【作者】 高原；

【导师】 张君；

【作者基本信息】 清华大学 ， 土木工程， 2013， 博士

【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。更多还原

【Abstract】 Drying and wetting cycles is a salient environment responsible for the deteriorationof concrete structures. The purpose of this study is to investigate the characteristics ofthe development of concrete shrinkage and shrinkage induced stresses, and to establisha prediction models for shrinkage strain and stress in concrete structures underdrying-wetting cycles. Hence, emphasizes are laid on the following topics: the patternsof concrete shrinkage under dry and wet cycles, distribution of moisture in concrete,tensile creep and calculations of shrinkage stresses in typical concrete structures.As an example, three kinds of concrete with compressive strength of30MPa,50MPa and80MPa at28days respectively, labeled as C30, C50and C80were used inthe study. The shrinkage and interior humidity of the specimen under dry-wet cycleswere continuously measured. The experimental results show that concrete expandsunder wetting and contracts under drying. A close relationship between shrinkage andinterior humidity exists and the interior humidity may serve as the driving force forconcrete shrinkage change, regardless the shrinkage happens during drying or wetting.Based on these test results, a relative-humidity based model for shrinkage prediction ofconcrete under dry-wet cycles was developed. The results of the model prediction haveshown good agreement with the test data, and the calculation models can be used for theprediction of concrete shrinkage under drying and wetting environment.Priro to developing the humidity field model of concrete under dry-wet cycles, themodel of humidity drop caused by cement hydration, moisture diffusion coefficients fordrying and wetting process, and concrete moisture diffusion surface factor weredetermined based on experimental data. The development of internal humidity ofconcrete under dry-wet cycles was experimentally investigated using a concrete slabs.The developed moisture calculation model was verified with above experimental results.The model predictions follow the test data well.Using the ring test method, the development of inner strain of the steel ring wasmeasured continuously since concrete cast. The effects of concrete strength, thicknessof steel ring on the development of inner strain of the steel ring were studied. A methodfor determination of stress relaxation parameters of concrete under tension was developed. Using the developed method, the stress relaxation parameters of the threekinds of concretes were obtained.Based on elasticity thorey, the calculation model for shrinkage induced stresses inconcrete column under dry-wet cycles was developed. The effects of drying and wettingcycle regime, environment humidity, wind velocity and the size of concrete column onshrinkage induced stresses of concrete structure under dry-wet cycles were studied. Theresults were verified with with finite element simulation. By dividing the nonlinearshrinkage strain along the slab depth into three components, an average straincomponent, a linear strain component, and a nonlinear strain component, a calculationmodel of the shrinkage induced sstresses of concrete pavement slab under dry-wetcycles was developed. In addition, calculation methods of this model were discussed,and the calculation results were verified with finite element simulation. The effects ofconcrete strength grade, the length and thickness of concrete pavementslab and onshrinkage-induced stresses were also investigated in this study.更多还原