Pavement Components Lec-1

 

Stru ruc ctural Desi n Of Pavements Dr. r. Md. Mizanur iza zanu nurr Ra Rahm ahman hma an

 

 

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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 the subgrade soil.    t s ou e structura y soun enoug to withstand the stresses imposed on it. surface, so that the abrasive action of  

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 It should be dust free so that traffic safety is no nott im aire aired. d.  Its riding quality should be good. Prof. Dr. Md. Mizanur Rahman

 

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 It should be smooth enough to provide comfort to the road users at the high speeds at which modern ve ic es are riv 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 low maintenance cost. Prof. Dr. Md. Mizanur Rahman

 

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 Design Design Precision Precision::  A rigid pavement is amenable to much more precise structural analysis than flexible pavement because of the flexural strength of concrete.  Flexible pavements design s ma n y emp r ca .

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Service ervice Life: ife A well designed rigid pavement has . flexible pavement varies from 10 to 20 years.

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Maintenance aintenance: A well desi n ne ed ri iid d avement needs practically very little maintenance. Flexible maintenance. Flexible pavements needs frequent maintenance. Prof. Dr. Md. Mizanur Rahman

 

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Initial nitial cost: ost High initial cost is required to constr struct uction ion cons co nstr tru uct rigi gid d pa pave veme ment nt .   Initial Initial con cost of flexible pavement is comparatively low.

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Stage tage Construction: onstruction A rigid pavement does not permit per mit sta stage ge con constr struct uction ion..   On the other hand, construction.

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Availability vailabi billity off Bin inding indi ding ng ma mate aterials: teri rial als s Cement is more available than bitumen in Bangladesh. Prof. Dr. Md. Mizanur Rahman

 

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 Surface Characteristics:   A good rigid pavement surface is smooth and free from rutting. Thus the riding quality of a rigid pavement is always assured.  In a bituminous surface, it is only the asp a c concre e sur ace a can g ve e comparable ride quality. Penetration enetrati enetration tio on off Water: ater practically impervious, except at joints. If joints are sealedand andsoften well maintained water will properly not penetrate the subgrade.  A flexible 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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Utility tili ti lity ty Location: ocat oc atio ion n In case of rigid pavement it is difficult to find find th the e plac place e of ut util ilit ity y loca locati tion on af afte terr cons constr truc ucti tion on..   In case of flexible avement it is eas to di the avement and find the place for utility locations. Glare lare and Night Visibility: isibility Ri id id avements have a re color which can cause glare under sunlight.   Black bitumen p avementpavement requiredis m free ore from streethis t lidefect. ghting But than flexible rigid .

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Traffic raff ra ffic ic Di Disl islo is sloc loca ocat cati atio tion ion on n du duri urin ur ring ing ng g Co Cons onstruction: nstr truc ucti tion on A rigid pavement traffic.   On the other hand, a flexible pavement can be traffic.  thrown open to traff traffic ic after it is rolled. Further traffic traffic will faci fa cili lita tate te it its s co comp mpac actio tion. n.   Thu Thus s rig igid id pa pave vem men entt caus cause e s ocat on o tra c, n case o t e wor s one on existing road. Prof. Dr. Md. Mizanur Rahman

 

lexible Pavements

Rigid Pavements

Prof. Dr. Md. Mizanur Rahman

 

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 Hot mix Asphaltic (HMA) pavements are classified as

" fle flexi xibl blee" pa pave veme ment ntss be beca caus usee th thee to tota tall pa pave veme ment nt structure deflects, or flexes, under loading. flexible xible pa pave veme ment nt str structur ucturee is typ typically ically composed of     A fle 

severall la l ayers of o f ma m aterial terial.. severa   ac ay er r ec e v es e o a s r o m e a o v e ay er, spreads them out, then passes on these loads to the

.    Thus, the further down in the pavement structure a art rtic icul ulaar la l a er is th thee le less ss loa loadd in te term rmss of fo forc rcee er  area rea)) it mus m ustt carry. Prof. Dr. Md. Mizanur Rahman

 

Load distribution at Surface course Prof. Dr. Md. Mizanur Rahman

 

Load distribution at Base course Prof. Dr. Md. Mizanur Rahman

 

Load distribution at Sub-Base course Prof. Dr. Md. Mizanur Rahman

 

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  In flexible pavements material layers are usually arranged in order of descending load bearing capacity with the highest load expensive) lowest bearin caonacthe it top maand teriathe l and lload east expensive) on the bottom.

Prof. Dr. Md. Mizanur Rahman

 

The typical flexible pavement structure 

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co cons Suns rfacse ng couors: e. This is the top layer and the be composed of one or several different HMA sublayers. Base course. s s e ayer rec y e ow the surface course and generally consists of  a re ate   (eit (either her sta stabil bilize ized d or uns unstab tabili ilized zed)) or HMA. Subbase course. This is the layer (or layers) . needed. Prof. Dr. Md. Mizanur Rahman

 

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  A ty typic picaal flexi flexibl blee pa pave veme ment nt stru st ruct ctur uree co cons nsis ists ts of the th e surface course and the underlying base and sub-base

 courses. Each of these layers contributes to structural support and draina e.    The surf surfaace course cour se (typ (typically ically an HMA laye layer) r) is the sti stiffest ffest (as measured by   resilient modulus) modulus ) and contributes the m o s o p av em en s r en g .    The underlyin underlyingg la l aye yers rs are less less stiff but are still import importaant 

t o av em en t s t r en t h as w el l as d r ai n a e an d f r o s t protection.    A typical structural design results in a series of layers a gr g r a uuaa y ec r eas e n m a er a qu qu a y w ep . Prof. Dr. Md. Mizanur Rahman

 

Basic asic Structural Elements of Flexible Pavement Prof. Dr. Md. Mizanur Rahman

 

Surf ace course cou rse 

sed s noremaaylleyr ncocnotnaiancs wthe t raeffiscur laocaedc souarn .

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 smoothness, It pr prov ovid ides es ch char arac acte teri rist stic ics s su such chand as shovin fr fric icti tion on,, noise control, rut resistance and drainage.    In addition, addition, it serves serves to prevent the entr entrance ance o ex exc ces essi sive ve qu quan anti titi ties es o su surr ac ace e wat ate er in into to the underlying base, subbase and subgrade.

Prof. Dr. Md. Mizanur Rahman

 

Surf ace course cou rse

s op s ruinto c urtwo a alayers yer o : ma er a subdivided

s some mes

. is meant to tak take the the brun runt of traffic traffic wear and can be rem removed and rep re plac laced as it becomes worn. rn. • proper y es gne an un e preservat on program s ou   e able to ide identify pavement surf rfa ace dis istr tre ess while it is still confine fined to the the wearin cou course. rse. •Th •T his way, the the wearing cou course rse can can be reh rehabilitate ilitated d before fore distres istress prop ropagates tes into the the underlying rlying inte interm rme ediate/b iate/bind inde er cou course rse. Intermediate/ ntermedia te/Bin Coourse ours :  Th  Tdhis istribu laye lay er lo pro rovid bulk o th the e HMA s truc tru ctu ture re.. Its cBinder hie ieffder purp rpo se iseto istrib ute loa advide . es the bulk Prof. Dr. Md. Mizanur Rahman

 

Base course The base cou course is immediatel

beneath the surface

cour co urs ovid ovide add itio iona lo is ut c on trsie. butIt es ptro de rasinad agd e it annal d l fload road st rdeistr stri isitb autio ncion e.n Baand se courses are usually constructed out of  Aggregates  Aggregates:

Base courses most constructed durable aggregates thatt will tha wil l not beare dama damage geddtypically by moist moisture ure or frost fros tfrom action. Agg action.  Aggregate regates s can be eith eitheer stabili stabilize zedd or uns unstabilize tabilized. d. In  In certain situations where high base ba se stiff stiffne ness ss is de desired, sired, ba base se courses ca c an be b e constructe construct ed using a , . course cou rse mixe mix es usually con contain tain larger Ma Maxim ximum um aggr ggreegate size sizes, are are more open graded and are subject to more lenient specifications.

Prof. Dr. Md. Mizanur Rahman

 

Sub ub-Base ase course The subbase course is between the base course and the subgrade. It functions pr mar y as s ruc ura suppor u can a so:

subgrade into the pavement structure. .   Minimize  Minimize frost  frost action damage. damage. Prov ovid ide e a wo work rkin in la latfo tform rm fo forr co cons nstr truc ucti tion on..    Pr Prof. Dr. Md. Mizanur Rahman

 

Sub ub-Base ase course 

  The sub subbase ase gen general erally ly consis nsistts of low lower quali ualitty

subgrade soils.   A subbase course is not always needed or used. For examp e, a pavement constructe over a g quality, subgrade may not course need the featuresstiff offered by a subbase so additional it may be omitted from design.    Ho However, a pavement constructed over a low additi addi tion onal al load load distr istrib ibut utio ion n char charac acte teri rist stic ic that that a subbase course can offer. high quality fill used to replace poor quality subgrade.  

Prof. Dr. Md. Mizanur Rahman

 

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 Rigid pavements are so named because the

pavemendue s rto ucthe urehigh modulus e  modulus ec s very of elasticity e un e err loading high of their surface course. rigid pavement structure is typically  A composed of a PCC surface course built on underlying base course. 

 structure Bec eca aus use e of its rel elat atiiveloads ri idi dit t , th the av avem emen entt distributes over ae wide area with only one, or at most two, structural

Prof. Dr. Md. Mizanur Rahman

 

Prof. Dr. Md. Mizanur Rahman

 

The

typical

rigid

consisting of:

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  Sur Surfac face e cou cours rse  e .

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  Base Base co cours urse  e .

pavement

structure

This is tth he to top p la lay yer, wh whiich .

Th This is iis s th the e la laye yerr di dire rect ctly ly b bel elow ow

aggregate or stabilized subgrade. 

  Subb Subbase ase cou course  rse .

This iis s tth he lla a er ((o or lla a ers) underr the base laye unde layer. r. A su subbase bbase is n not ot al always ways needed and therefore may often be omitted. Prof. Dr. Md. Mizanur Rahman

 

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

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stiiff st ffe est (a (as s me mea asu surred by   resil resilien ientt mod modulu ulus s) 

  The

underlying

layers

are

orders

of 

magnitude less but still make important contributions to stiff pavement strength as well as drainage and frost protection.

Prof. Dr. Md. Mizanur Rahman

 

Prof. Dr. Md. Mizanur Rahman

 

Surface urface course   The surface course is the layer in contact with traffic loads and is made of PCC. as   riction    It provi es c aracteristics suc 

smoothness, noise control and drainage. smoothness, , to the underlying base, subbase and sub ra sub rade de..   The surface course can vary in thickness but is usually between 150 mm (6 inches) (for light loading) and 300 mm (12 inches) (for heavy loads and high traffic). Prof. Dr. Md. Mizanur Rahman

 

PCC Surface

Rigid Course) Pavement Slab Surface Thickness Prof. Dr. Md. Mizanur Rahman

 

Base ase course surface course.

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(2) contributes to drainage and frost resistance, (3) uniform support to the pavement and (4) a stable platform for construction equipment .   ases a so e p preven su gra e so movement due to slab pumping.

Prof. Dr. Md. Mizanur Rahman

 

Base ase course 

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  Base courses are u usually sually constructed out of: Aggregate ggregate base . S ttabil tabilized a b i liized zed a aggregate agg g g rregate e g at a t e or o r so soil s o iill

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Dense ense graded raded HM A .

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P ermeabl e r m ea ermeable e a b le H HM MA. Lean ean con crete crete

Prof. Dr. Md. Mizanur Rahman

 

Sub ub Base The subbase course is the portion of the the subgra subgrade. de. It functio functions ns primar primarily ily as structur structural al support but it can also: 

  Minimize

the

intrusion

of

fines

from

the

subgrade into the pavement structure.  Im ro  Im rove ve dr drai aina na e.   Minimize  Minimize frost  frost action damage damage..    Provide a working platform for construction. construction.

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materials than the base course but better than the th e sub subgrad grade e soil soils. s. Appropri opriat ate e mater terials ials are are a re ate an and hi hi h ualit structural fi fill. A subbase course is not always needed or used. Prof. Dr. Md. Mizanur Rahman