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

由于其成本低，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，一个显著的局限性是它倾向于长时间蠕变。这在高层建筑中尤其成问题，因为不期望的蠕变变形可能涉及昂贵的维修、加固或更换，或者可能最终导致断裂和失效。这种变形发生的时间尺度很大（数年），即使不是不可能，也很难直接评估混凝土的徐变倾向。为此，已经提出了许多蠕变的预测模型。然而，他们中的大多数缺乏一个健全的物理基础，并严重参数化，这使得他们的预测值得怀疑的最好的，特别是对于新兴的粘合剂，其中普通波特兰水泥部分或全部取代更环保的材料，如粉煤灰，矿渣或石灰石。该项目旨在确定混凝土徐变的物理起源，以实现可靠的长期徐变变形预测。在此基础上，将研究新的测试方案，并确定抗蠕变水泥粘结剂。本研究整合了物理学、材料科学和土木工程等多个学科，将培养一批多元化的学生，使他们能够从事多维工程。为了阐明混凝土徐变的物理起源，并区分，例如，在滑动或溶解-沉淀机制之间，本研究依赖于模拟的组合。所有的模拟相互输入，并捕捉每个相关规模的水泥粘结剂的贡献。这种自下而上的策略从原子分子动力学与拓扑约束理论相结合开始，在连续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。每个模拟将系统地通知，补充，并通过实验验证，其中包括压痕，垂直扫描干涉法，和单轴蠕变试验。这种跨学科的努力将确定决定性的变量（例如，组成、纳米结构和化学不稳定性），这些因素使得材料对诸如蠕变的长期老化现象敏感或不敏感。先锋加速微扰为基础的模拟方法将进行评估，这将使长期的老化和退化现象的研究，在非晶材料迅速。最后，该项目将有助于揭示本体性质（化学成分，结构）和表面性质（例如，溶解速率）。

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).