Scrub Seal

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Construction Troubleshooting

Medium scrub wave when no proper stop

The following are some issues that could occur during construction of a scrub seal:

LARGE AMOUNT OF SCRUB SEAL EMULSION WHEN STOPPING BROOM:

  • This happens when the operator does not pull out the excess emulsion at the end of a pull.
  • Operator should shut off nozzles about 50 feet before the end point and pull out the remaining emulsion that has accumlated in the broom sled.

SCRUB SEAL EMULSION IS BEING PUSHED OUTSIDE THE FRONT ROW OF BROOM HEADS:

  • Too much emulsion is being sprayed or
  • Too much downward pressure on the front broom heads
Medium scrub emulsion correct wave pic
Correct Emulsion Wave

THERE IS NO EMULSION WAVE AHEAD OF THE FRONT ROW OF BROOM HEADS:

  • The front row of broom heads are not touching the surface
  • Not enough emulsion is being applied

WASHBOARDING:

Potential Solutions

  • Reduce aggregate spreader speed.  If the spreader’s forward travel speed is too fast, the spreader will begin to bounce or jump and the aggregate will fall out of the hopper. When this happens, the aggregate will be heavy for a few inches and then light for a few inches then heavy again. This cycle will continue repeating itself until the spreader speed is adjusted.
  • Follow correct patching procedures.  Poor patching can also cause this problem.

Post-Construction Troubleshooting

The following are the most common post-construction problems with potential solutions. It may take an investigative approach to determine the actual problem.

LOSS OF AGGREGATE:

Potential Solutions

  • Increase the emulsion application rate
  • Removing the dust off the aggregate or switching to a cleaner aggregate
  • Verifying that the aggregate gradation meets specification and is consistent with the mix design results
  • Decrease the aggregate application rate to ensure it is not too heavy
  • Pre-treat all patches with a fog seal prior to scrub seal emulsion application
  • Applying the treatment only when weather conditions are suitable
  • Ensure that the aggregate spreaders and rollers were operating closely behind the asphalt distributor
  • Control traffic speeds until emulsion is properly set
  • Ensure that brooming does not occur before the emulsion is properly set

BLEEDING OR FLUSHING:

Potential Solutions

  • Use a cubical shaped aggregate instead of a flat and elongated aggregate
  • Reduce the emulsion application rate
  • Increase the aggregate application rate
  • Verify that the distributor and aggregate spreader calibrations are correct

 

For potential remedies on bleeding and flushing scrub seals, please refer to Chip Seal Maintenance - Bleeding and Flushed Surfaces.pdf