View source for Asphalt

{{pp-semi-protected|small=yes}}{{dablink|The term '''asphalt''' is often used as an abbreviation for [[asphalt concrete]]. For the film, see [[Asphalt (film)]]; for the novel, see [[Carl Hancock Rux]].}}
[[Image:Asphalt base.jpg|thumb|right|250px|Base layer of [[asphalt concrete]] in a road under construction.]]
'''Asphalt''' ({{Audio-IPA|en-us-asphalt.ogg|ˈæs.fɒlt}}) is a sticky, black and highly [[viscosity|viscous]] liquid or semi-solid that is present in most crude [[petroleum]]s and in some natural deposits sometimes termed '''asphaltum'''.  It is most commonly modeled as a [[colloid]], with ''[[asphaltene]]s'' as the dispersed phase and ''[[maltenes]]'' as the continuous phase (though there is some disagreement amongst [[chemist]]s regarding its structure). In [[American English|U.S.]] terminology, asphalt (or asphalt cement) is the carefully refined residue from the distillation process of selected crude oils. Outside [[North America]], the product is called [[bitumen]].

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

==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 fluid|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]] between [[Israel]] & [[Jordan]], and [[Tar Sands]].  

Asphalt is typically stored and transported at temperatures around 150 degrees Celsius (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. Some [[dump truck]]s 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 (masonry)|mortar]] between bricks and stones, ship [[caulking]], and waterproofing. The [[Persian language|Persian]] word for asphalt is ''mumiya'', which may be 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 [[scabbard]]s and other objects that needed water-proofing. Statuettes of household [[deities]] were also cast with this type of material in Japan, and probably also in China.{{Facts|date=February 2007}}

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

=== Rolled asphalt concrete ===
The largest use of asphalt is for making [[asphalt concrete]] for road surfaces and accounts for approximately 80% of the asphalt consumed in the [[United States]].  [[Asphalt shingle|Roofing shingle]]s account for most of the remaining asphalt consumption. Other uses include [[cattle spray]]s, fence post treatments, and waterproofing for fabrics.

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.

=== 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 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===

The world has become increasingly concerned over the global climate change problem in recent years due to the pollution that is released into the atmosphere. Most of the emissions are derived primarily from burning fossil fuels. This has led to the introduction of bitumen alternatives that are more environmentally friendly and non toxic. Bitumen can now be made from non-petroleum based renewable resources such as sugar, molasses and rice, corn and potato starches etc. To further help the environment bitumen can also be made from the waste material vacuum tower bottoms produced in the process of cleaning used motor oils which helps the recycling industries, this waste is normally disposed by burning or dumping into land fills.
These new non-petroleum based bitumen binders can be colored, which thereby help reduce the temperatures of road surfaces which contribute to the [[Urban heat island]] which in turn contributes to global climate change.
For millions of people living in and around cities, heat islands are of growing concern. This phenomenon describes urban and suburban temperatures that are 2 to 10°F (1 to 6°C)  hotter than nearby rural areas Elevated temperatures can impact communities by increasing peak energy demand, air conditioning costs, air pollution levels, and heat-related illness and mortality. Fortunately, there are common-sense measures that communities can take to reduce the negative effects of heat islands, such as replacing conventional black asphalt road surfaces with the new pigmentable bitumen that gives lighter colors [http://www.epa.gov/heatisland/] [http://www.unep.org/Documents.Multilingual/Default.asp?DocumentID=469&ArticleID=5132&I=en].

Asphalt made with vegetable oil based binders was patented by Colas SA in France in 2004 (Vegecol), Colas was originally owned by the Royal Dutch Shell [http://www.answers.com/topic/colas-s-a?cat=biz-fin]. [http://www.colas-cst.com/_ACTU_TECH/nouveauxproduits.php?fiche=0]

A number of homeowners seeking an environmentally-friendly alternative to asphalt for paving have experimented with waste vegetable oil as a binder for driveways and parking areas in single-family applications. The earliest known test occurred in 2002 in Ohio, where the homeowner combined waste vegetable oil with dry aggregate to create a low-cost and non-polluting paving material for his 200-foot driveway. After five years, he reports the driveway is performing as well or better than petroleum-based materials.

This movement has led the Shell Oil Company (see also, [[Controversies surrounding Royal Dutch Shell]]) to pave two public roads in Norway in 2007 with the Colas vegetable-oil-based asphalt. 
Results of [http://www.shell.com/static/bitumen-en/downloads/wrc/bioflux.pdf this study] are still premature.

==Etymology==
{{wiktionary|asphalt}}
The word '''asphalt''' is derived from the late Middle English : from French '''asphalte''', based on late Latin '''asphalton''', '''asphaltum''', from Greek '''asphalton''', '''asphaltos''' (''άσφαλτος''), ásphaltos, -on, akin to asphalízein to make firm, to secure.

==References==
{{reflist|2}}
{{refbegin}}
* Barth, Edwin J., ''Asphalt:  Science and Technology'' Gordon and Breach (1962).  ISBN 0-677-00040-5.
{{refend}}

==See also==
*[[Blacktop]]
*[[Good Times]] (it's mentioned in the TV Series Ending Theme Song)

==External links==
*{{ICSC|0612|06}}
*[http://www.epa.gov/heatisland/ U.S EPA]
*[http://www.colas.fr/ Vegetable oil based Asphalt Binders]
*[http://www.cdc.gov/niosh/topics/asphalt/ National Institute for Occupational Safety and Health - Asphalt Fumes]


[[Category:Building materials]]
[[Category:Petroleum products]]
[[Category:Recyclable materials]]
[[Category:Road construction]]
[[Category:Chemical mixtures]]
[[Category:Amorphous solids]]
[[Category:Occupational safety and health]]

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