Civil Engineering Mini Project-Flexible Pavemet
Civil Engineering Mini Project-Flexible Pavemet
Civil Engineering Mini Project-Flexible Pavemet
1. PAVEMENT
2. ELEMENTS OF PAVEMET
3. TYPES OF PAVEMETS
a) Flexible pavement
Composition& structure
Preparation of layers
Failures of pavement
Testing of materials
b) Rigid pavements.
PAVEMENT:
ELEMENTS OF PAVEMENT:
1. Camber or cant: it is the cross slope provided to raise middle of the road
surface in the transverse direction to drain off rain water from road surface.
The objectives of providing camber are:
2. Shoulders: Shoulders are provided along the road edge and is intended
for accommodation of stopped vehicles, serve as an emergency lane for
vehicles and provide lateral support for base and surface courses. The
shoulder should be strong enough to bear the weight of a fully loaded truck
even in wet conditions. The shoulder width should be adequate for giving
working space around a stopped vehicle. It is desirable to have a width of
4.6 m for the shoulders. A minimum width of 2.5 m is recommended for 2-
lane rural highways in India.
4. Right of way: Right of way (ROW) or land width is the width of land
acquired for the road, along its alignment. It should be adequate to
accommodate all the cross-sectional elements of the highway and may
reasonably provide for future development.
TYPES OF PAVEMENTS:
1. Flexible Pavements:
The design of flexible pavements is based on the principle that for a load
of any magnitude, the intensity of a load diminishes as the load is
transmitted downwards from the surface by virtue of spreading over an
increasingly larger area, by carrying it deep enough into the ground through
successive layers of granular material.
Functions:
2) Base Course:
The base course serves as the principal structural component of the
flexible pavement. It distributes the imposed wheel load to the pavement
foundation, the sub-base, and/or the sub-grade.
The base course must have sufficient quality and thickness to prevent
failure in the sub-grade and/or sub-base, withstand the stresses produced in
the base itself, resist vertical pressures that tend to produce consolidation
and result in distortion of the surface course, and resist volume changes
caused by fluctuations in its moisture content.
The materials composing the base course are select hard and durable
aggregates, which generally fall into two main classes: stabilized and
granular. The stabilized bases normally consist of crushed or uncrushed
aggregate bound with a stabilizer, such as Portland cement or bitumen.
Functions:
3) Sub base:
This layer is used in areas where frost action is severe or the sub-grade soil
is extremely weak. The sub-base course functions like the base course.
The material requirements for the sub-base are not as strict as those
for the base course since the sub-base is subjected to lower load stresses .
The sub-base consists of stabilized or properly compacted granular material.
Functions:
TO remove heave
To project above layers from bad qualities from underlaying soils.
4) Sub-grade:
The sub-grade is the compacted soil layer that forms the foundation of the
pavement system. Sub-grade soils are subjected to lower stresses than the
surface, base, and sub-base courses. Since load stresses decrease with
depth, the controlling sub-grade stress usually lies at the top of the sub-
grade.
The combined thickness of sub-base, base, and wearing surface must be
great enough to reduce the stresses occurring in the sub-grade to values
that will not cause excessive distortion or displacement of the sub-grade soil
Functions:
Bitumen Surface:
The bituminous surface, or wearing course, is made up of a mixture
of various selected (graded smaller) aggregates bound together with
asphalt or bituminous binders. Thickness is about 25 -50 mm. This
surface prevents the penetration of surface water to the base course;
provides a smooth, well-bonded surface free from loose particles.
Base Course:
The base course serves as the principal structural component of the
flexible pavement. It distributes the imposed wheel load to the
pavement foundation, the sub-base, and/or the sub-grade .The
materials composing the base course are select hard and durable
aggregates, which generally fall into two main classes: stabilized and
granular. The stabilized bases normally consist of crushed or uncrushed
aggregate bound with a stabilizer, such as bitumen. Thickness is 5-
10cm.
Sub Base:
The sub-grade is the compacted soil layer that forms the foundation
of the pavement system. Sub-grade soils are subjected to lower stresses
than the surface, base, and sub-base courses. Since load stresses
decrease with depth, the controlling sub-grade stress usually lies at the
top of the sub-grade, Material used is natural sand, gravels, crushed
stone, and thickness is 100300mm
Compacted soil
The natural soil is compacted to so that it can firmly hold the above
layers.
Surface Preparation:
Before a pavement is placed the surface to be paved must be prepared.
Adequate surface preparation is essential to long-term pavement
performance. Pavements constructed without adequate surface preparation
may not meet smoothness specifications, may not bond to the existing
pavement (in the case of overlays) or may fail because of inadequate sub-
base support. Surface preparation generally takes one of two forms:
Preparing the sub-grade and granular base course for new pavement.
This can involve such activities as sub-grade stabilization, over-
excavation of poor sub-grade, applying a prime coat or compacting the
sub-grade.
Prime Coats:
The graded sub-grade or the top granular base layer can be prepared
with a prime coat. A prime coat is a sprayed application of a cut-backs (or)
asphalt emulsion applied to the surface of untreated sub-grade.
Fill the surface voids and protect the sub-base from weather.
Stabilize the fines and preserve the sub-base material.
Promote bonding to the subsequent pavement layers.
Tack Coats:
A tack coat is thin bituminous liquid asphalt, emulsion or cutback coating
applied between HMA pavement lifts to promote bonding. Adequate bonding
between contr. lifts and especially between the existing road surface and an
overlay is critical in order for the completed pavement structure to behave
as a single unit and provide adequate strength. If adjacent layers do not
bond to one another they essentially behave as multiple independent thin
layers none of which are designed to accommodate the anticipated traffic-
imposed bending stresses. Inadequate bonding between layers can result in
de-bonding followed by longitudinal wheel path cracking, fatigue cracking,
potholes, and other distresses such as rutting that greatly reduce pavement
life.
Sub base: it is the layer of aggregate material laid on the sub-grade, on which
the base course layer is located. It may be omitted when there will be only foot
traffic on the pavement, but it is necessary for surfaces used by vehicles.
Sub base is often the main load-bearing layer of the pavement. Its role is to
spread the load evenly over the sub grade. The materials used may be either
unbound granular, or cement-bound. The quality of sub base is very important for
the useful life of the road and can outlive the life of the surface, which can be
scrapped off and after checking that the sub base is still in good condition, a new
layer can be applied.
FAILURES OF FLEXIBLE PAVEMENT
Sub-grade
Sub-base course
Base course and
Surface course
If any one of the above mentioned layers becomes unstable or weak then it
will result in failure of flexible pavement.
Therefore it is very important to design and construct each layer with utmost
care.
Different types of failure encountered in flexible pavements are as follow.
4. Longitudinal cracking
This types of cracks extents to the full thickness of pavement.
Causes:
10. Pumping
Seeping or ejection of water and fines from beneath the pavement through
cracks is called pumping.
Pumping effect
TESTING OF MATERIALS :
AGE AT TEST: tests shall be made at recognize ages of the test specimens,
the most usual being 7 & 25 days. The ages shall be calculated from the
time of the addition of water of the dry ingredients.
Placing the specimen in the testing machine the bearing surface of the
testing machine shall be wiped clean and loose sand or other material
removed from the surface of the specimen, which are to be contact with the
compression platen in the case of cubes the specimen shall be placed in the
machine in such a manner that the load shall be applied to opposite sides of
the cubes as cast, that is not to the top and bottom. The access of the
specimen shall be carefully aligned with the centre of thrust of the
spherically seated platens. No packing shall be used between the faces of
the test specimen and the steel platen of the testing machine. As the
spherically seated block is brought to bear on the specimen the movable
portion shall be rotated gently by hand so that uniform seating may be
obtained the shall be applied without shock and increased continuously at a
rate of approximately 140kg/cm.cm minimum. Until the resistance of the
specimen to the increasing load breaks down and no greater load can be
sustained. The maximum load applied to the specimen shall thebe recorded
and the appearance of the concrete and any unusual features in the type of
failure shall be noted.
1 day 16%
3 days 40%
7 days 65%
14 days 90%
28 days 99%
Compressive strength of different grades of concrete at 7 and 28
days:
M15 10 15
M20 13.5 20
M25 17 25
M30 20 30
M35 23.5 35
M40 27 40
M45 30 45
FORMULAE:
RESULT:
OBJECT:
APPARATUS:
1) 425micron IS Sieve
PROCEDURE:
Take two 10grams of soil specimen passing through the 425microns sieve.
Two specimens are poured in a each separate cylinders of 100ml capacity.
One cylinder filled with kerosene and other with water up 100ml mark. After
removal of entrapped water each soil I cylinder shall be allowed to settle
.sufficient time (not less than 24h) shall be allowed for the soil sample to
attain equilibrium state of volume without any feature change I the value of
the soil. The final volume of the soils in each of the cylinders shall be read
out
FORMULAE:
The level of the soil in the kerosene graduated cylinder shall be read as the
original volume the soil sample, kerosene being a non polar liquid not cause
swelling (water) only causes the swelling
Unit weight is the weight of soil per unit volume is called unit weight or
density. It includes the whole soil mass, the solid particles plus all voids with
or without moisture. It depends upon saturation S. Since the dry unit
weight of solids per unit of total volume of a soil mass is called dry unit
weight.
APPLICATION:
APPARATUS:
2. Steel trolley 2.5 cm high and 10 cm internal diameter with wall thickness
7.5 mm.
3. Steel hammer.
4. Steel rule.
5. Straight edge.
6. Balance.
7. Container.
2. The mass of the core cutter without trolley was measured accurately.
3. Exposed the small area about 30 sq.cm for test level that surface put the
trolley on the top of the core cutter and driven the assembly into the soil
with the help of hammer with the top of the dolly about 1 cm above
surface.
4. Dry weight the container from the surrounding soil and allowed some soil
to project from the lower and of the cutter with the help of straight edge.
6. Kept some sample of soil for water content determination in the oven.
7. Repeat the test of the 3samples neat by end get the average density.
APPLICATION:
Core cutter method is commonly used for to know the amount of compaction
achieved, in the pavement layers and its value compared, to the design
density values.
OBSERVATIONS:
07 Container no. A B
10 Mass of container 23 gm 23 gm
This test is used to determine the particle shape of the aggregate and each
particle shape being preferred under specific conditions.
The degree of packing of the particles of one size depends upon their shape.
Due to high surface area to volume ratio, the flaky and elongated
particles lower the workability of concrete mixes.
Flaky and elongated particles are considered undesirable for base coarse
construction as they may cause weakness with possibilities of braking
down under heavy loads.
BS-1241 specifies a Flakiness index not exceeding 30% irrespective of
the aggregate size.
Maximum permitted Elongated index is 35, 40 or 45% for aggregate
sizes 2 2, 1 & 3/8.
Both Flakiness and Elongation tests are not applicable to sizes smaller
then 6.3mm i.e. sieve.
APPARATUS:
(in.) (in.)
ELONGATED PARTICLES
These are the particles having length considerably larger than the other two
dimensions and it is the particle whose greater dimension is 1.8 times its
mean size.
ELONGATION INDEX
Weight of
Weight Elongate Individual Weighted
Retained Percentag d Elongatio Elongatio
Sieve Size (gm) e Retained Particles n Index n Index
Passin Retaine
g d (%) (gm) (%) (%)
(in.) (in.)
=8913.
5 = 48.91
RIGID PAVEMENTS: