, but the activity of it was lowered. The chemical composition, water acidity, static or dynamic state of wetting water effected the activity slightly. The finer of the wetting fly ash, the lower of its later-period of activity, and its fineness had little function on its early activity changes. The declination speed and span of activity became wider with the content of CaO became higher. 5) Though there was a noticable declination of water reducing effect of low-calcium fly ash due to long-term wetting, but the slump loss lowered down while the bleeding and adaptation with admixture were quite the same with dry fly ash. 6) The early strength of long-term wetting fly ash concrete decreased rapidly but the later strength declined gentaly: The specific compressive strength of concrete with fly ash wetting for 5 months decreased by 5% while concrete with 30% fly ash wetting for 36 monthes still reached 75%, and there was no visible strength discrepancy of fly ash concrete wetting for 3 and 5 years at 28d. The durability of long-term wetting fly ash concrete was quite the same with dry ash ones.Though most concrete performance with long-term low-calcium wetting fly ash are declined, it can still be used as an admixture when applied in concrete supplimentarily.更多还原