Collaborative Research: Elucidating the Physical Origins of Creep in Cementitious Materials Towards Improved Prediction and Prescription of Creep-Resistant Binders

由于其低成本，易于使用和性能，混凝土是迄今为止世界上制造最多的材料。然而，一个重要的限制是它倾向于在较长的持续时间内爬行。这在高层建筑中尤其有问题，因为不希望发生的蠕变变形可能涉及昂贵的修复、加强或更换，或者最终导致断裂和失效。这种变形发生的大时间尺度（年）使得直接评估混凝土的徐变倾向具有挑战性，如果不是不可能的话。为此，已经提出了许多预测蠕变的模型。然而，它们中的大多数缺乏可靠的物理基础，并且大量参数化，这使得它们的预测充其量是值得怀疑的，特别是对于新兴的粘结剂，其中普通波特兰水泥部分或全部被更环保的材料如粉煤灰，矿渣或石灰石所取代。该项目旨在确定混凝土中徐变的物理起源，以便对徐变变形进行可靠的长期预测。基于这些知识，将研究新的测试方案，并确定抗蠕变胶凝粘合剂。本研究整合了多个学科，包括物理、材料科学和土木工程，并将培养多元化的学生进行多维工程。为了阐明混凝土徐变的物理根源，并区分滑移或溶解-沉淀机制，本研究依赖于模拟的组合。所有的模拟相互输入，并捕获胶凝粘合剂的每个相关尺度的贡献。这种自下而上的策略从原子分子动力学开始，结合拓扑约束理论，在连续体有限元模拟中达到高潮，并受益于中尺度建模，以确保所有考虑的空间尺度的握手。每个模拟将被系统地告知，补充，并通过实验验证，包括压痕，垂直扫描干涉测量和单轴蠕变测试。这种跨学科的努力将确定决定性的变量（例如，成分，纳米结构和化学不稳定性），使材料对蠕变等长期老化现象敏感或不敏感。开创性的基于加速微扰的模拟方法将被评估，这将允许快速研究非晶材料的长期老化和降解现象。最后，该项目将有助于揭示体积特性（化学成分、结构）和表面特性（如溶解速率）之间的联系。

Due to its low cost, ease of use, and performance, concrete is by far the most manufactured material in the world. However, a significant limitation is its tendency to creep over long durations. This is especially problematic in high-rise building, as undesirable creep deformations can involve expensive repairs, strengthening, or replacement, or can ultimately result in fracture and failure. The large time scales over which such deformations occur (years) make it challenging, if not impossible, to directly assess the creep propensity of concrete. To this end, numerous predictive models of creep have been suggested. However, most of them lack a sound physical basis and are heavily parameterized, which renders their predictions questionable at best, especially for new emerging binders in which ordinary portland cement is partially or fully replaced by more environment-friendly materials like fly ash, slag or limestone. This project aims to identify the physical origin of the creep in concrete to enable reliable long-term predictions of creep deformations. Based on this knowledge, new testing protocols will be studied, and creep-resistant cementitious binders will be identified. This research integrates multiple disciplines, including physics, material science, and civil engineering and will train a diverse group of students to multi-dimensional engineering.To elucidate the physical origin of creep in concrete, and to discriminate, e.g., between the sliding or dissolution-precipitation mechanisms, this research relies on a combination of simulations. All simulations mutually feed into each others and capture the contribution of each of the relevant scales of cementitious binders. This bottom-up strategy starts from atomistic molecular dynamics coupled with topological constraint theory, culminates in continuum finite element simulations, and benefits from mesoscale modeling to ensure the hand-shake of all the considered spatial scales. Each simulation will be systematically informed, complemented, and validated by experiments, which comprise indentation, vertical scanning interferometry, and uniaxial creep tests. This interdisciplinary effort will identify the decisive variables (e.g., composition, nanostructure, and chemical instability) that render a material sensitive, or not, to long-term aging phenomena such as creep. Pioneering accelerated perturbation-based simulation methods will be evaluated, which will permit the study of long-term aging and degradation phenomena in amorphous materials rapidly. Finally, the project will contribute to reveal the link between bulk properties (chemical composition, structure) and surface properties (e.g., dissolution rates).