  While it is widely accepted that the steel-concrete interface (SCI) plays an
important role in governing the long-term durability of reinforced concrete
structures, understanding about the primary features of the SCI that influence
corrosion degradation mechanisms has remained elusive. This lack of knowledge
can be attributed, on the one hand, to the complex heterogeneous nature of the
SCI, and, on the other hand, the absence of experimental techniques suitable
for studying the relevant features of the SCI. Here, we use focused ion beam -
scanning electron microscopy (FIB-SEM) nanotomography to obtain high resolution
3D tomograms of the steel-concrete interfacial zone. Five tomograms, spanning
volumes ranging from 8,000 to 200,000 cubic micrometer, were acquired for
situations representative of both non-corroded and corroded SCIs. The achieved
voxel size falls within the range of 30-50 nm, thus providing a resolution
clearly surpassing the capabilities of computed X-ray tomography. This
resolution enables the 3D characterization of the microstructure at the
capillary scale, which is the scale at which relevant corrosion and related
mass transport processes occur. Thus, FIB-SEM nanotomography is capable of
yielding datasets of the SCI that serve as basis for the generation of digital
twins of the interfacial microstructure, thereby enabling future studies about
durability and corrosion of reinforced concrete at the pore scale.
