Construction phases of Bituminous/Asphalt roadsArticles > Construction phases of Bituminous/Asphalt roads
Stages of construction of a bituminous road:
Bitumen Road, also called Asphalt road is the very smooth and soundless road. This type of road is a masterpiece of civil engineering. The construction of this road goes through a number of complex phases. The first phase of this road is “Preparation of Base Course”. In this phase, the irregular landscape is graded with the help of a grader machine. The landscape is once leveled, then, murrum consisting of fine gravels and soil is placed on the road. This layer is compacted by means of rollers and compactors. After compacting it well, a layer of larger border of stone is placed. The spaces of the border are filled with screening. Again the rolling work is conducted. Water is thrown all through this process. Now the second phase starts. The second phase of the construction of the road is the Placement of a Bituminous coat. The hot and molten bituminous is showered on the border filled with screening. The third phase of the construction starts with the Placement of a bituminous mix. The bituminous mixed consists of concrete mixed with bitumen. This layer is of 3 to 5 inches thickness. The layer of the bituminous mix is placed either by machines or by hands.
The fourth phase of the construction of this type of road starts and ends at rolling work. The rolling work is conducted by a roller machine. The purpose of rolling is to compact the road.
The construction of a bituminous road goes through the following five phases. Each phase follows the previous one in a definite order. The construction phases of the bituminous road are as follow:
- Surface Work
- Application of Coats
- Placing of Bituminous Mix
- Quality Control
(1). Surface Work:
The landscape is not available in a smooth form. The landscape needs to be smoothened while constructing a road. With the help of graders and bulldozers, the cutting and grading of the land surface are done. The rocks and hills are cut by means of heavy machinery. The uneven surfaces are filled with excavated soil. The highlands are cut to level accordingly.
The plane surface is, then filled with murrum. Murrum is the soil mixed with stone gravels. The murrum is scattered and planed with the help of graders. Water is thrown on the plane murrum surface to moisten the material, so as to compact. The rollers are run on the moisten material to compress it. After evening this surface, a layer of about 3 -4 inches of the border is placed. The spaces of the border/gravel are filled with screening. The border filled with screening is again compacted by means of rollers and compactors. The compacted layer of the border is fully moistened with water again and again and again, rolled over by rollers simultaneously. The moistening and compaction strengthen the bonding between the stone border, screening, and fine gravels.
(1). Application of Coats:
Once the surface work or the earthwork is completed, the second phase of the construction starts. The 2nd phase is known as the Coating Phase. Before starting the coating phase, the surface of the border layer is cleaned and washed by means of water and wiper. The cleaned surface is then covered or coated with the molten bitumen. The molten bitumen is showered on the road with the help of a bitumen sprayer. The purpose of the bitumen spray is to strictly stick the bitumen mix to the border surface.
(3). Placing of Bitumen Mix:
Bitumen Mix is composed of bitumen and rock gravels. The function of bitumen is to create strong bonding among the gravels. The hot mixed molten bitumen mix is placed on the road and scattered with the help of scattering equipment. If the bitumen mix is placed by laying machine, then it needs not to be leveled further. The machine has already leveled it.
(4). Rolling Work:
The rolling work is conducted with the help of rollers. Rollers are of two types. One is a Cylindrical Roller and the other is Pneumatic Tire Roller with a Cylinder Roller. The capacity of a roller is 10-12 tones. A pneumatic tired roller, which has an efficiency of 15-30 tones, exerts a pressure of 7 kg per sq. cm. The rollers are run to and fro very frequently in order to compress the bituminous mix. Water drops are poured on the bituminous mix in order to avoid sticking it with the rolling cylinders of the roller.
(5). Quality Control:
Quality control is carried out by the inspection team of the road. A small piece of the road is cut at road edges, to check the bitumen and aggregate. A good quality road prevents accidents on road due to damage.
The finishing materials used for asphalt pavement are typically liquid asphalt sealer, also known as emulsified asphalt, and paint for the roadway striping. The finishing seal-coat must be re-applied year after year to keep water from intruding into the surface. If the finishing seal-coat is not done, the rainwater intrudes into the spaces of asphalt or bitumen mix. The intruding water weakens the boding of the road material. Moreover, the intruded water reaches the earthwork of the road. As the water mixes with the earthwork of the road, the soil becomes mud and clay, thus softening the downside layer of the road. The heavy traffic passes over the soft-based road, compresses, and damages the road. The finishing of the road is as necessary as the construction of the road itself. After completing the finishing work, roads studs and road marking paint is done, to further secure the road for traffic. The installation of road studs, eye cats, and marking paint is also included in the finishing of the road.
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