Different Types of Bituminous Surfaces.: 1. Prime Coat

Bituminous road consist of their surface with bituminous materials which is
also called as Asphalt. It is sticky dark viscous liquid obtained from natural
deposits like crude petroleum.
Different Types of Bituminous Surfaces.

1. Prime Coat :
This is a single coat of low viscosity bituminous binder. This coat is applied to
existing untreated pervious layer like WBM. The main purpose is to improve
the adhesion between base and bituminous surface.
Functions :
 The most important function is to imporve the adhesion between
existing pervious base and wearing surface.
 To bind the dust and loose particles together to form hard and tough
surface.
 It provides temporary seal to prevent the surface water from
penetrating through the surface.
2. Tack Coat :
This is single coat of low viscosity bituminous binder applied to the existing
treated impervious layer such as bitumen or cement-concrete base. This boat
is applied between treated base and bituminous surface.
Function :
 It is provided to improve the adequate bond between existing
impervious base and wearing surface.
3. Seal Coat :
Seal coat is the final coat of bituminous material that is applied on the top of
surface to prevent the entry of moisture through the voids.
Function :
 To provide water tight surface.
 It improves the visibility at night and develops skid resistant texture.
 To improve the wearing resistance of an existing road surface.
ALSO READ : Earth Road : Types and Construction Procedure
4. Surface Dressing :
It is the process in which two or more coats of bituminous materials are
applied to prepared base. This coat consist of bituminous binders sprayed on
which chipped aggregates are properly rolled.
Function :
 It prevents the removal of binding material and prevents the damage of
road due to waterproofing effects.
 Roads can be easily cleaned and washed as it reduces dust nuisance.
 Smooth surface of the road reduces the wear and tear of tyres.
Bituminous Road Construction Steps and

Procedure :
1. Bituminous Penetration Macadam Road :
In this type of bituminous road the aggregates are bound together by
grouting bitumen into the voids of the compacted aggregates. This type of
bituminous road is generally adopted for the thickness of 50 and 75 mm.
Materials Required :
 The grade of bitumen to be used for this type of road suggested by IRC
ranges from 80/ 100, 60/ 70 & 30/ 40. Any one of the above grade can
be adopted.
 Road tars of grades such as RT-4 & RT-5 can also be used.
 Physical properties of the aggregates must fulfill the following standard
test values given below :
Equipments and Plants Required :
 Bitumen heating device.
 Bitumen distributor.
 Roller for compacting operation.
 Aggregate spreader.
Construction Procedure of Bituminous Penetration Macadam Road :
• Preparation of Existing Surface :
First of all the surface on which bitumen macadam is to be applied is cleaned
from dust and other debries. The gradient and the camber of the road is
properly checked. Priming coat can be also applied if necessary for porous
surfaces.
• Spreading of Course Aggregates :

Spreading of aggregates can be done manually or by machine. To achieve the
desired profile in cross-section, template cat or camber profile may be used.
• Rolling Operation :
After speeding of aggregates they are dry rolled with a minimum of 10 tonnes
roller. It is assured that the aggregates are properly compacted and
interlocked.
• Bitumen Application :
The uniform layer of bitumen binder is applied on the dry rolled compacted
aggregates with the help of pressure distributor or mechanical hand sprayer.
• Spreading of Key Aggregates :

Once the bitumen is properly applied key aggregated are properly laid and
rolling operation again continued for proper compaction. Cross Profile is also
checked at the same time.
• Seal Coat Application :

If the road is going to be made open for the traffic and another surface course
is not required then the seal coat is applied. It consist of sand bitumen or it
may be of surface dressing type.
• Finishing :
Cross profile of the road should be checked with template and the
longitudinal profile by straight edge of the road. The permissible undulation
on 3 m road is 12 mm.
• Open to Traffic :
The road is made open to traffic after minimum of 24 hours after its
construction.
2. Bitumen Carpet Road.

In the construction of bitumen carpet road the recommended bitumen binder
is 80/ 100 grade and the tar required should be of grade RT-3. The stone
chippings required for 2 cm carpet thickness should be 12 mm and 10 mm.
Below table should the requirement that should be satisfied by the aggregates
to be used.

Different Types of Bituminous Surfaces.: 1. Prime Coat

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Bituminous road consist of their surface with bituminous materials which is

Different Types of Bituminous Surfaces.

Bituminous Road Construction Steps and

• Spreading of Course Aggregates :

• Spreading of Key Aggregates :

• Seal Coat Application :

2. Bitumen Carpet Road.

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