For other uses, see Asphalt (disambiguation). Note: The terms bitumen and asphalt are mostly interchangeable, Commercial Paving Services in Randburg except where asphalt is used as a shorthand for asphalt concrete. Natural bitumen from the Dead Sea Refined asphalt The University of Queensland pitch drop experiment, demonstrating the viscosity of asphalt
Asphalt (/ˈæsˌfɔːlt, -ˌfɑːlt/), also known as bitumen (UK English: /ˈbɪtʃəmən, ˈbɪtjʊmən/, US English: /bɪˈt(j)uːmən, baɪˈt(j)uːmən/) 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 primary use (70%) of asphalt Asphalt Cost For Driveway 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 commonly used for a refined residue from the distillation process of selected crude oils. Outside the United States, the product is often called “bitumen”, and geologists worldwide often prefer the term for the naturally occurring variety. Common colloquial usage often refers to various forms of asphalt as “tar”, as in the name of the La Brea Tar Pits.
Naturally occurring asphalt is sometimes specified by the term “crude bitumen”. Commercial Paving Services 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.
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”. Asphalt Driveway Cost 2017 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 Australian English, “bitumen” is often used as the generic term for road surfaces.
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 tar sands of Alberta, Canada are a similar material.
Neither of the terms “asphalt” or “bitumen” should be confused with tar or coal tars.[further explanation needed]
See also: Asphaltene
The components of asphalt include four main classes of 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.
Bituminous outcrop of the Puy de la Poix, Clermont-Ferrand, France
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.
Natural deposits of bitumen include lakes such as the Pitch Lake in Trinidad and Tobago and Lake Bermudez in Venezuela. Natural seeps occur in the La Brea Tar Pits and in the Dead Sea.
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 (26.4×10^9 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.
Much smaller heavy oil or bitumen deposits also occur in the Uinta Basin in Utah, US. The Tar Sand Triangle deposit, for example, is roughly 6% bitumen.
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 millennia BC refined rock asphalt was in use, in the region, and was used to waterproof the Great Bath, 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 (ca. 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).
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. Pliny refers also to 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 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 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.
In 1553, Pierre Belon described in his work Observations that pissasphalto, a mixture of pitch and bitumen, was used in the Republic of Ragusa (now Dubrovnik, Croatia) for tarring of ships.
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)”. Indeed, mastic pavements had been previously employed at Vauxhall by a competitor of Claridge, but without success.
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”.
Commercial Paving Services in Randburg ?Sealcoating a road on the University of California, Davis campus in 2013.
Sealcoating, or pavement sealing, is the process of applying a protective coating to asphalt-based pavements to provide a layer of protection from the elements: water, oils, and U.V. damage.
Sealcoat or pavement sealer is a coating for asphalt-based pavements. Sealcoating is marketed as a protective coating that extends the life of asphalt pavements. There is not any independent research that proves these claims.
Sealcoating may also reduce the friction or anti-skid properties associated with the exposed aggregates in asphalt.
Not all pavement sealcoat are created equal. For example, refined tar-based sealer offers the best protecting against water penetration and chemical resistance. Asphalt-based sealer typically offers poor protection against environmental chemical and harsher climates (salt water). Petroleum-based sealer offer protection against water and chemicals somewhere between the other two sealers. Another difference between coatings is in terms of wear. Again, refined tar-based sealer offers the best wear characteristics (typically 3–5 years) while asphalt-based sealer may last 1–3 years. Petroleum-based sealer falls between refined tar and asphalt.
There are concerns about pavement sealer polluting the environment after it is abraded from the surface of the pavement. Some states in North America have banned the use of coal tar–based sealants primarily based on United States Geological Survey studies. The industry group that represents sealcoat manufacturers has performed numerous research and reviews of the USGS and have found it to be erroneous, biased (citation and white hat, to name a few) and too generalized in order to draw the conclusions that the United States Geological Survey claims.
There are primarily three types of pavement sealers. They are commonly known as refined tar-based (coal tar based), asphalt-based, and petroleum-based. All three have their advantages but are typically chosen by the contractors’ preference unless otherwise specified.
Prior to application the surface must be completely clean and dry using sweeping methods and/or blowers. If the surface is not clean and dry, then poor adhesion will result. Pavement sealers are applied with either pressurized spray equipment, or self-propelled squeegee machines or by hand with a squeegee. Equipment must have continuous agitation to maintain consistency of the sealcoat mix. The process is typically a two-coat application which requires 24 to 48 hours of curing before vehicles can be allowed back on the surface. Once the surface is properly prepared, then properly mixed sealer will be applied at about 60 square feet per gallon per coat.The Sealcoating Process
Some studies that suggest that refined tar sealants are a significant contributor to polycyclic aromatic hydrocarbon levels in streams and creek beds and that the continual application of sealcoats may be a significant factor. As a result, a few municipalities in the United States have banned this material. The same studies also suggest that it can be harmful if ingested before curing and ingesting soil or dust contaminated by eroded coal tar sealant. It is also known to have effects on fish and other animals that live in water.
LaneMacadam country road[dubious – discuss]
Macadam is a type of road construction, pioneered by Scottish engineer John Loudon McAdam around 1820, in which single-sized crushed stone layers of small angular stones are placed in shallow lifts and compacted thoroughly. A binding layer of stone dust (crushed stone from the original material) may form; it may also, after rolling, be covered with a binder to keep dust and stones together. The method simplified what had been considered state of the art at that point.
Pierre-Marie-Jérôme Trésaguet is sometimes considered the first person to bring post-Roman science to road building. A Frenchman from an engineering family, he worked paving roads in Paris from 1757 to 1764. As chief engineer of road construction of Limoges, he had opportunity to develop a better and cheaper method of road construction. In 1775, Tresaguet became engineer-general and presented his answer for road improvement in France, which soon became standard practice there.
Trésaguet had recommended a roadway consisting of three layers of stones laid on a crowned subgrade with side ditches for drainage. The first two layers consisted of angular hand-broken aggregate, maximum size 3 inches (7.6 cm), to a depth of about 8 inches (20 cm). The third layer was about 2 inches (5 cm) thick with a maximum aggregate size of 1 inch (2.5 cm). This top level surface permitted a smoother shape and protected the larger stones in the road structure from iron wheels and horse hooves. To keep the running surface level with the countryside, this road was put in a trench, which created drainage problems. These problems were addressed by changes that included digging deep side ditches, making the surface as solid as possible, and constructing the road with a difference in elevation (height) between the two edges, that difference being referred to interchangeably as the road's camber or cross slope.Laying Telford paving in Aspinwall, Pennsylvania, 1908
Thomas Telford, born in Dumfriesshire Scotland, was a surveyor and engineer who applied Tresaguet's road building theories. In 1801 Telford worked for the British Commission of Highlands Roads and Bridges. He became director of the Holyhead Road Commission between 1815 and 1830. Telford extended Tresaguet's theories, but emphasized high-quality stone. He recognized that some of the road problems of the French could be avoided by using cubical stone blocks.
Telford used roughly 12 in × 10 in × 6 in (30 cm × 25 cm × 15 cm) partially shaped paving stones (pitchers), with a slight flat face on the bottom surface. He turned the other faces more vertically than Tresaguet's method. The longest edge was arranged crossways to the traffic direction, and the joints were broken in the method of conventional brickwork, but with the smallest faces of the pitcher forming the upper and lower surfaces.
Broken stone was wedged into the spaces between the tapered perpendicular faces to provide the layer with good lateral control. Telford kept the natural formation level and used masons to camber the upper surface of the blocks. He placed a 6-inch (15 cm) layer of stone no bigger than 6 cm (2.4 in) on top of the rock foundation. To finish the road surface he covered the stones with a mixture of gravel and broken stone. This structure came to be known as "Telford pitching." Telford's road depended on a resistant structure to prevent water from collecting and corroding the strength of the pavement. Telford raised the pavement structure above ground level whenever possible.
Where the structure could not be raised, Telford drained the area surrounding the roadside. Previous road builders in Britain ignored drainage problems and Telford's rediscovery of these principles was a major contribution to road construction. Though notably of around the same time, John Metcalf was a strong advocate that drainage was in fact an important factor to road construction, and astonished colleagues by building dry roads through marshland. He accomplished this by installing a layer of brushwood and heather.John Loudon McAdam (1756–1836)
John Loudon McAdam was born in Ayr, Scotland, in 1756. In 1787, he became a trustee of the Ayrshire Turnpike in the Scottish Lowlands and during the next seven years this hobby became an obsession. He moved to Bristol, England, in 1802 and became a Commissioner for Paving in 1806. On 15 January 1816, he was elected Surveyor-General of roads for the Turnpike Trust and was now responsible for 149 miles of road. He then put his ideas about road construction into practice, the first 'macadamised' stretch of road being Marsh Road at Ashton Gate, Bristol. He also began to actively propagate his ideas in two booklets called Remarks (or Observations) on the Present System of Roadmaking, (which ran nine editions between 1816 and 1827) and A Practical Essay on the Scientific Repair and Preservation of Public Roads, published in 1819.Photograph of macadam road, ca 1850s, Nicolaus, California
McAdam's method was simpler, yet more effective at protecting roadways: he discovered that massive foundations of rock upon rock were unnecessary, and asserted that native soil alone would support the road and traffic upon it, as long as it was covered by a road crust that would protect the soil underneath from water and wear.
Unlike Telford and other road builders of the time, McAdam laid his roads as level as possible. His 30-foot-wide (9.1 m) road required only a rise of 3 inches (7.6 cm) from the edges to the centre. Cambering and elevation of the road above the water table enabled rain water to run off into ditches on either side.
Size of stones was central to the McAdam's road building theory. The lower 20-centimetre (7.9 in) road thickness was restricted to stones no larger than 7.5 centimetres (3.0 in). The upper 5-centimetre (2.0 in) layer of stones was limited to 2 centimetres (0.79 in) size and stones were checked by supervisors who carried scales. A workman could check the stone size himself by seeing if the stone would fit into his mouth. The importance of the 2 cm stone size was that the stones needed to be much smaller than the 10 cm width of the iron carriage tyres that travelled on the road.
McAdam believed that the "proper method" of breaking stones for utility and rapidity was accomplished by people sitting down and using small hammers, breaking the stones so that none of them was larger than six ounces in weight. He also wrote that the quality of the road would depend on how carefully the stones were spread on the surface over a sizeable space, one shovelful at a time.
McAdam directed that no substance that would absorb water and affect the road by frost should be incorporated into the road. Neither was anything to be laid on the clean stone to bind the road. The action of the road traffic would cause the broken stone to combine with its own angles, merging into a level, solid surface that would withstand weather or traffic.
Through his road-building experience, McAdam had learned that a layer of broken angular stones would act as a solid mass and would not require the large stone layer previously used to build roads. Keeping the surface stones smaller than the tyre width made a good running surface for traffic. The small surface stones also provided low stress on the road, so long as it could be kept reasonably dry.Construction of the first macadamized road in the United States (1823). In the foreground, workers are breaking stones "so as not to exceed 6 ounces [170 g] in weight or to pass a two-inch [5 cm] ring".
The first macadam road built in the United States was constructed between Hagerstown and Boonsboro, Maryland and was named at the time Boonsborough Turnpike Road. This was the last section of unimproved road between Baltimore on the Chesapeake Bay to Wheeling on the Ohio River. Stagecoaches traveling the Hagerstown to Boonsboro road in the winter took 5 to 7 hours to cover the 10-mile (16 km) stretch. This road was completed in 1823, using McAdam's road techniques, except that the finished road was compacted with a cast-iron roller instead of relying on road traffic for compaction. The second American road built using McAdam principles was the Cumberland Road which was 73 miles (117 km) long and was completed in 1830 after five years of work.
McAdam's renown is due to his effective and economical construction, which was a great improvement over the methods used by his generation. He emphasized that roads could be constructed for any kind of traffic, and he helped to alleviate the resentment travelers felt toward increasing traffic on the roads. His legacy lies in his advocacy of effective road maintenance and management. He advocated a central road authority and the trained professional official, who could be paid a salary that would keep him from corruption. This professional could give his entire time to his duties and be held responsible for his actions.
McAdam's road building technology was applied to roads by other engineers. One of these engineers was Richard Edgeworth, who filled the gaps between the surface stones with a mixture of stone dust and water, providing a smoother surface for the increased traffic using the roads. This basic method of construction is sometimes known as water-bound macadam. Although this method required a great deal of manual labour, it resulted in a strong and free-draining pavement. Roads constructed in this manner were described as "macadamized."New macadam road construction at McRoberts, Kentucky: pouring tar. 1926
With the advent of motor vehicles, dust became a serious problem on macadam roads. The area of low air pressure created under fast-moving vehicles sucked dust from the road surface, creating dust clouds and a gradual unraveling of the road material. This problem was approached by spraying tar on the surface to create tar-bound macadam. On March 13, 1902 in Monaco, a Swiss doctor, Ernest Guglielminetti, came upon the idea of using tar from Monaco's gasworks for binding the dust. Later a mixture of coal tar and ironworks slag, patented by Edgar Purnell Hooley as tarmac, was introduced.
A more durable road surface (modern mixed asphalt pavement) sometimes referred to in the US as blacktop, was introduced in the 1920s. This pavement method mixed the aggregates into the asphalt with the binding material before they were laid. The macadam surface method laid the stone and sand aggregates on the road and then sprayed it with the binding material. While macadam roads have now been resurfaced in most developed countries, some are preserved along stretches of roads such as the United States' National Road.
Because of the historic use of macadam as a road surface, roads in some parts of the United States (as parts of Pennsylvania) are often referred to as macadam, even though they might be made of asphalt or concrete. Similarly, the term "tarmac" is sometimes colloquially misapplied to asphalt roads or aircraft runways.