What are Pavements? How to Design a Pavement?

A highway pavement is a structure consisting of superimposed layers of processed materials above the natural soil subgrade, whose primary function is to distribute the applied vehicle loads to the subgrade. The pavement structure should be able to provide a surface of acceptable riding quality, adequate skid resistance, favorable light reflecting characteristics, and low noise pollution. The ultimate aim is to ensure that the transmitted stresses due to wheel load are sufficiently reduced, so that they will not exceed bearing capacity of the sub- grade.

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Two types of pavements are generally recognized as serving this purpose, namely flexible pavements and rigid pavements. This gives an overview of pavement types, layers and their functions, cost analysis. In India transportation system mainly is governed by Indian road congress (IRC)

Requirements of a pavement

An ideal pavement should meet the following requirements:

1. Sufficient thickness to distribute the wheel load stresses to a safe value on the sub-grade soil
2. Structurally strong to withstand all types of stresses imposed upon it
3. Adequate coefficient of friction to prevent skidding of vehicles
4. Smooth surface to provide comfort to road users even at high speed
5. Produce least noise from moving vehicles

Types of pavements

Flexible pavements

Rigid pavements

Factors which affect the selection of pavement type

1. Initial cost
2. Availability of good materials
3. Cost of maintenance
4. Environmental conditions
5. Availability of industrial wastes
6. Traffic intensity

PAVEMENT DESIGN PROCESS

1. Preliminary Pavement Design

A preliminary pavement design needs to be performed during the early phase of project development. This step ensures that a viable design is generated, balancing risk while ensuring adequate funding rather than allowing the project cost to dictate the pavement design. Preliminary design considerations are then discussed at a district level Pavement Design Concept Conference.

2. Pavement Design Standard Operating Procedure(SOP)

Communication between the district pavement engineer, planning staff, maintenance staff, construction staff and area engineers is key to designing, constructing, and maintaining quality pavements.

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General Pavement Design Considerations

Title 23 CFR 626 establishes the following requirement: "Pavements shall be designed to accommodate current and predicted traffic needs in a safe, durable, and cost-effective manner." The regulations do not specify the procedures to be followed to meet this requirement. Instead, each State Highway Agency (SHA) is expected to use a design procedure that is appropriate for its conditions. The SHA may use the design procedures outlined in the "AASHTO Guide for Design of Pavement Structures," or it may use other pavement design procedures that, based on past performance or research, are expected to produce satisfactory pavement designs.

Shoulder Structure

Research results have shown that widening the right pavement lane and placing the edge stripe 0.5 m from the outside pavement edge significantly improves both asphalt and concrete pavement performance by providing edge support. The SHAs are encouraged to use paved shoulders where conditions warrant. Shoulders should be structurally capable of withstanding wheel loadings from encroaching truck traffic. On urban freeways or expressways, strong consideration should be given to constructing the shoulder to the same structural section as the mainline pavement. This will allow the shoulder to be used as a temporary detour lane during future rehabilitation or reconstruction. On new and reconstructed pavement projects, the SHAs are encouraged to investigate the advantage of specifying that the shoulder be constructed of the same materials as the mainline, particularly on high-volume roadways. Constructing shoulders of the same materials as the mainline facilitates construction, reduces maintenance costs, improves mainline pavement performance, and provides additional flexibility for future rehabilitation.

Design Methods

1. Design of Flexible Pavement by Group Index Method
2. California Resistance Value Method
3. Triaxial Method

Software used for the design

AASHTOWARE

ROAD CEM

• roads

• pavement

Pavement design