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类型 基础研究 预答辩日期 2017-09-20
开始(开题)日期 2015-06-12 论文结束日期 2017-05-18
地点 九龙湖校区材料B楼523会议室 论文选题来源 973、863项目     论文字数 9.9 (万字)
题目 非饱和混凝土水分与氯离子传输行为研究
主题词 非饱和混凝土,氯离子传输,吸水,耐久性
摘要 随着“一带一路”、“西部大开发”和“海洋强国”国家战略的实施,大量的混凝土结构服役于严酷的环境中,其耐久性和安全性将面临严峻的挑战。实际工程中,处于水位变动区、浪溅区、干湿交界处的混凝土结构往往劣化最早,破坏也最为严重,主要原因是该区域的混凝土处于非饱和状态,外界有害介质在扩散、对流等多种机制下侵入,严重影响了混凝土结构的服役寿命,是结构耐久性设计的关键。研究非饱和混凝土的介质传输对于完善混凝土结构耐久性理论、提高耐久性设计水平具有重要意义,同时也为混凝土结构的寿命预测、维修与维护提供理论支撑。 本文基于多孔介质理论和复合材料理论,以试验研究与模拟相结合,综合运用传统试验方法与现代分析测试技术,首先研究混凝土对水蒸气的等温吸附、脱附,并从定量和可视化的角度系统研究了非饱和混凝土的毛细吸水过程、特征和规律,同时以模型计算与试验相结合的方法研究了非饱和混凝土的氯离子传输行为,最后探究了带裂缝和损伤混凝土的水分与氯离子传输特性。得到以下创新成果: 一、混凝土等温吸附-脱附特性 以不同种类饱和盐溶液创造特定湿度环境,通过试验获得混凝土对水蒸气的等温吸附-脱附曲线,基于Laplace方程和Kelvin公式进一步得到水分特征曲线,在此基础上建立混凝土液相/气相相对渗透系数、液态水/水蒸气扩散系数与混凝土饱和度的关系。系统研究了水灰比、矿物掺合料种类与掺量对混凝土等温吸附-脱附特性、水分渗透性与扩散系数的影响,得到以下结论:(1)混凝土的脱附存在明显的滞后效应,吸附-脱附曲线滞回环面积能有效表征混凝土孔结构特征。(2)RH<70%时,混凝土凝胶孔吸附达到饱和,当RH>70%毛细孔逐渐饱和,混凝土的饱和度迅速增大。(3)随着混凝土饱和度的增加,气相渗透系数逐渐减小,液相渗透系数逐渐增大;当混凝土处于低饱和度(θ<0.5)时,水分传输以水蒸气扩散为主,而当饱和度大于0.6~0.7时,孔隙水连通,液态水扩散逐渐占据主导地位。 二、非饱和混凝土水分传输的定量与可视化 发明了X-CT联合Cs离子增强原位、连续监测净浆、砂浆、混凝土毛细吸水过程的无损测试方法(专利申请号201510617455.2),显著提高了CT图像的对比度,可以准确判定水分的传输距离,为可视化追踪多孔材料的水分传输提供了有力工具,并利用该方法系统研究了水灰比、矿物掺合料、砂体积掺量等因素对水分传输的影响。基于重量法定量表征非饱和混凝土的毛细吸水,建立了混凝土吸水系数S与饱和度θ之间的定量关系:S=a(1-θ)b,为非饱和混凝土的耐久性研究提供基础。基于多孔介质水分传输理论与毛细吸水试验,构建了非饱和混凝土毛细吸水过程中水分时空分布计算模型,同时建立了毛细系数k与吸水系数S之间的理论关系:S/k=φ,并以试验予以验证。 三、非饱和混凝土氯离子传输试验研究与模型计算 分两种情况研究了非饱和混凝土的氯离子传输:(1)当混凝土不与外界发生水分交换,饱和度恒定时,氯离子的传输以扩散机制控制,修正了非饱和混凝土氯离子扩散模型,利用修正后的模型计算了不同饱和度混凝土的氯离子扩散系数;(2)当混凝土发生毛细吸水,饱和度动态变化时,采用自然浸泡法研究非饱和混凝土扩散-对流机制下的氯离子传输,系统研究了水灰比、粉煤灰掺量、矿渣掺量、盐溶液浓度、浸泡时间对氯离子传输的影响;建立了非饱和混凝土氯离子扩散系数与初始饱和度的经验关系,D(θ)/Ds=ea(1-θ);构建了非饱和混凝土吸水系数与氯离子扩散系数之间的关系,S2/D=100φ(1-θ)6.75(W/C)+0.42,为非饱和混凝土氯离子扩散系数的快速获取提供了新方法。 四、开裂混凝土(砂浆)的水分与氯离子传输 通过嵌入钢片制备带裂缝砂浆试件,采用X-CT联合Cs离子增强技术原位追踪了带裂缝砂浆的水分传输,获得了裂缝宽度(0.05mm、0.1mm、0.2mm、0.4mm、0.6mm)、取向(纵向、横向)对水分传输的影响规律。在考虑吸水方向(向上、向下)的情况下,基于重量法研究了裂缝宽度对吸水系数的影响。同时,试验与模拟相结合研究了裂缝宽度对氯离子传输深度、扩散系数的影响,且考虑了重力作用的影响。另外,利用有限元模拟的方法研究了裂缝形态、内部缺陷、ITZ对氯离子传输的影响。结果表明:水分的上升高度随着纵向裂缝宽度的增大而减小,非饱和砂浆内横向裂缝的出现阻断了水分的传输路径,使水分绕过裂缝在砂浆中传输;非饱和情况下,影响水分、氯离子传输的临界裂缝宽度为0.1mm;饱和情况下,影响氯离子传输的临界裂缝宽度为0.2mm;重力作用的存在促进了水分与氯离子的传输。 五、冻融、荷载损伤混凝土的水分与氯离子传输 以冻融、荷载两种方式制备了不同损伤程度的混凝土,通过毛细吸水、电通量法研究损伤混凝土的水分与氯离子传输,建立了吸水系数、电通量与混凝土损伤度的关系。研究结果表明:混凝土的吸水系数随着损伤度的增大以线性或指数增长,同等损伤程度下,冻融损伤混凝土的吸水系数大于荷载损伤混凝土;冻融、荷载损伤混凝土的电通量均随着损伤度的增大线性增加;在饱和状态下,同等损伤度的混凝土抗氯离子渗透性接近,而当处于非饱和状态时,冻融损伤混凝土更易受到有害介质的侵蚀。
英文题目 INVESTIGATION OF MOISTURE AND CHLORIDE ION TRANSPORT IN UNSATURATED CONCRETE
英文主题词 Unsaturated concrete,hloride transport,Water absorption,durability
英文摘要 With the strategy implementation of “One Belt and One Road”, “Western Development” and “Marine Potestatem”, a great deal of concrete structures are used in harsh environments, then the durability and safety of concrete structures meet great challenge. In actual project, the concrete structures serviced in tidal zone, splash zone and wetting-drying zone usually deteriorates at the earliest time and the damage degree is the most serious. The main reason is that the concrete structures in these zones are unsaturated and the harmful medium transport into concrete by the mechanisms of diffusion and convection, which seriously affect the service life of concrete structure and is the critical point to the durability design of concrete structures. Therefore, it is of great significance to investigate medium transport in unsaturated concrete, which not only improves the durability theory and design level but also provides theoretical support for the prediction of service life, repair and maintenance of concrete structures. Based on the theories of porous media and composite material, moisture and chloride ion transport in unsaturated concrete were systematically investigated by experiment and simulation. Traditional test methods and modern analysis techniques were used together in this study. The isothermal adsorption-desorption behaviors of concrete were investigated firstly and water capillary suction process, feature and law of unsaturated concrete were studied quantitatively and visually. Meanwhile, the behavior of chloride transport in unsaturated concrete was investigated by experiment combined with modeling. In addition, water and chloride transport in cracked and damaged concrete were also investigated in this work. Several important innovative results are as follows: (1) Isothermal adsorption-desorption behaviors of concrete Special environment with different relative humidity was produced by various saturated salt solution and the isothermal adsorption-desorption curves of concrete were obtained from the experiment. In accordance with the curves, combined with Laplace equation and Kelvin equation, the moisture characteristic curves of concrete were obtained in further. Based on above results, the relationships between liquid/gas relative permeability, diffusion coefficient and saturation degree of concrete were established. Effects of water to cement ratio (W/C), mineral admixture type and content on the isothermal adsorption-desorption behaviors, permeability and diffusion coefficient of concrete were investigated systematically. The results show that hysteresis effect is obvious in the process of desorption and the area of hysteresis ring can be used for the characterization of pore structure. Gel pores in concrete can be saturated by adsorption when RH<70%, while capillary pores are gradually saturated when RH>70% and the saturation degree of concrete increases rapidly. The relative permeability of gas phase decreases with the saturation degree of concrete increasing while the permeability of liquid phase improves gradually. Water vapor diffusion is the main transport method when the saturation degree of concrete is lower (θ<0.5), however, pore water is continuous when θ>0.6~0.7 and the diffusion of liquid water is more and more dominant. (2) Water transport in unsaturated concrete: quantitative and visualization A technique of X-CT combined with Cs enhancing was created to continuously monitor water transport in cement pastes, mortars and concretes (patent No.201510617455.2). The contrast of CT images was greatly improved and the distance of water transport in materials could be determined exactly, which provided a powerful tool for the visualization of water transport in porous materials. With this technique, effects of W/C, mineral admixture and volume content of sand on water transport in cement-based materials were studied systematically. Based on the gravimetric method, water absorption of unsaturated concrete was characterized quantitatively and the relationship between sorptivity (S) and saturation degree (θ) was established, S=a(1-θ)b, which is the basis for the durability research of unsaturated concrete. In accordance with water transport theory of porous media and water absorption experiment, a model for calculating moisture distribution in the process of water absorption was proposed. Meanwhile, the theoretical relationship between capillary coefficient (k) and sorptivity (S) was established, S/k=φ, which was also verified by experiment results. (3) Chloride transport in unsaturated concrete: experiment and modeling Chloride transport in unsaturated concrete was studied in two conditions: 1) When the moisture in concrete does not exchange with environment and the saturation degree is constant, chloride transport in concrete is controlled by the mechanism of diffusion. The model of chloride diffuses in unsaturated concrete was modified and the chloride diffusion coefficients of concrete with different saturation degree were calculated by the modified model. 2) When water absorption takes place in concrete and the saturation degree changes with time, natural immersion method was used to investigate chloride transport in unsaturated concrete with the mechanism of diffusion-convection. The influences of W/C, fly ash content, slag content, concentration of salt solution and immersion time on chloride transport were investigated systematically. An empirical relationship between chloride diffusion coefficient and initial saturation degree of concrete was established, D(θ)/Ds=ea(1-θ). The relationship between sorptivity and chloride diffusion coefficient for unsaturated concrete was proposed, S2/D=100φ(1-θ)6.75(W/C)+0.42, which provided a new method for calculating chloride diffusion coefficient of unsaturated concrete. (4) Water and chloride transport in cracked concrete (mortar) Cracked mortars were prepared by inserting steel slices. The process of water transport in cracked mortar was in situ continuously tracked by the technique of X-CT combined with Cs enhancing. Effects of crack width (0.05mm, 0.1mm, 0.2mm, 0.4mm and 0.6mm) and direction (longitudinal and horizontal) on water transport in cracked mortar were investigated. With the consideration of absorption direction (upward and downward), the effect of crack width on the sorptivity is investigated by the gravimetric method. At the same time, the effect of crack width on chloride penetration depth and diffusion coefficient was studied by experiment and simulation, besides, the gravity effect was also considered in this work. In addition, effects of crack type, void and ITZ on chloride transport were investigated by finite element method. Results show that the height of water uptake in cracked mortar decreases with crack width increasing. The paths of water transport in unsaturated mortar can be broken by internal cracks, and then water bypasses the cracks and transport in matrix. At unsaturated state, the critical width of crack that affects the transport behavior of water and chloride is 0.1mm; however, at saturated state, the critical width of crack that affects chloride transport is 0.2mm. The existence of gravity effect accelerates the transport of water and chloride. (5) Water and chloride transport in damaged concrete induced by freeze-thawing and loading Damaged concretes were prepared by the methods of freeze-thawing and loading. The behaviors of water and chloride transport in damaged concrete were investigated by water absorption and electric flux method. The relationship between sorptivity, charge passed and damage degree of concrete was established, respectively. Results show that the sorptivity of concrete increases in linear or exponential with the damage degree increasing. With same damage degree, the sorptivity of concrete damaged by freeze-thawing is larger than that of concrete damaged by loading. Charge passed through damaged concrete induced by freeze-thawing and loading increases linearly with the damage degree increasing. At saturated state, for concrete suffered from same damage degree of freeze-thawing or loading, the resistance of chloride permeability is closed to each other; however, at unsaturated state, the concrete damaged by freeze-thawing is more vulnerable to harmful medium.
学术讨论
主办单位时间地点报告人报告主题
东南大学材料学院 2016.5.30 五四楼材料学院 董必钦 滨海混凝土中水和二氧化碳的问题
东南大学材料学院 2016.8.17 材料B楼523会议室 Mingzhong Zhang Pore-scale Modelling of Moisture Distribution in Unsaturated Cementitious Materials
东南大学材料学院 2014.11.15 材料A楼401会议室 杨林 非饱和混凝土水分传输研究进展
东南大学材料学院 2016.01.07 材料A楼401会议室 杨林 非饱和混凝土水分传输与氯离子浓度测定
东南大学材料学院 2016.5.11 五四楼材料学院会议室 杨林 X-CT原位监测水泥基
东南大学材料学院 2013.12.06 材料B楼523会议室 苏权科 港珠澳大桥建设技术和耐久性
东南大学材料学院 2016.4.07 材料B楼523会议室 Tang Luping Innovative Research for Greener Construction Materials
东南大学材料学院 2013.11.07 材料B楼203A室 杨林 Moisture transport in concrete: experiment methods
东南大学材料学院 2015.11.23 材料A楼601会议室 杨林 压汞测试技术与数据
     
学术会议
会议名称时间地点本人报告本人报告题目
International Conference on Mechanics, Building Material And Civil Engineering 2015.8.15-16 广西,桂林 In-situ Monitoring Moisture Transport in Concrete Using Automatic Humidity Recorder
The 35th Cement and Concrete Science Conference 2015.8.26-28 Aberdeen, UK Preparation of cement-based self-leveling mortar using untreated phosphogypsum
The 3rd International Conferences on Microstructure Related Durability 2016.10.26-28 南京 Study on Water Transport in Cement-based Materials by X-ray CT
     
代表作
论文名称
In-situ tracking of water transport in cement paste using X-ray computed tomography combined with Cs
Utilization of original phosphogypsum as raw material for the preparation of self-leveling mortar
 
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
蒋林华 正高 教授 博导 河海大学
高建明 正高 教授 博导 东南大学
朱海堂 正高 教授 博导 郑州大学
余红发 正高 教授 博导 南京航空航天大学
蒋金洋 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
佘伟 其他 讲师 东南大学