A multiscale micromechanics model for the autogenous-shrinkage deformation of early-age cement-based materials

Abstract

Autogenous shrinkage is the term for the bulk deformation of a closed, isothermal, cement-based material system not subjected to external forces [Jensen OM, Freiesleben Hansen P. Autogenous deformation and RH-change in perspective. Cement and Concrete Research 2001;31:1859–65]. It is associated with the internal volume reduction of the cement/water mixture in the course of the hydration process. The question arising from engineering practice is the magnitude of the autogenous deformations, increasing the compliance of concrete support structures and inducing tensile stresses which may lead to cracking of early-age concrete. In this paper, a multiscale model for cement-based materials focusing on the prediction of autogenous-shrinkage deformations is presented. In addition to the formulation of the underlying multiscale framework, including the identification of observation scales and the development of appropriate upscaling schemes, shrinkage experiments on cement pastes were conducted and used for the validation of the developed multiscale model. Finally, the multiscale model is used to determine the early-age elastic and shrinkage properties of shotcrete. These properties are employed in the context of hybrid analyses of shotcrete tunnel linings, providing access to the level of loading of the tunnel support structure during NATM tunneling.