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
