干湿环境下混凝土收缩与收缩应力研究

发布时间：2018-09-12 15:43

【摘要】：干湿循环是导致混凝土结构性能衰退最为严酷的环境条件之一。本文旨在研究干湿循环下混凝土收缩和收缩应力的变化规律，建立相应的计算方法。重点对干湿循环下混凝土收缩发展、混凝土内部湿度场分布规律、混凝土抗拉徐变和典型混凝土结构的收缩应力等问题进行了研究。对3个强度等级混凝土（C30，C50，C80—分别代表普通强度、中等强度和高强混凝土），干湿循环下收缩和内部相对湿度的发展进行了同步试验测量，试验验证了混凝土干缩湿胀的特性。干湿环境下混凝土收缩的发展与其内部相对湿度发展具有很好的同步性，混凝土内部相对湿度变化是其收缩变化的驱动力。建立了基于混凝土内部湿度变化的收缩预测模型，模型结果能够很好的预测干湿循环下混凝土收缩的发展。建立了干湿循环下混凝土内部湿度场的计算模型，并对模型所需参数：水泥水化耗水引起的湿度下降、干燥和湿润阶段混凝土水分扩散系数和混凝土表面水分交换系数进行了确定。采用大尺寸混凝土试件，对干湿循环下混凝土内部不同位置处的相对湿度发展进行了试验测量。基于试验测定结果，对干湿循环下混凝土内部湿度场计算模型及相关模型参数进行了验证，模型结果和试验结果吻合良好。改进了传统环约束试验方法，试验测量了从混凝土浇筑开始钢环内表面环向应变的发展，研究了混凝土强度等级，钢环厚度和测量位置对试验结果的影响。建立了基于环约束试验的混凝土抗拉徐变系数的求解方法，依据环约束试验结果，对3个强度等级混凝土的抗拉徐变系数进行了确定。基于弹性力学原理，建立了干湿循环下混凝土圆柱收缩应力的计算模型，模型计算结果与有限单元法计算的结果吻合良好。对干湿循环制度、环境相对湿度、环境风速和构件尺寸等影响混凝土收缩应力的因素进行了分析；通过对收缩应变的分解，，建立了干湿循环下混凝土路面板收缩应力的计算模型，并对模型算法进行了讨论。模型计算结果与有限单元法计算的结果吻合良好。对混凝土强度等级、路面板长度等影响混凝土路面板收缩应力的因素进行了分析。
[Abstract]:Dry and wet cycle is one of the most severe environmental conditions that lead to the deterioration of concrete structure performance. The purpose of this paper is to study the change law of shrinkage and shrinkage stress of concrete under dry and wet circulation and to establish corresponding calculation method. The shrinkage and development of concrete under dry-wet cycle, the distribution law of moisture field in concrete, the tensile creep of concrete and the shrinkage stress of typical concrete structure are studied in this paper. The development of shrinkage and internal relative humidity of three strength grade concrete (C _ (30) C _ (50) C _ (80) on behalf of ordinary strength, medium strength and high strength concrete) under dry and wet cycles were measured simultaneously, and the characteristics of dry shrinkage and moisture expansion of concrete were verified by experiments. The development of concrete shrinkage in dry and wet environment has a good synchronism with the development of internal relative humidity. The change of relative humidity in concrete is the driving force of shrinkage change. A shrinkage prediction model based on the change of moisture in concrete is established. The results of the model can well predict the shrinkage development of concrete under dry-wet cycle. The calculation model of moisture field in concrete under dry and wet circulation is established, and the required parameters of the model are: the decrease of moisture caused by water consumption of cement hydration. The moisture diffusion coefficient of concrete and the moisture exchange coefficient of concrete surface were determined in drying and wetting stages. The development of relative humidity at different positions of concrete under dry and wet circulation was measured by using large size concrete specimens. Based on the experimental results, the calculation model of internal moisture field of concrete under dry-wet cycle and the related model parameters are verified. The results of the model agree well with the experimental results. The traditional ring confinement test method was improved to measure the development of the circumferential strain on the inner surface of the steel ring from the beginning of concrete pouring. The influence of the strength grade of concrete, the thickness of steel ring and the measuring position on the test results was studied. A method for solving the tensile creep coefficient of concrete based on ring confinement test is established. Based on the results of ring confinement test, the tensile creep coefficient of three strength grade concrete is determined. Based on the principle of elasticity, a model for calculating the shrinkage stress of concrete columns under dry and wet cycles is established. The results of the model are in good agreement with the results obtained by the finite element method (FEM). The factors influencing concrete shrinkage stress, such as dry-wet cycle system, environmental relative humidity, environmental wind speed and component size, are analyzed. The calculation model of shrinkage stress of concrete pavement slab under dry-wet cycle is established, and the algorithm of the model is discussed. The results of the model are in good agreement with that of the finite element method. The factors influencing the shrinkage stress of concrete slab such as concrete strength grade and pavement slab length are analyzed.
【学位授予单位】：清华大学
【学位级别】：博士
【学位授予年份】：2013
【分类号】：TU528

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