Bitumen

Bitumen

Bitumen is a sticky, black and highly viscous liquid or semi-solid form of petroleum. It may be found in natural deposits or may be a refined product; it is a substance classed as a pitch.The primary use of asphalt/bitumen is in road construction, where it is used as the glue or binder mixed with aggregate particles to create asphalt concrete. Its other main uses are for bituminous waterproofing products, including production of roofing felt and for sealing flat roofs.

It is estimated that the current world use of bitumen is approximately 102 million tons per year. Approximately 85% of all the bitumen produced is used as the binder in asphalt for roads. It is also used in other paved areas such as airport runways, car parks and footways. Bitumen can sometimes be confused with “tar”, which is a similar black, thermoplastic material produced by the destructive distillation of coal.

Of the 1,300 (or more) types of crude oils, only approximately 10% can be used to produce Bitumen that meet the stringent engineering requirements of end users today.

BITUMEN SPECIFICATIONS

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

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