What is Bituminous Road
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 :
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Bitumen heating device.
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Bitumen distributor.
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Roller for compacting operation.
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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.
Construction Procedure of Bitumen Carpet Road :
• Preparation of the Existing Surface :
For the existing layer if potholes or depressions are found then they are required to be filled with percolated chippings before the layer of carpet is applied. After the preparation of the surface the tack coat is applied to WBM surface or old bitumen surface. If there is presence of softer aggregates such as laterite, kankar or murum, then prime coat application is necessary to be applied first.
• Application of Tack Coat :
The bitumen binder is heated up to required temperature and a tack coat is applied to the surface.
• Preparation and Placing of Premix :
Preparation of premix is carried out in mechanical rotary mixer or hand drum mixer. For this mix, aggregates and bitumen are separately heated for specified temperature. Mixing is done to obtain through and homogeneous mix. These mix is then carried out to site and it is ready to be placed on the surface. Cross profile is effectively checked after its application.
• Rolling and Finishing :
Rolling operation for compaction is carried out once the premix application is finished. It is carried out for completion of every 15 m surface of road. The rollers which are generally used are tandem type or pneumatic type rollers having capacity of 6-10 tonnes. The wheels of the rollers are kept damp to prevent the adhesion of mix to the wheels of roller.
Note : for heavy rainfall areas liquid seal is sprayed on the carpet at 9-10 kg per 10m2 area. It is then covered with layer of tone chippings and properly compacted.
• Surface Finish :
The surface is properly checked for undulations. For 3 m straight edge the undulation should not exceed 10mm. Cross profile should not have undulations exceeding 6mm
• Open to Traffic :
Road is opened for the traffic after 24 hours of application of seal coat or surface dressing.
Advantages of Bituminous Road :
- Generally Bituminous road do not develop cracks on the surface for long period.
- Maintenance cost of this road is also very less.
- Bituminous road are waterproof, non-slippery, smooth, durable and it provides comfortable road surface for the traffic.
- It can withstand the adverse natural effects caused by heavy rain, excess heat and change in temperature.
Disadvantages of Bituminous Road :
- The viscosity of the bitumen and aggregate mix plays important role in defining the performance of bituminous road.
- If the bituminous material is used in excess than the value for given mix, it effects the performance of the bituminous road.
ALSO READ : WBM Road : Construction Procedure, Advantages and Disadvantages
Thank you for explaining the different layers of a bituminous road. I imagine it’s important to paint the lines with a material that’s compatible with the top layer. It’s also probably important to do that correctly with the right equipment.
Rolling operation for compaction is one of the most important part for the construction of road, preparation of sub base for road with proper increase the life of the road.
You wrote a very thorough article, thank you
I have done road carpet work in year 2014 ,thickness of carpet was 70 mm . Now in year 2022 when I took core of carpet to check its thickness I found it 50 to 60 mm in area where heavy material is loaded in trailer for dispatch. Load of single piece of this material is 10.00 MT Please . Road surface is in good condition without any defect.
Please give me reason for this reduction in thickness.
Heavy vehicles on the road can cause traction and abrasion of the surface, resulting in the reduction of road thickness even when the top surface is completely intact. This is very common in roads over period of time.