Multiphysical analysis methods to predict the ageing and durability of concrete

Sammanfattning: With the societal demand for sustainability and the increasing age of infrastructure, a crucial task for the civil engineering community is to improve the durability of concrete structures. This thesis aims to contribute to such development through theoretical studies using mathematical modelling and numerical simulations. During its service life, a concrete structure is subjected to many different actions, ranging from mechanical loads to chemical and physical processes. Hence, a sound modelling strategy requires multiphysics and the inclusion of coupled chemical and physical fields (e.g. temperature, moisture and cement hydration) in addition to methods that describe mechanical integrity of the material. Conditions and phenomena critical for concrete structures at hydropower facilities have been of particular interest to study.The thesis presents several mathematical models of various complexity to describe the multiphysical behaviour of concrete using a material point description. A significant focus is on models that describe the mechanical behaviour of concrete where aspects such as ageing, cracking, creep and shrinkage are investigated. For the creep behaviour, a state-of-the-art model based on the Microprestress–Solidification (MPS) theory is reviewed and further developed. The appended papers (III to IV) presents a mathematical framework for the modelling of durability aspects of concrete based on multiphase porous media theory. The governing equations are derived with the Thermodynamically Constrained Averaging Theory (TCAT) as a starting point. It is demonstrated how this framework can be applied to a broad variety of phenomena related to durability; from the casting and hardening of concrete to the long-term absorption of water into air-entrained concrete. The Finite Element Methods (FEM) is used to solve the proposed mathematical models, and their capabilities are verified using experimental data from the literature.The main research contribution is the development and evaluation of theoretical models that advance the understanding and improve knowledge of the ageing and durability of concrete and concrete structures. More precisely, it is shown how multiphysical models and the developed multiphase framework can be used to gain insights on the material behaviour of concrete at smaller scales while they are also applicable to structural-scale simulations. During all model development, the efficient solution of structural problems has been fundamental. Through case studies and several examples from the literature, it is exemplified how these models can be used to enhance the performance and thereby increase the durability of concrete structures.