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Corrosion Resistance of Bridge Strands Galvanized with a Zinc-Aluminium Alloy

Bridge strands consisting of steel wires galvanized with Zn-Al are expected to have higher corrosion resistance than the Zn galvanized ones. The strands consisting of 19 parallel steel wires galvanized with Al (10%) and Zn (90%) alloy were produced and corrosion acceleration tests were conducted. The anti-corrosion performance was then compared with the conventional strands galvanized with Zn. The strands were kept under three different corrosion environments: kept at a relative humidity (RH) of 60%, kept at a RH of 100%, and wrapped with wet gauze which simulates wet conditions. The strands were kept in the thermo-hygrostat at 40 o C for 150 days. The mass loss due to corrosion of the strands galvanized with Zn-Al under the relative humidity of 60% and 100% was small and the strands had sufficient corrosion resistance. Under the wet conditions, the corroded mass of the strands galvanized with Zn-Al was 15 times larger than that under the relative humidity of 100%. The strands galvanized with Zn-Al have less corrosion than those galvanized with Zn under the three environmental conditions. Corroded mass is larger in the surface wire, the inside wire and the center wire in this order. The cross-sections of corroded strands were investigated by a microscope showing that the corrosion product of Zn was loose and easy to exfoliate from the steel layer. On the contrary, the corrosion product of Zn-Al alloy wa s dense and hard to exfoliate from the steel layer. This difference is the rationale for the superiority of the Zn-Al galvanized wires.