highway engineering tran 3001 lecture 5

8/9/2019 Highway Engineering TRAN 3001 Lecture 5

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TRAN3001Highway Engineering Lecture

5PAVEMENT MATERIALS

Soil

Types

Phases

Solid Phase


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Pavement Materials

The most imortant avement materials are soil!aggregates o" roc# an$ slag %&y'ro$uct o" metalsmelting(! &ituminous &in$ers an$ Portlan$ cement)Soil*oravement construction! soil is the inorganic!

earthen material that is the "oun$ation "or all roa$s) +tis also e,cavate$ %cut( "rom higher elevations o" aroa$ construction site an$ haule$ %as -ll( to constructem&an#ments to the re.uire$ gra$es)

/here a$e.uate .uantities o" -ll cannot &e o&taine$"rom the earthwor#s on site! inorganic earthenmaterial has to &e imorte$)%The to layer o" mostly organic material is re"erre$ toas tosoil an$ tyically ranges "rom 5 cm to 30 cmthic#) rganic material is unsuita&le "or avementconstruction an$ has to &e remove$ ()


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Pavement Materials %ont2$(

Tyes o" oil

oil is the ro$uct o" the hysical an$ chemical weatheringo" &e$roc#) /in$ an$ other natural "orces have move$ alot o" this weathere$ material away "rom their original

locations)ne o" the ways soils can &e groue$ is accor$ing to the

means &y which they were naturally transorte$ an$$eosite$ in their resent locations! e,amles o" which areliste$ &elow)

Residual soilsThese were "orme$ "rom the un$erlying &e$roc# an$ never$islace$) Tyically -ne'graine$ near the sur"ace! thesesoils &ecome more coarse'graine$ with increasing $ethas they contain roc# "ragments)


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Tyes o" oil %ont2$(Colluvial soils

Accumulations o" roc# $e&ris which &ecome

$etache$ an$ are carrie$ %&y gravity( $own thesloes "orm these soils which are coarse an$ stonysince they result "rom hysical weathering)

Alluvial soils

These soils have &een $eosite$ &y moving river

waters! mostly onto their 4oo$ lains! which arewi$e! 4at arcels o" lan$ a$acent to the rivers)


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Tyes o" oil %ont2$(

Alluvial soils (Contd)As the velocity o" the 4oo$ water $ecreases the

"urther away it gets "rom the river! san$ an$ gravel

+s $eosite$ a$acent to the river &an#s! less coarse

graine$ material "urther out an$ the -nest materialis "urthest "rom the river)

This results in goo$ sources o" construction material

near to the river an$ swamy lan$ "urther out)


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oil Phases

oil can &e consi$ere$ as soli$ %mineral(articles interserse$ with voi$6ore saces

which may contain water as well as air)Highway engineering is concerne$ withminimi7ing the voi$ saces an$ ma,imi7ingthe volume occuie$ &y the mineral articles)

egregating the three constituent soil hasesro$uces the "ollowing schematic $iagram8


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oil Phases %ont2$(

e 9 :v

:s

whereVoid Ratio = e

:olume o" voi$s 9 :v

:olume o" soli$s 9 :s

Air

/ater

oli$s


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oil Phases %ont2$(

/hen the soil is saturate$! all the voi$s are-lle$ with water! i)e) the volume o" voi$s %Vv(

is e.ual to the volume o" water %Vw( an$ thevoid ratio of the saturated soil is es8

es = Vw

Vs+" m is the moisture content o" the soil 8

m = Ww

Ws


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oil Phases %ont2$(

Vw = m x s

Vs w

where /w 9 weight o" water

/s 9 weight o" soli$s

s 9 weight er unit volume o" soli$s

w 9 weight er unit volume o" water


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oil Phases %ont2$(

Theporosity n! o" a soil is the ratio o" thevolume o" the voi$s to the total volume o" the

soil) This is usually e,resse$ as a ercentage8n = Vv x 1 where : is the total

volume

V o" the soilPorosity can also &e e,resse$ in terms o" e8

n=Vv x 1 = e x 1

Vv! Vs 1 ! e


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oil Phases %ont2$(

The ercentage o" the total volume o" the soilwhich is occuie$ &y the air in the voi$s is

re"erre$ to as the percent air voids na!8na = :a x 1 where :a is the volume

: o" air voi$s

The ercentage o" the total volume o" the soilwhich is occuie$ &y the water in the voi$s isre"erre$ to as the percent "ater voids nw!8

nw = Vw x 1 V


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oil Phases %ont2$(#e$ree of saturation S! is the e,tent to whichthe voi$s resent in a soil are -lle$ with water) +tis the ratio o" the volume o" water to the volume

o" voi$s! e,resse$ as a ercentage8S =Vw x 1

:v

The e,tent to which the e,isting voi$ ratio %e( o" asoil reresents the range o" ossi&le voi$ ratios"or that soil is terme$ the de$ree ofcompaction %! or relative unit weight 8


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oil Phases %ont2$(

9 emax ; e x 1

emax ' emin

emax 9 voi$ ratio o" soil in its loosest state

emin 9 voi$ ratio o" soil in its $ensest

state

This means that a soil in its loosest state willhave a $egree o" comaction6relative unitweight o" 7ero while in its most comact stateit will have a relative unit weight o" 100


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oli$ Phase o" oil

The mineral articles o" soil range in si7e"rom &oul$ers to colloi$s) +n 1=0> the

we$ish soil scientist Atter&erg $evise$ aclassi-cation system which esta&lishe$limiting si7es o" the articles that comrisethe soli$ hase o" soil)

This was an imortant $eveloment as thehysical an$ chemical roerties o" soil arestrongly in4uence$ &y its particle si&e

distri'ution(


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oli$ Phase o" oil %ont2$(?ravel articles were classi-e$ as those &etween@0 mm an$ @ mm in si7e! san$ "rom @ mm to 0)@mm! silt 0)@ mm to 0)00@ mm an$ clay less than0)00@ mm)

?ravel was set &etween the limits within which nowater is hel$ in the ore saces an$ only wea#lyhel$)

The lower limit "or san$ %0)@ mm( was the oint atwhich water is hel$ in the ore saces &y caillary

action)*or silt the lower limit o" 0)00@ mm is the smallestsi7e article that can &e seen with the na#e$ eyean$ articles can &e coagulate$ to "orm crum&s)2


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oli$ Phase o" oil %ont2$(How coarse or how -ne a soil is $een$s on the

relativeamounts o" the $iBerent "ractions resent)

Review o" the technical literature on soils showsthat

$iBerent organisations %+nternational Cnion o" oilciences! AAHT! etc)( accet that the most

convenientway to $e-ne the various mineral constituents o"

soil ison the &asis o" article si7e)However! e,actly where the limits shoul$ &e set "orsan$! silt! etc) is not universally accete$)


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oli$ Phase o" oil %ont2$(

The physical and mineralo$ical characteristics o" soilarticles are imortant in $etermining the suita&ility o"the soil as a avement material)

oil articles are comose$ o" rimary mineral "ragmentstogether with any secon$ary minerals ro$uce$ &yweathering)oil "ractions ro$uce$ &y hysical weathering i)e) gravel!san$ an$ coarse silt are comrise$ mostly o" rimary

minerals) The .uantity o" rimary minerals is re$uce$ inthe -ne silt articles an$ in the clay "raction! thesecon$ary minerals re$ominate)


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oli$ Phase o" oil %ont2$(Sand and "#avel are comose$ rimarily o" .uart7%ilicon Dio,i$e! i)( articles an$ are chemically

inactive so the hysical characteristics are o" mostinterest)

The in$ivi$ual grains are generally &ul#y in shae an$$een$ing on the $egree o" hysical weathering

receive$rior to -nal $eosition! may &e angular or roun$)

They $o not e,hi&it any cohesive roerties an$resistance

to $islacement is cause$ &y interloc#ing o" the grains!calle$ inter'granular6internal "riction)

The &ul#iness o" the grains results in relatively large

ores! ma#ing san$y6gravel soils very ermea&le)


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Siltarticles are transitional &etween san$ an$ clay)

Physically they are similar to san$s in that their sta&ility is

$erive$ "rom internal "riction! articularly the coarser grains

which are &ul#y with the same $ominant .uart7 mineral)Cnli#e san$s! silts ossess a limite$ amount o" cohesion an$

water asses relatively slowly through the smaller ores)

/here articles at the lower limit o" the "raction re$ominate!

silt e,hi&its .ualities li#e clay an$ may un$ergo consi$era&le

shrin#age an$ e,ansion with changes in moisture content)


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lay articles $iBer "rom the other "ractions&oth chemically an$ hysically)

They are 4at an$ elongate$! comrising asilica sheet &on$e$ to an alumina sheet%two layer tye( or a three'layer tye where

two silica sheets are &on$e$ to a centralalumina sheet) %+ron or magnesium may &eresent instea$ o" aluminium()


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oli$ Phase o" oil %ont2$(ecause o" their shae they have a much largersur"ace area er unit weight than the &ul#ier"ractions an$ can in4uence a soil2s &ehaviour

seemingly out o" roortion to the amount resentin the soil)

The very small ore saces &etween the articlesma#e clay soils imermea&le "or all ractical

alications)

lay minerals carry negative electrical charges ontheir sur"aces which a$sor& water %hol$ water onthe sur"ace( an$ account "or cohesion! shrin#age

an$ swelling roerties)

highway engineering tran 3001 lecture 5

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