The concept of water bound macadam road was suggested by John Macadam, who was a Scottish engineer. The road whose wearing course consists of clean crushed aggregates, mechanically interlocked by rolling and bound together with filler material and water laid on a well compacted base course, is called water bound macadam (W.B.M) road.

Advantages of Water Bound Macadam

  1. Water bound macadam is superior in quality because the materials are carefully graded and the resulting mass is almost void less compacted mass.
  2. The interlocking of aggregate particles imparts adequate strength of the materials selected for filling the voids. These ensure non-entry of the plastic materials of the sub-grade into the voids.
  3. Water bound macadam is less costly as compared to bituminous base course.

Disadvantages of Water Bound Macadam

  1. The stone pieces used in water bound macadam road are keyed together by means of sand and clay and no other cementing material is used. The binding effects of sand and clay depend upon the pressure and moisture.
  2. When a fast moving vehicle passes over a W.B.M. road, the slurry of sand and clay is sucked out by pneumatic wheel tires, the stone pieces get disturbed and finally road surface is disintegrated. Due to this, the W.B.M. roads are not suitable for fast moving vehicles with pneumatic wheels.
  3. These roads are only suitable for slow moving iron wheeled traffic such as tongas, bullock carts etc.
  4. Constant use of road by iron wheels, the road metal gets crushed. Considering these factors, it may be inferred that a W.B.M road survives only for a short time.
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