27 Steps of Road Construction | Step by Step Road Construction Process | Construction Methods

#road_construction_process #Box_Cutting,#Improved_Sub_Grade,#ISG,#WBM,#WMM,#Widening,#Carpeting
Local Practice of road construction process in Bangladesh:
1.Box Cutting
2.Improved Sub-Grade
3.Sand Blinding,
4.Sub-grade
5.Wet based Macadam (WBM)
6.Water Mixed Macadam (WMM)
7.Prime Coat
8.Bitumenous Carpeting
9.Seal Coat
10.Road Widening
Road alignment should be cleared from tree roots, shrubs, grass and grass roots, structures below or above the ground etc. before start of any work. Pre-work measurement of original form of land should be taken so that the earth measurement can be done finally.
Earth fill materials shall be free from roots, shrubs, grass and grass roots, structures etc. Shall be approved by the Engineer as a suitable material for the purpose. CBR of embankment material shall be more than 3%. Embankment materials, when compacted shall achieve 95% maximum dry density (MDD) determined in accordance with Standard Testing Procedure (STP). One compaction test shall be carried out for each 1000 sq. meters of completed layer according to STP.
After clearing the area cross section of the original land, its approval should be taken before start of work. Embankment should be constructed in 150mm compacted layers and it should be parallel to the last compacted layer. This will remove water from the embankment easily. Before spreading a new layer, the engineer must approve the last compacted layer. Spongy materials should be removed from the embankment to get the desired compaction result. Places like ponds, marshes and canals in the alignment should be cleared and sandfilled, to strengthen the embankment. When this filled land shall be raised to a designed height level, it shall be compacted.
150mm layer above the earth layer or just below the pavement is known as Subgrade. Subgrade preparation with suitable soil and proper compaction. Subgrade is spread through entire breadth of the embankment including shoulder. During construction of embankment on an existing road, entire earth up to 150mm depth should be removed so that new materials are completely mixed with the old materials. Subgrade layers should be compacted to achieve 98% of maximum dry density (MDD). Subgrade should have LL5%or as specified in the contract document .
Improved subgrade materials should be natural or artificial mixture of sand or other mineral aggregates free from vegetation, soft particles and excess clay. Improved subgrade shall be compacted in 150mm layers or as per specification of the design, with vibratory roller to achieve 95% compaction. At this stage, optimum moisture content should be ±2% or as specified in the contract. The material should have a soaked CBR value not less than 8% when compacted to 95% of maximum dry density (MDD) or as specified in the contract document.
Sub-base is the middle load bearing layer of the pavement. Sub-base materials are spread over engineer-approved sub-grade and compacted to desired specification. Sub-base materials should be spread mechanically or manually in more thickness so that after compaction, 150mm thickness or as per specification of the approved design is achieved. It shall be done by sprinkling water as required in the contract. Every layer shall be compacted by vibrating roller to achieve 98% compaction of MDD with optimum moisture content (OMC) ±2%or as specified in the contract.
The contractor shall not commence bitumen surfacing work until the job-mix formula has been approved in writing by the Engineer, including any adjustment to the job mix formula which the Engineer considers are necessary. Apart from this, a short illustration of frequently used terms in bituminous pavement work is also given below:
Prime Coat: The principal function of prime coat in bituminous pavement is to protect the subgrade from moisture and weathering. Since the presence of moisture affects the strength of subgrade, the prevention of water entry during construction is essential to avoid the failure of the pavement. Prime coat is an asphalt which, when applied evenly to the surface of sub-base or subgrade, serves to seal the surface to hinder the penetration of moisture into subgrade.
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. The work shall consists of applying bituminous material to a previously prepared Road Bed, in accordance with the specifications and to the width and the area required by the engineer.

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