Asphalt
Asphalt is a sticky, black and highly viscous liquid or semi-solid that is present in most crude petroleums.It may be found in natural deposits or may be a refined product, and is classed as a pitch. Before the 20th century, the term asphaltum was also used.
For naturally occurring bituminous sands used for petroleum production, see Oil sands.
The primary use (70%) of asphalt 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.
Naturally occurring asphalt is sometimes specified by the term "crude bitumen".
Its viscosity is similar to that of cold molasses while the material obtained from the fractional distillation of crude oil boiling at 525 °C (977 °F) is sometimes referred to as "refined bitumen".
1. Normal Composition:
The components of asphalt include four main classes of compounds:
Naphthene aromatics (naphthalene), consisting of partially hydrogenated polycyclic aromatic compounds
Polar aromatics, consisting of high molecular weight phenols and carboxylic acids produced by partial oxidation of the material
Saturated hydrocarbons; the percentage of saturated compounds in asphalt correlates with its softening point
Asphaltenes, consisting of high molecular weight phenols and heterocyclic compounds
The naphthene aromatics and polar aromatics are typically the majority components.
Most natural bitumens also contain organosulfur compounds, resulting in an overall sulfur content of up to 4%. Nickel and vanadium are found at <10 parts per million, as is typical of some petroleum.The substance is soluble in carbon disulfide.
It is commonly modelled as a colloid, with asphaltenes as the dispersed phase and maltenes as the continuous phase.
"It is almost impossible to separate and identify all the different molecules of asphalt, because the number of molecules with different chemical structure is extremely large".
Most natural bitumens also contain organosulfur compounds, resulting in an overall sulfur content of up to 4%. Nickel and vanadium are found at <10 parts per million, as is typical of some petroleum.The substance is soluble in carbon disulfide.
It is commonly modelled as a colloid, with asphaltenes as the dispersed phase and maltenes as the continuous phase.
"It is almost impossible to separate and identify all the different molecules of asphalt, because the number of molecules with different chemical structure is extremely large".
Asphalt may be confused with coal tar, which is a visually similar black, thermoplastic material produced by the destructive distillation of coal.
Additives, mixtures and contaminants:
Additives, mixtures and contaminants:
For economic and other reasons, asphalt is sometimes sold combined with other materials, often without being labeled as anything other than simply "asphalt"
Of particular note, in the 21st century, is the use of re-refined engine oil bottoms -- "REOB" or "REOBs"—the residue of recycled autmotive engine oil, collected from the bottoms of re-refining vacuum distillation towers. It contains the various non-refined elements and compounds in recycled engine oil, leftover from the re-refining process—both additives to the original oil, and materials accumulating from its circulation in the engine (typically iron and copper).
Some research has indicated a correlation between this contamination of asphalt and poorer-performing pavement.
Some research has indicated a correlation between this contamination of asphalt and poorer-performing pavement.
Occurrence:
The majority of asphalt used commercially is obtained from petroleum. Nonetheless, large amounts of asphalt occur in concentrated form in nature. Naturally occurring deposits of 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 °C) and pressure of burial deep in the earth, the remains were transformed into materials such as bitumen, kerogen, or petroleum.Bitumen may occur in hydrothermal veins. An example of this is within the Uinta Basin of Utah, in the US, where there is a swarm of laterally and vertically extensive veins composed of a solid hydrocarbon termed Gilsonite. These veins formed by the polymerization and solidification of hydrocarbons that were mobilized from the deeper oil shales of the Green River Formation during burial and diagenesis.
2. Modern use:
Global use
The vast majority of refined asphalt is used in construction: primarily as a constituent of products used in paving and roofing applications.
According to the requirements of the end use, asphalt is produced to specification. This is achieved either by refining or blending.
It is estimated that the current world use of asphalt is approximately 102 million tonnes per year.
Approximately 85% of all the asphalt produced is used as the binder in asphalt concrete for roads.
It is also used in other paved areas such as airport runways, car parks and footways.
Typically, the production of asphalt concrete involves mixing fine and coarse aggregates such as sand, gravel and crushed rock with asphalt, which acts as the binding agent.
Other materials, such as recycled polymers (e.g., rubber tyres), may be added to the asphalt to modify its properties according to the application for which the asphalt is ultimately intended.
A further 10% of global asphalt production is used in roofing applications, where its waterproofing qualities are invaluable.
The remaining 5% of asphalt is used mainly for sealing and insulating purposes in a variety of building materials, such as pipe coatings, carpet tile backing and paint.
Asphalt is applied in the construction and maintenance of many structures, systems, and components,
such as the following:
Highways
Airport runways
Foot ways and pedestrian ways
Car parks
Racetracks
Tennis courts
Roofing
Damp proofing
Dams
Reservoir and pool linings
Sound proofing This is just some code.
Pipe coatings
Cable coatings
Paints
Building water proofing
Tile underlying waterproofing
Newspaper ink production
and many other applications
