foundation and pavement

1. By:Hassan Jamshed

2.  Road construction is the installation of soil
stabilisers, concrete, asphalt, and other
building materials on a path to create a
surface that vehicles can travel on from one
destination to another.
 While common types of road construction
methods differ based on the nature of the
envisioned road, every highway project
require months or years of planning before
work can begin on site.

4.  Here are the five most popular methods of
road construction, including gravel road
construction methods, asphalt road
construction methods, and other temporary
road construction methods.

5.  1. Earth Road Construction
 2. Gravel Road Construction
 3. Asphalt Road Construction
 4. Concrete Road Construction
 5. Water-Bound Macadam Road Construction

6.  Earth road is a type of road whose pavement
is made of soil.
 To build this type of road, a bulldozer or
scraper is driven along the demarcated path
to clear the site, remove the top soil and to
shape the subgrade.

8.  Once the sub-grade is ready, the desirable
type of soil is dumped into the channel, after
which the material is mixed, spread and
rolled in several layers – each with a
maximum thickness of 10 cm.
 The compacted surface is then allowed to dry
for a few days before opening to traffic.

9.  As the easiest form of temporary road
construction methods, earth roads are very
common in rural areas, mainly because they
do not require specialised skills and huge
budgets to put it in place.
 One of the drawbacks of earth roads is that
they are impassable during heavy rains, which
make them slippery and unsuitable for two-
wheel vehicles. The road is also not capable
of supporting heavy traffic

11.  A gravel road is an improved version of the
earth road – common in rural and semi-urban
areas.
 The procedure of building a gravel road is
similar to that of putting up an earth road,
only that you add a layer of gravel after the
soil is fully compacted.


13.  Gravel road construction methods begin by
preparing the subgrade. The soil is then
compacted properly to reduce its volume of
water and air – creating a harder, denser
surface.
 A solid base is then created by mixing a
binder (cement or lime) into the soil using a
stabilising machine. Once the base hardens,
gravel is then added in layers until you get to
the top.

15.  A one-off application of a bituminous surface
treatment can help a gravel road to remain
smooth and free of cracks and potholes.
 Unlike earth road, gravel road is free of dust
and does not get slippery during the rainy
season. However, this type of road wears off
quite easily and cannot support heavy traffic.

16.  Asphalt road is made of asphalt – a mixture
of fine aggregate particles and bitumen (a
sticky dark viscous liquid obtained through
unfinished distillation of crude petroleum.
 Asphalt road construction methods are very
popular due to asphalt roadway’s flexibility
and the ability to acquire the shape of the
load above it. This helps it to support heavy
commercial vehicles.

18.  This road construction technique starts with
the preparation of the subgrade, a process
that involves removing any existing
vegetation and the topsoil.
 The subgrade should be graded to allow the
water to run off to the sides or bottom. The
ideal slope is a quarter of an inch per foot
(0.635 cm per 30.48 cm).

20.  The base soil should be properly compacted,
preferably with a 1,361-kg twin drum roller
to reduce its volume of water and air – thus
creating a harder, denser surface.
 The base soil is then covered with crushed
rock, whose composition should be rough
and jagged. This type of crushed rock is
usually called ‘3/4″ minus’ or ‘road-base’
mix.
 In the case of clay base soil, 8 inches of
crushed rock is recommended.

21.  The next step involves laying the crushed
rock mixed with bitumen into the subsoil.
Once this is done, you should allow the base
to settle for a week. This will result in a
stronger, more naturally settled base.
 Once the road base is firmly in place, hot
asphalt is poured onto a bed of heavier
aggregate after which it is pressed into it with
a steamroller.

23.  When it finally cools down, the asphalt
becomes strong enough to support
automobile traffic.
 Depending on the expected traffic volumes
and local climatic settings, asphalt paving can
require up to four layers of asphalt.
 Thanks to impermeable properties of
bitumen, asphalt roads are not easily
damaged by rains and they remain motorable
even during heavy rains.

24.  Concrete roads, which are built using a
mixture of Portland cement and asphalt, are
common in towns. These roads are designed
to support heavy traffic and can last up to a
decade with little maintenance.

26.  Like in other methods of road construction,
concrete road projects start with the
preparation of the subgrade. This is followed
by installation of fixed forms – stationary
metal forms (at least 0.2 inch thick and 10 ft.
long) – to hold the concrete in place at the
proper grade and alignment during
construction.

28.  Road builders then mix and lay concrete into
the fixed forms after which a finishing
machine vibrates and trims it into the
required height.
 Traverse and longitudinal joints are cut
between slabs to prevent cracking that
happens due to restrained deformations
resulting from temperature and moisture
variations.
 The concrete surface is now left to cure
before opening the road to traffic.

30.  The downside of concrete road construction
method is that it is costlier compared to other
road building techniques. Besides, concrete
roads do not bend to support heavy loads –
making them less durable.

31.  The brainchild of John Macadam, who was a
Scottish engineer, a water-bound macadam
road is made of broken aggregates bound
together with water and filler material and
laid on a compacted base course.
 Water-bound macadam roads are considered
high quality due to the compacted material.

33.  This method of road construction produces a
roadway that is strong enough to support
heavy commercial vehicles. It is also cheaper
compared to bituminous road construction
technique.