Asphalt Properties

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TheImprovementofBitumenPropertiesby

AddingNanoSilicaFarhadZafari1,MohammadRahi2,NazaninMoshtagh3,HosseinNazockdast4

1HeadofResearchandDevelopmentDepartment,PasargadCompany,Tehran,Iran

2,3PolymerEngineeringDepartment,AmirkabirUniversityofTechnology,Tehran,Iran

4AssociatedProfessor,PolymerEngineeringDepartment,AmirkabirUniversityofTechnology,Tehran,Iran

[email protected];[email protected];[email protected];[email protected]

Abstract

Asphalt oxidative aging is one of the prevalent causes of

pavementdistresseswhichincreasepavementsusceptibility

to fatigueandlow temperaturecracking.Thisphenomenon

is mainly studied through oxidation kinetics and through

evaluating oxygen diffusivity rate into asphalt binders.

Whileoxidativeaginginpavementisinevitable,application

ofantiagingadditives shown tobeaneffectivemethod in

delayingoxidativeaging.Assuchthispaperinvestigatesthe

meritofapplicationofnanosilicaasanantiagingadditive.

Todoso,differentpercentagesofnanosilicawasadded to

neat asphaltbinder. Asphaltbinder was then exposed to

short term oxidative aging using a rolling thin film oven

(RTFO). To study the change in the chemical, rheological

andmorphologicalpropertiesofasphaltbindersinpresence

of nanosilica, the Superpave tests, Fourier transform

infrared spectroscopy (FTIR)aswellasSEM imagingwereconducted. The FTIR study shows that nanosilica can

improve the aging resistance of the asphalt binder as

reflectedinlowerlevelofcarboxylicacids(observedat1400

1440cm1)andsulfoxide(observedat~1050cm1) innano

silicamodifiedspecimencomparedtothoseinnonmodified

specimens. Carboxylic acids occur naturally in asphalt;

however its concentrationhasbeenknown tobe increased

significantly due to oxidative aging. This in turn reduces

oxidation aging in modified asphalt. In addition, it was

foundthatpresenceofnanosilicasignificantlyincreasesthe

complex modulus (G*) and complex viscosity (*) of the

asphaltbinder.Thisinturnimprovespavementresistancetorutting. Itwasconcluded that introductionofnanosilica to

asphaltbindercan improve theantiagingproperty,rutting

performanceandrheologicalpropertiesofasphaltbinder.

Keywords

Nanosilica;NanoModifiedAsphalt;Rheology;Aging

Introduction

Thechemicalcompositionofasphaltisquitecomplex,

therefore,researchersmainlyusepercentagesofSARA

(Saturates, Asphaltene, Resin and Aromatic) to

compare various asphalt binder produced from

differentorigins.Compositionofeachasphaltbinder

is typically grouped into two categories: asphaltenes

and maltenes. The latter can be further subdivided

into saturates, aromatics and resins (Petersen, 1984).

However,asphaltscolloidalsystemmaychangewhen

it is exposed to oxygen at elevated temperature

causing oxidative during asphalt production and

service life. Aging hasbeen known tobe one of the

principal factors expediting asphalt pavements

deterioration (Luand Isacsson,1998).Theoccurrence

of asphalt binder aging is further expedited by

thermaloxidation during storage, mixing, transport

and placing and compaction; this in turn negatively

affects asphaltbinder rheological properties causing

pavement tobemore susceptible to low temperature

cracking(LuandIsacsson,2002;GawelandBaginska,

2004). While pavement oxidative aging is inevitable,

therehavebeenmanystudiestobetterunderstandthe

oxidation mechanisms as well as to develop new

methods and additives to delay oxidative aging.

Among those additives are various resins, rubbers,

polymers, sulphur, metal complexes, fibres, chemical

agentsandnanomaterials.Theuseofnanomaterials

has seen a tremendous development in recent years

mainly due to their surface properties and their

effectiveness in altering hierarchical structure of

compositematerials(Youetal.,2011;Yaoetal.,2012b;

Onochieetal.,2013;Fini,2013).Ithasbeenshownthat

introduction of certain nanomaterials into asphalt

binder could offer a significant improvement in

asphaltphysicalandrheologicalproperties leadingto

developmentofnanomodifiedasphaltwith superior

performance. As such nanotechnology has been

gradually incorporated into the field of modified

asphalt with various kinds of nanomaterials being

usedtomodifyasphaltinrecentyears.Nanosilicahas

beenwidelyused inpolymers and asphaltbinderas

inorganicfillertoimprovethepropertiesofpolymeric

andbituminousmaterials(Zhouetal.,1999;Huetal.,

2004;Chengetal.,2006;LiuandPan,2007).Overthe


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last 10 years, nanosilica has served as a promising

material for designing and preparingnew functional

materialsbecauseofitshighsurfaceareaandstability

(Senffetal.,2009;ZhangandIslam,2012;Kongetal.,

2012;Singhetal.,2013).Theshapeanddimensionof

thesilicaparticlesareverydesirableforapplicationinasphalt binder mainly because the surface area of

interaction is much higher than that of conventional

fillers. By dispersing nanosilica into asphalt matrix

one can create polymeric nanocomposites with

enhanced mechanical behavior, thermal and gas

barrierproperties(LeBaronetal.,1999;SinhaRayand

Okamoto, 2003; Yao et al., 2012a). Therefore, in this

study, thenanosilicawasusedtomodifytheasphalt

binder. Nanosilica was added into the neat asphalt

binderatconcentrationsof2%,4%and6%byweight

ofthebase asphaltbinder.Rheological,chemicalandmorphological characterization of neat and modified

asphalt binder was conducted to evaluate the

performance of nanosilica modified asphalt binder.

Following sections of the paper is devoted to

description of materials and test methods including

materials and sample preparation, aging procedure,

dynamic rheological characterization and Fourier

transforminfraredspectroscopy(FTIR).Theresultsof

Physical properties of asphalt binder, dynamic

rheological characterization and Fourier Transform

InfraredSpectroscopy (FTIR)arepresented insection3. Dynamic rheological properties of asphaltbinders

are investigatedbasedon threeapproaches including

frequencysweep,temperaturesweepandshearcreep.

Finally, the merit of application of nanosilica to

improve antiaging properties of asphalt binder is

discussed.

MaterialsandTestMethods

This section will describe various materials used in

thisstudyaswellas thesourcesofeachmaterialand

itspreparationmethod.

1) MaterialsandSamplePreparation

Thebaseasphaltused in thisstudywasAC60/70

Pen grade.Asphaltbinder was thenblended with

2%, 4% and 6% nanosilica acquired through

NeutrinoCorporation located inTehran, Iran.The

quantityofeachadditivewasselectedbyweightof

based asphaltbinder. The mixing was conducted

usingan IKAbench tophighshearmixerat4000

rpm for 2 hours. To conduct the mixing, an

aluminium can was filled with 250 260 g ofasphalt and placed in a thermoelectric heater.

Whentheasphalttemperaturereachedto180o98C,

specified amount of nanosilica was added to the

can and mixing for two hours. Using this

procedure one neat sample and three nanosilica

modifiedasphalt(NSMA)sampleswereproduced.

For simplicity in referring to each sample, theywerenamedusing followingabbreviation:NEAT,

NSMA2%, NSMA4%andNSMA6%.Toensure

nanosilicaparticlesaredisperseduniformlywithin

the asphalt matrix. The Scanning Electron

Microscopy (SEM) imagesofasphaltweremainly

usedtounderstandthemicrostructuralchangesof

modified samples and to evaluate the matrix

structure suchas thephysicaldispersionofnano

silicaparticles (KavussiandBarghabani,2014).As

can be clearly seen in FIGURE 1, nanosilica

particlesarewelldispersedintheasphaltmatrix.

(a)

(b)

(c)

FIGURE1SEMMICROSTRUCTUREIMAGESOFNANOSILICA,

NEATANDNANOSILICAMODIFIEDASPHALTAT18000X

MAGNIFICATION,(A)NSMA2%,(B)NSMA4%AND(C)NSMA6%


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2) AgingProcedure

All asphaltbinder samples were agedby rolling

thin film oven test (RTFOT) (ASTM D287285) in

order to simulate the hot mixing process during

plantproduction.

DynamicRheologicalCharacterization

Dynamic Shear Rheometer (DSR) MCR101 from

AustriaAntonPaarCompanywasused in thisstudy

tomeasure complexmodulus and complexviscosity.

The repeated shear creep test with a loading and

recoveryperiodwasconductedoneachspecimen.The

creeptestsweredoneundertwofixedshearstressesof

100and3200Pafor10cycleswith1sloadingtimeand

9sofrecoverytimeat50C.

Fourier

Transform

Infrared

Spectroscopy

(FTIR)

Fourier Transform Infrared Spectroscopy (FTIR)

spectra were recorded by Jasco IRT 3000 FTIR

spectrometer. Infrared spectra can be utilized in

organic structure determination by identifying

interatomicbonds in chemical compounds. Chemical

bonds in different environments will absorb varying

intensitiesandatvaryingfrequencies.Thefrequencies

atwhichthereareabsorptionsofIRradiationreferred

toaspeakscanbecorrelateddirectlytobondswithin

the materials chemical structure. Each interatomic

bond may vibrate in several different motions

(stretchingorbending).Stretchingabsorptionsusually

producestrongerpeaksthanbending.

Results and discussion

PhysicalPropertiesofAsphaltBinder

1) BasicPhysicalProperties

The effect of nanosilica modification on the

conventional 128 asphalt binder rheological

properties can be seen in TABLE 1. It can beobservedthatthereisadecreaseinpenetrationand

anincreaseinthesofteningpointwhennanosilica

was introduced to the asphalt binder. It was

observed that all nanomodified asphalt samples

had lower penetration andhigher softening point

than control asphalt. This in turn can lead to

improvement in the asphalt binder stiffness and

flexibility. However, the result of ductility test

showedadeclining trend in thepresenceofnano

silica.Thiscanbeattributedtothepresenceofhigh

specific surface area in nanosilica which leads toincreaseofasphaltabsorption.

TABLE1CONVENTIONALPROPERTIESOFNEATANDNANOSILICA

MODIFIEDASPHALTBINDERS

SamplePenetration

(mm)

Softening

point(oC)

Ductility

(cm)

Elastic

recovery(%)

NEAT 58 47 >150 12

NSMA2% 56 50.5 93 16

NSMA4% 50 54.1 53 19NSMA6% 43 58 27 23

2) StorageStability

Thestoragestabilityresultsare listed inTABLE2.

The difference between the softening points was

usedtoevaluatestabilityofthemodifiedsamples.

The stability was deemed acceptable if the

differencebetween the softeningpointof samples

takenfromthetopandthebottomofthespecimen

waslessthan2.5C.

TABLE2STORAGESTABILITYOFNEATANDNANOSILICAMODIFIEDASPHALTBINDERS

SampleSofteningPoint(oC)

Top Bottom SPtop SPBottom

NEAT 47.8 47.8 0

NSMA2% 52.5 52.4 0.1

NSMA4% 57.3 57.6 0.3

NSMA6% 61.9 91.6 0.6

TABLE2showsthesofteningpointsofthetopand

bottomspecimensandthedifferencebetweenthese

twotemperatures.AscanbeobservedfromTABLE

2, the differences between the top and bottom

softeningpoints inallsamplesare less than2.5C.

This indicates thatnanosilicamodifiedspecimens

have appropriate storage stability. Therefore

addition of nanosilica into asphalt will not

negatively affect storage stability of the modified

samples.

DynamicRheologicalCharacterization

1) FrequencySweep

The relationship between frequency and

temperatureestablishedby theTimeTemperatureSuperposition Principle (TTSP); this principle

allowsrheologicalpropertiesofasphaltbinders to

beestimatedoveranextendedfrequencyrange.In

FIGURE2,complexmodulus(G*)andphaseangle

() values are presented in the form of black

diagrams.Blackdiagramsprovideauseful tool in

analyzingrheologicaldata for the identificationof

possiblediscrepancies inexperimentalresults,and

for the verification of time temperature

equivalencyinthermorheologicalsimplematerials

(Airey,2002).Blackdiagramcurvescorrespondingtoallasphaltbindershavemonotonictrend.Ascan


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be clearly seen, the samples with higher

concentration of nanosilica have lower complex

modulus at higher phase angle and higher

complex modulus at smaller phase angle. The

RTFOagingslightlyshiftsallcurvestowardlower

phaseangle,thusindicatingachangeinrheologicalbehaviour. In addition, comparison of Black

diagram for RTFO aged and unaged samples

shows that specimens with high concentration of

nanosilicaarelesssusceptibletooxidativeaging.

(a)

(b)

FIGURE2THEBLACKDIAGRAMOFASPHALTBINDERSAT30

C,(A)UNAGEDNEATANDMODIFIEDASPHALTBINDER

AND(B)AGEDNEATANDMODIFIEDASPHALTBINDER

2) TemperatureSweep

The values for the complex viscosity, complex

modulus and phase angle of the nanosilica

modified samples as a function of the nanosilica

concentrationandtemperatureat10rad/s(1.59Hz)

areshowninFIGURES3 5.

As it can be seen (FIGURE 3), asphalt complexviscosity increaseswith the increases in thenano

silicaconcentration.Ananosilicamodifiedasphalt

binderwithhighviscositycanleadtodevelopment

ofathickerfilmsurroundingtheaggregateswhich

increases the cohesive strength. This in turn can

promotepavementdurability.

(a)

(b)

FIGURE3THEISOCHRONALPLOTSOFCOMPLEXVISCOSITY

VERSUSTEMPERATUREAT10RAD/S,(A)UNAGEDNEAT

ANDMODIFIEDASPHALTBINDERAND(B)AGEDNEATAND

MODIFIEDASPHALTBINDER.

(a)


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(b)

FIGURE4THEISOCHRONALPLOTSOFCOMPLEXMODULUS

VERSUSTEMPERATUREAT10RAD/S,(A)UNAGEDNEAT

ANDMODIFIEDASPHALTBINDERAND(B)AGEDNEATAND

MODIFIEDASPHALTBINDER

FIGURE 4 indicates that the complex modulus ofallmodifiedsampleswerehigherthanthoseofthe

neatasphaltbinder.Inaddition,itcanbeseenthat

phase angles of modified asphaltbinder were all

lowerthanthoseofbaseasphaltbinder.

(a)

(b)

FIGURE5THEISOCHRONALPLOTSOFPHASEANGLEVERSUS

TEMPERATUREAT10RAD/S,(A)UNAGEDNEATAND

MODIFIEDASPHALTBINDERAND(B)AGEDNEATAND


Consequently, the modified asphaltbinders were

more elastic than neat asphalt binder and could

enhance the asphalt rutting resistance. To further

investigate asphalt performance in terms of

permanent deformation (rutting); Superpave

ruttingparameter(G*/sin)wasmeasuredforbothmodified and nonmodified specimens. Rutting is

defined as the progressive accumulation of

permanent deformation of each layer of the

pavement structure under repetitive loading

(Tayfuretal.,2007).FIGURE6 shows theG*/sin

versus temperature curves for (a)before and (b)

after RTFO aging. The G*/sin values were

calculatedforthetemperaturesrangingfrom30to

90C.The results show that introductionofnano

silica to the neat asphalt binder significantly

increased the rutting parameter G*/sin; this in

turn can enhance pavement resistance to

permanent deformation. This can further allow

extending the high temperature range within

whichasphaltbindercouldbeused.

(a)

(b)

FIGURE6THEISOCHRONALPLOTSOFG*/SIN VERSUS

TEMPERATUREAT10RAD/S,(A)UNAGEDNEATAND

MODIFIEDASPHALTBINDERAND(B)AGEDNEATAND



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3) ShearCreep

Theresultsofcreeptestat50Chavebeenshown

in FIGURE 7. At each loading cycle, the loading

and recovery time was equal to 1 s and 9 s,

respectively and loading cycles repeated for 20

times(10cycleswith100Pa loadingand10cycleswith3200Pa loading). Instantaneouselastic strain

ofasphaltdevelopedduringtheloadingstage,and

theviscoelastic strainofasphaltwascalculatedas

the total creep strain accumulated at the time of

unloading. The instantaneouselastic strain of

asphalt disappeared after unloading, and the

delayed elastic strain recovered gradually (Wang,

2011). The unrecoverable viscoelastic strain is the

permanentstrain(Wangetal.,2011).Analysisofthe

data indicates that increasing the nanosilica

content and aging inRTFOhavenoticeable effecton reducing the level of permanent strain. As

shown inFIGURE7 the trend isconsistentamong

various cycles. However, the level of total

permanentstrainincreasesasthenumberofcycles

increases.

(a)

(b)

FIGURE7THERESULTSOFCREEPTESTFORUNMODIFIED

ANDMODIFIEDSAMPLESAT50C,(A)UNAGEDNEATANDMODIFIEDASPHALTBINDERAND(B)AGEDNEATAND


FourierTransformInfraredSpectroscopy(FTIR)

The FTIR results show that nanosilica can improve

the aging resistance of the bitumen as reflected in

lower levelofcarboxylicacids(observedat14001440

cm1relatedtoOHband)andsulfoxide(observedat

~1050 cm1) in nanosilica modified specimencompared to those in nonmodified specimens. Even

though carboxylic acidsnaturally exist in asphalt, its

concentration increases significantly due to oxidative

aging(FIGURE8).Tofurtherquantifythe

effect of nanosilica on reducing asphalt oxidative

aging, carbonyl index was calculated forboth nano

silica modified and nonmodified specimens before

and after RTFO aging. As shown in TABLE 3, the

carbonyl index of aged nanosilica modified asphalt

binder decreases as the percentage of nanosilicaincreases. Therefore, the nanosilica can be a

promising candidate for delaying oxidative aging of

asphaltbinder.

TABLE3.CARBONYLINDEXOFAGEDANDUNAGEDMODIFIEDBITUMEN

FIGURE8FTIRSPECTRAANALYSISOFNEATANDMODIFIED

ASPHALTBINDER(A)UNAGEDASPHALTBINDERSAND(B)

AGEDASPHALTBINDERS

Conclusion

This paper investigates the merit of application of

nanosilicainasphaltbinderasanantiaging additive.

To investigate the effectiveness of the nanosilica inreducingasphaltaging,differentpercentagesofnano

Unaged C=O(1690cm1) Aged =O(1690cm1)

neatbitumen 0.082 neatbitumen 0.095

bitumen+2%

nanosilica 0.044

bitumen+2%

nanosilica 0.055

bitumen+2%

nanosilica 0.039

bitumen+2%

nanosilica 0.041

bitumen+2%nanosilica 0.052

bitumen+2%nanosilica 0.031


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silica were added to neat asphalt binder. Asphalt

binderwasthenexposedtoshorttermoxidativeaging

using a rolling thin film oven (RTFO). To study the

changeinthechemical,rheologicalandmorphological

propertiesofasphaltbindersinpresenceofnanosilica,

theSuperpave testsandFourier transform infraredspectroscopy (FTIR) were conducted. Rheological

characterizationofmodifiedandnonmodifiedasphalt

binder showed introduction of nanosilica enhances

therheologicalpropertiesofneatbinderbyincreasing

its storage modulus and elasticity. This in turn can

lead to improvement of pavement rutting resistance.

Furthermore, the FTIR spectrums showed that

introduction of nanosilica can delay the oxidative

aging process; this was reflected in the reduction of

therateofcarboxylformationafteragingasmeasured

bycarbonylindex.Therefore,thestudyconcludedthatnanosilicacanbeapromisingcandidatetobeusedas

an antiaging additive in asphalt while enhancing

asphaltruttingresistance.

ACKNOWLEDGMENT

The research was carried out in the department of

polymer engineering, Amirkabir University of

Technology(AUT).

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Farhad Zafari Born in Tehran, 1989, Graduate Student,

Department of Polymer Engineering(2012), Amirkabir

University of Technology (Tehran Polytechnic), Hafez

Avenue,Tehran,Iran

Mohammad Rahi Born in Tehran, 1980. BSc Polymer

Engineering (2004); MSc Polymer Engineering (2006)

Amirkabir University of Technology (Tehran Polytechnic),

HafezAvenue,Tehran,Iran

Nazanin Moshtagh Born in Mashhad, 1992, BSc Polymer

Engineering Student Amirkabir University of Technology

(TehranPolytechnic),HafezAvenue,Tehran,Iran

Hossein

Nazokdast

Born in Tehran, 1950, Associate

Professor, Department of Polymer Engineering, Amirkabir

University of Technology (Tehran Polytechnic), Hafez

Avenue,Tehran,Iran

Asphalt Properties

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