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For other uses, see Asphalt (disambiguation). Note: The terms bitumen and asphalt are mostly interchangeable, Sealcoating Contractor in Brakpan 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

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Asphalt (/ˈæsˌfɔːlt, -ˌfɑːlt/), also known as bitumen (UK English: /ˈbɪtʃəmən, ˈbɪtjʊmən/,[1] US English: /bɪˈt(j)uːmən, baɪˈt(j)uːmən/)[2] 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.

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The primary use (70%) of asphalt Driveway Pavement Quotes 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.

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Naturally occurring asphalt is sometimes specified by the term “crude bitumen”. Sealcoating Contractor Its viscosity is similar to that of cold molasses[6][7] 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.

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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”.  Laying Asphalt Driveway 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.[11] 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.

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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”,[13] but the term is less commonly used today.[citation needed]

Asphalt

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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”).

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In Canadian English, the word “bitumen” is used to refer to the vast Canadian deposits of extremely heavy crude oil,[14] 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”.[15]

“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.

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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.

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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.[16] “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.

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Bituminous outcrop of the Puy de la Poix, Clermont-Ferrand, France

The majority of asphalt used commercially is obtained from petroleum.[18] 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.

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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.

Alley

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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.[19] Isotopic studies show the oil deposits to be about 110 million years old.[20] 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.

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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.

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Bitumen is similar to the organic matter in carbonaceous meteorites.[23] However, detailed studies have shown these materials to be distinct.[24] 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.

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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.[25] 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.[3] The Greek historian Herodotus said hot bitumen was used as mortar in the walls of Babylon.

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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.[3][28] 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).

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Approximately 40 AD, Dioscorides described the Dead Sea material as Judaicum bitumen, and noted other places in the region where it could be found.[29] The Sidon bitumen is thought to refer to material found at Hasbeya.[30] 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.

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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,[3] 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.[32] 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.

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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.

Asphalt concrete

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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”.

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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.[35] 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.[37] By the fifth edition in 1685, he had included more asphaltum recipes from other sources.

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The first British patent for the use of asphalt was “Cassell’s patent asphalte or bitumen” in 1834.[35] Then on 25 November 1837, Richard Tappin Claridge patented the use of Seyssel asphalt (patent #7849), for use in asphalte pavement,[39][40] 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.[41][42] 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)”.[43] Indeed, mastic pavements had been previously employed at Vauxhall by a competitor of Claridge, but without success.

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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”.[45] “By the end of 1838, at least two other companies, Robinson’s and the Bastenne company, were in production”,[50] 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”.

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Asphalt Paving Cost Estimate An alley in Fira, Santorini, Greece Sana'a, Yemen Howey Place, Melbourne, Australia Hagay Street, Old City, Jerusalem Rua Sobre-o-Douro, Porto, Portugal Peg Washington's Lane, Graiguenamanagh, County Kilkenny, Ireland

An alley or alleyway is a narrow lane, path, or passageway, often reserved for pedestrians, which usually runs between, behind, or within buildings in the older parts of towns and cities. It is also a rear access or service road (back lane), or a path or walk in a park or garden.[1]

A covered alley or passageway, often with shops, may be called an arcade. The origin of the word alley is late Middle English, from Old French: alee "walking or passage", from aler "go", from Latin: ambulare "to walk".[2]

The word alley is used in two main ways:

Grand Bazaar, Istanbul

In older cities and towns in Europe, alleys are often what is left of a medieval street network, or a right of way or ancient footpath. Similar paths also exist in some older North American towns and cities. In some older urban development in North America lanes at the rear of houses, to allow for deliveries and garbage collection, are called alleys. Alleys and ginnels were also the product of the 1875 Public Health Act in the United Kingdom, where usually alleys run along the back of streets of terraced houses, with ginnels connecting them to the street every fifth house.[citation needed] Alleys may be paved, or unpaved, and a blind alley is a cul-de-sac. Modern urban developments may also provide a service road to allow for waste collection, or rear access for fire engines and parking.

Because of geography, steps (stairs) are the predominant form of alley in hilly cities and towns. This includes Pittsburgh (see Steps of Pittsburgh), Cincinnati (see Steps of Cincinnati), Minneapolis, Seattle,[3] and San Francisco[4] in the United States, as well as Hong Kong,[5] Genoa and Rome.[6]

Some alleys are roofed because they are within buildings, such as the traboules of Lyon, or when they are a pedestrian passage through railway embankments in Britain. The latter follow the line of rights-of way that existed before the railway was built.

Arcades are another kind of covered passageway and the simplest kind are no more than alleys to which a glass roof was added later, like, for example, Howey Place, Melbourne, Australia (see also Block Place, Melbourne). However, most arcades differ from alleys in that they are architectural structures built with a commercial purpose and are a form of shopping mall. All the same alleys have for long been associated with various types of businesses, especially pubs and coffee houses. Bazaars and Souqs are an early form of arcade found in Asia and North Africa.

Some attractive historic alleys are found in older American and Canadian cities, like New York City, Philadelphia, Charleston, South Carolina, Boston, Annapolis, New Castle, Delaware, Quebec City, St John's, Newfoundland,[7] and Victoria, British Columbia.

View into Fan Tan Alley, Victoria, British Columbia, Canada

Québec City was originally built on the riverside bluff Cap Diamant in the 17th century, and throughout Quebec City there are strategically placed public stairways that link the bluff to the lower parts of the city.[8] The Upper City is the site of Old Québec’s most significant historical sites, including 17th- and 18th-century chapels, the Citadel and the city ramparts.

Fan Tan Alley is an alley in Victoria, British Columbia's Chinatown. It was originally a gambling district with restaurants, shops, and opium dens. Today it is a tourist destination with many small shops including a barber shop, art gallery, Chinese cafe and apartments. It may well be the narrowest street in Canada. At its narrowest point it is only 0.9 metres (35 in) wide.[9] Waddington Alley is another interesting alley in Victoria and the only street in that city still paved with wood blocks, an early pavement common in the downtown core. Other heritage features are buildings more than a century old lining the alley and a rare metal carriage curb that edges the sidewalk on the southern end.[10]

Looking south down Shubert Alley in Manhattan's Theater District

In the United States alleys exist in both older commercial and residential areas, for both service purposes and automobile access. In residential areas, particularly in those that were built before 1950, alleys provide rear access to property where a garage was located, or where waste could be collected by service vehicles. A benefit of this was the location of these activities to the rear, less public side of a dwelling. Such alleys are generally roughly paved, but some may be dirt. Beginning in the late 20th century, they were seldom included in plans for new housing developments.

When Annapolis, Maryland, was established as a city at the beginning of the 18th century,[11] the streets were established in circles. That encouraged the creation of shortcuts, which over time became paved alleys. Some ten of these survive, and the city has recently worked on making them more attractive.[12]

Several residential neighborhoods in Austin, Texas, have comprehensive alley systems. These include Hyde Park, Rosedale, and areas northwest of the Austin State Hospital.

In the Beacon Hill district of Boston, Massachusetts, Acorn Street, a narrow cobbled lane with row houses, is one of Boston's more attractive and historic alleys. Another early settled American city, New Castle, Delaware has a number of interesting alleys, some of which are footpaths and others narrow, sometimes cobbled, lanes open to traffic. Many of the alleys in the Back Bay and South End area are numbered (e.g. "Public Alley 438").

In the French Quarter of Charleston’s historic district, Philadelphia Alley (c. 1766), originally named "Cow Alley", is one of several picturesque alleys. In 1810 William Johnson gave it the name of "Philadelphia Alley", although locals call the "elegantly landscaped thoroughfare" "Dueler’s Alley".[13] Starting on East Bay Street, Stolls Alley is just seventeen bricks wide at its start, and named for Justinus Stoll, an 18th-century blacksmith.[14] For three hundred years, another of Charleston's narrow lanes, Lodge Alley, served a commercial purpose. Originally French Hugenot merchants built homes on it, along with warehouses to store supplies their ships. Just ten-foot-wide this alley was a useful means of access to Charleston’s waterways.[15] Today it leads to East Bay Street's many restaurants.

Main article: Steps of Cincinnati

Cincinnati is a city of hills.[16] Before the advent of the automobile a system of stairway alleys provided pedestrians important and convenient access to and from their hill top homes. At the height of their use in the 19th century, over 30 miles (48 km) of hill side steps once connected the neighborhoods of Cincinnati to each other.[17] The first steps were installed by residents of Mount Auburn in the 1830s in order to gain easier access to Findlay Market in Over-the-Rhine.[18] In recent years many steps have fallen into disrepair but there is a movement now to rehabilitate them.[19]

Broadway Alley is a rare alley in Manhattan; it is not located near Broadway, East Broadway or West Broadway

New York City's Manhattan is unusual in that it has very few alleys, since the Commissioner's Plan of 1811 did not include rear service alleys when it created Manhattan's grid. The exclusion of alleys has been criticized as a flaw in the plan, since services such as garbage pickup cannot be provided out of sight of the public, although other commentators feel that the lack of alleys is a benefit to the quality of life of the city.[20]

Two notable alleys in the Greenwich Village neighborhood in Manhattan are MacDougal Alley and Washington Mews.[21] The latter is a blind alley or cul-de-sac. Greenwich Village also has a number of private alleys that lead to back houses, which can only be accessed by residents, including Grove Court,[22] Patchin Place and Milligan Place, blind alleys. Patchin Place is notable for the writers who lived there.[23]

Shubert Alley is a 300-foot (91 m) long pedestrian alley at the heart of the Broadway theater district of New York City. The alley was originally created as a fire exit between the Shubert Theatre on West 45th Street and the Booth Theatre on West 44th Street, and the Astor Hotel to their east. Actors once gathered in the alley, hoping to attract the attention of the Shubert Brothers and get employment in their theatrical productions.[24] When the hotel was torn down, and replaced with One Astor Plaza (1515 Broadway), the apparent width of the alley increased, as the new building did not go all the way to the westernmost edge of the building lot. However, official, Shubert Alley consists only of the space between the two theatres and the lot line.

In the Brooklyn Heights neighborhood of Brooklyn, Grace Court Alley is another converted mews,[25] as is Dennett Place in the Carroll Gardens neighborhood.[26] The former is a cul-de-sac.

Pedestrians walking along Elfreth's Alley, Philadelphia

The Old City and Society Hill neighborhoods of Philadelphia, the oldest parts of the city, include a number of alleys, notably Elfreth's Alley, which is called "Our nation's oldest residential street", dating from 1702.[27] As of 2012[update], there were 32 houses on the street, which were built between 1728 and 1836.[28]

There are numerous cobblestoned residential passages in Philadelphia, many no wider than a truck, and typically flanked with brick houses. A typical house on these alleys or lanes is called a Philadelphia "Trinity", named because it has three rooms, one to each floor, alluding to the Christian Trinity.[29] These alleys include Willings Alley, between S. 3rd and S. 4th Streets and Walnut and Spruce Streets.[30] Other streets in Philadelphia which fit the general description of an alley, but are not named "alley", include Cuthbert Street, Filbert Street, Phillips Street,[31] South American Street,[32] Sansom Walk,[33] St. James Place,[34] and numerous others.

Steps, Pittsburgh's equivalent for an alley, have defined it for many visitors. Writing in 1937, war correspondent Ernie Pyle wrote of the steps of Pittsburgh:

And then the steps. Oh Lord, the steps! I was told they actually had a Department of Steps. That isn’t exactly true, although they do have an Inspector of Steps. But there are nearly 15 miles (24 km) of city-owned steps, going up mountainsides.[35]

The City of Pittsburgh maintains 712 sets of city-owned steps, some of which are shown as streets on maps.[36]

In hilly San Francisco, California alleys often take the form of steps and it has several hundred public stairways.[37] Among the most famous is the stairway known as the Filbert steps, a continuation of Filbert Street.[38] The Filbert Street Steps descend the east slope of Telegraph Hill along the line where Filbert Street would be if the hill was not so steep. The stairway is bordered by greenery, that consists both backyards, and a border garden tended to and paid for by the residents of the "street", and runs down to an eastern stub of Filbert Street and the walkway through the plaza to The Embarcadero. Many houses in this residential neighborhood are accessible only from the steps.

Also in San Francisco, Belden Place is a narrow pedestrian alley, bordered by restaurants, in the Financial District, referred to as San Francisco's French Quarter for its historic ties to early French immigrants, and its popular contemporary French restaurants and institutions.[39] The area was home to San Francisco's first French settlers. Approximately 3,000, sponsored by the French government, arrived near the end of the Gold Rush in 1851.[40]

Alley in Sausalito, California

Seattle is a city of hills, bluffs, and canyons and many stairs. There are over 600 publicly accessible Seattle stairways within the city limits.[41]

Ruelle verte (Green alley) Montréal, Québec, Canada.

Numerous cities in the United States and Canada, such as Chicago,[42] Seattle,[43] Los Angeles,[44] Phoenix, Washington, D.C.,[45] and Montréal, have started reclaiming their alleys from garbage and crime by greening the service lanes, or back ways, that run behind some houses.[45][46] Chicago, Illinois has about 1,900 miles (3,100 km) of alleyways.[42] In 2007, the Chicago Department of Transportation started converting conventional alleys which were paved with asphalt into so called Green Alleys. This program, called the Green Alley Program, is supposed to enable easier water runoff, as the alleyways in Chicago are not connected directly to the sewer system. With this program, the water will be able to seep through semi-permeable concrete or asphalt in which a colony of fungi and bacteria will establish itself. The bacteria will help breakup oils before the water is absorbed into the ground. The lighter color of the pavement will also reflect more light, making the area next to the alley cooler.[47] The greening of such alleys or laneways can also involve the planting of native plants to further absorb rain water and moderate temperature.

New life has also come to other alleys within downtown commercial districts of various cities throughout the world with the opening of businesses, such as coffee houses, shops, restaurants and bars.

Another way that alleys and laneways are being revitalized is through laneway housing. A laneway house is a form of housing that has been proposed on the west coast of Canada, especially in the Metro Vancouver area. These homes are typically built into pre-existing lots, usually in the backyard and opening onto the back lane. This form of housing already exists in Vancouver, and revised regulations now encourage new developments as part of a plan to increase urban density in pre-existing neighbourhoods while retaining a single-family feel to the area.[48] Vancouver's average laneway house is one and a half stories, with one or two bedrooms. Typical regulations require that the laneway home is built on the back half of a traditional lot in the space normally reserved for a garage.[49][50]

Toronto also has a tradition of laneway housing and changed regulations to encourage new development.[51] However this was discontinued in 2006 after staff reviewed the impact on services and safety.[52]

London has numerous historical alleys, especially, but not exclusively, in its centre; this includes The City, Covent Garden, Holborn, Clerkenwell, Westminster and Bloomsbury amongst others.

An alley in London can also be called a passage, court, place, lane, and less commonly path, arcade, walk, steps, yard, terrace, and close.[53] While both a court and close are usually defined as blind alleys, or cul-de-sacs, several in London are throughways, for example Cavendish Court, a narrow passage leading from Houndsditch into Devonshire Square, and Angel Court, which links King Street and Pall Mall.[54] Bartholomew Close is a narrow winding lane which can be called an alley by virtue of its narrowness, and because through-access requires the use of passages and courts between Little Britain, and Long Lane and Aldersgate Street.[55]

In an old neighbourhood of the City of London, Exchange Alley or Change Alley is a narrow alleyway connecting shops and coffeehouses.[56] It served as a convenient shortcut from the Royal Exchange on Cornhill to the Post Office on Lombard Street and remains as one of a number of alleys linking the two streets. The coffeehouses[57] of Exchange Alley, especially Jonathan's and Garraway's, became an early venue for the lively trading of shares and commodities. These activities were the progenitor of the modern London Stock Exchange.

Boundary Passage, Shoreditch, London, England

Lombard Street and Change Alley had been the open-air meeting place of London's mercantile community before Thomas Gresham founded the Royal Exchange in 1565.[58] In 1698, John Castaing began publishing the prices of stocks and commodities in Jonathan's Coffeehouse, providing the first evidence of systematic exchange of securities in London.

Change Alley was the site of some noteworthy events in England's financial history, including the South Sea Bubble from 1711 to 1720 and the panic of 1745.[59]

In 1761 a club of 150 brokers and jobbers was formed to trade stocks. The club built its own building in nearby Sweeting's Alley in 1773, dubbed the "New Jonathan's", later renamed the Stock Exchange.[60]

West of the City there are a number of alleys just north of Trafalgar Square, including Brydges Place which is situated right next to the Coliseum Theatre and just 15 inches wide at its narrowest point, only one person can walk down it at a time. It is the narrowest alley in London and runs for 200 yards (180 m), connecting St Martin's Lane with Bedfordbury in Covent Garden.[61]

Close by is another very narrow passage, Lazenby Court, which runs from Rose Street to Floral Street down the side of the Lamb and Flag pub; in order to pass people must turn slightly sideways. The Lamb & Flag in Rose Street has a reputation as the oldest pub in the area,[62] though records are not clear. The first mention of a pub on the site is 1772.[63] The Lazenby Court was the scene of an attack on the famous poet and playwright John Dryden in 1679 by thugs hired by John Wilmot, 2nd Earl of Rochester,[64] with whom he had a long-standing conflict.[65]

In the same neighbourhood Cecil Court has an entirely different character than the two previous alleys, and is a spacious pedestrian street with Victorian shop-frontages that links Charing Cross Road with St. Martin's Lane, and it is sometimes used as a location by film companies.[66][67]

One of the older thoroughfares in Covent Garden, Cecil Court dates back to the end of the 17th century. A tradesman's route at its inception, it later acquired the nickname Flicker Alley because of the concentration of early film companies in the Court.[68] The first film-related company arrived in Cecil Court in 1897, a year after the first demonstration of moving pictures in the United Kingdom and a decade before London’s first purpose built cinema opened its doors. Since the 1930s it has been known as the new Booksellers' Row as it is home to nearly twenty antiquarian and second-hand independent bookshops.

It was the temporary home of an eight-year-old Wolfgang Amadeus Mozart while he was touring Europe in 1764. For almost four months the Mozart family lodged with barber John Couzin.[69] According to some modern authorities, Mozart composed his first symphony while a resident of Cecil Court.[70]

North of the centre of London, Camden Passage is a pedestrian passage off Upper Street in the London Borough of Islington, famous because of its many antiques shops, and an antique market on Wednesdays and Saturday mornings. It was built, as an alley, along the backs of houses on Upper Street, then Islington High Street, in 1767.[71]

An alley (usually called a ginnel) in Moss Side, Manchester Tolbooth Wynd, Edinburgh

In Scotland and Northern Ireland the Scots terms close, wynd, pend and vennel are general in most towns and cities. The term close has an unvoiced "s" as in sad. The Scottish author Ian Rankin's novel Fleshmarket Close was retitled Fleshmarket Alley for the American market. Close is the generic Scots term for alleyways, although they may be individually named closes, entries, courts and wynds. A close was private property, hence gated and closed to the public.

A wynd is typically a narrow lane between houses, an open throughway, usually wide enough for a horse and cart. The word derives from Old Norse venda, implying a turning off a main street, without implying that it is curved.[87] In fact, most wynds are straight. In many places wynds link streets at different heights and thus are mostly thought of as being ways up or down hills.

A pend is a passageway that passes through a building, often from a street through to a courtyard, and typically designed for vehicular rather than exclusively pedestrian access.[88] A pend is distinct from a vennel or a close, as it has rooms directly above it, whereas vennels and closes are not covered over.

A vennel is a passageway between the gables of two buildings which can in effect be a minor street in Scotland and the north east of England, particularly in the old centre of Durham. In Scotland, the term originated in royal burghs created in the twelfth century, the word deriving from the Old French word venelle meaning "alley" or "lane". Unlike a tenement entry to private property, known as a "close", a vennel was a public way leading from a typical high street to the open ground beyond the burgage plots.[89] The Latin form is venella.

Traboule, Vieux Lyon, France

The traboules of Lyon are passageways that cut through a house or, in some cases, a whole city block, linking one street with another. They are distinct from most other alleys in that they are mainly enclosed within buildings and may include staircases. While they are found in other French cities including Villefranche-sur-Saône, Mâcon, Chambéry, Saint-Étienne, Louhans, Chalon sur Saône and Vienne (Isère), Lyon has many more; in all there are about 500. The word traboule comes from the Latin trans ambulare, meaning "to cross", and the first of them were possibly built as early as the 4th century. As the Roman Empire disintegrated, the residents of early Lyon—Lugdunum, the capital of Roman Gaul—were forced to move from the Fourvière hill to the banks of the river Saône when their aqueducts began to fail. The traboules grew up alongside their new homes, linking the streets that run parallel to the river Saône and going down to the river itself. For centuries they were used by people to fetch water from the river and then by craftsmen and traders to transport their goods. By the 18th century they were invaluable to what had become the city’s defining industry, textiles, especially silk.[97] Nowadays, traboules are tourist attractions, and many are free and open to the public. Most traboules are on private property, serving as entrances to local apartments.

Venice is largely a traffic free city and there is, in addition to the canals, a maze of around 3000 lanes and alleys called calli (which means narrow). Smaller ones are callètte or callesèlle, while larger ones are calli large. Their width varies from just over 50 centimetres (19.7 in) to 5–6 metres (196.9–236.2 in). The narrowest is Calletta Varisco, which just 53 centimetres (20.9 in); Calle Stretta is 65 centimetres (25.6 in) wide and Calle Ca’ Zusto 68 centimetres (26.8 in). The main ones are also called salizada and wider calli, where trade proliferates, are called riga', while blind calli, used only by residents to reach their homes, are ramo.[98]

Spreuerhofstraße is the world's narrowest street, found in the city of Reutlingen, Baden-Württemberg, Germany.[99] It ranges from 31 centimetres (12.2 in) at its narrowest to 50 centimetres (19.7 in) at its widest.[100] The lane was built in 1727 during the reconstruction efforts after the area was completely destroyed in the massive citywide fire of 1726 and is officially listed in the Land-Registry Office as City Street Number 77.[99][101]

Lintgasse is an alley (German: Gasse) in the Old town of Cologne, Germany between the two squares of Alter Markt and Fischmarkt. It is a pedestrian zone and though only some 130 metres long, is nevertheless famous for its medieval history. The Lintgasse was first mentioned in the 12th century as in Lintgazzin, which may be derived from basketmakers who wove fish baskets out of Linden tree barks. These craftsmen were called Lindslizer, meaning Linden splitter. During the Middle Ages, the area was also known as platēa subri or platēa suberis, meaning street of Quercus suber, the cork oak tree. Lintgasse 8 to 14 used to be homes of medieval knights as still can be seen by signs like Zum Huynen, Zum Ritter or Zum Gir. During the 19th-century the Lintgasse was called Stink-Linkgaß, a because of its poor air quality.[102]

A view of Spreuerhofstraße in Germany, showing the sign indicating that is the world's record narrowest street

Gränd is Swedish for an alley and there are numerous gränder, or alleys in Gamla stan, The Old Town, of Stockholm, Sweden. The town dates back to the 13th century, with medieval alleyways, cobbled streets, and historic buildings. North German architecture has had a strong influence in the Old Town's buildings. Some of Stockholm's alleys are very narrow pedestrian footpaths, while others are very narrow, cobbled streets, or lanes open to slow moving traffic. Mårten Trotzigs gränd ("Alley of Mårten Trotzig") runs from Västerlånggatan and Järntorget up to Prästgatan and Tyska Stallplan, and part of it consists of 36 steps. At its narrowest the alley is a mere 90 cm (35 inches) wide, making it the narrowest street in Stockholm.[103] The alley is named after the merchant and burgher Mårten Trotzig (1559–1617), who, born in Wittenberg,[103] emigrated to Stockholm in 1581, and bought properties in the alley in 1597 and 1599, also opening a shop there. According to sources from the late 16th century, he was dealing in first iron and later copper, by 1595 had sworn his burgher oath, and was later to become one of the richest merchants in Stockholm.[104]

Mårten Trotzigs Gränd, 90 cm wide, the narrowest alley in Gamla stan, Stockholm, Sweden

Possibly referred to as Trångsund ("Narrow strait") before Mårten Trotzig gave his name to the alley, it is mentioned in 1544 as Tronge trappe grenden ("Narrow Alley Stairs"). In 1608 it is referred to Trappegrenden ("The Stairs Alley"), but a map dated 1733 calls it Trotz gränd. Closed off in the mid 19th century, not to be reopened until 1945, its present name was officially sanctioned by the city in 1949.[104]

The "List of streets and squares in Gamla stan" provides links to many pages that describe other alleys in the oldest part of Stockholm; e.g. Kolmätargränd (Coal Meter's Alley); Skeppar Karls Gränd (Skipper Karl's Alley); Skeppar Olofs Gränd (Skipper Olof's Alley); and Helga Lekamens Gränd (Alley of the Holy Body).

A hutong in Beijing

Hutongs (simplified Chinese: 胡同; traditional Chinese: 衚衕; pinyin: hútòng; Wade–Giles: hu-t'ung) are a type of narrow streets or alleys, commonly associated with northern Chinese cities, most prominently Beijing.

In Beijing, hutongs are alleys formed by lines of siheyuan, traditional courtyard residences.[105] Many neighbourhoods were formed by joining one siheyuan to another to form a hutong, and then joining one hutong to another. The word hutong is also used to refer to such neighbourhoods. During China’s dynastic period, emperors planned the city of Beijing and arranged the residential areas according to the social classes of the Zhou Dynasty (1027 – 256 BC). The term "hutong" appeared first during the Yuan Dynasty, and is a term of Mongolian origin meaning "town".[106]

At the turn of the 20th century, the Qing court was disintegrating as China’s dynastic era came to an end. The traditional arrangement of hutongs was also affected. Many new hutongs, built haphazardly and with no apparent plan, began to appear on the outskirts of the old city, while the old ones lost their former neat appearance.

Following the founding of the People’s Republic of China in 1949, many of the old hutongs of Beijing disappeared, replaced by wide boulevards and high rises. Many residents left the lanes where their families lived for generations for apartment buildings with modern amenities. In Xicheng District, for example, nearly 200 hutongs out of the 820 it held in 1949 have disappeared. However, many of Beijing’s ancient hutongs still stand, and a number of them have been designated protected areas. Many hutongs, some several hundred years old, in the vicinity of the Bell Tower and Drum Tower and Shichahai Lake are preserved amongst recreated contemporary two- and three-storey versions.[107][108]

A longtang in Shangxian Fang, a residential compound in Shanghai, China.

Hutongs represent an important cultural element of the city of Beijing and the hutongs are residential neighborhoods which still form the heart of Old Beijing. While most Beijing hutongs are straight, Jiudaowan (九道弯, literally "Nine Turns") Hutong turns nineteen times. At its narrowest section, Qianshi Hutong near Qianmen (Front Gate) is only 40 centimeters (16 inches) wide.[109]

The Shanghai longtang is loosely equivalent to the hutong of Beijing. A longtang (弄堂 lòngtáng, Shanghainese: longdang) is a laneway in Shanghai and, by extension, a community centred on a laneway or several interconnected laneways. On its own long (traditional Chinese 衖 or 弄, simplified Chinese 弄) is a Chinese term for "alley" or "lane", which is often left untranslated in Chinese addresses, but may also be translated as "lane", and "tang" is a parlor or hallway.[110] It is sometimes called lilong (里弄); the latter name incorporates the -li suffix often used in the name of residential developments in the late 19th and early 20th centuries. As with the term hutong, the Shanghai longdang can either refers to the lanes that the houses face onto, or a group of houses connected by the lane.[111][112][113][114]

A Golden Gai alley, Tokyo, Japan.

Shinjuku Golden Gai (新宿ゴールデン街) is a small area of Shinjuku, Tokyo, Japan,[115] famous both as an area of architectural interest and for its nightlife. It is composed of a network of six narrow alleys, connected by even narrower passageways which are just about wide enough for a single person to pass through. Over 200 tiny shanty-style bars, clubs and eateries are squeezed into this area.[116]

Its architectural importance is that it provides a view into the relatively recent past of Tokyo, when large parts of the city resembled present-day Golden Gai, particularly in terms of the extremely narrow lanes and the tiny two-storey buildings. Nowadays, most of the surrounding area has been redeveloped. Typically, the buildings are just a few feet wide and are built so close to the ones next door that they nearly touch. Most are two-storey, having a small bar at street level and either another bar or a tiny flat upstairs, reached by a steep set of stairs. None of the bars are very large; some are so small that they can only fit five or so customers at one time.[115] The buildings are generally ramshackle, and the alleys are dimly lit, giving the area a very scruffy and run-down appearance. However, Golden Gai is not a cheap place to drink, and the clientele that it attracts is generally well off.

Golden Gai is well known as a meeting place for musicians, artists, directors, writers, academics and actors, including many celebrities. Many of the bars only welcome regular customers, who initially should be introduced by an existing patron, although many others welcome non-regulars, some even making efforts to attract overseas tourists by displaying signs and price lists in English.[115]

Golden Gai was known for prostitution before 1958, when prostitution became illegal. Since then it has developed as a drinking area, and at least some of the bars can trace their origins back to the 1960s.[116]

A medina quarter (Arabic: المدينة القديمةal-madīnah al-qadīmah "the old city") is a distinct city section found in many North African cities. The medina is typically walled, contains many narrow and maze-like streets.[117] The word "medina" (Arabic: مدينةmadīnah) itself simply means "city" or "town" in modern Arabic.

Because of the very narrow streets, medinas are generally free from car traffic, and in some cases even motorcycle and bicycle traffic. The streets can be less than a metre wide. This makes them unique among highly populated urban centres. The Medina of Fes, Morocco or Fes el Bali, is considered one of the largest car-free urban areas in the world.[118]

Notes

Bibliography


Sealcoat

Asphalt Surfacing Company Cost Estimate Asphalt batch mix plant A machine laying asphalt concrete, fed from a dump truck

Asphalt concrete (commonly called asphalt,[1] blacktop, or pavement in North America, and tarmac or bitumen macadam or rolled asphalt in the United Kingdom and the Republic of Ireland) is a composite material commonly used to surface roads, parking lots, airports, as well as the core of embankment dams.[2] It consists of mineral aggregate bound together with asphalt, laid in layers, and compacted. The process was refined and enhanced by Belgian inventor and U.S. immigrant Edward de Smedt.[3]

The terms asphalt (or asphaltic) concrete, bituminous asphalt concrete, and bituminous mixture are typically used only in engineering and construction documents, which define concrete as any composite material composed of mineral aggregate adhered with a binder. The abbreviation, AC, is sometimes used for asphalt concrete but can also denote asphalt content or asphalt cement, referring to the liquid asphalt portion of the composite material.

As shown in this cross-section, many older roadways are smoothed by applying a thin layer of asphalt concrete to the existing portland cement concrete, creating a composite pavement.

Mixing of asphalt and aggregate is accomplished in one of several ways:[4]

Hot-mix asphalt concrete (commonly abbreviated as HMA) This is produced by heating the asphalt binder to decrease its viscosity, and drying the aggregate to remove moisture from it prior to mixing. Mixing is generally performed with the aggregate at about 300 °F (roughly 150 °C) for virgin asphalt and 330 °F (166 °C) for polymer modified asphalt, and the asphalt cement at 200 °F (95 °C). Paving and compaction must be performed while the asphalt is sufficiently hot. In many countries paving is restricted to summer months because in winter the compacted base will cool the asphalt too much before it is able to be packed to the required density. HMA is the form of asphalt concrete most commonly used on high traffic pavements such as those on major highways, racetracks and airfields. It is also used as an environmental liner for landfills, reservoirs, and fish hatchery ponds.[5] Asphaltic concrete laying machine in operation in Laredo, Texas Warm-mix asphalt concrete (commonly abbreviated as WMA) This is produced by adding either zeolites, waxes, asphalt emulsions, or sometimes even water to the asphalt binder prior to mixing. This allows significantly lower mixing and laying temperatures and results in lower consumption of fossil fuels, thus releasing less carbon dioxide, aerosols and vapors. Not only are working conditions improved, but the lower laying-temperature also leads to more rapid availability of the surface for use, which is important for construction sites with critical time schedules. The usage of these additives in hot mixed asphalt (above) may afford easier compaction and allow cold weather paving or longer hauls. Use of warm mix is rapidly expanding. A survey of US asphalt producers found that nearly 25% of asphalt produced in 2012 was warm mix, a 416% increase since 2009.[6] Cold-mix asphalt concrete This is produced by emulsifying the asphalt in water with (essentially) soap prior to mixing with the aggregate. While in its emulsified state the asphalt is less viscous and the mixture is easy to work and compact. The emulsion will break after enough water evaporates and the cold mix will, ideally, take on the properties of an HMA pavement. Cold mix is commonly used as a patching material and on lesser trafficked service roads. Cut-back asphalt concrete Is a form of cold mix asphalt produced by dissolving the binder in kerosene or another lighter fraction of petroleum prior to mixing with the aggregate. While in its dissolved state the asphalt is less viscous and the mix is easy to work and compact. After the mix is laid down the lighter fraction evaporates. Because of concerns with pollution from the volatile organic compounds in the lighter fraction, cut-back asphalt has been largely replaced by asphalt emulsion.[7] Mastic asphalt concrete, or sheet asphalt This is produced by heating hard grade blown bitumen (i.e., partly oxidised) in a green cooker (mixer) until it has become a viscous liquid after which the aggregate mix is then added. The bitumen aggregate mixture is cooked (matured) for around 6–8 hours and once it is ready the mastic asphalt mixer is transported to the work site where experienced layers empty the mixer and either machine or hand lay the mastic asphalt contents on to the road. Mastic asphalt concrete is generally laid to a thickness of around ​3⁄4–1 ​3⁄16 inches (20–30 mm) for footpath and road applications and around ​3⁄8 of an inch (10 mm) for flooring or roof applications. High-modulus asphalt concrete, sometimes referred to by the French-language acronym EMÉ (enrobé à module élevé) This uses a very hard bituminous (penetration 10/20), sometimes modified, in proportions close to 6% on the weight of the aggregates, and a proportion of mineral powder also high, between 8–10%, to create an asphalt concrete layer with a high modulus of elasticity, of the order of 13000 MPa, as well as very high fatigue strengths.[8] High-modulus asphalt layers are used both in reinforcement operations and in the construction of new reinforcements for medium and heavy traffic. In base layers, they tend to exhibit a greater capacity of absorbing tensions and, in general, better fatigue resistance.[9]

In addition to the asphalt and aggregate, additives, such as polymers, and antistripping agents may be added to improve the properties of the final product.

Asphalt concrete pavements—especially those at airfields—are sometimes called tarmac for historical reasons, although they do not contain tar and are not constructed using the macadam process.

A variety of specialty asphalt concrete mixtures have been developed to meet specific needs, such as stone-matrix asphalt, which is designed to ensure a very strong wearing surface, or porous asphalt pavements, which are permeable and allow water to drain through the pavement for controlling stormwater.

An airport taxiway, one of the uses of asphalt concrete

Different types of asphalt concrete have different performance characteristics in terms of surface durability, tire wear, braking efficiency and roadway noise. In principle, the determination of appropriate asphalt performance characteristics must take into account the volume of traffic in each vehicle category, and the performance requirements of the friction course. Asphalt concrete generates less roadway noise than a Portland cement concrete surface, and is typically less noisy than chip seal surfaces.[10][11]

Because tire noise is generated through the conversion of kinetic energy to sound waves, more noise is produced as the speed of a vehicle increases. The notion that highway design might take into account acoustical engineering considerations, including the selection of the type of surface paving, arose in the early 1970s.[12][13] With regard to structural performance, the asphalt behaviour depends on a variety of factors including the material, loading and environmental condition. Furthermore, the performance of pavement varies over time. Therefore, the long-term behaviour of asphalt pavement is different from its short-term performance. The LTPP is a research program by the FHWA, which is specifically focusing on long-term pavement behaviour.[14][15]

Asphalt damaged by frost heaves

Asphalt deterioration can include crocodile cracking, potholes, upheaval, raveling, bleeding, rutting, shoving, stripping, and grade depressions. In cold climates, frost heaves can crack asphalt even in one winter. Filling the cracks with bitumen is a temporary fix, but only proper compaction and drainage can slow this process.

Factors that cause asphalt concrete to deteriorate over time mostly fall into one of three categories: construction quality, environmental considerations, and traffic loads. Often, damage results from combinations of factors in all three categories.

Construction quality is critical to pavement performance. This includes the construction of utility trenches and appurtenances that are placed in the pavement after construction. Lack of compaction in the surface of the asphalt, especially on the longitudinal joint can reduce the life of a pavement by 30 to 40%. Service trenches in pavements after construction have been said to reduce the life of the pavement by 50%, mainly due to the lack of compaction in the trench, and also because of water intrusion through improperly sealed joints.

Environmental factors include heat and cold, the presence of water in the subbase or subgrade soil underlying the pavement, and frost heaves.

High temperatures soften the asphalt binder, allowing heavy tire loads to deform the pavement into ruts. Paradoxically, high heat and strong sunlight also cause the asphalt to oxidize, becoming stiffer and less resilient, leading to crack formation. Cold temperatures can cause cracks as the asphalt contracts. Cold asphalt is also less resilient and more vulnerable to cracking.

Water trapped under the pavement softens the subbase and subgrade, making the road more vulnerable to traffic loads. Water under the road freezes and expands in cold weather, causing and enlarging cracks. In spring thaw, the ground thaws from the top down, so water is trapped between the pavement above and the still-frozen soil underneath. This layer of saturated soil provides little support for the road above, leading to the formation of potholes. This is more of a problem for silty or clay soils than sandy or gravelly soils. Some jurisdictions pass frost laws to reduce the allowable weight of trucks during the spring thaw season and protect their roads.

The damage a vehicle causes is proportional to the axle load raised to the fourth power,[16] so doubling the weight an axle carries actually causes 16 times as much damage. Wheels cause the road to flex slightly, resulting in fatigue cracking, which often leads to crocodile cracking. Vehicle speed also plays a role. Slowly moving vehicles stress the road over a longer period of time, increasing ruts, cracking, and corrugations in the asphalt pavement.

Other causes of damage include heat damage from vehicle fires, or solvent action from chemical spills.

The life of a road can be prolonged through good design, construction and maintenance practices. During design, engineers measure the traffic on a road, paying special attention to the number and types of trucks. They also evaluate the subsoil to see how much load it can withstand. The pavement and subbase thicknesses are designed to withstand the wheel loads. Sometimes, geogrids are used to reinforce the subbase and further strengthen the roads. Drainage, including ditches, storm drains and underdrains are used to remove water from the roadbed, preventing it from weakening the subbase and subsoil.

Good maintenance practices center on keeping water out of the pavement, subbase and subsoil. Maintaining and cleaning ditches and storm drains will extend the life of the road at low cost. Sealing small cracks with bituminous crack sealer prevents water from enlarging cracks through frost weathering, or percolating down to the subbase and softening it.

For somewhat more distressed roads, a chip seal or similar surface treatment may be applied. As the number, width and length of cracks increases, more intensive repairs are needed. In order of generally increasing expense, these include thin asphalt overlays, multicourse overlays, grinding off the top course and overlaying, in-place recycling, or full-depth reconstruction of the roadway.

It is far less expensive to keep a road in good condition than it is to repair it once it has deteriorated. This is why some agencies place the priority on preventive maintenance of roads in good condition, rather than reconstructing roads in poor condition. Poor roads are upgraded as resources and budget allow. In terms of lifetime cost and long term pavement conditions, this will result in better system performance. Agencies that concentrate on restoring their bad roads often find that by the time they've repaired them all, the roads that were in good condition have deteriorated.[17]

Some agencies use a pavement management system to help prioritize maintenance and repairs.

A small-scale asphalt recycler

Asphalt concrete is 100% recyclable and is the most widely reused construction material in the world. Very little asphalt concrete — less than 1 percent, according to a 2011 survey by the Federal Highway Administration and the National Asphalt Pavement Association — is actually disposed of in landfills.[18]

There is asphalt recycling on a large scale (known as in-place asphalt recycling or asphalt recycling performed at a hot mix plant) and asphalt recycling on a smaller scale. For small scale asphalt recycling, the user separates asphalt material into three different categories:

Blacktop cookies Chunks of virgin uncompacted hot mix asphalt which can be used for pothole repair. The use of blacktop cookies has been investigated as a less expensive, less labor-intensive, more durable alternative to repairing potholes with cold patch. In a program in Pittsfield, Massachusetts, workers purchased new hot mix asphalt and spread it liberally on the ground to produce approximately 25 lb. wafers. Once cooled, the wafers could be stored until reheated in a hotbox to make minor road repairs. Blacktop cookies may also be produced from leftover material from paving jobs.[19] Reclaimed asphalt pavement (RAP) Chunks of asphalt that have been removed from a road, parking lot or driveway are considered RAP. These chunks of asphalt typically are ripped up when making a routine asphalt repair, man hole repair, catch basin repair or sewer main repair. Because the asphalt has been compacted, RAP is a denser asphalt material and typically takes longer to recycle than blacktop cookies. Asphalt millings Small pieces of asphalt produced by mechanically grinding asphalt surfaces are referred to as asphalt millings. Large millings that have a rich, black tint indicating a high asphalt cement content are best for asphalt recycling purposes. Surface millings are recommended over full depth millings when choosing asphalt millings to recycle. Full depth millings usually contain sub-base contaminants such as gravel, mud and sand. These sub base contaminants will leach oil away from original asphalt and dry out the material in the recycling process. Asphalt milled from asphalt is better than asphalt milled from concrete. When milling asphalt from concrete the dust that is created is not compatible with asphalt products because it is not asphalt.[20]

Small scale asphalt recycling will usually involve high speed on-site asphalt recycling equipment or overnight soft heat asphalt recycling.

Small scale asphalt recycling is used when wanting to make smaller road repairs vs. large scale asphalt recycling which is done for making new asphalt or for tearing up old asphalt and simultaneously recycling / replacing existing asphalt. Recycled asphalt is very effective for pothole and utility cut repairs. The recycled asphalt will generally last as long or longer than the road around it as new asphalt cement has been added back to the material.[21]

For larger scale asphalt recycling, several in-place recycling techniques have been developed to rejuvenate oxidized binders and remove cracking, although the recycled material is generally not very water-tight or smooth and should be overlaid with a new layer of asphalt concrete. Cold in-place recycling mills off the top layers of asphalt concrete and mixes the resulting loose millings with asphalt emulsion. The mixture is then placed back down on the roadway and compacted. The water in the emulsion is allowed to evaporate for a week or so, and new hot-mix asphalt is laid on top.

Asphalt concrete that is removed from a pavement is usually stockpiled for later use as aggregate for new hot mix asphalt at an asphalt plant. This reclaimed material, or RAP, is crushed to a consistent gradation and added to the HMA mixing process. Sometimes waste materials, such as asphalt roofing shingles, crushed glass, or rubber from old tires, are added to asphalt concrete as is the case with rubberized asphalt, but there is a concern that the hybrid material may not be recyclable.

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