| | When to Use Sealers & Rejuvenators One goal of the study is to determine the timing of sealing applications. Lessons Learned:  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. Several agencies also routinely use spray applied seals immediately after chip sealing because the seals keep down dust, blacken the surface, improve visibility, and, most importantly, reduce chip loss, raveling and vehicle damage. Minnesota also reports a greatly reduced incidence of snow plow damage.
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. As one example, a project condition survey at the Maple Island site was conducted during a light drizzle. (See photo.) The sealed sections appeared wet, whereas water was quickly soaking into comparable unsealed areas. Although still effective at reducing permeability to moisture, an earlier resealing was probably warranted to prevent excessive hardening between applications. There is a question if it is better to have a regular application schedule, or to use some critical test parameter to determine when it is time to reseal. Some of the analytical methods discussed later could be used. In particular, the bending beam procedure uses relatively inexpensive saws to cut thin surface specimens and BBR equipment already available in most agency and supplier laboratories. Unfortunately, the BBR method and similar protocols require frequent coring and significant testing time to monitor critical parameters. Because such monitoring protocols can be expensive, especially in relation to the cost of sealing, it may not be practical to run such tests routinely on all prospective pavements. However, because high summertime temperatures and crude source have a huge impact on aging rates, it is important to do enough testing to understand typical changes in local pavement material properties over time, and to understand how critical performance parameters respond to intervention with the various fog seal products available in that market. Once aging models and product performance criteria are understood, it should not be difficult to establish timing models that require minimal testing for verification. Therefore, once validated, a scheduled interval based on the climate, traffic and road surface (dense-graded, open-graded, chip seal) may be the best timing. An interval of "every x years or observation of low severity surface cracking, whichever comes first" may be the best for agencies that do not have the wherewithal to run tests on the pavements. 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 DSR or BBR tests indicating excessive hardening or embrittlement. Even if a simple timing approach is adopted, pavement permeability will always remain a critical variable that varies from pavement to pavement. Too many agencies have learned the same hard lesson: one slick job = accidents = moratorium on fog seals. If emulsions do not infiltrate into the surface, friction may be a problem and performance will not be satisfactory. It is important to insure that emulsion is applied at the proper rate and penetrates into the surface. This can be accomplished with field or lab permeability tests, infiltration tests (ring test), pour tests, or short trial sections on the pavement. A more aggressive alternative might be a performance test for friction upon release to traffic or following a prescribed curing period.  The DOT survey and test reports may be found in the Project Library, and photos of aged seals may be found in the Photo Gallery. | downloadable Documents:
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Sealer & Rejuvenator Overview FPP/FHWA Fog Seal Checklist Rejuvenator Seal Checklist Caltrans Fog Seal Technical Advisory Guide Full Project Report |