Slurry Seal

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Completed Slurry Seal Project

Slurry seal consists of a carefully designed mixture of asphalt emulsion (which may be polymer-modified), mineral aggregate, water and additives; proportioned, mixed and uniformly spread over a properly prepared surface at a single stone thickness. Slurry seal is applied as a homogenous mat which adheres firmly to the prepared surface and has a skid- resistant texture throughout its service life. Slurry seal is a quick-traffic system that allows traffic to return shortly (from one to four hours) after placement.


Equipment Variations

Slurry seal is typically performed by a truck-mounted paver, but can be placed with a continuous paver to minimize construction joints.

Material Variations

  • AGGREGATE: Quality aggregate is mandatory. In addition to the actual properties of the parent rock, quality includes proper gradation, particle shape, cleanliness and sand equivalence. The aggregate is a crushed stone such as granite, slag, limestone, chat, or other high-quality aggregate, or combination thereof.

  • ASPHALT EMULSION: The asphalt used in slurry seal is emulsified before use and may be modified with a polymer. The emulsification process allows the asphalt to be pumped and mixed with aggregate at ambient temperature and allows the asphalt characteristics to be fine tuned to work in conjunction with the aggregate selected for the project.

  • MINERAL FILLER: Mineral filler may be used to improve mixture consistency and to adjust mixture breaking and curing properties. Portland cement, hydrated lime, limestone dust or fly ash are typically used.

  • WATER: Water is used to provide stability and consistency to the mix. Potable water is recommended, it must be free from salts and contaminants. Water is best sourced from a city water supply, water from ponds or streams is not recommended.

  • ADDITIVE: Additives may be used to accelerate or retard the break/set time of the slurry seal. Emulsifier and aluminum sulfate are commonly used.

Common Combinations

CRACK SEAL + SLURRY SEAL: When cracks in the existing surface exceed 1/4 inch (0.6 CM) in width, crack sealing them in advance of slurry seal will help keep water from intruding deeper into the pavement structure after the cracks reflect through the new wearing surface.

Many pavement managers use a ⅛ inch (0.3 cm) rule-of-thumb, rather than ¼ inch (0.6 cm) rule of thumb when examining crack width in the possible application of crack seal + slurry seal.

CAPE SEAL (CHIP SEAL + SLURRY SEAL): For existing asphalt pavements with more extensive cracking than would be optimal for slurry seal alone, the chip seal application before slurry seal acts as a stress-absorbing interlayer more thoroughly sealing cracks and delaying the return of reflective cracking.

SCRUB CAPE SEAL (SCRUB SEAL + SLURRY SEAL): Utilizing a scrub seal broom behind the asphalt distributor during the chip seal phase of a cape seal project helps to force more of the chip seal emulsion into the existing cracks further delaying reflective cracking.

Some agencies also opt for a Cape Seal in lieu of a stand-alone Chip Seal in more heavily populated areas to provide a smoother texture finish wearing surface than the Chip Seal alone can provide.