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HIGHWAY
TYPES OF FAILURES IN FLEXIBLE PAVEMENTS
The different types of failures in flexible pavements are described below:
1. Subgrade failure.
2. Base failure or base course failure.
3. Surface failure or wearing course failure.
1. SUBGRADE FAILURE:
Excessive deformation in subgrade soil of a flexible failure is called subgrade failure.
This is one of the main causes of failure of flexible pavements. This type of failure
causes undulations (ups and downs) and corrugations in the pavement surface.
Causes Of Subgrade Failure:
1. Inadequate stability.
2. Inadequate road drainage.
3. Excessive stress application.
2. BASE COURSE FAILURE:
Excessive deformation in the base or foundation course of a flexible pavement is known
as base course failure.
This type of failure causes potholes, waves, and corrugations in the pavement surface.
Causes Of Base Course Failure:
1. Insufficient strength.
2. Loss of binding action.
3. Crushing of base course material.
4. Lack of lateral confinement of the granular base course.
5. Insufficient wearing course.
6. Inadequate quality control.
7. Inadequate road drainage.
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3. SURFACE FAILURE:
Excessive deformation in the wearing course of a flexible pavement is called surface
failure or wearing course failure.
This type of failure causes ruts, potholes, cracks etc in the pavement structure.
Causes Of Surface Failure:
1. lack of proper mix design
2. Use of the inferior type of binder.
3. Inadequate quality control.
4. Volatization and oxidation of binder.
RESULTS OF FLEXIBLE FAILURE:
1. RUTS:
The longitudinal depressions or cuts in flexible pavement is known as ruts. These are
usually formed ion earth or W.B.M roads of one lane width due to repetitive traffic wheel
loads on the same location, particularly under wheeled traffic.
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2. POT HOLES:
The isolated depressions, more or less circular in shape formed in flexible pavements
are called pot holes or patches. These are usually formed in all types of flexible
pavements due to disintegration of road metal or lack of binding surface course with the
underlying base.
3. FROST HEAVING:
A localized heaving up of pavement portion is known as frost heaving.
The water which may find access to pavement structure freezes in cold climates. The
expansion accompanying this frost action causes upheaval which in turn may crack the
pavement surface.
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4. SHEAR FAILURE CRACKING:
The formation of a fracture or cracking due to upheaval of pavement portion followed by
a depression called shear failure cracking. This type of failure occurs due to localized
weakness in the pavement.
5. LONGITUDINAL CRACKING:
The formation of cracks in the longitudinal direction of a road pavement is called
longitudinal cracking.
This failure is caused due to frost action, different volume changes in subgrade,
settlement of filling material or due to sliding of side slopes.
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6. MAP CRACKING:
The development of irregular cracks, usually formed on bituminous surfacing is called
map cracking.
This type of flexible road failure is due to excessive wear of the road surface or due to
localized weakness in the underlying base course.
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CEMENT CONCRETE ROADS – ADVANTAGES AND DISADVANTAGES
Cement Concrete Road
CEMENT CONCRETE ROADS:
The roads having their wearing surface consisting of cement concrete (plane or
reinforced) are known as cement concrete roads or concrete roads.
These roads are types of rigid pavements and remain in serviceable condition under all
weather conditions. Thus concrete roads are also considered as all weather roads. Due
to their excellent riding surface, pleasing appearance and long life under most severe
traffic conditions, cement concrete roads are much preferred.
Cement concrete roads are superior to most other types of roads including bituminous
roads. These roads are very popular as high cost pavements in developed countries like
America, Russia, Japan etc.
ADVANTAGES OF CEMENT CONCRETE ROADS:
1. Concrete roads have long life than any other roads.
2. These roads are durable and are practically unaffected by weathering agencies.
3. They provide an excellent riding surface under all weather conditions.
4. They provide an impervious, dustless and sanitary surface.
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5. They do not develop corrugations.
6 Can be laid on any subgrade.
7. Can be easily reinforced when they are to resist high stresses due to heavy wheel
loads of the traffic.
8. Concrete roads are non slipery and offer less tractive resistance.
9. They provide good visibility for traffic during night hours.
10. Maintenance cost is low.
DISADVANTAGES OF CEMENT CONCRETE ROADS:
1. The initial cost of concrete roads is high.
2. They are liable to crack and warp due to temperature variations.
3. Become noisy under iron-tyred traffic.
4. Skilled supervision and labour are required for construction.
5. less resilient than bituminous or W.B.M roads.
6. Require long time for curing and thus cannot be opened to traffic earlier.
7. It is very difficult to locate and repair sewers and water mains lying under the
pavement in their case.
COMPONENTS OF ROAD PAVEMENT STRUCTURE
COMPONENTS OF ROAD PAVEMENT STRUCTURE:
Following are the different components of road structure:
1. Subgrade
2. Sub-base
3. Base course
4. Surface course or wearing course
All these components belong to a typical flexible pavement, whereas rigid pavement
usually consists of subgrade, subbase and a concrete slab.
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1. SUBGRADE:
The finished and compacted surface of earthwork on which a road pavement rests is
called subgrade or formation.
The subgrade of a road may be provided on an embankment, in cutting or existing
ground level depending upon the topography and the finalized formation level. It
consists of well compacted natural soil brought to the required camber and gradient.
The thickness and type of pavement structure depend upon the supporting power of the
subgrade because the entire load of the pavement, including the load of traffic
transmitted through the pavement, is ultimately taken up by the subgrade.
2. SUB-BASE:
A layer of granular material provided in between the subgrade and the base course in a
road pavement is known as sub-base.
It is provided as an additional layer when subgrade is of poor quality. It consists of a
layer comparatively cheaper material like burnt clinker, natural gravel or slag.
3. BASE COURSE:
A layer of boulders or bricks provided over the subbase or immediately over the
subgrade in the absence of sub-base in a road pavement is called base course or soling
or foundation course.
This course is considered as the most important and major component of road structure
because this course is to bear the impact of traffic transferred through the wearing
course. It consists of a stable material like boulders, gravel, one or two layers of wellburnt bricks etc. In case of rocky subgrade, this course is not provided.
4. SURFACE COURSE OR WEARING COURSE:
The topmost layer of the road pavement directly exposed to traffic is called is called
wearing course or surfacing.
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It may consist of one or more number of layers in case of flexible pavements. A good
wearing course should be impervious and weather resisting. it should be able to resist
abrasive action of the traffic.
SUPERELEVATION OF ROAD – ADVANTAGES AND DESIGN OF SUPER
ELEVATION
SUPERELEVATION OF ROAD:
The inward transverse inclination provided to the cross-section of the carriageway at
horizontally curved portion of a road is called superelevation, cant or banking.
Superelevation is provided to counteract the effect of centrifugal force and to minimize
the tendency of the vehicle to overturn or skid by raising the outer edge of pavement
with respect to the inner edge, providing a transverse slope throughout the length of the
horizontal curve.
It is expressed as the ratio of elevation of the outer edge above the inner edge to the
horizontal width of carriageway or as the tangent of the angle of slope of the road
surface. It is generally denoted by ‘e’ or S.E.
OBJECTS OF PROVIDING SUPERELEVATION:
1. To counteract the effect of centrifugal force acting on the moving vehicle to pull out
the same outward on a horizontal curve.
2. To help a fast moving vehicle to negotiate a curved path without overturning and
skidding.
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3. To ensure safety to the fast moving traffic.
4. To prevent damaging effect on the road surface due to improper distribution of load.
ADVANTAGES OF SUPERELEVATION:
1. It allows running of vehicle at high speed on a curved path as on a straight path
without any danger of overturning and thus results into increased volume of traffic.
2. It provides more or less even distribution of load on wheels and hence uniform stress
is offered on the foundation which results into less wear on wheel tyres and springs as
well as economy in maintenance cost of the road.
3. It also helps to keep the vehicles to their proper side on the pavement and thus
prevents collision of vehicles moving in opposite directions on a curved portion of the
road.
4. It provides drainage of the whole width of road towards the inner side. Thus, there is
no necessity of providing side drain on the outer side of the road.
DESIGN OF SUPERELEVATION:
To design superelevation for mixed type of traffic is a complex problem. The Indian
Roads Congress has recommended to provide superelevation to counteract the
centrifugal force fully due to 75% of the design speed and limiting the maximum
superelevation to 1 in 15 or 7%.
Following are the steps adopted to design the superelevation of a road:
Step 1:
Calculate the superelevation for 75% of design speed neglecting the friction i.e f = 0
V = 75%(V) = 0.75 V
We know that, e+f = V²/127R
e + 0 = (0.75 V)²/127R
Step 2:
If the calculated value ‘e’ is less than 7% or 0.07, then provide the obtained value. If it
exceeds 0.07 then provide the limiting value of superelevation emax = 0.07 and proceed to
the next step.
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Step 3:
Check the coefficient of friction developed for the maximum value of e = 0.07 at the full
value of design speed,
If the value of ‘f’ thus calculated is less than 0.15, the superelevation of 0.07 is safe for
the design speed. If not, calculate the restricted speed as given in step 4.
Step 4:
If the calculated value of ‘f’ exceeds 0.15, then the speed of the vehicles is restricted to
the value Vr m/sec or Vr km/hr as calculated after allowing the limiting values of e and f
in the following equation:
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In case of an important highway, it is always desirable to design the road without speed
restriction at curves. Hence, the curve should be realigned, if possible with a longer
radius of curvature so that the design speed can be maintained without any restriction.
DIFFERENCE BETWEEN FLEXIBLE PAVEMENTS AND RIGID PAVEMENTS
FLEXIBLE PAVEMENTS:
The pavements having low or negligible flexural strength and are flexible in their
structural action under the loads are known as flexible pavements.
RIGID PAVEMENTS:
Rigid pavements are those which contain great amount of flexural strength or flexural
rigidity.
In rigid pavements, the stresses are not transferred from grain to grain to the lower
layers as in the ease of flexible pavement layers.
DIFFERENCE BETWEEN FLEXIBLE PAVEMENTS
AND RIGID PAVEMENTS:
POINT OF
DIFFERENCE
FLEXIBLE
PAVEMENTS
RIGID
PAVEMENTS
Initial cost
Life span
Their initial cost is low.
They have short life
span.
Their thickness is more.
Joints are not required.
Their initial cost is high.
They have long life span.
Thickness
Joints
Subgrade
Durability
Temperature effect
A reasonably good
subgrade is required.
They are less durable
Stresses are not induced
in these pavements due
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Their thickness is less.
Joints are essentially
required.
A good subgrade is not
necessary.
They are more durable.
Heavy stresses are
induced in these
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Repair work
Skill and supervision
Feasibility of providing
underground works
Openings to traffic after
construction
Resiliency
Corrugations
Behavior with subgrade
settlement.
Tractive resistance
Traffic suitability
Night visibility
Glaring effect
Feasibility of stage
development
to temperature
variations.
Easy repair work.
Moderate skill and less
supervision are required.
It is easy to lay, locate or
repair underground
pipes below these
pavements.
Can be opened to traffic
shortly after
construction.
pavements due to
temperature variations.
Difficult to repair.
More skill and
supervision is required.
It is very difficult to
provide or repair
underground pipes
below these pavements.
Require curing after
construction and thus
cause delay in opening to
traffic.
More resilient to traffic
load.
They develop
corrugations.
Less resilient to traffic
load.
No corrugations are
developed in these
pavements.
They do not adjust
according to any
deformation of subgrade
without rupture.
They have less tractive
resistance.
Noisy under iron
wheeled traffic.
They offer good visibility
at night.
They adjust according to
any deformation of
subgrade without
rupture.
They have more tractive
resistance.
Suitable for all types of
traffic.
Blacktop pavements
provide poor visibility at
night.
They do not usually
cause glare due to
reflected sunlight.
Stage development is
feasible.
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They often cause glare
due to reflected sunlight.
Stage development is not
feasible.
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Effect Of loading
Maintenance cost
They adjust themselves
to normal loading by
undergoing elastic
deformation.
Maintenance cost is
high.
They tend to act as a
beam or cantilever and
resist deformation.
Maintenance cost is low.
WHAT IS BITUMEN AND ITS USES
WHAT IS BITUMEN AND ITS USES:
Bitumen is the binding material present in asphalt. Sometimes it is also known as
mineral tar. Bitumen is produced by partial distillation of crude petroleum.
it is chemically a hydrocarbon and insoluble in water. But it totally dissolves in alkalies,
alkaline carbonates, benzol, chloroform, bisulphide, naptha, coal tar, petroleum spirit
and oil of turpentine.
It is obtained from 87% carbon, 11% hydrogen and 2% oxygen (By weight). The
bitumen is produced in solid or semi-solid state and black or brown in color.
FORMS OF BITUMEN:
The general forms of bitumen are as following
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1. BITUMEN EMULSION:
It is a liquid compound which contains a large amount of bitumen in aqueous medium. It
is suspended by some appropriate stabilizing agents in the aqueous medium.
2 CUT-BACK BITUMEN:
This form of bitumen is produced by fluxing asphaltic bitumen in presence of some
liquid distillates of petroleum or coal tar. Cut-back bitumen can be used as bitumen
paint in cold.
3 BLOWN BITUMEN:
It is a special form of bitumen produced by passing air under pressure at a higher
temperature. This type of bitumen can be used as heat insulating material, roofing and
damp-proofing felts, producing asphalt pipe and joint fillers etc.
4 PLASTIC BITUMEN:
It comprises of bitumen thinner and appropriate inert filler (40%-45%). Plastic bitumen
can be used for filling cracks in masonry structures, stopping leakages etc.
5 STRAIGHT RUN BITUMEN:
This type of bitumen is obtained by distillation of the bitumen to a definite viscosity or
penetration without further treatment:
APPLICATION OF BITUMEN:
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Road Construction.
Hydraulics & erosion control Catchment areas, basins.
Dam groutings,
Dam linings,
Embankment protection
Dam linings,
Embankment protection
Ditch linings, Reservoir linings
Reservoir linings
Jetties, Dyke protection
Dyke protection
Swimming pools
Waste ponds
Water barriers
Mattresses for levee & bank protection
Membrane linings,
Waterproofing
Revetments
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
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Sand dune stabilization,
Drainage gutters,
Backed felts
FIELD DENSITY TEST OF SOIL BY SAND CONE METHOD
FIELD DENSITY TEST ( SAND CONE METHOD):
The sand cone method is one of the most common methods that are used for field
density test in highway construction. The dry density test is carried out in the field to
check the compaction of the layers.
Compaction is very useful for preparing the sub-base grade and other layers of
pavement. Compaction is done in the construction of embankment for increasing the
stability as well as for decreasing the settlement.
In field compaction, the compacting moisture content should be controlled first and the
adequacy of rolling should be controlled by checking the achieved dry density and
comparing with the maximum dry density.
Base layer – 98%
Sub base layer – 98%
Type 1 layer – 95 %
ABC layer – 100%
PROCEDURE OF TEST:
1. First, take the weight of the empty sand cone and then fill it with dry sand and then
weight again.
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2. Collect the excavated soil from the hole and measure the weight.
3. After weighting, collect the specimen of soil to determine the water content in it.
4. Now place the sand cone on the test hole with the help of the base plate and allow
the sand to run by opening the control valve.
5. When the sand stops running, close the valve and weight the cone with the existing
sand. Finally, calculate the dry density of the soil by given below formula. If the test fails,
compact and perform the test again.
CALCULATION:
The volume of the hole = Mass of sand in hole/Density of used sand.
Wet density = Mass of wet excavated soil/Volume of hole
Dry density = Wet density × 100%/ Moisture content of soil + 100
Degree of compaction = Dry density × 100%/Maximun dry density.
TYPES OF ROAD CAMBER- ADVANTAGES AND METHODS OF
PROVIDING CAMBER
WHAT IS CAMBER?
Camber is the slope provided to the road surface in the transverse direction to drain off
the rainwater from the road surface. It is also known as cross slope of road.
WHY CAMBER IS PROVIDED IN ROAD?
1. To protect the road by preventing the entry of surface water into the subgrade soil
through pavement.
2. To prevent the entry of water into the bituminous pavement layers.
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3. To remove the rainwater from the pavement surface as quickly as possible and to
allow the pavement to get dry soon after the rain.
TYPES OF CAMBER:
1. COMPOSITE CAMBER:
It consists of two straight slopes from the edges with a parabolic or circular crown in the
center of camber. This type of camber can be easily constructed and maintained.
2. SLOPED OR STRAIGHT CAMBER:
It consists of two straight slopes from the edges joining at the center of the carriageway.
This type of camber is very simple and can be easily constructed and maintained.
3. PARABOLIC OR BARREL CAMBER:
It consists of a continuous curve either elliptical or parabolic. It provides a flat road
surface at the middle and steeper towards the edges. On account of steeper edges, this
type of camber provides better drainage property. This camber is therefore preferred by
fast moving vehicles and suggested for urban roads.
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This type of camber is difficult to construct and maintain. The barrel camber has more
steeper edges which are inconvenient to use. Moreover, the steeper edges are errored
quickly and hence additional kerbs are to be provided.
ADVANTAGES OF CAMBER:
1. Camber provides quick drainage of rainwater and thus saves the foundation course
of the road structure from weakening by percolation of rainwater to it through the road
surface.
2. This prevents rainwater to accumulate in local shrinkages or depressions and forming
water pool on the road surface, which are disagreeable to the public as well as to the
road structure.
METHOD OF PROVIDING CAMBER:
Usually, camber is provided on the straight roads by raising the center of the
carriageway with respect to the edges, forming a crown or highest point on the center
line.
At horizontal curves with superelevation, the surface drainage is effected by raising the
outer edge of pavement with respect to the inner edge while providing the desired
superelevation. the rate of camber or cross slope is usually designed by 1 in ‘n’ which
means the transverse slope is in ratio 1 vertical to “n” horizontal. Camber is also
expressed in percentage. If the camber is x %, the cross slope is x in 100.
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RECOMMENDED VALUES OF CAMBER FOR
DIFFERENT TYPES OF ROAD SURFACES BY
IRC:
TYPES OF CURVES ON HILL ROADS
TYPES OF CURVES ON HILL ROADS:
The types of curves provided on hill roads are as following:
1 Hair-pin curves,
2 salient curves,
3 Re-entrant curves.
1. HAIR-PIN CURVES:
‘The curve in a hill road which changes its direction through an angle of 180 or so, down
the hill on the same side is known as hair-pin curve.
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This curve is so called because it conforms to the shape of a hair-pin. The bend so
formed at the hair-pin curve in a hill road is known as pin bend. This type of curve
should be located on hill side having the minimum slope and maximum stability. It must
also be safe from the view point of land slides and ground water. Hair-pin bends
with long arms and farther spacing are always preferred. They reduce construction
problems and expensive protective works. Hair-pin curves or bends of serpentine nature
are difficult to negotiate and should, therefore,e be avoided as far as possible.
2. SALIENT CURVES:
The curves having their convexity on the outer edges of a hill road are called salient
curves.
The center of curvature of a salient curve lies toward the hill side. This type of curve
occurs in the road length constructed on the ridge of a hill. The bend so formed at the
salient curve in hill road is known as corner bend.
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Salient curves are very dangerous for fast-moving traffic. At such a curve or at corner
bend, the portion of projecting hill side is usually cut down to improve the visibility. The
outer edge of the road at such a curve is essentially provided with a parapet wall for
protection of the vehicles from falling down the hill slope.
3. RE-ENTRANT CURVES:
The curves having their convexity on the inner edge of a hill road are called re-entrant
curve.
The center of curvature of a re-entrant curve lies away from the hill side. This type of
curve occurs in the road length constructed in the valley of a hill.
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These curves are less dangerous as they provided adequate visibility to the fast-moving
traffic. At such curves, the parapet wall is provided only for safety of fast-moving traffic.
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