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Components of Road Structure

By: Haseeb Jamal / On: Apr 15, 2017 / Definition
Components of Road Structure
 
 

A road structure consists of the following components;

1. Sub Grade:

Subgrade is the foundation of the road, thus its the lowest and most important component of road structure.

Construction:

  • If natural surface is above the formation level then the surface is cut down to proposed sub grade surface
  • If natural surface is below the formation level then the sub grade will be above the ground level
  • It should be constructed at least 60 cm (2ft) high from highest flood level of the area

Function of Sub grade:

  • Bears all the load thus acts as a foundation of road

  • Transfer load through grain to grain contact

Material:

Material should be;

  • Strong enough
  • Easily accessible in the surrounding vicinity
  • Cheap

2. SUB BASE:

Consists of:

  1. Upper Base Course
  2. Sub or Lower Base Course

Construction:

  • Constructed above the sub grade
  • Not needed if the sub grade is of very high strength
  • In case of flexible pavement upper and lower base courses are separated having different materials
  • In case of rigid pavement only upper base course is provided
  • Thickness varies from 7.5(3in) to 15cm (6in)

Functions of sub base:

  • Prevent rise of water or capillary action

Material:

  • Should be better than the material of Sub Grade
  • The Upper Base Course is made up of sand, gravel, and stone
  • The Lower Base Course is made up of cheaply available material i-e rock and stone fragments

3. ROAD BASE:

Due to quality of material used in the road base it is divided into

  1. Upper Road Base
  2. Lower Road Base

Construction:

  • Constructed above the Sub Base

Functions of Raod Base:

  • To avoid the distortion of wearing course due to its sufficient density
  • Supports the wearing course

Material:

  • In case of Upper Road Base the material is of high quality as the load intensity is high
  • In case of Lower Road Base the material is of high quality as the load intensity decreases

4. SURFACING:

It is the upper most layer of road cross section. It can be provided in one or two layers:

Construction:

Constructed usually in two layers

  • Binder Course
  • Wearing Course (It is the layer which is in direct contact with the tyres of the vehicle)

Functions of Surfacing of Road:

  • Prevent penetration of water in to the pavement
  • Binder Course binds the Wearing Course with the Road Base
  • Wearing Course provide a smooth riding
  • Saves the lower layers from abrasion and weathering effects of the moving vehicles

Material:

  • Made up of bituminous material
  • For Flexible Pavement asphalt concrete is used
  • For Rigid Pavements Reinforced Cement Concrete (RCC) is used
 

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