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类型 基础研究 预答辩日期 2018-05-09
开始(开题)日期 2012-10-19 论文结束日期 2018-01-18
地点 材料楼B523 论文选题来源 企、事业单位委托项目    论文字数 7 (万字)
题目 荷载作用下纤维增强水泥基复合材料的传输性能研究
主题词 钢纤维增强混凝土,高延性水泥基复合材料,传输性能,荷载,传输性能模拟
摘要 近年来,我国基础工程建设规模空前,重大桥梁工程、隧道工程、高速铁路和高速公路工程、水利大坝工程等等全面启动。然而由于种种原因,混凝土开裂问题不断出现,工程过早失效和提前退出服役的现象时有发生,不仅需要花费巨额修补费用,而且严重危及到建筑结构的服役性能。提高重大工程的耐久性与服役寿命,已为国内外混凝土科学与工程界高度关注。 纤维增强水泥基复合材料(Fiber reinforced cementitious composites,FRCC)是混凝土改性的一个重要手段,它可以使混凝土的抗拉强度、韧性和耐久性能得到大幅提高。其中钢纤维增强混凝土(Steel fiber reinforced concrete, SFRC)以其优良的物理力学性能在多个领域得到推广,被应用于一系列重大混凝土结构和工程中,极大地改善了工程结构的服役性能。此外,高延性水泥基复合材料(High ductility cementitious composites,HDCC)作为一种新型的FRCC,具有极高的弯拉韧性和优异的裂缝控制能力,用作修复材料时可以限制修复层的裂缝宽度,更好地保护被修复混凝土结构。然而,这两种FRCC在实际工程中的应用并没有预期中广泛。 为了推动FRCC在实际工程中的应用,本文重点研究了荷载作用下两种FRCC的传输性能,以期定量描述其相对普通混凝土服役性能的优势。围绕这一研究目的,本文优化了SFRC和HDCC的原材料和配合比并测试了其基本力学性能;分别研究了弯曲荷载耦合作用下SFRC的氯离子传输性能和压应力作用下HDCC的水渗透性;最后使用HYMOSTRUC模型模拟了两种FRCC的浆体微观结构,计算了浆体和FRCC的传输性能,并考虑了荷载对传输性能的影响。 首先,采用粉煤灰代替部分水泥,确定了水胶比为0.35的SFRC的配合比,测试了SFRC的抗压强度、劈裂抗拉强度和和抗折强度等力学性能,研究了养护龄期和钢纤维掺量对力学性能的影响。结果表明,加入钢纤维后混凝土的抗压强度略有增长,但增幅有限,而劈裂抗拉强度和抗折强度随着钢纤维掺量的提高大幅增长,荷载-挠度曲线显示,SFRC的韧性远远高于普通混凝土。 其次,对主流HDCC的原材料进行优化,使用普通聚乙烯醇(polyvinyl alcohol, PVA)纤维代替表面特殊处理的PVA纤维,使用天然河砂代替了超细石英砂,提高了基体的粉煤灰掺量,并加入适量硅灰,制备出了单轴拉伸性能优异,具有应变硬化和多缝开裂特性的HDCC,极大地降低了HDCC的原材料成本。测试了HDCC的抗压强度和单轴拉伸性能,研究了基体组分、纤维掺量和加载速率等因素对其力学性能的影响。结果表明,随着粉煤灰掺量的提高,HDCC抗压强度和抗拉强度均明显下降,但延性有所改善,HDCC的极限拉伸应变提高。提高水胶比也有类似的作用。使用硅灰不仅可以提高抗压强度和抗拉强度,同时有利于改善纤维与基体的界面性能,从而提高极限拉伸应变。用砂量对抗压强度的影响不大,但提高用砂量对抗拉强度和极限拉伸应变均有较大的不利影响。改变纤维掺量和种类对抗压强度未见显著的影响,但降低PVA纤维掺量会显著降低材料的极限拉伸应变,采用聚酯(Polyesters, PET)纤维难以制备具备应变硬化和多缝开裂特性的HDCC,然而混掺PVA纤维和PET纤维可以制备得到性能较为优异的HDCC。极限拉伸应变随养护龄期的增加先提高,后开始下降并逐渐稳定。随着加载速率的提高,HDCC的强度明显提高,而极限拉伸应变则显著下降。 再次,通过加载装置对SFRC施加应力水平为0.5的弯曲荷载,将试件与加载装置一同放进NaCl溶液中浸泡,通过自然浸泡法测试弯曲荷载对氯离子扩散系数的影响,根据测得的自由氯离子浓度结合Fick第二扩散定律,计算表观氯离子扩散系数。在考虑氯离子扩散系数时间依赖性的基础上,对弯曲荷载作用下SFRC钢筋锈蚀的诱导期进行了预测。结果显示,表观氯离子扩散系数随着浸泡时间的延长呈下降趋势。未加载情况下,钢纤维对混凝土氯离子扩散系数的影响不大。对于弯曲荷载作用下的混凝土而言,SFRC受拉区的氯离子扩散系数明显低于普通混凝土,钢筋锈蚀的诱导期可以延长至普通混凝土的2.2~3.6倍。 采用一种改进的渗透性测试方法,不仅可以在稳态下持续地监测混凝土的水渗透系数,还可以更准确地评估加载和卸载过程对渗透性的影响。研究了HDCC和砂浆试件早龄期的渗透性变化和不同应力水平的压应力加载及卸载对渗透性的影响。结果显示,未加载的HDCC和砂浆试件渗透系数随着龄期的增长呈现出稳定的下降趋势,HDCC的渗透系数略低于砂浆。当压应力水平较低时,压应力对HDCC和砂浆的渗透系数均没有明显的影响。当应力水平超过一定的临界值(称为临界应力水平)后,对试件施加压应力会引起渗透系数的增长,而卸载压应力后渗透系数会有一定程度的下降,并且随着应力水平的提高,加载时渗透系数会出现较大幅度的增长。HDCC的临界应力水平在0.5~0.6之间,而普通砂浆的临界应力水平在0.4~0.5之间。当应力水平为0.7时,加载引起的砂浆渗透系数的增量比HDCC高两个数量级。 最后,使用HYMOSTRUC水化模型,分别模拟了SFRC浆体和HDCC浆体的三维微观结构,提取出孔结构信息后,利用孔隙率与氯离子扩散系数的关系计算浆体的氯离子扩散系数,根据一般有效介质理论计算浆体的水渗透系数,考虑集料粒径分布和界面过渡区的影响,根据广义自洽模型计算基体的传输性能,并引入应力影响因子表征荷载对传输性能的影响。结果表明,SFRC氯离子扩散系数的预测结果与试验结果吻合较好,HDCC的水渗透系数预测值低于实验值,误差在可接受范围内。
英文题目 Transport Property of Fiber Reinforced Cementitious Composites under External Load
英文主题词 Steel fiber reinforced concrete (SFRC), High ductility cementitious composites (HDCC), Transport property, Load, Transport property simulation
英文摘要 The scale of infrastructure construction in China is unprecedented in recent years. Many major projects have been under construction, including bridges, tunnels, high speed railways, highways, hydroelectric dams, etc. However, the cracking in concrete constantly occurs, resulting in premature failure and sharp reduction in their service life of concrete structures. The service characteristics of these structures would be greatly compromised and it costs enormous expenses for the repair work. Therefore, improving the durability and service life of concrete structures has attracted great attention in the field of concrete science and engineering at home and aboard. Fiber reinforced cementitious composites (FRCC) is an important and effective way to favorably modify the properties of concrete. The tensile strength, toughness and durability of concrete can be greatly improved by adding fibers. Steel fiber reinforced concrete (SFRC) had been applied in various fields due to its excellent mechanical properties. The application of SFRC in major constructions significantly improves their service characteristics. Moreover, a new type of FRCC, which is called high ductility cementitious composites (HDCC), exhibits extremely high toughness and excellent ability in crack control. The application of HDCC as a repair material can restrain its crack width and provide better protection for the parent concrete structure. Surprisingly, the applications of SFRC and HDCC are not wide enough as expected in real constructions. The purpose of this research is to promote the application of FRCC in real constructions. In order to prove the advantages of FRCC quantificationally over normal concrete, the dissertation focused on the transport properties of SFRC and HDCC under external load. The raw materials and mix proportions were optimized and the mechanical properties of SFRC and HDCC were tested. The chloride transport property of SFRC under applied bending load and the water permeability of HDCC under applied compressive stress were studied. The microstructure of SFRC paste and HDCC paste were simulated with HYMOSTRUC model. The transport properties of paste and FRCC were calculated and the effect of load was considered in the model. SFRC specimens with a w/b ratio of 0.35 were prepared. Cement in SFRC was partially replaced with fly ash (FA). The compressive strength, splitting tensile strength and flexural strength were tested. The influences of curing age and fiber volume fraction on the mechanical properties were investigated. The results showed that steel fibers could slightly improve the compressive strength of concrete, although the increase was generally small. The splitting tensile strength and flexural strength were greatly improved by steel fibers. The load-deflection curve indicated that the toughness of SFRC was much higher than that of plain concrete. The raw materials and mix proportions of HDCC were optimized to reduce the materials cost and improve its greenness. Surface-oiled polyvinyl alcohol (PVA) fibers were replaced with regular PVA fibers, and microsilica sand was replaced with natural sand. The FA content was increased and silica fume (SF) was added in the matrix as well. The HDCC prepared exhibited strain-hardening and multiple cracking behavior. The compressive strength and uniaxial tensile property of HDCC were tested and the influences of matrix composition, fiber volume fraction and loading rate were investigated. The results showed that as the content of FA increased, the compressive strength and tensile strength decreased, but the ductility of HDCC was improved and the tensile strain capacity was increased. The effect of w/b ratio on mechanical properties was similar with FA. The addition of SF could improve the compressive strength and tensile strength. The fiber/matrix interface was improved by SF, resulting in an increase in strain capacity of HDCC. The sand content had an insignificant effect on compressive strength, while the tensile strength and strain capacity would be reduced by increasing sand content. Fiber type and volume fraction didn’t affect the compressive strength significantly. Reducing the volume fraction of PVA fibers would greatly reduce the strain capacity of HDCC. Cementitious composites with Polyesters (PET) fibers didn’t exhibit strain-hardening or multiple cracking behavior. However, composites with hybrid fibers (PVA and PET fibers) attained strain-hardening behavior. As the curing age increased, the strain capacity increased firstly, then started to decrease. The tensile strength of HDCC increased remarkably under a higher loading rate, while the tensile strain capacity decreased greatly. The effect of load on chloride transport property of SFRC was investigated through bulk chloride diffusion test. SFRC specimens was subjected with bending load at a stress level of 0.5 through loading device. Based on the Fick’s second law, the apparent chloride diffusion coefficient was calculated with the concentration distribution of free chloride in SFRC. The time-dependence of chloride diffusion coefficient was taken into consideration. The corrosion initiation of SFRC under bending load was predicted. The results indicated that the apparent chloride diffusion coefficient decreased as the immersion time increased. For unstressed specimens, the addition of steel fiber had insignificant effect on chloride diffusion coefficient. For specimens under bending load, the chloride diffusion coefficient of SFRC under tension was much lower than that of plain concrete. The application of SFRC could prolong the initiation period of concrete structures to 2.2~3.6 times of that for plain concrete. Water permeability of HDCC was measured with an adapted permeability test setup under water equilibrium condition. The permeability could be monitored continuously, and the response of permeability to both loading and unloading could be evaluated. The permeability evolution of HDCC and control mortar specimens at early ages was recorded, and the influence of compressive stress at different stress levels was investigated. The results showed that the permeability of unstressed HDCC and mortar specimens decreased over time. Permeability of HDCC was slightly lower than mortar. Compressive stress at low stress levels had no obvious influence on permeability of both HDCC and mortar specimens. When the stress level exceeded a critical level (referred as critical stress level), permeability increased as the compressive stress was applied to the specimen, and it decreased to some extent when the specimen was unloaded. Beyond the critical stress level, the permeability increased remarkably as the stress level increased. The critical stress level was 0.5~0.6 for HDCC, and 0.4~0.5 for control mortar. When compressive stress at stress level of 0.7 was applied to the specimens, the increase in permeability of mortar due to loading was two orders of magnitude higher than that of HDCC. The microstructures of SFRC paste and HDCC paste were simulated with HYMOSTRUC hydration model. The pore structure information was obtained and used to calculate the chloride diffusion coefficient of paste. The permeability coefficient of paste was calculated based on the general effective media theory. The influences of grain size distribution and interfacial transition zone on transport property of concrete were taken into consideration with general self-consistent scheme. The transport property of FRCC was predicted accordingly and the effect of load was expressed with a stress factor. The chloride diffusion coefficient of SFRC from calculation agreed well with results from tests. The calculated water permeability coefficient of HDCC was lower than the measured value, while the error was acceptable.
学术讨论
主办单位时间地点报告人报告主题
东南大学材料科学与工程学院 2014.05.23 东南大学材料科学与工程学院 王倩楠 工程水泥基复合材料的制备和渗透性研究
Department of Civil Engineering, University of British Columbia 2013.12.06 Department of Civil Engineering, University of British Columbia 王倩楠 Development and permeability study of ECC
American Concrete Institute 2013.05.10 Vancouver Cristina Zanotti Physics behind why Repairs fail
American Concrete Institute 2012.04.27 Vancouver Sidney Mindess Sustainability of Concrete
Department of Civil Engineering, University of British Columbia 2012.04.26 Department of Civil Engineering, University of British Columbia 王倩楠 A sprayable high strain capacity repair material
Department of Civil Engineering, University of British Columbia 2012.01.20 Department of Civil Engineering, University of British Columbia 王倩楠 A study on the durability of SFRC under coupled effect of environment and load
东南大学材料科学与工程学院 2011.09.20 东南大学材料科学与工程学院 王倩楠 Stage Report of Bekaert-Southeast University Cooperation Project
东南大学材料科学与工程学院 2011.06.01 东南大学材料科学与工程学院 王倩楠 贝卡尔特项目阶段性汇报
     
学术会议
会议名称时间地点本人报告本人报告题目
Fiber Concrete 2013 2013.09.12-13 捷克布拉格 Development of ECC with Non-Oiled PVA Fibers and Natural Sand
第十三届纤维混凝土学术会议 2010.10.28-29 南京 钢纤维混凝土抗氯离子侵蚀性能的试验研究
     
代表作
论文名称
PREDICTION OF CHLORIDE INGRESS IN STEEL FIBRE REINFORCED CONCRETE UNDER BENDING LOAD
Water permeability of repair mortars under an applied compressive stress at early ages
Modeling chloride diffusion coefficient of steel fiber reinforced concrete under bending load
 
答辩委员会组成信息
姓名职称导师类别工作单位是否主席备注
缪昌文 正高 教授 博导 东南大学
蒋正武 正高 教授 博导 同济大学
范进 正高 教授 博导 南京理工大学
张亚梅 正高 教授 博导 东南大学
张云升 正高 教授 博导 东南大学
      
答辩秘书信息
姓名职称工作单位备注
冯攀 其他 讲师 东南大学