Process
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 binder 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.
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.
Material Variations
Material variations 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.
When selecting an aggregate type and size and binder types, local availability should be considered along with type of traffic. When working in areas where the streets are used by pedestrians, bicyclists, and roller bladers you may want to use a smaller size aggregate.
Common Combinations
CRACK SEAL + CHIP SEAL: When cracks in the existing surface exceed 1/4” in width, crack sealing them in advance of chip sealing will help keep water from intruding deeper into the pavement structure after the cracks reflect through the new wearing surface.
DOUBLE AND TRIPLE CHIP SEALS: Multiple course chip seals are used when more durability is warranted. These treatments have less traffic noise, provide additional waterproofing, and are more robust seals in comparison with a single chip seal. Multiple course chip seals are used in high stress situations, such as areas with a high percentage of truck traffic or on steep grades.
CHIP SEAL + FOG SEAL: This combination treatment is used to lock down any loose aggregate and to give the chip seal a nice asthetic appearance. Also, this combination provides a stripe delineation which could be a safety benefit.
CHIP SEAL + HOT MIX ASPHALT (SAMI - Stress Absorbing Membrane Interlayer) - the combination treatment is utilized to retard the rate of reflection cracking in new asphalt overlays. It usually consists of a modified chip seal binder with aggregate and then an asphalt overlay is placed on top.
CHIP SEAL + SLURRY OR MICRO SURFACING (CAPE SEAL) - For existing 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.
FDR or CIR or HIR + CHIP SEAL - This combination treatment is used primarily to protect the recycled mixture or reclaimed surface from intrusion of surface moisture. Chip seals are ususally utilized as a surface option on low traffic volume roadways.
Let's Connect
Get the latest in industry trends, research, success stories, and technical updates in a succinct e-newsletter.
