Introduction
The alkali-silica reaction (ASR) is a damage mechanism in concrete structures. Since its discovery in 1940, ASR has been detected in various structures all over the world. Structures affected by the ASR show expansion, cracking and often spalling resulting in a loss of strength and elastic modulus. In many cases a gel leaking out of the cracks or surface pop-outs are also observed. Often, the reaction in a structure becomes apparent only after many years of service. Studying the effects of ASR in massive concrete structures such as dams is of particular importance as they are designed for a long service life and repairs are very expensive. A better understanding of phenomena occurring at the meso-scale is crucial in order to formulate constitutive laws. This description of the material behavior can then be used for simulations at a structural level. The results of these simulations will be helpful to predict the time evolution of structures affected by ASR and to decide if, and when, a dam should be repaired or if a full replacement will be less expensive. Furthermore, a precise knowledge of the meso-scale processes can provide a deeper insight on how to stop or slow down the reaction in affected structures.
Current research
For our simulations we will use 3D microstructures that are obtained from particle size distributions of real mortars and concrete mixes. We explicitly model the gel pockets that form inside the aggregates and expand as the reaction advances. The microstructures are meshed with a non-conforming mesh. We apply the interface-enriched generalized finite element method (IGFEM) in order to capture the discontinuous strain field correctly. The resulting complex crack network is computed by means of a non-local damage law. Massively parallel simulations will allow to reproduce the percolation process of the crack networks and to estimate the reduction of strength.