COLLABORATIVE RESEARCH: ELUCIDATING THE PHYSICAL ORIGINS OF CREEP IN CEMENTITIOUS MATERIALS TOWARDS IMPROVED PREDICTION
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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).