Water-bound macadam roads have a wearing surface composed of clean, crushed aggregates of a varied size that are mechanically linked by the rolling process and joined with filler material (screening)The subgrade or base course is subsequently wetted with water. Water-bound macadam roads can be utilized as subgrade or surface courses. The thickness of the building layers of water-bound macadam roads is between 7.5 cm and 10 cm. The solution will be determined by the aggregate grade employed. Water Bound Macadam (WBM) roads require the use of coarse aggregates, screenings, and binding material during construction.
- coarse aggregates
For the construction of water-bound macadam roads, coarse aggregates, which typically consist of hard types of crushed aggregates and shattered stones, are utilized. The following requirements must be met by coarse aggregates used to construct WBM roads.The coarse aggregate must be durable. It should be sturdy enough to support the load.The coarse aggregate should have an appropriate shape.It should not contain any flaky or elongated particles.
The Indian Road Congress has specified the physical requirements for coarse aggregates for the construction of WBM roads.According to the IRC, the subbase, base course, and surface course layers of a road construction project have a Los Angeles abrasion value of 60%, 50%, and 40%, respectively, for coarse aggregate.The effect values for sub-base, base course, and surface course are, respectively, 50%, 40%, and 30%.
- Screenings
In the construction of WBM roads, screenings are utilized to fill any gaps or voids in the compacted layer of coarse aggregate.To fill the spaces left by coarse aggregates only aggregates smaller than coarse aggregates are used. The coarse aggregates are compacted using a roller, however, there are still some voids or gaps in the aggregates. These voids must be filled promptly with the use of fine aggregate. If the spaces between the coarse aggregates are not correctly filled and compacted, the load-bearing capacity of the road will be diminished. After coarse aggregates have been compacted, it is essential to filter them. Road institutes have recommended the use of non-plastic materials such as Kankar nodules, Murrum, and gravel. The following requirements must be met by this content: Less than twenty percent of this stuff must be liquid. The plasticity index should fall below 6%. Less than 10 percent of the material should flow through a 0.75-millimeter-mesh sieve.
- Binding Substance
When constructing water macadam roads, a suitable material that has been approved by the Engineer must be used as the binding material.
The binding ingredient of a WBM road must have a plasticity index of less than 6. Application of Binding Material is not necessary when screening is composed of gravel or other crushable material.
- Preparing the Foundation Course for the arrival of the water-bound macadam
The subgrade of the base course is initially prepared to the required grade and camber. On the surface of the road, depressions and potholes are repaired. In order to eliminate corrugations, the surface must be reshaped to the correct slope and camber when appropriate. If the WBM road is to be constructed over the existing surface, 50mm-deep and 50mm-wide furrows are cut at a 45-degree angle to the centerline of the carriageway before laying the coarse aggregate.
- Accessibility to Lateral Confinement
In order to achieve lateral confinement of coarse aggregate, it is necessary to construct a shoulder with the same thickness as the compacted WBM layer in advance. Shoulders must be constructed using either Murrum or Good Earth. Shoulders are appropriately prepared and rolled so as to preserve the road construction between them. It is completely prohibited to construct a WBM road in a bench section excavated in a completed formation.
- Distribution of Coarse Aggregates
The required quantities of the aggregates stored on the side of the road are then distributed uniformly and evenly over the newly constructed base. Depending on the pavement design and kind of traffic, the thickness and number of construction layers of a WBM road will vary. Typically, a single-layer road with a thickness of 75 mm is designated as standard. For the major routes, two layers of comparable 150 mm compacted thickness are available. When using coarse aggregates with a grading of 1, the layer is compacted to a thickness of 100 mm.
- rolling WBM
After distributing the coarse aggregate, rolling is one of the most important steps. For rolling, a three-wheeled power roller weighing between 6 and 10 tons is utilized. The rolling operation is supervised by an expert because the appropriate finishing of the water macadam road surface depends on it. The surface of the water macadam road should be uniformly covered by the roller. The roller should travel consistently and slowly. Beginning from the road's edge and moving up to the crown is the proper method for rolling a water macadam road. When rolling the road, care must be taken to ensure that each following strip overlaps the previous one. The road's finish will suffer if the rolling technique is not conducted under the guidance of an expert. Due to poor rolling, the road's surface may develop corrugations, and the finish will be uneven. If the road is elevated, the rolling technique should be performed from the inner or lower edge of the road toward the outside edge of the road.
- Procedures for Screening
The screens are used to fill the spaces left by the coarse aggregate rolling. Typically, three or more screening layers are utilized. It should be done constantly when traveling. Each road construction layer must be compacted with dry rolling; otherwise, the road would deteriorate.
- Grouting and Scattered
After the screening has been done, the roadway is liberally sprayed with water. With the assistance of a roller, the road surface will be rolled quickly.
With the use of hand brooms, the weight screening in the voids is swept. As soon as the coarse aggregates begin to bond, further screening material is added and rolled in. This will improve the load-bearing capacity and interlocking of the coarse aggregate.
- Application of Binding Material
The surface of the rolled-compacted layer of coarse aggregate is gradually and uniformly covered with the binding substance. The binding substance is frequently applied in two or three layers to the road surface. Following the application of each bonding material layer, water is sprayed over the surface. Hand brooms are used to remove the developed weight slurry so that a mechanical broom can be utilized to fill the area. Next, a 6- to 10-tonne capacity roller is utilized for rolling. As the binding substance is rolled, it adheres to the roller's wheels. Water is sprayed over the roller's wheel to eliminate the adhesive.
- Setting and Drying
After 24 hours of rolling, the road surface of water-bound macadam is given time to cure. If depressions are discovered the following day, they have been filled with screening or binding material.
- Shoulder conditioning
During the curing process, the shoulders are prepared by filling the soil to the proper cross slope. The shoulders are then properly compacted through rolling or tamping. Once all of the processes have been taken, the road can be usedContact us for more information or inquiries. Our sales executives are ready to give you all the help you need and answer all your questions.