Good quality crushed coarse stone metal aggregate is good to lay foundation of road. Size of the aggregate and thickness of layer depends of the traffic density and speed. Generally graded 100 or 150 mm aggregate is used. This should be at least in two layers, each 150 mm thick. Before and during rolling of this aggregate adequate quantity of sand/crushed stone and powder and water should be used. If crushed sand or natural sand is not available at leased disintegrated rock powder (murrum) should be used. Vegetable or any other material which is likely to disintegrate should not be mixed in this layer or any other layer above this. Such material creates voids after some time and is cause of potholes in road. Ideally compaction should be to the extent that the layer cannot accept even water. Another aspect is to maintain required slope in every layer. Maintaining slope reduces water accumulation on surface of the road and cost of construction of the top layer.
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