集料-基体界面对水泥基材料碳化性能的影响

发布时间：2018-10-05 07:31

【摘要】：水泥混凝土的碳化反应是指大气中的CO2通过混凝土的孔隙或裂缝进入溶解于孔溶液中与混凝土的氢氧化钙、C-S-H凝胶、钙矾石等物相发生中性化反应。混凝土的中性化反应会引起水泥石的收缩,产生裂缝.导致混凝土的劣化,缩短混凝土的服役寿命。碳化反应会引起混凝土内部微结构的变化,同时混凝上各种微结构特征也会对碳化过程产生不同影响。混凝土的微结构主要包含其物相组成、孔隙率、孔径分布等,可以分为界面过渡区和基体两部分。界面过渡区是混凝土的薄弱环节,界面过渡区及其微结构对其传输性能和耐久性有重要影响。界面过渡区及其微结构也必然是影响混凝土碳化过程的一个重要方面,能够为建立考虑界面影响的混凝土碳化模型提供依据。本文主要以界面碳化深度测试,纳米力学性能表征碳化前后界面过渡区微结构,使用背散射(BSE)图像分析技术研究界面过渡区微结构在碳化前后的演变规律,以及界面特征的改变对混凝土抗碳化性能的影响四个方面研究了集料-基体界面对水泥混凝土碳化过程的影响。由于界面过渡区与基体的微结构存在差别,碳化过程中必定会出现不同的碳化现象。界面过渡区具有孔隙率大、结构疏松,氢氧化钙含量较多且呈定向分布,未水化水泥含量较低等特征,使得界面的碳化速率快于基体。本文设计了规则形状的集料.基体界面碳化试验,成型了水胶比为0.60,0.53和0.35的含石灰石和花岗岩石片(作为集料)的净浆试件,把试件两端作为碳化面碳化28d,用酚酞法测量了界面与基体的碳化深度。实验结果表明：界面的碳化深度是基体的2-3倍,并且在碳化界面效应的影响下,碳化曲线在界面附近形成-个具有距离界面越近碳化深度越深的特征的曲线。因此,CO2在界面传输速度是基材传输速度的数倍,界面传输是形成部分碳化区的原因之一。在此基础上本文提出了考虑ITZ影响的水泥基材料碳化的物理模型。纳米压痕技术能够测试界面过渡区纳米力学性能,表征界面过渡区微结构,从而揭示碳化前后界面过渡区微结构的演变规律。本文设计了不同水胶比的模拟混凝土的界面,采用纳米压痕技术测试了碳化前后界面过渡区的微结构特征。实验结果表明：碳化后界面过渡区仍然存在,且其与基体的弹性模量和硬度值均有提高,界面过渡区尺寸由碳化前的约50-60μm降低到碳化后的约20～30μm。说明碳化后界面过渡区仍然是CO2扩散的快速通道。界面过渡区孔隙率等微结构在碳化前后的演变能揭示其碳化过程的混凝土性能变化的原因。本文对不同水胶比的界面试样进行了BSE实验,根据BSE图像分析了界面过渡区的形貌并定量分析了界面过渡区碳化前后孔隙率和物相组成的变化。实验表明,界面过渡区的孔隙(在孔尺寸不小于200nm的范围)率高于基体,且碳化后孔隙率均有所降低,未水化水泥含量均有不同程度的减少。碳化后界面过渡区的孔隙率仍然高于基体,而其未水化水泥的减少量较基体多。最后,为了探讨界面微结构的改变对混凝土整体抗碳化性能的影响,本文设计了改变界面条件的骨料裹浆混凝土试件的碳化实验。实验结果表明：高水胶比的襄浆骨料会提高混凝土的整体有效水胶比,增加碳化深度,降低了混凝土整体抗碳化性能。SEM图像分析表明.相同混凝土水胶比下,裹浆骨料的界面较非裹浆的界面结构疏松,孔隙率大。
[Abstract]:The carbonization reaction of cement concrete refers to the neutralization reaction between the carbon dioxide in the atmosphere and the calcium hydroxide, C-S-H gel, ettringite and the like dissolved in the pore solution through the pores or cracks of the concrete. The neutralization reaction of concrete results in shrinkage of cement stone and cracks. and the service life of the concrete is shortened. The carbonization reaction can cause the change of microstructure inside the concrete, and the various microstructure characteristics of the concrete can also have different influences on the carbonization process. The microstructure of concrete mainly consists of its phase composition, porosity, pore size distribution and so on. It can be divided into interface transition zone and matrix part. The interface transition zone is the weak link of concrete, and the interface transition zone and its microstructure have an important influence on its transmission performance and durability. The interface transition zone and its microstructure must also be an important aspect of the carbonization process of concrete, which can provide the basis for establishing concrete carbonation model considering interface effect. In this paper, the microstructure of interface transition zone before and after carbonization is characterized by interfacial carbonization depth test and nano mechanical properties, and the evolution law of interface transition zone microstructure before and after carbonization is studied by using back scattering (BSE) image analysis technique. The effect of aggregate-matrix interface on carbonization of cement concrete was studied in four aspects: the effect of the interface characteristics on the carbonization resistance of concrete. Due to the difference between the interface transition zone and the microstructure of the matrix, different carbonization phenomena must occur during the carbonization process. the interface transition zone has the characteristics of large porosity, loose structure, high calcium hydroxide content and directional distribution, low hydration cement content and the like, so that the carbonization rate of the interface is fast to the matrix. In this paper, a rule-shaped aggregate is designed. According to the carbonization test of matrix interface, a net slurry test piece with water-cement ratio of 0. 60, 0. 53 and 0. 35 was formed, and the two ends of the test piece were carbonized at the carbonization surface for 28d, and the carbonization depth of the interface and the substrate was measured by TUNEL method. The experimental results show that the carbonization depth of the interface is 2-3 times that of the matrix, and the carbonization curve is formed in the vicinity of the interface under the influence of the carbonization interface effect. Therefore, the transmission speed of CO2 is several times the transmission speed of the base material, and the interface transmission is one of the reasons for forming part of the carbonization zone. In this paper, the physical model of carbonization of cement-based material considering ITZ effect is presented. Nanoindentation technique can test the nano mechanical properties of interface transition zone and characterize the microstructure of interface transition zone, thus revealing the evolution law of microstructure of interface transition zone before and after carbonization. In this paper, the interface of the simulated concrete with different water-cement ratio is designed, and the microstructure characteristics of the interface transition zone before and after carbonization are tested by using nano-indentation technology. The results show that the transition area of the interface still exists after carbonization, and the elastic modulus and hardness value of the interface are improved. The size of the interface transition zone is reduced from about 50-60. m u.m before carbonization to about 20 ~ 30. m The evolution of the microstructure before and after carbonization can reveal the change of the concrete properties of the carbonization process. In this paper, BSE experiment was carried out on the interface sample with different water-cement ratio, the morphology of interface transition zone was analyzed according to BSE image, and the change of porosity and phase composition before and after carbonization of interface transition zone was quantitatively analyzed. The experimental results show that the porosity of the interface transition zone (in the range of not less than 200nm) is higher than that of the matrix, and the porosity after carbonization decreases and the content of unhydrated cement is decreased. The porosity of the transition zone of the post-carbonization interface is still higher than that of the matrix, and the amount of unhydrated cement is much lower than that of the matrix. Finally, in order to investigate the effect of the change of interface microstructure on the whole anti-carbonization performance of concrete, this paper designs the carbonization experiment of aggregate-wrapped concrete test piece which changes the interface condition. The experimental results show that the cement mortar aggregate with high water-cement ratio can improve the overall effective water-cement ratio of concrete, increase the carbonization depth, and reduce the overall anti-carbonization performance of concrete. SEM image analysis showed. Under the same concrete water-cement ratio, the interface between the interface of the slurry-wrapped aggregate and the non-wrapped slurry is loose and the porosity is large.
【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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