Asphalt
| Infobox on Asphalt | |
|---|---|
| Example of Asphalt |  |
| Facts | |
| Origin | See text |
| Stowage factor (in m3/t) |
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| Humidity / moisture | - |
| Ventilation | - |
| Risk factors | See text |
Asphalt
Description
The terms ‘Asphalt’ and ‘Bitumen’ are frequently interchangeable. A common shipping name is also Tar (Coal Tar).
Dark brown to black solid or semi-solid. Bituminous substance produced in the refining of petroleum. Occurs naturally or by distillation of Crude Oil (Bitumen).
Asphalt, also known as bitumen, is the sticky, black and highly viscous liquid or semi-solid present in most crude petroleums and in some natural deposits; it is a substance classed as a pitch. Until the 20th century, the term asphaltum was also used.
The terms asphalt and bitumen are often used interchangeably to mean both natural and manufactured forms of the substance. In American English, asphalt (or asphalt cement) is the carefully refined residue from the distillation process of selected crude oils. Outside the United States, the product is often called bitumen.
Naturally occurring asphalt is sometimes specified by the term "crude bitumen"; its viscosity is similar to that of cold molasses, whilst the material obtained from the fractional distillation of crude oil [boiling at 525 °C) is sometimes referred to as "refined bitumen".
Asphalt or bitumen can sometimes be confused with "tar", which is a similar black, thermoplastic material produced by the destructive distillation of coal. During the early and mid-20th century when town gas was produced, tar was a readily available product and extensively used as the binder for road aggregates. The addition of tar to macadam roads led to the word tarmac, which is now used in common parlance to refer to road-making materials. However, since the 1970s, when natural gas succeeded town gas, asphalt (bitumen) has completely overtaken the use of tar in these applications.
Asphalt can be separated from the other components in crude oil (such as naphtha, gasoline and diesel) by the process of fractional distillation, usually under vacuum conditions. A better separation can be achieved by further processing of the heavier fractions of the crude oil in a de-asphalting unit, which uses either propane or butane in a supercritical phase to dissolve the lighter molecules which are then separated. Further processing is possible by "blowing" the product: namely reacting it with oxygen. This makes the product harder and more viscous.
Asphalt is typically stored and transported at temperatures around 150°C. 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. Some dump trucks route the hot engine exhaust through pipes in the dump body to keep the material warm. The backs of tippers carrying asphalt, as well as some handling equipment, are also commonly sprayed with a releasing agent before filling to aid release. Diesel oil is no longer used as a release agent due to environmental concerns.
Additional information
Bitumen
In the context of this guide means paving grade bitumen. Bitumen is normal “straight-run bitumen” derived from crude oil and produced at a refinery. It is the most widely used bitumen and may also be considered as the parent bitumen from which the other types are produced.
Note: The terms ”bitumen“ and ”tar“ are often used interchangeably. “Tar” is a coal tar derivative and is known to cause skin cancer in humans. Bitumen is a product of petroleum crude oil distillation and IS NOT carcinogenic. The application of “tar” in road construction was abolished ][ in South Africa] as long ago as 1985 and it is therefore not appropriate to use “bitumen” and “tar” interchangeably.
Modified bitumen’s
Modified bitumen’s refers to other types of bituminous binders produced by altering the characteristics of “straight-run bitumen” and includes any of the following:
- Cut back bitumen
- Bitumen emulsions
- Polymer modified bitumen
Bitumen emulsion
A dispersion of bitumen in water achieved by the use of suitable chemical emulsifying agents
Cutback bitumen
Bitumen whose viscosity has been reduced by the addition of a relatively volatile flux such as petrol (motor gasoline), kerosene or diesel to render it more fluid for ease of application.
Application
The primary use 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.
Shipment / Storage
Native asphalt is a mineral resin formed by the natural drying up of rock oil or petroleum in its bed, deposits of which are found in Trinidad, also Cuba, Venezuela, Peru, etc. Asphalt or Asphaltum (Bitumen) is also obtained from petroleum by distillation and is exported in large quantities from the Caribbean and certain other oil producing and refining countries. It is principally used as paving material and shipped in bulk, in barrels, open ended or otherwise and in drums. In some form Asphalt is inflammable, see IMDG Code. Owing to its objectionable character the carriage of Asphalt, except in barrels or drums, is frequently excluded from Time Charter party. Trinidad crude asphalt averages 10 per cent water content. Bitumen is graded R.C. 5 to R.C. 0. All to a greater or lesser extent being diluted with naptha. R.C. 5 to R.C. 4 can only be carried in especially constructed tankers. Carrying temperature being about 132 degrees C.R.C. 3 to R.C. 0 can be carried in bulk in normal tank ships. Carrying temperature being about 140 degrees C. R.C. 3 and R.C. 0 is also carried in Drums or Barrels. Many of the drums are open headed and must of course, be stowed on end. Cool storage is desirable and remote from all edible and other goods liable to taint. Holds should be lime washed before loading. Care should be taken during handling to avoid "leakers". This is a most difficult cargo to clean up after, if the contents leak, the naptha evaporates in the atmosphere and the residue sets solid. All bilges must be thoroughly protected. Cases have been known where the asphalt or bitumen has even penetrated and filled the bilge suction pipes which had to be renewed. Drums should be well dunnaged every tier and packed hard with dunnage or cordwood to avoid any movement of the stow. 200 litre drums should be restricted to eight high.
Emulsified Asphalt - is asphalt rendered into liquid form which involved the addition of water, and is not inflammable. Is shipped from U.S.A. ports in steel drums of 250 litre capacity measuring about 0.3 cubic metres and weighing about 230 kg. It is also carried in bulk in deep tanks.
Rock Asphalt is exported from Cyprus etc., and consists of limestone rock with an average bitumen content of 12 percent.
Lake Asphalt is a naturally occurring blend of bitumen and fine aggregate. It is shipped in fibre drums and is hard with a high melting point. Cutback Asphalts (bitumen emulsions) should be protected against frost.
Asphalt may be shipped in closed or open-headed metal drums, fibre drums or plastic bags, also in specially designed containers and bulk tankers. Drums should be stowed on end and not over or under other cargo, or near to sensitive cargoes. There are a wide range of melting points, some very low. Suitability of packaging is important, especially when shipments pass through the tropics. Liable to leakage in drums, in which event considerable expense may occur in discharge and subsequent handling. Drums to be stowed in upright position to minimize the threat of leakage. Plastic sheets should be placed on the floor and along lower part of the container walls to contain any leakage. If leakage occurs it will seriously contaminate the container, requiring careful and expensive cleaning.
When involved in a fire, the products under this category evolve toxic fumes; in enclosed cargo spaces the fumes may form an explosive mixture with air.
Risk factors
- Reference is made to the relevant IMO regulations of hazardous cargo.
- Toxic by inhalation of fume. TLV (fume) 5 mg/m3.