Multiscale Model for Creep of Shotcrete - From Logarithmic-Type Viscous Behavior of CSH at the μm-Scale to Macroscopic Tunnel Analysis

A previously published multiscale model for early-age cement-based materials [Pichler et al. 2007. “A multiscale micromechanics model for the autogenous-shrinkage deformation of early-age cement-based materials.” Engineering Fracture Mechanics, 74, 34-58] is extended towards upscaling of viscoelastic properties. The obtained model links macroscopic behavior, i.e., creep compliance of concrete samples, to the composition of concrete at finer scales and the (supposedly) intrinsic material properties of distinct phases at these scales. Whereas finer-scale composition (and its history) is accessible through recently developed hydration models for the main clinker phases in ordinary Portland cement (OPC), viscous properties of the creep active constituent at finer scales, i.e., calcium-silicate-hydrates (CSH) are identified from macroscopic creep tests using the proposed multiscale model. The proposed multiscale model is assessed by different concrete creep tests reported in the open literature. Moreover, the model prediction is compared to empirical creep models, such as the so-called B3 model. Finally, the developed multiscale model is incorporated in the macroscopic analysis of shotcrete tunnel linings. Hereby, the early-age properties of shotcrete are specified by the presented multiscale model, taking mix design, cement characteristics, and on-site conditions into account.