27. Types of AC Flashcards
Primary materials
Asphalt binder, aggregate, RAP (reclaimed asphalt pavement)
Types of pavement binders
Asphalt, bitumen, tar, cutback, emulsion, modified binders
Tar vs Asphalt
Tar:
Dark brown, not naturally occurring, distillation of coal, doesn’t dissolve in petroleum
Asphalt:
Dark brown - black, naturally occurring, distillation of petroleum, dissolves in petroleum
What is asphalt?
High molecular thermoplastic hydrocarbon, found in crude petroleum oils
Where is asphalt naturally occurring?
Pitch Lake in Trinidad and Lake Bermudez in Venezuela
Sweet vs Sour crude
Sweet: less than 0.5% sulfur
Sour: more than 0.5% sulfur
Sour crude more common in Canada
Light vs Heavy crude
Light: lower density, lighter than water, floats
Heavy: higher density, heavier than water, sinks (harder to refine, known as tar sands)
Asphalt from crude petroleum
Properties depend on:
Refinery operations, composition crude source dependent
Crude oil breakdown
Asphalt cement is bottom of the barrel, aka heavy
Liquefying asphalt cement
Requires heat to reduce viscosity
Thin with solvents for cutbacks
Suspend in water for emulsions
Cutbacks
Asphalt cement and petroleum solvent, low viscosity asphalt
Cutback disadvantages
Environmental regulations: contain volatile chemicals that evaporate into atmosphere
Loss of high energy products: require high amounts of energy to produce, so expensive
Emulsions
Suspension of small asphalt cement droplets in water with an emulsifying agent (e.g. soap)
Anionic, cationic, or neutral
Asphalt emulsion classification
Rapid setting: tack coat, surface treatment
Medium setting: road mix
Slow setting: road mix, slurry seals, tack seals, fog seal
Advantages of emulsion
Don’t require petroleum solvent, can be used without additional heat, environmentally friendly, contribute to energy savings
Colour of emulsion tack coat
Brown when freshly placed, black when dry
Uses of asphalt emulsion
Crack filling, surface treatments, recycling, tack coat, prime coat, surface dressing
Polymer modified asphalt
Asphalt and polymer
Less cracking in cold weather, and stiffer at higher temperatures
Modified binders
Modification to meet requirements with elements like sulphur and rubber
Advantages of modified binders
Lower stiffness, higher stiffness, faster relaxation, increased adhesion
