| | Where to Use Sealers & Rejuvenators Emulsified sealers and rejuvenators are best used as a preventive maintenance treatment on HMA pavements in good condition, but with surfaces that have begun the aging process. They can be used on any asphalt pavement, but traffic should be controlled until they have fully cured. Lessons Learned: Fog seals should not be used when a pavement has poor surface texture, large cracks, rutting, shoving, or other structural deficiencies. The surface friction was generally lowered immediately after construction on the dense HMA pavements treated in this study, but was regained with time. The graph shows the change in friction number over time on the Marysville, California project. It is not recommended to treat pavements with low friction numbers with emulsified sealers or rejuvenators. The Maple Island project included crack sealing thermal cracks a few months after the sealing. The emulsified seals appeared to be effective where there had been sufficient maintenance. There were fewer new cracks than in the control sections, except, notably, in areas where cores had been taken.  Because of the initial drop in friction noted in this study, it is recommended that traffic be strictly controlled with pilot cars until the friction index reaches an acceptable level. As friction is a function of speed, this is especially important on high speed highways. Sanding strategies may vary depending upon the rheology of the emulsion residue. The supplier of the rejuvenator emulsion (Reclamite) recommended that the emulsion be allowed to penetrate into the pavement surface for twenty to forty minutes before sanding. It is very important that the soft residue not leave oil-saturated sand on the surface when traffic is returned. When fogging with emulsions that had harder residues, sand was applied immediately after the spray application, as one would do for a sand seal, creating more surface texture for enhanced friction. Although early friction numbers were low when sand was not used, the California projects showed that friction levels of the sealed surfaces returned to nearly the same friction numbers as the untreated control with time (see graph above). Some years ago, a serious accident following a poorly applied rejuvenator seal forced CALTRANS to place a moratorium on the use of fog seals. New specifications there will probably require a friction index typical of minimum HMA surface standards before full speed traffic can return. Such a specification, although appropriate from a safety perspective, is a very demanding limit that will require the very best of materials and practices. As one example, the following graph shows how sanding the Olmstead County, MN 112 project consistently improved friction numbers for all emulsions after less than four hours of cure time.  There is a renewed interest in open-graded friction courses and open asphalt rubber mixes to reduce back-spray in wet weather and to reduce tire noise. Fog seals have been found to be an effective solution to the raveling problems traditionally associated with aging open-graded mixes. For example, New Mexico DOT successfully maintains many miles of OGFC with a scheduled fog seal program, usually using dilute polymer modified emulsions. The U.S. 87 project near Winslow, Arizona included an asphalt rubber section. When developing a maintenance strategy for these open-graded mixes, it is important to remember the importance of maintaining sufficient air voids to allow for adequate drainage. Spraying too much binder, or applying fog seals which trap large amounts of dust and blow sand in the aggregate matrix may eventually create problems.  Some agencies, especially Mn/DOT, have had success with fog sealing new chip seals. The projects in Arizona (Winslow) and Minnesota (Maple Island) included chip seal sections. On the Arizona project, the southbound control section which had been chip sealed with CRS-2P exhibited severe chip loss after four years. There was no visible chip loss on the test sections that had been fog sealed immediately. The photo shows the difference in chip loss where the far lane was sealed and the near lane was not fog sealed. The fog seal serves several purposes: to control dust; to tie down chips, giving further protection; and to give a black surface. The fog seal reduces the likelihood of shelling and also protects the seal against snow plow damage. The black surface improves visibility and public acceptance. As a side observation, the value of chip seal as a protective coating to reduce the rate of asphalt aging was also verified. On the Maple Island project, the modulus of the HMA surface mix immediately below the chip seal was similar to the rejuvenated section after two and four years in service. The heavy binder application appears to seal the pavement to both oxygen and moisture.
 There is anecdotal evidence that sealing shoulders helps protect them, as well. Several agencies including Mn/DOT reported they have reduced the need for shoulder reconstruction with a regular schedule of fog seals. If there is sufficient color contrast between the travel lane and shoulder, fog seals can also improve nighttime visibility. With no traffic, maintaining friction is much less critical. However, the surface does not densify as it would under traffic, so pavement permeability is typically higher. Given all these considerations, emulsion application rates for shoulders are typically higher than those for adjacent travel lanes.
Full test reports and construction reports on some of the projects with field observations can be found in the Project Library, and additional field observations are 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 |