Bitumen

The term asphalt is often used as an abbreviation for asphalt concrete

For other uses, see Bitumen (disambiguation).

Base layer of asphalt concrete in a road under construction.

Asphalt () is a sticky, black and highly viscous liquid or semi-solid that is present in most crude petroleums and in some natural deposits sometimes termed asphaltum. It is most commonly modelled as a colloid, with asphaltenes as the dispersed phase and maltenes as the continuous phase (though there is some disagreement amongst chemists regarding its structure). One writer states that although a "considerable amount of work has been done on the composition of asphalt, it is exceedingly difficult to separate individual hydrocarbon in pure form", and "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"

In U.S. and Polish terminology, asphalt (or asphalt cement) is the carefully refined residue from the distillation process of selected crude oils. Outside these countries, the product is often called bitumen.

The primary use of asphalt is in road construction, where it is used as the glue or binder for the aggregate particles. The road surfacing material is usually called 'asphaltic concrete', AC in North America, or 'asphalt' elsewhere. Within North America the apparent interchangeability of the words asphalt and 'bitumen' causes confusion outside the road construction industry despite quite clear definitions within industry circles.

Etymology

The word asphalt is derived from the late Middle English : from French asphalte, based on Late Latin asphalton, asphaltum, from the Greek ásphalton, ásphaltos (άσφαλτος), a word of uncertain origin meaning "asphalt/bitumen/pitch" which some derive from α- "without" and σφάλλω "to make fall". Another description has it that the term derives from the Accadian term "asphaltu" or "sphallo," meaning "to split." It was later adopted from the Homeric Greeks as a verb

meaning "to make firm or stable," "to secure". It is a significant fact that the first use of asphalt by the ancients was in the nature of a cement for securing or joining together various objects, and it thus seems likely that the name itself was expressive of this application. From the Greek, the word passed into late Latin, and thence into French ("asphalte") and English ("asphalt"). The expression "bitumen" originated in the Sanskrit, where we find the words "jatu," meaning "pitch," and "jatu-krit," meaning "pitch creating," "pitch producing" (referring to coniferous or resinous trees). The Latin equivalent is claimed by some to be originally 'gwitu-men' (pertaining to pitch), and by others, "pixtumens" (exuding or bubbling pitch), which was subsequently shortened to "bitumen," thence passing via French into English. From the same root is derived the Anglo Saxon word "cwidu" (Mastix), the German word "Kitt" (cement or mastic) and the old Norse word "kvada".

Background

Asphalt or bitumen can sometimes be confused with tar, which is a similar black thermo-plastic material produced by the destructive distillation of coal. During the early- and mid-twentieth 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.

Natural deposits of asphalt include lake asphalts (primarily from the Pitch Lake in Trinidad and Tobago and Bermudez Lake in Venezuela), Gilsonite, the Dead Sea, and Tar Sands. Asphalt was mined at Ritchie Mines in Macfarlan in Ritchie County, West Virginia in the United States from 1852 to 1873.

Asphalt is typically stored and transported at temperatures around 300 degrees Fahrenheit (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 sometimes used as a release agent, although it can mix with and thereby reduce the quality of the asphalt.

Known uses

Ancient times

In the ancient Middle East, natural asphalt deposits were used for mortar between bricks and stones, to cement parts of carvings such as eyes into place, for ship caulking, and for waterproofing. The Persian word for asphalt is mumiya, which is related to the English word mummy. Asphalt was also used by ancient Egyptians to embalm mummies. In the ancient Far East, natural asphalt was slowly boiled to get rid of the higher fractions, leaving a material of higher molecular weight which is thermoplastic and when layered on objects, became quite hard upon cooling. This was used to cover objects that needed waterproofing, such as scabbards and other items. Statuettes of household deities were also cast with this type of material in Japan, and probably also in China.

In North America, archaeological recovery has indicated that asphaltum was sometimes used to apply stone projectile points to a wooden shaft.

Poured bitumen has also been used as a damp-proof course in building.

Early Use in the Europe

The use of asphalt in the United Kingdom and United States was preceded by its use in Europe. An 1838 edition of Mechanics Magazine cites an early use of asphalt in France. A pamphlet dated 1621, by "a certain Monsieur d'Eyrinys, states that he had discovered the existence (of asphaltum) in large quantities in the vicinity of Neufchatel", and that he proposed to use it in a variety of ways - "principally in the construction of air-proof granaries, and in protecting, by means of the arches, the water-courses in the city of Paris from the intrusin of dirt and filth", which at that time made the water unusable. "He expatiates also on the excellence of this material for forming level and durable terraces" in palaces, "the notion of forming such terraces in the streets not one likely to cross the brain of a Parisian of that generation". But it was generally neglected in France until the revolution of 1830. Then, in the 1830s, there was a surge of interest, and asphalt became widely used "for pavements, flat roofs, and the lining of cisterns, and in England, some use of it had been made of it for similar purposes". Its rise in Europe was "a sudden phenomenon", after natural deposits were found "in France at Osbann (BasRhin), the Parc (l'Ain) and the Puy-de-la-Poix (Puy-de-Dome)", although it could also be made artificially.

Early Use in the United Kingdom

In Britain, the first patent was 'Cassell's patent asphalte or bitumen' in 1834. Then on 25 November 1837, Richard Tappin Claridge patented the use of Seyssel asphalt (patent #7849), for use in asphalte pavement, having seen it employed in France and Belgium when visiting with Frederick Walter Simms, who worked with him on the introduction of asphalt to Britain. In 1838, he obtained patents in Scotland on 27 March, and Ireland on 23 April, and in 1851 he sought to extend the duration of all three patents. Claridge also "laid one of the first asphalt pavements in Whitehall". "Trials were made of the pavement in 1838 on the footway in Whitehall, and subsequently on the space at the bottom of the steps leading from Waterloo Place to St. James Park". "The formation in 1838 of Claridge's Patent Asphalte Company (with a distinguished list of aristocratic patrons, and Marc and Isambard Brunel as, respectively, a trustee and consulting engineer), gave an enormous impetus to the development of a British asphalt industry". "By the end of 1838, at least two other companies, Robinson's and the Bastenne company, were in production", with asphalt being laid as paving at Brighton, Herne Bay, Canterbury, Kensington, the Strand, and a large floor area in Bunhill-row, while meantime Claridge's Whitehall paving "continue(d) in good order". Indeed in 1838, there was a flurry of entrepreneurial activity over asphalt. On the London stockmarket, there were various claims as to the priority of asphalt quality from France, Germany and England. And numerous patents were granted in France, with similar numbers of patent applications being denied in England due to their similarity to each other. In England, "Claridge's was the type most used in the 1840s and 50s" Claridge's own company ceased operating in 1917.

Early Use in the United States

Roads in the US have been paved with asphalt since at least 1870, when a street in front of Newark, NJ's City Hall was paved. In 1876, asphalt was used to pave Pennsylvania Avenue in Washington, DC, in time for the celebration of the national centennial. [Paving the Way: Asphalt in America, published by National Asphalt Pavement Association, 2005]. Asphalt was also used for flooring, paving and waterproofing of baths and swimming pools during the early 1900s, following similar trends in Europe.

Rolled asphalt concrete

The largest use of asphalt is for making asphalt concrete for road surfaces and accounts for approximately 85% of the asphalt consumed in the United States. Due to its highly viscous nature, asphalt is commonly heated for road construction to make it soft and easy to work. Special heated tanker trucks are employed in road building to apply hot asphalt to the road bed.

Asphalt road surface is the most widely recycled material in the US, both by gross tonnage and by percentage. According to a report issued by the Federal Highway Administration and the United States Environmental Protection Agency, 80% of the asphalt from road surfaces' that is removed each year during widening and resurfacing projects is reused as part of new roads, roadbeds, shoulders and embankments.

Roofing shingles account for most of the remaining asphalt consumption. Other uses include cattle sprays, fence post treatments, and waterproofing for fabrics.

In areas of the world with winter climates, asphalt must be protected from cracking with a procedure called sealcoating. The freezing and thawing process that occurs causes small cracks in the asphalt. As more freezing water gets into these small cracks, the expansion causes further damage to the asphalt. Sealcoat is applied in an effort to prevent additional damage. The use of sealcoat can lengthen the life of asphalt driveways or parking lots significantly.

Mastic asphalt

Mastic asphalt is a type of asphalt which differs from dense graded asphalt (asphalt concrete) in that it has a higher bitumen (binder) content, usually around 7–10% of the whole aggregate mix, as opposed to roller asphalt, which has only around 5% added bitumen. Another asphalt which is fast gaining global popularity is stone mastic asphalt (SMA). SMA's advantages over rolled asphalt is its high anti-skid qualities due to its high aggregate density and the lack of void content (air pockets). Another advantage of SMA is its longer durability over alternative road asphalt surfaces, but its manufacture and application, if not controlled closely, can result in slippery road surfaces due to excess bitumen pooling (bleeding) onto the surface.

Asphalt is widely used in airports around the world. Due to the sturdiness, it is widely used for runways dedicated to aircraft landing and taking off.

Asphalt emulsion

A number of technologies allow asphalt to be mixed at much lower temperatures. These involve mixing the asphalt with petroleum solvents to form "cutbacks" with reduced melting point or mixtures with water to turn the asphalt into an emulsion. Asphalt emulsions contain up to 70% asphalt and typically less than 1.5% chemical additives. There are two main types of emulsions with different affinity for aggregates, cationic and anionic. Asphalt emulsions are used in a wide variety of applications. Chipseal involves spraying the road surface with asphalt emulsion followed by a layer of crushed rock or gravel. 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 pavements similar to hot-mixed asphalt, several inches in depth and asphalt emulsions are also blended into recycled hot-mix asphalt to create low cost pavements.

Mixing with petroleum-contaminated soil

Sometimes asphalt can be mixed with the output from low-temperature thermal desorption.

Alternatives and bioasphalt

Main articles: Peak oil, Global warming, and Bioasphalt

Certain activist groups have become increasingly concerned about the global peak oil and climate change problem in recent years due to by-products that are released into the atmosphere. Most of the emissions are derived primarily from burning fossil fuels. This has led to the introduction of petroleum bitumen alternatives that are more environmentally friendly and non-toxic.

See also

• Blacktop
• Asphalt Solar Collector
• Tarmac
• Carl Hancock Rux

References

• Barth, Edwin J., Asphalt: Science and Technology Gordon and Breach (1962). ISBN 0-677-00040-5.

External links

Template:All pages Media related to Asphalt at Wikimedia Commons

• International Chemical Safety Card 0612
• Pavement Interactive - Asphalt
• U.S EPA
• Asphalt Magazine
• CSU Sacramento, The World Famous Asphalt Museum!
• National Institute for Occupational Safety and Health - Asphalt Fumes