Autogenous Shrinkage and Creep of Early-Age Cement-Based Materials: Multiscale Modeling With Experimental Identification and Verification

Concrete is a porous medium gaining its strength and stiffness in the course of the hydration process, i.e., the chemical reaction between anhydrous cement and water. Multiscale models enable the modeling of the hydration process [1] by consideration of finer scales of observation and the respective physical/chemical processes at these scales. In this paper, the spectrum of multiscale modeling of cement-based materials, starting from material characterization by state-of-the-art experimental methods, development of homogenization schemes for determination of macroscopic material behavior, and finally the incorporation of the multiscale model into the design process of concrete structures is presented. Unlike material models formulated at the macroscopic scale of observation, multiscale models allow the explicit link of complex macroscopic behavior to its respective origin at finer scales of observation with a sound physical/ chemical basis of the employed constitutive laws at these scales. Recently developed experimental methods for material characterization at finer scales of observation, e.g., nanoindentation, are combined with analytical and numerical methods for (i) interpretation of experimental data [4] and (ii) upscaling towards the macroscopic scale. Whereas an upscaling scheme for elastic properties of early-age cement-based materials has recently been proposed in [1], a homogenization scheme for autogenous shrinkage [3], and viscoelastic properties of early-age cement-based materials is presented in this paper. Classical homogenization schemes, e.g. the Mori-Tanaka scheme [2], for upscaling of elastic properties are specialized in order to account for the loading of the microstructure comprising the effect of capillary depression in the liquid material phase and swelling phenomena resulting from crystallization pressure and viscoelastic material behavior of calcium-silicate-hydrates (CSH).