Asphalt can be classified by its chemical composition and physical properties. The pavement industry typically relies on physical properties for performance characterization.
Typically, the most important physical properties are:
- Durability - a measure of how asphalt binder physical properties change with age (sometimes called age hardening). In general, as an asphalt binder ages, its viscosity increases and it becomes more stiff and brittle. Therefore, more susceptible to cracking.
- Rheology - the study of deformation and flow of matter. Deformation and flow of the asphalt binder is important in Hot Mix Asphalt ("HMA") pavement performance. HMA pavements that deform and flow too much may be susceptible to rutting and bleeding, while those that are too stiff may be susceptible to fatigue cracking.
Asphalt cement volatilizes (gives off vapor) when heated. At extremely high temperatures (well above those experienced in the manufacture and construction of HMA asphalt cement can release enough vapor to increase the volatile concentration immediately above the surface to a point where it will ignite (flash) when exposed to a spark or open flame. This is called the flash point. For safety reasons, the flash point of asphalt cement is tested and controlled.
Asphalt cement, as used in HMA paving, should consist of almost pure bitumen. Impurities are not active cementing constituents and may be detrimental to asphalt performance. Contact Source Oil & Asphalt Supply to discuss which asphalt options are best suited for your needs.
Superpave Performance Grading (PG) System
The Superpave PG system was developed as part of the Superpave research effort to more accurately and fully characterize asphalt binders for use in HMA pavements. The PG system is based on the idea that a HMA asphalt binder’s properties should be related to the conditions under which it is used. For asphalt binders, this involves expected climatic conditions as well as aging considerations. Therefore, the PG system uses a common battery of tests (as the older penetration and viscosity grading systems do) but specifies that a particular asphalt binder must pass these tests at specific temperatures that are dependant upon the specific climatic conditions in the area of intended use. Therefore, a binder used in Southeast would be different than one used in Northeast.
Superpave performance grading is reported using two numbers – the first being the average seven-day maximum pavement temperature (in °C) and the second being the minimum pavement design temperature likely to be experienced (in °C). Thus, a PG 58-22 is intended for use where the average seven-day maximum pavement temperature is 58°C and the expected minimum pavement temperature is -22°C. Notice that these numbers are pavement temperatures and not air temperatures. If no other information is available, these grades should be the default choices for use in HMA.
Asphalt Products
Some of our asphalt products include:
- Hard Asphalt Products: 0-pen/10 pen, 16-pen/20 pen
- Performance Grades (PGs): PG 58-22/PG 64-16, PG 64-22/PG 64-28, PG 67-22/PG 70-22, PG 76-22/PG 76-28
- Asphalt Cements (ACs): AC-3/AC-5/AC-10, AC-15P/AC-20/AC-30