Recent collapses of degrading reinforced concrete (RC) structures have raised international awareness on the vulnerability of ageing infrastructure. Many severe cases of degradation are due to aggressive pitting corrosion of the reinforcing steel, caused by chloride penetration. As most research focuses either on chloride transport in concrete or on structural effects of rebar corrosion, an important research challenge lies in bridging these scales to advance our fundamental understanding of the interaction between the RC layout, chloride ingress, and corrosion damage. In this project, we will develop and experimentally validate multi-physics lattice discrete particle models (M-LDPM) that couple the mechanical analysis with reactive transport models, to study the spatial and temporal variability of the corrosion process in relation to concrete heterogeneities. Advanced 4D visualization techniques are applied for validation of the M-LDPM simulations. X-ray Computed Tomography (XCT) is used to characterize the inner structure of small RC samples as input for sample-specific M-LDPM, and 4D-XCT visualizes the kinetics of the corrosion process in space and time during natural corrosion tests. At the larger scale, RC prisms are subjected to accelerated corrosion and monitored with 4D Acoustic Emission (AE) sensing. RC samples with various layouts are tested to validate M-LDPM that account for randomly distributed aggregates and discrete pre-existing mechanical cracks.