Bridging The Gap
Duplex stainless steel reinforcing bar to protect Shenzhen Western Corridor Bridge against
concrete 'cancer'
Nickel Magazine, July 2005 -- Some 1,250 tonnes of stainless steel
S31600 (containing 12% nickel) and duplex stainless steel (containing 5.5% nickel) will be used to
reinforce select portion of a major three-lane highway bridge in Hong Kong.
Stretching 3.2 kilometres over a body of salt water known as Deep Bay, the bridge will connect Ngau Hom
Shek and the Hong Kong Shenzhen Western Corridor.
Marine environments are hard on concrete structures that have been reinforced with carbon steel
reinforcing bar: moist, salty air makes its way into the concrete, and chlorides attack the reinforcing bar.
In such cases, rust can build to a volume three to seven times that or the original steel. The
rust weakens the bond between the concrete and the metal and causes the concrete to crack, in which case
extensive maintenance may be required in as little as 15 to 20 years.
In such cases, designers usually recommend
S31600 stainless steel, but the Hong Kong Highways Authority has gone one step further by choosing
S32205 duplex stainless steel. The use of S32205 should prevent the need for extensive maintenance
for at least 120 years.
Although, concrete structures built in marine environments using S30400 stainless steel rebar have been
known to last more than 60 years, almost everyone recommends S31600 where there are significant amounts
of chloride. The resulting maintenance-free period, therefore fully justifies the higher initial
cost of the judicious use of stainless steel in this project.
The Shenzhen Western Corridor bridge is expected to cost US$2.7 billion, according to its owner, the
Hong Kong Highways Authority.
The S31600 and S32205 reinforcing bar is being supplied by Arminox Australia in diameters ranging
from 16 to 40 millimetres. The contractor is Gammon Constructions Ltd. Arminox is also supplying
specialized processing equipment and training to ensure the stainless steel is no contaminated during the
construction.
PHOTOS: Arminox Australia Pty Ltd.
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