Stages in Road Construction

Stages in Road Construction

The basic construction process for building a road is similar for any road. The differences arise in the finishing of the road or the surface materials used to finish a road. The process begins with road design, including surveying the route, allowing for drainage and considering the expected volume of traffic and planned development in the area. Next, the important base layers are completed using graders, bulldozers, compactors and levelers, and then the surface layer is applied.

Clearing and Excavation

The area on which the road is going to be built on must be cleared of all vegetation. This includes removing any unwanted material i.e. Tree roots, grass, loose soil, preparing the leveled surface. Excavation is done when the existing material is not suitable for the road, other suitable material is dumped in the excavated portion.

Sub-Grade Preparation

The road takes shape as diggers, excavation plant machinery and bulldozers mount gravel material over the area where the future pathway will run. The road surface is then formed with a camber, and leveled by graders. Culverts and drains, consisting of large concrete pipes, are laid to prevent the road from flooding by draining away groundwater, sewage or stormwater. Sub-grade act as a cushion for other layers i.e.  In order to achieve durable road sub-grade should be strong.

Sub- base and Base materials

The sub-base and base should be laid as soon as possible after final stripping to formation level, to prevent damage from rain or sun baking which could cause surface cracks. The most commonly used material for use in sub-bases is termed Type 1. This is an unbound material made from crushed rock, crushed slag, crushed concrete, recycled aggregates or well burnt non-plastic shale. It contains particles of various sizes, the percentage of each size being within a defined range. Up to 10% may be natural sand. The predefined and calculated range of material sizes contained means that once compacted, it will resist further movement within its structure. In other words, it tends not to sink with time (though it will sink if not compacted properly when laid).

All materials on arrival from the borrow pit must be protected from the weather, as drying or wetting changes the composition. They must be spread evenly. They are laid in layers of 100mm - 200mm compacted thickness, the thickness of the layers being gauged by various means including pegs and lines, sight rails and a guide wire.

                        Uncompacted type 1

                    After compaction

Surfacing

Both the surface course and binder course are included in the part of the road structure termed the surfacing. Normally, it is layed as two course binder and surface.
The binder course helps distribute the load of traffic above onto the base course, which is usually a weaker material. It also provides a flat surface onto which the normally thinner surface course is laid. In new construction, typical thickness is between 45mm and 105mm. Thickness may vary considerably where a new binder course is laid to an existing road structure for strengthening purposes. Stone sizes used are 10, 20 or 14mm. The thicker the binder course, the larger the stone size. Materials used include open graded macadam, dense coated macadam and rolled asphalt. 

Before the last layer of asphalt or chip seal is poured, the sidewalks and drains have to be be finished. The Construction work is concluded by placing the appropriate road signs at the places specified by engineers and the application of road markings.

  

Asphalt 

 

Chip Seal