Flexible Pavements and Components

Components of Flexible Pavement

Components Of Flexible Pavements

Flexible Pavements

It is one of the most convenient,safe and cost effective method of road construction throughout the world. It consists of HMA ( Hot Mix Asphalt) layers on the top surface of the road which is flexible due to contain of bitumen content and it is black in color, that’s why it is called flexible pavement or black top pavement.

Components of Flexible Pavements

Flexible pavements are consists of the following Components/Layers:


It is the natural soil which acts like foundation for the pavement. The stability of pavement depends upon Subgrade. In order to stabilize the road, the subgrade is compacted to achieve its maximum density. Through compaction all the voids are removed from the soil particle. To achieve required compaction, various laboratory test has to be conducted e.g FDT ( Field Density Test), Moisture Content etc.


It is the layer of coarse aggregate of the size 0.5″ to 1″. It is an optional layer and provide a base and level surface for its subsequent layer. It can increase the load carrying capacity of the road.


It consists of broken rocks or coarse aggregate of size 2.5″. Its is compact by roller to thoroughly compact the layer. Most of the strength provides by this layer of the pavement. To fill all the voids among the aggregates a thin layer of stone dust is provided on it and then water is sprinkle on it and again compact it. Then by brushes the surface dust is removed.



Binder is mixture of Bitumen and Lubricating oil. It is sprayed on the Base Course layer and then traffic is on for 3 to 4 months to thoroughly compact the pavements components and any rutting that can cause in future. After that another thin layer of bitumen called tack coat is sprayed on it in order to make a perfect bond between Base course and subsequent layer.


After Binder Course and Tack Coat, Asphalt Wearing Course is laid on it and it is the final layer of the flexible pavement. Its normal thickness is almost 4″ to 6″ and then compact it by roller. Its thickness can be increase according the traffic capacity. After that seal coat is sprayed on it which consists of Bitumen and emulsion in order to fully seal the wearing course. Th e rain water cannot percolate through Seal Coat.


Components of Flexible Pavements

Watch the Video:

Flexible & Rigid Pavements

Transportation Engineering



It is a subdiscipline of civil engineering that involves planning, design, and management of transportation systems that provide for the safe and efficient movement of people and goods.

                Transportation engineers focus on designing new transportation systems and upgrades to highways, urban roads, airports, railroads, and water transport networks. To facilitate their designs, engineers need to collate and analyze data on traffic flows, accident rates, and other statistics. They also have to take future demand for transport into account while considering the results of impact studies and local, state, and federal transportation policies.

Transportation Engineering
Transportation Engineering

Scope of the Field

Transportation engineering is vast and can allow for excellent career opportunities. Of the 18 technical divisions within the American Society of Civil Engineers (ASCE), six are related to transportation engineering:

  • Air transportation
  • Waterway, coastal, port, and ocean
  • Highway
  • Pipeline
  • Urban transportation
  • Aerospace

Scope According to Specialties 


Graduates with a master’s degree in transportation engineering can concentrate on one of several specialties. For example, highway engineers develop their expertise in the following areas

  • Analysis of traffic patterns, traffic flows, and collision rates during highway and road design
  • Planning, design, construction, and operation of highways and roads, as well as their associated bicycle and pedestrian facilities
  • Alignment, design, and construction of pavement and other roadway elements
  • Estimation of public transportation requirements and the associated costs
  • Design and construction of bridges, retaining walls, and tunnels
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Highway Engineering


Railroad engineers focus on the design, construction, and operation of railroads and mass transit systems. Their goal is to develop a safe railroad transportation system to meet future demand, working with federal officials to ensure the rail system meets the nation’s transportation requirements.

Railway engineering


Airport engineers become experts in the design and construction of new airports and upgrades to existing facilities. This is a special transportation engineering application where engineers must fulfill the following responsibilities:

  • Take into account the physical impact of aircraft and air traffic volumes to design airport facilities
  • Analyze wind patterns to determine runway orientation
  • Design the size of runway borders and safety areas
  • Determine wingtip clearances for boarding gates
Airport Engineering

Port & Harbor

Port and harbor engineers specialize in the design, construction, and operation of ports, harbors, and canals. As with the other branches of transportation engineering, the analysis of traffic volumes and maritime forecasts is essential for the design process.

Ports & Harbor Engg

The Transportation Planning Process

For any transportation project, engineers cannot take a purely clinical look at moving people and goods when planning new developments. Any new facility may have an impact on an area’s growth and economic activity, as well as the quality of life of the surrounding community. This means that transportation engineers must also consider the well-being of society in their plans.

Most local governments have a metropolitan planning organization (MPO), which is a policy-making body consisting of representatives from local government and transportation agencies. An MPO has the following main functions:

  • Establishing an impartial setting for regional decision-making
  • Identifying and evaluating alternatives for transportation improvement, using appropriate planning studies
  • Preparing and maintaining a long-term transportation plan for the metropolitan area
  • Developing a short-range program for transportation improvement
  • Involving the public in transportation planning


Career Prospect

To be successful in transportation engineering, strong organizational and analytical skills are required. Typically, a bachelor’s degree in civil engineering is a prerequisite for entry to a master’s degree program in transportation engineering, although many schools enable prospective students to complete bridge courses to qualify.

Transportation engineers typically secure employment with private engineering companies or engineering consulting firms. State and federal governments also employ transportation engineers in their relevant departments and agencies.Careers