Assessment of the mechanical behaviour of reinforcement bars with localised pitting corrosion by Digital Image Correlation

E Chen,Carlos G Berrocal,Ignasi Fernandez,Ingemar Löfgren,Karin Lundgren

doi:10.1016/j.engstruct.2020.110936

E Chen, Carlos G Berrocal + Show 3 more

Open Access

https://doi.org/10.1016/j.engstruct.2020.110936

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Journal: Engineering Structures	Publication Date: Jun 15, 2020
Citations: 44	License type: cc-by

Affiliation: Chalmers University of Technology

Abstract

Corrosion of reinforcement in concrete impairs the mechanical behaviour of rebars by decreasing their strength and deformation capacity. In this study, uniaxial tensile tests were carried out on 61 rebars taken from 22 pre- and un- cracked reinforced concrete beams subjected to drying and wetting cycles in chloride solution for over three years. A 3D-scanning technique was used to characterise the maximum local corrosion level, μmax, and different pit shape parameters. Digital Image Correlation (DIC) was used to capture the displacement field of the test bars; the engineering strain was measured through the virtual extensometers created in the DIC post-processing software. The proof and ultimate forces showed linear decreasing trends of μmax, while the proof and ultimate strengths (based on the minimum residual cross-sectional area) were not obviously affected by corrosion. The ultimate strain of corroded bars depended on the gauge length due to strain localisation in the pit. Thus, it was emphasised that the ultimate strain may be overestimated if measured based on a short gauge across the pit. It was also observed that when μmax exceeded a critical local corrosion level (μcrit depending on the ratio between the yield and ultimate strengths of the steel), the region outside the pit did not develop yielding. A lower bound of ultimate strain was further derived as a function of the mechanical parameters of uncorroded steel and maximum local corrosion level. This provided a good comparison with the experimental results. Ultimately, a hypothesis for time-dependent assessment of strain capacity is proposed, considering the evolution of corrosion morphology over time.

Highlights

Corrosion of steel in concrete is a major cause of impaired safety and durability of infrastructure
Existing research indicates that the load capacity and ductility of steel bars are reduced with increasing corrosion level, the empirical relationships derived for the mechanical parameters vary significantly between different studies and, in some cases, even contradict each other
The correlation between concrete cracks and corrosion characteristics of the beams in this study can be found in a previous study of the authors [26]

Summary

Introduction

Corrosion of steel in concrete is a major cause of impaired safety and durability of infrastructure. Corrosion damage in reinforced concrete mainly includes cover cracking, bond degradation of the steel-concrete interface, and undermining the mechanical behaviour of rebars. None of these three issues has been satisfactorily quantified with respect to the corrosion level, even though they have attracted wide interest in recent decades. Existing research indicates that the load capacity and ductility of steel bars are reduced with increasing corrosion level, the empirical relationships derived for the mechanical parameters (as a function of corrosion level) vary significantly between different studies and, in some cases, even contradict each other. This is most likely attributable to variations in the type of corrosion condition and type of steel, plus the different evaluation methods used in quantifying corrosion levels and mechanical

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