Roads: – Roads are constructed for making way for easy and uninterrupted access to various destinations. Area covered by roads is larger than area covered by structures, and hence it demands more supervision. Utmost care shall be taken while executing the road construction to have an ‘ IDEAL ROAD’.
The life & serviceability of a road depends mainly on its foundation. The final finish of the road surface can be bituminous or concrete type, as per the need, but the foundation shall be constructed very carefully.
FOUNDATION OF ROAD: –
A] Excavation: –
- Finalize the finished road levels and make pillars of road level at various points.
- Excavate the ground for a minimum depth of 0.6m for good strata & to a minimum depth of 1.5 meter in black cotton soil.
B] Murrum Filling: –
- Fill the murrum in 150mm thick layers and compact it for the desired density by simultaneously watering it. This process of filling the murum in layers with watering shall be carried out till the desired reduced level is obtained. Every layer of murum shall be watered and compacted at optimum moisture content (O.M.C.)
C] Metalling: –
- Carry out the first layer of metalling with 65 to 75mm size hand broken metal to a depth of 150mm, compacted to 110mm with 10-T to 12-T roller. Every layer shall be watered & then compacted. Desired cambers shall be maintained from these layers for the early runoff of the rain water.
- Carry out the second layer of 100mm thickness, compacted to 75mm with 10-T roller.
- Spread the blindage layer of stone grit over the metelled surface.
This process of construction was invented by one Mr.Macadam & hence is called water bound macadam road (W.B.M.). W.B.M. road serves as the foundation for the final surface finish of the road. The final finishes of roads could be in asphalt, concrete, paving blocks etc. The roadside gutters are recommended to collect & drain off the rain water. The life of any road, depends mainly on the early runoff of rain water.
Grouting by using Bitumin: –
- Hand broken metal of 40 mm size is spread and compacted in layers till the total thickness of 75 mm is achieved. Bitumen should be grouted at a minimum consumption rate of 3 to 3.5 Kg/m2 of road area.
- Spread a blindage layer of 12mm grit and dust. Compact this layer by a roller of 10 T capacity.
Tack coat & carpet : –
- Clean the surface properly with wire brush to remove the loose grit.
- Apply a coat of bitumen with minimum consumption of bitumen between 1.5 to 2 Kg/m2.
- Spread a layer of 12 to 20mm metal of thickness 40 mm, compacted to 25 mm mixed with the bitumen content of atleast 1.5 Kg/m2 .
Seal coat: –
- Spread a layer of 10 to 12 mm thick seal coat with a mix of 100 Kg grit & 5% of bitumen. During all these coats, proper cambare, super elevations shall be maintained to drain off the rain water as fast as possible.
VACCUM DEWATERED CONCRETE ROAD:
Work Procedure: –
The foundation for this type of road should be constructed by W.B.M. method.
- The area to be concreted shall be covered with plastic sheet of 100 microns thickness.
- M.S. Channels shall be fixed maintaining 3.5-meter maximum bay width and according to the slope and level dots.
- The reinforcement shall be provided as per design and specifications.
- Concreting shall be done in alternate bays.
- Concreting shall be started from one end and completed in 2 layers, each layer being vibrated by plate vibrator.
- The concrete shall be levelled with beam vibrator. This operation is to be done twice to get proper level.
- After completing the concrete of the bay, filter pad shall be placed above it and then the suction pad shall be placed. Care shall be taken to place the filter pad in such a way that the suction pad goes 6″ beyond the filter pad.
- Dewater the concrete with pressure of 80 kg/cm2 with dewatering time of 5 minutes for every one inch depth of concrete.
- After dewatering is completed, use disc float to get proper finish to the surface.
- Broom finish the surface.
- Cure the concrete for 7 days by ponding method and for 28 days by spraying water.
- After 7 days, make grooves 6mm wide and 50mm deep with grooves cutting machine in an appropriate pattern.
- Fill bituminous filler in groves.
- Allow the road for vehicular traffic after 28 days, from casting.Precautions to be taken while Vacuum Dewatered Concreting work : –
- Extra corner reinforcement is necessary for each bay.
- Cut the grooves in concrete to a depth of 1/3rd thickness of concrete.
- Provide expansion joints at every 30 meters.
- Provide dowel bars of 16mm diameter M.S. round, 600 mm long. at expansion joints.
- One end of dowel is embedded in concrete and the other should be greased before concreting of next panel to have free movement in concrete for absorbing shocks.
- Apply deshuttering agent to the construction joints before casting of adjacent bay.