The Service life evaluation of reinforced concrete structures is usually limited to initiation of corrosion, whilst in practice corrosion in many structures has already reached the propagation stage. To better understand the processes that lead to the cracking and detachment of concrete cover during this phase, knowledge of corrosion products’ development over time is required. This paper investigates corrosion products found in blast furnace slag cement concrete, in which natural carbonation acted upon original chloride-induced corrosion. The sample was cast in 1998, after curing subjected to wet-dry cycles to enhance chloride penetration, and later was exposed to unsheltered outdoor conditions. Corrosion products and textures at the concrete-steel interface and late carbonate veinlets within them have been characterized by a combination of optical microscopy, SEM, Raman spectroscopy and CT scanning.