Initiation et propagation de la corrosion dans un élément de béton armé
Chloride-induced corrosion of steel reinforcement is an important issue that greatly decreases the service life of all concrete structures exposed to marine environments or de-icing salts. This study analysed the phenomenon of corrosion initiation on reinforced mortar specimens and the behavior of several corroded reinforcing bars. The main objective of the study was to observe the actual influence of cement mineralogy on the various mechanisms of corrosion initiation on steel reinforcement. Contributing to the elaboration of a tool that will be able to predict the service life of a reinforced concrete structures exposed to chlorides, this research also allowed to put forward new information for the civil engineering community, helping engineers and owners optimizing concrete formulations, and improving the durability of concrete constructions.
The project was divided in two parts. The first one is aimed at isolating a threshold concentration of chloride-ions that would initiate corrosion. The mortar specimens were exposed to chloride-ions in a controlled environment, by chloride ponding, and the evolution of corrosion was observed with non-destructive electrochemical measurements. Different factors were taken into consideration during these tests: the water/cement ratio, the cement mineralogy, and the various type of reinforcing bars preparation. Going trough this paper, you will learn about the consequences that come from the variation of these factors on the corrosion initiation. The second part of the project studied the effects of corrosion on the mechanical properties of steel reinforcement. The data that resulted from the traction tests, on the bars, at different corrosion levels, are also presented in this document.
According to the results of the study, reducing the water/cement ratio and increasing the C3A content led to a longer corrosion initiation time. As for the cracking time of the different mortar specimens, it appeared to be independent from these two factors. Moreover, sandblasted bars were found to be a lot more resistant to corrosion than the brushed bars. In the end, the critical concentration of chloride-ions was found to be around 0.3% by weight of dry mortar or 1.2% by weight of cement. This threshold value was precisely evaluated studying different specimens with and without bars. Furthermore, this threshold value seems independent of the concentration of C3A, the type of bar preparation or the water/cement ratio.
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Advisor:Jolin, Marc; Marchand, Jacques
School Location:Canada - Quebec / Québec
Source Type:Master's Thesis
Date of Publication:03/01/2009