Strength and ductility performance of corroded steel bars in concrete exposed to 2D chloride ingress
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MRS Advances © 2020 Materials Research Society DOI: 10.1557/adv.2020.328
Strength and ductility performance of corroded steel bars in concrete exposed to 2D chloride ingress Mike Otieno and Ze Zakka School of Civil and Environmental Engineering, University of the Witwatersrand, Johannesburg
Abstract
This paper presents the residual tensile strength test results of corroded high yield steel bars. Single steel bars were embedded at a cover depth of 20 mm in 150 × 150 × 625 mm long cracked concrete beam specimens made with 70/30 PC/FA and 50/50 PC/SL binders with a constant w/b ratio of 0.40. The steel bars were placed in the cross-section centre and near the orthogonal edge of the beams, and selected beam faces epoxy-coated in order to simulate, respectively, 1D and 2D chloride ingress. The beams were subjected to 2-week wetting (with 5% NaCl) and 2-week air-drying cycles in the laboratory for 110 weeks after which the corroded steel bars were extracted, assessed for corrosion morphology, and tested in tension for ultimate strength, fracture strength and ductility performance. The steel bars in concretes exposed to 1D chloride ingress had isolated corrosion pits while both general and isolated corrosion pits were observed in specimens exposed to 2D chloride ingress. The residual ultimate and fracture tensile strengths, and ductility of corroded steel reinforcing bars in concretes exposed to 2D chloride ingress are lower than those for steel bars in concretes exposed to 1D chloride ingress. Corresponding author: Mike Otieno ([email protected])
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Corrosion of steel reinforcement is a common form of deterioration in steel reinforced concrete (RC) structures. In addition to serviceability failures such as cracking of the concrete cover, delamination, spalling and increased deflections, it also results in ultimate limit state failures such as the reduction in the effective steel cross-sectional-area (CSA) and a loss in steel-concrete interface (SCI) bond which lead to a reduction in the load carrying capacity of these structures due to a loss in composite action [1-5]. In severe cases, the loss in the steel CSA due to corrosion can also lead to not only a change in the mode of structural failure but also structural collapse. This is not desirable. In the past 3 to 4 decades, research on steel corrosion in RC has focused on deterioration due to 1-directional (1D) chloride ingress which is typical in slabs and walls. While valuable results and predictive models have been developed using this approach, it does not depict the ingress of corrosion agents at the intersection of the non-planar surfaces of concrete columns, beams and corbels which can be modelled using either 2directional (2D) or 3-directional (3D) approaches [6-8]. In particular, the 2D approach is recommended for the orthogonal edges of beams and columns while the 3D approach is recommended for the exposed terminal ends of columns and in corbels – see Figure 1. The results presented in this paper were part of a study which investigated the effect of
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