The concept of a water bound Macadam road was suggested by John Macadam, a Scottish engineer. The road whose wear way consists of clean crushed aggregates, mechanically interlocked by rolling and bound together with filler material and water placed on a well compacted base course, is called a water bound macadam ( WBM) road.
Benefits of Water Bound Macadam
- Water bound macadam is superior in quality because the material is carefully graded and the resultant mass is almost zero low coagulated mass.
- The interlocking of aggregate particles provides sufficient strength of the selected material to fill the vacancies. These ensure non-penetration of sub-grade plastic material into the voids.
- Water bound macadam is less expensive than a bituminous base course.
Disadvantages of Water Bound Macadams
- The stone pieces used in the Water Bound Macadam Road are sealed together through sand and clay and no other cementing material is used. The bonding effect of sand and soil depends on pressure and moisture.
- When a high-speed vehicle passes over a WBM road, the sand and mud solution is sucked up by the pneumatic wheel tyres, disturbing the stone pieces and eventually shattering the road surface. Because of this, WBM roads are not suitable for high-speed vehicles with pneumatic wheels.
- These roads are suitable only for slow moving iron wheeled traffic like tonga, bullock cart etc.
- The metal of the road gets crushed by the continuous use of the road with iron wheels. Considering these factors, it can be inferred that the WBM road survives only for a short period of time.