荷载作用下双掺混凝土碳化机理的试验与数值研究

发布时间：2018-02-25 00:29

本文关键词： 混凝土碳化弯曲荷载矿物掺合料细观层次 COMSOL Multiphysics　出处：《南京工业大学》2015年硕士论文　论文类型：学位论文

【摘要】：自上世纪70年代以来,大气中的二氧化碳浓度逐年升高,混凝土碳化问题显得愈加严重。同时现代混凝土大量掺入矿渣、粉煤灰等矿物掺合料,影响了混凝土的抗碳化性能。此外,服役中的混凝土工程结构往往伴随着复杂的应力场作用,尤其是拉应力会导致混凝土孔隙乃至裂缝的扩展,这就加剧了二氧化碳在混凝土中的传输。因此,需要进一步考虑掺合料,荷载等因素对真实服役环境中混凝土碳化过程的影响。本文围绕着含有两种掺合料混凝土在碳化和静力荷载耦合作用下的劣化过程和机理,揭示了掺合料对混凝土碳化深度、pH值、抗折强度的影响规律,同时分析了不同弯曲荷载应力对混凝土碳化深度的影响。基于Fick第二定律和质量守恒定律,提出了含有矿物掺合料混凝土在碳化和荷载耦合作用下的碳化模型,应用多物理场耦合有限元软件COMSOL Multiphysics进行求解。最后还从细观层次上研究了混凝土的碳化过程。主要研究内容和结果如下：(1)研究了单掺和双掺混凝土的碳化深度和pH值的时变规律。研究结果表明：对于单掺粉煤灰的试件,其抗碳化性能与掺量成正比关系；而对于单掺矿渣的试件,矿渣含量为10%时,碳化深度达到最低值,然而当矿渣含量达到40%时,其抗碳化能力大幅降低；对于双掺试件,在任一掺合料取代率达到40%时,抗碳化能力有着显著的降低；无论单掺还是双掺混凝土,pH值演变规律和碳化深度值演变规律保持一致。(2)分析了弯曲应力水平作用下混凝土的碳化深度和pH值的时变规律。分析表明弯曲应力种类和水平对碳化深度和pH值有着显著的影响：在一定应力范围内,弯曲拉应力能显著提高混凝土的碳化深度,而弯曲压应力改善了混凝土的抗碳化能力；(3)考虑荷掺合料种类和含量、弯曲荷载应力水平等因素,基于前人的研究成果,提出了考虑荷载和掺合料因素的碳化反应模型,用有限元软件COMSOL Multiphysics模拟了混凝土的碳化过程。(4)从混凝土细观层次出发,开发了二维圆形和多边形随机骨料结构,基于提出的碳化反应模型,从混凝土细观层次分析了不同骨料含量、形状和界面过渡区对碳化反应过程的影响。
[Abstract]:Since the last century since 70s, concentration of carbon dioxide in the atmosphere increased year by year, the problem becomes more and more serious. At the same time the concrete carbonization of modern concrete mixed with a large number of slag, fly ash and other mineral admixture, affecting the carbonation resistance of concrete. In addition, the construction of concrete structure in service is often accompanied by complex stress field, especially is the tensile stress will lead to concrete cracks and pore expansion, which is exacerbated by the transmission of carbon dioxide in concrete. Therefore, the need for further consideration of admixture, load factors such as serving the effect of concrete carbonization processes in the environment of reality. In this paper contains two kinds of admixtures in concrete carbonation and static load coupling effect the degradation process and mechanism, reveals the admixture of concrete carbonation depth, pH value, influence the flexural strength at the same time, analyzes the different bending load on the stress The effect of concrete carbonization depth. The Fick's second law and based on the mass conservation law, put forward with mineral admixture concrete in carbonation and load coupling carbonation model, coupling finite element software COMSOL Multiphysics application of multi physics field is solved. Finally, from the micro level of concrete carbonization process. The main research contents and the results are as follows: (1) change regularity of single or double mixture concrete carbonation depth and pH value. The results show that the specimen mixed with fly ash, the anti carbonation properties and content is proportional to the relationship; and for the specimens of slag, slag content is 10% the carbonation depth, reaching the lowest value when the slag content reaches 40%, the carbonation resistance is greatly reduced; the double doped specimen, aggregate replace rate reached 40% in either mixed, anti carbonization capability has a significantly reduced; No single or double mixture concrete admixture, pH value and the evolution of the carbonation depth value evolution is consistent. (2) analyzed the bending variation regularity of carbonation depth and pH concrete under horizontal force value. Analysis shows that the bending stress on the type and level of carbonation depth and pH values have a significant impact. In a certain range of stress, the bending tensile stress can significantly improve the carbonation depth of concrete, and the bending stress to improve the carbonation resistance of concrete; (3) Considering Bearing admixture types and content of bending load factors on stress level, based on the previous research results, proposed model considering the carbonation reaction load and admixture factors, the carbonation process of concrete is simulated with finite element software COMSOL Multiphysics. (4) starting from the concrete meso level, the development of two-dimensional circular and polygon random aggregate structure, based on the carbonization reaction The effect of different aggregate content, shape and interface transition zone on the carbonation process is analyzed from the concrete meso level.

【学位授予单位】：南京工业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TU528

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