Alaska Tests Surface Coatings for High-Friction Effectiveness

A tan-colored surface installed on Southcentral Alaska road­ways last summer might look like an odd patch job, but the Alaska Department of Transportation & Pub­lic Facilities is researching whether this surface - an advanced high-fric­tion surface treatment - could pro­vide a better future for Alaska roads.

Alaska tests surface coatings for high-friction effectiveness

The tan-colored surface treatment distinguishes itself next to regular pavement. The treat­ment costs $30 per square yard, but its high-friction value could help improve the safety and durability of Alaska roads. (Photo Courtesy of Alaska DOT&PF)

This high-friction surface treat­ment is expensive to install. The price tag is $30 a square yard, so the big question is whether paying for this treatment can be justified if it proves to make Alaska roads safer and more durable.

"Even though it's expensive, it might be more effective than doing an engineering correction," said Anna Bosin, a research engineer for the DOT&PF who has been tasked with researching the surface's effectiveness after installation.

Bosin was involved in the plan­ning process to bring this high­friction surface treatment to Alaska. She helped nominate the project for saf ty funds during the 2014 fiscal year while working in the traffic and safety section for a federal program called Highway Safety Improvement Program, which targets public roads - not just state roads - with a crash history that warrants a cost-benefit analysis.

"You choose a treatment, analyze the crashes, and based on the results you can either justify it or not," Bosin said about HSIP. "This treatment is expensive, so you have to justify it with a fair amount of severe crashes. The crash severity increases the benefit/cost ratio."

Last summer, the DOT&PF installed the HFST at 28 sites around Southcentral Alaska. The sites span between the cities of Soldotna and Wasilla. The selection of each site was based on having a history for single­vehicle and motorcycle run-off-the­road crashes, such as sharp curves that are difficult to negotiate. Target areas also included intersections known for rear-end crashes.

"We wanted to get a variety of locations to see how it performed in high traffic and low traffic," Bosin said. One of the caveats of the project is that the treatment needs to be in place for five years to see if it's beneficial.

"If the federal government is going to pay for it," Bosin said, "they don't want you to rip it up in a year and a half."

Labor-intensive process

Last summer, 148,000 square yards of HFST were installed in South­central Alaska for $6.3 million. EMC Engineering managed construction of the project, and Kinney Engineering in Anchorage performed the design of the project. Kinney also verified safe curve speeds, curve warning signs and super elevation (ball banking) to correct any misplaced, marked or out-of-date signage.

"It's a safety project using safety funds," Bosin said. "However, we also want to see how this material holds up here in Alaska. It's a fairly new technology to us, so we want to know how it performs with freeze-thaw, studded tire wear, high plowing and urban versus rural."

People have asked Bosin if the HFST can help improve driving under snowy and icy conditions. Her response is that it depends.

"The aggregate has to be exposed," she said. "So if it's fresh snow, then no. But if it's been plowed and exposed then it could potentially have an improvement."

The aggregate is a hard mineral called calcined bauxite, which is known for its anti-skid properties. According to a 2017 U.S. Geological Survey report, Australia, China, Brazil, India and Guinea were the world's top five producers of bauxite. Nearly al] of the bauxite used in the U.S. is imported.

To install the aggregate, federal guidelines call for a two-part epoxy resin coating, which goes down first before workers add the calcined bauxite to the top of it. The whole process is labor intensive, Bosin said. The $30 per square yard is for the entire i nsta lied cost.

"What you're getting is an auto­mated process," she said. "The truck comes and mixes the two-part epoxy resin, which has a very short period of time before it dries, so it's very temperature sensitive. It needs to be dialed in very carefully."

The surface needs to be cleaned beforehand, so it gets a good adhe­sion. The product also calls for dry and warm conditions during installation. If the pavement had ruts, workers had to mill it down, repave it and let it rest for 30 days before adding epoxy resin to assure good adhesion.

"I believe that project was the largest in the country at the time of installation," Basin said. "We had a lot of industry interest and phone calls. Lots of people noticed. Visu­ally you could tell that something was different."

Calcined bauxite vs. pre-coated chips

The DOT&PF did initial fric­tion values and got almost double to the adjacent pavement. Also, the Anchorage Police Department used its skid tester on the HFST along MLK Avenue. Basin said APO reported it was able to stop 34 feet shorter on the treated section versus the non-treated side.

Other states using HFST have seen a wide variety of crash benefits using this treatment, Bosin said, anything from 100 percent crash reductions at certain locations to 30 to 40 percent.

"Nobody has come out and said we're never putting this stuff on again," she said. "I've seen pretty positive things."

The DOT&PF is also looking into using pre-coated hard aggre­gate chips so it can get a comparison between the two applications, said Newton Bingham, a regional mate­rials engineer for DOT&PF. While the pre-coated chips would likely not provide as high a friction as the calcined bauxite, it would be some­where around one-third to one-fifth of the cost.

The calcined bauxite is a harder materia I than the aggregate sources used for pre-coated chips. Hard­ness is defined by material loss after it has been ground in a lab ball mill, Bingham said. The aggregate sources in the Anchorage, Kenai and Mat-Su Valley do not meet DOT&PF's criteria for hard aggregate. Even hard aggregate is not as hard as the calcined bauxite.

"We anticipate applying pre­coated chips on a project within the next three years," Bingham said. "A pre-coated chip seal would provide greater texture due to a larger aggregate being applied."

In the meantime, the federal government's HSIP will do its benefit­cost analysis of HFST after three years of post-construction crash data. At the same time, Bosin will be working on another federally funded, three-year study that will look at how the mate­rial is holding up in terms of rutting, cracking, rideability and friction value. The DOT&PF will be collection data once a year for three years.

"I want to take a hard look at the crash reduction and the types of crashes we were able to reduce as well as see how this material holds up," Bosin said.

The study could prove that calcined bauxite is the way to go for improving safety and durability of Alaska roads. But for now, Bosin stressed to drivers that seeing the HFST should not justify irresponsible driving.

"I encourage people to still drive for the conditions," she said. "This is not going to solve all of your problems."