Load bearing capacity of corroded reinforced steel bars

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Insinööritieteiden korkeakoulu | Master's thesis
Structural Engineering
Degree programme
Master's Programme in Structural Engineering
42 + 63
Concrete corrosion can be visualized as a combination of chemical reaction on concrete and electrochemical reaction on steel reinforcement. Failure of steel reinforcement due to corrosion can inflict significant stress on concrete during load distribution. As such, it is necessary to analyze the long term effects of corrosion on the load bearing capacity and bending strength of steel reinforcement. Furthermore, the influence of chemical reactions like carbonation and chloride ingress in concrete needs to be docu-mented in order to ascertain the changes in concrete structure due to corrosion. This research investigated the mechanical and electrochemical properties of concrete exposed to long term corrosion for a period of 16 years. An extensive literature research was documented on the corrosion reaction kinetics, factors influencing rate of corrosion in a controlled environment and the response of bonding strength between steel and concrete to corrosion. Non-destructive testing like crack width measurements, visual examination, electrochemical measurements using Galva Pulse and determination of average chloride content were undertaken in order to identify the state of corrosion and also to ascertain the impact of corrosion on the chemical properties of concrete. Further testing included mechanical tests for load bearing capacity and compressive strength. The electrochemical measurement results signified the condition of the corroded specimens and also provided the degree of corrosion at the time of experimentation. Hot-dip galvanized steel and austenitic steel with excellent corrosion resistance reached high values in resistivity and low in electrochemical potential. Specimens with large crack widths showed poor resistance to corrosion and majority of the samples in tap water were only partially carbonated. Load capacities of corroded specimens were obviously lower when compared to the original measurements in 2000. The reason was the reduction in cement-steel bonding due to the expansion of rust in the structure. However, compressive strength approximately doubled due to continuous hydration occurring during the cyclic wetting and drying period. This increase in compressive strength compensated the reduction in load bearing capacity. Improvement in load capacity can be realized by the addition of corrosion resistant reinforcement like hot-dip galvanized or austenitic steel. Fur-thermore, usage of high strength steel coupled with cathodic protection or surface coating (epoxy coatings, acrylic sealers) will provide better load bearing capacities and simultaneously reduce the chances of corrosion happening in the structure.
Leveinen, Jussi
Thesis advisor
Sistonen, Esko
concrete corrosion, electrochemical potential, load bearing capacity, Galva Pulse, carbonation, crack width
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