水泥基材料微结构特征与碳化模型关系的研究

发布时间：2018-04-03 16:39

本文选题：水泥净浆　切入点：碳化　出处：《东南大学》2015年硕士论文

【摘要】：碳化是指水泥石内的碱性物质与空气中的CO_2在湿度相宜的条件下发生中和反应的过程。碳化弱化了混凝土对钢筋的保护作用,加速钢筋锈蚀,产生体积膨胀,致使混凝土保护层开裂破坏。在设计混凝土建筑时,需要对其服役寿命进行预测,国内外众多学者对此做了大量研究,并建立了相关碳化模型。近年来,在水泥基材料微结构特征方面的研究揭示了微观机理与宏观现象之间的联系,进而建立了基于微结构特征的碳化模型。然而,目前已有的微结构碳化模型并没有考虑到水泥基材料完全碳化区、部分碳化区对CO_2传输速率以及碳化反应速率的影响。本文综合运用热重(TG)、X射线断层扫描(X-CT)、核磁共振(NMR)、纳米压痕、物理吸附(BET)和压汞(MIP)法对水泥净浆的不同碳化区微结构特征进行了分析,定量表征了CH、C-S-H、CaCO3等固相组成以及孔隙率、弯折度、饱和度等孔结构参数随碳化深度的演变,从而为传统微结构碳化模型的修正、验证提供试验依据。主要研究成果如下：首先,采用X-CT、TG法研究0.35W/C和0.53W/C净浆碳化后不同碳化深度的固相物质在灰度和组成方面的差异。结果表明：X-CT法可以测出水泥净浆碳化之后完全碳化区、部分碳化区和未碳化区的分布,且X-CT与TG试验测得的完全碳化区、部分碳化区范围基本一致。其次,采用TG、NMR法研究0.35W/C净浆碳化28天之后不同深度CH和C-S-H的碳化程度,结果表明：不同碳化区内的CH和C-S-H碳化程度不同,完全碳化区内C-S-H的碳化程度高于CH的,部分碳化区内C-S-H的碳化程度小于CH。同时,利用纳米压痕法分析了不同深度固相体积分数,分析结果也体现了不同碳化深度固相组成的渐变性。由表及里LD C-S-H和HD C-S-HLD的体积分数逐渐增加,且LD C-S-H碳化速率快于HD C-S-H的碳化速率。再次,采用MIP和BET法研究0.35W/C净浆碳化28天之后不同深度层孔隙率和孔径分布,提出了一种可避免单独采用MIP或BET法测试结果的缺陷,统一计算孔径概率分布的方法。研究结果表明：不同深度孔结构参数不同,传输性能不同,CO_2的扩散系数大小顺序是：完全碳化区部分碳化区未碳化区。此外,综合TG、MIP和NMR法研究了0.35W/C和0.53W/C净浆不同碳化龄期C-S-H平均链长与孔隙率之间的关系,提出了一种不依赖于C-S-H的分子式计算C-S-H碳化导致孔隙率变化量的新方法。研究结果还表明：C-S-H碳化引起的体积变化是净浆孔隙变化的主要因素。在C-S-H碳化程度较低时,C-S-H体积膨胀,其膨胀量占总体积变化量的70%左右；当C-S-H碳化程度达到88.7%时,C-S-H体积开始收缩。最后,从完全碳化区孔结构决定了CO_2传输速率,部分碳化区固相组成与饱和度决定了碳化速率角度考虑,对Papadakis模型进行修正。计算结果表明：修正后模型预测的碳化深度更加接近试验数值,修正后模型比原模型误差小50.5%。
[Abstract]:Carbonization refers to the neutralization reaction between alkaline substance in cement stone and CO_2 in air under the appropriate humidity.Carbonation weakens the protective effect of concrete on steel bar, accelerates the corrosion of steel bar, produces volume expansion, and causes cracking and destruction of concrete cover.In the design of concrete buildings, it is necessary to predict the service life of concrete buildings. Many scholars at home and abroad have done a lot of research on it, and established the relevant carbonization model.In recent years, the research on microstructure characteristics of cement-based materials reveals the relationship between microscopic mechanism and macroscopic phenomena, and then establishes a carbonization model based on microstructural characteristics.However, the existing microstructural carbonization models do not take into account the effects of the complete carbonation zone and partial carbonization zone on the CO_2 transport rate and the carbonation reaction rate.Bending degree, saturation and other pore structure parameters change with carbonation depth, thus providing experimental basis for the modification and verification of traditional microstructure carbonization model.The main results are as follows: firstly, the differences in gray and composition of solid materials with different carbonation depth after carbonization of 0.35W/C and 0.53W/C were studied by X-CTTG-TG method.The results show that the distribution of complete carbonation zone, partial carbonization zone and uncarbonated zone after carbonization of cement paste can be measured by the method of: X-CT, and the range of complete carbonation zone measured by X-CT and TG test is basically the same.Secondly, the carbonization degree of Ch and C-S-H in different depth after 28 days of carbonization of 0.35W/C paste was studied by TG-NMR method. The results showed that the carbonization degree of Ch and C-S-H in different carbonization zone was different, and the carbonization degree of C-S-H in complete carbonization zone was higher than that in Ch.The carbonization degree of C-S-H in partial carbonization zone is less than that of Ch.At the same time, the volume fraction of solid phase at different depth was analyzed by nano-indentation method, and the results showed the gradual denaturation of solid phase composition with different carbonation depth.The volume fraction of LD C-S-H and HD C-S-HLD increased gradually, and the carbonation rate of LD C-S-H was faster than that of HD C-S-H.Thirdly, MIP and BET methods are used to study the porosity and pore size distribution of different depth layers after 28 days of carburization of 0.35W/C slurry. A new method to calculate the probability distribution of pore size is proposed, which can avoid the defects measured by MIP or BET alone.The results show that the diffusivity of COK2 is in the order of partial carbonization and uncarbonation in the complete carbonization zone with different depth pore structure parameters and different transport properties.In addition, the relationship between the average chain length of C-S-H and porosity in different carbonation ages of 0.35W/C and 0.53W/C was studied by combining TG-MIP and NMR methods, and a new method was proposed to calculate the change of porosity caused by C-S-H carbonization, which is independent of C-S-H.The results also show that the volume change caused by carbonization is the main factor of the change of porosity.When the carbonization degree of C-S-H is low, the volume of C-S-H expands, and the volume of C-S-H begins to shrink when the carbonization degree of C-S-H reaches 88.7.Finally, the CO_2 transport rate is determined by the pore structure of the complete carbonized zone, and the carbonation rate angle is determined by the composition and saturation of the solid phase in the partial carbonization zone, and the Papadakis model is modified.The calculated results show that the predicted carbonation depth of the modified model is closer to the experimental value and the error of the modified model is 50.5 less than that of the original model.
【学位授予单位】：东南大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TU528

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