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类型 基础研究 预答辩日期 2018-03-05
开始(开题)日期 2015-11-30 论文结束日期 2017-12-14
地点 材料学院A401 论文选题来源 973、863项目     论文字数 8 (万字)
题目 碳化与荷载耦合作用下水泥基材料微结构演变与预测模型
主题词 水泥基材料,碳化,界面效应,集料效应,预测模型
摘要 混凝土结构处于自然大气环境中,不可避免的要与空气中的CO2发生碳化反应。引起钢筋混凝土结构劣化的诱因之一为混凝土的碳化。在混凝土结构实际应用中,其性能的劣化往往是在荷载及环境等多因素的耦合作用下发生。荷载作用往往更容易引发混凝土内部微结构的破坏,如增大混凝土内部微裂纹,改变孔的连通性,增加CO2扩散通道,导致碳化反应的加剧。荷载作用所引起的混凝土结构劣化,在很大程度上影响了混凝土的抗碳化性能。因此,研究水泥基材料在碳化荷载耦合作用下的耐久性能具有重要意义。 本文采用酚酞法、热分析、X射线断层扫描、纳米压痕、背散射、压汞法对水泥基材料的微观结构及物相组成进行定性及定量的分析表征。研究分析了不同碳化条件对水泥基材料微观结构及物相组成的影响规律、定量表征了碳化前后界面过渡区的物相组成及孔结构演变规律,同时分析了荷载作用对水泥基材料微结构的影响,并基于上述微观结构演变规律建立了考虑荷载、集料、界面过渡区等多因素影响的二氧化碳时空分布模型。本文的主要研究成果如下: 通过研究不同CO2浓度下不同碳化区孔结构的演变,发现与自然碳化相比,3%CO2浓度对试件各碳化区尺寸影响不大,而20%浓度条件对部分碳化区尺寸影响显著,且在相同碳化区间内,CO2浓度越低,碳化越充分,总孔隙率降低,对孔径细化越明显。采用XCT无损测试了不同水灰比的净浆试件,结果表明,低水灰比试件的碳化前沿线较清晰,且部分碳化区尺寸较小,而高水灰比试样则相反。对于掺加掺合料的试件,在水胶比0.35的情况下掺加30%粉煤灰或掺加50%矿渣对试件的完全碳化区尺寸影响不大,而对部分碳化区影响显著。在水胶比0.53情况下,掺加掺合料试件碳化深度高于纯水泥净浆试件。在同种掺合料的条件下,水胶比越小,完全碳化区及部分碳化区尺寸越小。对于不同湿度条件下的碳化结果表明湿度对碳化分区影响显著,湿度为90%时碳化基本不发生,湿度为70%时完全碳化区尺寸与部分碳化区尺寸相当,湿度为50%时,部分碳化区尺寸大于完全碳化区尺寸。 通过研究集料对水泥基材料碳化的影响,发现集料的稀释曲折效应提高混凝土和砂浆抗碳化性能,而界面逾渗效应降低抗碳化性能。哪种效应处于主导地位取决于集料的含量。集料的裹浆厚度与碳化深度有较好的相关性,可以采用裹浆厚度来表征骨料对碳化的影响。对界面效应进行放大实验,结果表明界面传输是基材传输速度的数倍;BSE试验结果证实了未碳化试件中集料-基材的界面过渡区(以下简称ITZ)孔隙率高于基材;碳化使得ITZ孔隙率降低,但仍大于基材孔隙率,ITZ在碳化后仍然是CO2传输的快速通道;纳米压痕试验结果表明,ITZ尺寸随水灰比的降低逐渐减小,碳化后ITZ厚度有所减小,但其尺寸依然保持在20μm~30μm。表明碳化后ITZ仍然是混凝土较薄弱的部位。与纯水泥试样相比,掺加粉煤灰后水泥基材料的微结构得到了改善,同等水胶比下,其孔隙率较纯水泥试样要小,水泥水化更充分。 采用热分析法及压汞法研究了荷载对碳化的影响,结果表明:在拉应力下碳化深度有所增加;在压应力下碳化深度有所减小;在相同深度范围内,受压一侧所残留的CH含量要高于受拉测,表明拉应力作用下试样碳化更充分,拉应力有加速碳化的效应;孔结构参数表明压应力对水泥基材料的孔有细化作用。 采用XCT无损测试了荷载对界面效应的影响,结果表明受拉区的界面效应范围要略高于受压区的界面效应范围。BSE试验结果表明,受压区ITZ与集料粘结较为紧密,与基体的差异不明显,而在受拉区界面过渡区与集料之间有明显的裂纹出现,且在基体上也产生了较明显的裂纹。灰度分析结果表明,不同的荷载形式对水泥基材料孔隙率有着显著的影响:压应力下ITZ及基体的孔隙率均小于未加载试样,而拉应力下ITZ及基体的孔隙率均要大于未加载试样。适当的压应力在一定程度上可以提高ITZ的强度,起到强化界面的效果,而拉应力有使水泥基材料材料劣化的效应。 最后,基于质量守恒和Fick扩散定律建立了考虑多种因素(荷载、集料、界面、孔隙率、孔分布、水灰比等)的CO2时空分布模型,确定了CO2在混凝土中的有效扩散系数和界面过渡区扩散系数。并通过离子平衡方程得到CO2浓度与pH之间的关系曲线及CH与pH之间的关系曲线。通过求解所建立的CO2时空分布模型,计算出不同应力水平下混凝土中CO2的时空分布情况,并采用孔溶液pH=9时所对应的CO2浓度,确定出完全碳化区深度;采用pH=9-11.5所对应的CO2浓度,确定出部分碳化区的尺寸,并与实测值对比,模拟结果与实测值具有较好的一致性。
英文题目 Micro structure evolution and prediction model of cementitious materials under carbonation and loading coupling effects
英文主题词 cement-based materials; carbonation; interfacial effect; aggregate effect; prediction model
英文摘要 It is inevitable that the concrete structure in the natural atmospheric environment is carbonated by CO2 in air. One of the causes of reinforced concrete structure deterioration is the carbonation of concrete. During the practical application of the concrete structure, the deterioration of its performance often occurs under the load and environment coupling effects. The damage of micro-structure in concrete is often caused by load, such as increasing the micro-cracks in concrete, changing the connectivity of pores, increasing the CO2 diffusion channel and leading to the intensification of carbonation reaction. The deterioration of concrete structure caused by load influences the carbonation resistance ability of concrete to a great extent. Therefore, it is significant to study the durability of cement based materials under coupling effect of carbonation and load. In this paper, phenolphthalein spraying method, thermal gravimetric and differential scanning calorimetric analysis, X-ray computed tomography method, nanoindentation, backscattered electron image analysis technology and mercury intrusion porosimetry method are carried out to analyze the microstructure and components of cement-based materials qualitative and quantitative. The law of the phase composition and microstructure of cement-based materials under different carbonation conditions was decided, and the phase composition and pore structure evolution of the interface transition zone before and after carbonation were quantitatively characterized, and at the same time the influence of load on the micro structure of cement based materials was also carried out. The carbon dioxide distribution model which based on the microstructure evolution law and considered the load, aggregate and interfacial transition zone was set up. The following conclusions can be drawn from the results: Compared with that in the natural carbonation condition, the effect of 20% carbon dioxide concentration on the size of the partially carbonated zone was significant. However, no effect was seen for 3% carbon dioxide concentration. MIP showed that, in the same carbonation zone, low carbon dioxide concentration led to low total porosity; there was a clear refinement in the pore size and there was a high degree of carbonation.The specimens with different water cement ratio were nondestructive tested by XCT. The results showed that the specimens with low water cement ratio had the clear carbonation front shape, and the size of partial carbonation zone was small, while the high water cement ratio samples had the opposite law.For the supplementary cementing materials (SCM) specimens with 0.35 water binder ratio, the addition of 30% fly ash and 50% slag had little effect on the carbonated zone size and had significant influence on the partial carbonation zone.For the specimens with 0.53 water binder ratio, the carbonation depth of the SCM specimen is higher than that of the pure cement paste. Under the condition of the same SCM, the smaller water binder ratio is, the smaller size of the carbonated zone and partial carbonation zone. The carbonation results of different humidity showed that the effect of humidity on the carbonation zone was significant. There was almost no carbonation occur when the humidity was 90%; when the humidity was 70%, the complete carbonation zone size and partial carbonation zone size was almost the same, when the humidity was 50%, the partial carbonation zone size was larger than the full carbonation zone size. Through researching on the influence of aggregate on the carbonation of cement based materials, found that the dilution and tortuosity effect of aggregate improves the carbonation resistance ability of concrete and mortar, while the interfacial percolation effect reduces the carbonation resistance ability. Which effect is in the dominant position depends on the aggregate content. The paste thickness had a good correlation with the carbonation depth, so the paste thickness can be used to characterize the effect of aggregate on carbonation. The ITZ effect amplification experiment results show that the diffusion rate of the ITZ is several times the matrix diffusion rate; the BSE test results show that before the carbonation the porosity of ITZ is higher than the matrix, and after carbonation the porosity of ITZ is reduced but still greater than the matrix porosity, after carbonation the ITZ is still the fast channel for CO2 transmission. The nanoindentation test results show that the size of ITZ decrease with the decrease of water cement ratio gradually, after carbonation ,the thickness of ITZ decreases, but its size still remains at 20μm ~30μm. It is shown that the ITZ is still the weakest part of concrete after carbonation. Compared with the pure cement sample, the microstructure of the specimen with fly ash is improved, and the porosity of the SCM specimen is smaller than that of the pure cement sample, and the hydration degree of the cement is more sufficient. The effect of loading on the carbonation is tested by thermal gravimetric analysis method and mercury intrusion porosimetry method, the results show that carbonation depth increased under the tensile stress and carbonation depth reduced under the compressive stress; in the same carbonation depth, the residual CH in the compressive side is higher than that in the tensile side, it’s shown that the sample carbonated more sufficient under the tensile stress, the tension stress can accelerate the carbonation process. The pore structure parameters show that the compressive stress can refine the pores of the cement based materials. The effect of load on the interface effect zone is tested by XCT, the results show that the interface effect zone in the tensile region is higher than that of the compression zone. The BSE results show that the ITZ and aggregate bond very close in the compression zone, and there is no obvious difference between the ITZ and the matrix, while in the tensile zone, there are obvious cracks between the interface transition zone and the aggregate, the obvious cracks also appear in the matrix. The gray scale analysis results show that the different load has significant influence on the porosity of cement-based materials: the porosity of ITZ and matrix under compressive stress is smaller than that of the specimens without loading, while the porosity of ITZ and matrix under tensile stress is greater than that of the specimens without loading. The appropriate compressive stress can improve the strength of ITZ in some extent, and strengthen the ITZ, while the tensile stress has the deterioration effect on the cement-based materials. Finally, based on the quality conservation law and Fick diffusion law the CO2 distribution model established. In the model a variety of factors (load, aggregate, interface, porosity, pore distribution, water cement ratio) are considered, and determine the effective diffusion coefficient of CO2 and the diffusion coefficient of interfacial transition zone in the concrete. The relation curve between CO2 concentration and pH and the relation curve between CH and pH were obtained by ion balance equation. By solving the CO2 distribution model, the distribution of CO2 under different stress levels is calculated. According to the CO2 concentration corresponding to the pore solution pH=9, the depth of the complete carbonation zone is determined and according to the CO2 concentration corresponding to the pH=9-11.5, the depth of the partial carbonation zone is determined, and compared with the measured value, the simulation results agree well with the measured values.
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 2017年9月21日 材料学院A601 单肖文 关于格子玻尔兹曼方法(lattice Boltzmann method, LBM)模拟
东南大学材料科学与工程学院 2017年6月14日 材料学院A601 马朝利 我国航空及海洋关键材料现状分析
东南大学材料科学与工程学院 2017年5月18日 材料学院A601 Shengmin Guo教授 Metal Based 3D Printing
东南大学材料科学与工程学院 2017年5月15日 材料学院B523 胡传林 水泥基材料微结构和微观力学性能研究
东南大学材料科学与工程学院 2014年5月20日 材料学院A439 沈奇真 CH及CSH在动力学、微观结构改变及含水量方面的碳化机理研究
东南大学材料科学与工程学院 2015年5月19日 材料学院A439 沈奇真 Micro-pore Structure Formation and Moisture Transport
东南大学材料科学与工程学院 2015年6月15日 材料学院A439 沈奇真 Fatigue life of structural concrete
东南大学材料科学与工程学院 2015年12月9日 材料学院A439 沈奇真 Quantitative Stereology
     
学术会议
会议名称时间地点本人报告本人报告题目
第十四届国际水泥化学大会 2015.10.13-16 北京 Effect of aggregate on the resistance to carbonation of cement-based materials
2016 3rd International Conference on Chemical and Material Engineering 2016.12. 28-31 韩国济州岛 The carbonation of cement-based materials with different aggregate content
     
代表作
论文名称
Effect of interfacial transition zone on the carbonation of cement-based materials
Influence of CSH carbonation on the porosity of cement paste
Test method to simulate the influence of the interface on the concrete carbonation process
The carbonation of cement-based materials with different aggregate content
加速碳化条件下ITZ过渡区的纳米力学性能
 
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
张亚梅 正高 教授 博导 东南大学
高建明 正高 教授 博导 东南大学
张云升 正高 教授 博导 东南大学
余红发 正高 教授 博导 南京航空航天大学
邓敏 正高 教授 博导 南京工业大学
      
答辩秘书信息
姓名职称工作单位备注
施锦杰 副高 副教授 东南大学