Impact of corrosion on axial load bearing capacity of low-strength concrete columns under monotonic compression and cyclic loading

Abstract

The durability of RC structures and bridges located in cold regions and marine environments is adversely affected by reinforcement corrosion, reducing the service lives, load-carrying capacities and seismic resistance. Several research studies have been undertaken to model the effect of corrosion on the behaviour of RC structures. However, many uncertainties exist due to problems in estimating the corrosion of the reinforcement within the concrete. This research thus explores the use of the X-ray CT scan technique to accurately estimate the volumetric mass loss resulting from the corrosion of a whole reinforcement cage embedded in RC columns and, at the same time, identify the location of pitting corrosion on the reinforcement bars. This will aid in the timely maintenance and retrofitting of degrading RC structures to prevent premature failure and collapse. Furthermore, the impact of corrosion and reinforcement confinement on the nonlinear stress-strain responses of ageing low-strength confined corroded RC columns under axial monotonic and axial cyclic compressive loading was investigated experimentally. The corrosion of the RC columns were simulated in the laboratory using the constant current (2A) accelerated corrosion technique. The time to obtain the desired corrosion was estimated using Faraday’s 2^nd law of electrolysis. A total of 60 short RC columns with varying degrees of corrosion and three different confinement levels were tested during the investigations. Five different degrees of reinforcement corrosion (i.e., 0%, 5%, 10%, 20% and 30%) with three confinement ratios based on the transverse reinforcements' spacing are investigated under axial monotonic and axial cyclic compressive loads. The confinement ratios are assigned through the centre-to-centre spacing of the transverse reinforcement (L) and the diameter of the longitudinal reinforcement (D), known as the spacing-diameter, L/D ratio. Hence, for the test, the three confinement ratios are high (L/D = 5), medium (L/D = 8) and low (L/D = 13). The impact of corrosion and confinement on the inelastic buckling of the longitudinal reinforcements under loading was also investigated. Corrosion of the reinforcement bars affects the effective confinement of the RC columns thereby reducing the ultimate strength of the columns. The strength of the highly confined reduced by about 38% at 30% mass loss while the mediumly and lowly confined reduced by about 39% and 70%, respectively. Hence, the better the confinement the less the impact of corrosion on the RC column and also the better the mechanical behaviour of the RC columns. Furthermore, circular columns have better load carrying capacity than the square columns as a result of the uniform confinement of the transverse bar which provides a constant stress distribution of the concrete along the cross-section. Finally, the numerical investigation was conducted on the confined corroded RC columns using the ABAQUS FEA software to validate the experimental results obtained from both axial and cyclic compressive loading. The numerical investigation accurately predicted the stress-strain response of the confined corroded RC columns under axial compressive monotonic loading. Furthermore, the location of the buckling of the longitudinal bars under load is clearly identified. This will aid in the parametric studies to develop constitutive models for low-strength concrete confined corroded RC columns.

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Identifiers

ORCID for Hammed Olanrewaju Aminulai: orcid.org/0000-0001-6185-5000

ORCID for Mehdi Kashani: orcid.org/0000-0003-0008-0007

ORCID for Neil Ferguson: orcid.org/0000-0001-5955-7477

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