Asphalt (US i// or UK //), also known as bitumen (/, /), is a sticky, black and highly viscous liquid or semi-solid form of petroleum. It may be found in natural deposits or may be a refined product; it is a substance classed as a pitch. Until the 20th century, the term asphaltum was also used.
The primary use (70%) of asphalt/bitumen 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.
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. Geological terminology often prefers the term bitumen. Common usage often refers to various forms of asphalt/bitumen as "tar", such as at the La Brea Tar Pits. Another term, mostly archaic, refers to asphalt/bitumen as "pitch". The pitch used in this mixture is sometimes found in natural deposits but usually made by the distillation of crude oil.
Naturally occurring asphalt/bitumen 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 Composition
- 2 Occurrence
- 3 History
- 4 Modern use
- 5 Production
- 6 Etymology
- 7 See also
- 8 Notes
- 9 References
- 10 External links
The components of asphalt are classified into four classes of compounds:
- saturates, saturated hydrocarbons, the %saturates correlates with softening point of the material
- Naphthene aromatics, consisting of partially hydrogenated polycyclic aromatic compounds.
- Polar aromatics, consisting of high molecular weight phenols and carboxylic acids
- Asphaltenes, consisting of high molecular weight phenols and heterocyclic compounds
The naphthene aromatics and polar aromatics are typically the majority components. Additionally, most natural bitumens contain organosulfur compounds, resulting in an overall sulfur content of up to 4%. Nickel and vanadium are found in the <10 ppm level, 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. 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".
Asphalt/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. Other examples of this confusion include the La Brea Tar Pits and the Canadian tar sands. Pitch is another term mistakenly used at times to refer to asphalt/bitumen, as in Pitch Lake.
The great majority of asphalt used commercially is obtained from petroleum. Nonetheless, large amounts of asphalt occur in concentrated form in nature. Naturally occurring deposits of asphalt/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 asphalt/bitumen, kerogen, or petroleum. Deposits at the La Brea Tar Pits are an example.
Natural deposits of asphalt/bitumen include lakes such as the Pitch Lake in Trinidad and Tobago and Lake Bermudez in Venezuela. Natural seeps of asphalt/bitumen occur in the La Brea Tar Pits and in the Dead Sea.
Asphalt/bitumen also occurs as impregnated sandstones known as bituminous rock and the similar "tar sands" such as in Athabasca, Canada and Utah, USA. The Athabasca tar sands are located in the McMurray Formation, Alberta. This Formation is of early Cretaceous age, and is composed of numerous lenses of oil-bearing sand with up to 20% oil. Isotopic studies attribute the oil deposits to be about 110 Ma old. Heavy oil or bitumen deposits also occur in the Uinta Basin in Utah, USA. The Tar Sand Triangle deposit, for example, is roughly 6% bitumen.
Asphalt/bitumen occurs in hydrothermal veins. An example of this is within the Uinta Basin of Utah, USA, where there is a swarm of laterally and vertically extensive veins composed of a solid hydrocarbon termed Gilsonite. These veins formed by the polymerisation and solidification of hydrocarbons that were mobilized from the deeper oil shales of the Green River Formation during burial and diagenesis.
The use of asphalt/bitumen for waterproofing and as an adhesive dates at least to the fifth millennium B.C. in the early Indus community of Mehrgarh, where it was used to line the baskets in which they gathered crops.
In the ancient Middle East, the Sumerians used natural asphalt/bitumen deposits for mortar between bricks and stones, to cement parts of carvings, such as eyes, into place, for ship caulking, and for waterproofing. The Greek historian Herodotus said hot asphalt/bitumen was used as mortar in the walls of Babylon.
In some versions of the Book of Genesis in the Bible, the name of the substance used to bind the bricks of the Tower of Babel is translated as bitumen (see Gen 11:3), while other translations use the word pitch. A one-kilometre tunnel beneath the river Euphrates at Babylon in the time of Queen Semiramis (ca. 800 B.C.) was reportedly constructed of burnt bricks covered with asphalt/bitumen as a waterproofing agent.
Asphalt/bitumen was used by ancient Egyptians to embalm mummies. The Persian word for asphalt is moom, which is related to the English word mummy. The Egyptians' primary source of asphalt/bitumen was the Dead Sea, which the Romans knew as Palus Asphaltites (Asphalt Lake).
Approximately 40 AD, Dioscorides described the Dead Sea material as Judaicum bitumen, and noted other places in the region where it could be found:
"The Judaicum Bitumen is better than others; that is reckoned the best, which doth shine like purple, being of a strong scent & weightie, but the black and fowle is naught for it is adulterated with Pitch mixed with it. It growes in Phoenice also, and in Sidon, & in Babylon, & in Zacynthum. It is found also moyst swimming upon wells in the country of the Agrigentines of Sicilie, which they use for lamps instead of oyle, and which they call falsely Sicilian oyle, for it is a kinde of moyst Bitumen."
The Sidon bitumen is thought to refer to asphalt/bitumen found at Hasbeya. Pliny refers also to asphalt/bitumen being found in Epirus. It was a valuable strategic resource; the object of the first known battle for a hydrocarbon deposit, between the Seleucids and the Nabateans in 312 B.C.
In the ancient Far East, natural asphalt/bitumen 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.
Early use in Europe
100 years after the fall of Constantinople in 1453, Pierre Belon described in his work Observations in 1553 that pissasphalto a mixture of pitch and bitumen was used in Dubrovnik for tarring of ships from where it was exported to a market place in Venice where it could be bought by anyone. 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 intrusion 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. One of the earliest uses in France was the laying of about 24,000 square yards of Seyssel asphalt at the Place de la Concorde in 1835.
Photography and art
Asphalt/bitumen was used in early photographic technology. In 1826 or 1827, it was used by French scientist Joseph Nicéphore Niépce to make the oldest surviving photograph from nature. The asphalt/bitumen was thinly coated onto a pewter plate which was then exposed in a camera. Exposure to light hardened the asphalt/bitumen and made it insoluble, so that when it was subsequently rinsed with a solvent only the sufficiently light-struck areas remained. Many hours of exposure in the camera were required, making asphalt/bitumen impractical for ordinary photography, but from the 1850s to the 1920s it was in common use as a photoresist in the production of printing plates for various photomechanical printing processes.
Asphalt/bitumen was the nemesis of many artists during the 19th century. Although widely used for a time, it ultimately proved unstable for use in oil painting, especially when mixed with the most common dilutents, such as linseed oil, varnish and turpentine. Unless thoroughly diluted, asphalt/bitumen never fully solidifies and will in time corrupt the other pigments with which it comes into contact. The use of asphalt/bitumen as a glaze to set in shadow or mixed with other colours to render a darker tone resulted in the eventual deterioration of a good many paintings, those of Delacroix being just one notable example. Perhaps the most famous example of the destructiveness of asphalt/bitumen is Théodore Géricault's Raft of the Medusa (1818-1819), where his use of asphalt/bitumen caused the brilliant colors to degenerate into dark greens and blacks and the paint and canvas to buckle.
Early use in the United Kingdom
Among the earlier uses of asphalt/bitumen in the United Kingdom was for etching. William Salmon's Polygraphice (1673) provides a recipe for varnish used in etching, consisting of three ounces of virgin wax, two ounces of mastic, and one ounce of asphaltum. By the fifth edition in 1685, he had included more asphaltum recipes from other sources.
The first British patent for the use of asphalt/bitumen 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. Dr T. Lamb Phipson claims that his father, Samuel Ryland Phipson, a friend of Claridge, was also "instrumental in introducing the asphalte pavement (in 1836)". Indeed, mastic pavements had been previously employed at Vauxhall by a competitor of Claridge, but without success.
In 1838, Claridge obtained patents in Scotland on 27 March, and Ireland on 23 April, and in 1851 extensions were sought for all three patents, by the trustees of a company previously formed by Claridge. This was Claridge's Patent Asphalte Company, formed in 1838 for the purpose of introducing to Britain "Asphalte in its natural state from the mine at Pyrimont Seysell in France", and "laid one of the first asphalt pavements in Whitehall". Trials were made of the pavement in 1838 on the footway in Whitehall, the stable at Knightsbridge Barracks, "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/bitumen, which had uses beyond paving. For example, asphalt could also used for flooring, damp proofing in buildings, and for waterproofing of various types of pools and baths, with these latter themselves proliferating in the 19th century. On the London stockmarket, there were various claims as to the exclusivity 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"
In 1914, Claridge's Company entered into a joint venture to produce tar-bound macadam, with materials manufactured through a subsidiary company called Clarmac Roads Ltd. Two products resulted, namely Clarmac, and Clarphalte, with the former being manufactured by Clarmac Roads and the latter by Claridge's Patent Asphalte Co., although Clarmac was more widely used.[note 1] However, the First World War impacted financially on the Clarmac Company, which entered into liquidation in 1915. The failure of Clarmac Roads Ltd had a flow-on effect to Claridge's Company, which was itself compulsorily wound up, ceasing operations in 1917, having invested a substantial amount of funds into the new venture, both at the outset, and in a subsequent attempt to save the Clarmac Company.
Early use in the United States
The first use of asphalt/bitumen in the New World was by indigenous peoples. On the west coast, as early as the 13th century, the Tongva, Luiseño and Chumash peoples collected the naturally occurring asphalt/bitumen that seeped to the surface above underlying petroleum deposits. All three used the substance as an adhesive. It is found on many different artifacts of tools and ceremonial items. For example, it was used on rattles to adhere gourds or turtle shells to rattle handles. It was also used in decorations. Small round shell beads were often set in asphaltum to provide decorations. It was used as a sealant on baskets to make them watertight for carrying water. Asphaltum was used also to seal the planks on ocean-going canoes.
Roads in the US have been paved with materials that include asphalt/bitumen since at least 1870, when a street in front of the Newark, NJ City Hall was paved. In many cases, these early pavings were made from naturally occurring "bituminous rock", such as at Ritchie Mines in Macfarlan in Ritchie County, West Virginia from 1852 to 1873. In 1876, asphalt-based paving was used to pave Pennsylvania Avenue in Washington, DC, in time for the celebration of the national centennial. Asphalt/bitumen was also used for flooring, paving and waterproofing of baths and swimming pools during the early 20th century, following similar trends in Europe.
Rolled asphalt concrete
The largest use of asphalt/bitumen is for making asphalt concrete for road surfaces and accounts for approximately 85% of the asphalt consumed in the United States. Asphalt concrete pavement material is commonly composed of 5% asphalt/bitumen cement and 95% aggregates (stone, sand, and gravel). Due to its highly viscous nature, asphalt/bitumen cement must be heated so it can be mixed with the aggregates at the asphalt mixing plant. There are about 4,000 asphalt concrete mixing plants in the U.S., and a similar number in Europe.
Asphalt concrete road surface is the most widely recycled material in the U.S., both by gross tonnage and by percentage. According to an industry survey conducted by the Federal Highway Administration and the National Asphalt Pavement Association and released in 2011, more than 99% of the asphalt removed each year from road surfaces during widening and resurfacing projects is reused as part of new pavements, roadbeds, shoulders and embankments.
Roofing shingles account for most of the remaining asphalt/bitumen consumption. Other uses include cattle sprays, fence-post treatments, and waterproofing for fabrics.
Asphalt concrete paving is widely used in airports around the world. Due to the sturdiness and ability to be repaired quickly, it is widely used for runways dedicated to aircraft landing and taking off.
Mastic asphalt is a type of asphalt which differs from dense graded asphalt (asphalt concrete) in that it has a higher asphalt/bitumen (binder) content, usually around 7–10% of the whole aggregate mix, as opposed to rolled asphalt concrete, which has only around 5% added asphalt/bitumen. This thermoplastic substance is widely used in the building industry for waterproofing flat roofs and tanking underground. Mastic asphalt is heated to a temperature of 210 °C (410 °F) and is spread in layers to form an impervious barrier about 20 millimeters (0.79 inches) thick.
A number of technologies allow asphalt/bitumen to be mixed at much lower temperatures. These involve mixing with petroleum solvents to form "cutbacks" with reduced melting point, or mixtures with water to turn the asphalt/bitumen into an emulsion. Asphalt emulsions contain up to 70% asphalt/bitumen 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, gravel or crushed slag. 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.
Asphalt/bitumen is used to make Japan black, a lacquer known especially for its use on iron and steel. Asphalt/bitumen also is used in paint and marker inks by some graffiti supply companies (primarily Molotow) to increase the weather resistance and permanence of the paint and/or ink, and to make the color much darker. Asphalt/bitumen is also used to seal some alkaline batteries during the manufacturing process.
About 40,000,000 tons were produced in 1984. It is obtained as the "heavy" (i.e., difficult to distill) fraction. Material with a boiling point greater than around 500 °C is considered asphalt. Vacuum distillation separates it from the other components in crude oil (such as naphtha, gasoline and diesel). The resulting material is typically further treated to extract small but valuable amounts of lubricants and to adjust the properties of the material to suit applications. In a de-asphalting unit, the crude asphalt is treated with either propane or butane in a supercritical phase to extract the lighter molecules, which are then separated. Further processing is possible by "blowing" the product: namely reacting it with oxygen. This step makes the product harder and more viscous.
Asphalt/bitumen is typically stored and transported at temperatures around 150 °C (302 °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 trucks route the hot engine exhaust through pipes in the dump body to keep the material warm. The backs of tippers carrying asphalt/bitumen, 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.
From oil sands
Naturally occurring crude asphalt/bitumen impregnated in sedimentary rock is the prime feed stock for petroleum production from "Oil sands", currently under development in Alberta, Canada. Canada has most of the world's supply of natural asphalt/bitumen, covering 140,000 square kilometres (an area larger than England), giving it the second-largest proven oil reserves in the world. The Athabasca oil sands is the largest asphalt/bitumen deposit in Canada and the only one accessible to surface mining, although recent technological breakthroughs have resulted in deeper deposits becoming producible by in situ methods. Because of oil price increases since 2003, upgrading bitumen to synthetic crude oil has become highly profitable. As of 2006, Canadian crude asphalt/bitumen production averaged about 1.1 million barrels (170,000 m3) per day and was projected to rise to 4.4 million barrels (700,000 m3) per day by 2020. The total amount of crude asphalt/bitumen in Alberta which could be extracted is estimated to be about 310 billion barrels (50×109 m3), which at a rate of 4,400,000 barrels per day (700,000 m3/d) would last about 200 years.
Alternatives and bioasphalt
Although uncompetitive economically, asphalt/bitumen can be made from nonpetroleum-based renewable resources such as sugar, molasses and rice, corn and potato starches. Asphalt/bitumen can also be made from waste material by fractional distillation of used motor oils, which is sometimes disposed by burning or dumping into landfills. Nonpetroleum-based asphalt/bitumen binders can be made light-colored. Lighter-colored roads absorb less heat from solar radiation, and have less surface heat than darker surfaces, reducing their contribution to the urban heat island effect.
The word asphalt is derived from the late Middle English, in turn from French asphalte, based on Late Latin asphalton, asphaltum, which is the latinisation of the Greek ἄσφαλτος (ásphaltos, ásphalton), a word meaning "asphalt/bitumen/pitch", which perhaps derives from α- "without" and σφάλλω, (sfallō), "make fall". Note that in French, the term asphalte is used for naturally occurring bitumen-soaked limestone deposits, and for specialised manufactured products with fewer voids or greater bitumen content than the "asphaltic concrete" used to pave roads. 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. Specifically Herodotus mentioned that bitumen was brought to Babylon to build its gigantic fortification wall. From the Greek, the word passed into late Latin, and thence into French (asphalte) and English ("asphaltum" and "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.
In British English, the word 'asphalt' is used to refer to a mixture of mineral aggregate and asphalt/bitumen (also called tarmac in common parlance). The earlier word 'asphaltum' is now archaic and not commonly used. In American English, 'asphalt' is equivalent to the British 'bitumen'. However, 'asphalt' is also commonly used as a shortened form of 'asphalt concrete' (therefore equivalent to the British 'asphalt' or 'tarmac'). In Australian English, bitumen is often used as the generic term for road surfaces. In Canadian English, the word bitumen is used to refer to the vast Canadian deposits of extremely heavy crude oil, while asphalt is used for the oil refinery product used to pave roads and manufacture roof shingles and various waterproofing products. Diluted bitumen (diluted with naphtha to make it flow in pipelines) is known as dilbit in the Canadian petroleum industry, while bitumen "upgraded" to synthetic crude oil is known as syncrude and syncrude blended with bitumen as synbit. Bitumen is still the preferred geological term for naturally occurring deposits of the solid or semi-solid form of petroleum. Bituminous rock is a form of sandstone impregnated with bitumen. The tar sands of Alberta, Canada are a similar material.
- The Building News and Engineering Journal contains photographs of the following roads where Clarmac was used, being "some amongst many laid with 'Clarmac'": Scott's Lane, Beckenham; Dorset Street, Marylebone; Lordswood Road, Birmingham; Hearsall Lane, Coventry; Valkyrie Avenue, Westcliff-on-Sea; and Lennard Road, Penge.
- Merriam-Webster: 
- Oxford Advanced Learner's Dictionary: 
- Dictionary Reference: bitumen
- The Free Dictionary: bitumen
- Abraham, Herbert (1938). Asphalts and Allied Substances: Their Occurrence, Modes of Production, Uses in the Arts, and Methods of Testing (4th ed.). New York: D. Van Nostrand Co. Retrieved 16 November 2009. Full text at Internet Archive (archive.org)
- Anja Sörensen and Bodo Wichert "Asphalt and Bitumen" in Ullmann's Encyclopedia of Industrial Chemistry Wiley-VCH, Weinheim, 2009. doi:10.1002/14356007.a03_169.pub2
- "Oil Sands - Glossary". Oil Sands Royalty Guidelines. Government of Alberta. 2008. Archived from the original on 1 November 2007. Retrieved 2 February 2008.
- Walker, Ian C. (1998), Marketing Challenges for Canadian Bitumen (PDF), Tulsa, OK: International Centre for Heavy Hydrocarbons, "Bitumen has been defined by various sources as crude oil with a dynamic viscosity at reservoir conditions of more than 10,000 centipoise. Canadian "bitumen" supply is more loosely accepted as production from the Athabasca, Wabasca, Peace River and Cold Lake oil-sands deposits. The majority of the oil produced from these deposits has an API gravity of between 8° and 12° and a reservoir viscosity of over 10,000 centipoise although small volumes have higher API gravities and lower viscosities."
- Muhammad Abdul Quddus (1992). "Catalytic Oxidation of Asphalt". thesis submitted to Department of Applied Chemistry; University of Karachi. Pakistan: Higher Education Commission Pakistan: Pakistan Research Repository. p. 6, in ch.2 pdf.
- Muhammad Abdul Quddus (1992), p.99, in ch.5 pdf
- J. Bunger, K. Thomas and S. Dorrence. 1979. Compound types and properties of Utah and Athabasca tar sand bitumens. Fuel 58(3), 183-195.
- D. Selby and R. Creaser. 2005. Direct radiometric dating of hydrocarbon deposits using rhenium-osmium isotopes. Science 308, 1293-1295.
- T. Boden and B. Tripp (2012). Gilsonite Veins of the Uinta Basin, Utah. Utah, USA: Utah Geological Survey, Special Study 141.
- Hayatsu et al., Meteoritics, Vol. 18, p.310
- Kim & Yang, Journal of Astronomy and Space Sciences, vol. 15, no. 1, p.163-174
- McIntosh, Jane. The Ancient Indus Valley. p. 57
- Herodotus, Book I, 179
- Abraham, Herbert (1920). Asphalts And Allied Substances. D. Van Nostrand.
- Pringle, Heather Anne (2001). The Mummy Congress: Science, Obsession, and the Everlasting Dead. New York, NY: Barnes & Noble Books. pp. 196–197. ISBN 0-7607-7151-0.
- Pedanius Dioscorides (ca. 40 A.D.). De Materia Medica. translated by Goodyer (1655)  or (Greek/Latin) compiled by Sprengel (1829)  p. 100 (p. 145 in PDF)
- Connan, Jacques; Nissenbaum, Arie (2004). "The organic geochemistry of the Hasbeya asphalt (Lebanon): comparison with asphalts from the Dead Sea area and Iraq". Organic Geochemistry 35 (6): 775–789. doi:10.1016/j.orggeochem.2004.01.015. ISSN 0146-6380.
- Arie Nissenbaum (May 1978). "Dead Sea Asphalts--Historical Aspects [free abstract]". AAPG Bulletin 62 (5): 837–844.
- The Megalithic Portal and Megalith Map. "C.Michael Hogan (2008) ''Morro Creek'', ed. by A. Burnham". Megalithic.co.uk. Retrieved 27 August 2013.
- Africa and the Discovery of America, Volume 1, page 183, Leo Wiener, BoD – Books on Demand, 1920 reprinted in 2012, ISBN 9783864034329
- "Nothing New under the Sun (on French asphaltum use in 1621)". The Mechanic's magazine, museum, register, journal and gazette 29. London: W.A. Robertson. 7th-29 April September 1838. p. 176.
- Miles, Lewis (2000). "Section 10.6: Damp Proofing". in Australian Building: A Cultural Investigation. p. 10.06.1. Retrieved 11 November 2009.. Note: different sections of Miles' online work were written in different years, as evidenced at the top of each page (not including the heading page of each section). This particular section appears to have been written in 2000
- R.J. Forbes (1958), Studies in Early Petroleum History, Leiden, Netherlands: E.J. Brill, p. 24, retrieved 10 June 2010
- Niépce Museum history pages. Retrieved 2012-10-27.
- The First Photograph (Harry Ransom Center, University of Texas at Austin). Retrieved 2012-10-27.
- Salmon, William (1673). Polygraphice; Or, The Arts of Drawing, Engraving, Etching, Limning, Painting, Washing, Varnishing, Gilding, Colouring, Dying, Beautifying and Perfuming (Second ed.). London: R. Jones. p. 81.
- Salmon, William (1685), Polygraphice; Or, The Arts of Drawing, Engraving, Etching, Limning, Painting, Washing, Varnishing, Gilding, Colouring, Dying, Beautifying and Perfuming (5th ed.), London: R. Jones, pp. 76–77, retrieved 18 August 2010 Text at Internet Archive
- "Specification of the Patent granted to Richard Tappin Claridge, of the County of Middlesex, for a Mastic Cement, or Composition applicable to Paving and Road making, covering Buildings and various purposes". Journal of the Franklin Institute of the State of Pennsylvania and Mechanics' Register. Vol. 22. London: Pergamon Press. July 1838 1838. pp. 414–418. Retrieved 18 November 2009.
- "Comments on asphalt patents of R.T. Claridge, Esq". Notes and Queries: A medium of intercommunication for Literary Men, General Readers, etc. Ninth series. Volume XII, July–December, 1903 (9th S. XII, 4 July 1903). London: John C. Francis. 20 January 1904. pp. 18–19. Writer is replying to note or query from previous publication, cited as 9th S. xi. 30
- "Obituary of Frederick Walter Simms". Monthly Notices of the Royal Astronomical Society (London: Strangeways & Walden) XXVI: 120–121. November 1865 - June 1866. Retrieved 12 November 2009.
- Broome, D.C. (1963). "The development of the modern asphalt road". The Surveyor and municipal and county engineer (London) 122 (3278 & 3279): 1437–1440 & 1472–1475Snippet view: Simms & Claridge p.1439
- Phipson, Dr T. Lamb (1902). Confessions of a Violinist: Realities and Romance. London: Chatto & Windus. p. 11. Retrieved 26 November 2009. Full text at Internet Archive (archive.org)
- "Claridge's UK Patents in 1837 & 1838". The London Gazette. 25 February 1851. p. 489.
- Hobhouse, Hermione (General Editor) (1994). "British History Online". 'Northern Millwall: Tooke Town', Survey of London: volumes 43 and 44: Poplar, Blackwall and Isle of Dogs. pp. 423–433 (see text at refs 169 & 170). Retrieved 8 November 2009.
- "Claridge's Scottish and Irish Patents in 1838". The Mechanic's magazine, museum, register, journal and gazette 29. London: W.A. Robertson. 7th-29 April September 1838. pp. vii, viii, 64, 128.
- "Joint Stock Companies (description of asphalte use by Claridge's company)". The Civil Engineer and Architects Journal. Vol. 1. London. p. 199. Retrieved 16 November 2009. Full text at Internet Archive (archive.org). Alternative viewing at: http://books.google.com/books?id=sQ5AAAAAYAAJ&pg
- Miles, Lewis (2000), pp.10.06.1-2
- Comments on asphalt patents of R.T. Claridge, Esq (1904), p.18
- Miles, Lewis (2000), p.10.06.2
- "1838 bitumen UK uses by Robinson's and Claridge's companies, & the Bastenne company". The Mechanic's magazine, museum, register, journal and gazette 29. London: W.A. Robertson. 22 September 1838. p. 448.
- Gerhard, W.M. Paul (1908). Modern Baths and Bath Houses (1st ed.). New York: John Wiley and Sons. (Enter "asphalt" into the search field for list of pages discussing the subject)
- "Claridge's Patent Asphalte Co. ventures into tarred slag macadam", Concrete and Constructional Engineering (London) IX (1), January 1914: 760, retrieved 15 June 2010
- "Registration of Clarmac Roads", The Law Reports: Chancery Division, Vol. 1, 1921: 544–547, retrieved 17 June 2010
- "Clarmac and Clarphalte", The Building News and Engineering Journal, Vol. 109: July to December 1915 (No. 3157), 7 July 1915: 2–4 (n13–15 in electronic page field), retrieved 18 June 2010
- Roads laid with Clarmac The Building News and Engineering Journal, 1915 109 (3157), p.3 (n14 in electronic field).
- Clarmac financial difficults due to WW1 Debentures deposited The Law Reports: Chancery Division, (1921) Vol. 1 p.545. Retrieved 17 June 2010.
- "Notice of the Winding up of Clarmac Roads", The London Gazette (29340), 26 October 1915: 10568, retrieved 15 June 2010
- Claridge's Patent Asphalte Co. compulsorily wound up Funds invested in new company The Law Times Reports (1921) Vol.125, p.256. Retrieved 15 June 2010.
- "Claridge's Patent Asphalte Co. winds up 10 November 1917". The London Gazette. 16 November 1917. p. 11863.
- Hobhouse, Hermione (General Editor) (1994). "British History Online". 'Cubitt Town: Riverside area: from Newcastle Drawdock to Cubitt Town Pier', Survey of London: volumes 43 and 44: Poplar, Blackwall and Isle of Dogs. pp. 528–532 (see text at refs 507 & 510). Retrieved 8 November 2009.
- McNichol, Dan (2005). Paving the Way: Asphalt in America. Lanham, MD: National Asphalt Pavement Association. ISBN 0-914313-04-5.
- The Asphalt Paving Industry: A Global Perspective, 2nd Edition (PDF). Lanham, Maryland, and Brussels: National Asphalt Pavement Association and European Asphalt Pavement Association. February 2011. ISBN 0-914313-06-1. Retrieved 27 September 2012.
- "New FHWA Survey Finds Asphalt Recycling Reaches 99 Percent". Asphalt Pavement Mix Production Survey: 2009-2010. National Asphalt Pavement Association. Retrieved 12 June 2012.
- "What is Oil Sands". Alberta Energy. 2007. Archived from the original on 21 December 2007. Retrieved 10 January 2008.
- "2007 Canadian Crude Oil Forecast and Market Outlook". Canadian Association of Petroleum Producers. June 2007. Retrieved 30 May 2008.
- "ST98-2007: Alberta's Energy Reserves 2006 and Supply/Demand Outlook" (PDF). Alberta Energy Resources Conservation Board. 2007. Retrieved 30 May 2008.
- Heat Island Effect. From the website of the U.S. Environmental Protection Agency.
- ἄσφαλτος, Henry George Liddell, Robert Scott, A Greek-English Lexicon, on Perseus
- σφάλλω, Henry George Liddell, Robert Scott, A Greek-English Lexicon, on Perseus
- Herodotus, The Histories, 1.179.4, on Perseus
- Abraham, Herbert (1938), p.1
- Barth, Edwin J., Asphalt: Science and Technology Gordon and Breach (1962). ISBN 0-677-00040-5.
- Forbes, R.J. (1993. Reprint of 1964 ed), Studies in Ancient Technology, Volume 1, The Netherlands: E.J. Brill, ISBN 90-04-00621-4
- Lay, Maxwell G (1992), The Ways of the World: A History of the World's Roads and of the Vehicles that Used Them, Rutgers University Press, ISBN 0-8135-2691-4
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|Wikisource has the text of the 1911 Encyclopædia Britannica article Asphalt.|
- International Chemical Safety Card 0612
- Pavement Interactive - Asphalt
- Asphalt Magazine
- CSU Sacramento, The World Famous Asphalt Museum!
- National Institute for Occupational Safety and Health - Asphalt Fumes
- "Bitumen". New International Encyclopedia. 1905.