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类型 综合研究 预答辩日期 2018-05-09
开始(开题)日期 2015-12-10 论文结束日期 2018-01-18
地点 材料楼B523 论文选题来源 973、863项目     论文字数 7.5 (万字)
题目 水泥基材料微结构、碳化以及考虑气候变化的碳化深度预测模型研究
主题词 碳化,水泥基材料,衰减法,断层扫描成像(CT),微结构
摘要 在与钢筋混凝土服役寿命相关的耐久性指标里,一个重要的指标即为混凝土的抗碳化性能。碳化反应的发生,会导致混凝土内部的碱度逐渐下降,从而引起钢筋脱钝、加速钢筋的锈蚀,并最终使得建筑物提前失效。从上个世纪开始,随着工业化进程的加速和全球人口的爆炸性增长,全球范围内的大气温度和CO2浓度均有显著上升,这些变化又会加快建筑物碳化的速率。 为了弄清混凝土碳化的机理,进而实现对碳化问题的有效控制,本文将一种新的材料表征方法(扩展X射线衰减测试方法,XRAM)引入到水泥基材料表征中,在明确了该方法在水泥基材料表征方面的可行性和适用范围以后,本文采用该方法研究了水泥基材料经历不同预处理后,在加速碳化过程中,内部物相、微结构以及水分分布的演变规律,从而得出了最适宜实验室的碳化预处理方案。在此基础上,本文还通过XRAM研究了粉煤灰替代部分水泥后,水泥基材料在碳化过程中的微结构演变情况,从而探究了粉煤灰替代条件下,水泥基材料的碳化机理。此外,本文通过开展加速碳化试验,测试了纤维素纤维的引入对水泥基材料碳化行为的影响。最后,基于XRAM的结果和加速碳化试验的结果,本文完善了一种考虑全球气候变化的碳化深度预测模型,在考虑纤维可能会影响微结构的前提下,采用模型预测了部分国内城市 ( 北京、南京、广州、济南 ) 的建筑物到2100年的碳化深度。本研究得到的主要结论如下: 1) 通过测试两相材料(硬化水泥浆体-石子)的界面过渡区宽度和平均孔隙率,并将结果与文献结果对比,本文验证了扩展X射线衰减系数方法 (XRAM) 在水泥基材料表征方面的可行性。 2) 率先将医学领域的增强造影方法引入水泥基材料领域,从而实现了砂浆内各物相的区分。同时,碘化钾首次被用作砂浆的造影剂,这种试剂可以选择性地增强硬化水泥浆体的线吸收系数,而不对石英砂产生影响。 3) 提出了一种改进的扩展X射线衰减测试方法(XRAM),在孔隙率测试时,将传统XRAM中的干燥步骤替换为饱碘步骤,从而避免干燥对水泥基材料微结构的损伤,得到更加接近完好试样的微结构。 4) 建立了基于实验的净浆、砂浆代表单元体积确定方法,明确了XRAM在水泥基材料表征上的适用条件,也验证了以往通过模拟得出的代表单元体积结果。在净浆方面,实验确定的代表单元体积与HYMOSTRUC模型确定的代表单元体积均在数百微米的量级;而在砂浆方面,实验测得的代表单元体积约为最大集料粒径的3到4倍,这一结果也与模拟中得到的3到5倍基本一致。 5) 评估了预处理方案对加速碳化试验的影响。本文研究表明,各种预处理方案均会对试样引入损伤。与水养的试样相比,标准养护的试样,在预处理后损伤程度相对较小。烘箱干燥后,试样表面有过度干燥的现象,这一现象会导致对早期碳化深度的高估。相比烘箱干燥,湿度平衡后,试样的内部水分分布更加均匀。同时,湿度平衡的试样在碳化过程中,内部湿度波动程度更小。此外,通过脱吸附曲线,本研究建立了碳化过程中,试样内部的湿度分布曲线,从而证实,实际发生碳化处的湿度水平,要高于碳化箱内部的湿度水平。 6) 研究了粉煤灰替代部分水泥后,碳化对微结构的影响。本文研究表明,碳化会导致粉煤灰替代水泥试样内部半径在3纳米以下的孔数目增加,而这部分孔的变化可以通过XRAM测得。同时,基于一维即时孔隙率曲线,本文判定,粉煤灰替代水泥后,大多数加速碳化过程仍为扩散控制的过程。此外,本文尝试性地借助干燥试样的CT重构图,分析了C-S-H在碳化过程中的放水量。 7) 研究了纤维增强水泥基材料碳化速率以及湿度对其的影响。本文研究表明,纤维掺加后,水泥基材料的碳化过程,仍可看作一个扩散主导的过程。在0.3%的纤维掺量下,净浆、砂浆与混凝土的碳化行为以及微结构、物相演变情况,均与未掺纤维试验组相近;而在0.6%的纤维掺量下,净浆、砂浆与混凝土的碳化速率,均高于同配比无纤维试验组的碳化速率,同时,可以观察到微结构因为高纤维掺量而出现劣化。在80%和65%的湿度水平下,无纤维组与0.3%纤维掺量试验组,碳化行为差异不显著;而在50%的湿度水平下,无纤维组的碳化速率更快。结合碳化前沿不规则的形貌,本论文总结,适量的纤维掺加,可以抑制水泥基材料的开裂,从而减慢碳化的速率。此外,根据实验拟合结果,本研究表明,在无纤维掺加时,最适宜碳化的湿度水平为50%,而在0.3%纤维掺量下,最佳的湿度水平约为57%。 8) 在考虑气候变化前提下,采用改善的碳化深度预测模型,预测了国内部分城市建筑物到2100年的碳化深度。本文结论表明,由于人口密集以及化石燃料的使用,城市局部的CO2浓度,要显著高于全球平均CO2浓度。这一现象,会对城市建筑物的碳化,产生显著的加速作用。在不掺加纤维的条件下,如果不控制气候恶化,2100年南京、济南、广州建筑物的预测碳化深度分别为50毫米,57毫米,40毫米,而北京建筑物的预测碳化深度则在2080年即可达到60毫米。如果考虑纤维的阻裂作用,北京建筑物碳化深度达到60毫米的时间点预测可以推后8 年,相应的,济南2100年的预测碳化深度,也从57毫米下降到52毫米(考虑不控制气候恶化的情形)。
英文题目 Microstructure, Carbonation of Cement-Based Materials and Models Predicting Carbonation Depths in the context of Global Climate Change
英文主题词 carbonation,cement-based materials,attenuation method,computed tomography(CT),microstructure
英文摘要 Among the variant durability indexes concerning the service life of reinforced concrete, one important index is the resistance toward carbonation. Carbonation incurs gradual reduction of pH inside concrete, which will further depassivate the reinforcement and accelerate the steel corrosion, leading to failure of the whole construction ahead of expected service life. With accelerated industrialization process and drastic population increase started from last century, both global temperature and the CO2 concentration have gained significant increase. The increase will further accelerate the carbonation speed. To understand the carbonation mechanism as well as to control the carbonation issue, one new material characterization technique (extended X-ray attenuation method, XRAM) was introduced in the present research for the characterization of cement-based materials. After confirming the reliability and applicable scope of XRAM, the method was applied to investigate the evolution patterns of chemical reaction, microstructure and moisture for cement-based materials during carbonation after different preconditioning schemes, and the most suitable preconditioning scheme for laboratory was determined then. By employing this extended XRAM, the evolved microstructure of cement-based materials blended with fly ash during carbonation was studied as well. Besides, through accelerated carbonation tests, the influence of cellulose fibre on carbonation was investigated. Moreover, combining results from XRAM and results from accelerated carbonation tests, a model which predicts carbonation depth in the context of global climate change was refined. The refined model was further applied to predict the carbonation depth of infrastructures in four China cities (Beijing, Nanjing, Guangzhou and Ji’nan) in year 2100. The main conclusions from this research are listed as follows, 1) The width and the average porosity of interfaces from a two-phase (hydrated cement paste - aggregate) material were measured by extended XRAM, the results were compared with literature, and the reliability of extended XRAM in characterization of cement-based materials was therefore, attested. 2) Staining technique, which is commonly used in medical science, was applied first time for characterization of cement-based materials, and phases of mortar were identified through the technique. Besides, potassium iodide (KI) was used first time as the staining agent in mortar, the chemical can selectively strengthen the attenuation coefficient of hydrated cement paste, while leave the quartz sand unaffected. 3) A refined X-ray attenuation method (XRAM) was introduced. During calibration of porosity, the drying procedure, which is indispensable in traditional attenuation method, was substituted with the staining procedure. Since drying is no longer necessary, the refined method can avoid additional, unspecified damage due to drying, so the revealed microstructure should be closer to that of the intact specimens. 4) Experimental validation of representative elementary volume (REV) was applied. The work can help determine the applicable scope of extended XRAM in cement-based materials, and can help validate the REV determined from modelling. For pastes, both REVs determined from experiments or from HYMOSTRUC model are of the order of hundreds of microns. For mortars, the REV is determined to be 3 to 4 times greater than the maximum sand size based on experiment, which is also in good agreement with that determined from modelling, where a REV is suggested to be 3 to 5 times greater than the maximum sand size. 5) The influence of preconditioning schemes on carbonation was evaluated. This research reveals that all preconditioning schemes would incur damage, and the damage extent would be lower for standard-cured specimens as compared to water-cured specimens. After oven drying, the specimen surface suffers from excessive dryness, which will further lead to an exaggeration of early-age carbonation speed. After mass balancing, the inner moisture distribution would be more uniform, and less fluctuation of humidity would occur during accelerated carbonation. In addition, with desorption isotherm curves, the profiles of local humidity were built in this research, and based on the humidity profiles, the local humidity where carbonation performed, was confirmed to be higher than the humidity level in the carbonation chamber. 6) The evolved microstructure of fly ash blended paste specimens subjected to accelerated carbonation was investigated. The results reveal that carbonation leads to an increase on the number of pores with radius smaller than 3 nm, and that part of increase can be quantified by XRAM. Besides, based on instant porosity profiles, most accelerated carbonations were proved to be diffusion-controlling processes. Moreover, exploratory work was carried out in this research to evaluate the content of released water by C-S-H carbonation. 7) The influence of cellulose fibre on carbonation speed subjected to different humidity levels was studied. This study reveals that, with the incorporation of cellulose fibre, carbonation processes can still be regarded as diffusion-controlling processes. With 0.3% fibre content, carbonation behaviours, microstructure and chemical compositions of both pastes, mortars and concretes evolved in a pattern similar to that of campaigns containing no fibre. However, with 0.6% fibre content, carbonation speed gained a significant increase, and clear microstructure deterioration was observed. Under the humidity level of 80% or 65%, the carbonation behaviours between no-fibre campaign and 0.3%-fibre campaign showed no clear difference; however, under humidity level of 50%, no-fibre campaign carbonated faster. Combining the irregular-shaped carbonation front in no-fibre campaign, this study attests, suitable fibre content could increase the resistance toward cracking in cement-based materials without altering their pore structure, the carbonation speed was therefore, slower. In addition, according to fitted results based on experimental data, this research refers 50% to be the optimal humidity level for no-fibre campaign, while 57% to be the optimal humidity level for 0.3%-fibre campaign regarding carbonation. 8) In the context of global climate change, one refined carbonation model was used to predict the carbonation depths of some mainland cities in year 2100. This study reveals that, due to booming population and large consumption of mineral fuels, urban CO2 concentrations are significantly higher than the average CO2 concentration worldwide, and that leads to faster carbonation speed. Without fibre incorporation, the carbonation depths of infrastructures in Nanjing, Ji’nan and Guangzhou will be 50 mm, 57 mm and 40 mm, respectively in year 2100 considering no environmental governance, and Beijing is expected to attain 60 mm carbonation depth already in year 2080. If suitable amount of fibre was incorporated to resist cracking, the year in which carbonation depth of Beijing attains 60 mm will be postponed by 8 years, and accordingly, the carbonation depth of Ji’nan would be reduced from 57 mm to 52 mm in year 2100 (considering no environmental governance).
学术讨论
主办单位时间地点报告人报告主题
不列颠哥伦比亚大学土木学院 2015.10.09 不列颠哥伦比亚大学土木学院206 崔冬 Microstructural and Chemical Characterization in Cement-Based Materials
不列颠哥伦比亚大学华人学生会 2015.06.08 UBC学生活动中心 崔冬 CT在微结构表征方面的应用调研
不列颠哥伦比亚大学土木学院 2015.04.10 不列颠哥伦比亚大学土木学院206 崔冬 Use of tomography to understand the influence of preconditioning schemes on carbonation
不列颠哥伦比亚大学土木学院 2015.03.17 不列颠哥伦比亚大学土木学院206 Doo Yeol Yoo Performance Enhancement of Ultra-High-Performance Fiber-Reinforced Concrete and Model Development for Practical Utilization
不列颠哥伦比亚大学土木学院 2014.10.23 不列颠哥伦比亚大学土木学院206 崔冬 Experimental validation of representative elementary volume for mortars stained with potassium iodide
不列颠哥伦比亚大学土木学院 2014.03.19 不列颠哥伦比亚大学土木学院206 崔冬 Microstructure evolution of partly carbonated paste specimens blended with fly ash
东南大学材料科学与工程学院 2012.09.25 东南大学材料学院孙伟课题组 崔冬 弯曲荷载与碳化耦合作用下水泥基材料损伤劣化机理
东南大学材料科学与工程学院 2012.05.16 东南大学材料学院孙伟课题组 崔冬 碱-激发矿渣水泥的水化产物
     
学术会议
会议名称时间地点本人报告本人报告题目
BEFIB 2016 2016.09.20 温哥华 Effect of Carbon Fiber on Mechanical Behavior and Microstructure of Mortar
Microdurability 2016 2016.10.23 南京 Investigation on Microstructure Evolution of Cement-Based Materials with Ferrite Oxide Addition Responding to Elevated Temperature
     
代表作
论文名称
Porosity Characterization in Interfacial Transition Zone Using Dual CT Scans
Use of Tomography to Understand the Influence of Preconditioning on Carbonation tests in Cement-
 
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