material of highway engineering

7/25/2019 Material of Highway Engineering

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MATERIAL IN HIGHWAY

ENGINEERING


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Sub Grade

Subgrades are commonly compacted before teconstruct!on of a road" pa#ement $ Te subgrade !ste foundationof te pa#ement structure" on%!c te subbase !s la!d$

'reparat!on of te subgrade for construct!on usually!n#ol#es d!gg!ng" !n order to remo#e surface

#egetat!on" topso!l and oter un%anted mater!al"and to create space for te upper layer of te

pa#ement$ T!s process !s (no%n as )subgradeformat!on) or )reduct!on to le#el)$

Te load*bear!ng strengt of subgrade !s measuredby +al!forn!a ,ear!ng Rat!o -+,R. test" fall!ng %e!gt

de/ectometer bac( calculat!on sand oter metods$


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Sub base

subbase!s te layer of aggregate mater!al la!d onte subgrade$$ Subbase !s often te main load-bearing layerof te pa#ement$

Its role !s to spread te load e#enly o#er te subgrade$ Temater!als used may be e!ter unbound granular" or cement*bound$

0nbound granular mater!als are usually crushed stone"crused slag or concrete" or slate$

M!n!mum t!c(ness des!gn are based on te force appl!ed onte road$


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,!nder +ourse

Te mater!al used as a b!nder course !s 1cun(!er1 tan a %ear!ngcourse" (no%n as Dense Bitumen Macadam (DBM.$ 2n publ!c!g%ays and oter ea#!er*use pro3ects" te b!nder course may beunderla!n by a base layer$

Te b!nder course mater!al sould be la!d and le#elled out reasonablyle#el -4 56mm. and torougly rolled and compacted beforepreced!ng %!t te %ear!ng course$ Larger areas may be la!d by apa#er mac!ne spec!7cally des!gned to lay b!tmac$ T!s usually g!#esa 1truer1 !$e$ more accurately le#elled" surface tan and*lay!ng$


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Surface course

This is the top layer of the pavement, the layerthat is seen and tracked

he !earing course should be at least "#-"$mmthick !hen rolled, and should not deviate from

the correct level by more than % &mm' hereshould be no roller marks in the nished surface


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Tac( +oat

Tac( coat -also (no%n as bond coat.!s a l!gt appl!cat!on of aspaltemuls!on bet%een ot m!8 aspalt

layers des!gned to create a strongades!#e bond$

W!tout tac( coat te aspalt layers

!n a road %ay may separate %!creduces te strengt$


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8/11

Mater!al !n ,!nder And Wear!ng

+ourse

Tar b!tumen and aspalt from a group of!nterrelated mater!al %!dely used !n !g%ayconstruct!on$

Tar !s a dar( blac( #!scous l!9u!d $depend!ngupon !t sources of or!g!n tar !s class!7ed !n tote follo%!ng categor!es

Bitumen!s a product of te o!l*re7n!ng and

petro*cem!cal !ndustr!es$ :ery bas!cally" !t !ste thick, sticky"

Aspalt" !s a m!8ture of b!tumen and m!nerals$


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ack )oats Tac( coat !s a bro%ny*blac( emuls!on of b!tumen tat !s

appl!ed to te prepared" e8!st!ng surface before lay!ng te!earing course'Te emuls!on bonds to te e8!st!ngsurface,

and ten te ne% %ear!ng course %!ll bond to teemuls!on" ensur!ng full ades!on$ It also elps ensure tat%ater does not 7nd !ts %ay bet%een te ne% and e8!st!ngsurfaces %ere !t can free;e and l!ft o< te ne% surface$

%ear!ng course !s la!d o#er a recently la!d -!e" %!t!n tepreced!ng =*5> days. base course'


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