highway engineering tran 3001 lecture 9.ppt

8/9/2019 Highway Engineering TRAN 3001 Lecture 9.ppt

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TRAN3001Highway Engineering

Lecture 9Structural Design

AASHTO Flexible Pavement Design

Rigid Pavement DesignRoad Note 29


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Structural Design

Flexible PavementA key element o !e"i#le $a%ement &esignin the 1993 AASHT' Guide for Design ofPavement Structures is the Structural

Num#er (SN)* which re$resents the o%erallstructural re+uirement nee&e& to sustainthe tra,c loa&s e"$ecte& in the &esign-

The SN &e$en&s on a com#ination o soilsu$$ort* ESAL loa&ing* $a%ementser%icea#ility an& en%ironmentalcon&itions- Nomogra$hs are generally

use& to &etermine the %alue o SN-


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Structural Design


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Structural Design (.ont/&)

Flexible Pavement (Cont’d)'nce the %alue o the Structural Num#er (SN)is known* the a$$ro$riate thickness o each o

the $a%ement layers can #e &etermine&- Theollowing e+uation shows the relationshi$#etween the SN an& layer thickness SN a1D1 2 aDm 2 a3D3m3

where a is a layer coe,cient re$resenting therelati%e strength o the material* D is the layerthickness an& m is a &rainage coe,cient-


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Flexible Pavement (Cont’d) The su#scri$t num#er use& in the e+uationin&icates which layer is meant* with the num#ering#eginning at the to$ o the $a%ement structure-

4or &esign $ur$oses* layer coe,cients are usually&etermine& em$irically #ase& on the $erormanceo the material- Some ty$ical layer coe,cient%alues are•Hot mi" as$halt 5 0-66•(Aggregate) roaase 5 0-13•Su##ase 5 0-10


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Structural Design (.ont/&)Flexible Pavement (Cont’d)

The &rainage coe,cient is a %alue assigne& toa $a%ement layer which re$resents its relati%eloss o strength &ue to &rainagecharacteristics or e"$osure to moisturesaturation-Layers that &rain slowly or are oten saturate&woul& ha%e a lower &rainage coe,cient* whilelayers that &rain +uickly an& rarely #ecomesaturate& woul& ha%e a higher coe,cient-4or $a%ement &esigns* the &rainagecoe,cients are generally set to 1 which

in&icates normal &rainage characteristics-


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Flexible Pavement (Cont’d)

7ith the a$$ro$riate layer an& &rainagecoe,cients known* suita#le thicknesses

or each o the $a%ement layers can then#e &etermine& - The relationshi$ #etween SN an& layer

thicknesses &oes not gi%e a single correctanswer or the thickness o each$a%ement layer- There will normally #e&i8erent com#inations o layer thicknesses

that coul& achie%e the re+uire& SN-


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Flexible Pavement (Cont’d) The nal &etermination o the thickness oeach layer woul& #e #ase& on the relati%ecosts o materials or &i8erent layers* alongwith $ractical &esign an& constructionconsi&erations (such as not making anyone layer too thick or thin)-

The SN can also #e use& toe%aluate:reha#ilitate e"isting $a%ements#y &etermining its %alue with the e"istinglayer thicknesses as com$are& to the

re+uire& SN or the u$&ate& &esign-


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Structural DesignRigid Pavement

The Design ;rocess The ste$s in the &esign o a rigi& $a%ementare similar to those or a !e"i#le $a%ementESAL loading on a rigi& (;ortlan& cementconcrete) $a%ement is com$ute& as or!e"i#le $a%ements* howe%er the &esign lieis generally longer* as much as 60 years-Subgrade strength is assesse&* #ut unlike!e"i#le $a%ements* rigi& $a%ements are&esigne& to ha%e su,cient #eam strength tos$an o%er locali


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Rigid Pavement (Cont’d) The Design ;rocess (.ont/&)De$ressions which occur #eneath $ro$erly

&esigne& an& constructe& rigi& $a%ementsare not re!ecte& in their running suraces- The ESAL loa&ing an& su#gra&e su$$ort isuse& to &etermine the type and thickness

o each o the $a%ement elements-Rigi& ;a%ement .ross=SectionLike !e"i#le roa&s* the cross=section o aconcrete roa& com$rises a $a%ement

su$erim$ose& on su#gra&e soil-


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Rigid Pavement (Cont’d)Rigi& ;a%ement .ross=Section (.ont/&)Rigi& $a%ements are concrete sla#s $lace&either &irectly on a $re$are& su#gra&e or more

commonly on a single layer o granularmaterial- The one layer o material #etween the concretesla# an& the su#gra&e is calle& the su##ase-

Su#gra&e7ith res$ect to rigi& $a%ements* the mostim$ortant unction o the su#gra&e is to $ro%i&euniorm su$$ort or the concrete sla#-


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Structural Design (.ont/&)Rigid Pavement (Cont’d)Su##ase> the su#gra&e cannot $ro%i&e a&e+uatesu$$ort throughout the &esign lie o the

$a%ement* a su##ase layer will nee& to #einclu&e& as $art o the $a%ement structure- The unsatisactory su#gra&e con&itionswhich $ro%ision o a su##ase will correct

inclu&e high volume-change characteristics* poor drainage an& mud- pumping, which isthe orce& e?ection o a mi"ture o soil an&

water rom the su#gra&e-


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Rigid Pavement (Cont’d)Su##ase (.ont/&).lays with high $lasticity are ty$ical o thesoils which nee& to #e $rotecte& #y a su##ase-

This layer $re%ents e%entual ailure o the$a%ement when concrete sla#s are lai& &irectlyon a su#gra&e soil which &oes not $ro%i&ea&e+uate su$$ort-

As the su#gra&e will #e su#?ecte& to loa&ingrom construction e+ui$ment* the su##asealso $ro%i&es a working $latorm-


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Rigid Pavement (Cont’d)Su##ase (.ont/&)inimi!ing volume changes

Soils which are susce$ti#le to %olumechanges when moisture is taken u$ or lost&uring the wet an& &ry seasonsres$ecti%ely* re+uire a su,cient thickness

o granular su##ase to #oth hol& &own thesu#gra&e an& control the moisture contentto re&uce %olume changes-


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Rigid Pavement (Cont’d)Su##ase (.ont/&)"mproving drainage The granular su##ase acts as a &rainage

layer to minimi $a%ement sla#s are $lace& &irectly on ne=graine& soils* water entering the $a%ementcan cause soil to #e e?ecte& through ?oints*e&ges an& cracks un&er re+uent hea%ytra,c-


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Rigid Pavement (Cont’d)Su##ase (.ont/&)Preventing mud-pumping #$ont%d&

>n a&&ition to the ingress o water an&continuous hea%y wheel loa&ing* or$um$ing to occur the su#gra&e soil must gointo sus$ension-

This makes ne=graine& soils susce$ti#le tomu&=$um$ing as this sus$ension is what ise?ecte& as the sla# re$eate&ly &e!ects

un&er constant* hea%y tra,c loa&s-


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Structural Design (.ont/&)Rigid Pavement (Cont’d)

Su##ase (.ont/&)Preventing mud-pumping #$ont%d& The su##ase com$rises a ree=&raining materialan& this layer shoul& ha%e su,cient &e$th an&e"ten& through the shoul&ers so that anywater entering the $a%ement can &rain-Providing a 'orking surface during constructionA su,cient &e$th o &ense* well=com$acte&su##ase material can $rotect the su#gra&e soilrom the &etrimental e8ects o constructionloa&s an& weather-


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Rigid Pavement (Cont’d);a%ement .oncrete @i" Design;ortlan& .ement .oncrete consists othree #asic com$onents aggregate*water an& ;ortlan& cement- The $ur$ose o the concrete mi" &esignis to &etermine the most economical an&

$ractical com#ination o rea&ily a%aila#lematerials to $ro&uce a concrete that willsatisy the $erormance re+uirements

un&er the $articular con&itions o use-


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;a%ement .oncrete @i" Design (.ont/&)4or concrete use& in $a%ements there+uirements inclu&e resistance to&eormation* &ura#ility o%er time* resistantto water &amage* controlle& shrinkagecracking* a goo& ski&=resistant surace* aswell as relati%ely ine"$ensi%e* rea&ily

manuacture& an& easily $lace&->n or&er to satisy these re+uirements mi"&esign can alter the ty$e an& +uantity o the#asic com$onents an& incor$orate

a&mi"tures to im$ro%e worka#ility* etc-


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Rigid Pavement (Cont’d);a%ement .oncrete @i" Design (.ont/&) The mi" &esign $roce&ure usuallyin%ol%es the ollowing three #asic ste$s

aterial selection which i&enties thesources an& s$ecications o thematerials to #e use& in the mi"-

i( proportioning which &etermines the$ro$ortions o the com$onent materialsnecessary to $ro&uce a mi" with the

&esire& $ro$erties-


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Rigid Pavement (Cont’d);a%ement .oncrete @i" Design (.ont/&)i( testing which uses la#oratory testing

to e%aluate an& characteri


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Rigid Pavement (Cont’d);a%ement .oncrete @i" Design (.ont/&)Bolume measurements are usually ma&ein&irectly #y &etermining each material/sweight an& s$ecic gra%ity an& thencalculating its %olume-Strength tests are carrie& out on concrete

cu#es or cylin&ers to &etermine thecharacteristic com$ressi%e strength o theconcrete* which is the %alue #elow whichless than a s$ecie& $ercentage (usually

C) o the sam$les will all-


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Rigid Pavement (Cont’d);a%ement .oncrete @i" Design (.ont/&) The water=cement ratio a8ects #othstrength an& worka#ility (ease o working

with the concrete)- 7ater or use in themi" is generally s$ecie& as $ota#le-Strength testing ensures that the

concrete is o $a%ement +uality an& orunreinorce& concrete in&irect tensiletests may also #e carrie& out- 'therwise*tensile strength %alues o 10 5 1 o

the com$ressi%e strength can #e use&-


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Rigid Pavement (Cont’d);a%ement .oncrete @i" Design (.ont/&)La#oratory tests are carrie& out at &i8erentwater contents to &etermine the o$timumamount o water that will $ro&uce aconcrete o ma"imum strength rom a$articular mi" o ne an& coarse aggregate

an& cement- The worka#ility also &e$en&s on the+uantity o water use&- The use o less thanthe o$timum amount o water may make

setting &i,cult an& re&uce worka#ility-


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Rigid Pavement (Cont’d);a%ement .oncrete @i" Design (.ont/&)7hen more water than the o$timum amount

is use& greater shrinkage an& a re&uction instrength will occur-4rom the water=cement content the cementcontent can #e &etermine&-

The total aggregate content is then&etermine& #ase& on an estimate o the&ensity o the (ully com$acte&) concrete-


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Rigid Pavement (Cont’d);a%ement .oncrete @i" Design (.ont/&)

The coarse:ne aggregate ratio is then teste&or the minimum %oi& content which in&icates

the o$timum $article $acking an& ratio- Ty$es o .oncrete ;a%ement.oncrete sla#s or roa& $a%ements may #e

plain or reinforced-7ith $lain concrete* trans%erse ?oints areusually $ro%i&e& at regular inter%als to$re%ent cracking rom e"$ansion an&

contraction o the concrete-


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Rigid Pavement (Cont’d) Ty$es o .oncrete ;a%ement (.ont/&)Reinorcement $ro%i&e& to control cracking*

such as $rea#ricate& mesh* terminate atthe trans%erse ?oints-4or $lain concrete an& where reinorcementis $ro%i&e& to control cracking* loa&

transer at the trans%erse ?oints is e8ecte&#y the use o &owels* which are short steel#ars treate& o%er hal their lengths with a

#on&=#reaking com$oun& like #itumen-


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Rigid Pavement (Cont’d) Ty$es o .oncrete ;a%ement (.ont/&) This $ro%i&es a mechanical connection

#etween sla#s without restrictinghori


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Rigid Pavement (Cont’d) Ty$es o .oncrete ;a%ement (.ont/&)

sealingcompound

transverse )ointcap

compressible material

longitudinal

)oint do'el bar painted over half its length 'ith

bitumen

.oncrete Sla# E"$ansion oint


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Rigid Pavement (Cont’d) Ty$es o .oncrete ;a%ement (.ont/&) The ree en&s o &owel #ars in ane"$ansion ?oint are tte& with &owel ca$sso that a s$ace is orme& at the en& oeach #ar* into which the #ar can mo%ewhen the sla# e"$an&s-

An e"$ansion ?oint $ermits contractionmo%ement an& also allows a small amounto angular rotation to release war$ingstresses cause& #y tem$erature &i8erences

#etween the to$ an& #ottom o the sla#-


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Roa& Note 9 Design @etho& This metho& o &esign* as outline& in the a#o%e&ocument (A gui&e to the Structural Design o;a%ements or New Roa&s* Thir& E&ition* 19F0)

is #ase& on an em$irical a$$roach using resultsrom roa&s in ser%ice-.oncrete use& in roa& construction is re+uire&to ha%e a minimum G=&ay com$ressi%estrength o G kN:m- The !e"ural strength orthis gra&e o concrete is more than 3 kN:m which in&icates that it has signicant #eam

strength-


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Rigid Pavement (Cont’d)Roa& Note 9 Design @etho&The mo&ulus o elasticity is in the or&er o 36@N:m which means that the concrete sla# has

a high &egree o rigi&ity-ecause o the #eam strength an& rigi&ity o theconcrete the wheel loa&s on the sla# are s$rea&o%er a large area* resulting in small &e!ections

an& %ery low $ressures on the su#gra&e-.onse+uently su#gra&e strength is lessim$ortant or rigi& $a%ement than or !e"i#le$a%ement &esign-


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Rigid Pavement (Cont’d)Roa& Note 9 Design @etho& (.ont/&) The ollowing are the three #roa& su#gra&e

classesSu#gra&e Descri$tion @in- Su##ase.lass Thickness (mm)7eak .R I 1C0

Normal Su#gra&es not in theother categories G0

Bery Sta#le .R J 1C 0


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Rigid Pavement (Cont’d)Roa& Note 9 Design @etho& (.ont/&) The thickness o either reinorce& or unreinorce&sla#s &e$en& on the su#gra&e ty$e an& on the

cumulati%e num#er o stan&ar& a"les (ESALs)carrie& #y the $a%ement &uring its &esign lie- The concrete sla# thickness* weight o

reinorcement (%aries with the ESALs) an& ?oint

s$acing (%aries with the weight oreinorcement) are in&icate&) on &esign charts inRoa& Note 9-


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highway engineering tran 3001 lecture 9.ppt

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