Micro surfacing consists of a carefully designed mixture of polymer-modified asphalt emulsion, mineral aggregate, water and additives; proportioned, mixed and uniformly spread over a properly prepared surface. Micro surfacing is applied as a homogenous mat which adheres firmly to the prepared surface and has a skid- resistant texture throughout its service life. Micro surfacing is a quick-traffic system that allows traffic to return shortly (typically less than one hour) after placement.
Micro surfacing can be performed using a continuous paver to minimize construction joints, and can also be placed using a truck-mounted paver. See EQUIPMENT section.
The most prevalent variation of micro surfacing is aggregate size:
Design variations make it possible to address additional asphalt pavement distresses such as rutting; as well as to address different traffic conditions from residential streets to Interstate highways. Notify the laboratory performing the mix design so they can create the optimal Job Mix Formula for the project.
CRACK SEAL + MICRO SURFACING: When cracks in the existing surface exceed 1/4 inch (0.6 cm) in width, crack sealing them in advance of micro surfacing 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 and micro surfacing.
RUT FILLING WITH MICRO SURFACING + SURFACE COURSE OF MICRO SURFACING: If ruts in the existing pavement exceed ½inch (1.3 cm) in depth, best practice is to fill them in advance of placing the full width surface course using a narrower paving box specifically designed for rut filling. Ruts deeper than 1-1/2 inch (3.8 cm) may require multiple applications with the rut filling box to restore the roadway cross-section.
LEVELING COURSE (SCRATCH COURSE) OF MICRO SURFACING + SURFACE COURSE OF MICRO SURFACING: Micro surfacing projects are often completed in this 2-lift fashion. The first course helps eliminate minor surface irregularities including rutting less than ½ inch (1.3 cm), and the second course provides a smooth wearing surface with additional durability and service life.
CAPE SEAL (CHIP SEAL + MICRO SURFACING): For existing pavements with more extensive cracking than would be optimal for micro surfacing alone, the chip seal application before micro surfacing acts as a stress-absorbing interlayer more thoroughly sealing cracks and delaying the return of reflective cracking.
SCRUB CAPE SEAL (SCRUB SEAL + MICRO SURFACING): 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.
Note: Some agencies also choose a cape seal rather than a stand-alone chip seal in more heavily populated areas, as it will provide a smoother texture finish wearing surface than the chip seal alone can provide.