Asphalt Flashcards
Why does the industry use performance-based specifications for asphalt cement and asphalt concrete rather than prescription-based specifications?
Asphalt is inherently very variable due to its nature as a by-product of another substance (up to 400% variation in range of some material components)
Instead of prescribing a certain ratio of components (hard to regulate), easier to set performance criteria (ex: certain strength) which can be adjusted by type of binder, aggregate gradation, production method
Why should aggregates be dry when being bound to asphalt cement?
Asphalt cement coats the surface of an aggregate bc of adsorption (the electrostatic interaction bw the polar asphalt cement and the charged surface of the aggregate)
Water molecules are more polar than the asphalt so they will preferentially wet the aggregate surface, preventing the asphalt from binding to the aggregates
Describe what asphalt concrete is composed of, what its components are composed of, and what the components of their components are composed of.
Asphalt concrete - asphalt cement and mineral aggregates
Asphalt cement - primarily bitumen
Bitumen - high molecular weight hydrocarbons
Describe how cutback asphalts work.
Produced by blending asphalt cement with hydrocarbon solvent
Lowers viscosity of asphalt cement which allows for it to be mixed with aggregates
Solvent evaporates after asphalt concrete is placed
Describe the process of the formation of potholes.
Water penetrates into subgrade below asphalt pavement
Water erodes/degrades subgrade material, forming water pockets
When temperature drops, asphalt pavement becomes brittle
Water pockets expand and freeze, cracking asphalt
Vehicle loading causes localized failure over voids (once ice melts there is now voids)
