What is the difference between WBM and WMM with respect to civil engineering?
Water bound macadam roads(WBM): Aggregates are placed one over the other and binded them in the presence of water. SO it is called water bound and macadam is the name of civil engineer who found that inferior material should be at bottom and superior material should be at top. This is the first scientific road construction method. But it takes to dry and we cannot allow the traffic immediately.
Wet mix macadam: This is new method where aggregate are mixed with water before laying and the wet mix is laid and then rolled. Wet mix roads are superior than WBM in all aspects.
What is the difference in GSB, DBM & WBM in road construction?
All three form different layers of Flexible pavement to distribute the wheel load from the wearing course ( Bituminous or Ashohalt concrete) to the foundation which is the Subgrade.
Granular Sub Base or GSB is the first layer above the subgrade and other than dispersing load to the Subgrade is a drainage layer to drain out any water that percolates and thus keeps the subgrade from losing its shear strength by getting wet. This layer is made of coarse granular materials but strong enough with a CBR of above 30. This layer is generally 300–500 mm thick depending on the pavement design.The material for this layer is either naturally available or has to be prepared by mechanical mixing . The mixed martial is transported in Dumpers ,spread by Graders and compacted by Vibratory Rollers.
The GSB layer is capped by 250–300 mm thick Water Bound Macadam (WBM) which forms the Base Course. This is normally laid in two layers with larger stone aggregate graded from 65mm to 40 mm which is spread to the right gradient and profile and compacted. The gaps or interstices are filled with 12 mm down stone chips and compacted well enough to ensure that the larger stones are well interlocked. Stone dust is then spread and watered in to fill the finer gaps thus sealing the layer. This same operaton is carried out for the second layer to achieve the designed thickness. The strength of this layer is achieved through interlocking. In current practices particularly for larger projects WBM has been replaced by Wet Mixed Macadam which is a mechanised way of mixing of well graded and shaped aggregates of 40 mm down with sufficient fines with required quantity of water in a pug mill transporting in dumpers and spreading using sensor pavers and compacting while retaining the optimum moisture content. The strength of this layer is measured by the Max dry density achieved at optimum moisture content.
The stone Base course layer is topped by a Bituminous Base course called Dense Bituminous Macadam. This layer is usually 100–125 mm thick and could be laid in a single layer using 30–40 mm down well graded stone aggregates heated and mixed in a Hot Mix Ashphalt in accordance with an approved Mix design which aims at optimising Bitumen content and Voids. The laying is done using sensor operated pavers to ensure gradient and profile to within permissible limits.(collected)