桥梁高性能混凝土早期收缩裂缝形成机理及控制

发布时间：2018-02-16 21:37

本文关键词： 桥梁高性能混凝土早期收缩变形开裂机理细观模拟裂缝控制　出处：《哈尔滨工业大学》2014年博士论文　论文类型：学位论文

【摘要】：混凝土早期由于水化作用和处在不饱和环境中,会产生收缩变形,随着龄期收缩变形累积增加,在约束下就会加大混凝土早期开裂的几率,特别是高性能混凝土的早期收缩开裂尤为显著。混凝土桥梁建造过程中,高性能混凝土早期开裂现象时常出现,收缩变形是混凝土早期开裂的主要源动力之一。如何降低甚至避免桥梁高性能混凝土的早期开裂,是目前的科研热点和难点。桥梁高性能混凝土的宏观收缩变形与其内部的细观结构密切相关。因此,混凝土宏观收缩行为的研究有赖于从细观层次出发,考虑混凝土细观结构对宏观表象的影响,这样才能够从深层次上反映高性能混凝土的收缩变形和应力特性,揭示桥梁高性能混凝土早期收缩开裂的机理从而提出控制措施。论文基于桥梁高性能混凝土早期收缩裂缝形成的研究现状,并通过现场调研充分了解桥梁工程中高性能混凝土结构早期收缩开裂的时间、形式和特点。在此基础上,通过室内试验从宏观层次上阐明了水胶比、粉煤灰含量、含气量、集浆比等配合比参数对桥梁高性能混凝土早期收缩变形的影响,并提出了能较全面反映配合比参数影响混凝土早期收缩变形的预测模型,同时探讨了配筋率和配筋方式以及养护方式和养护时间对混凝土早期收缩变形的影响,并得到了相应的结论。采用宏细观相结合的方法,基于工业CT扫描图像和图像重建技术建立了混凝土细观力学模型,混凝土在细观层次上视为骨料和砂浆组成的两相复合材料,并应用有限元显式算法进行数值分析,模拟了桥梁高性能混凝土早期收缩变形的发展全过程。考虑了骨料和砂浆的力学特性和收缩特性的差异,从细观层次上分析了骨料的分布和粒径大小以及砂浆的收缩变形大小对混凝土早期收缩变形的影响,并得到了混凝土室内测试结果的验证。从模拟结果得到了自由收缩状态下混凝土内应力的分布情况以及与骨料分布和粒径大小的关系。结合弹性力学、细观损伤力学和断裂力学在细观层次上来分析混凝土的收缩变形以及由于收缩变形导致的损伤和破坏过程。基于弥散式裂缝模型理论建立起较为完整的混凝土细观力学分析体系来模拟混凝土早期收缩开裂过程,揭示因收缩变形导致混凝土早期裂缝萌生和发展过程的内在机理。从混凝土收缩开裂过程的模拟结果看出,混凝土的内部开裂位置是在骨料和砂浆的界面处以及空隙处。这是由于骨料表面对砂浆的约束效应最显著,界面处出现应力集中现象导致界面处最先开裂。混凝土细观收缩裂缝随着龄期逐渐向薄弱区域延伸。骨料与砂浆的界面面积越大,对砂浆的约束效应更加显著导致砂浆的内应力更大,成为混凝土早期裂缝的起裂点。微裂缝随着龄期从起裂点位置逐渐延伸、扩展和汇集最后形成了混凝土的宏观裂缝。论文通过宏细观结合分析了混凝土早期收缩裂缝形成的机理,从理论到试验再到实际工程探寻了高性能混凝土早期裂缝有效的防治途径,并在实际工程中得到了应用,效果显著。提出了桥梁高性能混凝土早期收缩裂缝的防治措施,对于减少甚至避免混凝土桥梁的早期开裂、提高混凝土结构耐久性、延长混凝土结构使用寿命具有重要意义。
[Abstract]:Early concrete due to hydration and in unsaturated environments, shrinkage deformation, shrinkage deformation accumulation increased with age, the restriction would increase the probability of cracking in concrete, especially the early shrinkage cracking of high performance concrete is particularly significant. The concrete bridge construction process, often appear cracking of high performance concrete in early stage. Shrinkage deformation is one of the main sources of power in early cracking of concrete. How to reduce or even avoid the early cracking of high performance concrete bridge, is the research hotspot and difficulty at present. The bridge of high performance concrete shrinkage deformation and the macro meso structure are closely related. Therefore, research on macro shrinkage behavior of concrete depends on the level of the fine view, considering the concrete influence of microstructure on macroscopic appearance, so that it can reflect the high performance concrete from the deep contraction The deformation and stress characteristics, reveal the mechanism of early shrinkage cracking of high performance concrete bridge and control measures are put forward. The research status of high performance concrete bridge based on the early shrinkage crack formation, and through field investigation to fully understand the structure of high performance concrete early cracking time in bridge engineering, form and characteristics. On this basis, through the the indoor test on the macro level the water cement ratio, fly ash content, gas content, aggregate cement ratio etc. mix parameters of high performance concrete bridge early shrinkage effect, and put forward that can fully reflect the mix parameters prediction model of deformation shrinkage of concrete, and discusses the reinforcement ratio and reinforcement and maintenance and curing time on the effect of deformation and shrinkage of concrete, and get the corresponding conclusion. Using the method of combining macro and micro, based on Industrial CT image and image reconstruction techniques of concrete meso mechanics model of two-phase composite materials composed of concrete aggregate and mortar as fine in the view hierarchy, and explicit algorithm for numerical analysis by finite element simulation, the whole process of the development of high performance concrete bridges early shrinkage deformation. Considering the difference between mechanical properties and shrinkage the characteristics of aggregate and mortar, from the micro level analysis of the aggregate distribution and the particle size and the shrinkage deformation of the mortar size effect on deformation shrinkage of concrete, and verified by test results. The concrete chamber beta distribution of the concrete stress free contraction and aggregate distribution and the particle size from the simulation results. The combination of elastic mechanics, damage mechanics and fracture mechanics in the meso level analysis of concrete shrinkage deformation and Because of the damage and failure process of shrinkage deformation result. Establish the smeared crack model based on the theory of complete concrete meso mechanics analysis system to simulate the concrete early cracking process, because of the intrinsic mechanism of shrinkage deformation to reveal the concrete early crack initiation and development process. The simulation results from the concrete shrinkage cracking process that internal cracking position concrete is at the interface between aggregate and mortar and gaps. This is because the most significant restraining effect on mortar aggregate surface, the interface stress concentration at the interface of the first lead to cracking. Meso concrete shrinkage cracks with age gradually extended to the weak area. The interface area of aggregate and mortar is bigger, the the confinement effect is more pronounced in the internal stress of mortar mortar become more concrete early crack initiation point of micro cracks with age. From the initiation point extends gradually expanded and finally formed a collection of macro cracks of concrete. Through the combination of macro and micro analysis of the formation mechanism of early shrinkage cracking of concrete, from theory to experiment and practical projects to explore the high performance concrete early crack and effective way for prevention, and has been applied in practical engineering the effect is significant. The early shrinkage cracking of high performance concrete bridge and preventive measures to reduce or avoid the cracking of concrete bridge, improve the durability of concrete structure, prolong the service life of concrete structures is of great significance.

【学位授予单位】：哈尔滨工业大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：U445.57

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