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Degradation relations for the tensile properties of corroded reinforcement bar

Name: Raghava Kumar Vanama

Department: Civil Engineering

Program: Ph D (4th year)

Name of supervisor: Prof. Balaji Ramakrishnan

Importance and Novelty of the research:

According to a study, 50% of the reinforced concrete (RC) structures are experiencing premature failures and requires repair even before ten years from their construction. Repairing/strengthening these corrosion damaged RC structures requires the information on the extent of damage and its effect on their load-carrying capacity. Mechanical properties of corroded rebar have great significance in durability evaluation and assessing the load-carrying capacity of a damaged RC structure. Tensile properties of corroded rebar are also necessary for modelling the damaged concrete structures. As retrieving the rebar from any RC structure (for tensile testing) can further damage its condition, empirical relations are often used in modeling the damaged RC structure. The degradation equations to estimate the nominal stresses of corroded rebar (uniform and pitting) proposed in the past have got some drawbacks. For example, properties of the corroded rebar whose mass loss is more than 36% were neither considered nor been validated with past experimental results. They could not be applied when the type of corrosion is unknown, thereby restricting their application.

 

Methodologies adopted:

A part of the present study evaluates the tensile properties of the corroded rebar that are corroded up to 79.64% mass loss of three different grades subjected to natural carbonation and simulated chloride attack. Tensile tests were conducted on 38 corroded steel round rebars of 12.7mm nominal diameter (MS 250 & MS 350 grades) obtained from a 54-year-old inland concrete corridor structure, exposed to natural carbonation and on 15 ribbed bare rebars of 16mm nominal diameter (Fe 500D grade) subjected to chloride attack through an impressed current method. Mass losses were in the range of 0.81% to 79.64% for naturally corroded rebar and 9.95% to 50.51% for artificially corroded rebar. In the case of artificially corroded rebars, variations in rib loss with the level of corrosion were also captured. Customised end holders were designed to test the highly corroded rebar without slippage during the tensile loading. A set of degradation equations were formulated to estimate the yield and ultimate stresses of corroded rebar knowing the properties of uncorroded rebar. The proposed formulations are best fitted by adding the obtained test results to the previous studies. Finally, proposed equations were validated with the results obtained from the literature study. The comparison revealed that the equations proposed in this study provide improved prediction of yield and ultimate stresses of corroded rebar.

 

Salient conclusions:

i. Shank diameter found to be reduced by 26.45% at 50.48% of mass loss. At a given level of corrosion below 50.48%, on an average, transverse ribs and longitudinal ribs reduce by an excess of 4.93% and 4.60%, respectively as compared to the reductions observed for shank diameter.

ii. Based on the tensile tests performed for rebars that are corroded up to 79.64% mass loss, the average elastic modulus is estimated to be 1.99E+05 MPa and observed that value slightly decreases with increase in corrosion degree.

iii. The proposed decay laws are checked for their validity by comparing with the test results published in previous studies and are valid till the corrosion levels up to 50% mass loss.

 

Link to full-length paper (Published in ‘Construction and Building Materials’ Journal):

https://www.sciencedirect.com/science/article/abs/pii/S095006182030711X