Applications of X-ray computed tomography to characterize corrosion-induced cracking evolution in reinforced concrete: a review

Corrosion damage is the one of the most significant degradation factors to reinforced concrete structures. Developing reliable instrumentation and methodology to localize and track such damage is critical to evaluate the structural capability. X-ray computed tomography (CT) imaging is a promising non-destructive approach for qualitative and quantitative research of corrosion in reinforced concrete specimens. In this paper, we review the applications of CT in the study and analysis of the evolution of corrosion-induced cracking starting from pre-cracking corrosion product accumulation and deformation. CT images show corrosion-induced cracks appear with the formation of corrosion products that lead to an increase in localized tensile stresses and eventually cracking when these stresses exceed the strength of concrete. Some studies indicate that the initial cracks appears at the steel bar-cement paste interface; in others, it is in the transition zones between aggregate and cement paste. However, cracks can start at any location, including the above interfaces, that consists of the “weakest link” such as voids. The characteristics of corrosion-induced cracks, represented by the aperture and length, are associated with spatial distribution and volume of corrosion products. With the presence of oxygen at the rebar surface, the corrosion of a steel bar starts with the formation of a pit when the amount of chlorine reaches the threshold. As the corrosion progresses combined with the consequent cracking, the initial pits grow in size, depth, and number. CT imaging demonstrates that the presence of pores around the steel bar can intensify corrosion process. Also, the migration and spread of rust through cracks or voids depend on the composition of the corrosion products and mortar. However, regardless of the advances research methods and technologies, there are still uncertain and challenging issues related to corrosion process that require further investigations using high-resolution CT imaging and advanced analysis.