Multiscale modelling of ASR induced degradation in concrete

In this contribution, we present a multiscale approach to model Alkali-Silica Reaction (ASR) induced degradation in concrete. The model is characterized by a synthesis of a multi-scale semi-analytical model describing the mechanics of microcracking and a finite element model for describing the physics of diffusion and kinetics involved in the Alkali-Silica Reaction. The mechanics of ASR induced deterioration of a Representative Elementary Volume (REV) of concrete containing reactive aggregates is modelled using continuum microporomechanics. At the microscale, ASR gel-pressure induced microcrack growth in the reactive aggregates and in the cement paste is modelled using the framework of linear elastic fracture mechanics. Mean field homogenization across multiple scales is used to obtain the overall expansion and degradation of the material. Experimental data for concrete degradation as a function of the macroscopic expansion is found to lie within the theoretical upper and lower bounds that characterize the distribution of the gel in the aggregate or the cement paste. The diffusion processes and the kinetics involved in the alkali-silica reaction is described by a second-order reaction-diffusion equation solved by means of the finite element method. The chemical reaction as well as alkali, moisture and gel transport are taken into account to obtain a gel mass distribution in the concrete microstructure. The evolution of the gel volume is coupled to the aforementioned semi-analytical model for microcracking induced deterioration and expansion. Comparisons of model predictions with experimental data suggest, that the connectivity of the initial pore structure and microcracks in the aggregate has a significant influence on the overall expansion of concrete.