Several types of liquid asphalts can be used for bond coats; emulsions, cutbacks, and hot applied asphalts. The majority of bond coat projects use emulsions. Emulsions have the advantage of being more environmentally friendly and can be applied at lower binder temperatures which improve safety and reduce energy consumption.
Common Emulsions used for bond coats:
SS-1, SS-1H, CSS-1, CSS-1H, RS-1, RS-1H, RS-2, CRS-1, CRS-2, HFMS-2, PMAE, Non tracking tack or Reduced tracking tack
Emulsions are a combination of a paving grade asphalt binder blended with water and an emulsifying agent. Slow setting emulsions are the most common emulsion utilized as bond coat. (SS-1, SS-1H, CSS-1, CSS-1H). Slow set emulsions are typically diluted with additional water, usually one part emulsion and one part additional water. Slow setting emulsions tend to be stable and easy to handle. Originally, dilution was used to improve uniformity: modern computer rate controlled distributors have made dilution largely obsolete. When other emulsions are used they should not be diluted. The chemistry of these emulsions are designed to help them break faster. The important thing to keep in mind is the proper calculation of residual asphalt. When an emulsion breaks and cures, the water leaves the system and the residual asphalt does the job of keeping the pavement layers bound together.
Cutbacks are a paving grade asphalts diluted with a cutter stock. Similar to emulsions the cutter stock eventually leaves the system and the residual asphalt does the job of keeping the pavement layers together. Cutbacks were very common in the early years of the paving industry. Cost and environmental concerns have led to cutbacks being replaced with similar emulsion designs.
Hot Applied Asphalts
Hot applied asphalts can also be used as bond coats. Their lack of water means no breaking of the bond coat is required, but in order to make the aphalt sprayable it has to be heated to above 300 degrees. This requires more energy than other options and can pose a safety concern. Paving grade binders will allow paving to continue in conditions that might not be suited for options like night work and cooler temperatures.
Common Bond Coat Asphalts:
Storage Of Asphalt Emulsions