Scrub Seal

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Asphalt Distributor - the function of the asphalt distributor is to apply the emulsion uniformly and in specified quantities. The distributor consists of a truck- or trailer-mounted insulated tank ranging in capacity from 800 to 5,500 gallons (3,000-20,800 liters). 

Most distributors are equipped with a heating system that will maintain the binder at the proper spraying temperature and has a system of spray bars with nozzles that apply the emulsion to the roadway surface. These spray bars cover widths up to 30 feet (10 meters) in one pass. 

The asphalt distributor is the most complex piece of equipment used in scrub seal construction work because it has many components, and all must be operating properly. 

The major components are: 

  • Asphalt tank -  a distributor can consist of a truck- or trailer-mounted insulated tank ranging in capacity from 800 to 5,500 gallons.  The tank should also have baffle or surge plates to stabilize the load while in motion. 
  • Heating system - the tank should have one or two propane or diesel fired burners that direct heat into flues that pass through the tank. This allows the contents of the tank to be heated to the correct application temperature. A thermometer should be mounted in the side of the tank so that the correct temperature can be observed.
  • Circulating and pumping system - the asphalt pump, radar, control valve and strainer are important parts of the circulating and pumping system.  These parts should be checked to ensure they are set properly and there are no leaks.  
  • Spray bar and nozzles - ensure that the spray bar is at the correct height and that the proper size nozzles are installed and at the correct angle.
  • Distributor controls and gauges - the distributor operator should be familar with the following controls and gauges to ensure that a uniform and precise amount of asphalt binder is applied onto the roadway.  They include:  thermometer, volume gauge, strap stick pump pressure; and the control panel.

Scrub Broom - the function of the scrub broom is to gently scrub the emulsion into the cracks in the roadway.  The broom heads should be clean and not damaged or permanently bent back.

Aggregate Spreader - the function of the aggregate spreader is to apply a uniform aggregate cover at a specified rate over the freshly sprayed binder. Aggregate spreaders should be self propelled and have a continuous feed feature. The major components of the aggregate spreader are:

  • Truck hitch - visual check for anything broken or bent.  Ensure the locking mechanism is working properly.
  • Receiving hopper - the function of the receiving hopper is to receive the aggregate from the haul truck. The receiving hopper should be visually checked for overall condition.
    • There should not be any holes or large gaps that would allow aggregate to fall through to the road surface;
    • The conveyor belt system should have rubber, neoprene, or fabric cowling around it to prevent aggregate loss; and
    • There should be a flap on top of the receiving hopper to ensure tight fit against haul trucks as aggregate is being dumped into the receiving hopper.
    • A rubber shield prevents aggregate from piling up on the belt, being carried ahead of the receiving hopper and being spilled onto the ground. The rubber shield should be inspected to make sure it is not torn or missing.
  • Conveyor belts - check to ensure they are in good condition and not frayed enough to allow aggregate to spill over the sides onto the roadway. Check to ensure belts are tight.  Excessive amount of slack will cause sagging and loss of aggregate off the sides.
  • Spreading hopper - ensure the spreading hopper has no cracks or holes.
  • Discharge gates and roller - ensure that the discharge gates open and close correctly and that the roller is not warped.
  • Wheels and tires - make sure wheels do not wobble and that tires have correct air pressure.

 Rollers - the functions of the roller are to:

  • Orient the aggregate to their flattest side
  • Embed the aggregate into the binder
  • Achieve mechanical interlock between the pieces of aggregate.

A pneumatic roller is recommended for all scrub seal work and operates on rubber, air-inflated tires. A pneumatic roller must be self-propelled and capable of operating in both forward and reverse.

Sweeping Equipment - the functions of the sweeping equipment are to:

  • Clean the exisiting roadway of dust and/or foreign materials before scrub seal construction
  • Removing excess aggregate from constructed scrub seals


There are three different types of sweeping equipment typically used in scrub seal construction:

  1. Rotary Brooms - the most popular type of broom on scrub seal construction projects.  The downward pressure must be kept to a minimum in order to not dislodge the embedded aggregate.  The brush should be inspected to see that it can be raised/lowered and rotated horizontally.  Rotary brooms do generate dust, which can affect visibility for traffic.
  2. Pickup sweepers - these type of sweepers are generally used wherever dust must be minimized and it is desirable to remove all excess aggregate from the project limits.  A pickup sweeper features a broom that sweeps the aggregate to a suction head that deposits the material in a storage tank. Pickup sweepers are particularly useful in urban areas where aggregate accumulation in gutters or along the edge of the roadway is undesirable.
  3. Vacuum sweepers - these type of sweepers represent purpose-built equipment that removes the excess aggregate through suction only. The lack of contact with the scrub seal’s surface minimizes damage.

Front End Loader - the function of the front end loader is to move aggregate from the stockpile into the haul truck.  

Haul Truck - the function of the haul truck is to transport the aggregate and dump it into the aggregate spreader. They are normally either tandem-axle or single axle trucks. Haul truck components to check:

  • Size – single axle normally carry 6 cubic yards and tandem-axle usually 12 or 14 cubic yards
  • Condition – leak free
  • Hoist – should operate properly and leak free
  • Tailgate – should be hinged at the top and have capability of being latched closed at the bottom
  • Hitch – compatible with the one on the aggregate spreader.


  • Aggregate Spreader
  • Front End Loader
  • Haul Truck
  • Roller
  • Rotary Broom
  • Scrub Broom