Basic Road Construction Procedure
It is highly important for roads, irrespective of their classifications, to be in good shape to aid the movement of people and transportation of goods. Putting roads in the proper shape is achieved through construction and maintenance. Roads are classified based on factors like locations, materials and traffic.
Classification of Road Based on Materials
- Earthen roads
- Gravel roads
- Murrum roads
- Kankar roads
- WBM roads
- Bituminous roads
- Concrete roads
Classification of Road Based on Traffic
- Light traffic roads
- Medium traffic roads
- High traffic roads
Classification of Road Based on Traffic Type
- Pedestrian ways
- Cycle tracks
Bituminous road is the most popular and most used road in the world. It is low in cost and suitable for driving. The surface of bituminous road has bituminous materials which is also referred to as asphalt. It is a sticky dark viscous liquid obtained from natural deposits like crude petroleum. The thickness of a bituminous road largely depends on the subgrade soil conditions.
Types of Bituminous Surfaces
- Prime Coat
- Tack Coat
- Seal Coat
- Surface Dressing
This coat has low viscosity bituminous binder and is applied to existing untreated pervious layer like WBM to improve the adhesion between base and bituminous surface.
It is also a single coat of low viscosity bituminous binder. It is applied between treated base and bituminous surface to improve the adequate bond between existing impervious base and wearing surface.
This is the final coat of bituminous material. It is applied on the top of surface in order to prevent the entry of moisture through the voids.
This is the application of two or more coats of bituminous materials to prepared base. It consists of bituminous binders sprayed on which chipped aggregates are properly rolled.
Basic Procedure of Bituminous Road Construction
Bituminous road is flexible, smooth and allows for comfortable ride. The procedure of constructing bituminous road involves several steps ranging from preparation of surface, application of coats, preparation and placing of premix, rolling to quality control and finishing.
- Preparation of existing surface
- Application of tuck coat
- Quality control
- Surface finishing and opening to traffic
Construction of a bituminous road starts with the preparation of the existing surface through the removal of the pot holes or rust. The inconsistencies encountered are then filled with premix chippings. This can be done at least seven days before laying surface course. Peradventure the existing pavement is extremely way, a bituminous leveling course of adequate thickness is provided to lay a bituminous concrete surface course on a binder course rather than directly laying it on a WBM.
The second step of bituminous road construction is the application of coating which is known as tock coats. A bituminous base course and a binder course are applied on ready surface. The coating is sprayed either manually or through machinery to certain square meters according to the size of roads and pavements. It applies in 6 kg to 7.5 kg per 10 square meters.
The bitumen might be warmed up to 150 – 177 deg C and the total temperature ought not vary by more than 14 deg C from the folio temperature after the premix is set up in a hot mix plant of a required limit with the coveted quality control. The hot mixed material is gathered from the mixture by the transporters, conveyed to the area is spread by a mechanical paver at a temperature of 121 to 163 deg C. This is followed by the precise confirmation of the camber and the thickness of the layer. The control of the temperatures amid the mixing and the compaction are of extraordinary noteworthiness in the quality of the subsequent asphalt structure.
After the mix has been placed the base course, it is thoroughly compacted by rolling at a speed not more than 5km per hour.
The initial or break down rolling is done by 8 to 12 tonnes roller and the intermediate rolling is done with a fixed wheel pneumatic roller of 15 to 30 tonnes having a tyre pressure of 7kg per sq.cm. The wheels of the roller are kept damp with water.
The number of passes required depends on the thickness of the layer. In warm weather rolling on the next day, helps to increase the density if the initial rolling was not adequate. The final rolling or finishing is done by 8 to 10 tonne tandem roller.
Quality control is another important step in bituminous road construction. It involves checking of bitumen and the aggregates. A small quantity is collect at the site and tested to check the quality of the road and the distance of road construction. Proper quality control helps prevent damages and accidents.
The last step is to check the surface for undulations. For 3m straight edge, the undulation should not exceed 10mm. Cross profile should not have undulations exceeding 6mm. after this, the road is opened for the traffic. This happens after 24 hours of application of seal coat or surface dressing.