- Asphalt 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.
- Until the 20th century, the term asphaltum was also used.
- The term asphalt and bitumen are often used interchangeably to mean both natural and manufactured dorms of the substance.
- This article uses “asphalt/bitumen” where either term is acceptable.
- The terms asphalt and bitumen are often used interchangeably to mean both natural and manufactured forms of the substance.
- In American English, Asphalt is the carefully refined residue from the distillation process of selected crude oils.
- Outside the United States, the product is often called bitumen.
- Geological terminology often prefers the term bitumen.
- Another term, mostly archaic, refers to asphalt/bitumen as “pitch”.
- The pitch used in this mixture is sometimes is sometimes found in natural deposits but usually made by the distillation of crude oil.
- The viscosity of a fluid is a measure of its resistance to gradual deformation by shear stress or tensile stress.
- For liquids, it corresponds to the informal notion of “thickness”. For example, honeyhas a higher viscosity than water.
- Viscosity is due to friction between neighboring parcels of the fluid that are moving at different velocities.
- Petroleum is a naturally occurring flammable liquid consisting of a complex mixture of hydrocarbons of various molecular weights and other liquid compounds, that are found in geologic formations beneath the Earth’s surface.
- Pitch is a name for any of a number of viscoelastic, solid polymers.
- Pitch can be made from petroleum products or plants.
- Petroleum-derived pitch is also called bitumen or asphalt.
- Pitch produced from plants is also known as resin.
The viscoelastic property
- Tar pitch is a viscoelastic polymer.
- This means that even though it seems to be solid at room temperature and can be shattered with a hard impact, it is actually fluid and will flow over time, but extremely slowly.
- The word asphalt is derived from the late Middle English, in turn from French asphalt, based on late Latin asphalton, asphaltum, which is the latinisation of the Greek, a word meaning “asphalt/bitumen/pitch.
- In British English, the word ‘asphalt’ is used to refer to a mixture of mineral aggregate and asphalt/bitumen.
- The earlier work ‘asphaltum’ is now archaic and not commonly used.
- In American English, ‘asphalt’ is equivalent to the British ‘bitumen’. However, ‘asphalt’ is laso commonly used as a shortened form of ‘asphalt concrete’ (therefore equivalent to the ?British ‘asphalt’ or ‘tarmac’).
- Naturally occurring deposits of asphalt/bitumen are formed from the remains of ancient, microscopic algae (diatoms) and other once-living things.
- These remains were deposited in the mud on the bottom of the ocean or lake where the organisms lived.
- Under the heat (above 50 degree c) and pressure of burial deep in the earth, the remains were transformed into materials such as asphalt/bitumen, kerogen, or petroleum.
- Deposits at the La Brea Tar Pits are an example.
- There are structural similarities between asphalt/bitumen and the organic matter in carbonaceous meteorites.
- However, detailed studies have shown these materials to be distinct.
- Rolled Asphalt Concrete
- The largest use of asphalt/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).
- Due to its highly viscous nature, asphalt/bitumen cement must be heated so it can be mixed with the aggregates at the asphalt mixing plant.
- Asphalt concrete paving is widely used in airports around the world.
- Mastic Asphalt
- Is a type asphalt which differs from dense graded asphalt in that it has a higher asphalt/bitumen content, usually around 7-10% of the whole aggregate mix, as opposed to rolled asphalt concrete, which has only around 5% added asphalt/bitumen.
- This thermoplastic substance is widely used in the building industry for waterproofing flat roofs and tanking underground.
- Mastic asphalt is heated to a temperature of 210 degree C (410 degree F) and is spread in layers to form an impervious barrier about 20 millimeters (0..8 in) thick.
- Asphalt Emulsion
- Slurry seal involves the creation of a mixture of asphalt emulsion and fine crushed aggregate that is spread on the surface of a road.
- Cold-mixed asphalt can also be made from asphalt emulsion to create pavement similar to hot-mixed asphalt, several inches in depth and asphalt emulsion are also blended into recycled hot-mix asphalt to create low-cost pavements.
- Asphalt/bitumen is used to make Japan black, a lacquer known especially for its use on iron and steel.
- Asphalt/bitumen is also used to seal some alkaline batteries during the manufacturing process.