Slurry Seal

Slurry seals are a mixture of bitumen emulsion, graded aggregates, mineral filler, water and other additives. The mixture is made and placed on a continuous basis using a travel paver (Slurry Surfacing Machine). The travel paver meters the mix components in a predetermined order into a pug mill. The typical mixing order is aggregate followed by cement, water, the additive and the emulsion. The resulting slurry material is a free flowing composite material that is spread via a spreader box over the existing road surface. The consistency of the slurry material allows it to spread over the pavement, wetting it, and forming an adhesive bond to the pavement.

The slurry mixture contains bitumen emulsion that breaks onto the pavement surface through heterogeneous or homogenous flocculation. The bitumen particles coalesce into films, creating a cohesive mixture. The mixture then cures, by loss of water, into a hardwearing, dense-graded asphalt/aggregate mixture that is bonded to the existing pavement.

A slurry seal is used to:
  • Seal sound and oxidized pavements
  • Restore surface texture by providing a skid-resistant wearing surface
  • Improve waterproofing characteristics
  • Correct raveling
  • Provide a new surface where weight restrictions preclude the use of heavier overlays (e.g., bridge decks), and
  • Provide a new surface where height restrictions are a problem (e.g., overcrossings).
A slurry surfacing does not add any structural capacity to an existing pavement; they are applied as a maintenance treatment to improve the functional characteristics of the pavement surface. The main criteria for project selection are:
  • Sound and well drained bases, surfaces, and shoulders
  • Free of distresses, including potholes and cracking
Distress modes that can be addressed using slurry surfacing include:
  • Raveling: Loose surfaces or surfaces losing aggregate may be resurfaced using slurry seals
  • Oxidized pavement with hairline cracks: These surfaces may be resurfaced using slurry seals
  • Friction Loss: Skid resistance can be restored by application of slurry seals
A slurry seal should not be used to:
  • Correct surface profile
  • Fill potholes, and
  • Alleviate cracking (with or without polymer modification)
Distress modes that cannot be addressed using slurry surfacing include:
  • Rutting
  • Cracking (including reflection cracking)
  • Base Failures (of any kind)
  • HMA Layers that exhibit plastic shear deformation

Slurry surfacing will not alleviate the cause of these distresses. As a result, the distresses will continue to form despite the application of a slurry surfacing.

The performance of a slurry surfacing depends on the quality of the materials and how they interact during cure and after cure. The mix design procedure looks at the various phases of this process, which include:

  • Mixing: Will the components mix together and form slurry with desired consistency?
  • Breaking and Curing: Will the emulsion break in a controlled way on the aggregate, coat the aggregate, and form good films on the aggregate? Will the emulsion build up cohesion to a level that will resist abrasion due to traffic?
  • Performance : Will the slurry surfacing resist traffic-induced stresses?