Roads are made up of several layers that work together to provide a durable pavement surface. The bottom layer is the subgrade, made of compacted soil. Above that is the base layer, made of crushed rock. The top layer is the pavement, which can be asphalt or concrete. These layers distribute vehicle loads across the road structure to provide a smooth and durable driving surface for many years.

1. Introduction
What is Road /Pavement?
 An open, generally Road pavements
public way for the deteriorate over time
passage of vehicles, Roads have a life due to the impact of
people, and animals. expectancy of traffic, particularly
between 20 - 30 years. heavy vehicles, and
environmental factors.
Finish with a hard smooth
surface (pavement) helped Purpose :
make them durable and Many rely on paved roads
able to withstand traffic to move themselves and their
and the environment. products rapidly and reliably
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2. Functions :
 One of the primary functions of a pavement is load distribution
which can be characterized by the tire loads; tire configurations;
repetition of loads; distribution of traffic across the pavement; and
vehicle speed.
 Pavement material and geometric design can affect quick and
efficient drainage thus eliminating moisture problems such as
mud and ponding (puddles). Consist of:
i) Surface drainage : Removing all water present on the
pavement surface, sloping, chambers, and kerbs.
ii) Subsurface drainage : Removing water that seep into or is
contained in the underlying sub-grade.
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3. Typical Components
 Several elements
make up the
roadway.
 Each layer
represents one of the
elements of the
pavement system.
 All these elements
work together to
provide a quality
durable pavement.
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4. SUB-GRADE EMBANKMENT
BASE Typical Components PAVEMENT
SUB-DRAIN
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5. Embankment
 When roads are built higher than the surrounding
ground, a structure of compacted earth called an
embankment is built.
 The embankment is built to support the other three
layers of the pavement system.
 The construction of embankments for roadways can take
up a large part of the total cost.
 Embankments can be made from almost any common
type of deposit except topsoil.
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6. Sub-grade
 The sub-grade is made of soils that have been specially
prepared to meet the requirements to support the other
two layers.
 The sub-grade is a selected soil material that is
carefully compacted to provide uniform support to the
pavement.
 The sub-grade lies directly on either the embankment or
the native soil.
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7. Base
 The base is a mixture of crushed rock.
 The base layer provides uniform support to the
pavement and allows water that penetrates any joints
or cracks in the pavement to move quickly to the sub-
drain without saturating and softening the sub-grade.
 The base layer lies directly on top of the sub-grade and
is built of clean sand or rock.
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8. Pavement
 The top layer is the pavement.
 The pavement materials can either be Hot Mix
Asphalt (HMA) and Portland Cement Concrete (PCC).
 The pavement itself resists bending, and
distributes vehicle weights over a large area.
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9. Sub-Drain
 The sub-drain collects water from the base and the sub-grade and
drains that water into the ditch.
 The sub-drain sits alongside the pavement, base and sub-grade.
 The sub-drain is basically a trench with a perforated pipe near the
bottom, surrounded by clean coarse-size rock which allows
rapid transportation of water.
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10. Sub-Drain
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11.  Flexible pavements are those which are
surfaced with bituminous (or asphalt)
materials.
 Its "flexible" since the total pavement structure
"bends" or "deflects" due to traffic loads.
 Generally this type of pavement requires some
sort of maintenance or rehabilitation every 10
to 15 years.
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13. Each layer receives the
loads from the above
layer, spreads them out,
and then passes on these
loads to the next layer
below.
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14. Material layers are usually arranged in order of descending load
bearing capacity with the highest load bearing capacity material
(and most expensive) on the top and the lowest load bearing
capacity material (and least expensive) on the bottom QSM 602

15. Thus, the further down in the pavement
structure a particular layer is, the less load
(in terms of force per area) it must carry

17. 3.1 Sub-base Course
 This is the layer (or layers) under the base layer.
 A sub-base is not always needed.
 A proper sub-base consists of various sizes of crushed
stone aggregate, commonly known as crusher run.
 Depending on the sub soils on your site you may need
8-12 inches of various sizes of sub-base.
 With well drained sub soils, without movement, added
sub-base materials may be sufficient, along with proper
pitch & grade.
 If the sub-base is knowingly sufficient, grading &
compaction with vibratory roller or plate compactor in
small areas, may be all that is necessary.
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18. 3.1 Sub-base Course
 It functions primarily as structural support but it can also
help:
a) Minimize the intrusion of fines from the sub-grade
into the pavement structure.
b) Improve drainage.
c) Minimize frost action damage.
d) Provide a working platform for construction.
 The subbase generally consists of lower quality materials
than the base course but better than the sub-grade soils.
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19. 3.2 Base Course
 The first coat to be placed, on top of your proper sub-
base, is the base course .
 It provides additional load distribution and contributes
to drainage and frost resistance.
 The base is built of clean sand or rock.
 The base layer provides uniform support to the
pavement and allows water that penetrates any joints or
cracks in the pavement to move quickly to the sub-drain
without saturating and softening the sub-grade.
 This coat is put in place for strength, plus it works as a
true-leveler course, to take out any small imperfections
in the grade.
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20. 3.2 Base Course
 After the binder is put into place with paver, it is compacted with a
vibratory roller for tighter density and added strength.
 Base courses are usually constructed out of:
i) Aggregate: Base courses are most typically constructed
from durable aggregates that will not be damaged by
moisture or frost action such as dense bitumin macadam (dbm)
ii) HMA: In certain situations where high base stiffness is
desired, base courses can be constructed using a
variety of HMA mixes.
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22. 3.3 Surface Course
 This is the top layer which comes in contact with traffic.
 It normally contains the highest quality materials.
 It serves to prevent the entrance of excessive quantities of
surface water into the underlying base & sub-grade.
 It is sometimes subdivided into two layers:
i) Wearing Course: A layer in direct contact with traffic
loads. It is meant to take the impact of traffic wear and
can be removed and replaced as it becomes worn.
ii) Intermediate/Binder Course: This layer provides the bulk
of the HMA structure. It's main purpose is to distribute
load. It may compose of one or several HMA sublayers.
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23. 3.3 Surface Course
 Hot mix asphalt (HMA) is "the black stuff" used as a
pavement material.
 Its a combination of aggregate and asphalt binder
mixed together at elevated temperatures that forms a
hard, strong construction material when cooled to
suitable temperatures.
 Also known as "asphalt concrete" (AC or ACP), "asphalt",
"blacktop" or "bitumin“
 They must be mixed very well to make sure that the
rocks are evenly distributed in the mix.
 Each rock piece must be completely coated by the
asphalt.
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24. 3.3 Surface Course
 Once it is well mixed, it is laid down on the roadway as
pavement.
 The pavement must then be compacted to achieve
uniform density.
 If this is not done properly, it can reduce the lifetime of
the pavement and increase the costs of maintaining the
road.
 It usually costs less.
 The life expectancy of an asphalt pavement is between
15 to 20 years.
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27.  Rigid pavement composed of a PCC surface course.
 Such pavements are substantially "stiffer" than flexible
pavements due to the high modulus of elasticity of the
PCC material.
 Further, these pavements can have reinforcing steel,
which is generally used to reduce or eliminate joints.
 Because of its relative rigidity, the pavement structure
distributes loads over a wide area with only one, or at
most two, structural layers.
 This type of pavement can serve 20 to 40 years with
little or no maintenance or rehabilitation and often used
in urban and high traffic areas.
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30. 4.1 Sub-base Course
 This is the layer (or layers) under the base layer.
 The properties and function of this layer are similar to
those under flexible roads/pavements.
 A sub-base is not always needed and therefore may
often be omitted.
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31. 4.2 Base Course
 This is the layer directly below the PCC layer and
generally consists of aggregate or stabilized sub-grade.
 It provides additional load distribution, contributes to
drainage, uniform support to the pavement and a stable
platform for construction equipment.
 Bases also help prevent sub grade soil movement due to
slab pumping.
 Base courses are usually constructed out of:
a) Aggregate base.
b) Stabilized aggregate or soil.
c) Dense-graded HMA.
d) Lean concrete
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32. 4.3 Surface Course
 The surface course is the layer in contact with traffic loads.
 It consists of the PCC slab which is the stiffest layer and
provides the majority of strength.
 The surface course can vary in thickness but is usually
between 150 mm (for light loading) and 300mm (for
heavy loads and high traffic).
 Portland cement concrete is the "white stuff" used as
pavement material.
 Portland cement is made by heating shale, limestone and
small amounts of iron-ore to very high temperatures.
 It is then cooled and ground into a fine powder.
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33. 4.3 Surface Course
 Gypsum is added to the powder to keep the powder from
hardening instantly when water is added.
 Portland cement concrete is made by mixing portland
cement with water, and coarse- and fine-size rocks.
 All the materials, including the right amount of air
bubbles, must be in the correct proportions in order for
the mixture to harden properly.
 A properly mixed concrete has all the rock pieces
completely coated all the way around each piece.
 It initially can be more expensive.
 The life expectancy of portland cement pavement varies,
as little as 20 years or more than 40 years.
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35.  Combination of flexible and rigid pavements to give
riding quality.
 The layers for a composite road is similar to the
layers consist in rigid road.
 However, there is another bituminous layer on the
surfaces of concrete slab.
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36. There are several factors that affect pavement life:
 Traffic volume
 Quality of materials used
 Construction practices, and
 How well the other layers of the road perform.
All of these things function together — and any one of
them can add to or detract from the pavement’s
lifetime.
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37. Hard Shoulder
 Continuous strips alongside pavements, which vehicles
may drive during emergencies.
 Normally 3 m wide to fulfilled the functions of the slow
lane.
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38. Kerbs
 To define the limits of carriageway.
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39. Drainage- Surface and Subsurface
 Road Chamber – Cross falls.
 To cope with heavy water run-off during a storm.
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40. Street lamps
 Street lamps are
designed to
illuminate the
surrounding area at
night, not only as a
deterrent to criminals
but also to allow
people to see where
they're going.
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41. Road Markings
 This furniture is any kind of
device or material that is
used on a road surface in
order to convey official
information.
 They provide guidance and
information to drivers and
pedestrians.
 They can be used to
delineate traffic lanes or serve
as noise generators when run
across a road.
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42. Traffic Signs
 They warn drivers of upcoming road
conditions such as a "blind curve",
speed limits, etc.
 Direction signs tell the reader the way
to a location.
 Direction signs are usually mounted on
poles.
 Illumination is added in order to aid
nighttime users.
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43. Street Barriers and Railings
 These keep vehicles
within their roadway
and prevent vehicles
from colliding with
dangerous obstacles.
 Traffic barriers installed
at the road side also
prevent errant vehicles
from falling off to deep
slopes
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44.  An interchange is a road junction that typically uses grade
separation, and one or more ramps, to permit traffic on at
least one road to pass through the junction without crossing
any other traffic stream.
 It differs from an intersection, at which roads cross at grade.
 Interchanges are almost always used when at least one of
the roads is a limited-access divided highway (expressway or
freeway), though they may occasionally be used at
junctions between two surface streets.
 The type of road interchanges commonly used in road
construction are cloverleaf, stacked, diamond, and trumpet.
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