Multi-scale modelling of concrete structures affected by alkali-silica reaction: Coupling the mesoscopic damage evolution and the macroscopic concrete deterioration

A finite-element approach based on the first-order FE 2 homogenisation technique is formulated to analyse the alkali-silica reaction-induced damage in concrete structures, by linking the concrete degradation at the macro-scale to the reaction extent at the meso-scale. At the meso-scale level, concrete is considered as a heterogeneous material consisting of aggregates embedded in a mortar matrix. The mechanical effects of the Alkali-Silica Reaction (ASR) are modelled through the application of temperature-dependent eigenstrains in several localised spots inside the aggregates and the mechanical degradation of concrete is modelled using continuous damage model, which is capable of reproducing the complex ASR crack networks. Then, the effective stiffness tensor and the effective stress tensor for each macroscopic finite element are computed by homogenising the mechanical response of the corresponding representative volume element (RVE), thus avoiding the use of phenomenological constitutive laws at the macro-scale. Convergence between macro- and meso-scales is achieved via an iterative procedure. A 2D model of an ASR laboratory specimen is analysed as a proof of concept. The model is able to account for the loading applied at the macro-scale and the ASR-product expansion at the meso-scale. The results demonstrate that the macroscopic stress state influences the orientation of damage inside the underlying RVEs. The effective stiffness becomes anisotropic in cases where damage is aligned inside the RVE

Multi-Scale Modeling of the Alkali-Silica Reaction in Concrete

The alkali-silica reaction (ASR) is one of the most common causes of internal concrete degradation. This chemical reaction occurs between the amorphous silica contained inside the aggregates, and the alkalis of the cement pore solution. During the reaction hydrophilic silica gel forms, which starts swelling as it absorbs water. This induces internal stresses in the concrete, which in turn cause macroscopic expansion and cracking. Due to its deleterious effects on the mechanical properties of concrete, the ASR is more commonly known as concrete cancer. The speed of the chemical degradation process of ASR is slow and, thus, the consequences in an affected structure often become visible only after many service years. The need to assess the influence of the ASR-induced degradation process on the safety and serviceability of affected concrete structures has led to intensive research activities over the last decades. Both experimental and modeling studies, have provided fundamental insights on the physics of ASR at the meso-scale of concrete. At this scale concrete is typically described as a heterogeneous material, consisting of aggregates embedded in the cement paste. It is, however, not yet well understood how the mesoscopic damage evolution influences the overall material behavior of concrete at the macro-scale, i.e. the structural scale. In the present thesis a numerical framework for ASR is developed, which aims at providing answers regarding the link between the mesoscopic and macroscopic consequences of ASR. For this purpose an ASR meso-scale model is implemented in an open-source finite element library. This numerical development makes the execution of high-performance computing simulations possible, in which the complex ASR-induced crack networks can be captured with an unprecedented level of detail. Moreover, large sets of parametric studies are carried out in order to identify the main influencing numerical and physical parameters of the model. A multi-scale finite element approach is, subsequently, applied in order to up-scale the mesoscopic material response of ASR-affected concrete. This strategy allows to conduct simulations of the mechanical consequences of ASR in large concrete structures, in which the material behavior of concrete is directly governed by the physics of ASR occurring at the meso-scale