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 Marine Corps Air Station in Cherry Point, NC. Within about 8 weeks of the
start of construction, and after 3 runways had been completed, aircraft
operations reported the pick-up of slurry seal material on the undercarriage
of the AV-8A (Harrier) aircraft. Shortly thereafter were reports of large
"dust storms" whenever the Harrier operated near the surface.
Investigation by LANTNAVFACENGCOM engineers revealed that the slurry seals had
lost cohesion and that wide spread raveling was occurring. The slurry seal
was also stripping off the runway ends where it had been placed over rubber
deposits.
Solution/Alternatives: One lesson learned from this project was that built-up
rubber deposits must be removed before slurry sealing. Failure to remove
rubber deposits may result in sheet-like stripping of the slurry from the
pavement. After rubber removal a tack coat of emulsified asphalt must be
applied.
Although the specification requirements appeared to have been met, as
evidenced by submitted mix design information, no sampling and testing of the
slurry mix had actually been accomplished during the construction process.
The failure to exercise the quality assurance requirements of the
specifications made it virtually impossible to know what actual mix
proportions were applied to the pavements. The failure to sample and test the
materials, or to merely retain samples for possible testing at a later date,
made investigation of the raveling failures very difficult.
Under the direction of a consultant to the Navy, Mr. B. A. Vallerga, a number
of cores were cut from the pavements and the aggregate stockpiles were sampled
and tested. Based upon these tests as well as a review of other agency's
experience with slurry seal, the most probable causes of the disintegration
mode of failure were determined to be insufficient asphalt in the slurry
mixture and a deficiency in the coarse and fine aggregate fractions.
In order to correct the raveling problem, a series of trial fog seal
applications with varying application rates was undertaken. The remedial
treatment which was eventually applied consisted of 0.10 gal/sq.yd. of a 1:1
dilution of SS-1h asphalt emulsion. The emulsion application was followed by
3 passes of a rubber tired roller with 90 psi tire pressure. The fog seal was
successful in preventing any further raveling.
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