湿热力耦合作用下的混凝土力学性能研究

发布时间：2018-06-03 07:51

本文选题：湿热力耦合 + 失配本征应变　；参考：《北京交通大学》2017年博士论文

【摘要】：混凝土是由砂浆、骨料以及界面过渡区构成的复合材料,其湿热力状态之间互相影响,本文基于细观力学研究了其相关力学问题,具体内容如下:首先研究了混凝土的湿热力耦合计算方法。将混凝土视作砂浆骨料组成的二相复合材料,分析了二者的失配本征应变。作者把砂浆视作弹性损伤材料,将失配本征应变导致的应力引入砂浆的损伤分析中,建立了混凝土湿热力耦合计算方法。损伤通过传导系数的变化影响湿热传输,湿热状态对应力状态的影响体现在湿热应力和失配本征应变产生的损伤。混凝土骨料与砂浆的应力应变关系使用Mori-Tanaka方法计算。对路面板的计算表明,失配本征应变对混凝土湿热力状态的影响不可忽视。将该湿热力耦合计算方法应用到湿热扩散对混凝土强度影响的分析中,计算了干燥和降温情况下圆柱构件的应力分布和强度变化。研究表明,湿热扩散使得圆柱构件的应力分布不均匀,较长的扩散时间和较小的构件尺寸显著降低了构件的压缩强度。本文在考虑水灰比和矿物组成的基础上,提出了一个简单的水泥水化动力学模型。该模型使用Avrami方程描述初始阶段的水化进程,采用Bents模型刻画随后阶段的水化过程。使用该方法可以确定不同矿物的水化速度和各种水化产物的体积分数。该方法只需要一个待定参数,简单易用,可以预测较长时间的水化状态。本文进一步提出了考虑固体体积分数和初始水灰比的水泥初凝阈值计算方法,并以连通固体相体积为基础,结合细观力学均匀化方法,研究了水化水泥早期弹性模量的演化,模型预测结果与实验数据基本一致。随后,基于Powers水化模型,推导了适用于普通硅酸盐水泥的简化模型。界面过渡区是混凝土中最弱的一相,本文基于细观力学研究了其力学性能及其对混凝土力学行为的影响。将混凝土界面过渡区视作由两相复合材料组成的球壳,并假设其组分的体积分数沿半径方向变化。根据不同的细观力学均匀化方法,推导了不同的解析方法和数值方法,分析了界面过渡区的力学性能。在解析方法中,分别采用了并联材料和串联材料的细观力学均匀化方法,求得了梯度球壳的弹性解、塑性解和稳态热应力解。在数值方法中,将梯度球壳分成若干层球壳,每一层球壳的组分体积分数为常数,其力学性质分别采用并联材料、串联材料和M-T方法来确定。利用层间位移和应力连续条件得到了梯度球壳的解。该数值方法计算量小,精度高,与对应的解析解一致性良好。研究结果表明,界面过渡区对混凝土力学性能的影响与骨料体积分数和粒径有关,降低了混凝土刚度,但对初始损伤载荷影响不大。
[Abstract]:Concrete is a composite composed of mortar, aggregate and interfacial transition zone. The main contents are as follows: firstly, the wet-thermal coupling calculation method of concrete is studied. The concrete is regarded as a two-phase composite composed of mortar aggregate, and their mismatched intrinsic strain is analyzed. The mortar is regarded as an elastic damage material, and the stress caused by mismatched intrinsic strain is introduced into the damage analysis of mortar, and the coupled calculation method of moisture, heat and force of concrete is established. The damp-heat transfer is affected by the change of conduction coefficient, and the effect of damp-heat state on the stress state is reflected in the damage caused by the hygrothermal stress and mismatched intrinsic strain. The stress-strain relationship between concrete aggregate and mortar is calculated by Mori-Tanaka method. The calculation of the pavement panel shows that the effect of mismatched intrinsic strain on the wet and thermal state of concrete can not be ignored. The coupled method is applied to the analysis of the effect of hygrothermal diffusion on the strength of concrete, and the stress distribution and strength change of cylindrical members under the condition of drying and cooling are calculated. The results show that the stress distribution of cylindrical members is not uniform due to the hygrothermal diffusion. The compression strength of the members is significantly reduced by the longer diffusion time and the smaller member size. In this paper, a simple hydration kinetic model of cement is proposed on the basis of considering the ratio of water to cement and mineral composition. The Avrami equation is used to describe the hydration process in the initial stage and the Bents model is used to describe the hydration process in the subsequent stage. This method can be used to determine the hydration rate of different minerals and the volume fraction of various hydration products. The method requires only one parameter to be determined and is easy to use and can be used to predict the hydration state for a long time. In this paper, the calculation method of initial setting threshold of cement considering solid volume fraction and initial water-cement ratio is put forward, and the evolution of early elastic modulus of hydrated cement is studied based on the volume of connected solid phase and the mesomechanical homogenization method. The predicted results of the model are in good agreement with the experimental data. Then, based on the Powers hydration model, a simplified model for ordinary Portland cement is derived. The interfacial transition zone is the weakest phase in concrete. In this paper, the mechanical properties of the interfacial transition zone and its influence on the mechanical behavior of concrete are studied on the basis of meso-mechanics. The transition zone of concrete interface is regarded as a spherical shell composed of two phase composite materials, and the volume fraction of its components is assumed to vary along the radius. According to different meso-mechanical homogenization methods, different analytical methods and numerical methods are derived, and the mechanical properties of the interfacial transition region are analyzed. In the analytical method, the elastic solution, plastic solution and steady state thermal stress solution of gradient spherical shell are obtained by using the meso-mechanical homogenization method of parallel material and series material, respectively. In the numerical method, the gradient spherical shell is divided into several layers of spherical shells. The volume fraction of the components of each layer is constant. The mechanical properties of each layer are determined by parallel material, series material and M-T method respectively. The solution of gradient spherical shell is obtained by using the continuous condition of interlayer displacement and stress. The numerical method has the advantages of low computational complexity, high accuracy and good consistency with the corresponding analytical solution. The results show that the influence of interfacial transition zone on the mechanical properties of concrete is related to the volume fraction and particle size of aggregate, which reduces the stiffness of concrete, but has little effect on the initial damage load.
【学位授予单位】：北京交通大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TU528

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