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History of Asphalt
Asphalt, also known as bitumen, is a dark viscous substance that can be both naturally formed and artificially manufactured for a variety of uses. Strictly speaking, “asphalt is a mix of bitumen, sand and stone but, confusingly, the word is also used to describe bitumen without the additions” (Reid, 2015, p. 82). For the purposes of this paper, the words “asphalt” and “bitumen” are used interchangeably. There is a bewildering array of asphalt forms and products. Each has its distinct chemical and physical properties. Indeed, no two asphalts are chemically identical. For the purposes of this paper, however, two asphalts, natural asphalt and refined asphalt, are emphasized, while others are mentioned only obliquely.
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Natural asphalt comes from several multiple deposits scattered around the world, mainly in Trinidad, Venezuela, France, Switzerland, Israel, Canada and the US. The production of refined asphalt in contrast is an elaborate process that involves a series of phases: desalination, distillation, pulverization, emulsification and/or oxidization. It has also been proven that asphalt can be produced from plants, such as rice, corn, sugar beets and potatoes, although such production is not economically expedient. Once the refining process is complete, asphalt is ready for use. Pulverized, emulsified, oxidized and cemented asphalts are all used for distinct purposes. In general, however, asphalt’s applications include paving and roofing as well as undersealing, water proofing, pipe coating and production of paints. A short excursus into the history shows that asphalt has been in use for millennia, but the real boom began in the late 19th century. Since then, asphalt technologies have been constantly improved and the specter of its applications has broadened. The present paper begins with an overview of asphalt’s history and segues into a discussion of its chemical composition, physical properties, production processes and modern applications. The bottom line of the paper is the fact that asphalt is a versatile material, the invention of which had a range of benefits for communities around the world.
It may be difficult to believe today, when asphalt covers more than 95% of all paved roads in the US, that this material was a rarity only a century ago, not only in the US, but also in other parts of the world. Many relegate it to the domain of the presupposed or, in other words, take it for granted. In a sense, the bituminous carpeting is so ubiquitous today that it is almost invisible. But it has not always been this way. For example, most of London’s thoroughfares were covered with wooden blocks well into the 1910s. Victorian and Edwardian roads in Britain were topped with a mishmash of coverings – rubber, tarred wooden blocks, macadam, steel sheeting, cobblestones, cork road covering and sometimes, viscous asphalt, on which a cyclist on solid rubber tires would have had “to bounce, dip, glide and swerve” (Reid, 2015, p. 81).
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Although asphalt had been used to build roads and other structures since the ancient times, it became a major construction material only in the late 19th century. In the meantime, roads were capped with wooden boards, granite setts, “dusty macadam and forgiving rubber” or uncapped at all (Reid, 2015, p. 75). However, each of these materials had its significant drawbacks. Granite blocks were difficult to lay; wooden blocks got soaked with horse urine and manure; macadam proved ineffective, while steel sheeting was noisy with horse traffic. Cobblestones were comparatively inexpensive and readily available and represented the most popular paving material. Most of the materials used for paving had the disadvantage of being slippery in pluvial weather. It is not surprising that the communities looked for other ways of paving roads to make their street surfaces more solid and durable. A popular way to attain this effect was to spread coal tar over macadamized streets. However, this invention often backfired, as roads coated with coal tar easily became pockmarked with potholes from vehicle wheels. Paving streets with crushed stone was more efficient, but at the same time more expensive, as the process of crushing stones required a great deal of manual job. Eventually, by the end of the 19th century, asphalt had become blinding in its promised magnificence.
Even though asphalt became popular in the late 19th century, the history is littered with examples of its uses in earlier days. Thus, the earliest recorded use of asphalt, albeit not proved by unimpeachable historical sources, was in Babylon in 625 B.C., the streets of which were paved with bricks “grouted with pitch” (Reid, 2015, p. 84). At the time, pitch as the heaviest and most sticky part of petroleum could be procured from the clumps by the Dead Sea, which was known as the Lake of Asphaltites in the Roman Empire (Reid, 2015). It is believed that the Mesopotamians used the substance to make baths and water tanks in their temples impervious to water (Karnes, 2009). The Phoenicians, on their part, used asphalt to caulk the seams of their vessels (Karnes, 2009). The ancient Romans and Greeks also used asphalt to seal their aqueducts, baths, reservoirs and other similar constructions. Similarly, some historians argue that the Egyptians used asphalt as a mortar, which is a mixture put between bricks to stick them together, to erect the embankments along the Nile and prevent the erosion of the construction (Karnes, 2009). According to the Bible, there were “slime pits” that is, pools of natural asphalt, scattered in the Middle East and Noah’s Ark was caulked with asphalt as well (Reid, 2015). The dark resilient substance had myriad of other applications thereupon.
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However, it was not until the late 16th century that Europeans found out about the properties of asphalt and tried it as a paving material. It was at this time that European sailors began to use asphalt to caulk the underside of their ships. Two centuries later, in the early 1800s, two Scottish road-builders were the first to use hot tar to bond the crushed stones together, thereby reducing maintenance and preventing sinking. The resultant mixture became a prototype of the modern asphalt. They built nearly 1,000 miles of road, paying meticulous attention to proper drainage, foundation and roadbed (Reid, 2015). Approximately at that same time, engineers in different parts of the industrializing world including Yorkshire, Paris and New Jersey were making the first cautious attempts to duplicate the feat of their Scottish counterparts. Although sporadic, the first asphalted roads sprang up in various cities. The sheet asphalt was procured first from Trinidad Lake off the coast of Venezuela, discovered back in the late 16th century by European sailors, and later in local hot mix production facilities that cropped up in other countries, such as Seyssel in France and Val de Travers in Switzerland. Throughout the 19th century, a host of engineers took out patents for different sorts of asphalt, but the status of the father of asphalt belongs to Edward Smedt, a Belgian expatriate working in ColumbiaUniversity in New York. In 1870, he invented modern maximum-density asphalt paving (Karnes, 2009). It was not used extensively back at the time, but it was of high quality. It was also at that time that the engineers began to differentiate between asphalt, an artificially created mixture of dark bituminous pitch with sand or gravel, and asphalte, natural substance coming from natural deposits. The invention of the asphalted roads was eulogized around the world, receiving words of praise from cyclists and pedestrians alike.
The onslaught of the asphalt era was long time coming. Just like Jules Verne invented a fictional submarine in his book Twenty Thousand Leagues under the Sea long before the real submarine was built, Herbert Wells predicted the invention of new road carpeting in his novel. Several years before the first roads were paved with asphalt in Britain, he wrote that old roads, “strange barbaric tracks of flint and soil, hammered by hand or rolled by rough iron rollers, strewn with miscellaneous filth, and cut by iron hoofs and wheels into ruts and puddles often many itches deep” would soon be replaced with tracks made of something like asphalt (Reid, 2015, p 78). In the 1920s, Well’s vision of the solid running surface was gradually coming to life. But it took chemists over 50 years since then to make it evolve into a strong and reliable paving material as it is known today. This can be seen in Laura Wilder’s Little House on the Prairie:
In the very midst of the city, the ground was covered by some dark stuff that silenced all the wheels and muffled the sound of hoofs. It was like tar, but Papa was sure it was not tar, and it was something like rubber, but it could not be rubber because rubber cost too much. We saw ladies all in silks and carrying ruffled parasols, walking with their escorts across the street. Their heels dented the street, and while we watched, these dents slowly filled up and smoothed themselves out. It was as if that stuff were alive. It was like magic.
One of the reasons why officials scurried to build asphalt roads was to rid cities of horse manure, which overflowed such cities as New York and London up until the end of the 19th century. One of the earliest solutions was to repave towns and cities with Australian hardwoods instead of the commonly used softwoods, which absorbed more manure.
Horse urine still posed a challenge. According to some commentators of the time, nearly 40,000 gallons of horse urine were spilt on New York streets everyday (Reid, 2015). Some critics said that, when pressed, some softwood coverings sprayed urine back out (Reid, 2015). Public roads defiled with urine and manure created an ideal breeding ground for morbid germs, which, once drawn up into the atmosphere, were inhaled by the citizenry, stunting growth and otherwise debilitating them (Reid, 2015). The arising epidemics of typhus, cholera, tuberculosis and other highly communicable diseases spurred the society to find an imaginative solution to the problem as soon as possible. To a more disconcerted resident, the main problem was the stench emanating from the wooden coverings. Although the invention of asphalt did not resolve the long-standing problem, it contributed to its resolution. Oftentimes, the car gets the credit for – erroneously, perhaps – the elimination or at least decline in the spread of infectious diseases. One way or another, asphalt roads contributed to the improvement of hygienic and sanitation standards in that asphalt surfaces were easier to keep clean.
As asphalt won great acceptance among European and American people, the authorities ordered municipal workers to tear up cobblestones, wooden blocks, granite setts and whatever other coverings they had previously laid to replace them with the new asphalt sheets. Others simply put asphalt topping over their previous coverings. However, because the methods and materials were often imperfect, the new asphalt was crushed on multiple occasions within the first weeks. The capricious weather endemic in most parts of Europe and the US also prevented success. Because the contractors lacked expertise, they often could not lay asphalt with a guarantee of success (Karnes, 2009). Nonetheless, despite some overtly disappointing experiences, more and more American and European cities were paved with asphalt. The Barber Company, a rising colossus of the asphalt paving business at the time, had paved more than 1,500 miles of roads in over 100 American cities by 1898 (Karnes, 2009). The surging demand for asphalted roads led to a quick expansion of the business, as new companies sprang up in droves. As many projects failed, engineers came to a dawning conclusion that asphalts procured from different locations had different composition, something that demanded more careful treatment of this pliant, yet tricky, material.
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Ellice-Clark was the first to observe that asphalt was only a generic term for mixtures of bitumen and many other components in different quantities. He further argued that for a project to be successful, the peculiarities of the asphalt used had to be considered (Reid, 2015). This simple discovery spurred further scientific interest to the problem and the body of academic literature soon started to grow. Improvements of the quality of roads gave a powerful fillip to the development of the car industry. Curiously enough, the burgeoning of the car industry in its turn stimulated the construction of roads.
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In the early 20th century, the use of refined petroleum asphalt exceeded the use of asphalt from natural deposits for the first time in history (Karnes, 2009). Initially, this type of asphalt was mixed with the natural asphalt to soften it a bit. But it was soon found out that refined petroleum asphalt could be used on its own. Producers of both types of asphalt were besieged with orders from local governments, and the paving industry boomed. Production and laying techniques were also modernized. There could be observed an overall improvement in the asphalt paving industry. The first several decades of boom winnowed out some firms as more competitive, whereas others, betrayed by shoddy workmanship and inability to meet long-term warranties on materials, faced bankruptcy. By the same token, the standards for asphalt roads grew more stringent in the US and many European countries (Reid, 2015). The quality of the hot mix asphalt no longer depended on the skills of operators. Unlike the first hot mix asphalt production units, which required manual stirring of the dried aggregate and hot iron, the new mechanical mixers were commonly employed in the early 20th century, and they were constantly modernized. Every new model of a mechanical mixer required less time to produce a batch of asphalt.
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Companies on both side of the Atlantic Ocean offered a wide range of mixers and dryers. However, the delivery of asphalt to remote areas remained a problem throughout the century. Some companies used railroads, while others developed mobile hot mix asphalt machines, but both had only limited success. As time went by, engineers developed pressure injection systems, cold feeds, vibrating screens, pollution control systems and a variety of other important components still used today (Reid, 2015).
Remarkable advances in science, growing governmental spending on infrastructure and the initiatives of local communities all contributed to the sustained interest to asphalt, as the substance proved its superiority over other paving materials. In 1956, the US government earmarked an astonishing $51 billion for the construction of roads (Reid, 2015). Other countries also bestirred themselves to adopt new technologies, paving central streets in towns, interstate highways and in richer areas, remote village roads for the pleasure of the citizens. The technology diffused around the world, reaching most populated territories. During an average lifetime, the society has gone all the way from the one “with very few bituminous roads to the one that is deemed uncivilized without them” (Reid, 2015, p. 75). In recent years, the emphasis has been laid on improving asphalt production processes in regard to environmental issues.
Occurrence, Composition and Properties of Asphalt
It is a matter of conventional wisdom that the bulk of asphalt used for commercial purposes is a product of oil refinement. However, few laypeople know that this dark, cement-like substance is obtained from the non-destructive distillation of crude oil in the process of oil refinement. Likewise, few would guess that there vast deposits of asphalt in nature. It takes thousands, if not hundreds of thousands, of years for naturally formed asphalt reserves to form in places of high algae concentration.
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Among other microscopic trouvailles to be found in bitumen are the remains of Pleistocene vertebrates and other once-living creatures (Usmani, 1997). The remains deposited deep in the bowels of mud under lakes or other bodies of water transmogrify into bitumen or any other related materials under the influence of heat. Among the most famous natural deposits of bitumen are chains of lakes in Venezuela, France, Trinidad and Tobago, and the Dead Sea in the Middle East. In addition to that, it also happens that natural asphalt occurs in the form of impregnated sandstones and tar sands (Usmani, 1997). Impregnated sandstones, also known as rock asphalt deposits, can “contain from 5 to 30% asphalt and the remainder is either sandstone or limestone” (Lavin, 2003, p. 3).Gilsonite is yet another naturally occurring type of resinous hydrocarbon that is “better described as a rock asphalt” (Lavin, 2003, p. 3). The US and Canada have seemingly infinite reserves of these substances. Asphalt also commonly occurs in the so-called hydrothermal veins. The American state of Utah boasts with both the largest reserves of tar sands and the vastest hydrothermal veins in the country. What is more interesting, studies have repeatedly shown that asphalt is similar in nature to the organic substance that occurs in carbonaceous meteorites, although the two materials have differences (Usmani, 1997). Speaking in a humorous tone, a perspective of humans shooting down meteorites to pave roads once the deposits of asphalt on earth are depleted is not at all promising. According to Lavin (2003), native asphalts are “not commonly used as a binder for asphalt pavements” (p. 3). As to asphalt made of oil residue, it can be found wherever there is an oil deposit at hand.
Apropos asphalt composition, it may sound too obscure for an unprepared ear. Chemists have been reportedly dissuaded from studying the issue because of its complexity (Reid, 2015). Indeed, it is next to impossible to identify all the molecules of asphalt, because the number of different chemical structures is unusually large. Whereas the exact chemical structure of natural asphalts depends on the area of origin of a particular sort of asphalt and other concomitant factors, the composition of bitumen hinges heavily on the chemical structure of the original crude petroleum as well as the specifics of the manufacturing process. As Wess, Olsen, and Sweeney (2004) explain, “the asphalt may be air-blown or further processed by solvent precipitation or propane deasphalting… the products of other refining processes may be blended with the asphalt to achieve the desired performance specifications” (p. 12). However, “while the manufacturing process may change the physical properties of asphalt dramatically, the chemical nature of asphalt does not change unless thermal cracking occurs” (Wess, Olsen & Sweeney, 2004, p. 7). To put it simple, asphalt consists of four major categories of compounds, namely saturated hydrocarbons, asphaltenes, polar and napthene aromatics (Lavin, 2003). The exact proportions of these chemical compounds in asphalt vary from one oil field to another or from one natural asphalt deposit to another (Wess, Olsen, & Sweeney, 2004).
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The polar and napthene aromatics are typically the main components of any asphalt. Vanadium and nickel, two elements used in the production of rechargeable batteries, can also be found in all sorts of asphalts in quantities that are typical for oil products. Unlike refined asphalts, sulfur compounds in natural asphalts may account for as much as 5% of content (Lavin, 2003). As for other elements, most asphalts contain about “79-88% of weight per cent (wt%) carbon, 7-13 wt% hydrogen, 2-8 wt% oxygen, and traces to 3 wt% nitrogen” (Wess, Olsen, & Sweeney, 2004, p. 7). Because of its appearance, bitumen is commonly mistaken for coal tar, which is “a thick black liquid produced by the destructive distillation of bituminous coal”, and vice versa (Lavin, 2003). However, the two substances have distinct chemical composition. Like bitumen, coal tar was used to bind road aggregates including gavel, sand and stone in the early 20th century. At the time, it was a ubiquitous by-product of the coal gas production process. Its heavy use in combination with macadam was responsible for the appearance of the word “tarmac”, which is a mixture of broken stones and tar, that is now used in common parlance to denote almost any paving material. However, its popularity as a binding material was diminished together with the debacle of the coal gas industry, as asphalt was becoming more and more available. One last thing concerning chemical composition of asphalt is that it is soluble in carbon disulfide among other things (Lavin, 2003).
As it has been mentioned earlier, asphalt has had a plethora of applications, ranging from caulking ships to building roads and beyond, as will be shown later in the paper. The success of the substance can be attributed to its useful physical properties. Among the most valuable properties of asphalt are its hardness, adhesiveness, ductility, viscosity, and moisture impermeability. While all these properties are endearing to users of asphalt, its hardness is perhaps the most important property. To gauge the hardness of asphalt, testers try to penetrate a sheet of viscous asphalt with a needle weighing 0.2 pounds in 5 seconds at the temperature of 77°F (Lavin, 2003). It is generally accepted that penetration of 0.04 inches is a good result of hardness for hard-coated asphalt, while penetration of 0.06 to 0.18 inches is a good result for roofing asphalt (Lavin, 2003). Adhesiveness is yet another endearing property of asphalt. Everybody who has touched asphalt in their lives knows that it is extremely sticky, just as resin, which is a tacky substance produced by some trees.
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The two substances are somewhat similar in this regard. The adhesiveness of asphalt is in fact the first thing that many notice about it. Asphalt has the capacity to adhere in a fluid or semi-fluid state to most surfaces to which it is applied, depending on the nature of each particular surface. However, the presence of water or even moisture can obstruct adhesion. Asphalt’s resistance to water has lured communities and municipalities in droves for decades. Unlike most of the road-building materials used up to the late 19th century, asphalted streets do not get soaked and are not slippery at the same time. What is more, in some conditions, asphalt may absorb large quantities of water without any detriment to its durability. Ductility is an equally important property of asphalt, which means that asphalt stretches well. Just as asphalt hardness, asphalt ductility can be measured through a series of tests. There are different ductility standards for different applications of asphalt, but generally it must be fairly pliant. Viscosity of asphalt matters both in situations of regular temperature during service and high temperatures to which the substance is subjected during processing and application (Wess, Olsen, & Sweeney, 2004). Viscosity of asphalts depends on the temperature of the environment and multifarious stress conditions. Generally, however, the higher the temperature of the environment, the higher the viscosity of asphalt is. It is imperative that asphalt should possess all these qualities in an ideal proportion. If used incorrectly, hardening of asphalt occurs at the expense of its viscosity and ductility. The rule works the other way round too. Most often, any deterioration of asphalt’s properties results in its hardening (Reid, 2015).
Production of Asphalt and Asphalt Products
The two greatest sources of asphalt are natural asphalt and refined asphalt. Whereas the former comes from natural deposits and does not need additional processing, refined asphalt, judging by its name, must be processed before it can be used in hot mix asphalt production. The production of refined asphalt is an elaborate process, but not as difficult as it may seem at the first sight. At a refining facility, a distillation process helps divide crude oil into several different fractions, which could be further used for the production of oil materials, such as kerosene, gasoline, diesel oil, naphtha, asphalt and so on. Asphalt is the heaviest component of crude oil, meaning that it does not vaporize during the process of distillation (Wess, Olsen, & Sweeney, 2004). That is exactly the reason why asphalt is often referred to as “the residuum produced from the distillation of crude petroleum” (Wess, Olsen, & Sweeney, 2004, p. 12).
Once crude oil is piped into a heat exchanger, the initial distillation process begins. It is thereupon placed in an atmospheric distillation tower for lighter fractions to evaporate after a range of condensing and cooling operations. The resultant mixture is then refined into kerosene, diesel oil, gasoline as well as some other light, medium and heavy distillates, with the topped crude that is, heavy residue left after the second distillation phase and is further refined into fuel oil and asphalt. At this point, the topped crude is either placed in a vacuum distillation unit or treated with a solvent extraction. Depending on the circumstances and chemical composition of particular asphalt, either of these two techniques can be used to produce asphalt cement.
At the request of clients, asphalt cement is often blended with volatile elements for the substance to be more malleable at lower temperatures. Such volatile elements, alternatively called cutting agents, evaporate during the construction process because of the premeditated exposure to heat and air (Yen & Chilingarian, 2000). The produced asphalt cement, either blended or not, is ready for use in construction, but it can have other forms too. For example, refiners often emulsify asphalt cement to make a liquid that would be easy to transport through pipelines, sprayed through nozzles and/or mixed with aggregates on construction sites. At this point, asphalt cement is refined into tiny droplets, which are immediately mixed with water and an emulsifying agent (Yen & Chilingarian, 2000). Alternatively, the produced asphalt cement may be crushed with the help of huge fine mesh sieves into granules of uniform size. This process is known as pulverizing to asphalt engineers. Pulverized asphalts are spread on the delivered surface and then mixed with aggregates and binding oil on the construction site. The heat and pressure from the special paving machines consistently amalgamate the pulverized asphalt with other components, and the substance hardens. Asphalts designed for uses other than paving may take an additional refining process known as oxidization. To oxidize, engineers at a refinery, an asphalt processing plant or other related facilities bubble air through asphalt heated to about 500°F for several hours (Yen & Chilingarian, 2000). As a result, the oxidized asphalt softens at higher temperatures, but water does not percolate through it anyway.
Usually, however, before being delivered to the end user, asphalt is mixed at a factory. It can be either cold mixed or hot mixed. The main difference between cold-mix asphalts and hot-mix asphalts is that the former does not involve the process of heating mixture constituents before application. In contrast, the production of hot-mix asphalts necessitates the heating of both asphalt cement and aggregates to ensure proper fluidity of the asphalt cement and eliminate moisture in the aggregate (Yen & Chilingarian, 2000). Conventional wisdom holds it that hot-mix asphalts endure harsher environmental conditions and other external pressures. Their weaker cold-mix counterparts are mainly used for paving secondary roads with light or medium traffic. Cold-mix asphalts often rely on emulsified and/ or blended asphalts as a basis. Hot-mix asphalts, on the other hand, are generally composed of reliable aggregates capped with asphalt cement. Hot-mix facilities can have a permanent location or they can be moved from one construction site to another. There exist two categories of hot-mix asphalt plants, which are batch mix plants and drum mix plants. Both can be stationary or portable. Whereas asphalt and binding agent need to be dumped into the pugmill of a batch-type facility in an ordered succession, they are added and blended all at the same time in a drum-type mixing plant (Yen & Chilingarian, 2000). Once the process is complete, cold-mix and hot-mix asphalts can be delivered to a paving or construction site, provided that they are located far away. The choice between batch-type and drum-type mixing plants is contingent due to a variety of factors, with production requirements and operating costs being the most weighty among them. Drum-type mixing plants hold incontestable preponderance over their batch-type rivals: they run at production capacities of up to 1,000 metric tons of asphalt per hour, while batch plants do not usually produce more than 500 metric tons per hour (Yen & Chilingarian, 2000).
Applications of Asphalt
Most of the uses of asphalt documented by historians have withstood the test of time, at least in rural and underdeveloped areas, as people still use it to caulk their boats and for other domestic purposes. But the most popular application of asphalt is, of course, road building. By the same token, asphalt is used for roofing, pipe coating, undersealing, water proofing as well as the manufacture of paints and membrane envelopes (Lavin, 2003).
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Apparently, the most widespread use of asphalt is attributed to the road building business. In the United States, for instance, 85% of all asphalt produced is intended to satisfy the needs of road builders (Karnes, 2009). Asphalt concrete used for the paving purposes generally consists of 95% aggregate and only 5% pure asphalt. According to a report released by the US National Asphalt Pavement Association & European Asphalt Pavement Association, “Europe has about 4,000 asphalt production sites and produces about 435 million metric tonnes per year”, while the US has roughly the same number of asphalt production sites yielding “about 410 million metric tons” annually (2011, pp. 5-6). Once delivered to a paving site, a special-purpose paving machine spreads asphalt over an even surface. The layered mixture is then pressed by a heavy rolling machine, alternatively called a compacting machine, to smooth the surface. Similar materials and techniques are used to build runways in the airports. Because the asphalt pavements can stand up to extreme static loads, they are also used for the construction of freight yards. The report mentioned somewhat earlier also suggests that all the asphalt removed from surfaces during infrastructure modernization processes either ends up as a material for roadbeds or in recycling factories, a rejuvenated old trend in the asphalt production industry (National Asphalt Pavement Association & European Asphalt Pavement Association, 2011).
Apart from road building, asphalt is used to manufacture roofing shingles, especially in the North America. Asphalt shingles are comparatively cheap and easy to install. Moreover, asphalt shingles appeal to the customer because of their durability, solar reflecting qualities, as well as resistance to winds, hail and algae (Yen & Chilingarian, 2000). Mastic asphalt, which is a thermoplastic substance with a higher content of pure asphalt than asphalt concrete, is increasingly used in the construction industry for tanking underground and sealing flatter roofs. For mastic asphalt to be truly impervious, it must be applied in layers 0.8 inches thick (Yen & Chilingarian, 2000).
Moreover, asphalt is used to waterproof wooden vessels, pipes and pipelines, fences and cattle sprays. Again, those who use asphalt for these purposes value it for its durability and resistance to corrosion. As mentioned earlier, asphalt can also be used to manufacture various paints, emulsion, varnishes and lacquers, which are then used in construction. Because of high asphalt content, all these paints and lacquers are durable and dry quickly. Asphalt-based paints and lacquers have gained an equally vast niche in the car industry and house construction, for they can be applied to various surfaces, including wood, iron, steel, plastic and glass (Karnes, 2009). In addition to all this, asphalts are also used in “lining irrigational canals, water reservoirs, dams, and sea defense works; in adhesives in electronic laminates; and a base for synthetic turf” (Wess, Olsen, & Sweeney, 2004, p. 5).
Asphalt is a truly versatile material. Its uses range from paving, roofing, pipe coating and undersealing to water proofing, production of paints and membrane envelopes, and many other domestic and industrial purposes. Since its rapid development in the late 19th century, asphalt has attracted a vivid interest in scientific quarters. As a result, the knowledge base has been constantly improving. However, because chemical composition of asphalt is not yet fully studied, the material may possess some hitherto-unknown physical properties when combined with other chemical agents. Hence, there are ample grounds to believe that asphalt will be used in other spheres in future, as the science progresses. For now, asphalt recycling, which declined in the early 20th century with the opening of new refineries, is rejuvenating once again, meaning that old pavements can be recycled into raw materials for building the new ones. Likewise, researchers are now on the prowl for new sources of raw materials for asphalt production. The production of the so-called synthetic asphalts from the sewage mud is a potential solution to the problem. New processes, machines and monitoring systems are also being researched for improvement. As the industry is poised for continuous modification, it is likely that asphalt cracking, rutting as well as oxidation and corrosion will be easier to prevent sometime in the near future.
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