How do low-cost steels with improved weathering characteristics stack up to the weathering steels now in use?
That’s the focus of a new Federal Highway Administration report.
“Improved Corrosion-Resistant Steel for Highway Bridge Construction” is a new FHWA Tech Brief that provides a technical summary of agency research that compares life-cycle costs (LCC) of various steels used in bridges.
|Stainless steel is a desirable material for bridges in highly corrosive environments, but it is more than twice the cost of carbon steel. The stainless-steel Bridge Apaté, in Stockholm, won the European Steel Design Award in 2004.|
The study identifies steels with lower potential cost than structural stainless steel (ASTM A1010, Standard Specification for Higher-Strength Martensitic Stainless Steel Plate, Sheet, and Strip) that could be candidates for bridge construction while still providing low corrosion rates.
The initial cost of stainless steel is more than twice the cost of carbon or weathering steel, the study notes.
To Paint or Not to Paint?
“Plate girder bridges are usually fabricated from painted carbon steels or unpainted weathering steels,” the study says. “Weathering steels, including the modern high-performance steels, offer the lowest life-cycle cost (LCC) over the design life of the bridge because, in most service environments, ongoing maintenance due to steel deterioration is not necessary.
“However, where the bridge is subject to high time-of-wetness or high chloride exposures—coastal areas and areas that use large quantities of deicing salt—weathering steels are not effective, because the protective patina does not develop and the steel has a high corrosion rate.”
Being able to reduce the cost of stainless steel would thus improve the LCC of bridges in severe corrosion service conditions, FHWA says.
Experimental Steel Testing
The study tested several experimental steels for strength and impact resistance, to determine which could meet the steel specifications for steel bridges. The corrosion resistance of the alloyed steels was studied in the laboratory using accelerated test methods.
Several steels were further studied by exposing them for one year on an existing weathering steel bridge that has a high corrosion rate, due to deicing salt use.
The agency also conducted an LCC analysis to examine the benefits of using maintenance-free, corrosion-resistant steel in place of regularly repainting conventional steel.
In the end, researchers said they were unable to develop a less costly but equally corrosion-resistant bridge steel than currently available, because the strength and impact toughness required for steel bridge members could not be achieved with the lower Cr steels.
The Tech Brief is a technical summary of the FHWA report, Improved Corrosion-Resistant Steel for Highway Bridge Construction (FHWA-HRT-11-062).