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Soil corrosion behavior of hot-dipped galvanized steel in infrastructure applications

University of British Columbia

Galvanized steel is one of the most common materials used in the construction industry for its relatively low cost paired with an acceptable corrosion resistance. Nevertheless, the early failure of a number of structures around the world that use galvanized steel has raised some controversy on the understanding of the corrosion behavior of zinc. This dissertation presents the results of several electrochemical studies and mathematical models done on zinc and galvanized steel as an attempt to fill in the gaps of current knowledge. Results indicate an increase on the corrosion rate with increasing amounts of Na₂SO₄, as well as a potential difference between samples in oxygen saturated, aerated, and de-aerated conditions is large enough to promote macrocell formation under aggresive conditions. The presence of sulphate in the soil significantly increased the corrosion rates and, thus, it is important to consider the effect of sulphate in determining the type of de-icing salt. In sulphate-free solutions, potassium acetate appeared to be the best option; while in the presence of sulphate, MgCl₂ and CaCl₂ had the lowest corrosion rate. The improved performance was attributed to the formation of a more evenly distributed corrosion product with better protective properties. Furthermore, when measuring corrosion at temperatures ranging from -5°C to 25°C, the rate observed at sub-zero temperatures is still higher than the rate acceptable for galvanized steel reinforced structures. SEM pictures show that the corrosion products grows preferentially in the vicinity of zinc grain boundaries and that it is apt to cracking with increasing thickness. A numerical model was developed to calculate the corrosion rate of galvanized steel in soil at three different stages of corrosion by considering key soil corrosion parameters. This thesis focuses on the effect of field conditions relevant to the Canadian climate on the corrosion performance of Mechanically Stabelized Earth (MSE) wall soil reinforcement and facings. Results indicate that the proposed model is suitable to be used for the service-life design and risk assessment of MSE walls and to determine the optimum zinc cover thickness.

Text

2014-12-23

Attribution-NonCommercial-NoDerivs 2.5 Canada

http://hdl.handle.net/2429/51650

Materials Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/2.5/ca/