CPD SEMINAR ON

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• CPD SEMINAR ON
• CAUSES OF PREMATURE ROAD FAILURE AND STRATEGIES
  ADOPTED FOR REPAIR AND
  RE-HABILITATION

By
Engr. Muhammad Uzair, Executive Engineer CW
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
  Block cracks)
• Rutting
• Shoving
• Raveling
• Bleeding
• Potholes Patches

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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
  re-habilitation, 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 some light on the types of Distresses.

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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/
  re-habilitation 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 SUMMARY OF FAILURES, CAUSES AND CURES SUMMARY OF FAILURES, CAUSES AND CURES SUMMARY OF FAILURES, CAUSES AND CURES
S.No Type of Failure Causes Cures
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, in-adequate 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 in-adequate 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
7 Bleeding Excessive Asphalt content in HMA, excessive application of binder in BST or low HMA air voids Sand blotting OR in severe cases the excessive Asphalt is removed through motor grader and surface rectified through BSTs.
8 Potholes Patches Final result of Alligator cracking or sometimes due to utility cuts. Filling of potholes with Base and Asphalt as needed.
 
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THANK YOU