Abstract
A new technology has been developed for high strength bridge wires: steel wires are coated with aluminium (Al) and zinc (Zn) alloy. It is expected that the bridge wires coated with Al-Zn have higher corrosion resistance than the Zn coated ones. The steel wire with a diameter of 5mm coated with Al (10%) and Zn (90%) alloy is produced and corrosion acceleration tests have been conducted and the corrosion resistance is compared with the steel wires coated with Zn. The steel wires are 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 the wet condition. The wire specimens are kept in the thermo-hygrostat at 40°C for 150 days.
The mass loss due to corrosion under the relative humidity of 60% and 100% is much smaller than that under the wet environment, and there isn't much difference between Al-Zn coated wires and Zn coated wires. On the other hand, the mass loss of the steel wires coated with Al-Zn is distinctively smaller than those coated with Zn under the wet condition. The mass loss of the NaCl attached wires is twice larger than that without NaCl under the wet condition.
The corroded wires are investigated by EPMA analysis showing that the corrosion product of Zn is loose and easy to exfoliate from the steel layer. On the contrary, the corrosion product of Al-Zn alloy is dense and hard to exfoliate from the steel layer. This difference is the reason of the superiority of the Al-Zn coated wires.
