Pavement Components Lec-1

7/30/2019 Pavement Components Lec-1

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Structural Desi n OfPavements

Dr. Md.r. Md. Mizanurizanur Rahmanahman


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A highway pavement is designed to

from traffic moving over it.

Additional stresses are also imposed by

changes in the temperature of environment.

resists the stresses imposed on it and

external loads on the subgrade.Prof. Dr. Md. Mizanur Rahman


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It should be sufficiently thick to distribute

the loads and stress to a safe value on thesubgrade soil.

t s ou e structura y soun enoug to

withstand the stresses imposed on it.

surface, so that the abrasive action of

It should be dust free so that traffic safetyis not im aired.

Its riding quality should be good.Prof. Dr. Md. Mizanur Rahman


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It should be smooth enough to provide comfort tothe road users at the high speeds at which modernve ic es are riven.

The surface of the pavement should develop as low

The surface of the pavement should have adequate

roughness to prevent skidding of vehicles. The surface should not produce excessive level of

sound.

does not penetrate the pavement.

The pavement should have long life and lowmaintenance cost.

Prof. Dr. Md. Mizanur Rahman


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DesignDesign PrecisionPrecision:: A rigid pavement is amenableto much more precise structural analysis than

flexible pavement because of the flexuralstrength of concrete. Flexible pavements designs ma n y emp r ca .

Serviceervice Lifeife: A well designed rigid pavement has.flexible pavement varies from 10 to 20 years.

Maintenanceaintenance: A well desi ned ri id avementneeds practically very little maintenance. Flexiblepavements needs frequent maintenance.



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Initialnitial costost: High initial cost is required toconstruct rigid pavement . Initial construction

cost of flexible pavement is comparatively low.

Stagetage Constructiononstruction: A rigid pavement does notpermit stage construction. On the other hand,

construction.

Availabilityvailability off Bindinginding materialsaterials: Cement is moreavailable than bitumen in Bangladesh.



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Surface Characteristics: A good rigid pavementsurface is smooth and free from rutting. Thus

the riding quality of a rigid pavement is alwaysassured. In a bituminous surface, it is only theasp a c concre e sur ace a can g ve ecomparable ride quality.

Penetrationenetration off Waterater:enetrationenetration off Waterater:practically impervious, except at joints. If jointsare properly sealed and well maintained water

will not penetrate and soften the subgrade. Aflexible pavement surface is not impervious.

a er can n s way n o e ower ayer

through cracks and pores.Prof. Dr. Md. Mizanur Rahman


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Utilitytility Locationocation: In case of rigid pavement it is difficult tofind the place of utility location after construction. Incase of flexible avement it is eas to di the avementand find the place for utility locations.

Glarelare andnd Nightight Visibilityisibility: Ri id avements have a reycolor which can cause glare under sunlight. Blackbitumen pavement is free from this defect. But flexible

pavement required more street lighting than rigid.

Trafficraffic Dislocationislocation duringuring Constructiononstruction: A rigid pavementtraffic. On the other hand, a flexible pavement can bethrown open to traffic after it is rolled. Further traffic willfacilitate its compaction. Thus rigid pavement cause

s ocat on o tra c, n case o t e wor s one on

existing road.Prof. Dr. Md. Mizanur Rahman


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Rigid Pavementslexible Pavementslexible Pavements



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Hot mix Asphaltic (HMA) pavements are classified as

" flexible" pavements because the total pavementstructure deflects, or flexes, under loading.

A flexible pavement structure is typically composed of

several layers of material. ac ayer rece ves e oa s rom e a ove ayer,

spreads them out, then passes on these loads to the

. Thus, the further down in the pavement structure a

articular la er is the less load in terms of force er

area) it must carry.Prof. Dr. Md. Mizanur Rahman


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Load distribution at Surface courseProf. Dr. Md. Mizanur Rahman


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Load distribution at Base courseProf. Dr. Md. Mizanur Rahman


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Load distribution at Sub-Base courseProf. Dr. Md. Mizanur Rahman


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In flexible pavements material layers areusually arranged in order of descending loadbearing capacity with the highest load

expensive) on the top and the lowest load

bearin ca acit material and leastexpensive) on the bottom.



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The typical flexible pavement structurecons s ng o :

Surface course. This is the top layer and thebe composed of one or several different HMA

sublayers.B Base course. s s e ayer rec y e owthe surface course and generally consists ofa re ate (either stabilized or unstabilized)

or HMA. Subbase course. This is the layer (or layers)

.

needed. Prof. Dr. Md. Mizanur Rahman


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A typical flexible pavement structure consists of thesurface course and the underlying base and sub-basecourses.

Each of these layers contributes to structural supportand draina e.

The surface course (typically an HMA layer) is the stiffest

(as measured by resilient modulus) and contributes themos o pavemen s reng .

The underlying layers are less stiff but are still importantto avement stren th as well as draina e and frost

protection. A typical structural design results in a series of layers

a gra ua y ecrease n ma er a qua y w ep .



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Basic Structural Elements of Flexible Pavementasic Structural Elements of Flexible PavementProf. Dr. Md. Mizanur Rahman


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Surface courseSurface course

e sur ace course s e ayer n con ac w

traffic loads and normally contains the.

It provides characteristics such as friction,

smoothness, noise control, rut and shovinresistance and drainage.

In addition, it serves to prevent the entrance

o excessive quantities o sur ace water intothe underlying base, subbase and subgrade.



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Surface courseSurface course

s op s ruc ura ayer o ma er a s some mes

subdivided into two layers :

.

is meant to take the brunt of traffic wear and can be removed and

replaced as it becomes worn. proper y es gne an un e preservat on program s ou e

able to identify pavement surface distress while it is still confined to the

wearin course.

This way, the wearing course can be rehabilitated before distresspropagates into the underlying intermediate/binder course.

Intermediate/Binder Course: This layer provides the bulk o the HMA

structure. Its chief purpose is to distribute load.Prof. Dr. Md. Mizanur Rahman


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The base course is immediatel beneath the surface

Base courseBase course

course. It provides additional load distribution andcontributes to drainage and frost resistance. Basecourses are usually constructed out ofAggregatesAggregates:

Base courses are most typically constructed from durable aggregates

that wil l not be damaged by moisture or frost action. Aggregatescan be either stabilized or unstabilized. In certain situations where high

base stiffness is desired, base courses can be constructed using a

. ,

course mixes usually contain larger Maximum aggregate sizes, are more

open graded and are subject to more lenient specifications.



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Subub-Base coursease courseThe subbase course is between the basecourse and the subgrade. It functionspr mar y as s ruc ura suppor u can a so:

subgrade into the pavement structure.

.

Minimize frost action damage.

Provide a workin latform for construction.



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The subbase generally consists of lower quality

Subub-Base coursease course

subgrade soils. A subbase course is not always needed or used. For

examp e, a pavement constructe over a gquality, stiff subgrade may not need the additional

features offered by a subbase course so it may beomitted from design.

However, a pavement constructed over a low

additional load distribution characteristic that asubbase course can offer.

high quality fill used to replace poor qualitysubgrade. Prof. Dr. Md. Mizanur Rahman


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Rigid pavements are so named because thepavemen s ruc ure e ec s very e un er

loading due to the high modulus of elasticityof their surface course.

A rigid pavement structure is typically

composed of a PCC surface course built on

underlying base course. Because of its relative ri idit , the avement

structure distributes loads over a wide areawith only one, or at most two, structural



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The typical rigid pavement structureconsisting of:

Surface course. This is the top layer, which.

Base course. This is the layer directly below

aggregate or stabilized subgrade.

Subbase course. This is the la er (or la ers)

under the base layer. A subbase is not alwaysneeded and therefore may often be omitted.



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A typical rigid pavement structure consists ofthe surface course and the underlying baseand subbase courses (if used).

stiffest (as measured by resilient modulus)

The underlying layers are orders ofmagnitude less stiff but still make important

contributions to pavement strength as well asdrainage and frost protection.



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Surface courseurface course

The surface course is the layer in contact withtraffic loads and is made of PCC.

It provi es c aracteristics suc as rictionsmoothness, noise control and drainage.

,to the underlying base, subbase andsub rade.

The surface course can vary in thickness butis usually between 150 mm (6 inches) (forlight loading) and 300 mm (12 inches) (for

heavy loads and high traffic).Prof. Dr. Md. Mizanur Rahman


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PCC Surface Rigid Pavement Slab(Surface Course) ThicknessProf. Dr. Md. Mizanur Rahman


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Base coursease coursesurface course.

(2) contributes to drainage and frost

resistance, (3) uniform support to thepavement and (4) a stable platform forconstruction equipment .

ases a so e p preven su gra e somovement due to slab pumping.



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Base coursease course Base courses are usually constructed out of:

Aggregate baseggregate base.Stabilized aggregate or soiltabilized aggregate or soiltabilized aggregate or soiltabilized aggregate or soil

Denseense-graded HMAraded HMA.Permeable HMAermeable HMAermeable HMAermeable HMA.

Lean concreteean concrete



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The subbase course is the portion of the

Sub Baseub Base

the subgrade. It functions primarily as structuralsupport but it can also:

Minimize the intrusion of fines from thesubgrade into the pavement structure.

Im rove draina e. Minimize frost action damage. Provide a working platform for construction.

materials than the base course but better thanthe subgrade soils. Appropriate materials area re ate and hi h ualit structural fill. Asubbase course is not always needed or used.


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