In winter weather, transportation agencies often use chemical deicers to maintain safety and mobility on roads and highways. While effective, these chemicals are corrosive and can cause damage to maintenance vehicles and equipment, according to the Clear Roads national research consortium.
Protective coatings are available to prevent this damage, and agencies routinely apply them to ferrous-based materials, such as steels and stainless steels, and non-ferrous materials, such as aluminum alloys and copper. But there are numerous coating products available for each of these metallic substrates, and they vary in price and performance.
To get the best return on their investment, departments of transportation (DOTs) should select the coating products that will meet their specific needs. Recent research on a range of these products was presented in an August 2024 research brief, with the study led by the Minnesota Department of Transportation (Saint Paul, Minnesota, USA).
This research, which updates guidance provided by a previous Clear Roads project, offers extensive testing of multiple coating products for common metallic substrates to provide insight into how each product performs relative to other products.
Understanding how DOTs can effectively and efficiently use the coatings for their purposes should enable agencies to make more informed purchasing decisions, according to Clear Roads researchers.
Objectives and Methodology
This project’s primary goal was to identify and test the most frequently used anticorrosion coatings for DOT vehicles and equipment that are regularly exposed to humid, salt-laden environments. Transportation agencies were surveyed to better understand snow and ice management practices and other details regarding deicer corrosion to vehicles and equipment.
Additionally, to determine which products would be tested, a market analysis identified the most commonly used anticorrosion coatings. From this analysis, six coatings were chosen to be tested for the project. Investigators applied four of the products to steel, stainless steel, and aluminum, and they applied two products to copper. Coatings were tested using electrochemical impedance spectroscopy (EIS), a cyclic salt spray test, an adhesion test, a pencil hardness test. and a Vickers hardness test.
The EIS and the salt spray test results were the primary indicators of coating performance in resisting deterioration and providing corrosion protection. The EIS test periodically measures any change of coating properties such as the coating’s capacitance and pore resistance, which can accurately indicate the performance of a coating over a specific time period.
The salt spray test consists of 60 cycles, which is equivalent to five years of on-vehicle exposure to corrosion. With each cycle, the coating was exposed to six hours of humidity and 15 minutes of salt exposure. It was then left to dry for approximately 18 hours until the next cycle.
Results
Survey results indicated that dump trucks, liquid deicer applicators, front-end loaders, and hoppers are most susceptible to corrosion. Further, 62% of respondents indicated they attempt to mitigate corrosion by replacing corrosion-prone materials on vehicles and equipment with more corrosion-resistant materials.
The results of the product testing indicated that Fluid Film provides the maximum corrosion protection to steel and aluminum alloys, as it performed well in both EIS and salt spray testing. Aquapon performed the best for steel protection when used with a salt-blend deicer, but it is more costly than Fluid Film. Armour Seal performed well in both the EIS and salt spray testing for stainless steel and aluminum alloys, but it has a low adhesion strength and negligible hardness—which makes it a less effective option, according to the Clear Roads researchers.
For copper, Deox-IT and Permatex grease both failed the salt spray test by showing signs of failure after only two weeks. This indicated that they may last for only six months after application. Additionally, results indicated they could not adequately resist corrosion in salt-laden, wet/dry environments. Therefore, using either lubricant would require regular inspections to avoid sudden failures.
Survey responses indicated that most DOTs do not dry their winter maintenance vehicles and equipment after use, which can help minimize corrosive effects.
Implementation and Benefits
As Clear Roads explains, this project provides guidance to DOTs for purchasing anticorrosion coating products to protect winter maintenance vehicles and equipment. Agencies can use the results to determine which products will be most effective for their operations. The complete results are being made available to DOT staff and winter maintenance managers.
“This project provides DOTs with up-to-date information on how to protect our valuable winter maintenance equipment from deicing product corrosion in order to make the best purchasing decisions for their winter maintenance operations,” says Todd Law, a project champion with the Vermont DOT. Law led the research in tandem with Xianming Shi of Washington State University (Pullman, Washington, USA), who served as investigator.
DOTs may want to revisit the practice of not drying vehicles after winter maintenance use, Clear Roads concludes. However, since the costs of corrosion losses are not specifically known at this time, it may be difficult to evaluate the cost savings from installing drying stations.
About Clear Roads
Clear Roads is described as a national research consortium focused on the rigorous testing of winter maintenance materials, equipment, and methods for use by highway maintenance crews.
Since getting under way in 2004, Clear Roads has grown to include 39 member agencies, each contributing $25,000 annually to fund research and technology transfer efforts. Representatives from the participating DOTs meet twice a year to discuss and prioritize projects, share effective practices, and review research results.
The consortium’s activities include evaluating winter maintenance materials, equipment, and methods under real-world conditions; developing specifications and recommendations; studying and promoting innovative techniques and technologies to save agencies money while improving safety and efficiency; and supporting technology transfer by developing practical field guides and training curriculums to promote research findings.
Source: Clear Roads, www.clearroads.org.