A unique research partnership could enhance the life of bridges in Ontario.
A unique research partnership holds the potential to enhance the life of bridges in Ontario. Engineers at the Surface Science Western laboratories at The University of Western Ontario are working to solve a problem with weathering steel box girders that rust more quickly than they should.
Surface Science Western, a commercial and research materials analysis facility, is partnering with the Ministry of Transportation Ontario (MTO), Essar Steel Algoma Inc. and The Canadian Institute for Steel Construction (CISC) to prevent dangerous corrosion on steel girders.
Surface Science Western specializes in using advanced analytical techniques to examine the surface of materials and products for improving their performance and reliability.
MTO has been using ‘weathering steel’ for bridge girders since 1968. Under normal weathering cycles, it forms a tough outer oxide layer referred to as ‘patina’ that protects the steel from unabated corrosion. In some cases however, the patina has been detaching from the steel girders.
Sridhar Ramamurthy, a senior researcher at Surface Science Western, and his colleagues examined samples taken from several MTO bridges using several high-tech methods including electron microscopy, elemental X-ray analysis, laser Raman spectroscopy and Mossbauer spectroscopy.
“The findings were very clear,” says Ramamurthy. “In samples with more serious corrosion and de-bonding, we found a greater amount of a mineral called akaganeite. In areas where corrosion was less prevalent, there was a greater amount of a mineral called goethite. This was our clue to the cause of the corrosion.”
Ramamurthy explains that, based on the analytical data, the scientists concluded the presence of de-icing salts and water caused corrosion and the formation of akaganeite. This type of oxide layer is generally porous and would allow more salt to enter and attack the steel girder, thus building in volume and eventually breaking away from the steel girder.
In contrast, the goethite structure is more compact and more stable, thus protecting the steel girder from further corrosion.
The objectives of the research are to develop a coating (paint) system for existing bridges that will promote a higher content of goethite, and, more importantly, develop a new grade of steel that will promote the formation of a protective and stable oxide layer, such as goethite structure.
Essar Steel Algoma and CISC were brought on board by MTO, and working with Natural Resources Canada’s CANMET Materials Technology Laboratory (CANMET-MTL), new steel alloys are being developed that contain greater amounts of nickel, chromium and molybdenum compared with the current standard for weathering steel – all beneficial in the formation of goethite.
Financial contributions for this work have been provided by MTO under its Highway Infrastructure Innovations Funding Program (HIIFP), Essar Steel Algoma, and CISC. HIFFP funds research at Ontario colleges and universities to encourage basic and applied reserarch in transportation and infrastructure engineering.
CANMET-MTL has produced five new steel alloys that will be tested in MTO’s environmental chambers containing a high concentration of salt solution, and some of the samples are already showing promise.
When it is clear that one alloy out-performs the others, further refinements will take place and eventually a test bridge could be built.
Ramamurthy says the detective work done at Surface Science Western, and with partners at MTO, Essar, CISC and CANMET-MTL, could lead to steel bridges with a longer lifespan.
“Currently, bridges made of uncoated weathering steel may require major rehabilitation after 30-40 years in service. We think that with the right alloy, the required design life of 75 years could possibly be achieved without any major rehabilitation.”