Introduction of WBM Road
The full form of WBM is Water Bound Macadam. India as a country has one of the largest road networks in the world covering around 3.3 million kilometers. It basically consists of National Highway, District Roads, State Highways, and Village Roads. Apart from this, there are Expressways and International Highways being developed recently.
The real development of roads was made during the Mughal period, Sher Shah Suri came up with the idea of Grand Trunk Road, The concept is being followed nowadays in the construction of Grand Trunk Road across India.
Road construction basically includes the issues appropriate to the process of maintenance and road construction. Includes the supervision of roads and related structures along with the highway and road layout design, implementation, and contracting of the fixed parameters.
The various types of Road Constructions are as given:
- Earth Road and Gravel Roads
- Soil Stabilization Roads
- Water Bound Macadam Road
- Bituminous or Black Top Road
- Cement Concrete Road
What is (WBM) Water Bound Macadam Road?
For road construction when the base is constructed with the help of broken stones and the surface of the road is bound by stone dust with the help of moisture, That particular form of road construction is called the Water Bound Macadam Road. It is one of the most commonly used processes at the time of road construction. Named after the famous Scottish engineer John Loudon Macadam around 1820.
The process of macadam-type pavement came into the limelight between 1750-1830 when two Scottish engineers were active in promoting and developing their respective road construction techniques. Thomas Telford and John Loudon Macadam used fairly large stones on level roadbed to build the foundation layer.
Macadam was of the view that a road should always be raised to improve drainage to avoid stagnancy of water helping in improving the life of the constructed road. The thickness of each compressed layer of Water Bound Macadam road ranges from 10cm to 7.5 cm and it totally depends on the gradation and size of the mixture used.
Also Read: What are the different types of roads in India?
What are WBM and WMM?
The difference between Water Bound Macadam Road and Wet Mix Macadam Road is that in the case of WBM the base is prepared with the help of broken stones and then the surface of the base is bound by the stone dust with the help of moisture. Whereas in the case of WMM, which is also considered as the new method.
The mixture of the composition is mixed with water first and then The wet mixture is laid and rolled with the help of a Road roller. Wet Mix Roads are considered of better quality than that of Water Bound Macadam Road in all aspects.
Materials required for WBM Road Construction
There are basically three major types of material that is used in the construction of water Bound Macadam Road.
- Binding Material
- Coarse mixture or aggregate
Binding material: The binding material that is supposed to be used in the construction of the Water Bound Macadam Road needs to be approved by the authorized engineer and the material should have less than 6 plasticity index values.
Screening: These are the materials that are used to fill the extra space or the unfilled part in the compressed layer of the coarse mixture.
Coarse Mixture: This basically consists of properly graded broken stones and crushed mixtures used for each layer of the Water Bound Macadam Road.
Construction Procedure of WBM Road
There are several steps included in the construction process of the Water Bound Macadam Road. They are as Under:
Preparation of the base or foundation
The mixture is prepared based on the grade of the Water Bound Macadam Road. The depressions and the potholes are filled and compacted properly on the surface of the road with the help of the prepared mixture.
Provision of Lateral Confinement
It is done by constructing road shoulders to a thickness same as that of the compressed water Bound
Macadam Road. The basic purpose behind the construction of the road the shoulder is to trim the inner sides vertically so that the further construction of the road surface remains in between two road shoulders and helps in the further laying of the coarse mixture.
Spreading of Coarse Aggregates or Mixtures
Post-construction of the road shoulders the coarse mixture or aggregates are uniformly spread over the prepared base. The total thickness and the number of layers of Water Bound Macadam Road totally depend on the details of the pavement design.
For an ordinary road, a single layer of compressed thickness 75 mm is considered sufficient. For special roads that are constructed with double layers of 150 mm each, the compressed thickness may be provided.
Post spreading the mixture properly, the aggregate is compressed with the help of a three-wheeled road roller or vibrating roller. The Water Bound Macadam Road is very important and for that purpose skilled operators are used so that they do not commit any fault. A fault rolling operation could cause the formation of loops such as the wearing of the road or the unequal finish of the road surface.
After the rolling operations is done the process of screening is applied. With the help of screening the extra space that is leftover post the compression of the mixture. Depending on the site condition the process of screening could be applied on multiple layers that could be either 3 or more.
Grouting and Sprinkling
Once the process of screening is completed the upper surface of the constructed Water Bound Macadam Road is swept, sprinkled with water, and rolled. Once the water is sprinkled on the surface the wet screening is put in the extra space left, with the help of a broom.
Drying of Surface
After the final rolling the newly constructed road is allowed to dry and set over-night. The following day if the extra space is visible then an adequate amount of screening is done.
Preparations of Road Shoulders
They are properly compacted and constructed alongside by the process of filling earth to the level of the specified cross slope.
Open for Traffic
Once the drying of the newly constructed road is done and it is found without any depressions. Traffic is allowed over the road with barricading using drums to equally distribute the traffic on the road. The drums are placed as obstacles longitudinally.
Also Read: Factors affecting the geometric design of Highway
Maintenance of WBM Road
- Within a period of time, if any type of ruts or potholes occurs on the newly constructed Water Bound Macadam Road, the concerned authority should repair it by filling it with the required material, and combining of the material should be done properly.
- The unevenness that occurred should be removed from the constructed road by means of dragging. It might lead to creating the situation worse for the constructed roads.
- Fresh materials should be used in place of any broken materials of the constructed road.
- In every 2-5 years the surface of the constructed road needs to be renewed, keeping in view the volume of traffic.
- The loose mixture should be removed that comes on the top of the road surface. With the help of fresh binding material, the Lavelle road surface should be added and it should be properly compacted and watered.
Advantages of Water Bound Macadam Road
- It is cost-effective as the cost of constructing Water Bound Macadam Road is comparatively low.
- No skilled labors required while constructing WBM road.
- WBM roads are constructed with the help of easily available materials.
- If these roads are maintained properly from time to time then they could resist heavy traffic, approximately around 900 tonnes on a daily basis.
Disadvantages of WBM Road
- As compared to any other form of road construction, the maintenance cost is high.
- The overall life span of Water Bound Macadam Road is less.
- A high probability of danger to traffic and inconvenience is there if these roads do not receive proper maintenance.
- This leads to yielding and softening of the subsoil as these roads are absorbent to rainwater.
Water Bound Macadam (WBM) Road at Site Video
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