Blythe Construction Maintains Carolina Pavements, Overall Budget with Fog Seal
BY Ron DiGiacomandrea
For paving professionals, the sight of a brand new pavement surface gives them a feeling of satisfaction from the realization of a job well done. It’s almost like the sight of all those presents under the tree on Christmas morning before the unwrapping chaos. But as soon as the traffic hits it, the new pavement will begin to wear. How can you maintain the pavement surface to stave off costly pavement repairs or major rehabilitation as you reach for the pavement service life you were hoping for?
Agencies and owners across the country continue to pursue pavement preservation techniques as a means of maintaining their road infrastructure. With lots of lane miles to maintain, keeping good pavements in good shape through timely pavement maintenance is a big key for agencies and owners in getting the most out of their budget dollars. One cost-effective way to do that is through the use of fog seal applications.
As with any pavement preservation technique, the key is to choose the right application for the right road at the right time. A new road surface would be at 100 percent of its expected service life. For fog seals, the right time is around 80 to 95 percent of the expected service life. Assuming an intended pavement service life of 20 years, to keep a good road surface in good condition, fog seals can be applied every three to five years.
The Asphalt Institute’s Publication MS 19, The Basic Asphalt Emulsion Manual, describes a fog seal as “a light spray application of binder applied to the surface of a chip seal, an open-graded mix, or a weathered hot mix surface.” The material used for such a light spray application starts with an emulsified asphalt meeting the applicable specifications as directed by the overseeing agency (typically AASHTO M 140, AASHTO M 208, or some modified versions of these specifications).
The specification compliant emulsified asphalt is then diluted with water, usually at a 1:1 ratio. This diluted emulsified asphalt is then spray applied using a conventional tack distributor truck. The emulsified asphalt grade used and rates of application for fog seals are usually set by, and will vary by, the agency. The rates are also dependent on the type and texture of the surface to which they are applied. When making fog seals, slow setting emulsified asphalts are a typical grade selection (i.e. CSS-1h or similar), with application rates somewhere around 0.12 gallons per square yard being common. Rapid setting emulsion grades can also be used to produce fog seal. After a fog seal application has broken and set, the finished roadway will be ready to return to traffic, often within 30 to 60 minutes after application.
Real world application
After initial discussions and consultation with the different agencies for some of Blythe Construction’s 2017 fog seal projects, the decision was made to use GSB-88® asphalt emulsion as the base material to produce the fog seals. As GSB-88 can be classified as a slow setting emulsified asphalt, and is already approved for provisional use by the North Carolina Department of Transportation (NCDOT), this seemed like a perfect fit for these projects. As well, BCI Materials (a part of Blythe Construction) has a GSB-88 fog seal product which meets the specification requirements of, and is approved by, the South Carolina Department of Transportation (SCDOT) for use on open-graded friction courses.
GSB-88 is a sealer/binder that rejuvenates and weatherizes asphalt surfaces. It is designed for use on both commercial and military airport runways, and meets the requirements that are specified in P-608 of the Federal Aviation Administration’s (FAA) AC# 150/5370-10G. BCI Materials manufactures GSB-88 at our emulsion plant in Charlotte, North Carolina, under our licensing agreement with the technology owner, Asphalt Systems Inc. of Salt Lake City, Utah.
With contracts in hand, and expectations set high, Blythe Construction’s crews began work on a set of maintenance projects. Each crew began with a review of the process and execution of work events, including resident notifications, traffic control procedures, best practices to be used, equipment inspections and insuring any potential safety issues were fully addressed before starting work each day.
Spartanburg County, South Carolina fog seal over hot mix asphalt (HMA)
After an initial application in 2016 on 50,000 square yards of existing pavement to evaluate the use of a fog seal application, Spartanburg County requested covering another 100,000 square yards for 2017. The roads that were selected had a pavement condition index (PCI) of 60 to 75, with the goal of mitigating surface cracking or raveling of the existing pavement. The fog seal was prepared using a 2:1 dilution ratio. Depth patching and crack filling with an approved crackseal product had been performed prior to the fog seal application. Some of the selected roads had concrete curbing, while others did not.
A couple of days prior to beginning the operation, flyers were placed at each residence on the project to notify citizens about the project details and timeline.
After cleaning the pavement, the first step was to edge along any concrete curbing. A device designed to allow fog seal application along curb and gutter was used to keep the curbing surface clean.
Ronald E. Kirby Jr., PE, a Certified Floodplain Manager and Spartanburg County Engineer overseeing the project for the agency, likes the results he is getting with these GSB-88 fog seal applications. Kirby said, “I have been pleased with GSB-88. We have used the product in 2016 and 2017. I intend to apply GSB-88 in 2018 as well. We typically use it on roads that have been depth patched and crack sealed.
The dark black color helps hide the crack seal. I have noticed that cracks are not propagating as quickly as the cracks on untreated roads. We typically put GSB-88 on pavements that are a little farther down on the Kendall curve.”
He also said that he sees the GSB-88 fog seal applications are retaining the fines well. Regarding service life, he said, “We are watching the performance to determine how much additional pavement life we are getting.”
NCDOT Division 10 Maintenance Office fog seal over chip seal surface treatment
The North Carolina DOT has 14 divisions that are responsible for their geographical areas within the state. Each division typically has its own maintenance office that is responsible for the division’s maintenance operations and budget. In Division 10, which includes the city of Charlotte and some surrounding counties, their maintenance office requested a fog seal application to cover a chip seal surface treatment.
For chip seal surface treatments, a fog seal application is a good way to help lock the stone chips in place. A quality fog seal application over chip seal can leave the road surface looking like a freshly paved surface and seals the surface against the elements.
After the existing chip seal surfaces were swept, application of fog seal on areas abutting driveways was accomplished using the wand attachment of the distributor truck. The dilution rate of 2:1 was used for the project.
Blythe Construction expects the demand for fog seal applications to continue to grow in our marketplace as more agencies and owners seek to employ this cost-effective pavement preservation technique. With agencies and owners looking for ways to maintain more miles each year of their road inventories, fog seal is a great tool to have in their maintenance toolbox.
Ron DiGiacomandrea is the quality control manager, emulsions, for BCI Materials, a division of Blythe Construction Inc., Charlotte, North Carolina.