HISTORY OF ROADS AND BITUMEN
 Via Appia - Rome, Italy
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To the South of Rome lies the fabled via Appia or the ‘Appian way’, built in 302 B.C., a stone paved road running 196 kilometres connecting Rome to the South Eastern city of Capua. Roman tour guides may wish us to believe is the oldest paved road in the world, but sadly for them, that it is not. However, it may well be the first paved road in the world connecting two cities.
At its peak, the Roman empire built more than 400,000 km of which 80,500 km were paved roads. These roads were a vital part of the development of the Roman state and enabled its armies and trade goods to move and communicate. The Roman empire, divided into 113 provinces was traversed by a network of 372 road links. Dated to approximately 450 BC, the laws of Twelve Tables, specified that a road shall be 2.45 m wide where straight and 4.90 m where curved. |
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Archaeology tells us that city roads were, indeed, the first paved roads in the world. The earliest of which date back to 4,000 BC in the cities of Harappa and Mohenjo-Daro, which were a part of the Valley Civilisation located in present day Pakistan.
Harappa, at one time lay on the banks of the Ravi river, a major tributary of the mighty Indus river. The main streets of Harappa ran from north to south and east to west intersecting one another at right angles. The streets were broad varying from 2.75 m to 10.36 m. They ran straight to a 1.60 km and were paved with fire burnt bricks. They were suitable for wheeled traffic. Lanes were joined with the streets. Each lane had a public welt. Street lamps were provided for welfare of public. |
Harappa - Indus Valley, Pakistan
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In Egypt, a stretch of 12 kilometres of road paved with slabs of limestone, sandstone and logs was constructed around 2600 to 2200 B.C., and may well be the first paved road in the history of the African continent. The road was built to facilitate the transportation of the heavy blocks of limestone to build the Pyramids of Gaza.
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In Europe, the earliest known paved road is the one found in Crete lined with flagstone and built in 2000 B.C.
For over five thousand seven hundred years, humans have tried to build better roads for ease of movement of people and transport. |
Bitumen
Petroleum or Bitumen Spring
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The word ‘Bitumen’ originates from Latin ‘Bithumen’ and found its way into the English language in the 15th Century. However, Bitumen has been known to humans for over four thousand years. The Sumerians called it esir, the Akkadians iddu, and the Arabs of Iraq sayali or zift or qar. It is the first petroleum product ever used by the human race.
Bitumen is a black or dark brown-coloured viscous material that is solid or semi-solid (depending on ambient temperature). This amorphous, cementitious material that can be found in different natural forms, such as rock asphalt, natural bitumen and tar, as well as bitumen derived from oil, which is referred to as petroleum bitumen. Bitumen, Tar and Asphalt are all derived from fossil fuels and are made up of complex hydrocarbons. Historically in the lands East of the Dead Sea and in Persia, natural bitumen springs and lakes were to be found, but the land between the Tigris and Euphrates rivers in Mesopotamia was littered with bitumen seepages, crude oil springs and even bituminous rock which released crude oil when heated. The Assyrians and Babylonians were the first people to use bitumen extensively, almost 4000 years ago, for building of structures such as the fabled Tower of Babel, and for waterproofing mud walls and roofs, as well as waterproofing hulls of boats. |
By about 350 B.C., the Egyptians found that the resin they used for mummification was running out and found bitumen to be a good alternate for the process. After the Egyptians ceased to mummify their dead, the demand for bitumen fell.
For nearly 12 centuries bitumen usage was largely restricted to the localities where it was found in nature, until in the year 675 A.D. when the Byzantines found its use in "Greek fire" in sea warfare; at the naval battle of Cyzicus - after which once more the demand for bitumen increased manifold. While raw bitumen occurs naturally in different forms, refined bitumen can be obtained through crude oil processing. In this process, bitumen is essentially the residue yielded through a distillation process of petroleum. Currently, the world relies on crude oil refining for production of bitumen. Bitumen obtained from refining process of crude oil is then sent to a bitumen plant for processing this bitumen so that in can be used in paving roads, payments, parking lots and runways for having specification that meets the demand of modern air and land transport and varied weather conditions. |
BITUMEN REFINING
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In a modern refinery crude oil, after a cleaning process, is sent to the Crude Distillation Unit (CDU), which is also called the Atmospheric Distillation Unit. In the CDU high atmospheric pressure is applied to the crude that helps in separating different fractions of crude oil. The following diagram explains the separation process in its simplest form:
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The first refining, primitive as it was, was probably carried out in Babylon. According to available texts, a hide was stretched over a kettle containing boiling bitumen so that liquid oil could be obtained by wringing the condensed liquid from the hide. Egyptian scientists obtained an oily product from natural bitumen by a process reminiscent of modern cracking techniques using two superimposed jars separated by a screen or sieve. The upper jar, filled with bitumen, was heated with a fire, and the oily distillate allowed to drip through the screen into the bottom jar buried in damp sand.
The world’s first commercial large scale refinery was built in 1856-57 in the Romanian town of Ploiesti and consisted, mostly, of cylindrical cast iron recipients under which a wood fire was lit. There onwards, it was just a matter of time and development of technology in tandem with the advancement of the automobile that led to the to the design of the latest technologies in the building of crude oil refineries.
‘Sour’ crude oils are the preferred over ‘sweet’ crude oil as feedstock for the production of bitumen as they give higher and more suitable Atmospheric Bottom Residue. The Atmospheric Bottoms or the bottom residue from Atmospheric Distillation Unit are then sent to a Vacuum Distillation Unit.
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The Vacuum Distillation Unit reduces the pressure in the Vacuum column to that less than the ambient atmospheric pressure thereby causing the Atmospheric Bottom Residue to boil and its various constituents to evaporate at different pressures & temperatures. The evaporated gasses are then trapped and condensed to produce Light Gas Oil and Heavy Gas Oil. The residue left at the bottom of the Vacuum Distillation Unit is called GUDRON, which is in fact raw bitumen that now needs to be processed into usable bitumen having specific properties to meet needs of different applications and climatic conditions.
Sometimes the Vacuum residue is sent to a Visbreaker Unit, which then thermally breaks or cracks large hydrocarbon molecules thermally and produces small quantities of LPG and gasoline. This is done to maximise the output of more valuable middle distillates. The residue obtained from the Visbreaker can be mixed with Gudron for production of Bitumen. There are different types of Visbreakers the most common of which are the Stroker and Coil types. The diagram alongside shows generally the flow process of a Visbreaker. |
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BITUMEN AND ROAD CONSTRUCTION
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The earliest use of Tar in the paving of roads can be found in the Muslim Empire of the 8th and 9th Centuries. The roads of Baghdad were considered most sophisticated and were built using bitumen obtained from bitumen and crude oil springs and lakes. Since fossil fuel was readily available, it was heated to very high temperature through a method called destructive distillation to produce bitumen, which was then used for road construction.
In the Western world during the early part of the 19th Century, a Scottish engineer, John McAdam, developed modern road-construction techniques by topping multi-layer roadbeds with a soil and crushed stone aggregate, packed down with heavy rollers to lock it all together. As automobile industry grew, contemporary asphalt roads capable of supporting the vehicles that emerged in the 20th century built upon McAdams' methods by adding bitumen, as a binder, to the final crushed stone layer. |
In the United States the first bitumen paved road was the Pennsylvania Avenue constructed in 1876.
The growth in the usage of bitumen is tightly linked to that of the automobile and aircraft industry. The speed allowed by automobiles required smoother and durable roads to be built. Reliance on imported Bitumen was costly and time consuming so, in 1902, bitumen production from crude oil distillation started in the United States. |
Only in the second half of the last century, with the progress of technology in the manufacture and placement of hot bitumen mixes, and given the considerable increase in heavy goods vehicle traffic and extensive air traffic that bituminous mixtures were used to form thick layers we recognise in roads and runways today. Most likely, close to 95% of the ‘paved’ roads in the world now have bituminous surfacing.
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Bitumen is used in road construction from cold mountainous roads to tropical areas with a lot of rain to hot desert roads. This is possible because there is a whole spectrum of bitumen, resulting from different processes for refining crude oil, products with well-defined and consistent classes of properties to meet the specific needs of different applications and climatic contexts of use, while accommodating differences in the composition of crude oils.
Physicochemical modification of bitumen, by addition or combination with polymers, has extended the performance of neat bitumen to today’s wide range of applications, including acting as an adhesive as well as waterproofing. The annual global consumption of bitumen is currently estimated at around 120 million tonnes and is growing rapidly. It is expected that by 2020 the global demand will top 250 million tonnes per year. |
DIFFERENCE BETWEEN ASPHALT, BITUMEN AND TAR
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Asphalt: is a mixture consisting of alumina, lime, silica and asphaltic bitumen. At low temperatures, it is in solid state and at high temperatures it is in liquid state. The different forms of Asphalt are:
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Bitumen: is obtained by the partial distillation of crude petroleum. It is also called as mineral tar and is present in asphalt also. It contains 87% carbon, 11% hydrogen and 2% oxygen. There are generally 5 types of Bitumen:
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Tar: Tar is a high viscous liquid which contains high amount of carbon content. General forms of Tar are:
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The following Table shows the general differences between Asphalt, Bitumen and Tar.
