Flexible Road Construction Method Process Step by Step- Sub-grade, Sub-base, Base, Pavement, Rolling, Test

Flexible Road Construction Method Process Step by Step
Flexible Road Construction Method Process Step by Step- Sub-grade, Sub-base, Base, Pavement, Rolling, Test
Road Construction Step
The methods of constructing roads have changed a lot since the first roads were built around 4,000 BC – made of stone and timber
Modern roads tend to be constructed using asphalt and/or concrete.
Bitumen road construction consists of various steps such as these steps follows one by one.
          1.    Preparation of Sub-grade,
          2.      Preparation of Sub-base course,
          3.      Preparation of base course,
          4.      Bituminous Coat
a.       Prime Coat
b.      Tack Coat
          5.      Paving of Bituminous Mix
          6.       Rolling
          7.      Seal Coat

1.      Preparation of Sub-Grade
Sub-grade preparation works involve Earthwork is one of the major works involved in road construction. It involves the removal of top layer of soil, vegetation. Road area is prepared for the finished formation level. This is usually done using a manually and mechanically like tractor shovelgrader etc.  Below the formation level, the soil is known as the sub - grade.
The required thickness of the pavement layer is determined by the strength of sub-grade, so it is must important to make the strong subgrade as far as possible.
The can make strength of the subgrade by doing these works:
          -  Compacting subgrade mechanically to a high dry density.
          -  Remove vegetation and poor material.
          -  Remove the bad and loose soil by cuttings and replacing with selected fill.
          -  Providing adequate subsoil drainage system.
          -  Maintain camber on sub-sub grade for sub soil drainage.
Earthworks are formed by cut-and-fill, and the type of ‘fill’ material must be considered, not only in terms of its physical properties, but on the conditions in which it is to be used, and the methods of compaction.
Method of Stabilization of Sub-Grade
Generally before sub-base course if we need to make more strength of road  we prepare sub-grade course with RBM to stabilize the soil and make the sub-grade strong to bear adequate load which comes from traffic.
River Bed Material (RBM), debris etc. are used at road area for soil stabilization generally RBM consist of sand, aggregate, stone and some stone dust for binder. There is no any fix size of the material but we conform that material should be free from bolder.
Method of Stabilization of Sub-Grade

2.      Preparation  of Sub - Base Course
Generally before base course we prepare sub-base course with the crushed aggregate 63mm down. We place these materials on road and with the help of grader on such a way that it provide uniform camber. We should compact the sub base material with the help of Roller and water browser by draining water on the surface. Provide roller 0.022 hr/cum with vibration to obtain dry (95-98) % dry density.
  Preparation  of Sub - Base Course

3.      Preparation  of  Base Course
After preparing of layer of sub base course we provide base material which is 43mm down aggregate. Process are same as sub base course but material and time of rolling should change i.e 0.033 hr/cum, to make Water Bond Macadam WBM road. The irregularities are filled in with premix chippings at least a week before laying surface course. If 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 instead of directly laying it on a WBM.

Preparation  of  Base Course
Base Course

4.      Bituminous Coat
a.      Prime coat
This coast is applied after base course for this reasons :
·         To fill the capillary voids
·         To coat and bond loose material on the surface
·         To harden or toughen the surface.
·         To provide adhesion between bituminous and granular material.
We must provide (6-9) kg per 10sqm prime coat on WBM road.
To make 1-ltr prime coat se need (80/100) bitumen 1.05 kg and Kerosene 0.10 kg and burn it on adequate temperature.
It is vital to be aware of weather conditions when apply an asphalt prime coat. In the case of wet weather, you should postpone this step to avoid runoff into the water supply.
b.      Tack coat
A tack coat is applied after the prime coat, to form an adhesive bond between the tack coat and the next layer of coating. The tack coat prevents slippage and may sometimes function as a more long-term sealer to protect the substrate from moisture and bacteria.
A tack coat of bitumen is applied at 6.0 to 7.5 kg per 10 sqm area, this quantity may be increased to 7.5 to 10 kg for non-bituminous base.

tack coat
Tack coat

5.      Paving of Bituminous mix

Bituminous mix paving with equal thickness and making camber on the road surface. At first 10mm down silicon aggregate and 80/100 bitumen material used for premix or it is  prepared in a hot mixture plant of a required capacity with the desired quality control. The bitumen may be heated up to 150 – 177 deg C and the aggregate temperature should not differ by over 14 deg C from the binder temperature. Both are mixed up
The hot mixed material is collected from the bitumen mixture by the transporters, carried to the location is spread by a manually of mechanical paver at a temperature of 121 to 163 deg. Celsius the camber and the thickness of the layer are accurately verified.
The control of the temperatures during the mixing and the compaction are of great significance in the strength of the resulting pavement structure. The temperature of mixed material during laying is not less than 105 degree Celsius.
  Paving of Bituminous mix

6.      Rolling
When after placing bitumen mixture on the base course is than it is equally and thoroughly compacted by static rolling at a speed not more than 5km per hour or use vibration. In rolling a graded area with a side slope, as a crowned or banked road, you should work from the edge to the center of the of the road which is known as camber
The static rolling is done by (8 – 12) tonnes roller and the intermediate rolling is done with a fixed wheel pneumatic roller of (15 – 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. The final rolling or finishing is done by 8 to 10 tonne tandem roller.

7.      Seal coat
Final coat of bituminous material applied during construction to a bituminous macadam or concrete for sealing the surface of the pavement. In this coat sand mix up with bitumen and spread on road to plug the void and final rolling is done with 8-10 tonne roller.

Some Test is important during Road Construction
          1.      Sub grade test for thickness of pavement
          2.      Aggregate gradation Test
          3.      Grade of Bitumen Test
          4.      Field Density Test after Rolling
Most important thing temperature of mixture check during unloading or paving it should not less than 105 degree Celsius & for every 100 sq.m of the compacted surface, one test of the field density is conducted to check whether it is at least (95-98) % of the density obtained in the laboratory. The variation in the thickness allowed is 6mm per 4.5m length of construction.

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