Numerical and experimental investigations for the modeling of the time-dependent deformation characteristics of concrete on the mesoscale with coupled models for mechanical and hygric effects

混凝土时变变形的建模通常采用纯现象学方法，其中通常引入由于徐变和收缩引起的附加变形。然而，有实验证据表明，这些影响是耦合在一个非线性的方式（皮克特效应），并强烈相关的机械引起的损伤和水分分布内的testies.The项目的目的是开发和实施的数值模型，能够模拟机械载荷和时间依赖性的局部水分分布的耦合效应的混凝土。模拟将进行显式表示的非均质细观结构的基础上的几何模型，由作者开发的混凝土。混凝土被建模为一个三相复合材料与集料，水泥浆和界面过渡区（ITZ）作为一个额外的薄弱环节。水泥石的非线性行为，包括软化的损伤-塑性组合模型，这是正则化的梯度损伤列式。这减少了数值工作相比，在以前的版本中使用的大非局部半径的非局部方法。混凝土的粘性特性与塑性模型的扩展，使用Perzyna型蠕变模型硬化。这允许机械引起的损伤和粘性蠕变变形之间的直接耦合。与时间相关的宏观性能（强度，刚度）的发展作为硬化过程中的水泥浆的水分含量的函数建模与修改后的固化理论，同时确保满足热力学原理。力学模型和含水量之间的相互作用是通过将混凝土建模为多孔介质来实现的，该多孔介质具有与骨架和毛细压力相关的宏观应力分量的分解。此外，水分含量影响固化速率。ITZ采用内聚界面方法进行建模，该方法扩展到准确描述作为裂缝开口函数的水分传输。该项目的目标是开发一个基于物理的蠕变和收缩数值模型，该模型能够准确捕获复杂的宏观效应。它应该调查，如果耦合的物理效应（粘性水泥基质，水分传输，水泥水化）的建模和直接表示的介观结构是能够解释复杂的现象学性质和相互作用。其结果是，实验结果的解释与中尺度上的物理过程的现实理解是便利的。此外，由于本构参数的物理意义明确，简化了模型的标定过程。

The modeling of time-dependent deformations of concrete is commonly performed with pure phenomenological approaches, where usually additional deformations due to creep and shrinkage are introduced. However there is experimental evidence that these effects are coupled in a nonlinear way (Picket effect) and are strongly related to mechanically induced damage and the moisture distribution within the specimen.The purpose of the project is the development and implementation of a numerical model for concrete that is able to simulate the coupled effects of mechanical loading and time-dependent local moisture distribution. The simulation will be performed with an explicit representation of the heterogeneous mesoscale structure based on a geometry model for concrete developed by the author. Concrete is modeled as a three phase composite with aggregates, cement paste and the interfacial transition zone (ITZ) as an additional weak link. The nonlinear behavior of the cement paste including the softening is modeled with a combined damage-plasticity model, which is regularized with a gradient damage formulation. This reduces the numerical effort compared to the nonlocal approach used in previous versions for large nonlocal radii. The viscous character of concrete is modeled with an extension of the plasticity model using a Perzyna-type creep model with hardening. This allows for a direct coupling between the mechanically induced damage and viscous creep deformations. The development of the time-dependent macroscopic properties (strength, stiffness) as a function of the moisture content during hardening of the cement paste is modeled with a modified solidification theory while ensuring to satisfy thermodynamic principles. The interaction between the mechanical model and the moisture content is realized by modeling concrete as a porous medium with a decomposition of the macroscopic stress components related to the skeleton and the capillary pressure. In addition, the moisture content influences the solidification rate. The ITZ is modeled using a cohesive interface approach that is extended to accurately describe the moisture transport as a function of the crack opening.The objective of the project is the development of a physics-based numerical model for creep and shrinkage that is able to accurately capture the complex macroscopic effects. It should be investigated if the modeling of coupled physical effects (viscous cement matrix, moisture transport, cement hydration) and the direct representation of the mesostructure are able to explain the complex phenomenological properties and interactions. As a result, the interpretation of experimental results with a realistic understanding of the physical processes on the mesoscale is facilitated. Additionally, the calibration process of the model is simplified due to clear physical meaning of the constitutive parameters.