Tour of the City
Every day you see signs of the increasing corrosion problem throughout North America. It is so prevalent today, most of us don’t even notice it, as we take corrosion for granted as a natural, unavoidable, and uncontrollable condition affecting our city or community and wasting tax dollars. The tour of the city will examine common sights of corrosion we all see daily.
Corrosion is a natural phenomenon, and thus can never be completely eliminated; however, it is a misconception nothing can be done. Estimates show 25-30% of corrosion could be eliminated if proper corrosion protection methods were employed. Let’s take a tour of the city, and view common sights of corrosion we all see daily.
Infrastructure
One increasingly common site for corrosion is infrastructure, and namely bridges. The photo above demonstrate what can happen when bridges use unprotected or inadequately protected reinforcing steel. You can see complete structural failure of the bridge, with spalled concrete and exposed reinforcing steel. Many cities across North America have employed an expensive, “diaper-type” system to cover the underpass and catch spalling concrete so as not to threaten pedestrian and/or interstate traffic passing underneath.
The American Society of Civil Engineers (ASCE) estimates a $1.6 trillion investment is needed just to maintain America’s infrastructure. The bridge and highway markets are a huge contributor to that investment, with 27% or approximately 160,000of the nation’s bridges rated structurally deficient or functionally obsolete. Additionally poor road conditions cost US motorists $54 billion annually in repairs and operating costs, which is $275 per motorist.
In addition to the decaying roads and bridges, the nation’s public parks, beaches, water and wastewater systems, ports and locks, and electricity grids are also beginning to fail. There are more than 3,500 unsafe dams, 50% of inland locks are functionally oboslete, wastewater management systems discharge billions of gallons of untreated sewage into US surface waters each year, and the nation’s public parks, beaches, and recreational harbors are in disrepair.
Much of the initial infrastructure construction on bridges, roads, utility systems, and shore protection was done more than 50 years ago, and the current state of the infrastructure is not just depressing, but also a catastrophe in progress.
Private and Commercial Corrosion
Infrastructure is not the only place where corrosion is a serious problem. Many private and commercial projects are also suffering from a corrosion epidemic. Consider these two examples:
The painted structure on the left is blistering, peeling and rusting throughout the entire structure. If you look closely, you can see many of the edges of the beam are the centers of the corrosion formation. Corners and edges are a common place for corrosion to start on painted structures because most coatings tend to thin at these areas.
The painted underbody of this trolley (right) used on the urban streets of cities across the country, after years of use and exposure to road salts and natural weathering has yielded to corrosion. As you can see, corrosion has eaten away sections of the steel frame rendering the trolley unsafe for use. In this instance, the paint coating could not provide adequate corrosion protection to ensure long-term service life for the steel frame.
Corrosion Case Study – Williamsburg Bridge
And finally, one of the most severe examples of corrosion available (left). This is a severely corroded beam from the famous Williamsburg Bridge, built in 1903 and located in New York City. When this photo was taken, the bridge was still in use and traveled by over 100,000 vehicles per day as well as train traffic on the deck below. Inspected in 1991 and subsequently closed for 7 months, the direct cost to repair the corrosion problems was $750 million. The indirect cost, that is to local businesses that relied on passersby and the inconvenience and time of commuters to take a less direct route to and from work was estimated to be $8.2 billion! If the bridge structural steel had been galvanized initially, that money could have been allocated for other infrastructure needs.