Steel corrosion is one of the main factors leading to degradation of reinforced concrete structures. However, the mechanical behaviour that develops where the corroded steel surface meets the surrounding concrete is still not well defined. This project applies an image-based modelling approach to examine how the expanding corrosion layer interacts with the concrete and drives crack formation. Three-dimensional X-ray and neutron tomography are used to quantify deformation at the steel–concrete interface caused by corrosion. These experimentally obtained displacements are incorporated as boundary conditions in non-linear finite element analyses to evaluate how variations in corrosion patterns affect stress distribution and crack initiation. The study aims to establish a more detailed mechanical description of the corrosion layer and its influence on concrete damage. The findings will support the development of improved numerical models and more reliable durability assessments for reinforced concrete structures.