Water bound macadam road layers or foundation | WBM road specification | What are the components of WBM road?

Water bound macadam road layers or foundation: -

Water bound macadam road foundation, also known as WBM, is a type of road construction technique that involves a mix of stone aggregates and fines in different layers to create a strong and durable surface.

WBM road layers

The foundation of a water bound macadam road is made up of several layers.

1. Sub-grade - The first layer is the sub-grade layer which is the natural soil or aggregate layer before any modification.

Function - The sub-grade layer is the natural or prepared surface on which the pavement is constructed. Its primary function is to provide a stable and even surface for the pavement layers.

2. Sub-base - The second layer is the sub-base layer made up of graded aggregates in varying sizes, thicker in depth and laid to a specific level of compaction.

Function - The sub-base layer, placed above the sub-grade, is primarily designed to improve the structural capacity of the pavement system. It helps in distributing the load evenly and reducing the deformation of the sub-grade. The sub-base layer also serves as a drainage layer by allowing water to permeate through the pavement layers.

3. Base course - The third layer is the base course layer, consisting of larger stones (2-4 inches), smaller than the subbase. This layer is then compacted with a roller to approximately 85% density.

Function - The base course layer is a primary layer in the pavement structure that provides additional support to the pavement system. It is placed on top of the sub-base layer and helps in distributing the traffic loads uniformly. The base course also acts as a barrier to prevent the water from entering into the lower layers of pavement.

4. Wearing course - The fourth layer, called the wearing course, is made up of finer stones, up to 1 inch in size. Finally, a 1/8 inch layer of screenings is then used to fill up the voids and provide a smoother surface.

Function - The wearing course layer is the topmost layer of the pavement structure designed to provide a smooth and durable surface for vehicles to travel on. The wearing course layer provides skid resistance, noise reduction, and also protects underlying pavement layers from the effects of weather and traffic.

The materials used in the construction of WBM roads are locally sourced from quarries and are cheap compared to asphalt and concrete. The construction of WBM roads offers cost-effective solutions to rural communities in developing countries with limited resources. In addition, WBM provides high resistance to heavy traffic and adverse weather conditions. However, it can lead to erosion and dust pollution if not adequately managed.

In conclusion, the water bound macadam road foundation offers a viable alternative to traditional asphalt or concrete construction, especially in rural areas. WBM provides a strong and durable road surface, is cost-effective to construct, and can be done with basic equipment and local resources.

WBM road specification: -

WBM (Water Bound Macadam) Road specification, then here are its features:

1. Layer Formation: The WBM road consists of three layers of stones or aggregates.

2. Stone Size: The stone size should be 20mm to 60mm.

3. Surface Drainage: The WBM road should have a slight slope from the center towards the edges to prevent stagnant water.

4. Binding Material: Binding material like clay, sand, or silt should be used to bind the stones and aggregates together.

5. Thickness: The thickness of the WBM road varies depending on traffic intensity. For low traffic areas, 100mm thick WBM is adequate, while for high traffic areas, it should be 200mm thick.

6. Compaction: The final layer of WBM road should be thoroughly compacted to achieve maximum density.

7. Maintenance: Regular maintenance is necessary to keep WBM roads in good condition. The maintenance includes re-surfacing, re-compaction, and patching up potholes.

Note: Always check the local or regional regulatory compliance of road specifications.

What are the components of WBM road?

WBM (Water Bound Macadam) road is a type of road construction that is popular for its durability and low cost. The components of WBM road are:

1. Subgrade: The natural soil or gravel layer beneath the road is known as subgrade.

2. Sub-base: A layer of crushed stones or gravel is used to provide stability to the road. The sub-base can be made from materials such as sandstone, limestone, or granite.

3. Base course: The next layer above the sub-base is the base course, which is made of broken stones or gravel. The thickness of the base course can vary depending on the traffic load.

4. Binder course: This layer is composed of smaller stone pieces than the base course. The binder course provides a smooth surface for the top layer.

5. Surface course: The topmost layer of WBM road is the surface course. The surface course is made up of stones of a small size that are evenly graded. The surface course provides a smooth and durable surface for vehicular traffic.

6. Drainage: Proper drainage is essential for the longevity of WBM road. Drainage is ensured using channels, porous ditches or culverts depending on the terrain and climate conditions.

7. Binding material: Tar or cement is used to bind the different layers of WBM road together. The binding material helps to keep the stones in place and creates a cohesive surface.
What is the size of WBM Grade?WBM roads aggregates are divided into 3 grades according to their size. Grade 1 - particles of size 90 mm to 40 mm. Grade 2 - particles of size 63 to 40 mm. Grade 3 - particles of size 50 to 20 mm.

8. Shoulder: A water-bound macadam road shoulder is a type of road shoulder that is made up of compacted layers of crushed stone and gravel. It is specially designed to withstand the weight and pressure of vehicular traffic, particularly heavy trucks. The road shoulder is built with a sloping surface to allow for proper drainage of rainwater and prevent surface water from accumulating on the road surface.

Que. What are the types of macadam road?

Ans - Macadam roads can be classified into following types:
i. Water bound macadam.
ii. Traffic bound macadam.
iii. Bituminous macadam.
iv. Cement macadam.

Que. What is a WBM road an example of?

Ans - A pavement which consist of a mixture of asphaltic or bituminous material and aggregate placed on a good quality and compacted granular material is termed as flexible pavement.

Que. What is the WBM layer of the road?

Full form of WBM is Water Bound Macadam. It is the layer of broken stone aggregates bound together by stone dust or screening material and water applied during construction and compacted by heavy smoothed wheel roller.

Que. What are the grades of WBM?

Ans - Three different gradations, namely grading – 1, grading – 2 and grading – 3 with different size ranges have been suggested by the IRC and also MORTH specifications.

Que. What is the thickness of WBM layer?

Ans - The WBM Course shall be constructed in layers such that thickness of each compacted layer is not more than 100 mm for grading 1.

Que. What is density of WBM?

Ans - Crush slag obtain from blast furnace having density more than 112 kg/m^3.

Que. What is the minimum thickness of WBM?

Ans - Thickness varies from 0.75 m to 1.2 m. Stone-crushed aggregates, screening materials and binders are overlaid one after the other in the construction of Water Bound Macadam (WBM).

Que. Which material is used in WBM road?

Ans - Water bound macadam roads: The roads whose wearing course consist of clean crushed aggregates, mechanically interlocked by rolling and bound together with filler material such as stone dust and water and laid on a well-compacted base course, is called water bound macadam road.

Que. What is the size of WBM aggregate?

Ans - Water Bound Macadam Sub-Base / Base (WBM) (Coarse Aggregates (53 mm to 22.4 mm)).

Que. What is the unit weight of WBM?

Ans - Generally, the unit weight of WBM per cum is 2200-2300 Kg.

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