Prime Coat, Tack Coat and Seal Coat
Prime Coat
It is the first application of low viscosity liquid bituminous material over an existing porous surface like WBM base course. The main object of priming is to plug in the capillary voids of the porous surface using a low viscosity binding material. Mainly SC or MC cutbacks are the suitable grades chosen on the porosity of surface.
Tack Coat
The application of bituminous material over an existing impervious pavement surface which has already been treated by a prime coat. Tack coat is generally of higher viscosity at the rate of kg/10m2 depends on type of surface.
Seal Coat
Seal coat is mainly applied on impervious surface of bituminous pavements as a top coat. A pre mixed sand bitumen (hot mix) seal coat is commonly used over the premixed carpet. The main function of seal coat is to seal against the ingress of water and to develop skid resistance texture.
Functions of various components of flexible pavement:
Subgrade layer
- To receive the stress generated from the above layers
- To receive the materials of the above layers and act as a bedding layer.
Sub-base course
- Act as a support for the base and wearing course
- To improve drainage condition
- To remove heave
- To protect above layers from bad qualities from underlying soils.
Base course
- To prevent horizontal shear stresses and vertical pressure produced by moving or standing wheel load
- To provide density and resistance to wathering
- Distribution of higher wheel load pressure.
Wearing course
- to provide resistance against wear and tear due to traffic movements
- to provide smooth and dense riding surfaceto resist the pressure exerted by vehicle and to resist surface water infiltration.
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