Editing Bitumen (section)

== Composition ==
{{See also|Asphaltene}}

=== Normal composition ===
The components of bitumen 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 acid]]s 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 compound]]s

Bitumen typically contains, elementally 80% by weight of carbon; 10% hydrogen; up to 6% sulfur; and molecularly, between 5 and 25% by weight of asphaltenes dispersed in 90% to 65% maltenes.<ref>{{cite magazine | date=22 November 1999 |volume=77|issue=47 |page=81 | title=Asphalt |magazine=Chemical & Engineering News | author=Michael Freemantle | url=https://pubsapp.acs.org/cen/whatstuff/stuff/7747scit6.html}}</ref> Most natural bitumens also contain [[organosulfur compound]]s, [[nickel]] and [[vanadium]] are found at <10 parts per million, as is typical of some petroleum.<ref name=UllmannAsph/> The substance is soluble in [[carbon disulfide]]. It is commonly modelled as a [[colloid]], with [[asphaltene]]s as the dispersed phase and [[maltenes]] as the continuous phase.<ref>{{cite book|author=Muhammad Abdul Quddus|year=1992|title=Thesis submitted to Department of Applied Chemistry; University of Karachi|chapter=Catalytic Oxidation of Asphalt|publisher=Higher Education Commission Pakistan: Pakistan Research Repository|location=Pakistan|page=6, in ch. 2 pdf|chapter-url=http://eprints.hec.gov.pk/1171/1/891.html.htm|archive-url=https://web.archive.org/web/20110205060447/http://eprints.hec.gov.pk/1171/1/891.html.htm|archive-date=5 February 2011}}</ref> "It is almost impossible to separate and identify all the different molecules of bitumen, because the number of molecules with different chemical structure is extremely large".<ref>Muhammad Abdul Quddus (1992), p. 99, in ch. 5 pdf</ref>

Asphalt may be confused with [[coal tar]], which is a visually similar black, thermoplastic material produced by the [[destructive distillation]] of [[coal]]. During the early and mid-20th century, when [[town gas]] was produced, coal tar was a readily available byproduct and extensively used as the binder for road aggregates. The addition of coal tar to [[macadam]] roads led to the word "[[Tarmacadam|tarmac]]", which is now used in common parlance to refer to road-making materials. However, since the 1970s, when natural gas succeeded town gas, bitumen has completely overtaken the use of coal tar in these applications. Other examples of this confusion include [[La Brea Tar Pits]] and the Canadian [[tar sands]], both of which actually contain natural bitumen rather than tar. "Pitch" is another term sometimes informally used at times to refer to asphalt, as in [[Pitch Lake]].

=== Additives, mixtures and contaminants ===
For economic and other reasons, bitumen is sometimes sold combined with other materials, often without being labeled as anything other than simply "bitumen".<ref name="whats_in_your_asphalt_2017_09_fhwa">Arnold, Terence S. (senior research chemist, Pavement Materials Team, Office of Infrastructure Research and Development, [[Federal Highway Administration]]; Federal lab manager for the chemistry lab, [[Turner-Fairbank Highway Research Center]]; fellow of the [[Royal Society of Chemistry]] in the United Kingdom), [https://highways.dot.gov/public-roads/september-2017/whats-your-asphalt "What's in Your Asphalt?,"] September 2017 (last modified 25 October 2017), ''Public Roads'', FHWA-HRT-17-006.htm," Office of Research, Development, and Technology, Office of Corporate Research, Technology, and Innovation Management, [[Federal Highway Administration]], [[U.S. Department of Transportation]]</ref>

Of particular note is the use of [[Automotive oil recycling#REOB|re-refined engine oil bottoms – "REOB" or "REOBs"]]{{snd}}the residue of [[Automotive oil recycling|recycled automotive engine oil]] collected from the bottoms of re-refining [[vacuum distillation]] towers, in the manufacture of asphalt. REOB contains various elements and compounds found in recycled engine oil: 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 adulteration of bitumen and poorer-performing pavement.<ref name="whats_in_your_asphalt_2017_09_fhwa" />