WBM Stands for Water Bound Macadam which is the most commonly used road construction procedure for over more than 190 years.Pioneered by Scottish Engineer John Loudon McAdam around 1820 Macadam is a type of Road Construction. The broken stones of base and surface course,if any are bound by the stone dust is presence of moisture is called WBM Roads.
Macadam means the pavement base course made of crushed or broken aggregate mechanically interlocked by rolling and the voids filled with screening and binding material with the assistance of water.WBM may be used as a sub-base,base or a surface course.The thickness of each compacted layer of WBM ranges from 10cm to 7.5cm depending on size and the gradation of aggregate used.
Construction Procedure:
1.Prepare the foundation for receiving the WBM course.
2.Lateral confinement may be done by compacting the shoulder to advance,to a thickness equal to that of the compacted WBM layer and by trimming the inner side vertically.
3.Spreading of Coarse Aggregate.
4.Compaction of coarse aggregate is done by wheeled power roller of capacity 6 to 10 tonnes or alternately by an equivalent vibratory roller.
5.Dry screening is applied gradually over the surface to fill the interstices in these.
6.The surface is sprinkled with water,swept and rolled.
7.Binding material is applied at a uniform and slow rate at two and more layers.
8.WBM Coarse is allowed to set overnight.
