Water Bound Macadam Road - an example of a Flexible pavement

Introduction:
The road pavement is categorized based on the type of materials used and its behavior under the load. The three types of pavement are Rigid pavement, Semi-rigid pavement, and Flexible pavement. Water Bound Macadam (WBM) is a type of pavement mostly used in rural areas, where the traffic load is less.

Flexible pavement:
Flexible pavement is also called bituminous pavement. In this pavement, the bituminous material is used as a binder to hold the aggregates together. The flexible pavement moves and deforms under the load and distributes the load to the subgrade. The flexible pavement has a thickness of 150mm to 300mm.

Water Bound Macadam:
Water Bound Macadam is a type of flexible pavement, where the aggregates are bound together by a film of stone dust and water. The WBM pavement consists of three layers: Sub-base, Base course, and surface course. The sub-base layer is made up of broken stones of size 100 to 150mm, the base course is made up of broken stones of size 63 to 75mm, and the surface course is made up of broken stones of size 25 to 50mm. The thickness of each layer varies depending upon the traffic load.

Advantages of WBM:
- It is an economical pavement for low traffic areas.
- The maintenance cost is low.
- It has good drainage characteristics.

Disadvantages of WBM:
- It is not suitable for high traffic areas.
- It has a rough surface, which is uncomfortable for driving.
- It is prone to erosion and damage due to rainwater and heavy traffic.

Conclusion:
Water Bound Macadam is a type of flexible pavement, where the aggregates are bound together by a film of stone dust and water. It is an economical pavement suitable for low traffic areas. However, it is not suitable for high traffic areas due to its rough surface and prone to erosion and damage.