Asphalt, also known as bitumen (UK: //, US: / -/,), 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, and is classed as a pitch. Before the 20th century, the term asphaltum was also used. The word is derived from the Ancient Greek ἄσφαλτος ásphaltos.
The primary use (70%) 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.
In material sciences and engineering, the terms "asphalt" and "bitumen" are often used interchangeably to mean both natural and manufactured forms of the substance, although there is regional variation as to which term is most common. Worldwide, geologists tend to favor the term "bitumen" for the naturally occurring material. For the manufactured material, which is a refined residue from the distillation process of selected crude oils, "bitumen" is the prevalent term in much of the world; however, in American English, "asphalt" is more commonly used. To help avoid confusion, the phrase "liquid asphalt", "asphalt binder", or "asphalt cement" is used in the U.S. Colloquially, various forms of asphalt are sometimes referred to as "tar", as in the name of the La Brea Tar Pits, although tar is a different material.
Naturally occurring asphalt 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". The Canadian province of Alberta has most of the world's reserves of natural asphalt in the Athabasca oil sands, which cover 142,000 square kilometres (55,000 sq mi), an area larger than England.
Asphalt properties change with temperature, which means that there is a specific range where viscosity permits adequate compaction by providing lubrication between particles during the compaction process. Low temperature prevents aggregate particles from moving, and the required density is not possible to achieve.
- 1 Terminology
- 2 Composition
- 3 Occurrence
- 4 History
- 5 Modern use
- 6 Production
- 7 Economics
- 8 Health and safety
- 9 See also
- 10 Notes
- 11 References
- 12 External links
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 ἀ-, "without" and σφάλλω (sfallō), "make fall". 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"). In French, the term asphalte is used for naturally occurring asphalt-soaked limestone deposits, and for specialised manufactured products with fewer voids or greater bitumen content than the "asphaltic concrete" used to pave roads.
The expression "bitumen" originated in the Sanskrit words jatu, meaning "pitch", and jatu-krit, meaning "pitch creating" or "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, "bitumen" is used instead of "asphalt". The word "asphalt" is instead used to refer to asphalt concrete, a mixture of construction aggregate and asphalt itself (also called "tarmac" in common parlance). Bitumen mixed with clay was usually called "asphaltum", but the term is less commonly used today.
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 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. 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 is called "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 oil sands of Alberta, Canada are a similar material.
Neither of the terms "asphalt" or "bitumen" should be confused with tar or coal tars. Tar is the thick liquid product of the dry distillation and pyrolysis of organic hydrocarbons primarily sourced from vegetation masses, whether fossilized as with coal, or freshly harvested. The majority of bitumen, on the other hand, was formed naturally when vast quantities of organic animal materials were deposited by water and buried hundreds of metres deep at the diagenetic point, where the disorganized fatty hydrocarbon molecules joined together in long chains in the absence of oxygen. Bitumen occurs as a solid or highly viscous liquid. It may even be mixed in with coal deposits. Bitumen, and coal using the Bergius process, can be refined into petrols such as gasoline, and bitumen may be distilled into tar, not the other way around.
The components of asphalt 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 acids 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 compounds
The naphthene aromatics and polar aromatics are typically the majority components. Most natural bitumens also contain organosulfur compounds, resulting in an overall sulfur content of up to 4%. Nickel and vanadium are found at <10 parts per million, 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. "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 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 "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 has completely overtaken the use of coal tar in these applications. Other examples of this confusion include the La Brea Tar Pits and the Canadian oil 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, asphalt is sometimes sold combined with other materials, often without being labeled as anything other than simply "asphalt".
Of particular note is the use of re-refined engine oil bottoms -- "REOB" or "REOBs"—the residue of 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 asphalt and poorer-performing pavement.
The majority of asphalt used commercially is obtained from petroleum. Nonetheless, large amounts of asphalt occur in concentrated form in nature. Naturally occurring deposits of 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 bitumen, kerogen, or petroleum.
Bitumen also occurs in unconsolidated sandstones known as "oil sands" in Alberta, Canada, and the similar "tar sands" in Utah, US. The Canadian province of Alberta has most of the world's reserves, in three huge deposits covering 142,000 square kilometres (55,000 sq mi), an area larger than England or New York state. These bituminous sands contain 166 billion barrels (26.4×109 m3) of commercially established oil reserves, giving Canada the third largest oil reserves in the world. Although historically it was used without refining to pave roads, nearly all of the output is now used as raw material for oil refineries in Canada and the United States.
The world's largest deposit of natural bitumen, known as the Athabasca oil sands, is located in the McMurray Formation of Northern Alberta. This formation is from the early Cretaceous, and is composed of numerous lenses of oil-bearing sand with up to 20% oil. Isotopic studies show the oil deposits to be about 110 million years old. Two smaller but still very large formations occur in the Peace River oil sands and the Cold Lake oil sands, to the west and southeast of the Athabasca oil sands, respectively. Of the Alberta deposits, only parts of the Athabasca oil sands are shallow enough to be suitable for surface mining. The other 80% has to be produced by oil wells using enhanced oil recovery techniques like steam-assisted gravity drainage.
Bitumen may occur in hydrothermal veins. An example of this is within the Uinta Basin of Utah, in the US, where there is a swarm of laterally and vertically extensive veins composed of a solid hydrocarbon termed Gilsonite. These veins formed by the polymerization and solidification of hydrocarbons that were mobilized from the deeper oil shales of the Green River Formation during burial and diagenesis.
Bitumen is similar to the organic matter in carbonaceous meteorites. However, detailed studies have shown these materials to be distinct. The vast Alberta bitumen resources are considered to have started out as living material from marine plants and animals, mainly algae, that died millions of years ago when an ancient ocean covered Alberta. They were covered by mud, buried deeply over time, and gently cooked into oil by geothermal heat at a temperature of 50 to 150 °C (120 to 300 °F). Due to pressure from the rising of the Rocky Mountains in southwestern Alberta, 80 to 55 million years ago, the oil was driven northeast hundreds of kilometres and trapped into underground sand deposits left behind by ancient river beds and ocean beaches, thus forming the oil sands.
The use of natural bitumen for waterproofing, and as an adhesive dates at least to the fifth millennium BC, with a crop storage basket discovered in Mehrgarh, of the Indus Valley Civilization, lined with it. By the 3rd millennium BC refined rock asphalt was in use in the region, and was used to waterproof the Great Bath in Mohenjo-daro.
In the ancient Middle East, the Sumerians used natural 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 bitumen was used as mortar in the walls of Babylon.
The 1 kilometre (0.62 mi) long Euphrates Tunnel beneath the river Euphrates at Babylon in the time of Queen Semiramis (c. 800 BC) was reportedly constructed of burnt bricks covered with bitumen as a waterproofing agent.
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 bitumen was the Dead Sea, which the Romans knew as Palus Asphaltites (Asphalt Lake).
In 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 Sidon bitumen is thought to refer to material found at Hasbeya in Lebanon. Pliny also refers to bitumen being found in Epirus. Bitumen was a valuable strategic resource. It was the object of the first known battle for a hydrocarbon deposit — between the Seleucids and the Nabateans in 312 BC.
In the ancient Far East, natural bitumen was slowly boiled to get rid of the higher fractions, leaving a thermoplastic material of higher molecular weight that 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 bitumen was sometimes used to adhere stone projectile points to wooden shafts. In Canada, aboriginal people used bitumen seeping out of the banks of the Athabasca and other rivers to waterproof birch bark canoes, and also heated it in smudge pots to ward off mosquitoes in the summer.
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 the substance was generally neglected in France until the revolution of 1830. 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 (Bas-Rhin), the Parc (Ain) and the Puy-de-la-Poix (Puy-de-Dôme)", 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.
Among the earlier uses of 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 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 writes that his father, Samuel Ryland Phipson, a friend of Claridge, was also "instrumental in introducing the asphalte pavement (in 1836)".
Claridge obtained a patent in Scotland on 27 March 1838, and obtained a patent in Ireland on 23 April 1838. In 1851, extensions for the 1837 patent and for both 1838 patents were sought by the trustees of a company previously formed by Claridge. 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",—"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".
In 1838, there was a flurry of entrepreneurial activity involving asphalt, which had uses beyond paving. For example, asphalt could also be used for flooring, damp proofing in buildings, and for waterproofing of various types of pools and baths, both of which were also 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 ruined 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.
Bitumen was thought in 19th century Britain to contain chemicals with medicinal properties. Extracts from bitumen were used to treat catarrh and some forms of asthma and as a remedy against worms, especially the tapeworm.
The first use of 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 bitumen that seeped to the surface above underlying petroleum deposits. All three groups 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, possibly poisoning those who drank the water. Asphalt was used also to seal the planks on ocean-going canoes.
Asphalt was first used to pave streets in the 1870s. At first naturally occurring "bituminous rock" was used, 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.
In the horse-drawn era, US streets were mostly unpaved and covered with dirt or gravel. Especially where mud or trenching often made streets difficult to pass. pavements were sometimes made of diverse materials including wooden planks, cobble stones or other stone blocks, or bricks. Unpaved roads produced uneven wear and hazards for pedestrians. In the late 19th century with the rise of the popular bicycle, bicycle clubs were important in pushing for more general pavement of streets.  Advocacy for pavement increased in the early 20th century with the rise of the automobile. Asphalt gradually became an ever more common method of paving. St. Charles Avenue in New Orleans was paved its whole length with asphalt by 1889.
In 1900 Manhattan alone had 130,000 horses, pulling streetcars, wagons, and carriages, and leaving their waste behind. They were not fast, and pedestrians could dodge and scramble their way across the crowded streets. Small towns continued to rely on dirt and gravel, but larger cities wanted much better streets. They looked to wood or granite blocks by the 1850s. In 1890, a third of Chicago's 2000 miles of streets were paved, chiefly with wooden blocks, which gave better traction than mud. Brick surfacing was a good compromise, but even better was asphalt paving, which was easy to install and to cut through to get at sewers. With London and Paris serving as models, Washington laid 400,000 square yards of asphalt paving by 1882; it became the model for Buffalo, Philadelphia and elsewhere. By the end of the century, American cities boasted 30 million square yards of asphalt paving, well ahead of brick. The streets became faster and more dangerous so electric traffic lights were installed. Electric trolleys (at 12 miles per hour) became the main transportation service for middle class shoppers and office workers until they bought automobiles after 1945 and commuted from more distant suburbs in privacy and comfort on asphalt highways.
Canada has the world's largest deposit of natural bitumen in the Athabasca oil sands, and Canadian First Nations along the Athabasca River had long used it to waterproof their canoes. In 1719, a Cree named Wa-Pa-Su brought a sample for trade to Henry Kelsey of the Hudson's Bay Company, who was the first recorded European to see it. However, it wasn't until 1787 that fur trader and explorer Alexander MacKenzie saw the Athabasca oil sands and said, "At about 24 miles from the fork (of the Athabasca and Clearwater Rivers) are some bituminous fountains into which a pole of 20 feet long may be inserted without the least resistance."
The value of the deposit was obvious from the start, but the means of extracting the bitumen was not. The nearest town, Fort McMurray, Alberta, was a small fur trading post, other markets were far away, and transportation costs were too high to ship the raw bituminous sand for paving. In 1915, Sidney Ells of the Federal Mines Branch experimented with separation techniques and used the product to pave 600 feet of road in Edmonton, Alberta. Other roads in Alberta were paved with material extracted from oil sands, but it was generally not economic. During the 1920s Dr. Karl A. Clark of the Alberta Research Council patented a hot water oil separation process and entrepreneur Robert C. Fitzsimmons built the Bitumount oil separation plant, which between 1925 and 1958 produced up to 300 barrels (50 m3) per day of bitumen using Dr. Clark's method. Most of the bitumen was used for waterproofing roofs, but other uses included fuels, lubrication oils, printers ink, medicines, rust- and acid-proof paints, fireproof roofing, street paving, patent leather, and fence post preservatives. Eventually Fitzsimmons ran out of money and the plant was taken over by the Alberta government. Today the Bitumount plant is a Provincial Historic Site.
Photography and art
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 bitumen was thinly coated onto a pewter plate which was then exposed in a camera. Exposure to light hardened the 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 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.
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 diluents, such as linseed oil, varnish and turpentine. Unless thoroughly diluted, bitumen never fully solidifies and will in time corrupt the other pigments with which it comes into contact. The use of bitumen as a glaze to set in shadow or mixed with other colors to render a darker tone resulted in the eventual deterioration of many paintings, for instance those of Delacroix. Perhaps the most famous example of the destructiveness of bitumen is Théodore Géricault's Raft of the Medusa (1818–1819), where his use of bitumen caused the brilliant colors to degenerate into dark greens and blacks and the paint and canvas to buckle.
The vast majority of refined asphalt is used in construction: primarily as a constituent of products used in paving and roofing applications. According to the requirements of the end use, asphalt is produced to specification. This is achieved either by refining or blending. It is estimated that the current world use of asphalt is approximately 102 million tonnes per year. Approximately 85% of all the asphalt produced is used as the binder in asphalt concrete for roads. It is also used in other paved areas such as airport runways, car parks and footways. Typically, the production of asphalt concrete involves mixing fine and coarse aggregates such as sand, gravel and crushed rock with asphalt, which acts as the binding agent. Other materials, such as recycled polymers (e.g., rubber tyres), may be added to the asphalt to modify its properties according to the application for which the asphalt is ultimately intended.
A further 10% of global asphalt production is used in roofing applications, where its waterproofing qualities are invaluable. The remaining 5% of asphalt is used mainly for sealing and insulating purposes in a variety of building materials, such as pipe coatings, carpet tile backing and paint. Asphalt is applied in the construction and maintenance of many structures, systems, and components, such as the following:
- Airport runways
- Footways and pedestrian ways
- Car parks
- Tennis courts
- Damp proofing
- Reservoir and pool linings
- Pipe coatings
- Cable coatings
- Building water proofing
- Tile underlying waterproofing
- Newspaper ink production
- and many other applications
Rolled asphalt concrete
The largest use of asphalt is for making asphalt concrete for road surfaces; this accounts for approximately 85% of the asphalt consumed in the United States. There are about 4,000 asphalt concrete mixing plants in the US, and a similar number in Europe.
Asphalt concrete pavement mixes are typically composed of 5% asphalt cement and 95% aggregates (stone, sand, and gravel). Due to its highly viscous nature, asphalt cement must be heated so it can be mixed with the aggregates at the asphalt mixing facility. The temperature required varies depending upon characteristics of the asphalt and the aggregates, but warm-mix asphalt technologies allow producers to reduce the temperature required.
The weight of an asphalt pavement depends upon the aggregate type, the asphalt, and the air void content. An average example in the United States is about 112 pounds per square yard, per inch of pavement thickness.
When maintenance is performed on asphalt pavements, such as milling to remove a worn or damaged surface, the removed material can be returned to a facility for processing into new pavement mixtures. The asphalt in the removed material can be reactivated and put back to use in new pavement mixes. With some 95% of paved roads being constructed of or surfaced with asphalt, a substantial amount of asphalt pavement material is reclaimed each year. According to industry surveys conducted annually by the Federal Highway Administration and the National Asphalt Pavement Association, 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 or stockpiled for future use.
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.
Mastic asphalt is a type of asphalt that differs from dense graded asphalt (asphalt concrete) in that it has a higher asphalt (binder) content, usually around 7–10% of the whole aggregate mix, as opposed to rolled asphalt concrete, which has only around 5% asphalt. 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 (0.8 inches) thick.
A number of technologies allow asphalt to be mixed at much lower temperatures. These involve mixing with petroleum solvents to form "cutbacks" with reduced melting point or mixing 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, 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.
Synthetic crude oil
Synthetic crude oil, also known as syncrude, is the output from a bitumen upgrader facility used in connection with oil sand production in Canada. Bituminous sands are mined using enormous (100 ton capacity) power shovels and loaded into even larger (400 ton capacity) dump trucks for movement to an upgrading facility. The process used to extract the bitumen from the sand is a hot water process originally developed by Dr. Karl Clark of the University of Alberta during the 1920s. After extraction from the sand, the bitumen is fed into a bitumen upgrader which converts it into a light crude oil equivalent. This synthetic substance is fluid enough to be transferred through conventional oil pipelines and can be fed into conventional oil refineries without any further treatment. By 2015 Canadian bitumen upgraders were producing over 1 million barrels (160×103 m3) per day of synthetic crude oil, of which 75% was exported to oil refineries in the United States.
In Alberta, five bitumen upgraders produce synthetic crude oil and a variety of other products: The Suncor Energy upgrader near Fort McMurray, Alberta produces synthetic crude oil plus diesel fuel; the Syncrude Canada, Canadian Natural Resources, and Nexen upgraders near Fort McMurray produce synthetic crude oil; and the Shell Scotford Upgrader near Edmonton produces synthetic crude oil plus an intermediate feedstock for the nearby Shell Oil Refinery. A sixth upgrader, under construction in 2015 near Redwater, Alberta, will upgrade half of its crude bitumen directly to diesel fuel, with the remainder of the output being sold as feedstock to nearby oil refineries and petrochemical plants.
Non-upgraded crude bitumen
Canadian bitumen does not differ substantially from oils such as Venezuelan extra-heavy and Mexican heavy oil in chemical composition, and the real difficulty is moving the extremely viscous bitumen through oil pipelines to the refinery. Many modern oil refineries are extremely sophisticated and can process non-upgraded bitumen directly into products such as gasoline, diesel fuel, and refined asphalt without any preprocessing. This is particularly common in areas such as the US Gulf coast, where refineries were designed to process Venezuelan and Mexican oil, and in areas such as the US Midwest where refineries were rebuilt to process heavy oil as domestic light oil production declined. Given the choice, such heavy oil refineries usually prefer to buy bitumen rather than synthetic oil because the cost is lower, and in some cases because they prefer to produce more diesel fuel and less gasoline. By 2015 Canadian production and exports of non-upgraded bitumen exceeded that of synthetic crude oil at over 1.3 million barrels (210×103 m3) per day, of which about 65% was exported to the United States.
Because of the difficulty of moving crude bitumen through pipelines, non-upgraded bitumen is usually diluted with natural-gas condensate in a form called dilbit or with synthetic crude oil, called synbit. However, to meet international competition, much non-upgraded bitumen is now sold as a blend of multiple grades of bitumen, conventional crude oil, synthetic crude oil, and condensate in a standardized benchmark product such as Western Canadian Select. This sour, heavy crude oil blend is designed to have uniform refining characteristics to compete with internationally marketed heavy oils such as Mexican Mayan or Arabian Dubai Crude.
Radioactive waste encapsulation matrix
Asphalt was used starting in the 1960s as a hydrophobic matrix aiming to encapsulate radioactive waste such as medium-activity salts (mainly soluble sodium nitrate and sodium sulfate) produced by the reprocessing of spent nuclear fuels or radioactive sludges from sedimentation ponds. Bituminised radioactive waste containing highly radiotoxic alpha-emitting transuranic elements from nuclear reprocessing plants have been produced at industrial scale in France, Belgium and Japan, but this type of waste conditioning has been abandoned because operational safety issues (risks of fire, as occurred in a bituminisation plant at Tokai Works in Japan) and long-term stability problems related to their geological disposal in deep rock formations. One of the main problem is the swelling of asphalt exposed to radiation and to water. Asphalt swelling is first induced by radiation because of the presence of hydrogen gas bubbles generated by alpha and gamma radiolysis. A second mechanism is the matrix swelling when the encapsulated hygroscopic salts exposed to water or moisture start to rehydrate and to dissolve. The high concentration of salt in the pore solution inside the bituminised matrix is then responsible for osmotic effects inside the bituminised matrix. The water moves in the direction of the concentrated salts, the asphalt acting as a semi-permeable membrane. This also causes the matrix to swell. The swelling pressure due to osmotic effect under constant volume can be as high as 200 bar. If not properly managed, this high pressure can cause fractures in the near field of a disposal gallery of bituminised medium-level waste. When the bituminised matrix has been altered by swelling, encapsulated radionuclides are easily leached by the contact of ground water and released in the geosphere. The high ionic strength of the concentrated saline solution also favours the migration of radionuclides in clay host rocks. The presence of chemically reactive nitrate can also affect the redox conditions prevailing in the host rock by establishing oxidizing conditions, preventing the reduction of redox-sensitive radionuclides. Under their higher valences, radionuclides of elements such as selenium, technetium, uranium, neptunium and plutonium have a higher solubility and are also often present in water as non-retarded anions. This makes the disposal of medium-level bituminised waste very challenging.
Different type of asphalt have been used: blown bitumen (partly oxidized with air oxygen at high temperature after distillation, and harder) and direct distillation bitumen (softer). Blown bitumens like Mexphalte, with a high content of saturated hydrocarbons, are more easily biodegraded by microorganisms than direct distillation bitumen, with a low content of saturated hydrocarbons and a high content of aromatic hydrocarbons.
Concrete encapsulation of radwaste is presently considered a safer alternative by the nuclear industry and the waste management organisations.
Roofing shingles and roll roofing account for most of the remaining asphalt consumption. Other uses include cattle sprays, fence-post treatments, and waterproofing for fabrics. Asphalt is used to make Japan black, a lacquer known especially for its use on iron and steel, and it is also used in paint and marker inks by some exterior paint supply companies to increase the weather resistance and permanence of the paint or ink, and to make the color darker. Asphalt is also used to seal some alkaline batteries during the manufacturing process.
About 40,000,000 tons were produced in 1984.[needs update] 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 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, 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.
Naturally occurring crude 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 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 are the largest 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 after 2003, producing bitumen became highly profitable, but as a result of the decline after 2014 it became uneconomic to build new plants again. By 2014, Canadian crude bitumen production averaged about 2.3 million barrels (370,000 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 bitumen in Alberta that 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 can be made from nonpetroleum-based renewable resources such as sugar, molasses and rice, corn and potato starches. Asphalt can also be made from waste material by fractional distillation of used motor oil, which is sometimes otherwise disposed of by burning or dumping into landfills. Use of motor oil may cause premature cracking in colder climates, resulting in roads that need to be repaved more frequently.
Nonpetroleum-based asphalt binders can be made light-colored. Lighter-colored roads absorb less heat from solar radiation, reducing their contribution to the urban heat island effect. Parking lots that use asphalt alternatives are called green parking lots.
Selenizza is a naturally occurring solid hydrocarbon bitumen found in native deposits in Selenice, in Albania, the only European asphalt mine still in use. The bitumen is found in the form of veins, filling cracks in a more or less horizontal direction. The bitumen content varies from 83% to 92% (soluble in carbon disulphide), with a penetration value near to zero and a softening point (ring and ball) around 120 °C. The insoluble matter, consisting mainly of silica ore, ranges from 8% to 17%.
Albanian bitumen extraction has a long history and was practiced in an organized way by the Romans. After centuries of silence, the first mentions of Albanian bitumen appeared only in 1868, when the Frenchman Coquand published the first geological description of the deposits of Albanian bitumen. In 1875, the exploitation rights were granted to the Ottoman government and in 1912, they were transferred to the Italian company Simsa. Since 1945, the mine was exploited by the Albanian government and from 2001 to date, the management passed to a French company, which organized the mining process for the manufacture of the natural bitumen on an industrial scale.
Today the mine is predominantly exploited in an open pit quarry but several of the many underground mines (deep and extending over several km) still remain viable. Selenizza is produced primarily in granular form, after melting the bitumen pieces selected in the mine.
Selenizza is mainly used as an additive in the road construction sector. It is mixed with traditional asphalt to improve both the viscoelastic properties and the resistance to ageing. It may be blended with the hot asphalt in tanks, but its granular form allows it to be fed in the mixer or in the recycling ring of normal asphalt plants. Other typical applications include the production of mastic asphalts for sidewalks, bridges, car-parks and urban roads as well as drilling fluid additives for the oil and gas industry. Selenizza is available in powder or in granular material of various particle sizes and is packaged in sacks or in thermal fusible polyethylene bags.
A life-cycle assessment study of the natural selenizza compared with petroleum asphalt has shown that the environmental impact of the selenizza is about half the impact of the road asphalt produced in oil refineries in terms of carbon dioxide emission.
Although asphalt typically makes up only 4 to 5 percent (by weight) of the pavement mixture, as the pavement's binder, it is also the most expensive part of the cost of the road-paving material.
During asphalt's early use in modern paving, oil refiners gave it away. However, asphalt is, today, a highly traded commodity. Its prices increased substantially in the early 21st Century. A U.S. government report states:
- "In 2002, asphalt sold for approximately $160 per ton. By the end of 2006, the cost had doubled to approximately $320 per ton, and then it almost doubled again in 2012 to approximately $610 per ton."
The report indicates that an "average" 1-mile (1.6-kilometer)-long, four-lane highway would include "300 tons of asphalt," which, "in 2002 would have cost around $48,000. By 2006 this would have increased to $96,000 and by 2012 to $183,000... an increase of about $135,000 for every mile of highway in just 10 years."
Health and safety
People can be exposed to asphalt in the workplace by breathing in fumes or skin absorption. The National Institute for Occupational Safety and Health (NIOSH) has set a recommended exposure limit of 5 mg/m3 over a 15-minute period.
Asphalt is basically an inert material that must be heated or diluted to a point where it becomes workable for the production of materials for paving, roofing, and other applications. In examining the potential health hazards associated with asphalt, the International Agency for Research on Cancer (IARC) determined that it is the application parameters, predominantly temperature, that affect occupational exposure and the potential bioavailable carcinogenic hazard/risk of the asphalt emissions. In particular, temperatures greater than 199 °C (390 °F), were shown to produce a greater exposure risk than when asphalt was heated to lower temperatures, such as those typically used in asphalt pavement mix production and placement. IARC has classified asphalt as a Class 2B possible carcinogen.
- 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.
- Jones, Daniel (2011). Roach, Peter; Setter, Jane; Esling, John (eds.). Cambridge English Pronouncing Dictionary (18th ed.). Cambridge University Press. ISBN 978-0-521-15255-6.
- 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., Inc. Retrieved 16 November 2009. Full text at Internet Archive (archive.org)
- Sörensen, Anja; Wichert, Bodo (2009). "Asphalt and Bitumen". Ullmann's Encyclopedia of Industrial Chemistry. doi:10.1002/14356007.a03_169.pub2. ISBN 978-3527306732.
- Brown, E.R.; Kandhal, P.S.; Roberts, F.L.; Kim, Y.R.; Lee, D.-Y.; Kennedy, T.W. (1991). Hot Mix Asphalt Materials, Mixture Design, and Construction (Third ed.). Lanham, Maryland: NAPA Education and Research Foundation. ISBN 978-0914313021.
- "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, archived from the original (PDF) on 13 March 2012,
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.
- "ST98-2015: Alberta's Energy Reserves 2014 and Supply/Demand Outlook 2015–2024" (PDF). Statistical Reports (ST). Alberta Energy Regulator. 2015. Retrieved 19 January 2016.
- Polaczyk, Pawel; Han, Bingye; Huang, Baoshan; Jia, Xiaoyang; Shu, Xiang (30 October 2018). "Evaluation of the hot mix asphalt compactability utilizing the impact compaction method". Construction and Building Materials. 187: 131–137. doi:10.1016/j.conbuildmat.2018.07.117. ISSN 0950-0618.
- 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
- census, 1900, United States Census Office 12th; Steuart, William Mott; Census, United States Bureau of the (1905). Mines and quarries 1902. Govt. Print. Off.
- "What is Oil Sands". Alberta Energy. 2007. Archived from the original on 5 February 2016. Retrieved 10 January 2008.
- "2007 Canadian Crude Oil Forecast and Market Outlook". Canadian Association of Petroleum Producers. June 2007. Archived from the original on 26 February 2014. Retrieved 30 May 2008.
- 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. Archived from the original on 5 February 2011.
- Muhammad Abdul Quddus (1992), p.99, in ch.5 pdf
- 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), "What's in Your Asphalt?," September 2017 (last modified October 25, 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
- Speight, James G. (2015). Asphalt Materials Science and Technology. Elsevier Science. p. 82. ISBN 978-0-12-800501-9.
- Bunger, J.; Thomas, K.; Dorrence, S. (1979). "Compound types and properties of Utah and Athabasca tar sand bitumens". Fuel. 58 (3): 183–195. doi:10.1016/0016-2361(79)90116-9.
- Selby, D.; Creaser, R. (2005). "Direct radiometric dating of hydrocarbon deposits using rhenium-osmium isotopes". Science. 308 (5726): 1293–1295. Bibcode:2005Sci...308.1293S. doi:10.1126/science.1111081. PMID 15919988.
- "Facts about Alberta's oil sands and its industry" (PDF). Oil Sands Discovery Centre. Archived from the original (PDF) on 23 November 2015. Retrieved 19 January 2015.
- T. Boden and B. Tripp (2012). Gilsonite veins of the Uinta Basin, Utah. Utah, US: Utah Geological Survey, Special Study 141.
- Hayatsu; et al. Meteoritics. 18: 310.CS1 maint: untitled periodical (link)
- Kim; Yang. Journal of Astronomy and Space Sciences. 15 (1): 163–174.CS1 maint: untitled periodical (link)
- McIntosh, Jane. The Ancient Indus Valley. p. 57
- Herodotus, Book I, 179
- Pringle, Heather Anne (2001). The Mummy Congress: Science, Obsession, and the Everlasting Dead. New York, NY: Barnes & Noble Books. pp. 196–197. ISBN 978-0-7607-7151-8.
- Pedanius Dioscorides. De Materia Medica. Original written c. 40 AD, 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. doi:10.1306/c1ea4e5f-16c9-11d7-8645000102c1865d.
- 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 978-3864034329
- "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. 7 April – 29 September 1838. p. 176.
- Miles, Lewis (2000). "Section 10.6: Damp Proofing" (PDF). in Australian Building: A Cultural Investigation. p. 10.06.1. Archived from the original (PDF) on 15 December 2010. 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
- 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 (7 September 1685). "Polygraphice, or The arts of drawing, engraving, etching, limning, painting, washing, varnishing, gilding, colouring, dying, beautifying and perfuming : in seven books ... to which also is added, I. The one hundred and twelve chemical arcanums of Petrus Johannes Faber ... II. An abstract of choice chemical preparations...The 5th edition..." London : Printed for Thomas Passinger... and Thomas Sawbridge – via 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. 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. 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. 7 April – 29 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. October 1837 – December 1838. p. 199. Retrieved 16 November 2009. Full text at Internet Archive (archive.org). Alternative viewing at: https://books.google.com/books?id=sQ5AAAAAYAAJ
- 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): 760, January 1914, retrieved 15 June 2010
- "Registration of Clarmac Roads", The Law Reports: Chancery Division, 1: 544–547, 1921, retrieved 17 June 2010
- "Clarmac and Clarphalte", The Building News and Engineering Journal, Vol. 109: July to December 1915 (3157): 2–4 (n13–15 in electronic page field), 7 July 1915, 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): 10568, 26 October 1915, 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.
- The National Cyclopaedia of Useful Knowledge, Vol III, (1847) London, Charles Knight, p.380.
- Stockton, Nick (23 June 2017). "Plastic Water Bottles Might Have Poisoned Ancient Californians". Wired. Retrieved 26 June 2017.
- McNichol, Dan (2005). Paving the Way: Asphalt in America. Lanham, MD: National Asphalt Pavement Association. ISBN 978-0-914313-04-5. Archived from the original on 29 August 2006.
- Pintak, Lawrence (19 March 2015). ""Roads were not built for cars": how cyclists, not drivers, first fought to pave US roads". Vox. Retrieved 7 September 2019.
- "title". Catharinecole.startlogic.com. 1 January 1970. Retrieved 7 September 2019.
- David O. Whitten, "A Century of Parquet Pavements: Wood as a Paving Material In The United States And Abroad, 1840–1940." Essays in Economic and Business History 15 (1997): 209-26.
- Arthur Maier Schlesinger, The Rise of the City: 1878–1898 (1933), pp. 88–93.
- John D. Fairfield, "Rapid Transit: Automobility and Settlement in Urban America" Reviews in American History 23#1 (1995), pp. 80-85 online.
- "Robert C. Fitzsimmons (1881–1971)". Canadian Petroleum Hall of Fame. 2010. Retrieved 20 January 2016.
- "Bitumount". Government of Alberta. 2016. Retrieved 20 January 2016.
- Niépce Museum history pages. Retrieved 27 October 2012. Archived 3 August 2007 at the Wayback Machine
- The First Photograph (Harry Ransom Center, University of Texas at Austin). Archived 27 December 2009 at the Wayback Machine Retrieved 27 October 2012.
- Spiegelman, Willard (21 August 2009). "Revolutionary Romanticism: 'The Raft of the Medusa' brought energy to French art". The Wall Street Journal. New York City. Retrieved 27 January 2016.
- 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 978-0-914313-06-9. Retrieved 27 September 2012.
- "How Should We Express RAP and RAS Contents?". Asphalt Technology E-News. 26 (2). 2014. Archived from the original on 9 June 2015. Retrieved 13 August 2015.
- "Highway Statistics Series: Public Road Length Miles by Type of Surface and Ownership". Federal Highway Administration. 1 October 2013. Retrieved 13 August 2015.
- "Asphalt Pavement Recycling". Annual Asphalt Pavement Industry Survey on Recycled Materials and Warm-Mix Asphalt Usage: 2018. National Asphalt Pavement Association. Retrieved 14 January 2020.
- "Crude Oil and Petroleum Products". National Energy Board of Canada. Retrieved 21 January 2016.
- "2015 CAPP Crude Oil Forecast, Markets & Transportation". Canadian Association of Petroleum Producers. Archived from the original on 20 January 2016. Retrieved 21 January 2016.
- "The Project". North West Redwater Partnership. Retrieved 21 January 2016.
- Rodier, J., Scheidhauer, J., & Malabre, M. (1961). The conditioning of radioactive waste by bitumen (No. CEA-R—1992). CEA Marcoule.
- Lefillatre, G., Rodier, J., Hullo, R., Cudel, Y., & Rodi, L. (1969). Use of a thin-film evaporator for bitumen coating of radioactive concentrates (No. CEA-R—3742). CEA Marcoule.
- Sato, Y., Miura, A., Kato, Y., Suzuki, H., Shigetome, Y., Koyama, T., ... & Yamanouchi, T. (2000). Study on the cause of the fire and explosion incident at Bituminization Demonstration Facility of PNC Tokai Works. In Nuclear waste: from research to industrial maturity. International conference (pp. 179–190).
- Okada, K., Nur, R. M., & Fujii, Y. (1999). The formation of explosive compounds in bitumen/nitrate mixtures. Journal of hazardous materials, 69(3), 245–256.
- Johnson, D.I., Hitchon, J.W., & Phillips, D.C. (1986). Further observations of the swelling of bitumens and simulated bitumen wasteforms during γ-irradiation (No. AERE-R—12292). UKAEA Harwell Lab. Materials Development Division.
- Phillips, D. C., Hitchon, J. W., Johnson, D. I., & Matthews, J. R. (1984). The radiation swelling of bitumens and bitumenised wastes. Journal of nuclear materials, 125(2), 202–218.
- Ait-Langomazino, N., Sellier, R., Jouquet, G., & Trescinski, M. (1991). Microbial degradation of bitumen. Experientia, 47(6), 533–539.
- Hesp, Simon A.M.; Herbert F. Shurvell (2010). "X-ray fluorescence detection of waste engine oil residue in asphalt and its effect on cracking in service". International Journal of Pavement Engineering. 11 (6): 541–553. doi:10.1080/10298436.2010.488729. ISSN 1029-8436.
- Heat Island Effect. From the website of the US Environmental Protection Agency.
- Giavarini, Carlo (March 2013). Six Thousand Years of Asphalt. SITEB. pp. 71–78. ISBN 978-88-908408-3-8.
- , Selenice Bitumi for more information about Selenizza
- Giavarini, C.; Pellegrini, A. "Life cycle assessment of Selenice asphalt compared with petroleum bitumen". The 1st Albanian Congress on Roads: 234–237.
- "CDC – NIOSH Pocket Guide to Chemical Hazards – Asphalt fumes". www.cdc.gov. Retrieved 27 November 2015.
- IARC (2013). Bitumens and Bitumen Emissions, and Some N- and S-Heterocyclic Polycyclic Aromatic Hydrocarbons. 103. Lyon, France: International Agency for Research on Cancer. ISBN 978-92-832-1326-0. Retrieved 7 December 2015.
- Cavallari, J. M.; Zwack, L. M.; Lange, C. R.; Herrick, R. F.; Mcclean, M. D. (2012). "Temperature-Dependent Emission Concentrations of Polycyclic Aromatic Hydrocarbons in Paving and Built-Up Roofing Asphalts". Annals of Occupational Hygiene. 56 (2): 148–160. doi:10.1093/annhyg/mer107. ISSN 0003-4878. PMID 22267131.
- 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 978-90-04-00621-8
- 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 978-0-8135-2691-1
|Wikimedia Commons has media related to Asphalt.|
|Look up asphalt in Wiktionary, the free dictionary.|
- Redwood, Boverton (1911). Encyclopædia Britannica. 2 (11th ed.). p. 768. .
- New International Encyclopedia. 1905. .
- International Chemical Safety Card 0612
- Pavement Interactive – Asphalt
- CSU Sacramento, The World Famous Asphalt Museum!
- National Institute for Occupational Safety and Health – Asphalt Fumes