Friday, 10 December 2010

Middle Layer {Water Bound Macadm (WBM)}:

Middle layer is again with graded stone aggregate but of smaller size usually 40 mm. Thickness of this layer depends on density and speed of traffic.
This layer needs even more compaction. Plenty of water should be used during compaction. Sand is ideal material for achieving the best compaction. Maintaining proper slope saves material of the top layer. It recommended that estimated slope must be maintained in all layers starting from formation. WBM may be replaced with Portland cement concrete (PCC) or reinforced cement concrete (RCC) if road is required to support heavy and or fast traffic. PCC/RCC roads need techniques as prescribed in engineering practice. Where PCC/RCC layer is used top layer may not be necessary.

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