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Road Construction

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Road construction is perhaps one of man’s earliest forms of construction. Roads are defined as routes or paths that begin at one destination and lead to another. The modern day road is defined as a paved or easily accessible path, made so by the use of modern day road construction equipment such as hydraulic excavators, motor graders, asphalt pavers, wheel loaders and vibratory compactors.

Roads that lead into cities and towns can also be referred to as streets, avenues, boulevards, and more. Any route that has a navigable destination can be referred to as a road, including those that are unpaved or dirt.

Wheel loaders are just one of many pieces of heavy-duty equipment used in road construction.

Contents

[edit] History

[edit] Roadways a Necessity for Growing Cities

While paths leading to water and food sources have been traced back as far as 4,000 B.C. in the form of paved stones and later as logs and bricks in some communities, roadways began to take off when civilization formed into a network of cities and towns. Foot was the most common form of transportation, and later, the horse and buggy. Roadways had to be easily navigable and accessible. The oldest such road to date is in the English kingdom of Wessex; it has been traced back as early as 2700 B.C. The road, which begins at the River Avon and ends at Heel Stone near Stonehenge is 1.9 miles (3 km) long and is said to be the origin of the word "avenue." [1]

Building roadways quickly became the responsibility of cities as more and more people flocked to city centers for jobs and food. Soon, roadbuilding was recognized as a crucial way to map the world; thus began a series of road construction projects in Rome. The project became so expansive that the distance of the roads constructed in Rome could run around the equator twice.[2]

[edit] Early Road-building Methods

Some of the first roads in England were built by men such as John Metcalfe, a Scotsman who built roads with a distance of 180 miles (290 km) in Yorkshire, England. Despite being blind, Metcalfe drained roads and built them with three layers consisting of gravel, excavated road material, and large stones. [3]

Modern tarred roads in England were also the work of two Scots, engineers Thomas Telford and John Loudon MacAdam. Telford came up with the system of raising the road’s foundation in order to prevent flooding. He also devised methods of analyzing the thickness of stones, road traffic, road alignment, and gradient slopes. This allowed him to employ methods that would improve the way roads were built, using better, more sustainable materials that could withstand weather and traffic conditions. His design eventually became the standard for roadbuilding projects.

Similarly, MacAdam designed a method that involved laying broken stones in symmetrical patterns. He developed the idea of covering the large stones with aggregate in order to create a solidified, hardened surface. His design, known as the “MacAdam road” was crucial to the evolution of roadbuilding methods.[4]

[edit] Establishing Trading and Transportation Routes in the 19th Century

Road construction became increasingly popular in Europe as international trading for commodities became an ever-expanding market.

At the end of the 19th century, early roadbuilding machines such as the motor grader, scraper, and excavator appeared. Even the plow in its primitive form was used for roadbuilding. The excavator or shovel, a steam-driven tool with a bucket used for digging, was invented by William S. Otis when his contracting company Carmichael and Fairbanks took on a railway project. In a bid to earn more commission for the work they could produce, Otis invented the Otis Shovel, a machine with a one-cubic yard (0.8-m3) dipper with a partial swing. The 1835 invention built in Canton, Massachusetts, remains one of the most important inventions in the construction industry and has become crucial in processes such as roadbuilding. Its invention has prompted other pioneers to produce machines capable of earthmoving.

It was the building of the railway and in the use of steam power during the Industrial Revolution that kick-started the development of most of the machines used for road construction. Although the railway was a path of a different sort, it was still evidence of a need for growing cities and towns throughout the western world—Europe and North America—to build passageways that could transport goods and masses of people. The need for such passageways prompted more developed machines, utilizing steam power, such as James Watt’s 1765 steam engine, in order to produce results with speed, accuracy, and power, that could only be dreamed of in the past. Such earthmoving inventions, although prompted by building the railway, led to roadbuilding advancements as well. Eventually diesel, hydraulics, and pneumatics replaced steam as a source of power for these machines, granting them even more speed, power, and accuracy.

[edit] First Asphalt Roads

The first asphalt roads appeared in 1824 on the Champs-Elysees in Paris. Asphalt soon became widely used throughout Europe and North America and is now used on 96 percent of all paved roads and streets in America; that is about two million miles (3.2 million km) of road covered with asphalt. The first use of asphalt on modern-day roads comes from the work of Belgian immigrant Edward de Smedt at Columbia University in New York City. De Smedt created an asphalt material with maximum density in 1872, and used this material while constructing roadways in Battery Park and on Fifth Avenue in New York in 1872. It was also used on Pennsylvania Avenue in Washington D.C., five years later.[5]

Some of the first roads in North America were constructed in order to carry more than 300,000 people from the old world into the new. The first roads, the Santa Fe Trail linking to a Mexican highway to Santa Fe, New Mexico, and the Oregon Trail were made navigable by wagons in the 1800s.[6]

[edit] Today

Today there are 20 million miles (32.3 million km) of roadway in the world (as of 2002). The U.S. holds the record for the highest number of roadways, measuring 3.9 million miles (6.4 million km) combined, as of 2005. The European Union and India follow with 3.3 million miles (5.3 million km) and 2.1 million miles (3.3 million km) of roadway respectively.[7]

Roads continue to play a vital factor in modern civilization, with the majority of roads being constructed according to city and national standards.

[edit] Process

[edit] Planning

Before earthmoving machinery can be put to work, the land undergoes a series of surveys to determine the route, distance, direction, and elevation. Previously, the distance was measured with an iron chain that extended 66 feet (20 m), also known as Gunter’s Chain. Eighty chains were used to measure one mile (1.6 km) and ten square chains would measure an acre (0.4 ha). A compass was used to measure the direction that the constructed road would take.[8]

Other important factors in considering the construction of a road is what materials would be used and what method would be employed. Some experts say that all some roads require is a scraping off of the top layer of soil and laying four inches (10 cm) of soil.

[edit] Clearing

The first task in the roadbuilding process is to clear the road of any obstructions that may disturb the pathway. This may include removing things such as trees, bushes, stumps, and rock. In the early days of construction, these obstructions were removed by hand or with the help of horse-drawn plows. After the construction of the Erie Canal, a workman invented a stump-puller that could remove stumps and trees. Today, they can easily be removed by a hydraulic excavator, which digs the items out of the soil with its long, extended arm and bucket, removing the tree or rock.

[edit] Leveling

The next step involves leveling the land. Before the advent of modern machinery, this task was undertaken with hand-held rakes and hoes, or even primitive scrapers that were hauled by horses and oxen. Today, this is completed by wheel loaders that remove larger chunks of dirt and rock and leveled out by motor scrapers. Motor scrapers usually consist of a scraper blade that cuts into the dirt, removes it, and hauls it into the machine’s bowl. The motor scraper, depending on the type, may be assisted by a crawler tractor or similar machine to assist in loading the materials.

Once the road is leveled, a motor grader is used to create a more even, flat surface. The grader typically smoothens the surface before the application of asphalt or other materials.

[edit] Materials

[edit] Gravel and Asphalt

Other materials can be used for road construction, although asphalt is one of the most common. Some experts recommend using a geotextile membrane under a soil base to strengthen the surface. The base is then covered by about nine inches (23 cm) of soil, followed by six inches (15 cm) of coarse gravel or asphalt. A four-inch (10-cm)  thick layer of crushed gravel, also known as “bank-run gravel”, is deposited atop the base.[9]

Gravel roads are typically built at a width of 12 to 20 feet (3.7 to 6.1 m) and should be graded as designed by the engineer.

[edit] Sand and Clay

When preparing the sub-grade with materials such as sand and clay, the job is best completed on a dry roadbed that has been plowed and harrowed by a disc harrow. The disc harrow pulverizes the clay to a depth of about four inches (10 cm), at which point the clay should be relatively dry. The roadbed is then leveled by a grader.

The sub-grade material consists of about six to eight inches (15 to 20 cm) of sand, which is evenly deposited and compacted on the dry road surface. Both the sand and clay undergo a mixing process that is carried out by a spike or spring-tooth harrow. The road is consolidated by sprinkling and harrowing it until sand and clay are sufficiently mixed. Once this has occurred, a road machine produces a crown and smoothes the road’s surface. Sand and clay materials can be compacted further by a roller to the point where they are hardened and the tracks of machines no longer shows. Rollers used for this project typically weigh between six and ten tons.

Maintenance of roads constructed with sand and clay are generally very easy. As long as potholes are filled and the surface is kept smooth, the road should fare well against traffic and weather conditions. Some pulverization or harrowing may be necessary but the creation of a crown (if necessary) and drain ditches, remove the risk that face all roads.

[edit] Stones

Some road surfaces are made up on stones. The process for this is somewhat similar to pavement and asphalt surfaces. In employing stones, each unit is spread over the surface in a symmetrical fashion and settled with a sledgehammer. The larger stones are infiltrated with smaller ones to ensure the crevices are filled and compacted. Atop the stones, hard clay or gravel is used to cover the stones. The clay or gravel will eventually wear away, at which point the stones are in need of a breakage, a task that is done with hammers. The stones should be broken a number of times, usually four, in order to ensure the sufficiency of the stone road.[10]

[edit] Maintenance

[edit] Crowns

Maintenance of gravel roads can be as easy as scraping off the layer of material that covers the road area and replacing it with about four inches (10 cm) of gravel. Sometimes this is not enough and factors such as weather conditions and improper construction can lead to breakages and incorrect sloping, requiring further maintenance.

There are certain features of roadbuilding that can aid in the maintenance and longevity of a road. Gravel two-way roads are recommended to meet at a crown, a raised A-shape, or midpoint section of a road. The pitch of road crowns should have ½ to ¾ inch (1.3 to 1.9 cm) for every foot (0.3 m) of road that extends out from the crown. Crowns can be constructed with a blade, a tool with the ability to scrape and form the crown, while work on the roadway is undertaken by machinery. Although it is recommended that roads with two ways should have crowns, single-lane roads do not require them. The best time to pursue reshaping the road is after rainfall so the surface is looser and the amount of dust is reduced, allowing the ground to compact more effectively following a grading.[11]

Grading is completed by positioning the blade perpendicular to the direction in which it is operating. The blade then cuts deep into the soil in order to fill bumps and level potholes. A motor grader is used to push gravel into the road’s center where the crown is formed.

[edit] Ditches

Other features of roadbuilding crucial to maintenance are ditches, which are essentially trenches that cling to the sides of a road and help rainwater run off the road. Side-of-the road ditches should have a flat bottom or contain parabolic shapes, as opposed to the v-shaped ditch, which only delays water flow rather than remedy it. Ditches should follow the convention of being shallow and wide rather than narrow and deep to remove safety and hazard concerns. Ditches typically measure four to five feet (1.2 to 1.5 m) wide and one to 1.5 feet (0.3 to 0.5 m) deep.

[edit] Equipment List

[edit] References

  1. Cohrs, Heinz –Herbert. The Classic Construction Series: 500 Years of Earthmoving. KHL Group: Wadhurst, 1995.
  2. Cohrs, Heinz –Herbert. The Classic Construction Series: 500 Years of Earthmoving. KHL Group: Wadhurst, 1995.
  3. Bellis, Mary. The History of Roads and Asphalt. About.com, 2008-09-29.
  4. Bellis, Mary. The History of Roads and Asphalt. About.com, 2008-09-29.
  5. Bellis, Mary. The History of Roads and Asphalt. About.com, 2008-09-29.
  6. Lay, M.G. and Vance, James E. Ways of the World. Rutgers University:1992.
  7. Rank Order - Roadways. CIA, 2008-09-29.
  8. How to Build a Road: A 19th Century Primer. University of Virginia, 2008-09-29.
  9. Keller, Des. Build a Road That Will Last. The Progressive Farmer, 2008-09-29.
  10. How to Build a Road: A 19th Century Primer. University of Virginia, 2008-09-29.
  11. Keller, Des. Build a Road That Will Last. The Progressive Farmer, 2008-09-29.