Reinforced concrete (RC) structures are the most popular structural type in many parts of the world due to its cost effectiveness, high durability, and worldwide availability of steel and concrete. However, many of the old RC structures are facing one common problem, i.e. corrosion of embedded steel bars, due to carbonation of concrete and chloride attack. Generally, carbonation tends to cause uniform corrosion and chloride attack tends to cause pitting corrosion. Uniform corrosion reduces evenly the cross sectional area and decreases the load-carrying capacity of steel bars. Pitting corrosion causes non-uniform reduction in the cross sectional area, which leads to higher strains in the pitting locations and hence reduces the deformation capacity of steel bars in addition to the reduction in load-carry capacity. There are two common methods in simulating the tensile behavior of a corroded steel bars. In one method, a corroded steel bar is modelled using the reduced cross-sectional area based on corrosion weight loss; and the yield stress, ultimate stress, and ultimate strain of the bar are modified to consider pitting corrosion. In the other method, a corroded steel bar is modelled using the original cross-sectional area and the corrosion effect is accounted for by modifying the stress-strain behavior of the bar (elastic modulus, yield stress, ultimate stress, and ultimate strain). The latter method is considered in this research since it is easier to be implemented in a large-scale structural analysis.

Reinforced concrete (RC) structures are the most popular structural type in many parts of the world due to its cost effectiveness, high durability, and worldwide availability of steel and concrete. However, many of the old RC structures are facing one common problem, i.e. corrosion of embedded steel bars, due to carbonation of concrete and chloride attack. Generally, carbonation tends to cause uniform corrosion and chloride attack tends to cause pitting corrosion. Uniform corrosion reduces evenly the cross sectional area and decreases the load-carrying capacity of steel bars. Pitting corrosion causes non-uniform reduction in the cross sectional area, which leads to higher strains in the pitting locations and hence reduces the deformation capacity of steel bars in addition to the reduction in load-carry capacity. There are two common methods in simulating the tensile behavior of a corroded steel bars. In one method, a corroded steel bar is modelled using the reduced cross-sectional area based on corrosion weight loss; and the yield stress, ultimate stress, and ultimate strain of the bar are modified to consider pitting corrosion. In the other method, a corroded steel bar is modelled using the original cross-sectional area and the corrosion effect is accounted for by modifying the stress-strain behavior of the bar (elastic modulus, yield stress, ultimate stress, and ultimate strain). The latter method is considered in this research since it is easier to be implemented in a large-scale structural analysis.
This research examined the monotonic tensile behavior of naturally corroded D13 (#4), D16 (#5), and D19 (#6) deformed steel bars and artificially corroded D13 (#4) and D29 (#9) deformed steel bars. Naturally corroded steel bars were obtained from a corroded residential building near the coastline. In total 18 bars were obtained. Moreover, artificially corroded steel bars were obtained from accelerated corrosion tests on observation specimens of reinforced concrete beams. In total, 29 corroded bars were obtained. Both the strength and deformation properties were examined. The artificial corrosion was achieved by impressed current technique. Based on the test data from this study and those from the literatures, the objectives of this research are to examine the tensile properties of naturally and artificially corroded steel bars and to compare their differences.
The tensile test results have shown that when corrosion weight loss increases, the strength and deformation capacities of bars tend to decrease. However, the trend for the decrease of the deformation capacity is less clear than of the strength. More factors affecting the measured deformation than the measured strength, leading to more scatter results. It was also found that corrosion had a greater effect on the ductility of steel bars than other mechanical properties. This research also found that it is likely conservative to use the artificial corrosion results to predict the structural capacity of naturally corroded structure subjected to chloride attack.

MAIN CHAPTERS TABLE OF CONTENT

ABSTRACT i

ACKNOWLEDGEMENT ii

MAIN CHAPTERS TABLE OF CONTENT iv

LIST OF TABLES vi

LIST OF FIGURES vii

NOTATION x

1. Introduction and Scope of the Research 1
1.1. Research Motivation 1
1.2. Objectives and Scope of the Research 6
1.3. Organization and Thesis Overview 8
References 9

2. Fundamentals of Mechanical Behavior of Corroded Steel Bars 11
2.1. Problem Definition 11
2.2. Fundamentals of Corrosion 12
2.2.1. Corrosion Mechanism 12
2.3. Artificial Corrosion Setup 14
2.3.1. Impressed Current Method 14
2.3.2. Salt Spray Exposure 15
2.3.3. Artificial Climate 15
2.3.4. Mechanical Section Reduction 16
2.3.5. General 16
2.4. Mechanical Behavior of Corroded Steel Bars 17
References 20

3. Experimental Study 23
3.1. Process to Obtain Naturally Corroded Steel Bars 23
3.2. Process to Obtain Artificially Corroded Steel Bars 25
3.2.1. Specimen Design 25
3.2.2. Accelerated Corrosion 26
3.3. Corrosion Weight Loss Measurement 27
3.4. Chloride-ion Content Analysis 30
3.5. Tensile Test Setup and Stress-strain Curves 32
References 38

4. Mechanical Properties of Corroded Steel Bars 39
4.1. Non-corroded Mechanical Properties of Naturally Corroded Steel Bars 39
4.2. Discussion of Mechanical Properties of Corroded Steel Bars 41
4.2.1. Test Results from This Research 41
4.2.2. Comparison of Naturally and Artificially Corroded Steel Bars in This Research with Previous Studies 48
4.2.3. Yield Plateau of Corroded Steel Bars 51
4.2.4. Stress-strain Curve Reconstruction of Corroded Steel Bars 52
References 54

5. Conclusions and Future Research 56
5.1. Thesis Key Conclusions 56
5.1.1. Chloride-ion Analysis Conclusions 56
5.1.2. Tensile Testing Conclusions 56
5.2. Recommendations for Future Research 58

APPENDICES
A. Naturally Corroded Steel Bars Testing Photos a
B. Artificially Corroded Steel Bars Testing Photos d
C. APPENDIX C. Validation of Non-corroded Mechanical Properties of Naturally Corroded Steel Bars j

Chapter 1
1.Palsson, R., and Mirza, M. S., “Mechanical Response of Corroded Steel Reinforcement of Abandoned Concrete Bridge,” ACI Structural Journal, V. 99, No. 2, Mar.-Apr. 2002, pp. 157-162.
2.Lee, H. S., and Cho, Y. S., “Evaluation of the Mechanical Properties of Steel Reinforcement Embedded in Concrete Specimen as a Function of the Degree of Reinforcement Corrosion,” International Journal of Fracture, V. 157, 2009, pp. 81-88.
3.Cairns, J., Y. Du, et al., "Structural performance of corrosion-damaged concrete beams," Magazine of Concrete Research, V. 60, No. 5, 2008, pp. 359-370.
4.Stewart, M. G., “Mechanical Behaviour of Pitting Corrosion of Flexural and Shear Reinforcement and Its Effect on Structural Reliability of Corroding RC Beams,” Structural Safety, V. 31, 2009, pp. 19-30.
5.Kallias, M. I., and Rafiq, M. I., “Finite Element Investigation of the Structural Response of Corroded RC Beams,” Engineering Structures, V. 32, 2010, pp. 2984-2994.
6.Kallias, M. I., and Rafiq, M. I., “Performance Assessment of Corroding RC Beams Using Response Surface Methodology,” Engineering Structures, V. 49, 2013, pp. 671-685.
7.Cairns, J., Plizzari, G. A., Du, Y., Law, D. W., and Franzoni, C., “Mechanical Properties of Corrosion-Damaged Reinforcement,” ACI Materials Journal, V. 102, No. 4, July-August 2005, pp. 256-264.
8.Ou, Y.-C., Tsai, L.-L., and Chen, H.-H., “Cyclic Performance of Large-Scale Corroded Reinforced Concrete Beams,” Earthquake Engineering and Structural Dynamics, V. 41, No. 4, April 2012, pp. 593-604.
9.Kashiwabara, S., Tanimura, Y., Izuminami, R., and Kimura, M., “A Study on Evaluation Method of the Tensile Yield Strength of Corroded Reinforcing Bar Cut Out from Structure,” Proc. Of the 55th Annual Conference of the Japan Society of Civil Engineers, V. 357, 2000, pp. 716-717. (in Japanese)
10.Gu, X. L., Zhang, W. P., Shang, D. F., and Wang, X. G., “Flexural Behavior of Corroded Reinforced Concrete Beams,” Earth and Space 2010: Engineering, Science, Construction, and Operations in Challenging Environments, ASCE, 2010, pp. 3545-3552.
11.Zhang, W.; Song, X.; Gu, X.; and Li, S., “Tensile and Fatigue Behavior of Corroded Rebars,” Construction & Building Materials, V. 34, 2012, pp. 409-417.
12.Cho, Y. S., “Shear Behavior Evaluation of Corroded RC Beams and Seismic Behavior of RC Beams with Corroded Longitudinal Steel Reinforcement,” M.S. Thesis, Department of Construction Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan, 2012. (In Chinese)
http://ndltd.ncl.edu.tw/cgi-bin/gs32/gsweb.cgi?o=dnclcdr&s=id=%22100NTUS5512065%22.&searchmode=basic
13.Ou, Y.-C., and Chen, H.-H. "Cyclic Behavior of Reinforced Concrete Beams with Corroded Transverse Steel Reinforcement," Journal of Structural Engineering, ASCE, 2013.
14.Vu, N. N., “Residual Shear Strength and Ductility Evaluation of Corroded RC Beams,” M.S. Thesis, Department of Construction Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan, 2013.
http://ndltd.ncl.edu.tw/cgi-bin/gs32/gsweb.cgi?o=dnclcdr&s=id=%22101NTUS5512008%22.&searchmode=basic

Chapter 2
1.Gu, X. L., Zhang, W. P., Shang, D. F., and Wang, X. G., “Flexural Behavior of Corroded Reinforced Concrete Beams,” Earth and Space 2010: Engineering, Science, Construction, and Operations in Challenging Environments, ASCE, 2010, pp. 3545-3552.
2.Hansson, C. M., Poursaee, A., et al., "Macrocell and Microcell Corrosion of Steel in Ordinary Portland Cement and High Performance Concretes," Cement and Concrete Research, V. 36, No. 11, 2006, pp. 2098-2102.
3.Mohammed, T. U., Yamaji, T., et al., "Chloride Diffusion, Microstructure, and Mineralogy of Concrete after 15 Years of Exposure in Tidal Environment," ACI Materials Journal, V.99, No. 3, 2002, pp. 256-263.
4.Raupach, M., "Chloride-induced Macrocell Corrosion of Steel in Concrete - Theoretical Background and Practical Consequences," Construction and Building Materials, V. 10, No. 5, 1996, pp. 329-338.
5.Ou, Y.-C., Tsai, L.-L., and Chen, H.-H., “Cyclic Performance of Large-Scale Corroded Reinforced Concrete Beams,” Earthquake Engineering and Structural Dynamics, V. 41, No. 4, April 2012, pp. 593-604.
6.Apostolopoulos, C. A., Papadopoulos, M. P., and Pantelakis, S. G., “Tensile Behavior of Corroded Reinforcing Steel Bars BSt 500s,” Construction & Building Materials, V. 20, 2006, pp. 782-789.
7.Apostolopoulos, C. A., “Mechanical Behavior of Corroded Reinforcing Steel Bars S500s Tempcore under Low Cycle Fatigue,” Construction & Building Materials, V. 21, 2007, pp. 1447-1456.
8.Apostolopoulos, C. A., and Papadopoulos, M. P., “Tensile and Low Cycle Fatigue Behavior of Corroded Reinforcing Steel Bars S400,” Construction & Building Materials, V. 21, 2007, pp. 855-864.
9.Tsai, W.-P., Chen, H.-J., et al., “The Accelerated Method for Estimating Corrosion of Reinforced Concrete Structure in Seawater, Vancouver, BC, Canada, American Society of Civil Engineers, 2008.
10.Yingshu, Y., Yongsheng, J., et al., "Comparison of Two Accelerated Corrosion Techniques for Concrete Structures," ACI Structural Journal, V. 104, No.3, 2007, pp. 344-347.
11.Cairns, J., Du, Y., et al., "Structural Performance of Corrosion-Damaged Concrete Beams," Magazine of Concrete Research, V. 60, No. 5, 2008, pp. 359-370.
12.Zhang, W.; Song, X.; Gu, X.; and Li, S., “Tensile and Fatigue Behavior of Corroded Rebars,” Construction & Building Materials, V. 34, 2012, pp. 409-417.
13.Almusallam, A. A., "Effect of Degree of Corrosion on the Properties of Reinforcing Steel Bars," Construction and Building Materials, V. 15, No. 8, 2001, pp. 361-368.
14.Allam, I. M., Maslehuddin, M., Saricimen, H., and Al-Mana, A. I., “Influence of Atmospheric Corrosion on the Mechanical Properties of Reinforcing Steel,” Construction & Building Materials, V. 8, No. 1, 1994, pp. 35-41.
15.Richardson, M. G., “Fundamentals of Durable Reinforced Concrete,” Taylor & Francis, London, UK, 2002.
16.Williamson, S. J. and Clark, L. A., “Pressure Required to Cause Cover Cracking of Concrete Due to Reinforcement Corrosion,” Magazine of Concrete Research, V. 52, No. 6, 2000, pp. 455-467.
17.Carrion-Viramontes, F. J., Hernandez-Rivera, J., Martinez-Madrid, M. et al., “Corrosion Behaviour of Prestressed Steel-Reinforced Structures,” Corrosion Reviews, V. 17, No. 2, 1999, pp. 119-129.
18.Darmawan, M. S. and Stewart, M. G., “Effect of Pitting Corrosion on Capacity of Prestressing Wires,” Magazine of Concrete Research, V. 59, No. 2, 2007, pp. 131-139.
19.Evans, R. H., “Use of Calcium Chloride in Prestressed Concrete,” Proceedings of World Conference on Prestressed Concrete, San Francisco, CA, USA. University of California / Prestressed Concrete Institute, San Francisco, CA, USA, 1957, pp. A31-1- A31-8.
20.Trejo, D., Pillai, R. G., Hueste, M., Reinschmidt, K. F., and Gardoni, P., “Parameters Influencing Corrosion and Tension Capacity of Post-Tensioning Strands,” ACI Materials Journal, V. 106, No. 2, 2009, pp. 144-153.
21.Andrade, C., Alonso, C., Garcia, D., and Rodriguez, J., “Remaining Lifetime of Reinforced Concrete Structures: Effect of Corrosion in the Mechanical Properties of the Steel,” Life Prediction of Corrodible Structures, NACE, Cambridge, UK, Sept. 1991, pp. 12/1-12/11.
22.Palsson, R., and Mirza, M. S., “Mechanical Response of Corroded Steel Reinforcement of Abandoned Concrete Bridge,” ACI Structural Journal, V. 99, No. 2, Mar.-Apr. 2002, pp. 157-162.
23.Zhang, P. S., Lu, M., and Li, X. Y., “Mechanical Property of Rustiness Reinforcement Steel,” Journal of Industrial Buildings, V. 25, No. 9, 1995, pp. 41-44.
24.Du, Y. G., Clark, L. A., and Chan, A., “Residual Capacity of Corroded Reinforcing Bars,” Magazine of Concrete Research, V. 57, pp. 3, 2005, pp. 135-147.
25.Maslehuddin, M., Allam, I. M., Al-Sulaimani, G. J., Al-Mana, A. I., and Abduijauwad, S. N., “Effect of Rusting of Reinforcing Steel on Its Mechanical Properties and Bond with Concrete,” ACI Materials Journal, V. 87, No. 5, Sept.-Oct. 1990, pp. 496-502.
26.Cairns, J., Plizzari, G. A., Du, Y., Law, D. W., and Franzoni, C., “Mechanical Properties of Corrosion-Damaged Reinforcement,” ACI Materials Journal, V. 102, No. 4, July-August 2005, pp. 256-264.
27.Lee, H. S., Tomosawa, F., and Noguchi, T., “Effect of Rebar Corrosion on the Structural Performance of Singly Reinforced Beams,” Durability of Building Materials and Components, V. 7., C. Sjostrom, ed., E&FN Spon, London, 1996, pp. 571-580.
28.Morinaga, S., “Remaining Life of Reinforced Concrete Structures after Corrosion Cracking,” Durability of Building Materials and Components, C. Sjostrom, ed., E&FN Spon, London, 1996, pp. 127-137.
29.Clark, L. A., and Saifullah, M., “Effect of Corrosion Rate on the Bond Strength of Corroded Reinforcement,” Corrosion and Corrosion Protection of Steel in Concrete, R. N. Swamy, ed., Sheffield Academic Press, Sheffield, 1994, pp. 591-602.
30.Apostolopoulos, C. A. and Papadakis, V. G., “Mechanical Behavior of Reinforcement Stirrups BSt 500(s) at Corrosive Environment,” Journal of Materials Engineering and Performance, V. 16, No. 2, 2007, pp. 236-241.
31.Yuan, Y. S. and Ji, Y. S., “Development of Corrosion Layer of Steel Bar in Concrete and Its Mechanical and Electrochemical Effects,” International Journal of Structural Engineering, V. 1, No. 2, 2010, pp. 199-206.
32.Yuan, Y. S. and Ji, Y. S., “Modeling Corroded Section Configuration of Steel Bar in Concrete Structure,” Construction and Building Materials, V. 23, No. 6, 2009, pp. 2461-2466.
33.Apostolopoulos, C. A. and Pasialis, V. P., “Effects of Corrosion and Ribs on Low Cycle Fatigue Behavior of Reinforcing Steel Bars S400,” Journal of Materials Engineering and Performance, V. 19, No. 3, 2010, pp. 385-394.
34.Kashiwabara, S., Tanimura, Y., Izuminami, R., and Kimura, M., “A Study on Evaluation Method of the Tensile Yield Strength of Corroded Reinforcing Bar Cut Out from Structure,” Proc. Of the 55th Annual Conference of the Japan Society of Civil Engineers, V. 357, 2000, pp. 716-717. (in Japanese)

Chapter 3
1.Cho, Y. S., “Shear Behavior Evaluation of Corroded RC Beams and Seismic Behavior of RC Beams with Corroded Longitudinal Steel Reinforcement,” M.S. Thesis, Department of Construction Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan, 2012. (In Chinese)
http://ndltd.ncl.edu.tw/cgi-bin/gs32/gsweb.cgi?o=dnclcdr&s=id=%22100NTUS5512065%22.&searchmode=basic
2.Vu, N. N., “Residual Shear Strength and Ductility Evaluation of Corroded RC Beams,” M.S. Thesis, Department of Construction Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan, 2013.
http://ndltd.ncl.edu.tw/cgi-bin/gs32/gsweb.cgi?o=dnclcdr&s=id=%22101NTUS5512007%22.&searchmode=basic
3.Ou, Y.-C., and Chen, H.-H. "Cyclic Behavior of Reinforced Concrete Beams with Corroded Transverse Steel Reinforcement," Journal of Structural Engineering, ASCE, 2013.
4.American Concrete Institute (ACI) Committee 318, “Building Code 479 Requirements for Structural Concrete and Commentary.” ACI 318-08 and 480 ACI 318R-08, ACI, Farmington Hills, MI. 2008.
5.American Association of State and Highway Transportation Officials (AASHTO) T 260-97, “Standard Method of Test for Sampling and Testing for Chloride Ion in Concrete and Concrete Raw Materials,” AASHTO, 2011.

Chapter 4
1.Zhang, W.; Song, X.; Gu, X.; and Li, S., “Tensile and Fatigue Behavior of Corroded Rebars,” Construction & Building Materials, V. 34, 2012, pp. 409-417.
2.Kashiwabara, S., Tanimura, Y., Izuminami, R., and Kimura, M., “A Study on Evaluation Method of the Tensile Yield Strength of Corroded Reinforcing Bar Cut Out from Structure,” Proc. Of the 55th Annual Conference of the Japan Society of Civil Engineers, V. 357, 2000, pp. 716-717. (in Japanese)
3.Palsson, R., and Mirza, M. S., “Mechanical Response of Corroded Steel Reinforcement of Abandoned Concrete Bridge,” ACI Structural Journal, V. 99, No. 2, Mar.-Apr. 2002, pp. 157-162.
4.Lee, H. S., and Cho, Y. S., “Evaluation of the Mechanical Properties of Steel Reinforcement Embedded in Concrete Specimen as a Function of the Degree of Reinforcement Corrosion,” International Journal of Fracture, V. 157, 2009, pp. 81-88.
5.Cairns, J., Plizzari, G. A., Du, Y., Law, D. W., and Franzoni, C., “Mechanical Properties of Corrosion-Damaged Reinforcement,” ACI Materials Journal, V. 102, No. 4, July-August 2005, pp. 256-264.
6.Du, Y., “Effect of Reinforcement Corrosion on Structural Concrete Ductility,” PhD thesis, University of Birmingham, UK, Mar. 2001, 320 pp.
7.Andrade, C., Alonso, C., Garcia, D., and Rodriguez, J., “Remaining Lifetime of Reinforced Concrete Structures: Effect of Corrosion in the Mechanical Properties of the Steel,” Life Prediction of Corrodible Structures, NACE, Cambridge, UK, Sept. 1991, pp. 12/1-12/11.
8.Clark, L. A., and Saifullah, M., “Effect of Corrosion Rate on the Bond Strength of Corroded Reinforcement,” Corrosion and Corrosion Protection of Steel in Concrete, R. N. Swamy, ed., Sheffield Academic Press, Sheffield, 1994, pp. 591-602.
9.Lee, H. S., Tomosawa, F., and Noguchi, T., “Effect of Rebar Corrosion on the Structural Performance of Singly Reinforced Beams,” Durability of Building Materials and Components, V. 7., C. Sjostrom, ed., E&FN Spon, London, 1996, pp. 571-580.
10.Apostolopoulos, C. A., Papadopoulos, M. P., and Pantelakis, S. G., “Tensile Behavior of Corroded Reinforcing Steel Bars BSt 500s,” Construction & Building Materials, V. 20, 2006, pp. 782-789.
11.Apostolopoulos, C. A., “Mechanical Behavior of Corroded Reinforcing Steel Bars S500s Tempcore under Low Cycle Fatigue,” Construction & Building Materials, V. 21, 2007, pp. 1447-1456.
12.Apostolopoulos, C. A., and Papadopoulos, M. P., “Tensile and Low Cycle Fatigue Behavior of Corroded Reinforcing Steel Bars S400,” Construction & Building Materials, V. 21, 2007, pp. 855-864.