Process
A cape seal is a process that includes placing a chip seal on the existing surface and then after a few days placing a slurry seal or micro surfacing layer on top of the chip seal.
To place the chip seal, an asphalt distributor provides application of the binder to the pavement surface. A chip spreader immediately applies a uniform, predetermined rate of aggregate onto the binder. These two operations are at the heart of constructing a surface that is one stone thick and has enough asphalt to retain the aggregate, but not an excess amount of binder that causes the surface to bleed. Depending on the binder, aggregate, and actual type of chip seal being constructed, various rollers will be used to orient the aggregate to achieve appropriate embedment. Pneumatic rollers are typically found on all chip seal projects. The rollers are followed by the brooms that remove excess aggregate from the finished surface.
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.
Micro surfacing consists of a carefully designed mixture of polymer-modified asphalt, mineral aggregate, water and additives, proportioned, mixed and uniformly spread over a properly prepared surface which is typically greater than one stone thick. 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.
Variations
Equipment Variations
Equipment variations can include the following:
- Aggregate spreaders - a self-propelled aggregate spreader is common on chip seal projects but tailgate box spreaders are sometimes utilized where strip sealing is done.
- Rollers - pneumatic rollers and steel static wheel rollers can be used for chip seal projects however, caution should be used when using steel static wheel rollers due to crushing and degrading the aggregate. Some agencies only have access to steel wheel rollers but pneumatic rollers are recommended.
- Sweepers - the rotary broom is the common sweeper on chip seal projects however vacuum sweepers can be seen where dust has to be minimized and loose aggregate cannot be seen off the road. Urban roadway that have gutters would classify as an area where loose aggregate would be undesirable.
- Micro surfacing is typically performed using a continuous paver to expedite construction rates and minimize construction joints, and can also be placed using a truck-mounted paver. Slurry seal is typically performed with a truck mounted paver, however a continuous run paver can be used as well.
Material Variations
Material variations for chip seals can come from either different types or sized aggregates and from the different binders utilized in the chip seal process.
- Aggregates
- Types - granite, slag, limestone, or lightweight aggregates are some of the types that are usually utilized in chip seals. Which type that is utilized is usually dependent on local availability and the local specification.
- Sizes - chip seal aggregates can range from 1/4" to 1/2" in size.
- Binders - there are a host of different binders that could be utilized in chip sealing but they can be divided into 2 major categories: emulsified binders and hot applied binders.
The most prevalent variation of slurry seal/micro surfacing is aggregate size:
- Type II aggregate is most common as it provides a smoother surface.
- Type III aggregate is a bit larger and increases skid resistance and structure for leveling.
Design variations make it possible to address additional 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.
Common Combinations
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 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.
Let's Connect
Get the latest in industry trends, research, success stories, and technical updates in a succinct e-newsletter.
