Pocatello Fog Seals with GSB-88
BY Asphalt Systems Inc.
The City of Pocatello, Idaho, fog seals using GSB-88 emulsified asphalt seal coat product to mitigate the impacts of surface oxidation and moisture damage.
Founded in 1889, the City of Pocatello in southeastern Idaho earned the moniker “Gateway to the Northwest.” More than 125 years later, Pocatello’s dedication to transportation excellence and keeping its streets in superior shape continues to be a large part of its exceptional reputation.
Over the years, Pocatello has maintained its 269 centerline miles of streets using a number of pavement preservation methods, including crack seal, chip seal, micro surfacing and cape seals. More extensive required roadwork includes overlays and reconstruction. As part of its pavement preservation arsenal, each year Pocatello also targets a number of streets for fog seal application. For the past decade, at least 10 percent of the city’s annual pavement management budget has been allocated to fog sealing (See the March/April edition of AsphaltPro for a how-to primer on rejuvenating fog seals).
“The City of Pocatello uses a Pavement Condition Index (PCI) rating for the streets within the community,” Tom Kirkman said. He’s the deputy director of Public Works for the City of Pocatello. “For each treatment type, such as a fog seal, we run a model where it shows the streets that fall within the PCI parameters for which that treatment is recommended.”
An asphalt surface with a PCI score of 75 or higher (considered to be in “good” condition) is an ideal candidate for a fog seal treatment. “We follow the approach of ‘the right treatment, at the right time, on the right road,’” he added.
Pocatello experiences all four seasons. During winter, the freeze/thaw cycles can cause severe cracking and potential water intrusion. In the spring, summer and fall, rain can bring water intrusion into cracks, which may then produce potholes.
Additionally, oxidation also wreaks havoc on road surfaces.
“In applying a fog seal, we extend the life of the streets by rejuvenating the pavement to reduce further deterioration. It should protect the road from weathering, seal small cracks, and prevent water from penetrating the road,” Kirkman said.
The typical fog seal application is expected to last approximately four to five years before another treatment is required. It also is often used as a follow-up treatment approximately four years after a street is chip sealed.
Do the Treatment Right
Pocatello handles its own fog sealing work, using a truck-mounted emulsion distributor operated by its own street crews. The city targets the months of July and August each year for its fog sealing projects, as weather conditions are mostly likely to be favorable for the work during that timeframe, with highs in the 80s and less chance of rain than other months.
For several years now, the city has used GSB-88® emulsified asphalt seal coat product, mixed in a 2:1 ratio with water for its fog sealing projects. In 2017, the city treated 39 streets, covering approximately 230,100 square yards with 21,000 gallons of GSB-88 mixture at 0.09 gallons per square yard. In 2018, Pocatello treated another 50 streets, fog sealing 269,766 square yards of pavement with the GSB-88 mixture.
Pavement treatments using GSB-88 are designed to mitigate the impacts of surface oxidation and moisture damage, halting deterioration, sealing the surface to help repel water, and also mitigating surface raveling. The primary deteriorating factor for most asphalt pavements is surface oxidation, and studies have proven that application of GSB-88 very early in the life of a pavement, with timely repeat applications every four to seven years, can eliminate surface oxidation as a significant factor in pavement deterioration.
Kirkman listed a number of challenges that any pavement preservation project presents. These include nuisance to the public while roads are closed for the process, time and efforts to ensure parked cars are moved from the construction area, adverse weather, construction debris or a dirty surface, and the curing rate of the treatment.
Certainly, any type of roadwork is a nuisance in the eyes of the public. But a good outreach program can work wonders in gaining approval and cooperation from residents. Pocatello has perfected a communications program about its street maintenance work that includes ongoing information on its website, timely news releases to the media, and announcements on social media—including Facebook, Twitter and the use of the Nextdoor.com website and app, which is a private social network for residents within specific communities and neighborhoods.
As for the challenges associated with the application, the city has found success with GSB-88 in that it applies quickly with standard bituminous distributors. The shot length is about 2,650 feet, and the spread rate is dependent upon the existing asphalt pavement’s texture, porosity and age. While the product typically cures in two to four hours, Kirkman noted that for Pocatello’s fog sealing projects, the treatment has completely cured in approximately two hours when applied under optimal conditions of 80-plus degrees Fahrenheit, in low humidity, with a breeze.
Pocatello follows a specific procedure to determine which of its streets need maintenance, and what type of maintenance they need. Each year the city examines a percentage of its streets, so that every street in Pocatello is examined once every three years. By tracking the number of cracks, raveling areas, potholes and other pavement issues on each road, the city’s engineers are able to calculate a PCI to determine when the pavement needs what type of maintenance.
Pocatello’s public works department makes every effort to educate residents about preventative maintenance, and how it is necessary to apply before a street begins to develop significant problems. A two-hour preventative inconvenience now is much better than a two-week reconstruction inconvenience would be later. Pavement maintenance has often been compared to wood siding on a house; if the siding begins to experience some peeling paint, a homeowner doesn’t tear off all of the siding simply because it needs painting. Just as a homeowner protects a house from the elements by painting it before it deteriorates to the point that it is no longer serviceable, streets must be maintained before they become so deteriorated that expensive reconstruction is the only answer.
“Our fog sealing projects using GSB-88 seem to be well-accepted by our residents. They like the fast cure time, and the resulting surface,” Kirkman said. “Preventative treatments such as this save money on long-term road maintenance costs, and we plan to continue using fog seal as a pavement preservation method for years into the future.”