The last weblog was a brief overview regarding asphalt seal coats. This blog will specifically focus on asphalt fog seals.
What are fogs seal and why are they used?
A fog seal is a cost-effective maintenance option that can improve the life of the pavement by delaying the need for major maintenance or rehabilitation.
A fog seal is a single application of an asphalt emulsion onto an existing pavement surface for maintenance purposes. The reason for a fog seal is to renew oxidized pavement surfaces. This will also seal minor cracks, inhibit raveling while at the same time improving the surface appearance. Fog seals can be used to preserve any distressed sections of a paved road until funds became available for long-term repair options.
The benefits of using an asphalt fog seal include:
- Protecting the pavement surface from moisture intrusion
- Shielding the pavement structure from oxidation
- Improving pavement life
- Delaying the raveling of existing pavement aggregates
- Delaying the need for major maintenance or rehabilitation
- Sealing minor cracks in the pavement surface
- Improving color contrast between pavement and striping
Road Requirements for Fog Seals
Fog seals can be used on a variety of road types, with a full range of traffic types, and applied in any climate type. Fog seals are applicable for pavement surfaces where the penetration of the diluted emulsion can be expected. This typically includes roads with aged and raveled asphalt surfaces, as well as chip and seal and open-graded surfaces. In addition, the roads need to have adequate structural capacity and not applied on any roads that have signs of structural distresses such as excessive cracking and rutting or shoving.
Generally, you can expect up to 4-years life extension on road surfaces that are in satisfactory to good condition (Pavement Condition Index (PCI) value of 70-100); up to 3-years life extension on road surfaces that are in fair to satisfactory condition (PCI value of 65-75); or up to 2-years life extension on road surfaces that are in fair condition (PCI value of 55-65).
Types of Emulsions used for Fog Seals
For fog seals, slow-setting and low-viscosity grade such as SS-1, SS-1h, CSS-1, or CSS-1h asphalt emulsions are commonly used. These emulsions are also diluted with water for application purposes. This allows the emulsion to coat aggregate particles and to flow easily into cracks and voids on the road surfaces. Typical dilutions range from 1:1 to 5:1 (parts water to parts emulsion) and applied at rates ranging from 0.05-0.15-gallons per square yard. Fog seals should only be applied if the temperature of the road is 59oF and higher, and when air temperatures are greater than 50oF. In addition, fog seals should not be applied when there is a threat of precipitation.
Blue Line Road Products manufactures asphalt emulsions specifically engineered for fog seals. For more information, please contact a Blue Line Road products sales engineer at 503-279-2600.
Asphalt Institute: Glossary of Terms
Pavement Preservation and Recycling Alliance