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

C. Pichler, R. Lackner and H. A. Mang

Journal of Advanced Concrete Technology, 6(1) 91-110, 2008

A recently presented multiscale model for early-age cement-based materials [Pichler et al. A multiscale micromechanics model for the autogenous-shrinkage deformation of earlyage cement-based materials. Engineering Fracture Mechanics 2007;74:3-58] is extended towards upscaling of viscoelastic properties. The obtained model links macroscopic behavior, i.e., creep compliance of concrete, to the composition of concrete at finer scales and the material properties of distinct phases at these scales. Whereas finer-scale composition (and its history) is accessible through so-called multiphase hydration models for the main clinker phases in ordinary Portland cement (OPC), viscous properties of thecreep-active constituent at finer scales, i.e., calcium-silicate-hydrates (CSH) are identified from macroscopic creep tests using the proposed multiscale model and assessed by nanoindentation experiments. 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.

The research expresses its value in term of relating the micro-scale hydration behavior to the macro scale structure level for creep behavior, though a few simple assumptions were made and the effects of environment such as temperature and RH were still not considered. The developed model was also proved to be more precise when compared to the currently popularly applied one.(Prof. Somnuk Tangtermsirikul, Thailand)