Road Pavement: Overview, Components, and Functions

A road pavement is a layered structure that forms the carriageway of a road and is supported by subgrade soil.

Generally, pavement design involves determining the thickness of the pavement or the layers that make up it, in order to resist the wheel loads of the traffic and transmit them safely to the foundation.

For this reason, the pavement must be strong enough to resist wheel loads, and the thickness must be adequate to transmit this pressure to a larger area of the soil below to avoid excessive deformation or shear failure. To meet traffic needs during the whole design period, a strong and stable pavement structure will be maintained.

An overview of road pavements

• It is primarily used for carrying heavy wheel loads of vehicular traffic.
• The purpose is to spread the vehicular load over a large area of the subgrade soil beneath the grade.
• For smoothing out the surface of the road pavement.
• The purpose of this is to prevent subgrade soil from being harmed by weathering agencies.

Pavement components include the following:

1. Sub-grade or formation
2. Sub-base course
3. Base course
4. Surface course or wearing course

1. Sub-grade or formation

Basically, the subgrade is the compacted natural soil that lies beneath the pavement layers, and it's the finished or compacted surface where the pavement lies. Also known as the formation, they form the foundation for pavement layers.
There are several types of sub-grades, depending on the terrain, including embankments, cuttings, and natural ground levels. The California bearing ratio test (CBR) measures the load-bearing capacity of a subgrade structure.
Suitable, strong, and inexpensive material shall be used for subgrade.

Subgrade functions

1. Supporting the road pavement adequately and uniformly.
2. Ultimately, to carry the entire load of pavement, including a load of traffic transmitted through the pavement, and distribute that load over a larger area below the pavement.
3. In response to excessive stress, behave elastically and adapt.

2. Sub-base course

Sub-base refers to the layer of granular material between the subgrade and base course of a road pavement.
This layer is added to sub-grades that are of poor quality. Compared to natural gravel, quarry waste, cinders, sand, and stabilized soil, it is constructed from comparatively cheaper materials.
There is no sub-base layer for cement concrete roads. The material is usually needed for flexible pavements built on fine-grained soils.

Sub-base course functions

1. The subgrade should be strengthened so that it can bear more weight.
2. The aim of this project is to improve drainage conditions and to decrease subsoil water capillary rise.
3. To prevent the capillary rise of water in frost-affected areas in order to eliminate frost heave.
4. The material serves as a filler and enhances the pavement's thickness at a low cost

3. Base course

In pavement, the base course is a double layer of boulders or bricks placed over the subbase or immediately over the subgrade in the absence of a sub base.

Base course functions

1. High shear stresses develop because of traffic impacts on the wearing course.
2. The sub-base and sub-grade lie beneath the pavement, which acts as the foundation for the pavement.

4. Surface course or wearing course

The top layer of a surface course is directly exposed to traffic, consisting of multiple layers of the pavement structure. Surface courses are also called wearing courses. The bituminous surface of flexible pavements acts as the wearing surface, whereas the concrete surface of rigid pavements serves as the base course and the wearing surface. By reducing water percolation and providing an abrasion-resistant and antiskid surface, the wearing course reduces water percolation and provides a safe riding surface.

Surface course or wearing course functions

1. The purpose is to provide a smooth and uniform rigid surface.
2. To resist abrasion from traffic.
3. As a preventative measure.
4. The function of the pavement is to act as a structural component.