Bitumen is available in a variety of grades. Specifications vary to meet the needs of the consuming industries and are based on a series of physical tests that define the safety, solubility, physical properties and durability of bitumen. The physical properties are designed to define performance characteristics that are required under the climatic and loading conditions that the bitumen will experience in service.
Penetration graded bitumen
Bitumen is classified by the depth to which a standard needle will penetrate under specified test conditions. This “pen” test classification is used to indicate the hardness of bitumen, lower penetration indicating a harder bitumen. Specifications for penetration graded bitumen normally state the penetration range for a grade, e.g. 60/70.
Viscosity graded bitumen
Bitumen are also graded and specified by their viscosity at a standard temperature (typically 60°C). Specifications for viscosity graded bitumen normally give the nominal viscosity prefixed by a V, e.g. V1500.
Oxidized bitumen grades
Passing air through bitumen at elevated temperature can be used to alter its physical properties for certain commercial applications. The degree of oxidation can range from very small, often referred to as air-rectification, or semi-blowing, which only slightly modifies the bitumen properties, through to “full” blowing, whereby the properties of the bitumen are significantly different to penetration grade bitumen.
Bitumen is typically stored and transported at temperatures around 150°C (300°F). Sometimes diesel oil or kerosene are mixed in before shipping to retain liquidity; upon delivery, these lighter materials are separated out of the mixture. This mixture is often called “bitumen feedstock”, or BFS.
The largest use of bitumen is for making asphalt concrete for road surfaces and accounts for approximately 85% of the asphalt consumed in the United States. Asphalt concrete pavement material is commonly composed of 5% asphalt/bitumen cement and 95% aggregates (stone, sand, and gravel).
A number of technologies allow bitumen to be mixed at much lower temperatures. These involve mixing with petroleum solvents to form “cutbacks” with reduced melting point, or mixtures with water to turn the bitumen into an emulsion. Asphalt emulsions contain up to 70% bitumen and typically less than 2% chemical