Chloride-induced corrosion of steel in concrete—insights from bimodal neutron and X-ray microtomography combined with ex-situ microscopy

Chloride-induced corrosion of steel in concrete—insights from bimodal neutron and X-ray microtomography combined with ex-situ microscopy

Angst, Ueli M. (ETH Zürich)
Rossi, Emanuele (ETH Zürich)
Boschmann Käthler, Carolina (ETH Zürich)
Mannes, David (Paul Scherrer Institute)
Trtik, Pavel (Paul Scherrer Institute)
Elsener, Bernhard (ETH Zürich)
Zhou, Z. (TU Delft RST/Neutron and Positron Methods in Materials)
Strobl, Markus (University of Copenhagen)

2024

The steel–concrete interface (SCI) is known to play a major role in corrosion of steel in concrete, but a fundamental understanding is still lacking. One reason is that concrete’s opacity complicates the study of internal processes. Here, we report on the application of bimodal X-ray and neutron microtomography as in-situ imaging techniques to elucidate the mechanism of steel corrosion in concrete. The study demonstrates that the segmentation of the specimen components of relevance—steel, cementitious matrix, aggregates, voids, corrosion products—obtained through bimodal X-ray and neutron imaging is more reliable than that based on the results of each of the two techniques separately. Further, we suggest the combination of tomographic in-situ imaging with ex-situ SEM analysis of targeted sections, selected based on the segmented tomograms. These in-situ and ex-situ characterization techniques were applied to study localized corrosion in a very early stage under laboratory chloride-exposure conditions, using reinforced concrete cores retrieved from a concrete bridge. Several interesting observations were made. First, the acquired images revealed the formation of several corrosion sites close to each other. Second, the morphology of the corrosion pits was relatively shallow. Finally, only about half of the total 31 corrosion initiation spots were in close proximity to interfacial macroscopic air voids, and > 90% of the more than 160 interfacial macroscopic air voids were free from corrosion. The findings have implications for the mechanistic understanding of corrosion of steel in concrete and suggest that multimodal in-situ imaging is a valuable technique for further related studies.

Concrete
Corrosion
In-situ characterization
Neutron imaging, X-ray imaging
Tomography

http://resolver.tudelft.nl/uuid:64daccae-ad6e-45ea-ad67-a098cfdd0ba6

https://doi.org/10.1617/s11527-024-02337-7

1359-5997

Materials and Structures, 57 (4)

Institutional Repository

journal article

© 2024 Ueli M. Angst, Emanuele Rossi, Carolina Boschmann Käthler, David Mannes, Pavel Trtik, Bernhard Elsener, Z. Zhou, Markus Strobl