March 20, 2014
No matter where you live, you have read about “the crumbling infrastructure” in our regions, whether it be Europe, North America, Asia or elsewhere. Most of us can point to examples of roads and bridges that have deteriorated, some to the point where structural failure is imminent. Yet lack of funds means repairs are delayed and ultimately need to be more comprehensive.
Most of the deteriorating concrete in our bridges is due to the corrosion of the carbon steel rebar, whether coated or not, in the concrete.
The worst corrosion occurs in regions where road salt is heavily used or in areas near to salt water, but stainless steel rebar prevents damage to structures caused by rebar corrosion. In our story starting on page 7, Pier Review, the Life Cycle Assessment of a pier in the Gulf of Mexico constructed around 1941 which used stainless steel rebar is featured. It would have been considered an odd choice at the time, but today looks to have been a very wise one. Stainless steel rebar is used in ever increasing amounts today both in North America and around the world. The Stonecutters Bridge shown on the inside front cover used stainless rebar in Type 2205 (UNS S32205) as well as plate. While stainless steel is more expensive than carbon steel rebar, its selective use can be justified financially when all the costs of maintaining the structure over its life are considered.
In Edmonton, the provincial capital of Alberta, Canada, with a metropolitan population of over one million, a new ring road around the city is in the final stages of completion, with the Northeast Anthony Henday Drive portion being 27km of 6 or 8 lane highway. Winter is especially hard on the roads in Edmonton. The average daily temperature in January is -10.4°C, with an annual snowfall of about 124cm. Large amounts of salt, both sodium and the more corrosive calcium chloride, are applied to keep the roads as free from ice as possible. In
2011, Type 2304 (S32304) stainless steel was specified for a trial for one highway interchange on the ring road. The success of that venture led to the specification of Type 2304 rebar for a major portion of this new section, reported to being the region of 6,000 tonnes. Perhaps in 75 years of so, a Life Cycle Assessment will be done of one of these Edmonton bridges, leaving no doubt that the engineers in charge made the right decision.