Experimentally-validated stochastic model for freeze-thaw microstructural degradation and damage of hardened cement paste

经过实验验证的硬化水泥浆体冻融微观结构退化和损坏的随机模型

• 批准号: 496491159
• 负责人: Professor Dr.-Ing. Michael Beer
• 金额: --
• 依托单位: Department of Civil and Environmental Engineering
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/496491159?language=en
• 关键词: Experimentally; validated; stochastic; model; freeze

The sustainability of concrete structures is highly influenced by their durability with regard to environmental exposures, such as freeze-thaw (FT) attack. So far, no sufficiently accurate model is available in the literature, which correctly predicts and quantifies the durability, i.e. the concrete degradation due to cyclic freezing and thawing. The reasons for that are numerous: on the one hand, the loading, i.e. the FT exposure is a highly variable process and the population of FT events is extremely difficult to classify. On the other hand, freezing and thawing cause very localized changes in the materials properties (which eventually lead to spalling), which due to their very small spatial extent, are hard to detect and to quantify and which are highly variable in nature, depending very much on the moisture content in the concrete as well as the freezing conditions. We address both these aspects by aiming to introduce a stochastic, spatially resolved model for the FT degradation of concrete. We focus our investigations on hardened cement paste (hcp) as the key material and formulate a representative volume element (RVE) consisting of a mixture of larger capillary pores with diameters between 10 µm to 100 µm, which are embedded in a homogeneous, isotropic solid, with sub-micron size porosity and structural features. The mechanical and physical properties of this RVE are simulated numerically, calibrated using statistical nanoindentation and NMR testing (amongst other techniques) characterizing the properties of the solid and µCT and microindentation, characterizing the properties of the entire RVE. The evolution of the properties of this RVE due to FT action is closely studied. We perform FT testing on hcp samples, numerically and experimentally, with high spatial resolution and with various porosities, pore size distributions and minimum temperatures. This study will form the basis for a layered model of the structure. As for the current state of the art, (i) such measurements until now were limited to bulk (non spatially resolved) measurements only and (ii) did not measure the actual mechanical properties but rather used auxiliary parameters such as ultrasound runtime. Here we clearly expect pronounced progress in knowledge with the proposed setup. Also, the strong interlink between experimental work and numerical simulation will allow for a much more complete understanding of the underlying processes, building the basis of a stochastic extrapolation of the experimental findings. The work in the project shall be carried out in close collaboration between Prof. Michael Beer and Dr. Matteo Broggi, who will focus on the stochastic model and analysis, and Prof. Michael Haist, who will carry out the experimental work and the physical modelling. The work will be greatly supported by 4 international collaborators.

混凝土结构的可持续性受到其在环境暴露方面的耐久性的高度影响，例如冻融（FT）攻击。到目前为止，在文献中还没有足够准确的模型，它正确地预测和量化的耐久性，即混凝土退化由于循环冻融。原因有很多：一方面，负荷，即FT暴露是一个高度可变的过程，FT事件的总体极难分类。另一方面，冻结和融化导致材料性质的非常局部的变化（这最终导致剥落），由于其非常小的空间范围，这些变化很难检测和量化，并且其本质上是高度可变的，这在很大程度上取决于混凝土中的水分含量以及冻结条件。我们解决这两个方面的目的是引入一个随机的，空间分辨模型的FT降解混凝土。我们将研究重点放在硬化水泥浆（hcp）作为关键材料上，并制定了一个代表性体积元（RVE），该体积元由直径在10 µm至100 µm之间的较大毛细孔的混合物组成，这些毛细孔嵌入均匀的各向同性固体中，具有亚微米尺寸的孔隙度和结构特征。该RVE的机械和物理特性进行数值模拟，使用表征固体特性的统计纳米压痕和NMR测试（以及其他技术）以及表征整个RVE特性的µCT和微压痕进行校准。由于FT行动的RVE的属性的演变进行了仔细研究。我们进行FT测试HCP样品，数值和实验，具有高空间分辨率和各种孔隙率，孔径分布和最低温度。这项研究将形成一个分层模型的结构的基础。至于现有技术，（i）到目前为止，这种测量仅限于批量（非空间分辨）测量，以及（ii）不测量实际的机械性能，而是使用辅助参数，如超声运行时间。在这里，我们显然期望在所提出的设置的知识的显着进步。此外，实验工作和数值模拟之间的紧密联系将使人们能够更全面地了解潜在的过程，为实验结果的随机外推奠定基础。该项目的工作将由Michael Beer教授和Matteo Broggi博士密切合作进行，他们将专注于随机模型和分析，Michael Haist教授将进行实验工作和物理建模。这项工作将得到4个国际合作者的大力支持。