Spray Applied Polymer Surface Seals - TSP2

Lessons Learned
Fog Seal
When to Use?
Pavement Age
• Seal newer pavements
• Rejuvenate age-embrittled pavements
Permeability Enables Infiltration
• Mix design (coarse, fine, open, SMA)
• Construction density
• Densification under traffic
When to Use Fog and Rejuvenator Seals
One goal of the study is to determine the timing of sealing applications. The DOT survey showed
that many agencies have a scheduled fog seal application program for preventive maintenance that
begins between two and ten years after HMA construction, and some routinely use spray applied
seals immediately after chip sealing.
Observations of four-year old seals in this study showed that most materials exhibited minimal visible
color difference between sealed and control sections because most asphalt residue had worn off of
the surface aggregate. However, the water, raveling and cracking protection still appeared to be
intact. While the most accurate approach would be a test parameter for determining when to reseal,
the required testing is not practical for most agencies. Once aging models and product performance
criteria are understood, it should not be difficult to establish timing models that require minimal testing
for verification. A scheduled interval based on the climate, traffic and surface type of "every x years
or observation of minor distress, whichever comes first" may be the best strategy. Possible triggers
for sealing or resealing might include: very small surface cracks, permeability above a specified
level, raveling, loss of fines or mastic from the surface, or rheological (DSR and/or BBR) tests
indicating excessive age hardening. Older conventional wisdom suggests that surface pitting and
raveling begins when binder ductility measured at 15ºC falls below 10 cm, and block cracking begins
when the ductility reaches 5 cm.
Even if a simple timing approach is adopted, pavement permeability will remain a critical variable. If
emulsions do not infiltrate into the surface, friction may be a problem and performance will not be
satisfactory, resulting in accidents and potential disuse of spray applied seals. Field or lab
permeability tests, infiltration tests such at the ring test (12), pour tests, or short trial sections on the
pavement may be used. A more aggressive alternative might be a performance test for friction upon
release to traffic or following a prescribed curing period, preferably based on a pre-project test strip.
Caltrans recently funded research to be led by Dr. Gary Hicks at the regional Pavement Preservation
Technical Center at Chico State which will deliver a performance specification for fog seals, including
friction requirements.
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