Experimentally supported multi-scale Reactive Transport modeling of cementitious materials under Acid attack (ExpeRTa)

混凝土是应用最广泛的建筑材料，其劣化机理是制约民用基础设施使用寿命的主要因素。特别地，酸侵蚀使混凝土结构中的胶凝材料降解。随着人们对水泥基材料耐久性研究的不断深入，深入了解混凝土材料在多尺度下的反应输运过程是十分必要的。然而，这还没有从根本上考虑在流行的实验和计算方法，试图阐明酸攻击机制。到目前为止，只使用了均质化的数值模型，忽略了在一系列尺度上发生的具体非均匀性描述。一个基本的方法是需要耦合的化学，即反应热力学和动力学以及运输现象与混凝土成分的多尺度分布。多孔介质中的多尺度反应输运现象一般刚刚开始探索这些天，但很可能成为一个主要的焦点，在几个科学领域迅速ExpeRTa的主要目标是调查和阐明的基本机制，造成混凝土退化，由于酸侵蚀的反应输运特性在一系列尺度上的异质性效应的重点。这包括：O 1）使用Hymostruc 3D虚拟微观结构的孔隙尺度数值模拟和酸侵蚀反应性传输退化模型的实施; O2）反应性传输模型的中尺度数值模拟和放大; O3）关于材料设计和侵蚀参数的膏体、砂浆和混凝土退化的实验程序; O 4）利用获得的实验结果对数值模型进行多尺度分析、校准和验证。计划的实验方法包括：µ-XRF、SAXS、纳米压痕、MIP、气体吸附、热分析、XRD、光学显微镜、带EDX的ESEM和3D-µ-CT成像。实验活动的设计方式，其结果可用于校准和验证开发的数值模型。将研究混凝土配合比设计（水灰比和粘结剂中的Ca/Si比、骨料类型以及数量和尺寸）、酸类型和边界（侵蚀）条件参数的影响。在这种协同合作中，达姆施塔特大学团队作为反应传输计算的混凝土耐久性建模专家，将与KIT团队密切合作，KIT团队是材料测试和分析以及水泥材料酸侵蚀实验研究的专家。这种独特的基本建模方法的结果与基于已建立的科学原理和加速耐久性试验的已知校准的外推相结合，将显着提高混凝土结构使用寿命预测的准确性。

Service-life of civil infrastructure is dominantly limited by deterioration mechanisms of concrete, the most widely used construction material. Particularly, acid attack is degrading cementitious materials in concrete structures. With increasing interest in the durability of cementitious materials, a better understanding of the underlying reactive-transport phenomena for concrete material in multi-scale is essential. Hitherto, this is not yet fundamentally considered in the prevailing experimental and computational approaches trying to elucidate the acid attack mechanisms. Only homogenized numerical models have been used so far, neglecting concrete heterogeneity descriptions occurring across a range of scales. A fundamental approach is needed that couples the chemistry, i.e. reaction thermodynamics and kinetics as well as transport phenomena with a multi-scale distribution of concrete components. Multiscale reactive-transport phenomena in porous media in general just starting to be explored these days, but are likely to become a primary focus in several scientific fields rapidly.Key objectives of ExpeRTa are to investigate and elucidate the fundamental mechanisms that cause concrete degradation due to acid attack with an emphasis on heterogeneity effects in the reactive-transport characteristics across a range of scales. This includes: O1) pore-scale numerical modelling using Hymostruc 3D virtual microstructures and implementation of the reactive transport degradation model for acid attack; O2) Meso-scale numerical modelling and upscaling of the reactive transport model; O3) An experimental program on paste, mortar and concrete degradation regarding materials design and attack parameters; O4) Multiscale analysis, calibration and validation of the numerical models with the obtained experimental results.Planned experimental methods comprise: µ-XRF, SAXS, Nanoindentation, MIP, gas sorption, thermal analysis, XRD, light microscopy, ESEM with EDX, and 3D-µ-CT imaging. The experimental activities are designed in such a way that the results can be used to calibrate and validate the developed numerical models. The influence of concrete mix design (water-to-cement-ratio and Ca/Si -ratio in binder, aggregate type as well as amount and size), acid type and parameters of boundary (attack) conditions will be investigated. In this synergetic cooperation, the Darmstadt University team, as concrete durability modelling experts for reactive transport computations, will cooperate intensively with the KIT team, who are experts for material testing and analysis and experimental investigation of acid attack on cementitious materials. The results of this unique fundamental modelling approach combined with extrapolations based on established scientific principles and known calibrations from accelerated durability tests, will significantly enhance the accuracy of the concrete structures service-life predictions.