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MDT Applies Paint to Cool Walkway

Thursday, July 1, 2021

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The Montana Department of Transportation has recently announced plans to paint a walkway on the Beartracks Bridge in downtown Missoula.

According to reports, locals reported that the newly constructed walkway on the west side, or downstream side of the reconstructed bridge on Higgins Avenue seemed to be much hotter than usual, prompting the decision for a coating.

Bridge Background

Previously known as the Higgins Bridge (the name was officially changed in April to Beartracks Bridge), the first edition of the structure was constructed in 1873, and then rebuilt in 1893. Some years later, in 1908, the bridge was washed away during a flood in the area, and was rebuilt yet again, the following year.

By the 1950s, the town determined that the area needed a better bridge and in 1962 constructed the Higgins Avenue Bridge as most knew it prior to its name change earlier this year. The request to change the name came from the Missoula County Commission and the City of Missoula and was approved by the five person Montana Transportation Commission on April 22.

In October 2020, it was announced that the bridge would undergo additional construction. According to MDT, the bridge was deteriorating and would require rehabilitation in order to extend the life of the structure.

“The deck concrete is distressed and needs to be replaced, the steel structure elements need repair and/or replacement, and the entire steel portion of the bridge needs a new protective coating of paint,” wrote MDT.

At the time of its name change, the structure was still undergoing the $17 million reconstruction, which was slated to last until this fall.

Most recently reported, demolition on the bridge’s east side is still ongoing and crews are also focusing on bridge demoing north of the river near Caras Park. The Department has also issued a warning that the surface of the bridge has been becoming extremely hot during the daytime heat and associates this to the structure’s fiber reinforced polymer panels.

The panels were installed on the structure as a means to ease weight from the wider walkway on the side of the bridge, but have been absorbing the heat, rather than reflecting it. In additional reports, the polymer material was recorded to reach temperatures as high as 147 degrees Fahrenheit.

In the meantime, the Department has erected signage about the heat concerns and asks that travelers take precautions to protect their feet, as well as the feet of children and animals before crossing the bridge on hot, sunny days.

Coatings Mitigation

At the end of June, crews applied a fresh strip of white paint to the walkway over the Beartracks Bridge on Higgins Avenue in Missoula. MDT engineering project manager Matt Straub said the concrete stain that was painted on the bridge is a short-term solution, but it could potentially become a long-term solution.

“This is possibly a permanent solution, but we're still investigating a solution for the long term,” he said.

Prior to coatings applications, the paint was tested in several spots over the bridge and compared to surface temperatures on the bridge panels, painted spots, asphalt and concrete. According to Straub, the painted sections were significantly cooler, and in preliminary trials, reduced the surface temperature by 20-30 F.

However, a 20 F reduction still means the bridge could reach upwards of 120 degrees. (It only takes 60 seconds for paws to burn at 125 F.)

In total, the coatings mitigation is slated to cost between $1,000 and $1,500.

Similar Projects

In 2019, PPG Industries announced the production of a heat-reflective paint to mitigate harmful sidewalk temperatures. Initially intended for the exteriors of planes and buildings, PPG’s coating comes with a specific topcoat that can be made in any color, which is placed over white paint. This results in light passing through the topcoat and being reflected by the white paint.

PPG senior technical manager Kristi Kauffman demonstrated for WESA, using a heat lamp and two similar black panels—one treated with the special topcoat—that the one with the topcoat warmed more slowly, while the other heated up more quickly. By the end of the test, there was a 50-degree difference between the two. Though Kaufman noted that this was an extreme example, it provided a snapshot of what could happen if the coating was used on sidewalks.

Though the specific coating was unnamed at the time of its announcement, PPG also produces another, similar, coating known as Durastar Ultra-Cool coil coatings, which are composed of an advanced silicone-modified polyester coatings formulation with infrared-reflective pigments. The Ultra-Cool IR-reflective pigments deflect solar heat, and provide chalk and fade resistance, and is used to protect buildings.

And last year, Arizona State University in collaboration with the Phoenix Street Transportation Department reported it was nearing the completion of a series of “cool pavement” applications around the city.

The cool pavement treatments are a part of the city’s pilot program, where ASU planned to study the pavement coatings' possible impact regarding the area’s heat island effect over the course of several years.

The idea for the pilot study was launched following a ASU-led study on solar reflective coatings back in July 2019. For the study, ASU researchers took two mobile biometeorological instrument platforms (MaRTy 1 and MaRTy 2) to Los Angeles in order to read how the city’s streets affected radiant heat and ultimately, pedestrians’ comfort.

At the time, the Los Angeles Bureau of Street Surfaces was pioneering the use of solar reflective coatings in a quest to cool city streets.

The study was the first to measure the thermal performance of solar reflective coatings using instruments that sense meteorological variables relevant to a pedestrian’s experience: radiant heat, ambient temperature, wind and humidity.

In the study’s findings, researchers found that the temperature of the coated asphalt road was up to 6 degrees C (almost 43 degrees F) cooler than the regular road in the afternoon. However, the radiant heat over coated asphalt was 4 degrees higher than non-coated areas. Additionally, the study also found that the coating didn’t have a big impact on air temperature, only half a degree in the afternoon and 0.1 degree at night.

The research study, “Solar reflective pavements — A policy panacea to heat mitigation?” was published in April of this year in the journal Environmental Research Letters.

In developing the Cool Pavement Pilot Program from the study, the City of Phoenix Street Transportation Department selected portions of eight neighborhoods and one city park to receive cool pavement treatment as part of the project. The portions cover 36 street miles at a cost of $3.3 million, which has come from the city’s street maintenance budget.

The nine areas chosen as they were already due for resurfacing and money would have gone toward rehabilitating those areas regardless of the material used, reported David Sailor, director of the Arizona State Urban Climate Research Center.

However, instead of using the reflective solar coatings like in Los Angeles, the city announced that it would be using cool pavement technology, CoolSeal, developed by California-based GuardTop LLC.

According to the Department, the application is made up of asphalt, water, an emulsifying agent (soap), mineral fillers, polymers and recycled materials. It contains no harmful chemicals, is compatible with traditional asphalt and can be spray- or squeegee-applied.

The city adds that it chose to use this form of cooling technology as opposed to the reflective coatings because, “Cool pavement reflects back the sunlight that hits it. Because the surface reflects rather than retains heat, cool pavement has the potential to offset rising nighttime temperatures in Phoenix. The use of cool pavement technology may help reduce the heat island effect and reduce temperatures in the city. It is also useful to cool neighborhood areas that don’t have much shade from the sun.”

A team from ASU intends to study the cool pavement’s effects over the next several years, with early results slated to be posted on the Street Transportation Department website by the end of 2021.

In addition to the Street Transportation Department and ASU, the City of Phoenix Office of Sustainability have also partnered on the project to see if the technology can help with the city’s continuing efforts to be environmentally sustainable while improving the quality of life for all who enjoy Phoenix.


Tagged categories: Bridges; Bridges; Coating Application; Coating Materials; Coatings Technology; Fiber Reinforced Polymer (FRP); NA; North America; Ongoing projects; polymer tiles; Program/Project Management; Project Management; Protective Coatings; Rehabilitation/Repair; Transportation

Comment from Tim Specht, (7/6/2021, 11:42 AM)

Six degrees C are not equivalent to 43 F

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