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Transportation

Triple Bitumen Surface Dressing

Triple bitumen surface dressing is carried out to improve the condition of existing bitumen paved roads and to protect the base course. It does not have any specific thickness. The thickness varies as per requirement. A thin layer of bituminous material is laced over the existing pavement with aggregates and rolled.

Materials Required For Construction Of Bitumen Surface Dressing!!

The coarse aggregates should be of crushed stones. It should be clean, strong and durable having the following properties:

  1. Los angles abrasion value (LAA) = 35%
  2. Aggregate impact value (AIV) = 30%
  3. Flakiness index(FI) = 25%
  4. Water absorption = 1%
  5. Stripping value = 25%

Plants AND Equipment’s Required for Bitumen Surface Dressing !!

  1. Bitumen heating device
  2. Mechanical sweeper
  3. Bitumen Sprayer
  4. Pneumatic roller
  5. Aggregate spreader

Construction Steps for Triple Bitumen Surface Dressing!!

  1. Preparation of existing surface
  2. Application of prime coat or tack coat
  3. Application of 16-18 mm stone chippings.
  4. Rolling the pneumatic roller over the first coat for at least four passes
  5. Opening to traffic with a controlled lower speed of less than 10 kph for a couple of weeks
  6. Brooming is done and the loose aggregates are cleaned.
  7. Application of binder material and 10 mm stone chipping for a second coat.
  8. Rolling off the second coat by pneumatic roller for at least four passes.
  9. Opening to traffic with a controlled lower speed of less than 10 kph for one or two weeks
  10.  Once again brooming and cleaning of loose aggregates is done.
  11.  For the third coat, the binder is applied with 8 mm stone chippings
  12.  A pneumatic roller is passed over the third coat at least four passes.
  13.  Finishing and opening to traffic.
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Construction Road Transportation

Water bound macadam road construction procedure

The water-bound macadam construction named after john macadam. In the macadam road construction, the crushed or broken aggregates are bound together by using the rolling procedure.

Binding can be achieved by the use of stone dust as a filler in the presence of water.

The WBM roads are divided into the following types according to the materials used for construction:

  1. WBM roads with gravel including crushed gravel
  2. WBM roads with hard broken stones
  3. WBM roads with soft broken stone and brick residue

Procedure for macadam road construction

a) The thickness of WBM should be from 8cm to 30 cm with each layer of compaction from 7.5cm to 15 cm.

b) The camber provided should be a minimum of 1 in 36 to a maximum of 1 in 48.

c) Materials:

  1. Coarse aggregates:
    1. the crushed and broken stones should be hard,
    2. durable,
    3. strong,
    4. and free from excess of flaky and elongation.

The requirements of coarse aggregates are:

  • Aggregate impact value (AIV) = 30%
  • Los angles abrasion value (LAA) = 40%
  • Flakiness index (FI) = 15%

2. Screening materials of grade A with passing through screening size of 12.5 mm and grade B with a size of screening 10 mm

3. Filler materials of plasticity index (PI) up to 9 shall be used

d) Equipment used

  1. Aggregate spreader
  2. Water tankers
  3. Grader
  4. Compaction equipment (road roller)

e) Construction procedure

  1. 20% of extra broken stones should be provided than estimated.
  2. The subgrade surface is prepared
  3. Pavement construction is carried out by lateral confinement and spreading of coarse aggregates
  4. Dry rolling is done by roller with a load of 6 to 10 tons
  5. Application of screening materials
  6. Wet rolling is carried out to fil about 50% of remaining voids
  7. Filer materials with plasticity index up to 9 are applied in two successive thin layers
  8. Finishing off is done by 6 mm thick sand or earth spreading, sprinkled with water and rolled.
  9. Shoulders are prepared
  10. The WBM is opened for traffic after a few days of construction.

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