【作者】 龚灵力；

【导师】 金贤玉； 金南国；

【作者基本信息】 浙江大学 ， 结构工程， 2010， 博士

【摘要】 自密实混凝土以其优异的工作性能及环保性,逐渐得到广大工程界的接受。本文以核电工程应用自密实混凝土为工程背景,试验研究自密实混凝土配合比设计及力学性能、耐久性、收缩抗裂性能,并与普通振捣混凝土性能进行了比对;针对复杂环境中混凝土结构耐久性问题,探讨多因素作用下混凝土时变性模拟分析,论文的主要研究工作有:(1)根据Heywood单颗粒骨料表面积计算方程,考虑实际操作的简便性建立了表征骨料比表面积简易计算方法,以表征骨料比表面积反映骨料粗细程度以及各粒径分布,提出富余砂裹厚度以及净浆包裹骨料厚度概念,并以此为切入点,提出新的自密实混凝土配合比设计方法。用此方法成功配制C35和C50自密实混凝土,经实验室及现场试验进行比对,效果良好。(2)以现场材料配制的C35、C50自密实混凝土与基准普通振捣混凝土为研究对象,通过试验研究长达560天的立方体抗压强度、立方体劈裂抗拉强度、棱柱体轴心抗压强度、受压静弹性模量、四点弯拉(抗折)强度、钢筋握裹粘结强度以及弯拉初裂拉应变,研究自密实混凝土与对比普通振捣混凝土各长期力学性能随龄期发展规律及相互关系;同时通过抗渗性、抗氯离子渗透性、抗碳化性试验以及自由收缩、平板约束抗裂、环形约束抗裂试验以综合评价自密实混凝土与对比普通混凝土耐久性与收缩抗裂性能差异。结果表明自密实混凝土力学性能、耐久性以及收缩抗裂性能均不弱于同强度的对比普通振捣混凝土。(3)根据Fick扩散定律与质量守恒定律建立湿度场理论模型,依据湿度场与温度场的相似性,实现湿度场问题转化为温度场问题模拟求解;结合湿度场的干缩湿胀效应,提出基于不同干燥环境下混凝土自由收缩实测曲线去实现湿度场参数自动识别的方法,并通过4种不同混凝土配合比的算例验证表明,此法是方便可行的。(4)在基于混凝土单元各向异性应变损伤假定的基础上,引入损伤系数,提出各向异性湿度、氯离子、二氧化碳扩散放大因子对因应力损伤开裂的混凝土单元各扩散系数进行修正调整。这些扩散放大因子均易于在有限元程序中实现并通过算例分析表明其效果良好。(5)在参考国内外相关文献资料的基础上,根据Fick扩散定律与质量守恒定律建立了考虑温度、湿度、应力等多因素作用下二氧化碳分布场以及氯离子分布场的理论模型;依据两场理论模型与温度场的相似性,将氯离子与二氧化碳在混凝土中的扩散问题实现映射到温度场中模拟分析,并与快速碳化试验以及带裂缝混凝土氯离子侵蚀试验的测试结果的对比表明,两场模拟结果均与试验测试结果吻合良好。同时基于目前通用有限元程序平台,提出了考虑应力、温度、湿度、氯离子以及二氧化碳等因素耦合作用下混凝土结构时变性数字模拟分析的基本流程框架。论文的研究一方面为自密实混凝土更广泛的应用于核电工程或其它工程建设提供了简便可行的配合比设计方法与可靠的试验依据;另一方面为今后能有效的对复杂环境下混凝土结构耐久性分析以及服役寿命预测提供了参考。更多还原

【Abstract】 Self-compacting concrete (SCC) is widely accepted by engineers and researchers due to its excellent workability and environmental friendly properties. In this research, the properties of SCC which was utilized in nuclear power plant, such as mix design, mechanical properties, durability and shrinkage crack resistance, were investigated in comparison with normal vibrating concrete (NVC). Focusing on the concrete structure durability in complicated environment, the time dependence properties simulation and analysis of concrete were discussed in multi-factor coupling conditions. The subjects of this research include:(1) In considering the operation convenience, a simplified method on estimating the specific surface of aggregate was put forward based on improved Heywood single aggregate surface calculation equation. The coarse-to-fine degree and particle size distribution of aggregate were taken into account in this method and two new concepts, surplus thickness of sand and thickness of paste around aggregate, were introduced. Then take the two new concepts as the breakthrough point, this research proposed a new mix design method of SCC. Two kinds of SCC, C35 and C50, were designed with this method and tested through both indoor and outdoor experiments. The test results indicated that the SCC designed with new method showed good behaviors in mechanical properties and workability.(2) The cubic compressive strength, cubic splitting tensile strength, axial compressive strength, elastic modulus, flexural tensile strength, steel bonding strength and flexural cracking strain of both SCC and NVC in C35 and C50 were investigated from 3d to 560d. The research revealed the long term development of mechanical properties with time and the inter-relationship between them of SCC against NVC. A further comparison of the durability and shrinkage cracking resistance between SCC and NVC was conducted in terms of permeability resistance test, chloride penetration resistance test and carbonation resistance test, as well as the free shrinkage test, plate cracking restraint test and ring cracking restraint test. The test results showed that mechanical properties, durability and shrinkage cracking resistance of SCC all beat NVC.(3) Based on Fick diffusion law and mass conservation law, a theoretical model of concrete moisture field was established. The high similarity between moisture field and temperature field of concrete was applied to digitally solve the moisture field problems with converted temperature field. In view of dry-shrinkage and wet-expansion effect of moisture field, this research put forward a new method to identify the moisture field parameters by concrete shrinkage curve under different drying conditions. The calculation on 4 kinds of concretes verified the accuracy and convenience of the new method.(4) Based on the assumption of anisotropic strain damage and introduction of damage factor in concrete element, a new concept of anisotropic diffusion enhancing factor was defined and applied to modify moisture, carbon dioxide and chloride diffusion coefficients on damage and cracking of concrete element. The diffusion enhancing factors of moisture, carbon dioxide and chloride can all be easily implemented in finite element analysis and improve the accuracy of simulation calculation.(5) Based on literatures review, Fick diffusion law and mass conservation law were applied in theoretically modeling the carbon dioxide field and chloride field under multi-factor coupling conditions, such as temperature, moisture and stress. Carbon dioxide field and chloride field were both translated to temperature field for simulation analysis according to the high similarity between carbon dioxide field, chloride field and temperature field. Simulation analysis of carbon dioxide field and chloride field was verified by accelerated carbonation experiment and chloride penetration experiment with pre-cracked concrete specimen. Both the simulation results of carbon dioxide field and chloride field showed good agreement with experiments results. Aiming at the application on the generally used finite element program platform, basic process framework of time dependence simulation analysis of concrete under multi-factor coupling conditions was built.The research can provide a simple and practical mix design method and reliable test data base for a wider application of SCC in nuclear power constructions and other engineering projects. At the same time, this investigation will offer some useful references for durability analysis and service-life-span prediction of concrete structure in complicated environments.The research was financially supported by National Science Foundation (Grant No. 50838008), National Basic Research Program of China (973 Program, Grant No. 2009CB623200), Doctoral Program of Higher Education (No. 20070335087) and High Technology Research and Development Program of China (863 Program, 2006AA04Z415).更多还原