Downtown Anchorage, Alaska, United States
Alaska, United States
Rutting due to Studded Tires
Rutting caused by studded tire wear is a serious problem in the American Pacific Northwest, costing Oregon, Washington and Alaska millions of dollars annually in damage to both asphalt and Portland cement concrete roads. According to a study by the University of Alaska-Anchorage, “In 2019, the estimated total cost of mitigating road damage from studded tire use in Alaska over the next 20 years will amount to $203.2 million.”
In Anchorage, Alaska, the studded tire rutting issues are especially prevalent due to high traffic. According to Drew Pavey, State Pavement Management Engineer for the Alaska Department of Transportation & Public Facilities (DOT&PF), “In some areas, we are seeing average wear rates of an eighth-inch (3 mm) a year.”
Attempting to mitigate the studded tire damage, the Alaska DOT&PF decided to test HiMA in the wearing course mixtures. The project took place in Anchorage where a PG 64E-40 HiMA binder was used in a Superpave mix incorporating hard aggregate. The HiMA mix was placed on 5th and 6th Avenues and cross streets in downtown Anchorage. This project was a standard street resurfacing with a 1.75 in (44 mm) mill and 2 in (50 mm) fill. Traffic on 5th and 6th Avenues average from 10,000-15,000 vehicles per day.
The PG 64E-40 HiMA binder was supplied by Denali Materials Inc., and the project was constructed by Granite Construction. Paving began for a month in September 2014 and was completed the following June. Paving was done at night and static rolling was required due to noise and sensitive infrastructure. The mat temperature behind the paver averaged 310°F (155°C). Even with difficult conditions and equipment restrictions, the contractor achieved the required mat density of 95 percent and joint density of 93 percent.
To date, performance has been good with minimal damage caused by studded tire wear or traffic loads. In 2019, after four years of traffic including studded tires, the average rut depths were 0.204 in (5.2 mm) on 5th Avenue and 0.198 in (5 mm) on 6th Avenue. Following the successful project performance, Alaska DOT&PF specified the same PG 64E-40 HiMA binder grade for resurfacing Glenn Highway.
Glenn Highway was paved in 2017, and after two winters, the rut depth was 0.21 in (5.3 mm). Previously, a trial with PG 64-34 and ground tire rubber experienced 0.32 in (8.1 mm) rut depth after two winters, so the HiMA solution reduced rutting by a third. This translates to a 50 percent increase in pavement life before resurfacing is required.