Asphalt
Asphalt is a dark brown to black, highly viscous, hydrocarbon produced from petroleum distillation residue. This distillation can occur naturally, resulting in asphalt lakes, or occur in a petroleum refinery using crude oil. In 2020, the U.S. produced about 21 million tons of asphalt (US EIA).
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Introduction to Asphalt
Viscosity Grading
In the early 1960s an improved asphalt grading system was developed that incorporated a rational scientific viscosity test. This scientific test replaced the empirical penetration test as the key asphalt binder characterization.
Foamed Asphalt
Foamed asphalt is formed by combining hot asphalt binder with small amounts of cold water.
Superpave Performance Grading
Penetration grading and viscosity grading are somewhat limited in their ability to fully characterize asphalt binder for use in HMA pavement.
Asphalt Safety
Asphalt cement, like most other materials, volatilizes (gives off vapor) when heated.
Asphalt Specific Gravity
Because the specific gravity of asphalt binders change with temperature, specific gravity tests are useful in making volume corrections based on temperature.
Cutback Asphalt
A cutback asphalt is simply a combination of asphalt cement and petroleum solvent.
Asphalt Durability
Asphalt durability is 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.
Asphalt Production and Oil Refining
Asphalt is produced through the refining of petroleum. It is a viscous adhesive that, along with aggregate, forms HMA pavement surfaces.
Emulsified Asphalt
Emulsified asphalt is simply a suspension of small asphalt cement globules in water, which is assisted by an emulsifying agent (such as soap).
Asphalt Additives
Asphalt additives are any of a number of substances that can be added to the asphalt binder to alter the characteristics of the final blend of HMA.
Asphalt Modifiers
Some asphalt cements require modification in order to meet specifications. Asphalt cement modification has been practiced for over 50 years but has received added attention in the past decade or so.
Penetration Grading
The penetration grading system was developed in the early 1900s to characterize the consistency of semi-solid asphalts. Penetration grading quantifies the following asphalt concrete characteristics:
Purity
Asphalt cement, as used for HMA paving, should consist of almost pure bitumen. Impurities are not active cementing constituents and may be detrimental to asphalt cement performance.
Performance-Graded Binder Specifications Today
How the PG binder specification has moved on: M 320 replaced MP 1, and M 332 grades high-temperature performance with the MSCR test and a traffic letter.