Multiscale modelling of ASR induced degradation in concrete

Tagir Iskhakov, Ruhr-University Bochum, Bochum, Germany
Jithender Jaswant Timothy, Ruhr-University Bochum, Bochum, Germany
Günther Meschke, Ruhr-University Bochum, Bochum, Germany

ASR (Alkali-Silica Reaction) is a detrimental expansive reaction in concrete resulting in severe deterioration and loss of structural integrity. It occurs in concrete at the microscale when diffusing alkali and hydroxyl ions in the pore fluid break the silanol and siloxane bonds in the reactive aggregates, leading to formation of a hydrophilic gel. The alkali-silica gel fills the pre-existing voids in concrete, namely the microcracks in the aggregates and cement paste. The gel swells in the presence of moisture in the concrete pore space. Such swelling leads to the growth of microcracks. Propagation of microcracks at the microscale manifests itself as an expansion and stiffness reduction of the concrete at the macroscale. In order to predict such detrimental macroscopic ASR induced effects on the concrete structure, a multiscale approach is proposed. Using mean-field homogenization, we upscale the microcracking processes characterized by linear elastic fracture mechanics and microporomechanics. Along with the growth of pre-existing flaws in the concrete, the model takes into account the localization of damage around the aggregates. The kinetics of the alkali-silica gel formation is analysed by means of numerical modelling which describes the diffusion of alkali ions into the aggregate and the subsequent reaction with silica. The capabilities of the multiscale chemo-mechanical model are illustrated with select validated examples.

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