CPD SEMINAR ON
CAUSES OF PREMATURE ROAD FAILURE AND
STRATEGIES ADOPTED FOR REPAIR AND
RE-HABILITATION
By
Engr. Muhammad Uzair, Executive Engineer
C&W Department
November 7, 2012
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SEQUENCE OF PRESENTATION

IMPORTANCE OF THE SUBJECT

CAUSES OF PREMATURE ROAD FAILURE

STATEGIES FOR RE-HABILITATION

QUESTION & ANSWER SESSION
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IMPORTANCE OF THE SUBJECT
The Seminar on the subject will help:

TO SENSITIZE THE ROAD ENGINEERS AGAINST THE
POTENTIAL CAUSES OF ROAD FAILURE AND TO ACQUAINT
THEM WITH APPROPRIATE REMEDIAL TOOLS

TO IMPART AWARNESS REGARDING THE MENACE OF
OVER- LOADING AND AXLE CONTROL REGIME

TO CONCENTRATE MORE ON DESIGN & QUALITY ISSUES
FOR PRESERVATION OF PRECIOUS ROAD NETWORK
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CAUSES OF PREMATURE ROAD
FAILURE
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MAJOR CAUSES OF PREMATURE ROAD
FAILURE
Following are the major causes of Premature road
failure:
 IN-ADEQUATE PAVEMENT DESIGN
 FAULTY CONSTRUCTION
 IMPEDED DRAINAGE
 OVER-LOADING
 LACK OF PROPER & TIMELY REPAIR
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IN-ADEQUATE PAVEMENT DESIGN
Under-estimation or carelessness in design parameters
leads to in-adequate pavement design which results into
premature road failure much before the predicted
design life.
It may be due to :

Incorrect traffic count or traffic analysis.

Incorrect assessment of Subgrade material

Incorrect selection of design parameters like
serviceability indices, Reliability, and drainage
coefficient etc.
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FAULTY CONSTRUCTION
Effective Quality control at the time of construction is
the essence of good quality work. The design
specification, if not followed in construction as well as
in selection of materials, will obviously lead to some
type of distress resulting into premature road failure.
It may be due to:

Use of Sub-standard materials

Poor workmanship.

In-adequate Compaction of various pavement layers

Deviation from specified construction methodology
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IMPEDED DRAINAGE
Surface drainage is the most important factor
affecting the performance and serviceability of flexible
pavement. A well-designed and well-constructed road
with poor drainage system will fail much ahead of its
design life.
 Water damage is initially caused by hydraulic pressure.
 This pressure pushes the water down into the road
fabrics and break it up.
 Freezing & Thawing phenomena during winter season
further aggravate the situation.
 Eventually, the water descends into the Subgrade layer,
lowers its CBR and results into the deep seated road
failure.
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OVER-LOADING
The most dangerous cause of premature road failure is
the overloaded vehicles carrying load much heavier than
the legal weight anticipated in the pavement design.

The failure on this account is usually very fast as the
damaging factor used in the pavement design has a 4th
degree exponential effect.

This phenomenon results into severe rutting under the
wheel track particularly during hot weather.

The over-loading needs to be checked through an
effective Axle control regime as this menace itself is
sufficient for destruction of an ideal road
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LACK OF PROPER & TIMELY MAINTENANCE
One of the basic factors of premature road failure is the
lack of proper and timely maintenance. Any distress if not
taken care of at initial stage with proper approach will
certainly multiply and increase till such time that it will
result into complete road failure.
The following distresses need timely repair before causing
major road failure :
Cracking (Alligator, Longitudinal, Transverse
Rutting
Shoving
Raveling
Bleeding
Potholes & Patches
& Block cracks)
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SRATEGIES FOR REPAIR &
REHABILITATION
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SRATEGIES FOR REPAIR & REHABILITATION
Once the distress is noticed in the road pavement, the same
should be repaired immediately with appropriate technique
otherwise the damages will multiply with the passage of
traffic and subsequent rainy spills.
While selecting an appropriate mode of repair or rehabilitation, the following factors should be kept in mind:
Type of road
Type and volume of traffic
Material availability
Economic considerations
Before discussing various repair techniques, lets through
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some light on the types of Distresses.
TYPES OF ROAD FAILURE
The following distresses usually develop in flexible pavements due
to premature road failure :
Cracking
(Alligator, Longitudinal and Transverse cracks)
Rutting
Settlement
Shoving
Raveling
Fretting
Bleeding
Potholes & Patches
Details of these failures and their repair/ rehabilitation are mentioned in the next slides:-
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CRACKING
CRACKING is the most significant distress causing roughness and
leading to water infiltration deep into the underlying pavement layers. Cracks
should be sealed as soon as possible with appropriate Crack seals, Fog seals or
Slurry seals according to their intensity, nature and locations. Cracks are
further sub divided into the following categories:
Alligator Cracking
These are series of interconnected cracks formed due to fatigue
failure of Asphalt surface generally caused by repeated traffic
loading. These may be “Bottom –up” or “Top-Down” cracking depending
upon the thickness of Asphalt concrete. The cracked area should be
cold milled and re-filled with fresh HMA layers.
Longitudinal Cracking
These cracks are formed parallel to the road centerline; caused usually
due to fatigue action or faulty construction joint.
Transverse Cracking
These cracks are formed perpendicular to the road centerline; caused
due to shrinkage of Asphalt in low temperatures. Longitudinal and
transverse cracks when interconnect, become Block cracking.
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Longitudinal Crack
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Transverse Crack
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Alligator Crack
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Alligator Cracking
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Block Cracking
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RUTTING
Rutting usually occurs under the wheel track during hot weather when
the Asphalt concrete in the wheel path softens and displaces to both
sides forming longitudinal humps and depressions along the traffic
flow. The rutted area should be removed and reconstructed with the
required pavement layers according to its severity.
Rutting is of two types:
Mix Rutting
Subgrade Rutting
Rutting is caused due to:
 Over loading
 Excessive mineral filler
 High Asphalt content
 Deficiency of angular aggregate in the mix
 Insufficient compaction of HMA layers during
construction.
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QUESTIONS ?
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SETTLEMENT
This is the most serious road failure caused due to faulty
design, sub-standard construction, poor drainage or excessive
over-loading.
In this type of failure, the damage extends down to the
subgrade bottom. It can be rehabilitated through complete
reconstruction only.
SHOVING
It is a form of plastic movement typified by ripples or
corrugations visible as an abrupt wave across the pavement
surface. The distortion is usually perpendicular to the traffic
direction and occurs at points where traffic starts or stops. It
is caused by traffic action coupled with poor JMF or mix
contamination. It is corrected through cold milling and re-laying
of Fresh HMA or resurfacing.
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SHOVING
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COLD MILLING
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COLD MILLING
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COLD MILLING ON MARDAN –SWABI ROAD
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TACK COAT APPLIED TO MILLED SURFACE
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FILLING OF MILLED SURFACE WITH ASPHALT CONCRETE
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RAVELING
This is the progressive disintegration of Bituminous layers
as a result of the dislodgement of aggregate particles. It leads
to surface roughness due to loose debris on the pavement and
loss of skid resistance. Raveling may be treated with appropriate
Bituminous Surface Treatment(BST)
BLEEDING
It is the formation of a thin film of Asphalt binder due
high Asphalt content commonly observed in hot weather. It
usually creates a shiny surface that can become quite sticky.
Minor bleeding can often be corrected by applying coarse sand
to blot up the excess asphalt binder.
Major bleeding can be treated by cutting off excessive asphalt
with motor grader. If the resulting surface become excessively
rough, resurfacing may be necessary.
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FRETTING
This is a phenomenon in which the surface material gradually
loose its control with the surface due to ageing or overheated mixture
causing premature ageing. It not only causes undulated surface but also
invite ponding of water in the fretted out surface. Such type of
damage can economically be restored with single or double coat of
surface dressing according to its severity.
POTHOLES & PATCHES
Small Bowl-shaped depressions in the pavement surface that
penetrate all the way through the HMA layers down to the base course
are called potholes. They generally have sharp edges and vertical sides
near the top. Serious vehicular damage can result from driving across
potholes at higher speeds. Potholes are the end result of alligator
cracking. For repair, the potholes should be trimmed to geometrical
shape and filled with base and/or Asphalt concrete. Interconnected
potholes can be combined to form a patch and treated in the same way
as that of individual pothole.
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Extensive Cracking and potholes
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CRACK SEALS
Crack seal products are used to fill individual pavement cracks
to prevent entry of water or non-compressible substance such as sand,
dirt or weeds. Crack sealant is typically used on early stage
longitudinal cracks ,transverse cracks ,reflection cracks and block
cracks. Alligator cracks are most often too extensive to warrant filling
with crack sealer; they usually require an area treatment such as MILL
& FILL or reconstruction. Crack filler material is typically some form
of rubberized asphalt or sand slurry.
FOG SEALS
A fog seal is a light application of a diluted slow-setting
asphalt emulsion to the surface of an aged(oxidized) pavement
surface. Fog seals are low-cost and are used to restore flexibility to
an existing HMA pavement surface. They may be able to temporarily
postpone the need for a surface treatment or non-structural overlay
for an year or two.
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SLURRY SEALS
A slurry seal is a homogeneous mixture of emulsified
asphalt, water, well-graded fine aggregate and mineral filler
that has a creamy fluid-like appearance when applied. Slurry
seals are used to fill existing pavement surface defects as
either a preparatory treatment for other maintenance
treatments or as a wearing course. There are three basic
aggregate gradations used in slurry seals:
 Type I : Fine Slurry Seals (with aggregate size upto 0.25 in)
 Type II : General Slurry Seals(with aggregate size upto 0.25 in)
 Type III: Coarse Slurry Seals(with aggregate size upto 0.25 in)
The performance of Slurry seals can further be improved with the
addition of polymers for specialized cases; the process being called
Micro surfacing.
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BITUMINOUS SURFACE TREATMENT (BST)
Bituminous surface treatment, also known as a seal coat
or chip seal, is a thin protective wearing surface that is
applied to a pavement or base course. BSTs can provide
the following functions:
 A waterproof layer to protect the underlying pavement.
 Increased skid resistance.
 A fill for existing cracks or raveled surfaces.
 A anti-glare surface during wet weather and an increased
reflective surface for night driving.
BST can be Single Surface Treatment (SST), Double Surface
Treatment(DST) or Triple Surface Treatment (TST) depending upon
the number of coats needed to restore a worn out surface.
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BITUMINOUS SURFACE TREATMENT (BST)
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SUMMARY OF FAILURES, CAUSES AND CURES
S.No
Type of
Failure
1
Cracking
Fatigue failure of HMA, Loss of pavement
supporting characteristics and
Temperature cycling.
Crack seals, Fog seals, Slurry seals or
ultimately “MILL & FILL” for severe
alligator cracking.
2
Rutting
In-adequate pavement design, Excessive
mineral filler, high asphalt content, inadequate compaction and over-loading
Cold milling and relaying of fresh
HMA layers OR Bituminous
Surface Treatment (BST)
3
Settlement
Faulty pavement design, Sub-standard
materials, impeded drainage and inadequate compaction
Removal of damaged layers and
reconstruction as per fresh
pavement design
4
Shoving
Traffic action and faulty JMF
Cold milling and relaying of fresh
HMA layers OR Bituminous
Surface Treatment (BST)
5
Raveling
Dust coating on aggregate, segregation of
aggregate, Sub standard asphalt binder
and in-adequate compaction
Bituminous Surface Treatment (BST)
with single or double coats as per
surface condition
6
Fretting
Dust coating on aggregate, Sub standard
asphalt binder and in-adequate
compaction
Bituminous Surface Treatment (BST)
with single or double coats as per
surface condition
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Bleeding
Excessive Asphalt content in HMA,
excessive application of binder in BST or
low HMA air voids
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Potholes &
Patches
Sand blotting OR in severe cases the
excessive Asphalt is removed
through motor grader and surface
rectified through BSTs.
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Filling of potholes with Base
Asphalt as needed.
Causes
Final result of Alligator cracking or
sometimes due to utility cuts.
Cures
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THANK YOU
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