考虑双界面过渡区影响的再生混凝土中氯离子扩散规律分析

发布时间：2018-04-01 03:10

本文选题：再生混凝土　切入点：氯离子　出处：《广西大学》2017年硕士论文

【摘要】：再生混凝土作为一种可持续发展的绿色建筑材料,实现了资源的循环利用,符合国家可持续发展战略的需求。由于再生粗骨料表面附着旧砂浆,所以再生混凝土存在旧砂浆—原生粗骨料和新砂浆—旧砂浆双界面过渡区,从而影响到再生混凝土的耐久性。本文把再生混凝土视为由新砂浆、附着旧砂浆、原生粗骨料、新砂浆—附着旧砂浆之间的新界面过渡区、附着旧砂浆—原生粗骨料之间的旧界面过渡区组成的五相复合材料,从有限元数值模型和等效扩散系数计算模型两方面对再生混凝土中的氯离子扩散规律进行分析,并通过自然扩散试验对数值模型和计算模型进行了验证。本文的主要研究工作和结论包括:(1)建立了考虑粗骨料随机分布的再生混凝土中氯离子扩散的五相数值模型。基于再生粗骨料随机投放的双向游走法,研究建立圆形粗骨料随机投放下的再生混凝土五相模型和再生混凝土三相+五相复合模型,并讨论了模型中各参数的合理取值,分析表明,建立再生混凝土五相模型能够考虑附着旧砂浆和双界面过渡区的影响,能够更为合理地评估氯离子在再生混凝土中的扩散行为;(2)利用粗骨料级配分布理论提出了再生混凝土中双界面过渡区的面积分数计算模型,结合双界面过渡区的氯离子扩散系数,基于Viogt-Reuss模型分析再生混凝土扩散系数的上下限,在此基础上研究建立了定量计算再生混凝土等效扩散系数的计算模型,分析表明,所提出的再生混凝土中双界面过渡区的面积分数计算模型精度较高,当粗骨料在模型中分布较为均匀时,等效扩散系数计算模型的结果与数值模拟结果吻合较好;(3)以粗骨料含量、水胶比、再生粗骨料取代率、粉煤灰掺量、矿粉掺量、粗骨料级配作为考察因素,设计了 8组再生混凝土的配合比并进行制备,进而开展了再生混凝土中氯离子自然扩散试验,试验结果表明,降低再生粗骨料取代率能够提高再生混凝土的抗氯盐侵蚀性能,粗骨料含量为45%的再生混凝土抗氯盐侵蚀性能较好,控制粗骨料粒径在10～15mm、降低水胶比均能较好地提高再生混凝土的抗氯盐侵蚀性能,单掺粉煤灰的再生混凝土的耐久性低于复掺粉煤灰和矿粉的再生混凝土和单掺矿粉的再生混凝土;(4)基于自然扩散试验所测定的再生混凝土试块中氯离子浓度与扩散深度的关系,将试验数据分别与再生混凝土中氯离子扩散的五相数值模型的分析结果和再生混凝土等效扩散系数计算模型的分析结果进行对比分析,验证了再生混凝土中氯离子扩散的五相数值模型和再生混凝土等效扩散系数计算模型的合理性和适用性。
[Abstract]:As a green building material for sustainable development, recycled concrete realizes the recycling of resources and meets the needs of the national sustainable development strategy. Therefore, there is a transition zone between old mortar and primary coarse aggregate and new mortar and old mortar in recycled concrete, which affects the durability of recycled concrete. In this paper, recycled concrete is regarded as new mortar, attached old mortar, primary coarse aggregate. A five-phase composite consisting of a new interfacial transition zone between new mortar and attached old mortar, and a five-phase composite composed of an old interface transition zone between old mortar and primary coarse aggregate, The diffusion law of chloride ions in recycled concrete is analyzed from two aspects: finite element numerical model and equivalent diffusion coefficient calculation model. The numerical model and computational model are verified by natural diffusion test. The main research work and conclusions in this paper include: 1) the five-phase numerical model of chloride diffusion in recycled concrete considering the random distribution of coarse aggregate is established. Bidirectional walking method based on random drop of recycled coarse aggregate, The five-phase model of recycled concrete and three-phase five-phase composite model of recycled concrete under random dropping of circular coarse aggregate are studied and the reasonable values of each parameter in the model are discussed. The five-phase model of recycled concrete can take into account the influence of the adhesion of the old mortar and the transition zone between the two interfaces. The diffusion behavior of chloride ions in recycled concrete can be evaluated more reasonably. Based on the theory of coarse aggregate gradation distribution, a model for calculating the area fraction of double interface transition zone in recycled concrete is proposed. Combined with the chloride ion diffusion coefficient in the transition zone between the two interfaces, the upper and lower limits of the reclaimed concrete diffusion coefficient are analyzed based on Viogt-Reuss model. Based on the above analysis, a quantitative calculation model for the equivalent diffusion coefficient of recycled concrete is established, and the results show that the equivalent diffusion coefficient of recycled concrete is calculated quantitatively. The proposed model for calculating the area fraction of the double interface transition zone in recycled concrete has a high accuracy, and when coarse aggregate is distributed uniformly in the model, The results of the equivalent diffusion coefficient model are in good agreement with the numerical simulation results. The main factors are the content of coarse aggregate, the ratio of water to binder, the replacement rate of regenerated coarse aggregate, the content of fly ash, the amount of mineral powder and the gradation of coarse aggregate. Eight groups of recycled concrete were designed and prepared, and the natural diffusion test of chloride ions in recycled concrete was carried out. The results showed that reducing the replacement rate of recycled coarse aggregate could improve the corrosion resistance of recycled concrete. The recycled concrete with 45% coarse aggregate has better resistance to chloride erosion. Controlling coarse aggregate particle size at 1015 mm and reducing the water-binder ratio can improve the chloride corrosion resistance of recycled concrete. The durability of recycled concrete with single fly ash is lower than that of recycled concrete mixed with fly ash and mineral powder and recycled concrete with single mineral powder. Based on the relationship between chloride concentration and diffusion depth in recycled concrete samples measured by natural diffusion test, The experimental data are compared with the analytical results of the five-phase numerical model of chloride diffusion in recycled concrete and the analytical results of the equivalent diffusion coefficient of recycled concrete. The validity and applicability of the five-phase numerical model of chloride diffusion in recycled concrete and the calculation model of equivalent diffusion coefficient of recycled concrete are verified.
【学位授予单位】：广西大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU528

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