北京市预拌混凝土矿物掺合料应用问题分析及解决问题的思路

通过实地调研、信息采集、问卷调查等方式,调研了北京市矿物掺合料的生产、供应和使用情况,对一些关键问题开展了试验研究,从中发现了矿物掺合料多个环节存在的问题,进行了原因分析,提出了对策建议。     

二灰稳定碎石基层混合料配合比设计的探讨

石灰粉煤灰稳定级配碎石作为路面基层(以下简称二灰碎石基层)具有后期强度高、刚度大、抗水稳定性优良等优点。用其作为公路养护工程路面基层时,就与新建公路路面基层的施工有着较大区别。为了基层稳定,避免行车对基层强度的破坏,施工中应严格控制混合料的集料级配和各类材料的配合比例。只有这样,其才能既具有较高的强度、刚度、抗拉裂,缩缝少,雨季施工时,行车偶然碾压不至于大面积翻浆,工程效果较为理想。     

大掺量粉煤灰泵送混凝土早期抗压强度的试验研究

通过理论分析和试验,研究了大掺量粉煤灰对混凝土早期抗压强度及成本的影响。试验所选用的胶凝材料总量为375kg,以0~55%的粉煤灰替代水泥,减水剂的掺量固定为1.0%,引气剂的掺量固定为1.2酃。通过坍落度及不同龄期抗压强度等对比分析粉煤灰掺量对混凝土和易性及早期强度的影响。结果表明,混凝土早期抗压强度及成本随着粉煤灰掺量的增大而逐渐减小,运用粉煤灰等质量代替水泥(P·O42.5级水泥)可配制出28 d抗压强度为20 MPa以上,成本大大降低的大掺量粉煤灰混凝土。研究的结论为新疆地区粉煤灰的应用提供了有效途径,有助于制备高性能混凝土。     

大掺量粉煤灰混凝土长龄期的微观结构

对深圳平安金融中心2年龄期大掺量粉煤灰混凝土基础底板钻芯取样试件进行了强度、渗透性、碳化深度测试,并通过扫描电镜观察了试件中硬化浆体的微观结构。结果显示:大掺量粉煤灰混凝土长龄期力学性能和耐久性能优异;复合胶凝材料硬化浆体密实,骨料与浆体之间结合紧密;粉煤灰反应程度较高,体系中Ca(OH)2含量较低,硬化浆体中生成大量低Ca/Si的C-S-H凝胶。     

粉煤灰掺量对聚乙烯醇纤维增强水泥基复合材料抗硫酸盐侵蚀性能影响的研究

为了研究粉煤灰掺量对聚乙烯醇纤维增强水泥基复合材料(Polyvinyl alcohol fiber reinforced cementitious composites,简写为PVA-FRCC)抗硫酸钠侵蚀的影响,在长期浸泡和干湿循环两种不同的侵蚀环境下,对若干次试验周期后的试件表观形貌变化、质量变化、体积变化、抗压强度和微观结构进行分析研究。试验结果表明,粉煤灰的掺入一定程度上密实了PVA-FRCC,在不同的侵蚀环境下均使其抗硫酸钠侵蚀性能得到改善,质量分数在50%之内时随着掺量的增加而更加明显。     

干熄焦除尘灰配入钒钛矿烧结的研究

烧结固体燃料中配加一定量的干熄焦除尘灰,在保证烧结过程主要参数和烧结矿指标变化不大的前提下,可以适当降低烧结矿固体燃料消耗和生产成本。对干熄焦除尘灰配入钒钛矿烧结固体燃料的可行性及其合理配比进行了探讨,认为干熄焦除尘灰配入钒钛矿烧结是可行的,且配比在0.2%较为适宜。     

海水条件下矿山充填应用粉煤灰的可行性研究

三山岛金矿充填用水中Cl-、SO2-4和Mg2+等离子浓度较高,影响充填体的强度。根据海水和粉煤灰的化学成分检测结果,分析研究海水中氯盐、硫酸盐、镁盐对充填体的破坏机理以及在尾砂胶结充填中粉煤灰在活性效应、粉末效应和形态效应3个方面的作用机理。分析认为,海水成分中的硫酸盐、氯盐和海水的弱碱性成分对化学激发粉煤灰活性发挥重要作用。因此,为了提高海水条件下充填体的强度,添加粉煤灰不仅可以减少海水中相关离子对充填体强度的影响,而且海水中的部分化学成分对粉煤灰活性的激发作用可以进一步提高粉煤灰的胶凝作用。     

高温蒸养对粉煤灰水泥基材料水化产物结构的影响

运用基本力学及导热系数测定实验系统对高温蒸养作用后的粉煤灰水泥基材料的抗压强度和热导率进行了试验研究,并借助于X射线衍射（XRD）、扫描电镜（SEM）和热重-差热分析（TG-DTA）等手段对水化产物的微观结构对其宏观性能的决定性机理进行了分析。结果表明：随蒸养温度的增加,粉煤灰水泥基材料的强度和保温性能均增强。钙矾石（AFt）转变为单硫型水化硫铝酸钙（AFm）,粉煤灰释放珠状的铝、硅成分形成莫来石,水化产物失水后重新结合,晶相、晶形稳定性增强是蒸养后强度及保温性能增强的主要原因。     

Application of fly ash as a catalyst for synthesis of carbon nanotube ribbons

The larger diameter-based carbon nanotube (CNT) ropes and ribbons are currently synthesized by catalytic decomposition of hydrocarbons with transition metal-based catalysts e.g., Co, Ni, Fe and Mo at 1100-1200 °C, using chemical vapour deposition (CVD) and electric arc methods. We produced CNT ribbons by fly ash (FA) catalyzed pyrolysis of a composite film of poly (vinyl alcohol) (PVA) with FA at 500 °C for 10 min under a nitrogen flow of 2 L/min. Different geometrical structures, e.g.; knotted and twisted, U- and spiral-shaped CNT ribbons were observed in the images of scanning and transmission electron microscopy. The widths of the CNT ribbons measured varied in the ranges 18-80 nm. X-ray photoelectron spectroscopy analysis showed five types of carbon binding peaks, C-C/C-H (∼77%), C-O-H (∼9%), -C-O-C (∼5%), CO (∼5%) and -O-CO (∼3%). The ratio of intensities of G and D bands, IG/ID was 1.61 analysed by Raman Spectroscopy. CNT ribbons grown on the surface of FA have potential for the fabrication of high-strength composite materials with polymer and metal.     

Mitigation of damage from molten fly ash to air-plasma-sprayed thermal barrier coatings

Ceramic thermal barrier coatings (TBCs) used in gas-turbine engines afford higher operating temperatures, resulting in enhanced efficiencies and performance. However, in the case of syngas-fired engines, fly ash particulate impurities that may be present in syngas can melt on the hotter TBC surfaces and form glassy deposits. These deposits can penetrate the TBCs leading to their failure. In experiments using lignite fly ash to simulate these conditions we show that conventional TBCs of composition 93 wt% ZrO₂ + 7 wt% Y₂O₃ (7YSZ) fabricated using the air plasma spray (APS) process are completely destroyed by the molten fly ash. The molten fly ash is found to penetrate the full thickness of the TBC. The mechanisms by which this occurs appear to be similar to those observed in degradation of 7YSZ TBCs by molten calcium-magnesium-alumino-silicate (CMAS) sand and by molten volcanic ash in aircraft engines. In contrast, APS TBCs of Gd₂Zr₂O₇ composition are highly resistant to attack by molten lignite fly ash under identical conditions, where the molten ash penetrates ∼25% of TBC thickness. This damage mitigation appears to be due to the formation of an impervious, stable crystalline layer at the fly ash/Gd₂Zr₂O₇ TBC interface arresting the penetrating molten-fly-ash front.