Cape Seal Road Surface Material Selection

For the chip seal application, the following materials are used:

• AGGREGATE:  The quality of aggregate is important to the overall success of the chip seal program.  Quality involves a number of constructability issues about using aggregates that are clean, durable, and abrasion resistant.  The cover aggregate is expected to transfer the load to the underlying surface. It should provide adequate skid resistance and should be durable against climatic effects and traffic wear.  Typically, aggregate selection is a function of geography where availability and transportation distance define the aggregate selection process.  Local availability often constrains the quality of the aggregate, causing agencies to select lower-quality local aggregates based on cost and availability.  The aggregate is usually a crushed stone such as granite, slag, limestone, or other high-quality aggregate.

• ASPHALT BINDER:  There are two main types of binders selected when constructing chip seals, emulsified asphalt and hot asphalt cements.  The selection of either is a function of the surface type, size of aggregate, compatibility with that aggregate and local availbility of binders.  Some binders can be modified with polymer or tire rubber.  Here are some requirments that binders should meet regardless of type:
  • The binder should not bleed when applied at the appropriate rate.
  • At the time of application, the binder needs to be fluid enough to uniformly cover the surface, yet viscous enough to not puddle or run off the pavement.
  • The binder should develop adhesion quickly and hold the aggregate tightly to the roadway surface.

For the slurry seal/micro surfacing application, the following materials are used:

• 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/micro surfacing 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.  The asphalt emulsion characteristics can then 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.