Chapter 6: Fog Seals

3.0 Fog Seal Materials & Specifications

3.1 What Materials Are Used?

The materials used in fog seals are usually asphalt emulsion and water.  In some cases, the emulsions are made with a range of additives for special purposes.  For example, rejuvenation oils may be used to soften and revitalize the aged binder in the pavement.  Rejuvenation treatments require special attention in design and application and should conform to an Agency’s specifications.

The emulsion types recommended for fog seals may be cationic (i.e., a positive surface charge on the asphalt particles), or anionic (i.e., a negative surface charge on the asphalt particles).  The primary types used are CSS-1h and SS-1h.  In some circumstances, CQS-1h (and LMCQS-1h) will give a faster set.  These are still nominally CSS type emulsions, but will not usually pass the AASHTO cement-mixing test.  The cement-mixing test (a part of AASHTO test method T59) may be omitted as this relates to aggregate mixing stability and not fog sealing.

Note that asphalt emulsions of this type contain up to 43% water.  However, any dilution referred to is additional water added to the emulsion.  Residual asphalt is the binder left after all water  (i.e., any added water and the original emulsion water) has evaporated.

Rejuvenating emulsions may take several forms and should only be used on pavement showing significant age-related distress associated with stiffening of existing binder.  They may be emulsions of rejuvenating oils and may include asphalt, polymer latex, and other additives.  These are defined in manufacturer’s literature.

3.2 Design Considerations

Fog seals are designed according to an application rate and sometimes dilution rate.  This is also a part of the construction process as it is very surface dependent (see Section 4.4).