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8/18/2019 Cppcs Vc Pdcs

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TYPICAL PAVEMENT DISTRESSES

(CLAYEY SUBGRADE???)

Dr. Venkaiah Chowdary

Assistant ProfessorDepartment of Civil Engineering

National Institute of Technology, WarangalEmail: [email protected]

Construction Practices of Pavements on Clayey Subgrade

G. Pulla Reddy Engineering College, Kurnool


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Pavement cross-section

Distresses in flexible pavements

Distresses in rigid pavements

Expansive soils as subgrade

Drainage measures

Geosynthetics

• Classification

• Functions

• Applications

Overview


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Pavement cross-section

Distresses in flexible pavementsDistresses in flexible pavements

Distresses in rigid pavementsDistresses in rigid pavements

Expansive soils as subgradeExpansive soils as subgrade

Drainage measuresDrainage measures

GeosyntheticsGeosynthetics

•• ClassificationClassification

•• FunctionsFunctions

•• Applications Applications

Overview


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Flexible Pavement (MORTH, 2001)


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Rigid Pavement (MORTH, 2001)


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Conventional Flexible Pavements (Huang, 2004)


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Pavement crossPavement cross--sectionsection

Distresses in flexible pavements








Overview


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Distresses in Flexible Pavements

Fatigue or Alligator Cracking

Bleeding

Block Cracking

Corrugation and Shoving

Depression

Joint Reflection Cracking

Longitudinal Cracking

Polished Aggregate

Potholes

Ravelling

Rutting

Transverse (Thermal) Cracking


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Fatigue or Alligator Cracking

Series of interconnected cracks caused by fatigue failure of HMA

surface under repeated traffic loading In thin pavements, crack initiates at the bottom of the HMA layer

where the tensile stress is high and propagates to the surface as oneor more longitudinal cracks ( Bottom-up cracks!!! )

In thick pavements, the cracksinitiate from the top in areas ofhigh localized tensile stressesresulting from tyre-pavementinteraction and asphalt binder

aging ( Top-down cracks!!! )


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Bleeding

A film of asphalt binder on the pavement surface

Usually creates a shiny, glass-like reflecting surface that can becomesticky

Bleeding occurs when asphalt binder fills the aggregate voids duringhot weather and then expands onto the pavement surface

This can be due to:

• Excess asphalt in HMA

• Less air voids in HMA


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Block Cracking

Interconnected cracks dividing the pavement into rectangular pieces

Larger blocks are classified as longitudinal and transverse cracks Block cracking normally occurs over a large portion of pavement

area but sometimes will occur only in non-traffic areas

Caused due to HMA shrinkageand daily temperature cycling

Typically caused by an inability ofasphalt binder to expand andcontract with temperature cyclesbecause of asphalt binder aging


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Corrugation and Shoving

A form of plastic movement typified by ripples (corrugation) or an

abrupt wave (shoving) across the pavement surface The distortion is perpendicular to the traffic direction

Usually occurs at points where traffic starts and stops (corrugation)or areas where HMA touches a rigid object (shoving)

Caused by starting and stoppingof vehicles combined with anunstable HMA layer (or) excessivemoisture in the subgrade


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Depression

Localized pavement surface areas with slightly lower elevations than

the surrounding pavement Depressions are very noticeable after a rain when they fill with water

Caused due to frost heave orsubgrade settlement resultingfrom inadequate compactionduring construction


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Joint Reflection Cracking

Cracks in a flexible overlay of a rigid pavement

Cracks occur directly over the underlying rigid pavement joints

Caused due to movement of thePCC slab beneath the HMAsurface because of thermal andmoisture changes

Generally not load initiated,however loading can acceleratedeterioration


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Longitudinal Cracking

Cracks parallel to the pavement centreline

Usually a type of fatigue cracking Caused due to poor joint construction/location; joints should be

constructed outside wheel path so that they are not frequently loaded


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Polished Aggregate

Areas of HMA pavement where the portion of aggregate extending

above the asphalt binder is either very small or there are no rough orangular aggregate particles

Causes decrease in skid resistance

Caused due to repeated trafficapplications

As the pavement ages, theprotruding rough, angularparticles becomes polished

This can occur quicker if theaggregate is susceptible toabrasion


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Potholes

Small, bowl-shaped depressions in the pavement surface that

penetrate all the way through the HMA layer down to the basecourse

They generally have sharp edges and vertical sides near the top ofthe hole

Potholes are most likely to occuron roads with thin HMA surfaces(25 to 50 mm) and may not occuron roads with 100 mm or deeperHMA surfaces

End result of alligator cracking


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Ravelling

The progressive disintegration of an HMA layer from the surface

downward as a result of the dislodgement of aggregate particles Caused due to loss of bond between aggregate particles and asphalt

binder

Ravelling may also be due tomechanical dislodging by certaintype of traffic (studded-tyres,tracked vehicles, snowplowblades, etc.)


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Rutting

Surface depression in the wheel path; pavement uplift (shearing) may

occur along the sides of the rut Ruts are particularly evident after a rain when they are filled with

water (hydroplaning); can be hazardous because ruts tend to pull a vehicle towards the rut path as it is steered across the rut

Caused due to permanentdeformation in any of thepavement layers or subgradeusually caused by verticalcompression or consolidation or

lateral movement of the materialsdue to traffic loading


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Transverse (Thermal) Cracking

Cracks perpendicular to the pavement centerline

A type of thermal cracking caused due to shrinkage of the HMAsurface due to low temperatures or asphalt binder hardening

May also be due to reflective cracking


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Distresses in rigid pavements







Overview


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Distresses in Rigid Pavements

Blowup (buckling)

Corner break

Durability cracking (“D” cracking)

Faulting

Linear (panel) cracking

Popouts

Pumping

Patching

Polished aggregate

Reactive aggregate distresses

Shrinkage cracking

Spalling


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Blowup (Buckling)

A localized upward slab movement at a joint or crack

Usually occurs in summer and is the result of insufficient room forslab expansion during hot weather


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Corner Break

A crack that intersects the PCC slab joints near the corner

“Near the corner” is typically defined as within about 2 m A corner break extends through the entire slab and is caused by high

corner stresses.

It is due to severe corner stressescaused by load repetitionscombined with a loss of support,poor load transfer across thejoint, curling stresses and warping

stresses


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Durability Cracking (“D” Cracking)

Series of closely spaced, crescent-shaped cracks near a joint, corner

or crack; caused by freeze-thaw expansion of the large aggregate within the PCC slab

Durability cracking is a general PCC distress and is not unique toPCC pavements


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Faulting

A difference in elevation across a joint or crack usually associated

with undoweled JPCP Faulting is noticeable when the average faulting in the pavement

section reaches about 2.5 mm

Most commonly, faulting is aresult of slab pumping

Faulting can also be caused byslab settlement, curling and

warping


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Linear ( Panel) Cracking

Linear cracks not associated with corner breaks or blowups that

extend across the entire slab These cracks divide an individual slab into two to four pieces.

Caused due to a combination oftraffic loading, thermal gradientcurling, moisture stresses and lossof support


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Popouts

Small pieces of PCC that break loose from the surface leaving small

divots or pock marks Popouts range from 25-100 mm in dia. and from 25 - 50 mm deep

Popouts usually occur as a resultof poor aggregate durability

Poor durability can be a result ofa number of items such as: (i)poor aggregate freeze-thawresistance, (ii) expansiveaggregates, and (iii) alkali-aggregate reactions


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Pumping

Movement of material underneath the slab or ejection of material

from underneath the slab as a result of water pressure Water accumulated underneath a PCC slab will pressurize when the

slab deflects under load

Caused due to wateraccumulation underneath the slab

This can be caused by: a high water table, poor drainage, andpanel cracks or poor joint sealsthat allow water to infiltrate theunderlying material


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Patching

An area of pavement that has been replaced with new material to

repair the existing pavement A patch is considered a defect no matter how well it performs

Caused due to previous localizedpavement deterioration that hasbeen removed and patched

Also caused due to utility cuts


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Polished Aggregate

Areas of PCC pavement where the portion of aggregate on the

surface contains few rough or angular aggregate particles Caused due to repeated traffic applications

Generally, as a pavement ages theprotruding rough, angularparticles become polished

This can occur quicker if theaggregate is susceptible toabrasion or subject to excessivestudded tyre wear


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Reactive Aggregate Distress

Pattern or map cracking (crazing) on the PCC slab surface caused by

reactive aggregates Reactive aggregates are those that either expand or develop expansive

byproducts when introduced to certain chemical compounds

This type of distress is indicativeof poor aggregate qualities

Most commonly, it is a result ofan alkali-aggregate reaction


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Shrinkage Cracking

Hairline cracks formed during PCC setting and curing that are not

located at joints; they do not extend through entire depth of the slab Shrinkage cracks are considered a distress if they occur in an

uncontrolled manner (e.g., at locations outside of contraction jointsin JPCP or too close together in CRCP)

PCC will shrink as it sets andcures, therefore shrinkage cracksare expected in rigid pavementand provisions for their controlare made


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Spalling

Cracking, breaking or chipping of joint/crack edges

Usually occurs within about 0.6 m of joint/crack edge

Caused due to excessive stresses at the joint/crack caused byinfiltration of incompressible materials and subsequent expansion(can also cause blowups)

Caused due to disintegration ofthe PCC from freeze-thaw actionor “D” cracking

May also be due to misalignmentor corroded dowel

Also due to heavy traffic loading


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Expansive soils as subgrade





••

Applications Applications

Overview


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Expansive Soils as Subgrade (IRC:37, 2001)• Top 500 mm portion of the roadway.

• Heavy compaction recommended for Expressways, NHs,SHs, and MDRs.

• Shall be compacted to 97% of dry density achieved withheavy compaction.

• Material used for subgrade shall have dry density not lessthan 1.75 g/cm3.

• CBR at most critical moisture conditions likely to occur in

the field.

• Use of expansive clay is not allowed for subgrade.

• If unavoidable, following procedure shall be adopted.


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• Expansive soils (black cotton soils, montmorillonite clays)

are characterized by extreme hardness and deep cracks when dry and tendency to heave during wetting.

• Moisture changes due to seasonal wetting and dryingcauses volumetric changes and leads to pavement

distortion, cracking, and unevenness.

• Volume changes in these soils depends on (i) dry densityof compacted soil, (ii) moisture content, and (iii) structure

of soil and method of compaction.• Expansive soils swell very little when compacted at low

densities and high moisture content; recommended tocompact the soils to slightly wet of OMC.

Expansive Soils as Subgrade (IRC:37, 2001)


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• Thickness design shall be based on 4-day soaked CBR.

Buffer Layer:

• Buffer layer made of non-expansive cohesive soil cushionof 0.6 to 1.0 m thickness:

i. prevents ingress of water into the underlyingexpansive soil,

ii. counteracts swelling and if the underlying expansivesoil heaves, movement will be more uniform.

• If buffer layer is not economically feasible, blanketcourse made of suitable material and thickness shall beprovided.



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Blanket Course:

• At least 225 mm thickness.• Composed of coarse/medium sand (or) non-plastic

moorum with PI less than 5%.

•

Provided above expansive soil to serve as sub-base.• Extended over entire formation width.

• Alternatively, lime-stabilized black cotton sub-baseextending over entire formation width may be providedtogether with measures for efficient drainage.

• Improvement of drainage can significantly reduce themagnitude of seasonal heaves.



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Drainage Measures:

• Provision must be made for lateral drainage of thepavement section.

• Granular sub-base/base shall be extended across the

shoulders.• Camber of 1:40 for BT surface and cross-slope of 1:20

for berms to shed-off surface run-off quickly.

•

Standing water not allowed on either side ofembankment.



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Drainage Measures:

• Difference between subgrade level and highest watertable shall be at lest 1 m.

• 40 mm thick BT surfacing shall be provided to prevent

ingress of water through surface.• Shoulders shall be made of impervious material.

• Lime stabilized black cotton soil shoulder of 150 to 200

mm thickness is an economical option.



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Drainage measures




••


Overview


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• Performance of a pavement can be affected by accumulation

of moisture in pavement• Measures to guard against poor drainage:

i. Proper camber

ii. Provision of surface and sub-surface drains

• Important when road is in cutting (or) built on low permeablesoils (or) situated in heavy rainfall/snowfall areas

• Difference between bottom of subgrade level and level of water table or high flood level should not be less than 0.6 to

1.0 m.

• In water logged areas where subgrade is within the capillarysaturation zone, suitable capillary cut-off may be installed

Drainage Measures (IRC:37, 2001)


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• When pavement is constructed over low permeable subgrade,

GSB layer shall be extended over entire formation width• Exposed ends of GSB layer should not be covered by soil

•

If GSB is of softer variety which may get crushed duringrolling leading to denser gradation and low permeability, thetop 100 to 150 mm shall be substituted by open gradedcrushed stone layer to ensure proper drainage



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Requirements of drainage layer:

•

Criteria for high permeability drainage layer:

• To prevent entry of soil particles into drainage layer:

• Following materials are considered as good for drainage:

where, D85 is the size of sieve that allows 85% by weight of

material passing through it

5subgradeof D

layer drainageof D

15

15

5subgradeof D

layer drainageof Dand5,

subgradeof D

layer drainageof D

50

50

85

15

mm2.5Dand,D4D 21585



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• Permeable sub-base when placed on soft erodible soils shall be

underlain by a layer of filter material to prevent intrusion ofsoil fines into the drainage layer

• Non-woven geosynthetic can be used as filter



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• Base course shall be constructed 300 to 450 mm wider than

the bituminous surfacing so that run-off water disperses wellclear off the carriageway

• Shoulders shall have requisite cross-fall

• Shoulders shall not be at higher level than carriageway



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Geosynthetics

• Classification

• Functions

•

Applications

Overview


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Geosynthetics

• Classification


••


Overview


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Classification of GeosyntheticsClassification of Geosynthetics

Geotextiles

Geogrids

Geonets

Geomembranes

Geocomposites

Geosynthetic clay liners

Geopipes

Geocells

Geofoam

Source: http://www.geosyntheticssociety.org/Resources.aspx?pg=Education


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Geosynthetics


• Functions

••


Overview


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Functions of GeosyntheticsFunctions of Geosynthetics

Separation

Separates two layers of soilthat have different particlesize distributions

Used to prevent road basematerials from penetratinginto underlying soft subgradesoils

Prevents fine grainedsubgrade soils from being

pumped into permeablegranular road bases



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Reinforcement

Geotextiles and geogrids areused to add tensile strengthto a soil mass in order tocreate vertical or near-

vertical changes in grade

(reinforced soil walls)




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Filtration

Acts similar to a sand filterby allowing water to movethrough the soil whileretaining all upstream soilparticles

Geotextiles are used toprevent soils from migratinginto drainage aggregate orpipes while maintaining flow

through the system




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Drainage

Acts as a drain to carry fluidflows through less permeablesoils

Geotextiles are used todissipate pore waterpressures at the base ofroadway embankments




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Type ofGeosynthetics

Separation Reinforcement FiltrationDrainag

eContainment

Geotextiles -

Geogrids - - - -

Geonets - - - -

Geomembranes - - - -

Geocomposites



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Geosynthetics



•

Applications

Overview

G h i A li i i PG h i A li i i P


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Geosynthetics Applications in PavementsGeosynthetics Applications in Pavements

can be effectively used to reduce or avoid reflective cracking




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works as a barrier to avoid pumping of soil fines





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can be effectively used to reduce asphalt cap thickness





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can be effectively used to reduce pavement thickness





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can be effectively used to increase the life of the pavement

can be effectively used to decrease the rut depth





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Dust particulate originates from the fines of the subgrade, which migrate upward into the unbound surface over time.

Vehicular traffic causes the fines in the unbound layer to bemobilized into the atmosphere.

Geotextile separators limit the migration of fines into theoverlying aggregate and also the intrusion of aggregate into the

subgrade.




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Thank You

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