Prime coat typically is application of low viscosity Bitumen over a granular base, preparing it for laying an asphalt mixture on it. A prime coat performs several important functions.
Coats and bonds loose material particles on the surface of the base.
Hardens or toughens the surface of the base.
Waterproofs the surface of the base by plugging capillary or interconnected voids
Provides adhesion or bond between the base and the asphalt mixture.
Bitumen emulsions used for Prime Coat are Cationic Slow Setting Emulsion 1 and Cationic Slow Setting Emulsion 2 as per latest MOST specifications.
Tack Coat is a very light spray application of diluted asphalt emulsion to create a bond between an asphalt overlay being placed and the existing surface. The functions performed by Tack Coat are
It is essential for good patching operation
To avoid skidding of top layer from bottom layer
To add strength to both the layers as it makes both layers act as one.
Bitumen emulsion used for Tack Coat is Cationic Rapid Setting Emulsion 1 as per latest MOST specifications.
Four types of surface dressing are commonly adopted using Bitumenous emulsions, they are
Single layer surface dressing
Racked in surface dressing
Double layer surface dressing
Sandwich surface dressing
The various techniques are explained in the picture below.
Bitumen emulsion used for Surface Dressing is Cationic Rapid Setting 2 as per latest MOST specifications.
Seal coat is an application of asphalt emulsion to an existing paved asphalt surface. The asphalt emulsion may be sprayed or squeegeed on the existing pavement surface. This is primarily employed to
Improve aesthetics of an existing pavement by providing uniform black colour to the surface.
Seal coat also provides an impervious membrane that will slow the rate of weathering of the asphalt in the underlying pavement.
Bitumen emulsion used for Seal Coat is Cationic Rapid Setting as per latest MOST specifications.
Maintenance
Changing weather conditions and heavy traffic deteriorate the quality of Bitumenous pavements, hence it is necessary to ensure pavement upkeep in order to maintain good traffic, safety and comfort conditions for users. Commonly used maintenance techniques are
Patching
Surface Dressings
Slurry Seal
Cold Mix Concrete
Patchwork is the most common technique adopted for maintenance in our country. Patching is a technique used for
Potholes
Surface damage
Hollows
Cracks etc…
Bitumen emulsion used for Patchwork is Cationic Medium Setting as per latest MOST specifications.
Pre-Mix Method of Shallow Pot Hole Repairs
Micro-surfacing is a mixture of well graded aggreagate, bitumen emulsion, fillers, additive and water, with addition of polymers and the use of specialised design techniques, micro-surfacing can achieve multiple stone depths. Micro-surfacing features and benefits are
Quick set, quick traffic feature.
Chemical break permits night time application
Suitable for use on high traffic volume, limited access highways
Scratch course followed by a finishing course provides minor re-profiling and a new riding surface.
Rut filling followed by a finishing course provides proper water drainage and reduces the possibility of vehicle hydroplaning.
Fog spray is a light application of diluted slow setting emulsion sprayed on an existing bitumenous surface. The uses of fog spray are
Seal very small cracks and surface voids.
To renew old asphalt surfaces that have become dry and brittle over age.
It can help delay the need for major maintenance when applied in a timely manner.