Standing for Water Bound Macadam road, WBM road refers to a particular type of road construction where the base is built with broken stones and the road’s surface is bound by stone dust with the help of moisture. When building roads, it is among the methods that are most frequently utilised. In around 1820, it received its name from renowned Scottish engineer John Loudon Macadam.
Between 1750 and 1830, when two Scottish engineers were actively pushing and refining their distinct road-building techniques, the process of Macadam-type pavement came into the spotlight. The foundation layer was constructed using rather large stones on a flat roadbed by Thomas Telford and John Loudon Macadam.
According to Macadam, a road should always be elevated to enhance drainage in order to prevent water stagnation, which extends the life of the built-up road. Each compacted layer of Water Bound Macadam road has a thickness that varies from 10 cm to 7.5 cm and is entirely dependent on the size and gradation of the mixture utilised.
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See also: CC road: Meaning, construction process, and benefits
WBM road: Materials needed
The building of a Water-bound Macadam road primarily utilises three types of materials.
Binding material
The binding material required for the WBM road construction must have authorisation from the authorised engineer and have a plasticity index value of no more than six.
Screening
The materials used in screening are utilised to fill up any surplus space or voids in the crushed layer of the coarse mixture.
Coarse mixture
The WBM road’s coarse mixture is generally made up of well-graded shattered stones and crushed mixes.
WBM road: Construction process
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The Water-Bound Macadam road is built in phases over a number of steps. They are listed below:
Preparation of the foundation or base
The combination is created using the Water-Bound Macadam Road’s grade as a guide. With the aid of the created mixture, depressions and potholes are correctly filled and compacted on the road’s surface.
Provision of lateral confinement
It is accomplished by building the road shoulders to be the same thickness as the compacted WBM road. The primary goal of building the road shoulder is to vertically trim the inner sides so that the subsequent construction of the road surface stays between the two road shoulders and aids in the additional application of the coarse mixture.
Coarse aggregates or mixtures being spread
After the road shoulders are built, a coarse combination of aggregates is evenly placed over the base that has been laid out. The specifics of the pavement design determine both the overall thickness and the number of layers of the WBM road. One compressed layer measuring 75 mm in thickness is thought to be adequate for a typical road. The compressed thickness may be offered for unique roads that are built with two layers of 150 mm each.
Rolling
After the mixture has been evenly dispersed, the aggregate is compacted with a vibrating or three-wheeled road roller. The WBM road is crucial; thus, competent workers are employed there to prevent mistakes from being made. Loops may emerge as a result of incorrect rolling operations that wear down the road or unevenly finish the surface.
Screening
The screening process involves passing the base course material through a series of screens or sieves of different sizes. This separates the material into different size fractions and removes any unwanted debris or particles. The resulting material is then graded and sorted to ensure that it meets the specified requirements for the WBM road construction project.
Sprinkling and grouting
The created WBM road’s upper surface is swept, wetted and rolled once the screening process is finished. With the aid of a broom, wet screening is positioned in the additional area after the water has been sprinkled over the surface.
Surface drying
The freshly built road is allowed to dry and set overnight after the final rolling. If the additional area is still visible the next day, a sufficient amount of screening is performed.
Getting the road shoulders ready
By appropriately compacting and constructing them next to one another, the soil is filled until it reaches the necessary cross slope.
Accessible to traffic
Once the freshly built road has dried and been checked for depressions, it will be finished. To evenly disperse the traffic on the road, barricading is used to allow traffic to cross the road. The drums are positioned lengthwise to act as impediments.
Know about: coarse aggregate
WBM road: Maintenance
- In a short amount of time, if any ruts or potholes appear on the freshly built Water-Bound Macadam road, the responsible authority should repair them by filling them with the necessary material and correctly blending the material.
- Any damaged parts of the built-road should be replaced with new materials.
- The completed road’s surface has to be updated every 2 to 5 years, taking traffic volume into consideration.
- The loose mixture that collects on the road surface must be removed.
WBM road: Advantages
- Given how inexpensive it is to build Water Bound Macadam Road, it is cost-effective.
- No specialised labour is needed to build the WBM road.
- WBM roads are built using materials that are readily available.
- If these roads are regularly maintained adequately, they should be able to withstand daily traffic of about 900 tonnes.
WBM road: Disadvantages
- The expense of upkeep is higher as compared to other types of road building.
- The lifespan of Water-Bound Macadam Road is shorter overall.
- If these roads are not properly maintained, there is a considerable likelihood of traffic hazards and discomfort.
- Due to these roads’ ability to absorb precipitation, the subsoil yields and softens as a result.
FAQs
What is a Water-Bound Macadam Road?
A Water-Bound Macadam Road is a type of road construction made by laying stones and gravel on a base layer and binding it with water and sand.
What is the lifespan of a Water Bound Macadam Road?
The lifespan of a Water Bound Macadam Road varies depending on various factors such as the climate, traffic volume, and maintenance but typically ranges from 15-20 years.
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