The following 6 basic steps are involved in the construction of a water bound macadam road as given below.

  1. Sub grade preparation
  2. Preparation of sub-base
  3. base preparation
  4. course wear preparation
  5. Shoulder preparation
  6. open to traffic

step 1 (build sub-grade)

The sub-grade acts as a cushion for the other layers i.e. the sub-grade must be strong to get a durable road. The sub-grade is provided by excavating the sub-soil and the level of the sub-grade is determined by subtracting the total thickness of the pavement from the finished level of the road pavement. The sub-grade is thoroughly compacted by rollers weighing 8 tonnes by sprinkling water the night before. Low spots that develop during rolling should be built up and brought to grade as needed. In rocky areas the sub-grades are not rolled whereas in clay soil area, a layer of natural sand, moorum or gravel is provided at the sub-grade and duly packed.

sub grade preparation
sub grade preparation

step 2 (creation of sub-base)

On a well compacted sub-grade, spread boulders or broken stone of 10 to 20 cm size, or burnt bricks in layers of 15 cm thickness and keeping the total width of the sub-base 60 cm wider than the width of the pavement Go, which is projected 30 cm on each side. The sub-base must be compacted by a roller to provide a uniform surface.

roller compaction
roller compaction

step 3 (building the base)

The specified material of the base course is spread over the prepared sub-base or directly on the sub-grade, as the case may be, and the proper grade, thickness and cross section is maintained as per the design shown on the drawing supplied .

step 4 (preparing the wear course)

The course can be laid in one or two layers as per the total designed thickness and the thickness of each layer should not exceed 10 cm. This component being very important, following steps can be taken systematically.

  1. Check for bad parts/patches of newly laid base course i.e. fix them by soldering
  2. Provide bricks or mud curbs at either end edges strong enough to prevent the new road material from spreading outward and to retain the water used in the consolidation of the wear course.
  3. Spread the road metal evenly on the prepared base to the specified thickness and pack them by hand to bring the finished surface to the required camber.
  4. Spread the coarse aggregate over the surface and roll it with a suitable roller until interlocking of the aggregate with sufficient free space is achieved. Rolling is started from the edges and gradually shifted towards the centre.
  5. After dry rolling, spread the screening material (stones up to 12 mm in size) at a uniform rate so that the blanks of coarse aggregate are filled properly. This is achieved by dry rolling and alternately sweeping, until the voids of the coarse aggregate are filled.
  6. After dispensing the filtrate material, sprinkle enough water, clean the surface and roll with the roller again.
  7. Now apply the binding material in two to three thick layers at a slow and uniform rate. Each layer of binding material is rolled after sufficient water has been added. The solution is cleaned with a broom to fill the void properly. The moving wheel of the roller should be cleaned with water. Continue spreading the binder, spraying water, sweeping and rolling until the empty space is filled and the solution forms a wave in front of the wheel as the roller moves.
  8. Let it dry overnight after proper compaction. Spread a layer of sand or clay about 6 mm thick and re-roll the surface after sprinkling it lightly.
  9. The surface may be allowed to cure for 7 to 10 days.
spread binder
spread binder

Step – 5 (shoulder build)

While fixing the pavement surface, prepare the shoulders by filling the soil at the specified cross slope and compact them properly by rolling or tamping. Shoulder width and thickness should be as per specification.

build shoulders
build shoulders

Step – 6 (opening for traffic)

Once properly dried, road pavements can now be opened to traffic, ensuring that traffic is evenly distributed over the entire width of the pavement.

Er. Mukesh Kumar

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Er. Mukesh Kumar is Editor in Chief and Co-Funder at ProCivilEngineer.com Civil Engineering Website. Mukesh Kumar is a Bachelor in Civil Engineering From MIT. He has work experience in Highway Construction, Bridge Construction, Railway Steel Girder work, Under box culvert construction, Retaining wall construction. He was a lecturer in a Engineering college for more than 6 years.