Research ArticleEffect of Silicone Oil on Dispersion and Low-TemperatureFracture Performance of Crumb Rubber Asphalt

Nonde Lushinga Liping Cao and Zejiao Dong

School of Transportation Science and Engineering Harbin Institute of Technology Huanghe Road 73 Nangang DistrictHarbin 150090 Heilongjiang China

Correspondence should be addressed to Liping Cao caoliping79163com

Received 12 July 2019 Accepted 10 September 2019 Published 17 October 2019

Academic Editor Hom Kandel

Copyright copy 2019 Nonde Lushinga et alis is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Low-temperature cracking is one of the major pavement distresses in cold regions To reduce the prevalence of such cracks crumbrubber modified asphalt (CRMA) has been applied for a long time However CRMA experiences compatibility and segregationproblems with asphalt Silicone oil has long been seen to improve compatibility and segregation problems of polymers in asphaltbut its benefits on low temperature performance of crumb rubber asphalt have not been explored Furthermore silicone oil can beobtained as virgin or recycled from industrial transformers however the recycled silicone oilrsquos influence on low-temperaturecrack performance of asphalt has also not been explored erefore the purpose of this study was to investigate the effect ofrecycled silicone oil (SO) on dispersion and low-temperature fracture performance of crumb rubber asphalt e fracturemechanics-based single-edge notch beam (SENB) test was performed at temperatures of minus 12degC minus 18degC and minus 24degC In additionfluorescence microscopy (FM) atomic force microscopy (AFM) and Fourier-transform infrared (FTIR) experiments were alsoconducted Results show that the addition of SO to CRMA increases displacement fracture energy and fracture toughness at lowtemperature while it decreases stiffness which reduces cracking In addition AFM results show that surface roughness increaseswith the addition of SO which indicates that bonding of asphalt and rubber particles had also improved FM also confirmed thatdispersion of rubber particles had improved with addition of silicone oil FTIR results revealed that asphalt samples with SOtreatment were hydrophobic which potentially repels water ingress and delays the freezing of asphalt Lastly statistical analysisrevealed that the influence of silicone oil on low-temperature performance of rubber asphalt was significant erefore the studyconcluded that fracture cracking resistance is improved by addition of silicone oil to crumb rubber asphalt

1 Introduction

In cold regions low-temperature cracking has been one ofthe major pavement distresses [1 2] Pavements often ex-perience thermal contraction when temperatures drop tosubzero At low temperature asphalt becomes brittle and thegenerated thermal stress is only relieved when the transversecrack is initiated is cracking gives rise to prematurefailure of the pavement and poor rideability [3] To reducethis type of distress and maintenance costs asphalt mixturesshould be designed and built with materials that are able tosustain the stresses generated by both low-temperatureconditions and vehicular loads

Crumb rubber (CR) a waste material from vehiculartires has been suggested as an asphalt modifier for pavement

applications to improve low-temperature performance Forexample many researchers have studied the performance ofthe CR asphalt binder Results in all respects have led to theconclusion that crumb rubber improves mechanical prop-erties of asphalt binders particularly low temperatureperformance is performance is attributed to severalfactors such as decrease in stiffness of rubber asphalt at lowtemperature due to improvement in aging susceptibility ofthe asphalt binder low sensitivity of rubber to low tem-perature and good elasticity properties [4ndash10]

Despite the enhanced performance attributed to crumbrubber asphalt CR as an asphalt modifier has a setback ofcompatibility and separation problems with asphalt binders Inquest to solve the problem of separation the Federal HighwayAdministration (FHWA) in 1998 prepared a crumb rubber

HindawiAdvances in Materials Science and EngineeringVolume 2019 Article ID 8602562 12 pageshttpsdoiorg10115520198602562

asphalt which was chemically modified e prepared asphaltbinders had increased separation resistance especially duringhot storage when compared to conventional crumb rubberasphalt binders is was achieved by modifying the crumbrubber with chemical additives which makes CR to mix anddisperse well in asphalt matrix [11]

Previous studies used virgin silicone oil to preparechemical crumb rubber asphalt Results suggested that sil-icone oil can improve both dispersion and mechanicalproperties of crumb rubber asphalt binders [12]

Silicone oil whose important component is poly-dimethysiloxane (PDMS) has excellent thermal stabilityand high- and low-temperature properties which make itsuitable as a compatibilizer of choice at low-temperatureconditions is polymetric material is mostly used aslubricants and coolants in electrical appliances such asindustrial transformers erefore silicon oil can becheaply purchased locally since it is discharged from theseindustrial transformers as waste oil often reclaimed andregenerated through the industrial process to removecontaminants to make it suitable for use To date no studiesexist on the use of silicone oil to improve low-temperatureperformance of crumb rubber asphalt hence the motiva-tion for this research

Zhihao et al [13] stated that most polymers such assteryne-butadieme-styrene (SBS) polyphosphate (PPA)polyethylene (PE) and vinyl acetate B-copolymer (EVA) havesegregation problems when blended with asphalt e authorfurther noted that maleic anhydride and PPA often causeadverse effects on low-temperature performance when addedto asphalt erefore polydimethysiloxane (PDMS) in par-ticular dimethyl silicone oil was suggested as an alternativematerial that can be used to solve the problem of segregation ofpolymers with asphalt at low-temperature conditions becauseof its excellent thermal stability low-temperature performanceeffect excellent flexibility and weather resistance Besides thatno studies were undertaken in that regard

However some scholars such as Li et al [14] studied theperformance of composite asphalt materials where they addeddicumyl peroxide and silicone oil (used to enhance compati-bilization) into high density polyethelenecrumb rubbermodified (HDPECRM) composite mixed with ethylene pro-pylene diene monomers (EPDM) It was found that silicone oilencapsulates the scrap rubber powder particles to form a softthick layer between CRM and the polymer matrix is liquidlayer in the polymer and filler could inhibit fracture phe-nomena (ie crack formation and propagation) Under thisconsideration the encapsulation of silicone oil should havereleased the stress concentration around the CR powderparticles and hence the mechanical properties are improved

In the recent past an investigation of coated poly-dimethysiloxane (PDMS) or room temperature vulcanisedsilicone rubber (RTV) with layered double hydroxides(LDHs) to produce superhydrophobicity (super-water re-pellent) coatings was applied to asphalt mixtures by Peng et al[15] e results suggest that the freezing time of asphaltmixtures with RTVLDHs is extended by about 3 times whencompared with asphalt mixtures without RTVLDHscoatings

Furthermore other studies have demonstrated thatsilicones can be used in improving moisture and thermalaging resistance of asphalt mixtures because of their superiorhydrophobicity and weather resistance properties [16 17]

On the other hand it is worth noting that oil-basedsoftening agents and rejuvenators have also been used toimprove low-temperature cracking resistance For instanceZhang et al [18] used bio-oil-based rejuvenator to improvethe low-temperature performance of aged asphalt bindere author found that biorejuvenator softened aged asphaltsignificantly decreased the rutting index at a temperature of52degC to 76degC and restored low-temperature crack resistance

Overall extant literature has confirmed that no studieshave been undertaken to investigate the influence of recycledsilicone oil on low-temperature cracking performance ofrubber asphalt Hence the research gap exists for furtherstudy

2 Objectives and Scope

e purpose of this paper was to investigate the effect ofsilicone oil on dispersion and low-temperature fractureperformance of crumb rubber-asphalt binders e study isimportant as it contributes towards efforts of providingsustainable paving materials while improving asphalt per-formance yet even further e asphalt binders were eval-uated at low temperatures ranging from minus 12 to 24degC especific objectives and scope of the research are summarisedas follows

(1) To evaluate the effect of silicone oil on crumb rubberasphaltrsquos low-temperature fracture performancebased on single-edge notch beam (SENB) test

(2) To understand the morphology of crumb rubbermodified asphalt samples based on fluorescencemicroscopy (FM) and atomic force microscopy(AFM) tests

(3) To determine the molecular structure of silicone oiland crumb rubber modified asphalt samples basedon Fourier-transform infrared (FTIR) test

(4) To evaluate the effect of notch depth on low-tem-perature cracking of crumb rubber asphalt con-taining silicone oil based on the SENB test

(5) To conduct statistical test on laboratory experimentalresults in order to determine the significance of thefindings

3 Materials

In this study asphalt binder 60ndash80 penetration grade bi-tumen was used to prepare crumb rubber modified asphaltsamples Silicone oil was treated with crumb rubber asphaltto produce two replicates for one sample while for anothercrumb rubber asphalt without silicone oil was used toproduce replicates for control experiment samples Materialsused in this research can be found in Tables 1ndash3e binderswere tested without being subjected to short- or long-termaging As an assumption it was envisaged that aging of

2 Advances in Materials Science and Engineering

asphalt was not going to significantly change the conclusionsobtained from the study In addition the silicone oil andcrumb rubber mesh 40 were used to prepare crumb rubbermodified asphalt

4 Experimental Test Methods

41 Preparation of Samples About 18 percent content ofcrumb rubber by weight was added to asphalt binder One ofthe blends was reacted with recycled silicone oil duringshearing while the other was prepared as conventionalcrumb rubber asphalt binder without silicone oile crumbrubber was added slowly and followed by silicone oil (3 byweight of the binder) and the mixture was sheared for onehour at 175degC

After preparation the binders were poured into the single-edge notch beam test moulds and cooled to 0degC and quicklytaken from the moulds measuring 127mmtimes 635mmtimes

127mm for length width and depth respectively e depthof the precrack was 28mm Both the precracked and theuncracked samples were used to facilitate the study of theeffect of silicone oil on crumb rubber modified asphaltrsquosperformance on low-temperature cracking Before testingeach specimen was conditioned in cold bath to testing tem-peratures minus 12degC 18degC and minus 24degC respectively To simplify theexperiment physical hardening both on unmodified asphaltand crumb rubbermodified asphalt (with andwithout siliconeoil) was tested after 1 hour of conditioning at respectivetemperatures

42 Fourier-Transform Infrared (FTIR) Test FTIR can beused for identifying polymer additives in asphalt bindermatrix In addition FTIR offers accurate data concerningoxygenation rate aliphaticity and aromaticity [19] usthe FTIR spectroscopy was conducted using a Jasco FT-IR4200 spectrometer with 32 numbers of scan and theresolution of 4 cmminus 1 To prepare the control and modifiedasphalt samples for the FTIR experiment the conventionalcrumb rubber asphalt samples and the silicone-modifiedcrumb rubber asphalt samples were heated to 180degC until

liquid enough to be poured With the aid of a brush theliquefied asphalt binders were then painted onto the surfaceof a silicon slide to create a uniform asphalt coating of05mm approximate thickness

Prepared samples were tested and the concentration ofthe functional groups associated with silicone oil absorptionin asphalt binder was deduced from the intensity of theabsorption bands Further the structural functional indexfor aromatics was determined with a view of understandingthe contribution of silicone to the aromatic content of as-phalt binder

43 Fluorescence Microscopy Test In order to study themorphology of CRMA fluorescent microscopy (FM) wasused by determining the rubber particles distribution inasphalt e FM test is premised on the principle thatpolymers undergo swelling owing to absorption of some ofthe key constituents of the base bitumen Similarly in thisstudy FM was used to study the morphology of CRMA withand without silicone oil treatment so as to observe thequality and particles dispersion in the binder Samples wereplaced on glass slides and taken to the laboratory for testingwith magnification of 100 μm

44 Atomic Force Microscopy Analysis In this study AFMwas used to determine the surface roughness (Ra) of asphaltsamples based on equation (1) Furthermore the morpho-logical distribution of rubber particles in asphalt binder wasevaluated CRMA samples with and without silicone oil wereprepared by pouring hot binder on the thin clean glass slidesand allowing the binder to flow on the glass slide Experi-ments were conducted at a temperature of 30degC Both 3Dheight images as well as 2D phase images were obtained

Ra 1N

1113944

N

j1Zi (1)

where Zi is the current height value and N is the number ofpoints within the scan area

45 Single-Edge Notch Beam (SENB) Testing A fracturemechanics-based SENB test was carried out on a three-pointbending test apparatus that was placed on a bending beamrheometer (BBR) chamber mounted e BBR water

Table 1 Physical properties of silicone oil (SO)

Technical properties Colour Viscosity 25degC Density (kgm3) Molecular weightDescription Colourless 1000 097 28000

Table 3 Gradation of crumb rubber

Sieve 30 40 50 100 200 passing 100 90ndash100 65 14 3

Table 2 Basic material properties asphalt binders

Binder tests Neat asphalt Neat + 18 CR Neat + 18 CR+ 3 SO Rubber asphaltspecification limits

Penetration 4degC 200 g 60 sec 110mm (ASTM D5) 70 49 60 10Softening point ASTM D36 (degC) 45 65 62 57Ductility 15degC (cm) 100 mdash mdash mdash

Advances in Materials Science and Engineering 3

chamber was utilized solely for conditioning samples torequired temperatures e temperature inside the waterchamber was controlled with water supply and held within03degC from the desired value A displacement rate of 001mmwas applied to break the sample at a rate that had previouslybeen determined to be convenient

e justification for the choice of the SENB test waspremised on the fact that good fracture parametric prop-erties of asphalt materials are important in building long-lasting asphalt pavements in cold regions [1] Furthermorealthough the BBR test has been seen to be sound in in-vestigating low-temperature performance of unmodifiedbinders it is not quite so for modified binders [5] StrategicHighway Research Program (SHRP) researchers recognizedthat a full fracture mechanics-based evaluation at appro-priate temperatures and rates of loading should be done toevaluate a binder for fracture performance [20] When fieldresults of asphalt mixtures in particular BBR-SENB testresults were compared with fracture properties researchersconcluded that the BBR test should be complimented withfracture tests [21] e SENB test therefore offers results thatcorrelates well with field experimentations and thus wasused in this study

5 Fracture Approach

e fracture approach is based on fracture mechanics theoryand is used to estimate the resistance of the material to crackpropagation [2] In this theory a preexisting crack or notchis punched in the specimen and used to reduce the effectivestrength of the material by amplifying the stress level nearthe crack e parametric properties obtained with thistheory are fracture energy (Gf ) and fracture toughness (KIc)e single-edge notch test (SENB) test has been developedbased on the theory of fracture mechanics and ASTM E 399testing protocols [5] is test assumes linear elastic fracturemechanicsrsquo conditions Equations (2) and (3) were used forcalculations of fracture toughness and fracture energy A lowfracture toughness value is an indication that materials aregoing through brittle fractures while high values of fracturetoughness are a sign of ductility improvement A largedeformation on the load-displacement curve and fractureenergy is an indication of superior crack resistance of theasphalt binder Fracture toughness was calculated accordingto the following equation [5]

KIc PfS

bW32

2(aW)12 199 minus (aW)(1 minus (aW)) 215 minus 393(aW) + 27(aW)21113960 11139611113966 1113967

2(1 + 2(aW))(1 minus (aW))32⎡⎣ ⎤⎦ (2)

where KIc fracture toughness under plain-strain condi-tions (Nm32) Pf applied failure load (N) S load span(m) b specimen thickness (m) W specimen height (m)and a notched depth (m)

Forceload-displacement results were used to calculate astiffness modulus assuming the beam was un-notched byusing equation (3) Using the stiffness modulus fractureenergy was calculated from the fracture toughness Poissonrsquosratio needed in the calculation was assumed to be equal to 05(purely elastic materials) e values of fracture energy wereobtained from the determined fracture toughness and thestiffness modulus and Poissonrsquos ratio was assumed to be 05for the asphalt binder according to Hoare and Hesp [5]

GIc K2

Ic 1 minus v2( 1113857

E 075

K2Ic

E (3)

where GIc = fracture energy or critical elastic energy releaserate (Jm2) E=Youngrsquos modulus (KIc test (Nm2)) andv=Poissonrsquos ratio

6 Results and Discussion

61 Fourier-Transform Infrared (FTIR) Result AnalysisFunctional groups of silicone oil in crumb rubber asphalt weredetermined using the FTIR test e analysis of infraredspectrum of various materials including silicone oil base andcrumb rubber asphalt and crumb rubber asphaltmodifiedwithsilicone oil is shown in Figure 1 e study revealed that the

peaks observed in the region of 2850ndash2960 cmminus 1 are typicallyC-H stretching vibrations ose observed around 1400ndash1500 cmminus 1 and 1300ndash1350 cmminus 1 are C-H symmetric deformingvibrations e peaks in the region within 1000ndash1100 cmminus 1 areSi-O-Si bond vibrationse Si-O bond in silicone oil forms themain chain that makes silicone oil to have high hydrophobicityand chemical durability which ensures that the silicone oilgenerally being able to be applied in the asphalt [17 22]

Comparing the infrared spectra of crumb rubber withand without silicone oil it was observed that new absorptionpeaks exist in the infrared spectra of crumb rubber asphaltcontaining recycled silicone oil which were 2964 cmminus 11258 cmminus 1 1009 cmminus 1 and 788 cmminus 1 respectively At788 cmminus 1 the peaks correspond to Si-C bond e identifiedabsorption peaks represent polydimethysiloxane or siliconeoil [23] After adding silicone oil to crumb rubber asphaltthe peaks did not disappear in asphalt is meant that thereaction between crumb rubber and silicone oil waschemical and not physical All the new absorption peakshave corresponding peaks in silicone oil spectrum [24]

Additionally the aromatic index (CC) was determinedusing the equation provided elsewhere [18] Zhang used thearomatic index to determine the degree of restoration ofaged binders by applying bio-oil-based rejuvenator to im-prove the low-temperature performance It was found thatbio-oil restores the aged asphalt and increases temperaturesusceptibility of asphalt thereby enduring higher thermalstress caused by cooling In our study the aromatic index for

4 Advances in Materials Science and Engineering

asphalt binder was calculated to determine the content ofaromatics in asphalt binder with and without silicone oiltreatment e results revealed that the aromatic index forcrumb rubber asphalt with and without silicone oil was 10and 06 respectively is result gave rise to the conclusionthat the addition of silicone oil to crumb rubber asphaltincreases the aromatic content and indices significantlyAccording to Kanabar highway pavements that do notexperience the spate of thermal distress are built withasphalt cements that have high IR aromatic indices or havemore aromatics [25] In addition the increase in aromaticcontent also decreases the dynamic modulus of the binder[18] erefore the high IR aromatic index found in thisstudy suggests that low-temperature cracking performancecan be improved with addition of silicone oil to asphaltbinder

62 Atomic Force Microscopy (AFM) Result Analysis Toevaluate the morphology of asphalt samples the AFM testwas used e AFM topographical images in Figure 2 gaverise to the following observations the bee-like structureswere CR particles in asphalt binder Based on equation (1)the average roughness for crumb rubber asphalt withoutsilicone oil was calculated as 037 nm whereas averageroughness for crumb rubber asphalt containing silicone oilwas 129 nm respectively e increase in surface roughnessof asphalt indicated that there was a change in the micro-structure of the asphalt samples after addition of silicone oilIn our study the increased surface roughness of crumbrubber asphalt with silicone oil indicates improved bondingbetween rubber particles and asphalt which may lead tocontinuous rubber particles dispersion in asphalt Visualcomparison of AFM images confirmed that the addition ofsilicone oil to crumb rubber asphalt greatly influenced theobserved microstructure and showed a continuous homo-geneity of rubber particles dispersion in asphalt ConverselyAFM topographical images for CR asphalt sample without

silicone oil revealed that rubber particle distribution was nothomogeneous

63 Fluorescence Microscopy (FM) Result Analysis e re-sults of AFM were further confirmed by FM analysis einfluence of silicone oil on the dispersion of crumb rubberparticles in asphalt binder was studied using the FM testwhich was conducted on two crumb rubber asphalt sampleswith and without silicone oil From Figure 3 results of FMimages revealed that the crumb rubber modified binderswith silicone oil showed uniformly dispersed rubber par-ticles in asphalt Conversely images of dispersion forconventional crumb rubber asphalt without silicone oilshowed noncontinuous bitumen matrix

64 Effect of Silicone Oil on Low-Temperature Performance ofCrumb Rubber Asphalt Binder Figure 4 shows that load-displacement curves stiffness modulus fracture toughnessand fracture energy values at three temperatures for the crumbrubber asphalt binders gave rise to the following observations

e results of load and displacement curve found thatthe addition of silicone oil to samples leads to increase indisplacement Asphalt binders having lower deflection atfracture perform very poorly in the field as regards thethermal cracking [4] erefore higher deflection values inour study indicate good low-temperature cracking re-sistance In addition the addition of silicone oil also in-creases stiffness modulus of the sample High stiffnessmodulus asphalt mixes at low temperature are prone tocracking [6] erefore the lower stiffness modulus ob-tained in our study is an indication of improved low-temperature performance of crumb rubber containingsilicone oil

It is also worth noting that rubber asphalt with siliconeoil did not break at minus 12degC owing to its increased low-temperature resistance is result demonstrated the effect

Silicone oil (SO)

C-H stretching of CH3

CH 3 asymmetric deformation of Si-CH

CH 3 symmetric deformation of Si-CH

Neat + crumb rubber (CR)

Neat asphalt

Neat + CR + SO

2964

12581009

788

Si-O-Si stretching

3500 3000 2500 2000 1500 1000 500Wavenumber (cmndash1)

Tran

smitt

ance

()

Figure 1 FTIR spectrum of silicone oil neat asphalt and crumb rubber asphalt modified with silicone oil

Advances in Materials Science and Engineering 5

of silicone oil on low-temperature performance of crumbrubber asphalt binders having high fracture energy wouldperform very well in the field in terms of thermal crackingresistance is was added to show that our findings agreewith other researchers [2] In our study results havedemonstrated that the addition of silicone oil to rubberasphalt increased the fracture energy therefore we foundthat the increase in fracture energy demonstrated thatsamples modified with silicone oil have superior crackresistance

Fracture toughness is yet another critical parameterused in evaluating low temperature performance of asphaltbinders in SENB test Increased fracture toughness valuesat low temperatures such as ndash20degC in polymer modifiedasphalt mixtures imply that resistance to fracture has in-creased Some polymers make asphalt less brittle at lowtemperatures and therefore polymer modified asphalt(PMA) concretes are expected to become tougher thannormal asphalt concrete at low temperatures e im-proved tensile property allows greater resistance to materialcracking [26] Similarly in our study it has been estab-lished that adding 3 content of silicone oil to crumbrubber asphalt resulted in increased fracture toughness of

the binder than binders without silicone oil is dem-onstrates that tensile property has improved leading togreater low-temperature crack resistance

65 Low-TemperaturePerformanceAnalysis ofCrumbRubberAsphalt considering Notched and Unnotched ConditionsTo investigate the effect of notch on low-temperature per-formance of crumb rubber asphalt the samples with andwithout a notch were subjected to fracture testing after 1-hour conditioning in cold bath e study gave rise to thefollowing observations

As seen in Figure 5 the load-displacement curve resultsshow an increase in stiffness modulus for unnotched samples ofcrumb rubber modified with silicone oil when compared withthe unnotched samples e preexisting crack renders thesample vulnerable to cracking therefore unnotched sampleswillmost likely have delayed cracking than the notched samples

Additionally the fracture toughness KIc and fractureenergy GIc increased with an increase in temperature fromminus 24 to minus 12degC this indicates that less potential fractureenergy is needed for crack propagation at lower tempera-tures Fracture energy and fracture toughness also increased

21nm

ndash23nmHeight sensor 20μm

(a)

65nm

ndash96nmHeight sensor 20μm

(b)

(c) (d)

Figure 2 AFM images of crumb rubber asphalt (with and without silicone oil) (a) Neat +CRndash2D AFM images (b) Neat +CR+ SOndash2DAFM images (c) Neat +CR 3D AFM images (d) Neat +CR+ SO 3D AFM images

6 Advances in Materials Science and Engineering

(a) (b)

Figure 3 FM images of crumb rubber asphalt (with and without waste silicone oil) (a) Neat +CRndashFM images (b) Neat +CR+ SOndashFMimages

ndash12degCndashneat + CRndash12degCndashneat + CR + SOndash18degCndashneat + CRndash18degCndashneat + CR + SOndash24degCndashneat + CRndash24degCndashneat + CR + SO

0

2000

4000

6000

8000

10000

12000

14000

16000

0 1 2 3 4 5 6 7Displacement (mm)

Forc

e (m

N)

(a)

35 30

162

102

179

151

020406080

100120140160180200220240

Neat + CR Neat + CR + SOAsphalt binder

Stiff

ness

mod

ulus

(kPa

)

ndash12degC

ndash18degC

ndash24degC

(b)

400

600

200

580

150

475

0

100

200

300

400

500

600

700

800

900

Neat + CR Neat + CR + SOAsphalt binder

Frac

ture

ener

gy (J

m2 )

ndash12degC

ndash18degC

ndash24degC

(c)

45 6

65 7

982

101

0

2

4

6

8

10

12

14

16

Neat + CR Neat + CR + SOAsphalt binder

Frac

ture

toug

hnes

s (kP

a m0

5)

ndash12degC

ndash18degC

ndash24degC

(d)

Figure 4 (a) Force-displacement curves (b) Change Detection to Stiffness modulus (c) Fracture energy (d) Fracture toughness plots

Advances in Materials Science and Engineering 7

14000

12000

10000

8000

6000

4000

2000

00 1 2 3 4 5 6 7

Forc

e (m

N)

Displacement (mm)

ndash12degC neat + CR ndash notchedndash12degC neat + CR ndash unnotchedndash12degC neat + CR + SO ndash notchedndash12degC neat + CR + SO ndash unnotched

(a)

18000

16000

14000

12000

10000

8000

6000

4000

2000

00 1 2 3 4 5 6 7

Forc

e (m

N)

Displacement (mm)

ndash18degCndashneat + CR ndash notchedndash18degCndashneat + CR ndash unnotchedndash18degCndashneat + CR + SO ndash notchedndash18degCndashneat + CR + SO ndash unnotched

(b)

18000

16000

14000

12000

10000

8000

6000

4000

2000

0

22000

20000

0 1 2 3 4 5 6 7

Forc

e (m

N)

Displacement (mm)

ndash24degCndashneat + CR ndash notchedndash24degCndashneat + CR ndash unnotchedndash24degCndashneat + CR + SO ndash notchedndash24degCndashneat + CR + SO ndash unnotched

(c)

025

020

015

010

005

000

Stiff

ness

mod

ulus

(MPa

)

Neat + CR + SO ndashnotched

Neat + CR + SO ndashunnotched

ndash12degC

ndash18degC

ndash24degC

004

009

016

005

5

011

3

021

5

(d)800

700

600

500

400

300

200

100

0Neat + CR ndash notched Neat + CR ndash unnotched

Frac

ture

ener

gy (J

m2 )

ndash12degC

ndash18degC

ndash24degC

407

17

195

64

136

94

662

58

461

27

283

24

(e)

1200

1000

800

600

400

200

0Neat + CR + SO ndash

notchedNeat + CR + SO ndash

unnotched

Frac

ture

ener

gy (J

m2 )

ndash12degC

ndash18degC

ndash24degC

600

978

575

02

506

07

998

64

970

99

700

2

(f )

Figure 5 Continued

8 Advances in Materials Science and Engineering

for unnotched samples than for notched samples In generala study found that unnotched binders are more resistant tolow-temperature cracking than notched binders In addi-tion examining the tested samples it was observed that forunmodified samples cracks initiated from the bottom of thesample under the load Whereas for notched samples crackspropagated from the preexisted cracks upwards

66 Statistical Analysis of Displacement in Asphalt BindersSeveral studies have used the analysis of variance(ANOVA) statistic test to determine the significance oflaboratory based experimental results [27 28] In thisstudy the ANOVA test was conducted for purposes ofdetermining whether or not there was a statistically sig-nificant difference on low-temperature performance ofcrumb rubber asphalt binders modified with and withoutsilicone oil Since asphalt binders having lower deflection(uf ) at fracture performed very poorly in the field as regardsthermal cracking [4] this study used load-deflection valuesfrom SENB test in statistical analysis e higher the de-flection values the better the low temperature crackingresistance SPSS statistical software was utilized to aid the

statistical computations at three temperatures minus 12degCminus 18degC and minus 24degC respectively by applying one-wayANOVA and a t-test and the results of which are presentedin Tables 4 and 5 respectively

Table 4 indicates that the amount of displacement atminus 12degC was T (6054) 0001 Plt 001 whereas at minus 18degC thedisplacement was T (8061) 0001 Plt 001 and at minus 24degCdisplacement was T (minus 83146) 0001 (Plt 001) Since P

values lt001 significance level the influence of silicone oil ondisplacement of asphalt samples at different temperatureswas found to be statistically significant

Table 5 indicates that the displacement analysis result atminus 12degC was F (5732) 276e minus 30 (Plt 001) whereas thatdisplacement result at minus 18degC was F (2763) 976e minus 15(Plt 001) Finally displacement result at minus 24degC was F(2662) 0000174 (Plt 001) Since all P values are signifi-cant at lt001 level the influence of silicone oil on low-temperature performance of crumb rubber asphalt is foundto be statistically significant

Standard error (SE) is the estimated standard deviationfor the distribution of sample means for an infinite pop-ulation e SE values of the estimates of displacement inSENB test were calculated by performing a paired t teste

Table 4 T test results of displacement at different test temperature

Asphalt binder type Mean (mm) N Std deviation Std error mean T Df SigTest temperature minus 12degCNeat +CR 36009 3289 215842 03764 6054 3288 0001Neat +CR+ SO 32363 3289 185615 03237Test temperature minus 18degCNeat +CR 19971 2027 113464 002520 8061 2026 0001Neat +CR+ SO 19999 2027 114478 002543Test temperature minus 24degCNeat +CR 22378 1553 114058 002894 minus 83146 1552 0001Neat +CR+ SO 15337 1553 087921 002231

12

10

8

6

4

2

0

Neat + CR + SO ndashnotched

Neat + CR + SO ndashunnotched

Frac

ture

toug

hnes

s (kP

a m0

5)

ndash12degC

ndash18degC

ndash24degC

494

646

83

703

100

1

120

(g)

16

14

12

10

8

6

4

2

0

Neat + CR + SO ndashnotched

Neat + CR + SO ndashunnotched

Frac

ture

toug

hnes

s (kP

a m0

5)

ndash12degC

ndash18degC

ndash24degC

607

79

101

666

119

3

139

1

(h)

Figure 5 Low-temperature performance of crumb rubber asphalt considering influence of precracked and uncracked notches Load-displacement curves at (a) minus 12degC (b) minus 18degC and (c) minus 24degC (d) Stiffness modulus of asphalt binders (e) Fracture energy of binders (f )Fracture energy of binders (g) Fracture toughness of binders (h) Fracture toughness of binders

Advances in Materials Science and Engineering 9

laboratory test results before and after silicone oil treat-ment to crumb rubber asphalt were compared e resultsfound that standard error at three temperatures was notmore than 000602 as shown in Table 6 Since a smallervalue of the standard error of the mean indicates a moreprecise estimate of the population mean the results wereconsidered valid

7 Conclusion

In this paper the effect of silicone oil on dispersion and low-temperature fracture performance of crumb rubber binderwas investigated based on SENB AFM and FM testsMaterialcharacterization was analysed by performing the FTIR teste research was driven by the notion that although CR hassucceeded in improving low-temperature performance ofasphalt pavements compatibility between asphalt and crumbrubber still remains a challenge to be solved As part of aneffort to solve the problem and develop sustainable materialssilicone oil was used to improve both rubber particle dis-persion in asphalt and low-temperature fracture perfor-mance is study led to following conclusions

(1) e analysis of molecular structure of siliconeconfirmed that the material was vinyl silicone oilFurther the analysis of asphalt modified with sili-cone oil resulted in generation of new absorptionpeaks with the main peak having Si-O-Si bond isbond indicates that silicone oil is a highly hydro-phobic material (water repellent) and also has

chemical durability which ensures that the siliconeoil is applied in asphalt

(2) e morphological images from the FM test revealedthat the addition of silicone oil improves the dispersionof crumb rubber particles in asphalt binder matrix

(3) e atomic force microscopy results suggested thatsurface roughness increases with the addition ofsilicone oil which implied that there was a change inmicrostructure of the sample Moreover the increasein roughness of the surface implied that bonding ofasphalt with rubber particles was enhanced therebyresulting in improved distribution of rubber particlesin asphalt

(4) e addition of crumb rubber to asphalt generallydecreased the stiffness of the material at low tem-peratures In addition the study concluded thataddition of silicone oil to crumb rubber asphaltresulted in a further decrease of stiffness therebyimproving low-temperature crack resistance evalues of fracture toughness as well as fracture energyindicated that crumb rubber asphalt binders con-taining silicone oil had superior crack resistance thanthe one without silicone oil modification

(5) Analysis of variance and t test results confirmed thatthe influence of silicone oil on displacement wasstatistically significant is means that low-tem-perature performance of a crumb rubber modifiedasphalt is strongly influenced by the addition of thesilicone oil

Table 6 Paired sample test results of displacement at different test temperatures for notched samples

Asphalt binder type N Mean (mm) Std deviation Std error mean99 CI

t Df Sig (2 tailed)Lower Upper

Test temperature minus 12degCNeat +CR 3289 minus 036459 034538 000602 minus 03812 minus 034907 minus 60540 3288 0001Neat +CR+ SOTest temperature minus 18degCNeat +CR 2027 000272 001520 000034 000185 000359 8061 2026 0001Neat +CR+ SOTest temperature minus 24degCNeat +CR 2667 002056 002075 000040 001952 002159 51163 2666 0001Neat +CR+ SO

Table 5 ANOVA test results of displacement at different test temperatures

Displacement Sum of squares Df Mean square F SigTest temperature minus 12degCBetween groups 15196637 3144 4834 5732 276e minus 30Within groups 121428 144 0843Total 15318064 3288Test temperature minus 18degCBetween groups 18759285 3730 5029 2763 976e minus 15Within groups 291212 160 1820Total 19050497 3890Test temperature minus 24degCBetween groups 5993014 2628 2280 2662 0000174Within groups 32556 38 0857Total 6025570 2666

10 Advances in Materials Science and Engineering

(6) Furthermore this study concluded that the im-provement in low-temperature performance ofcrumb rubber modified with silicone oil can becaptured from two perspectives Firstly as indicatedby the analysis of stiffness in FTIR and FM thesilicone oil softened the modified crumb rubberasphalt and enhanced the dispersion of rubberparticles in the binder Softening of asphalt improvescrack resistance Secondly as seen in IR spectrumthe Si-O bond in silicone oil makes it highly hy-drophobic (water repellent) and thus could delay thewater penetration and subsequent freezing of asphaltbinder during water conditioning of samples at lowtemperature resulting in lower stiffness

(7) e comparison between the notched andunnotched samples indicated that the modulus of thenotched binders was lower than that of theunnotched one In addition the unnotched asphaltbinders containing silicone oil did not break at minus 12degCwhich confirmed the great influence of silicone oil onrubberised asphalt low-temperature performance

In spite of results obtained in this study it should bementioned that the research had the following limitationsthe low-temperature performance of crumb rubber con-taining SO was limited to SENB test No BBR test wasconducted Future research can incorporate the BBR test andother techniques to better understand the behaviour ofasphalt modified with silicone oil

Data Availability

e data used to support the findings of this study are in-cluded within the article

Conflicts of Interest

e authors declare that there are no conflicts of interestregarding the publication of this article

Acknowledgments

e authors would like to express their gratitude to theHarbin Institute of Technology for providing laboratoryequipment and materials for experiments is research wasfunded by the National Natural Science Foundation of Chinawith Grant nos 51478152 and 51478154 Furthermore thefees relating to the publication of the manuscript was fundedby the Copperbelt University in Zambia

References

[1] M Marasteanu W Buttlar H Bahia et al Investigation ofLow Temperature Cracking in Asphalt Pavements NationalPooled Fund StudyndashPhase II Minnesota Department ofTransportation Saint Paul MN USA 2012 httphdlhandlenet11299135177

[2] R Velasquez and H Bahia ldquoCritical factors affecting thermalcracking of asphalt pavements towards a comprehensivespecificationrdquo Road Materials and Pavement Design vol 14no sup1 pp 187ndash200 2013

[3] E V Dave H Benjamin H Chelsea M Jared and J LukeldquoImplementation of laboratory testing to predict low tem-perature cracking performance of asphalt pavementsrdquo in 8thRILEM International Symposium on Testing and Character-ization of Sustainable and Innovative Bituminous MaterialsSpringer Berlin Germany 2016

[4] H U Bahia and A Davies ldquoEffect of crumb rubber modifiers(CRM) on performance related properties of asphalt bindersrdquoJournal of Association of Asphalt Paving Technology vol 63pp 414ndash449 1994

[5] T R Hoare and S A M Hesp ldquoLow-temperature fracturetesting of asphalt binders regular and modified systemsrdquoTransportation Research Record Journal of the TransportationResearch Board vol 1728 no 1 pp 36ndash42 2000

[6] P E Sebaaly V T Gopal and J A Epps ldquoLow temperatureproperties of crumb rubber modified bindersrdquo RoadMaterialsand Pavement Design vol 4 no 1 pp 29ndash49 2003

[7] S-S Kim Z D Wysong and J Kovach ldquoLow-temperaturethermal cracking of asphalt binder by asphalt binder crackingdevicerdquo Transportation Research Record Transportation Re-search Record Journal of the Transportation Research Boardvol 1962 no 1 pp 28ndash35 2006

[8] A Zofka and A Braham ldquoComparison of low-temperaturefield performance and laboratory testing of 10 test sections inthe midwestern United Statesrdquo Transportation Research Re-cord Journal of the Transportation Research Board vol 2127no 1 pp 107ndash114 2009

[9] M Pszczoła J Mariusz S Cezary J Jozef and D BohdanldquoEvaluation of low temperature properties of rubberized as-phalt mixturesrdquo Procedia Engineering vol 172 pp 897ndash9042017

[10] P S Wulandari and D Tjandra ldquoUse of crumb rubber as anadditive in asphalt concrete mixturerdquo Procedia Engineeringvol 171 pp 1384ndash1389 2017

[11] M Mull M A Stuart and K Yehia ldquoFracture resistancecharacterization of chemically modified crumb rubber asphaltpavementrdquo Journal of Materials Science vol 37 no 3pp 557ndash566 2002

[12] A Hussain and S A Elmasry ldquoChemically modified crumbrubber effects on rubberized asphalt propertiesrdquo InternationalJournal of Environmental Sciences vol 2 no 4 pp 158ndash1622013

[13] S Zhihao Z-J Wang and G Y Xie ldquoPreparation andperformances of silicone modified asphaltrdquo Fine and SpecialChemical vol 11 2017

[14] Y Li Y Zhang and Y Zhang ldquoMechanical properties ofhigh-density polyethylenescrap rubber composites modifiedwith ethylene-propylene-diene terpolymer dicumyl peroxideand silicone oilrdquo Journal of Applied Polymer Science vol 88no 8 pp 2020ndash2027 2003

[15] C Peng H Zhang Y Zhanping et al ldquoPreparation and anti-icing properties of a superhydrophobic silicone coating onasphalt mixturerdquo Construction and Building Materialsvol 189 pp 227ndash235 2018

[16] C Gorkem and S Burak ldquoPredicting stripping and moistureinduced damage of asphalt concrete prepared with polymermodified bitumen and hydrated limerdquo Construction andBuilding Materials vol 23 no 6 pp 2227ndash2236 2009

[17] J Lin C Meizhu W Shaopeng et al ldquoUtilization of siliconemaintenance materials to improve the moisture sensitivity ofasphalt mixturesrdquo Construction and Building Materialsvol 33 pp 1ndash6 2012

[18] R Zhang Y Zhanping W Hainian Y Mingxiao K Y Yokeand S Chundi ldquoe impact of bio-oil as rejuvenator for aged

Advances in Materials Science and Engineering 11

asphalt was not going to significantly change the conclusionsobtained from the study In addition the silicone oil andcrumb rubber mesh 40 were used to prepare crumb rubbermodified asphalt

4 Experimental Test Methods

41 Preparation of Samples About 18 percent content ofcrumb rubber by weight was added to asphalt binder One ofthe blends was reacted with recycled silicone oil duringshearing while the other was prepared as conventionalcrumb rubber asphalt binder without silicone oile crumbrubber was added slowly and followed by silicone oil (3 byweight of the binder) and the mixture was sheared for onehour at 175degC

After preparation the binders were poured into the single-edge notch beam test moulds and cooled to 0degC and quicklytaken from the moulds measuring 127mmtimes 635mmtimes

127mm for length width and depth respectively e depthof the precrack was 28mm Both the precracked and theuncracked samples were used to facilitate the study of theeffect of silicone oil on crumb rubber modified asphaltrsquosperformance on low-temperature cracking Before testingeach specimen was conditioned in cold bath to testing tem-peratures minus 12degC 18degC and minus 24degC respectively To simplify theexperiment physical hardening both on unmodified asphaltand crumb rubbermodified asphalt (with andwithout siliconeoil) was tested after 1 hour of conditioning at respectivetemperatures

42 Fourier-Transform Infrared (FTIR) Test FTIR can beused for identifying polymer additives in asphalt bindermatrix In addition FTIR offers accurate data concerningoxygenation rate aliphaticity and aromaticity [19] usthe FTIR spectroscopy was conducted using a Jasco FT-IR4200 spectrometer with 32 numbers of scan and theresolution of 4 cmminus 1 To prepare the control and modifiedasphalt samples for the FTIR experiment the conventionalcrumb rubber asphalt samples and the silicone-modifiedcrumb rubber asphalt samples were heated to 180degC until

liquid enough to be poured With the aid of a brush theliquefied asphalt binders were then painted onto the surfaceof a silicon slide to create a uniform asphalt coating of05mm approximate thickness

Prepared samples were tested and the concentration ofthe functional groups associated with silicone oil absorptionin asphalt binder was deduced from the intensity of theabsorption bands Further the structural functional indexfor aromatics was determined with a view of understandingthe contribution of silicone to the aromatic content of as-phalt binder

43 Fluorescence Microscopy Test In order to study themorphology of CRMA fluorescent microscopy (FM) wasused by determining the rubber particles distribution inasphalt e FM test is premised on the principle thatpolymers undergo swelling owing to absorption of some ofthe key constituents of the base bitumen Similarly in thisstudy FM was used to study the morphology of CRMA withand without silicone oil treatment so as to observe thequality and particles dispersion in the binder Samples wereplaced on glass slides and taken to the laboratory for testingwith magnification of 100 μm

44 Atomic Force Microscopy Analysis In this study AFMwas used to determine the surface roughness (Ra) of asphaltsamples based on equation (1) Furthermore the morpho-logical distribution of rubber particles in asphalt binder wasevaluated CRMA samples with and without silicone oil wereprepared by pouring hot binder on the thin clean glass slidesand allowing the binder to flow on the glass slide Experi-ments were conducted at a temperature of 30degC Both 3Dheight images as well as 2D phase images were obtained

Ra 1N

1113944

N

j1Zi (1)

where Zi is the current height value and N is the number ofpoints within the scan area

45 Single-Edge Notch Beam (SENB) Testing A fracturemechanics-based SENB test was carried out on a three-pointbending test apparatus that was placed on a bending beamrheometer (BBR) chamber mounted e BBR water

Table 1 Physical properties of silicone oil (SO)

Technical properties Colour Viscosity 25degC Density (kgm3) Molecular weightDescription Colourless 1000 097 28000

Table 3 Gradation of crumb rubber

Sieve 30 40 50 100 200 passing 100 90ndash100 65 14 3

Table 2 Basic material properties asphalt binders

Binder tests Neat asphalt Neat + 18 CR Neat + 18 CR+ 3 SO Rubber asphaltspecification limits

Penetration 4degC 200 g 60 sec 110mm (ASTM D5) 70 49 60 10Softening point ASTM D36 (degC) 45 65 62 57Ductility 15degC (cm) 100 mdash mdash mdash

Advances in Materials Science and Engineering 3

chamber was utilized solely for conditioning samples torequired temperatures e temperature inside the waterchamber was controlled with water supply and held within03degC from the desired value A displacement rate of 001mmwas applied to break the sample at a rate that had previouslybeen determined to be convenient

e justification for the choice of the SENB test waspremised on the fact that good fracture parametric prop-erties of asphalt materials are important in building long-lasting asphalt pavements in cold regions [1] Furthermorealthough the BBR test has been seen to be sound in in-vestigating low-temperature performance of unmodifiedbinders it is not quite so for modified binders [5] StrategicHighway Research Program (SHRP) researchers recognizedthat a full fracture mechanics-based evaluation at appro-priate temperatures and rates of loading should be done toevaluate a binder for fracture performance [20] When fieldresults of asphalt mixtures in particular BBR-SENB testresults were compared with fracture properties researchersconcluded that the BBR test should be complimented withfracture tests [21] e SENB test therefore offers results thatcorrelates well with field experimentations and thus wasused in this study

5 Fracture Approach

e fracture approach is based on fracture mechanics theoryand is used to estimate the resistance of the material to crackpropagation [2] In this theory a preexisting crack or notchis punched in the specimen and used to reduce the effectivestrength of the material by amplifying the stress level nearthe crack e parametric properties obtained with thistheory are fracture energy (Gf ) and fracture toughness (KIc)e single-edge notch test (SENB) test has been developedbased on the theory of fracture mechanics and ASTM E 399testing protocols [5] is test assumes linear elastic fracturemechanicsrsquo conditions Equations (2) and (3) were used forcalculations of fracture toughness and fracture energy A lowfracture toughness value is an indication that materials aregoing through brittle fractures while high values of fracturetoughness are a sign of ductility improvement A largedeformation on the load-displacement curve and fractureenergy is an indication of superior crack resistance of theasphalt binder Fracture toughness was calculated accordingto the following equation [5]

KIc PfS

bW32

2(aW)12 199 minus (aW)(1 minus (aW)) 215 minus 393(aW) + 27(aW)21113960 11139611113966 1113967

2(1 + 2(aW))(1 minus (aW))32⎡⎣ ⎤⎦ (2)

where KIc fracture toughness under plain-strain condi-tions (Nm32) Pf applied failure load (N) S load span(m) b specimen thickness (m) W specimen height (m)and a notched depth (m)

Forceload-displacement results were used to calculate astiffness modulus assuming the beam was un-notched byusing equation (3) Using the stiffness modulus fractureenergy was calculated from the fracture toughness Poissonrsquosratio needed in the calculation was assumed to be equal to 05(purely elastic materials) e values of fracture energy wereobtained from the determined fracture toughness and thestiffness modulus and Poissonrsquos ratio was assumed to be 05for the asphalt binder according to Hoare and Hesp [5]

GIc K2

Ic 1 minus v2( 1113857

E 075

K2Ic

E (3)

where GIc = fracture energy or critical elastic energy releaserate (Jm2) E=Youngrsquos modulus (KIc test (Nm2)) andv=Poissonrsquos ratio

6 Results and Discussion

61 Fourier-Transform Infrared (FTIR) Result AnalysisFunctional groups of silicone oil in crumb rubber asphalt weredetermined using the FTIR test e analysis of infraredspectrum of various materials including silicone oil base andcrumb rubber asphalt and crumb rubber asphaltmodifiedwithsilicone oil is shown in Figure 1 e study revealed that the

peaks observed in the region of 2850ndash2960 cmminus 1 are typicallyC-H stretching vibrations ose observed around 1400ndash1500 cmminus 1 and 1300ndash1350 cmminus 1 are C-H symmetric deformingvibrations e peaks in the region within 1000ndash1100 cmminus 1 areSi-O-Si bond vibrationse Si-O bond in silicone oil forms themain chain that makes silicone oil to have high hydrophobicityand chemical durability which ensures that the silicone oilgenerally being able to be applied in the asphalt [17 22]

Comparing the infrared spectra of crumb rubber withand without silicone oil it was observed that new absorptionpeaks exist in the infrared spectra of crumb rubber asphaltcontaining recycled silicone oil which were 2964 cmminus 11258 cmminus 1 1009 cmminus 1 and 788 cmminus 1 respectively At788 cmminus 1 the peaks correspond to Si-C bond e identifiedabsorption peaks represent polydimethysiloxane or siliconeoil [23] After adding silicone oil to crumb rubber asphaltthe peaks did not disappear in asphalt is meant that thereaction between crumb rubber and silicone oil waschemical and not physical All the new absorption peakshave corresponding peaks in silicone oil spectrum [24]

Additionally the aromatic index (CC) was determinedusing the equation provided elsewhere [18] Zhang used thearomatic index to determine the degree of restoration ofaged binders by applying bio-oil-based rejuvenator to im-prove the low-temperature performance It was found thatbio-oil restores the aged asphalt and increases temperaturesusceptibility of asphalt thereby enduring higher thermalstress caused by cooling In our study the aromatic index for

4 Advances in Materials Science and Engineering

asphalt binder was calculated to determine the content ofaromatics in asphalt binder with and without silicone oiltreatment e results revealed that the aromatic index forcrumb rubber asphalt with and without silicone oil was 10and 06 respectively is result gave rise to the conclusionthat the addition of silicone oil to crumb rubber asphaltincreases the aromatic content and indices significantlyAccording to Kanabar highway pavements that do notexperience the spate of thermal distress are built withasphalt cements that have high IR aromatic indices or havemore aromatics [25] In addition the increase in aromaticcontent also decreases the dynamic modulus of the binder[18] erefore the high IR aromatic index found in thisstudy suggests that low-temperature cracking performancecan be improved with addition of silicone oil to asphaltbinder

62 Atomic Force Microscopy (AFM) Result Analysis Toevaluate the morphology of asphalt samples the AFM testwas used e AFM topographical images in Figure 2 gaverise to the following observations the bee-like structureswere CR particles in asphalt binder Based on equation (1)the average roughness for crumb rubber asphalt withoutsilicone oil was calculated as 037 nm whereas averageroughness for crumb rubber asphalt containing silicone oilwas 129 nm respectively e increase in surface roughnessof asphalt indicated that there was a change in the micro-structure of the asphalt samples after addition of silicone oilIn our study the increased surface roughness of crumbrubber asphalt with silicone oil indicates improved bondingbetween rubber particles and asphalt which may lead tocontinuous rubber particles dispersion in asphalt Visualcomparison of AFM images confirmed that the addition ofsilicone oil to crumb rubber asphalt greatly influenced theobserved microstructure and showed a continuous homo-geneity of rubber particles dispersion in asphalt ConverselyAFM topographical images for CR asphalt sample without

silicone oil revealed that rubber particle distribution was nothomogeneous

63 Fluorescence Microscopy (FM) Result Analysis e re-sults of AFM were further confirmed by FM analysis einfluence of silicone oil on the dispersion of crumb rubberparticles in asphalt binder was studied using the FM testwhich was conducted on two crumb rubber asphalt sampleswith and without silicone oil From Figure 3 results of FMimages revealed that the crumb rubber modified binderswith silicone oil showed uniformly dispersed rubber par-ticles in asphalt Conversely images of dispersion forconventional crumb rubber asphalt without silicone oilshowed noncontinuous bitumen matrix

64 Effect of Silicone Oil on Low-Temperature Performance ofCrumb Rubber Asphalt Binder Figure 4 shows that load-displacement curves stiffness modulus fracture toughnessand fracture energy values at three temperatures for the crumbrubber asphalt binders gave rise to the following observations

e results of load and displacement curve found thatthe addition of silicone oil to samples leads to increase indisplacement Asphalt binders having lower deflection atfracture perform very poorly in the field as regards thethermal cracking [4] erefore higher deflection values inour study indicate good low-temperature cracking re-sistance In addition the addition of silicone oil also in-creases stiffness modulus of the sample High stiffnessmodulus asphalt mixes at low temperature are prone tocracking [6] erefore the lower stiffness modulus ob-tained in our study is an indication of improved low-temperature performance of crumb rubber containingsilicone oil

It is also worth noting that rubber asphalt with siliconeoil did not break at minus 12degC owing to its increased low-temperature resistance is result demonstrated the effect

Silicone oil (SO)

C-H stretching of CH3

CH 3 asymmetric deformation of Si-CH

CH 3 symmetric deformation of Si-CH

Neat + crumb rubber (CR)

Neat asphalt

Neat + CR + SO

2964

12581009

788

Si-O-Si stretching

3500 3000 2500 2000 1500 1000 500Wavenumber (cmndash1)

Tran

smitt

ance

()

Figure 1 FTIR spectrum of silicone oil neat asphalt and crumb rubber asphalt modified with silicone oil

Advances in Materials Science and Engineering 5

of silicone oil on low-temperature performance of crumbrubber asphalt binders having high fracture energy wouldperform very well in the field in terms of thermal crackingresistance is was added to show that our findings agreewith other researchers [2] In our study results havedemonstrated that the addition of silicone oil to rubberasphalt increased the fracture energy therefore we foundthat the increase in fracture energy demonstrated thatsamples modified with silicone oil have superior crackresistance

Fracture toughness is yet another critical parameterused in evaluating low temperature performance of asphaltbinders in SENB test Increased fracture toughness valuesat low temperatures such as ndash20degC in polymer modifiedasphalt mixtures imply that resistance to fracture has in-creased Some polymers make asphalt less brittle at lowtemperatures and therefore polymer modified asphalt(PMA) concretes are expected to become tougher thannormal asphalt concrete at low temperatures e im-proved tensile property allows greater resistance to materialcracking [26] Similarly in our study it has been estab-lished that adding 3 content of silicone oil to crumbrubber asphalt resulted in increased fracture toughness of

the binder than binders without silicone oil is dem-onstrates that tensile property has improved leading togreater low-temperature crack resistance

65 Low-TemperaturePerformanceAnalysis ofCrumbRubberAsphalt considering Notched and Unnotched ConditionsTo investigate the effect of notch on low-temperature per-formance of crumb rubber asphalt the samples with andwithout a notch were subjected to fracture testing after 1-hour conditioning in cold bath e study gave rise to thefollowing observations

As seen in Figure 5 the load-displacement curve resultsshow an increase in stiffness modulus for unnotched samples ofcrumb rubber modified with silicone oil when compared withthe unnotched samples e preexisting crack renders thesample vulnerable to cracking therefore unnotched sampleswillmost likely have delayed cracking than the notched samples

Additionally the fracture toughness KIc and fractureenergy GIc increased with an increase in temperature fromminus 24 to minus 12degC this indicates that less potential fractureenergy is needed for crack propagation at lower tempera-tures Fracture energy and fracture toughness also increased

21nm

ndash23nmHeight sensor 20μm

(a)

65nm

ndash96nmHeight sensor 20μm

(b)

(c) (d)

Figure 2 AFM images of crumb rubber asphalt (with and without silicone oil) (a) Neat +CRndash2D AFM images (b) Neat +CR+ SOndash2DAFM images (c) Neat +CR 3D AFM images (d) Neat +CR+ SO 3D AFM images

6 Advances in Materials Science and Engineering

(a) (b)

Figure 3 FM images of crumb rubber asphalt (with and without waste silicone oil) (a) Neat +CRndashFM images (b) Neat +CR+ SOndashFMimages

ndash12degCndashneat + CRndash12degCndashneat + CR + SOndash18degCndashneat + CRndash18degCndashneat + CR + SOndash24degCndashneat + CRndash24degCndashneat + CR + SO

0

2000

4000

6000

8000

10000

12000

14000

16000

0 1 2 3 4 5 6 7Displacement (mm)

Forc

e (m

N)

(a)

35 30

162

102

179

151

020406080

100120140160180200220240

Neat + CR Neat + CR + SOAsphalt binder

Stiff

ness

mod

ulus

(kPa

)

ndash12degC

ndash18degC

ndash24degC

(b)

400

600

200

580

150

475

0

100

200

300

400

500

600

700

800

900

Neat + CR Neat + CR + SOAsphalt binder

Frac

ture

ener

gy (J

m2 )

ndash12degC

ndash18degC

ndash24degC

(c)

45 6

65 7

982

101

0

2

4

6

8

10

12

14

16

Neat + CR Neat + CR + SOAsphalt binder

Frac

ture

toug

hnes

s (kP

a m0

5)

ndash12degC

ndash18degC

ndash24degC

(d)

Figure 4 (a) Force-displacement curves (b) Change Detection to Stiffness modulus (c) Fracture energy (d) Fracture toughness plots

Advances in Materials Science and Engineering 7

14000

12000

10000

8000

6000

4000

2000

00 1 2 3 4 5 6 7

Forc

e (m

N)

Displacement (mm)

ndash12degC neat + CR ndash notchedndash12degC neat + CR ndash unnotchedndash12degC neat + CR + SO ndash notchedndash12degC neat + CR + SO ndash unnotched

(a)

18000

16000

14000

12000

10000

8000

6000

4000

2000

00 1 2 3 4 5 6 7

Forc

e (m

N)

Displacement (mm)

ndash18degCndashneat + CR ndash notchedndash18degCndashneat + CR ndash unnotchedndash18degCndashneat + CR + SO ndash notchedndash18degCndashneat + CR + SO ndash unnotched

(b)

18000

16000

14000

12000

10000

8000

6000

4000

2000

0

22000

20000

0 1 2 3 4 5 6 7

Forc

e (m

N)

Displacement (mm)

ndash24degCndashneat + CR ndash notchedndash24degCndashneat + CR ndash unnotchedndash24degCndashneat + CR + SO ndash notchedndash24degCndashneat + CR + SO ndash unnotched

(c)

025

020

015

010

005

000

Stiff

ness

mod

ulus

(MPa

)

Neat + CR + SO ndashnotched

Neat + CR + SO ndashunnotched

ndash12degC

ndash18degC

ndash24degC

004

009

016

005

5

011

3

021

5

(d)800

700

600

500

400

300

200

100

0Neat + CR ndash notched Neat + CR ndash unnotched

Frac

ture

ener

gy (J

m2 )

ndash12degC

ndash18degC

ndash24degC

407

17

195

64

136

94

662

58

461

27

283

24

(e)

1200

1000

800

600

400

200

0Neat + CR + SO ndash

notchedNeat + CR + SO ndash

unnotched

Frac

ture

ener

gy (J

m2 )

ndash12degC

ndash18degC

ndash24degC

600

978

575

02

506

07

998

64

970

99

700

2

(f )

Figure 5 Continued

8 Advances in Materials Science and Engineering

for unnotched samples than for notched samples In generala study found that unnotched binders are more resistant tolow-temperature cracking than notched binders In addi-tion examining the tested samples it was observed that forunmodified samples cracks initiated from the bottom of thesample under the load Whereas for notched samples crackspropagated from the preexisted cracks upwards

66 Statistical Analysis of Displacement in Asphalt BindersSeveral studies have used the analysis of variance(ANOVA) statistic test to determine the significance oflaboratory based experimental results [27 28] In thisstudy the ANOVA test was conducted for purposes ofdetermining whether or not there was a statistically sig-nificant difference on low-temperature performance ofcrumb rubber asphalt binders modified with and withoutsilicone oil Since asphalt binders having lower deflection(uf ) at fracture performed very poorly in the field as regardsthermal cracking [4] this study used load-deflection valuesfrom SENB test in statistical analysis e higher the de-flection values the better the low temperature crackingresistance SPSS statistical software was utilized to aid the

statistical computations at three temperatures minus 12degCminus 18degC and minus 24degC respectively by applying one-wayANOVA and a t-test and the results of which are presentedin Tables 4 and 5 respectively

Table 4 indicates that the amount of displacement atminus 12degC was T (6054) 0001 Plt 001 whereas at minus 18degC thedisplacement was T (8061) 0001 Plt 001 and at minus 24degCdisplacement was T (minus 83146) 0001 (Plt 001) Since P

values lt001 significance level the influence of silicone oil ondisplacement of asphalt samples at different temperatureswas found to be statistically significant

Table 5 indicates that the displacement analysis result atminus 12degC was F (5732) 276e minus 30 (Plt 001) whereas thatdisplacement result at minus 18degC was F (2763) 976e minus 15(Plt 001) Finally displacement result at minus 24degC was F(2662) 0000174 (Plt 001) Since all P values are signifi-cant at lt001 level the influence of silicone oil on low-temperature performance of crumb rubber asphalt is foundto be statistically significant

Standard error (SE) is the estimated standard deviationfor the distribution of sample means for an infinite pop-ulation e SE values of the estimates of displacement inSENB test were calculated by performing a paired t teste

Table 4 T test results of displacement at different test temperature

Asphalt binder type Mean (mm) N Std deviation Std error mean T Df SigTest temperature minus 12degCNeat +CR 36009 3289 215842 03764 6054 3288 0001Neat +CR+ SO 32363 3289 185615 03237Test temperature minus 18degCNeat +CR 19971 2027 113464 002520 8061 2026 0001Neat +CR+ SO 19999 2027 114478 002543Test temperature minus 24degCNeat +CR 22378 1553 114058 002894 minus 83146 1552 0001Neat +CR+ SO 15337 1553 087921 002231

12

10

8

6

4

2

0

Neat + CR + SO ndashnotched

Neat + CR + SO ndashunnotched

Frac

ture

toug

hnes

s (kP

a m0

5)

ndash12degC

ndash18degC

ndash24degC

494

646

83

703

100

1

120

(g)

16

14

12

10

8

6

4

2

0

Neat + CR + SO ndashnotched

Neat + CR + SO ndashunnotched

Frac

ture

toug

hnes

s (kP

a m0

5)

ndash12degC

ndash18degC

ndash24degC

607

79

101

666

119

3

139

1

(h)

Figure 5 Low-temperature performance of crumb rubber asphalt considering influence of precracked and uncracked notches Load-displacement curves at (a) minus 12degC (b) minus 18degC and (c) minus 24degC (d) Stiffness modulus of asphalt binders (e) Fracture energy of binders (f )Fracture energy of binders (g) Fracture toughness of binders (h) Fracture toughness of binders

Advances in Materials Science and Engineering 9

laboratory test results before and after silicone oil treat-ment to crumb rubber asphalt were compared e resultsfound that standard error at three temperatures was notmore than 000602 as shown in Table 6 Since a smallervalue of the standard error of the mean indicates a moreprecise estimate of the population mean the results wereconsidered valid

7 Conclusion

In this paper the effect of silicone oil on dispersion and low-temperature fracture performance of crumb rubber binderwas investigated based on SENB AFM and FM testsMaterialcharacterization was analysed by performing the FTIR teste research was driven by the notion that although CR hassucceeded in improving low-temperature performance ofasphalt pavements compatibility between asphalt and crumbrubber still remains a challenge to be solved As part of aneffort to solve the problem and develop sustainable materialssilicone oil was used to improve both rubber particle dis-persion in asphalt and low-temperature fracture perfor-mance is study led to following conclusions

(1) e analysis of molecular structure of siliconeconfirmed that the material was vinyl silicone oilFurther the analysis of asphalt modified with sili-cone oil resulted in generation of new absorptionpeaks with the main peak having Si-O-Si bond isbond indicates that silicone oil is a highly hydro-phobic material (water repellent) and also has

chemical durability which ensures that the siliconeoil is applied in asphalt

(2) e morphological images from the FM test revealedthat the addition of silicone oil improves the dispersionof crumb rubber particles in asphalt binder matrix

(3) e atomic force microscopy results suggested thatsurface roughness increases with the addition ofsilicone oil which implied that there was a change inmicrostructure of the sample Moreover the increasein roughness of the surface implied that bonding ofasphalt with rubber particles was enhanced therebyresulting in improved distribution of rubber particlesin asphalt

(4) e addition of crumb rubber to asphalt generallydecreased the stiffness of the material at low tem-peratures In addition the study concluded thataddition of silicone oil to crumb rubber asphaltresulted in a further decrease of stiffness therebyimproving low-temperature crack resistance evalues of fracture toughness as well as fracture energyindicated that crumb rubber asphalt binders con-taining silicone oil had superior crack resistance thanthe one without silicone oil modification

(5) Analysis of variance and t test results confirmed thatthe influence of silicone oil on displacement wasstatistically significant is means that low-tem-perature performance of a crumb rubber modifiedasphalt is strongly influenced by the addition of thesilicone oil

Table 6 Paired sample test results of displacement at different test temperatures for notched samples

Asphalt binder type N Mean (mm) Std deviation Std error mean99 CI

t Df Sig (2 tailed)Lower Upper

Test temperature minus 12degCNeat +CR 3289 minus 036459 034538 000602 minus 03812 minus 034907 minus 60540 3288 0001Neat +CR+ SOTest temperature minus 18degCNeat +CR 2027 000272 001520 000034 000185 000359 8061 2026 0001Neat +CR+ SOTest temperature minus 24degCNeat +CR 2667 002056 002075 000040 001952 002159 51163 2666 0001Neat +CR+ SO

Table 5 ANOVA test results of displacement at different test temperatures

Displacement Sum of squares Df Mean square F SigTest temperature minus 12degCBetween groups 15196637 3144 4834 5732 276e minus 30Within groups 121428 144 0843Total 15318064 3288Test temperature minus 18degCBetween groups 18759285 3730 5029 2763 976e minus 15Within groups 291212 160 1820Total 19050497 3890Test temperature minus 24degCBetween groups 5993014 2628 2280 2662 0000174Within groups 32556 38 0857Total 6025570 2666

10 Advances in Materials Science and Engineering

(6) Furthermore this study concluded that the im-provement in low-temperature performance ofcrumb rubber modified with silicone oil can becaptured from two perspectives Firstly as indicatedby the analysis of stiffness in FTIR and FM thesilicone oil softened the modified crumb rubberasphalt and enhanced the dispersion of rubberparticles in the binder Softening of asphalt improvescrack resistance Secondly as seen in IR spectrumthe Si-O bond in silicone oil makes it highly hy-drophobic (water repellent) and thus could delay thewater penetration and subsequent freezing of asphaltbinder during water conditioning of samples at lowtemperature resulting in lower stiffness

(7) e comparison between the notched andunnotched samples indicated that the modulus of thenotched binders was lower than that of theunnotched one In addition the unnotched asphaltbinders containing silicone oil did not break at minus 12degCwhich confirmed the great influence of silicone oil onrubberised asphalt low-temperature performance

In spite of results obtained in this study it should bementioned that the research had the following limitationsthe low-temperature performance of crumb rubber con-taining SO was limited to SENB test No BBR test wasconducted Future research can incorporate the BBR test andother techniques to better understand the behaviour ofasphalt modified with silicone oil

Data Availability

e data used to support the findings of this study are in-cluded within the article

Conflicts of Interest

e authors declare that there are no conflicts of interestregarding the publication of this article

Acknowledgments

e authors would like to express their gratitude to theHarbin Institute of Technology for providing laboratoryequipment and materials for experiments is research wasfunded by the National Natural Science Foundation of Chinawith Grant nos 51478152 and 51478154 Furthermore thefees relating to the publication of the manuscript was fundedby the Copperbelt University in Zambia

References

[1] M Marasteanu W Buttlar H Bahia et al Investigation ofLow Temperature Cracking in Asphalt Pavements NationalPooled Fund StudyndashPhase II Minnesota Department ofTransportation Saint Paul MN USA 2012 httphdlhandlenet11299135177

[2] R Velasquez and H Bahia ldquoCritical factors affecting thermalcracking of asphalt pavements towards a comprehensivespecificationrdquo Road Materials and Pavement Design vol 14no sup1 pp 187ndash200 2013

[3] E V Dave H Benjamin H Chelsea M Jared and J LukeldquoImplementation of laboratory testing to predict low tem-perature cracking performance of asphalt pavementsrdquo in 8thRILEM International Symposium on Testing and Character-ization of Sustainable and Innovative Bituminous MaterialsSpringer Berlin Germany 2016

[4] H U Bahia and A Davies ldquoEffect of crumb rubber modifiers(CRM) on performance related properties of asphalt bindersrdquoJournal of Association of Asphalt Paving Technology vol 63pp 414ndash449 1994

[5] T R Hoare and S A M Hesp ldquoLow-temperature fracturetesting of asphalt binders regular and modified systemsrdquoTransportation Research Record Journal of the TransportationResearch Board vol 1728 no 1 pp 36ndash42 2000

[6] P E Sebaaly V T Gopal and J A Epps ldquoLow temperatureproperties of crumb rubber modified bindersrdquo RoadMaterialsand Pavement Design vol 4 no 1 pp 29ndash49 2003

[7] S-S Kim Z D Wysong and J Kovach ldquoLow-temperaturethermal cracking of asphalt binder by asphalt binder crackingdevicerdquo Transportation Research Record Transportation Re-search Record Journal of the Transportation Research Boardvol 1962 no 1 pp 28ndash35 2006

[8] A Zofka and A Braham ldquoComparison of low-temperaturefield performance and laboratory testing of 10 test sections inthe midwestern United Statesrdquo Transportation Research Re-cord Journal of the Transportation Research Board vol 2127no 1 pp 107ndash114 2009

[9] M Pszczoła J Mariusz S Cezary J Jozef and D BohdanldquoEvaluation of low temperature properties of rubberized as-phalt mixturesrdquo Procedia Engineering vol 172 pp 897ndash9042017

[10] P S Wulandari and D Tjandra ldquoUse of crumb rubber as anadditive in asphalt concrete mixturerdquo Procedia Engineeringvol 171 pp 1384ndash1389 2017

[11] M Mull M A Stuart and K Yehia ldquoFracture resistancecharacterization of chemically modified crumb rubber asphaltpavementrdquo Journal of Materials Science vol 37 no 3pp 557ndash566 2002

[12] A Hussain and S A Elmasry ldquoChemically modified crumbrubber effects on rubberized asphalt propertiesrdquo InternationalJournal of Environmental Sciences vol 2 no 4 pp 158ndash1622013

[13] S Zhihao Z-J Wang and G Y Xie ldquoPreparation andperformances of silicone modified asphaltrdquo Fine and SpecialChemical vol 11 2017

[14] Y Li Y Zhang and Y Zhang ldquoMechanical properties ofhigh-density polyethylenescrap rubber composites modifiedwith ethylene-propylene-diene terpolymer dicumyl peroxideand silicone oilrdquo Journal of Applied Polymer Science vol 88no 8 pp 2020ndash2027 2003

[15] C Peng H Zhang Y Zhanping et al ldquoPreparation and anti-icing properties of a superhydrophobic silicone coating onasphalt mixturerdquo Construction and Building Materialsvol 189 pp 227ndash235 2018

[16] C Gorkem and S Burak ldquoPredicting stripping and moistureinduced damage of asphalt concrete prepared with polymermodified bitumen and hydrated limerdquo Construction andBuilding Materials vol 23 no 6 pp 2227ndash2236 2009

[17] J Lin C Meizhu W Shaopeng et al ldquoUtilization of siliconemaintenance materials to improve the moisture sensitivity ofasphalt mixturesrdquo Construction and Building Materialsvol 33 pp 1ndash6 2012

[18] R Zhang Y Zhanping W Hainian Y Mingxiao K Y Yokeand S Chundi ldquoe impact of bio-oil as rejuvenator for aged

Advances in Materials Science and Engineering 11

chamber was utilized solely for conditioning samples torequired temperatures e temperature inside the waterchamber was controlled with water supply and held within03degC from the desired value A displacement rate of 001mmwas applied to break the sample at a rate that had previouslybeen determined to be convenient

e justification for the choice of the SENB test waspremised on the fact that good fracture parametric prop-erties of asphalt materials are important in building long-lasting asphalt pavements in cold regions [1] Furthermorealthough the BBR test has been seen to be sound in in-vestigating low-temperature performance of unmodifiedbinders it is not quite so for modified binders [5] StrategicHighway Research Program (SHRP) researchers recognizedthat a full fracture mechanics-based evaluation at appro-priate temperatures and rates of loading should be done toevaluate a binder for fracture performance [20] When fieldresults of asphalt mixtures in particular BBR-SENB testresults were compared with fracture properties researchersconcluded that the BBR test should be complimented withfracture tests [21] e SENB test therefore offers results thatcorrelates well with field experimentations and thus wasused in this study

5 Fracture Approach

e fracture approach is based on fracture mechanics theoryand is used to estimate the resistance of the material to crackpropagation [2] In this theory a preexisting crack or notchis punched in the specimen and used to reduce the effectivestrength of the material by amplifying the stress level nearthe crack e parametric properties obtained with thistheory are fracture energy (Gf ) and fracture toughness (KIc)e single-edge notch test (SENB) test has been developedbased on the theory of fracture mechanics and ASTM E 399testing protocols [5] is test assumes linear elastic fracturemechanicsrsquo conditions Equations (2) and (3) were used forcalculations of fracture toughness and fracture energy A lowfracture toughness value is an indication that materials aregoing through brittle fractures while high values of fracturetoughness are a sign of ductility improvement A largedeformation on the load-displacement curve and fractureenergy is an indication of superior crack resistance of theasphalt binder Fracture toughness was calculated accordingto the following equation [5]

KIc PfS

bW32

2(aW)12 199 minus (aW)(1 minus (aW)) 215 minus 393(aW) + 27(aW)21113960 11139611113966 1113967

2(1 + 2(aW))(1 minus (aW))32⎡⎣ ⎤⎦ (2)

where KIc fracture toughness under plain-strain condi-tions (Nm32) Pf applied failure load (N) S load span(m) b specimen thickness (m) W specimen height (m)and a notched depth (m)

Forceload-displacement results were used to calculate astiffness modulus assuming the beam was un-notched byusing equation (3) Using the stiffness modulus fractureenergy was calculated from the fracture toughness Poissonrsquosratio needed in the calculation was assumed to be equal to 05(purely elastic materials) e values of fracture energy wereobtained from the determined fracture toughness and thestiffness modulus and Poissonrsquos ratio was assumed to be 05for the asphalt binder according to Hoare and Hesp [5]

GIc K2

Ic 1 minus v2( 1113857

E 075

K2Ic

E (3)

where GIc = fracture energy or critical elastic energy releaserate (Jm2) E=Youngrsquos modulus (KIc test (Nm2)) andv=Poissonrsquos ratio

6 Results and Discussion

61 Fourier-Transform Infrared (FTIR) Result AnalysisFunctional groups of silicone oil in crumb rubber asphalt weredetermined using the FTIR test e analysis of infraredspectrum of various materials including silicone oil base andcrumb rubber asphalt and crumb rubber asphaltmodifiedwithsilicone oil is shown in Figure 1 e study revealed that the

peaks observed in the region of 2850ndash2960 cmminus 1 are typicallyC-H stretching vibrations ose observed around 1400ndash1500 cmminus 1 and 1300ndash1350 cmminus 1 are C-H symmetric deformingvibrations e peaks in the region within 1000ndash1100 cmminus 1 areSi-O-Si bond vibrationse Si-O bond in silicone oil forms themain chain that makes silicone oil to have high hydrophobicityand chemical durability which ensures that the silicone oilgenerally being able to be applied in the asphalt [17 22]

Comparing the infrared spectra of crumb rubber withand without silicone oil it was observed that new absorptionpeaks exist in the infrared spectra of crumb rubber asphaltcontaining recycled silicone oil which were 2964 cmminus 11258 cmminus 1 1009 cmminus 1 and 788 cmminus 1 respectively At788 cmminus 1 the peaks correspond to Si-C bond e identifiedabsorption peaks represent polydimethysiloxane or siliconeoil [23] After adding silicone oil to crumb rubber asphaltthe peaks did not disappear in asphalt is meant that thereaction between crumb rubber and silicone oil waschemical and not physical All the new absorption peakshave corresponding peaks in silicone oil spectrum [24]

Additionally the aromatic index (CC) was determinedusing the equation provided elsewhere [18] Zhang used thearomatic index to determine the degree of restoration ofaged binders by applying bio-oil-based rejuvenator to im-prove the low-temperature performance It was found thatbio-oil restores the aged asphalt and increases temperaturesusceptibility of asphalt thereby enduring higher thermalstress caused by cooling In our study the aromatic index for

4 Advances in Materials Science and Engineering

asphalt binder was calculated to determine the content ofaromatics in asphalt binder with and without silicone oiltreatment e results revealed that the aromatic index forcrumb rubber asphalt with and without silicone oil was 10and 06 respectively is result gave rise to the conclusionthat the addition of silicone oil to crumb rubber asphaltincreases the aromatic content and indices significantlyAccording to Kanabar highway pavements that do notexperience the spate of thermal distress are built withasphalt cements that have high IR aromatic indices or havemore aromatics [25] In addition the increase in aromaticcontent also decreases the dynamic modulus of the binder[18] erefore the high IR aromatic index found in thisstudy suggests that low-temperature cracking performancecan be improved with addition of silicone oil to asphaltbinder

62 Atomic Force Microscopy (AFM) Result Analysis Toevaluate the morphology of asphalt samples the AFM testwas used e AFM topographical images in Figure 2 gaverise to the following observations the bee-like structureswere CR particles in asphalt binder Based on equation (1)the average roughness for crumb rubber asphalt withoutsilicone oil was calculated as 037 nm whereas averageroughness for crumb rubber asphalt containing silicone oilwas 129 nm respectively e increase in surface roughnessof asphalt indicated that there was a change in the micro-structure of the asphalt samples after addition of silicone oilIn our study the increased surface roughness of crumbrubber asphalt with silicone oil indicates improved bondingbetween rubber particles and asphalt which may lead tocontinuous rubber particles dispersion in asphalt Visualcomparison of AFM images confirmed that the addition ofsilicone oil to crumb rubber asphalt greatly influenced theobserved microstructure and showed a continuous homo-geneity of rubber particles dispersion in asphalt ConverselyAFM topographical images for CR asphalt sample without

silicone oil revealed that rubber particle distribution was nothomogeneous

63 Fluorescence Microscopy (FM) Result Analysis e re-sults of AFM were further confirmed by FM analysis einfluence of silicone oil on the dispersion of crumb rubberparticles in asphalt binder was studied using the FM testwhich was conducted on two crumb rubber asphalt sampleswith and without silicone oil From Figure 3 results of FMimages revealed that the crumb rubber modified binderswith silicone oil showed uniformly dispersed rubber par-ticles in asphalt Conversely images of dispersion forconventional crumb rubber asphalt without silicone oilshowed noncontinuous bitumen matrix

64 Effect of Silicone Oil on Low-Temperature Performance ofCrumb Rubber Asphalt Binder Figure 4 shows that load-displacement curves stiffness modulus fracture toughnessand fracture energy values at three temperatures for the crumbrubber asphalt binders gave rise to the following observations

e results of load and displacement curve found thatthe addition of silicone oil to samples leads to increase indisplacement Asphalt binders having lower deflection atfracture perform very poorly in the field as regards thethermal cracking [4] erefore higher deflection values inour study indicate good low-temperature cracking re-sistance In addition the addition of silicone oil also in-creases stiffness modulus of the sample High stiffnessmodulus asphalt mixes at low temperature are prone tocracking [6] erefore the lower stiffness modulus ob-tained in our study is an indication of improved low-temperature performance of crumb rubber containingsilicone oil

It is also worth noting that rubber asphalt with siliconeoil did not break at minus 12degC owing to its increased low-temperature resistance is result demonstrated the effect

Silicone oil (SO)

C-H stretching of CH3

CH 3 asymmetric deformation of Si-CH

CH 3 symmetric deformation of Si-CH

Neat + crumb rubber (CR)

Neat asphalt

Neat + CR + SO

2964

12581009

788

Si-O-Si stretching

3500 3000 2500 2000 1500 1000 500Wavenumber (cmndash1)

Tran

smitt

ance

()

Figure 1 FTIR spectrum of silicone oil neat asphalt and crumb rubber asphalt modified with silicone oil

Advances in Materials Science and Engineering 5

of silicone oil on low-temperature performance of crumbrubber asphalt binders having high fracture energy wouldperform very well in the field in terms of thermal crackingresistance is was added to show that our findings agreewith other researchers [2] In our study results havedemonstrated that the addition of silicone oil to rubberasphalt increased the fracture energy therefore we foundthat the increase in fracture energy demonstrated thatsamples modified with silicone oil have superior crackresistance

Fracture toughness is yet another critical parameterused in evaluating low temperature performance of asphaltbinders in SENB test Increased fracture toughness valuesat low temperatures such as ndash20degC in polymer modifiedasphalt mixtures imply that resistance to fracture has in-creased Some polymers make asphalt less brittle at lowtemperatures and therefore polymer modified asphalt(PMA) concretes are expected to become tougher thannormal asphalt concrete at low temperatures e im-proved tensile property allows greater resistance to materialcracking [26] Similarly in our study it has been estab-lished that adding 3 content of silicone oil to crumbrubber asphalt resulted in increased fracture toughness of

the binder than binders without silicone oil is dem-onstrates that tensile property has improved leading togreater low-temperature crack resistance

65 Low-TemperaturePerformanceAnalysis ofCrumbRubberAsphalt considering Notched and Unnotched ConditionsTo investigate the effect of notch on low-temperature per-formance of crumb rubber asphalt the samples with andwithout a notch were subjected to fracture testing after 1-hour conditioning in cold bath e study gave rise to thefollowing observations

As seen in Figure 5 the load-displacement curve resultsshow an increase in stiffness modulus for unnotched samples ofcrumb rubber modified with silicone oil when compared withthe unnotched samples e preexisting crack renders thesample vulnerable to cracking therefore unnotched sampleswillmost likely have delayed cracking than the notched samples

Additionally the fracture toughness KIc and fractureenergy GIc increased with an increase in temperature fromminus 24 to minus 12degC this indicates that less potential fractureenergy is needed for crack propagation at lower tempera-tures Fracture energy and fracture toughness also increased

21nm

ndash23nmHeight sensor 20μm

(a)

65nm

ndash96nmHeight sensor 20μm

(b)

(c) (d)

Figure 2 AFM images of crumb rubber asphalt (with and without silicone oil) (a) Neat +CRndash2D AFM images (b) Neat +CR+ SOndash2DAFM images (c) Neat +CR 3D AFM images (d) Neat +CR+ SO 3D AFM images

6 Advances in Materials Science and Engineering

(a) (b)

Figure 3 FM images of crumb rubber asphalt (with and without waste silicone oil) (a) Neat +CRndashFM images (b) Neat +CR+ SOndashFMimages

ndash12degCndashneat + CRndash12degCndashneat + CR + SOndash18degCndashneat + CRndash18degCndashneat + CR + SOndash24degCndashneat + CRndash24degCndashneat + CR + SO

0

2000

4000

6000

8000

10000

12000

14000

16000

0 1 2 3 4 5 6 7Displacement (mm)

Forc

e (m

N)

(a)

35 30

162

102

179

151

020406080

100120140160180200220240

Neat + CR Neat + CR + SOAsphalt binder

Stiff

ness

mod

ulus

(kPa

)

ndash12degC

ndash18degC

ndash24degC

(b)

400

600

200

580

150

475

0

100

200

300

400

500

600

700

800

900

Neat + CR Neat + CR + SOAsphalt binder

Frac

ture

ener

gy (J

m2 )

ndash12degC

ndash18degC

ndash24degC

(c)

45 6

65 7

982

101

0

2

4

6

8

10

12

14

16

Neat + CR Neat + CR + SOAsphalt binder

Frac

ture

toug

hnes

s (kP

a m0

5)

ndash12degC

ndash18degC

ndash24degC

(d)

Figure 4 (a) Force-displacement curves (b) Change Detection to Stiffness modulus (c) Fracture energy (d) Fracture toughness plots

Advances in Materials Science and Engineering 7

14000

12000

10000

8000

6000

4000

2000

00 1 2 3 4 5 6 7

Forc

e (m

N)

Displacement (mm)

ndash12degC neat + CR ndash notchedndash12degC neat + CR ndash unnotchedndash12degC neat + CR + SO ndash notchedndash12degC neat + CR + SO ndash unnotched

(a)

18000

16000

14000

12000

10000

8000

6000

4000

2000

00 1 2 3 4 5 6 7

Forc

e (m

N)

Displacement (mm)

ndash18degCndashneat + CR ndash notchedndash18degCndashneat + CR ndash unnotchedndash18degCndashneat + CR + SO ndash notchedndash18degCndashneat + CR + SO ndash unnotched

(b)

18000

16000

14000

12000

10000

8000

6000

4000

2000

0

22000

20000

0 1 2 3 4 5 6 7

Forc

e (m

N)

Displacement (mm)

ndash24degCndashneat + CR ndash notchedndash24degCndashneat + CR ndash unnotchedndash24degCndashneat + CR + SO ndash notchedndash24degCndashneat + CR + SO ndash unnotched

(c)

025

020

015

010

005

000

Stiff

ness

mod

ulus

(MPa

)

Neat + CR + SO ndashnotched

Neat + CR + SO ndashunnotched

ndash12degC

ndash18degC

ndash24degC

004

009

016

005

5

011

3

021

5

(d)800

700

600

500

400

300

200

100

0Neat + CR ndash notched Neat + CR ndash unnotched

Frac

ture

ener

gy (J

m2 )

ndash12degC

ndash18degC

ndash24degC

407

17

195

64

136

94

662

58

461

27

283

24

(e)

1200

1000

800

600

400

200

0Neat + CR + SO ndash

notchedNeat + CR + SO ndash

unnotched

Frac

ture

ener

gy (J

m2 )

ndash12degC

ndash18degC

ndash24degC

600

978

575

02

506

07

998

64

970

99

700

2

(f )

Figure 5 Continued

8 Advances in Materials Science and Engineering

for unnotched samples than for notched samples In generala study found that unnotched binders are more resistant tolow-temperature cracking than notched binders In addi-tion examining the tested samples it was observed that forunmodified samples cracks initiated from the bottom of thesample under the load Whereas for notched samples crackspropagated from the preexisted cracks upwards

66 Statistical Analysis of Displacement in Asphalt BindersSeveral studies have used the analysis of variance(ANOVA) statistic test to determine the significance oflaboratory based experimental results [27 28] In thisstudy the ANOVA test was conducted for purposes ofdetermining whether or not there was a statistically sig-nificant difference on low-temperature performance ofcrumb rubber asphalt binders modified with and withoutsilicone oil Since asphalt binders having lower deflection(uf ) at fracture performed very poorly in the field as regardsthermal cracking [4] this study used load-deflection valuesfrom SENB test in statistical analysis e higher the de-flection values the better the low temperature crackingresistance SPSS statistical software was utilized to aid the

statistical computations at three temperatures minus 12degCminus 18degC and minus 24degC respectively by applying one-wayANOVA and a t-test and the results of which are presentedin Tables 4 and 5 respectively

Table 4 indicates that the amount of displacement atminus 12degC was T (6054) 0001 Plt 001 whereas at minus 18degC thedisplacement was T (8061) 0001 Plt 001 and at minus 24degCdisplacement was T (minus 83146) 0001 (Plt 001) Since P

values lt001 significance level the influence of silicone oil ondisplacement of asphalt samples at different temperatureswas found to be statistically significant

Table 5 indicates that the displacement analysis result atminus 12degC was F (5732) 276e minus 30 (Plt 001) whereas thatdisplacement result at minus 18degC was F (2763) 976e minus 15(Plt 001) Finally displacement result at minus 24degC was F(2662) 0000174 (Plt 001) Since all P values are signifi-cant at lt001 level the influence of silicone oil on low-temperature performance of crumb rubber asphalt is foundto be statistically significant

Standard error (SE) is the estimated standard deviationfor the distribution of sample means for an infinite pop-ulation e SE values of the estimates of displacement inSENB test were calculated by performing a paired t teste

Table 4 T test results of displacement at different test temperature

Asphalt binder type Mean (mm) N Std deviation Std error mean T Df SigTest temperature minus 12degCNeat +CR 36009 3289 215842 03764 6054 3288 0001Neat +CR+ SO 32363 3289 185615 03237Test temperature minus 18degCNeat +CR 19971 2027 113464 002520 8061 2026 0001Neat +CR+ SO 19999 2027 114478 002543Test temperature minus 24degCNeat +CR 22378 1553 114058 002894 minus 83146 1552 0001Neat +CR+ SO 15337 1553 087921 002231

12

10

8

6

4

2

0

Neat + CR + SO ndashnotched

Neat + CR + SO ndashunnotched

Frac

ture

toug

hnes

s (kP

a m0

5)

ndash12degC

ndash18degC

ndash24degC

494

646

83

703

100

1

120

(g)

16

14

12

10

8

6

4

2

0

Neat + CR + SO ndashnotched

Neat + CR + SO ndashunnotched

Frac

ture

toug

hnes

s (kP

a m0

5)

ndash12degC

ndash18degC

ndash24degC

607

79

101

666

119

3

139

1

(h)

Figure 5 Low-temperature performance of crumb rubber asphalt considering influence of precracked and uncracked notches Load-displacement curves at (a) minus 12degC (b) minus 18degC and (c) minus 24degC (d) Stiffness modulus of asphalt binders (e) Fracture energy of binders (f )Fracture energy of binders (g) Fracture toughness of binders (h) Fracture toughness of binders

Advances in Materials Science and Engineering 9

laboratory test results before and after silicone oil treat-ment to crumb rubber asphalt were compared e resultsfound that standard error at three temperatures was notmore than 000602 as shown in Table 6 Since a smallervalue of the standard error of the mean indicates a moreprecise estimate of the population mean the results wereconsidered valid

7 Conclusion

In this paper the effect of silicone oil on dispersion and low-temperature fracture performance of crumb rubber binderwas investigated based on SENB AFM and FM testsMaterialcharacterization was analysed by performing the FTIR teste research was driven by the notion that although CR hassucceeded in improving low-temperature performance ofasphalt pavements compatibility between asphalt and crumbrubber still remains a challenge to be solved As part of aneffort to solve the problem and develop sustainable materialssilicone oil was used to improve both rubber particle dis-persion in asphalt and low-temperature fracture perfor-mance is study led to following conclusions

(1) e analysis of molecular structure of siliconeconfirmed that the material was vinyl silicone oilFurther the analysis of asphalt modified with sili-cone oil resulted in generation of new absorptionpeaks with the main peak having Si-O-Si bond isbond indicates that silicone oil is a highly hydro-phobic material (water repellent) and also has

chemical durability which ensures that the siliconeoil is applied in asphalt

(2) e morphological images from the FM test revealedthat the addition of silicone oil improves the dispersionof crumb rubber particles in asphalt binder matrix

(3) e atomic force microscopy results suggested thatsurface roughness increases with the addition ofsilicone oil which implied that there was a change inmicrostructure of the sample Moreover the increasein roughness of the surface implied that bonding ofasphalt with rubber particles was enhanced therebyresulting in improved distribution of rubber particlesin asphalt

(4) e addition of crumb rubber to asphalt generallydecreased the stiffness of the material at low tem-peratures In addition the study concluded thataddition of silicone oil to crumb rubber asphaltresulted in a further decrease of stiffness therebyimproving low-temperature crack resistance evalues of fracture toughness as well as fracture energyindicated that crumb rubber asphalt binders con-taining silicone oil had superior crack resistance thanthe one without silicone oil modification

(5) Analysis of variance and t test results confirmed thatthe influence of silicone oil on displacement wasstatistically significant is means that low-tem-perature performance of a crumb rubber modifiedasphalt is strongly influenced by the addition of thesilicone oil

Table 6 Paired sample test results of displacement at different test temperatures for notched samples

Asphalt binder type N Mean (mm) Std deviation Std error mean99 CI

t Df Sig (2 tailed)Lower Upper

Test temperature minus 12degCNeat +CR 3289 minus 036459 034538 000602 minus 03812 minus 034907 minus 60540 3288 0001Neat +CR+ SOTest temperature minus 18degCNeat +CR 2027 000272 001520 000034 000185 000359 8061 2026 0001Neat +CR+ SOTest temperature minus 24degCNeat +CR 2667 002056 002075 000040 001952 002159 51163 2666 0001Neat +CR+ SO

Table 5 ANOVA test results of displacement at different test temperatures

Displacement Sum of squares Df Mean square F SigTest temperature minus 12degCBetween groups 15196637 3144 4834 5732 276e minus 30Within groups 121428 144 0843Total 15318064 3288Test temperature minus 18degCBetween groups 18759285 3730 5029 2763 976e minus 15Within groups 291212 160 1820Total 19050497 3890Test temperature minus 24degCBetween groups 5993014 2628 2280 2662 0000174Within groups 32556 38 0857Total 6025570 2666

10 Advances in Materials Science and Engineering

(6) Furthermore this study concluded that the im-provement in low-temperature performance ofcrumb rubber modified with silicone oil can becaptured from two perspectives Firstly as indicatedby the analysis of stiffness in FTIR and FM thesilicone oil softened the modified crumb rubberasphalt and enhanced the dispersion of rubberparticles in the binder Softening of asphalt improvescrack resistance Secondly as seen in IR spectrumthe Si-O bond in silicone oil makes it highly hy-drophobic (water repellent) and thus could delay thewater penetration and subsequent freezing of asphaltbinder during water conditioning of samples at lowtemperature resulting in lower stiffness

(7) e comparison between the notched andunnotched samples indicated that the modulus of thenotched binders was lower than that of theunnotched one In addition the unnotched asphaltbinders containing silicone oil did not break at minus 12degCwhich confirmed the great influence of silicone oil onrubberised asphalt low-temperature performance

In spite of results obtained in this study it should bementioned that the research had the following limitationsthe low-temperature performance of crumb rubber con-taining SO was limited to SENB test No BBR test wasconducted Future research can incorporate the BBR test andother techniques to better understand the behaviour ofasphalt modified with silicone oil

Data Availability

e data used to support the findings of this study are in-cluded within the article

Conflicts of Interest

e authors declare that there are no conflicts of interestregarding the publication of this article

Acknowledgments

e authors would like to express their gratitude to theHarbin Institute of Technology for providing laboratoryequipment and materials for experiments is research wasfunded by the National Natural Science Foundation of Chinawith Grant nos 51478152 and 51478154 Furthermore thefees relating to the publication of the manuscript was fundedby the Copperbelt University in Zambia

References

[1] M Marasteanu W Buttlar H Bahia et al Investigation ofLow Temperature Cracking in Asphalt Pavements NationalPooled Fund StudyndashPhase II Minnesota Department ofTransportation Saint Paul MN USA 2012 httphdlhandlenet11299135177

[2] R Velasquez and H Bahia ldquoCritical factors affecting thermalcracking of asphalt pavements towards a comprehensivespecificationrdquo Road Materials and Pavement Design vol 14no sup1 pp 187ndash200 2013

[3] E V Dave H Benjamin H Chelsea M Jared and J LukeldquoImplementation of laboratory testing to predict low tem-perature cracking performance of asphalt pavementsrdquo in 8thRILEM International Symposium on Testing and Character-ization of Sustainable and Innovative Bituminous MaterialsSpringer Berlin Germany 2016

[4] H U Bahia and A Davies ldquoEffect of crumb rubber modifiers(CRM) on performance related properties of asphalt bindersrdquoJournal of Association of Asphalt Paving Technology vol 63pp 414ndash449 1994

[5] T R Hoare and S A M Hesp ldquoLow-temperature fracturetesting of asphalt binders regular and modified systemsrdquoTransportation Research Record Journal of the TransportationResearch Board vol 1728 no 1 pp 36ndash42 2000

[6] P E Sebaaly V T Gopal and J A Epps ldquoLow temperatureproperties of crumb rubber modified bindersrdquo RoadMaterialsand Pavement Design vol 4 no 1 pp 29ndash49 2003

[7] S-S Kim Z D Wysong and J Kovach ldquoLow-temperaturethermal cracking of asphalt binder by asphalt binder crackingdevicerdquo Transportation Research Record Transportation Re-search Record Journal of the Transportation Research Boardvol 1962 no 1 pp 28ndash35 2006

[8] A Zofka and A Braham ldquoComparison of low-temperaturefield performance and laboratory testing of 10 test sections inthe midwestern United Statesrdquo Transportation Research Re-cord Journal of the Transportation Research Board vol 2127no 1 pp 107ndash114 2009

[9] M Pszczoła J Mariusz S Cezary J Jozef and D BohdanldquoEvaluation of low temperature properties of rubberized as-phalt mixturesrdquo Procedia Engineering vol 172 pp 897ndash9042017

[10] P S Wulandari and D Tjandra ldquoUse of crumb rubber as anadditive in asphalt concrete mixturerdquo Procedia Engineeringvol 171 pp 1384ndash1389 2017

[11] M Mull M A Stuart and K Yehia ldquoFracture resistancecharacterization of chemically modified crumb rubber asphaltpavementrdquo Journal of Materials Science vol 37 no 3pp 557ndash566 2002

[12] A Hussain and S A Elmasry ldquoChemically modified crumbrubber effects on rubberized asphalt propertiesrdquo InternationalJournal of Environmental Sciences vol 2 no 4 pp 158ndash1622013

[13] S Zhihao Z-J Wang and G Y Xie ldquoPreparation andperformances of silicone modified asphaltrdquo Fine and SpecialChemical vol 11 2017

[14] Y Li Y Zhang and Y Zhang ldquoMechanical properties ofhigh-density polyethylenescrap rubber composites modifiedwith ethylene-propylene-diene terpolymer dicumyl peroxideand silicone oilrdquo Journal of Applied Polymer Science vol 88no 8 pp 2020ndash2027 2003

[15] C Peng H Zhang Y Zhanping et al ldquoPreparation and anti-icing properties of a superhydrophobic silicone coating onasphalt mixturerdquo Construction and Building Materialsvol 189 pp 227ndash235 2018

[16] C Gorkem and S Burak ldquoPredicting stripping and moistureinduced damage of asphalt concrete prepared with polymermodified bitumen and hydrated limerdquo Construction andBuilding Materials vol 23 no 6 pp 2227ndash2236 2009

[17] J Lin C Meizhu W Shaopeng et al ldquoUtilization of siliconemaintenance materials to improve the moisture sensitivity ofasphalt mixturesrdquo Construction and Building Materialsvol 33 pp 1ndash6 2012

[18] R Zhang Y Zhanping W Hainian Y Mingxiao K Y Yokeand S Chundi ldquoe impact of bio-oil as rejuvenator for aged

Advances in Materials Science and Engineering 11

asphalt binder was calculated to determine the content ofaromatics in asphalt binder with and without silicone oiltreatment e results revealed that the aromatic index forcrumb rubber asphalt with and without silicone oil was 10and 06 respectively is result gave rise to the conclusionthat the addition of silicone oil to crumb rubber asphaltincreases the aromatic content and indices significantlyAccording to Kanabar highway pavements that do notexperience the spate of thermal distress are built withasphalt cements that have high IR aromatic indices or havemore aromatics [25] In addition the increase in aromaticcontent also decreases the dynamic modulus of the binder[18] erefore the high IR aromatic index found in thisstudy suggests that low-temperature cracking performancecan be improved with addition of silicone oil to asphaltbinder

62 Atomic Force Microscopy (AFM) Result Analysis Toevaluate the morphology of asphalt samples the AFM testwas used e AFM topographical images in Figure 2 gaverise to the following observations the bee-like structureswere CR particles in asphalt binder Based on equation (1)the average roughness for crumb rubber asphalt withoutsilicone oil was calculated as 037 nm whereas averageroughness for crumb rubber asphalt containing silicone oilwas 129 nm respectively e increase in surface roughnessof asphalt indicated that there was a change in the micro-structure of the asphalt samples after addition of silicone oilIn our study the increased surface roughness of crumbrubber asphalt with silicone oil indicates improved bondingbetween rubber particles and asphalt which may lead tocontinuous rubber particles dispersion in asphalt Visualcomparison of AFM images confirmed that the addition ofsilicone oil to crumb rubber asphalt greatly influenced theobserved microstructure and showed a continuous homo-geneity of rubber particles dispersion in asphalt ConverselyAFM topographical images for CR asphalt sample without

silicone oil revealed that rubber particle distribution was nothomogeneous

63 Fluorescence Microscopy (FM) Result Analysis e re-sults of AFM were further confirmed by FM analysis einfluence of silicone oil on the dispersion of crumb rubberparticles in asphalt binder was studied using the FM testwhich was conducted on two crumb rubber asphalt sampleswith and without silicone oil From Figure 3 results of FMimages revealed that the crumb rubber modified binderswith silicone oil showed uniformly dispersed rubber par-ticles in asphalt Conversely images of dispersion forconventional crumb rubber asphalt without silicone oilshowed noncontinuous bitumen matrix

64 Effect of Silicone Oil on Low-Temperature Performance ofCrumb Rubber Asphalt Binder Figure 4 shows that load-displacement curves stiffness modulus fracture toughnessand fracture energy values at three temperatures for the crumbrubber asphalt binders gave rise to the following observations

e results of load and displacement curve found thatthe addition of silicone oil to samples leads to increase indisplacement Asphalt binders having lower deflection atfracture perform very poorly in the field as regards thethermal cracking [4] erefore higher deflection values inour study indicate good low-temperature cracking re-sistance In addition the addition of silicone oil also in-creases stiffness modulus of the sample High stiffnessmodulus asphalt mixes at low temperature are prone tocracking [6] erefore the lower stiffness modulus ob-tained in our study is an indication of improved low-temperature performance of crumb rubber containingsilicone oil

It is also worth noting that rubber asphalt with siliconeoil did not break at minus 12degC owing to its increased low-temperature resistance is result demonstrated the effect

Silicone oil (SO)

C-H stretching of CH3

CH 3 asymmetric deformation of Si-CH

CH 3 symmetric deformation of Si-CH

Neat + crumb rubber (CR)

Neat asphalt

Neat + CR + SO

2964

12581009

788

Si-O-Si stretching

3500 3000 2500 2000 1500 1000 500Wavenumber (cmndash1)

Tran

smitt

ance

()

Figure 1 FTIR spectrum of silicone oil neat asphalt and crumb rubber asphalt modified with silicone oil

Advances in Materials Science and Engineering 5

of silicone oil on low-temperature performance of crumbrubber asphalt binders having high fracture energy wouldperform very well in the field in terms of thermal crackingresistance is was added to show that our findings agreewith other researchers [2] In our study results havedemonstrated that the addition of silicone oil to rubberasphalt increased the fracture energy therefore we foundthat the increase in fracture energy demonstrated thatsamples modified with silicone oil have superior crackresistance

Fracture toughness is yet another critical parameterused in evaluating low temperature performance of asphaltbinders in SENB test Increased fracture toughness valuesat low temperatures such as ndash20degC in polymer modifiedasphalt mixtures imply that resistance to fracture has in-creased Some polymers make asphalt less brittle at lowtemperatures and therefore polymer modified asphalt(PMA) concretes are expected to become tougher thannormal asphalt concrete at low temperatures e im-proved tensile property allows greater resistance to materialcracking [26] Similarly in our study it has been estab-lished that adding 3 content of silicone oil to crumbrubber asphalt resulted in increased fracture toughness of

the binder than binders without silicone oil is dem-onstrates that tensile property has improved leading togreater low-temperature crack resistance

65 Low-TemperaturePerformanceAnalysis ofCrumbRubberAsphalt considering Notched and Unnotched ConditionsTo investigate the effect of notch on low-temperature per-formance of crumb rubber asphalt the samples with andwithout a notch were subjected to fracture testing after 1-hour conditioning in cold bath e study gave rise to thefollowing observations

As seen in Figure 5 the load-displacement curve resultsshow an increase in stiffness modulus for unnotched samples ofcrumb rubber modified with silicone oil when compared withthe unnotched samples e preexisting crack renders thesample vulnerable to cracking therefore unnotched sampleswillmost likely have delayed cracking than the notched samples

Additionally the fracture toughness KIc and fractureenergy GIc increased with an increase in temperature fromminus 24 to minus 12degC this indicates that less potential fractureenergy is needed for crack propagation at lower tempera-tures Fracture energy and fracture toughness also increased

21nm

ndash23nmHeight sensor 20μm

(a)

65nm

ndash96nmHeight sensor 20μm

(b)

(c) (d)

Figure 2 AFM images of crumb rubber asphalt (with and without silicone oil) (a) Neat +CRndash2D AFM images (b) Neat +CR+ SOndash2DAFM images (c) Neat +CR 3D AFM images (d) Neat +CR+ SO 3D AFM images

6 Advances in Materials Science and Engineering

(a) (b)

Figure 3 FM images of crumb rubber asphalt (with and without waste silicone oil) (a) Neat +CRndashFM images (b) Neat +CR+ SOndashFMimages

ndash12degCndashneat + CRndash12degCndashneat + CR + SOndash18degCndashneat + CRndash18degCndashneat + CR + SOndash24degCndashneat + CRndash24degCndashneat + CR + SO

0

2000

4000

6000

8000

10000

12000

14000

16000

0 1 2 3 4 5 6 7Displacement (mm)

Forc

e (m

N)

(a)

35 30

162

102

179

151

020406080

100120140160180200220240

Neat + CR Neat + CR + SOAsphalt binder

Stiff

ness

mod

ulus

(kPa

)

ndash12degC

ndash18degC

ndash24degC

(b)

400

600

200

580

150

475

0

100

200

300

400

500

600

700

800

900

Neat + CR Neat + CR + SOAsphalt binder

Frac

ture

ener

gy (J

m2 )

ndash12degC

ndash18degC

ndash24degC

(c)

45 6

65 7

982

101

0

2

4

6

8

10

12

14

16

Neat + CR Neat + CR + SOAsphalt binder

Frac

ture

toug

hnes

s (kP

a m0

5)

ndash12degC

ndash18degC

ndash24degC

(d)

Figure 4 (a) Force-displacement curves (b) Change Detection to Stiffness modulus (c) Fracture energy (d) Fracture toughness plots

Advances in Materials Science and Engineering 7

14000

12000

10000

8000

6000

4000

2000

00 1 2 3 4 5 6 7

Forc

e (m

N)

Displacement (mm)

ndash12degC neat + CR ndash notchedndash12degC neat + CR ndash unnotchedndash12degC neat + CR + SO ndash notchedndash12degC neat + CR + SO ndash unnotched

(a)

18000

16000

14000

12000

10000

8000

6000

4000

2000

00 1 2 3 4 5 6 7

Forc

e (m

N)

Displacement (mm)

ndash18degCndashneat + CR ndash notchedndash18degCndashneat + CR ndash unnotchedndash18degCndashneat + CR + SO ndash notchedndash18degCndashneat + CR + SO ndash unnotched

(b)

18000

16000

14000

12000

10000

8000

6000

4000

2000

0

22000

20000

0 1 2 3 4 5 6 7

Forc

e (m

N)

Displacement (mm)

ndash24degCndashneat + CR ndash notchedndash24degCndashneat + CR ndash unnotchedndash24degCndashneat + CR + SO ndash notchedndash24degCndashneat + CR + SO ndash unnotched

(c)

025

020

015

010

005

000

Stiff

ness

mod

ulus

(MPa

)

Neat + CR + SO ndashnotched

Neat + CR + SO ndashunnotched

ndash12degC

ndash18degC

ndash24degC

004

009

016

005

5

011

3

021

5

(d)800

700

600

500

400

300

200

100

0Neat + CR ndash notched Neat + CR ndash unnotched

Frac

ture

ener

gy (J

m2 )

ndash12degC

ndash18degC

ndash24degC

407

17

195

64

136

94

662

58

461

27

283

24

(e)

1200

1000

800

600

400

200

0Neat + CR + SO ndash

notchedNeat + CR + SO ndash

unnotched

Frac

ture

ener

gy (J

m2 )

ndash12degC

ndash18degC

ndash24degC

600

978

575

02

506

07

998

64

970

99

700

2

(f )

Figure 5 Continued

8 Advances in Materials Science and Engineering

for unnotched samples than for notched samples In generala study found that unnotched binders are more resistant tolow-temperature cracking than notched binders In addi-tion examining the tested samples it was observed that forunmodified samples cracks initiated from the bottom of thesample under the load Whereas for notched samples crackspropagated from the preexisted cracks upwards

66 Statistical Analysis of Displacement in Asphalt BindersSeveral studies have used the analysis of variance(ANOVA) statistic test to determine the significance oflaboratory based experimental results [27 28] In thisstudy the ANOVA test was conducted for purposes ofdetermining whether or not there was a statistically sig-nificant difference on low-temperature performance ofcrumb rubber asphalt binders modified with and withoutsilicone oil Since asphalt binders having lower deflection(uf ) at fracture performed very poorly in the field as regardsthermal cracking [4] this study used load-deflection valuesfrom SENB test in statistical analysis e higher the de-flection values the better the low temperature crackingresistance SPSS statistical software was utilized to aid the

statistical computations at three temperatures minus 12degCminus 18degC and minus 24degC respectively by applying one-wayANOVA and a t-test and the results of which are presentedin Tables 4 and 5 respectively

Table 4 indicates that the amount of displacement atminus 12degC was T (6054) 0001 Plt 001 whereas at minus 18degC thedisplacement was T (8061) 0001 Plt 001 and at minus 24degCdisplacement was T (minus 83146) 0001 (Plt 001) Since P

values lt001 significance level the influence of silicone oil ondisplacement of asphalt samples at different temperatureswas found to be statistically significant

Table 5 indicates that the displacement analysis result atminus 12degC was F (5732) 276e minus 30 (Plt 001) whereas thatdisplacement result at minus 18degC was F (2763) 976e minus 15(Plt 001) Finally displacement result at minus 24degC was F(2662) 0000174 (Plt 001) Since all P values are signifi-cant at lt001 level the influence of silicone oil on low-temperature performance of crumb rubber asphalt is foundto be statistically significant

Standard error (SE) is the estimated standard deviationfor the distribution of sample means for an infinite pop-ulation e SE values of the estimates of displacement inSENB test were calculated by performing a paired t teste

Table 4 T test results of displacement at different test temperature

Asphalt binder type Mean (mm) N Std deviation Std error mean T Df SigTest temperature minus 12degCNeat +CR 36009 3289 215842 03764 6054 3288 0001Neat +CR+ SO 32363 3289 185615 03237Test temperature minus 18degCNeat +CR 19971 2027 113464 002520 8061 2026 0001Neat +CR+ SO 19999 2027 114478 002543Test temperature minus 24degCNeat +CR 22378 1553 114058 002894 minus 83146 1552 0001Neat +CR+ SO 15337 1553 087921 002231

12

10

8

6

4

2

0

Neat + CR + SO ndashnotched

Neat + CR + SO ndashunnotched

Frac

ture

toug

hnes

s (kP

a m0

5)

ndash12degC

ndash18degC

ndash24degC

494

646

83

703

100

1

120

(g)

16

14

12

10

8

6

4

2

0

Neat + CR + SO ndashnotched

Neat + CR + SO ndashunnotched

Frac

ture

toug

hnes

s (kP

a m0

5)

ndash12degC

ndash18degC

ndash24degC

607

79

101

666

119

3

139

1

(h)

Figure 5 Low-temperature performance of crumb rubber asphalt considering influence of precracked and uncracked notches Load-displacement curves at (a) minus 12degC (b) minus 18degC and (c) minus 24degC (d) Stiffness modulus of asphalt binders (e) Fracture energy of binders (f )Fracture energy of binders (g) Fracture toughness of binders (h) Fracture toughness of binders

Advances in Materials Science and Engineering 9

laboratory test results before and after silicone oil treat-ment to crumb rubber asphalt were compared e resultsfound that standard error at three temperatures was notmore than 000602 as shown in Table 6 Since a smallervalue of the standard error of the mean indicates a moreprecise estimate of the population mean the results wereconsidered valid

7 Conclusion

In this paper the effect of silicone oil on dispersion and low-temperature fracture performance of crumb rubber binderwas investigated based on SENB AFM and FM testsMaterialcharacterization was analysed by performing the FTIR teste research was driven by the notion that although CR hassucceeded in improving low-temperature performance ofasphalt pavements compatibility between asphalt and crumbrubber still remains a challenge to be solved As part of aneffort to solve the problem and develop sustainable materialssilicone oil was used to improve both rubber particle dis-persion in asphalt and low-temperature fracture perfor-mance is study led to following conclusions

(1) e analysis of molecular structure of siliconeconfirmed that the material was vinyl silicone oilFurther the analysis of asphalt modified with sili-cone oil resulted in generation of new absorptionpeaks with the main peak having Si-O-Si bond isbond indicates that silicone oil is a highly hydro-phobic material (water repellent) and also has

chemical durability which ensures that the siliconeoil is applied in asphalt

(2) e morphological images from the FM test revealedthat the addition of silicone oil improves the dispersionof crumb rubber particles in asphalt binder matrix

(3) e atomic force microscopy results suggested thatsurface roughness increases with the addition ofsilicone oil which implied that there was a change inmicrostructure of the sample Moreover the increasein roughness of the surface implied that bonding ofasphalt with rubber particles was enhanced therebyresulting in improved distribution of rubber particlesin asphalt

(4) e addition of crumb rubber to asphalt generallydecreased the stiffness of the material at low tem-peratures In addition the study concluded thataddition of silicone oil to crumb rubber asphaltresulted in a further decrease of stiffness therebyimproving low-temperature crack resistance evalues of fracture toughness as well as fracture energyindicated that crumb rubber asphalt binders con-taining silicone oil had superior crack resistance thanthe one without silicone oil modification

(5) Analysis of variance and t test results confirmed thatthe influence of silicone oil on displacement wasstatistically significant is means that low-tem-perature performance of a crumb rubber modifiedasphalt is strongly influenced by the addition of thesilicone oil

Table 6 Paired sample test results of displacement at different test temperatures for notched samples

Asphalt binder type N Mean (mm) Std deviation Std error mean99 CI

t Df Sig (2 tailed)Lower Upper

Test temperature minus 12degCNeat +CR 3289 minus 036459 034538 000602 minus 03812 minus 034907 minus 60540 3288 0001Neat +CR+ SOTest temperature minus 18degCNeat +CR 2027 000272 001520 000034 000185 000359 8061 2026 0001Neat +CR+ SOTest temperature minus 24degCNeat +CR 2667 002056 002075 000040 001952 002159 51163 2666 0001Neat +CR+ SO

Table 5 ANOVA test results of displacement at different test temperatures

Displacement Sum of squares Df Mean square F SigTest temperature minus 12degCBetween groups 15196637 3144 4834 5732 276e minus 30Within groups 121428 144 0843Total 15318064 3288Test temperature minus 18degCBetween groups 18759285 3730 5029 2763 976e minus 15Within groups 291212 160 1820Total 19050497 3890Test temperature minus 24degCBetween groups 5993014 2628 2280 2662 0000174Within groups 32556 38 0857Total 6025570 2666

10 Advances in Materials Science and Engineering

(6) Furthermore this study concluded that the im-provement in low-temperature performance ofcrumb rubber modified with silicone oil can becaptured from two perspectives Firstly as indicatedby the analysis of stiffness in FTIR and FM thesilicone oil softened the modified crumb rubberasphalt and enhanced the dispersion of rubberparticles in the binder Softening of asphalt improvescrack resistance Secondly as seen in IR spectrumthe Si-O bond in silicone oil makes it highly hy-drophobic (water repellent) and thus could delay thewater penetration and subsequent freezing of asphaltbinder during water conditioning of samples at lowtemperature resulting in lower stiffness

(7) e comparison between the notched andunnotched samples indicated that the modulus of thenotched binders was lower than that of theunnotched one In addition the unnotched asphaltbinders containing silicone oil did not break at minus 12degCwhich confirmed the great influence of silicone oil onrubberised asphalt low-temperature performance

In spite of results obtained in this study it should bementioned that the research had the following limitationsthe low-temperature performance of crumb rubber con-taining SO was limited to SENB test No BBR test wasconducted Future research can incorporate the BBR test andother techniques to better understand the behaviour ofasphalt modified with silicone oil

Data Availability

e data used to support the findings of this study are in-cluded within the article

Conflicts of Interest

e authors declare that there are no conflicts of interestregarding the publication of this article

Acknowledgments

e authors would like to express their gratitude to theHarbin Institute of Technology for providing laboratoryequipment and materials for experiments is research wasfunded by the National Natural Science Foundation of Chinawith Grant nos 51478152 and 51478154 Furthermore thefees relating to the publication of the manuscript was fundedby the Copperbelt University in Zambia

References

[1] M Marasteanu W Buttlar H Bahia et al Investigation ofLow Temperature Cracking in Asphalt Pavements NationalPooled Fund StudyndashPhase II Minnesota Department ofTransportation Saint Paul MN USA 2012 httphdlhandlenet11299135177

[2] R Velasquez and H Bahia ldquoCritical factors affecting thermalcracking of asphalt pavements towards a comprehensivespecificationrdquo Road Materials and Pavement Design vol 14no sup1 pp 187ndash200 2013

[3] E V Dave H Benjamin H Chelsea M Jared and J LukeldquoImplementation of laboratory testing to predict low tem-perature cracking performance of asphalt pavementsrdquo in 8thRILEM International Symposium on Testing and Character-ization of Sustainable and Innovative Bituminous MaterialsSpringer Berlin Germany 2016

[4] H U Bahia and A Davies ldquoEffect of crumb rubber modifiers(CRM) on performance related properties of asphalt bindersrdquoJournal of Association of Asphalt Paving Technology vol 63pp 414ndash449 1994

[5] T R Hoare and S A M Hesp ldquoLow-temperature fracturetesting of asphalt binders regular and modified systemsrdquoTransportation Research Record Journal of the TransportationResearch Board vol 1728 no 1 pp 36ndash42 2000

[6] P E Sebaaly V T Gopal and J A Epps ldquoLow temperatureproperties of crumb rubber modified bindersrdquo RoadMaterialsand Pavement Design vol 4 no 1 pp 29ndash49 2003

[7] S-S Kim Z D Wysong and J Kovach ldquoLow-temperaturethermal cracking of asphalt binder by asphalt binder crackingdevicerdquo Transportation Research Record Transportation Re-search Record Journal of the Transportation Research Boardvol 1962 no 1 pp 28ndash35 2006

[8] A Zofka and A Braham ldquoComparison of low-temperaturefield performance and laboratory testing of 10 test sections inthe midwestern United Statesrdquo Transportation Research Re-cord Journal of the Transportation Research Board vol 2127no 1 pp 107ndash114 2009

[9] M Pszczoła J Mariusz S Cezary J Jozef and D BohdanldquoEvaluation of low temperature properties of rubberized as-phalt mixturesrdquo Procedia Engineering vol 172 pp 897ndash9042017

[10] P S Wulandari and D Tjandra ldquoUse of crumb rubber as anadditive in asphalt concrete mixturerdquo Procedia Engineeringvol 171 pp 1384ndash1389 2017

[11] M Mull M A Stuart and K Yehia ldquoFracture resistancecharacterization of chemically modified crumb rubber asphaltpavementrdquo Journal of Materials Science vol 37 no 3pp 557ndash566 2002

[12] A Hussain and S A Elmasry ldquoChemically modified crumbrubber effects on rubberized asphalt propertiesrdquo InternationalJournal of Environmental Sciences vol 2 no 4 pp 158ndash1622013

[13] S Zhihao Z-J Wang and G Y Xie ldquoPreparation andperformances of silicone modified asphaltrdquo Fine and SpecialChemical vol 11 2017

[14] Y Li Y Zhang and Y Zhang ldquoMechanical properties ofhigh-density polyethylenescrap rubber composites modifiedwith ethylene-propylene-diene terpolymer dicumyl peroxideand silicone oilrdquo Journal of Applied Polymer Science vol 88no 8 pp 2020ndash2027 2003

[15] C Peng H Zhang Y Zhanping et al ldquoPreparation and anti-icing properties of a superhydrophobic silicone coating onasphalt mixturerdquo Construction and Building Materialsvol 189 pp 227ndash235 2018

[16] C Gorkem and S Burak ldquoPredicting stripping and moistureinduced damage of asphalt concrete prepared with polymermodified bitumen and hydrated limerdquo Construction andBuilding Materials vol 23 no 6 pp 2227ndash2236 2009

[17] J Lin C Meizhu W Shaopeng et al ldquoUtilization of siliconemaintenance materials to improve the moisture sensitivity ofasphalt mixturesrdquo Construction and Building Materialsvol 33 pp 1ndash6 2012

[18] R Zhang Y Zhanping W Hainian Y Mingxiao K Y Yokeand S Chundi ldquoe impact of bio-oil as rejuvenator for aged

Advances in Materials Science and Engineering 11

of silicone oil on low-temperature performance of crumbrubber asphalt binders having high fracture energy wouldperform very well in the field in terms of thermal crackingresistance is was added to show that our findings agreewith other researchers [2] In our study results havedemonstrated that the addition of silicone oil to rubberasphalt increased the fracture energy therefore we foundthat the increase in fracture energy demonstrated thatsamples modified with silicone oil have superior crackresistance

Fracture toughness is yet another critical parameterused in evaluating low temperature performance of asphaltbinders in SENB test Increased fracture toughness valuesat low temperatures such as ndash20degC in polymer modifiedasphalt mixtures imply that resistance to fracture has in-creased Some polymers make asphalt less brittle at lowtemperatures and therefore polymer modified asphalt(PMA) concretes are expected to become tougher thannormal asphalt concrete at low temperatures e im-proved tensile property allows greater resistance to materialcracking [26] Similarly in our study it has been estab-lished that adding 3 content of silicone oil to crumbrubber asphalt resulted in increased fracture toughness of

the binder than binders without silicone oil is dem-onstrates that tensile property has improved leading togreater low-temperature crack resistance

65 Low-TemperaturePerformanceAnalysis ofCrumbRubberAsphalt considering Notched and Unnotched ConditionsTo investigate the effect of notch on low-temperature per-formance of crumb rubber asphalt the samples with andwithout a notch were subjected to fracture testing after 1-hour conditioning in cold bath e study gave rise to thefollowing observations

As seen in Figure 5 the load-displacement curve resultsshow an increase in stiffness modulus for unnotched samples ofcrumb rubber modified with silicone oil when compared withthe unnotched samples e preexisting crack renders thesample vulnerable to cracking therefore unnotched sampleswillmost likely have delayed cracking than the notched samples

Additionally the fracture toughness KIc and fractureenergy GIc increased with an increase in temperature fromminus 24 to minus 12degC this indicates that less potential fractureenergy is needed for crack propagation at lower tempera-tures Fracture energy and fracture toughness also increased

21nm

ndash23nmHeight sensor 20μm

(a)

65nm

ndash96nmHeight sensor 20μm

(b)

(c) (d)

Figure 2 AFM images of crumb rubber asphalt (with and without silicone oil) (a) Neat +CRndash2D AFM images (b) Neat +CR+ SOndash2DAFM images (c) Neat +CR 3D AFM images (d) Neat +CR+ SO 3D AFM images

6 Advances in Materials Science and Engineering

(a) (b)

Figure 3 FM images of crumb rubber asphalt (with and without waste silicone oil) (a) Neat +CRndashFM images (b) Neat +CR+ SOndashFMimages

ndash12degCndashneat + CRndash12degCndashneat + CR + SOndash18degCndashneat + CRndash18degCndashneat + CR + SOndash24degCndashneat + CRndash24degCndashneat + CR + SO

0

2000

4000

6000

8000

10000

12000

14000

16000

0 1 2 3 4 5 6 7Displacement (mm)

Forc

e (m

N)

(a)

35 30

162

102

179

151

020406080

100120140160180200220240

Neat + CR Neat + CR + SOAsphalt binder

Stiff

ness

mod

ulus

(kPa

)

ndash12degC

ndash18degC

ndash24degC

(b)

400

600

200

580

150

475

0

100

200

300

400

500

600

700

800

900

Neat + CR Neat + CR + SOAsphalt binder

Frac

ture

ener

gy (J

m2 )

ndash12degC

ndash18degC

ndash24degC

(c)

45 6

65 7

982

101

0

2

4

6

8

10

12

14

16

Neat + CR Neat + CR + SOAsphalt binder

Frac

ture

toug

hnes

s (kP

a m0

5)

ndash12degC

ndash18degC

ndash24degC

(d)

Figure 4 (a) Force-displacement curves (b) Change Detection to Stiffness modulus (c) Fracture energy (d) Fracture toughness plots

Advances in Materials Science and Engineering 7

14000

12000

10000

8000

6000

4000

2000

00 1 2 3 4 5 6 7

Forc

e (m

N)

Displacement (mm)

ndash12degC neat + CR ndash notchedndash12degC neat + CR ndash unnotchedndash12degC neat + CR + SO ndash notchedndash12degC neat + CR + SO ndash unnotched

(a)

18000

16000

14000

12000

10000

8000

6000

4000

2000

00 1 2 3 4 5 6 7

Forc

e (m

N)

Displacement (mm)

ndash18degCndashneat + CR ndash notchedndash18degCndashneat + CR ndash unnotchedndash18degCndashneat + CR + SO ndash notchedndash18degCndashneat + CR + SO ndash unnotched

(b)

18000

16000

14000

12000

10000

8000

6000

4000

2000

0

22000

20000

0 1 2 3 4 5 6 7

Forc

e (m

N)

Displacement (mm)

ndash24degCndashneat + CR ndash notchedndash24degCndashneat + CR ndash unnotchedndash24degCndashneat + CR + SO ndash notchedndash24degCndashneat + CR + SO ndash unnotched

(c)

025

020

015

010

005

000

Stiff

ness

mod

ulus

(MPa

)

Neat + CR + SO ndashnotched

Neat + CR + SO ndashunnotched

ndash12degC

ndash18degC

ndash24degC

004

009

016

005

5

011

3

021

5

(d)800

700

600

500

400

300

200

100

0Neat + CR ndash notched Neat + CR ndash unnotched

Frac

ture

ener

gy (J

m2 )

ndash12degC

ndash18degC

ndash24degC

407

17

195

64

136

94

662

58

461

27

283

24

(e)

1200

1000

800

600

400

200

0Neat + CR + SO ndash

notchedNeat + CR + SO ndash

unnotched

Frac

ture

ener

gy (J

m2 )

ndash12degC

ndash18degC

ndash24degC

600

978

575

02

506

07

998

64

970

99

700

2

(f )

Figure 5 Continued

8 Advances in Materials Science and Engineering

for unnotched samples than for notched samples In generala study found that unnotched binders are more resistant tolow-temperature cracking than notched binders In addi-tion examining the tested samples it was observed that forunmodified samples cracks initiated from the bottom of thesample under the load Whereas for notched samples crackspropagated from the preexisted cracks upwards

66 Statistical Analysis of Displacement in Asphalt BindersSeveral studies have used the analysis of variance(ANOVA) statistic test to determine the significance oflaboratory based experimental results [27 28] In thisstudy the ANOVA test was conducted for purposes ofdetermining whether or not there was a statistically sig-nificant difference on low-temperature performance ofcrumb rubber asphalt binders modified with and withoutsilicone oil Since asphalt binders having lower deflection(uf ) at fracture performed very poorly in the field as regardsthermal cracking [4] this study used load-deflection valuesfrom SENB test in statistical analysis e higher the de-flection values the better the low temperature crackingresistance SPSS statistical software was utilized to aid the

statistical computations at three temperatures minus 12degCminus 18degC and minus 24degC respectively by applying one-wayANOVA and a t-test and the results of which are presentedin Tables 4 and 5 respectively

Table 4 indicates that the amount of displacement atminus 12degC was T (6054) 0001 Plt 001 whereas at minus 18degC thedisplacement was T (8061) 0001 Plt 001 and at minus 24degCdisplacement was T (minus 83146) 0001 (Plt 001) Since P

values lt001 significance level the influence of silicone oil ondisplacement of asphalt samples at different temperatureswas found to be statistically significant

Table 5 indicates that the displacement analysis result atminus 12degC was F (5732) 276e minus 30 (Plt 001) whereas thatdisplacement result at minus 18degC was F (2763) 976e minus 15(Plt 001) Finally displacement result at minus 24degC was F(2662) 0000174 (Plt 001) Since all P values are signifi-cant at lt001 level the influence of silicone oil on low-temperature performance of crumb rubber asphalt is foundto be statistically significant

Standard error (SE) is the estimated standard deviationfor the distribution of sample means for an infinite pop-ulation e SE values of the estimates of displacement inSENB test were calculated by performing a paired t teste

Table 4 T test results of displacement at different test temperature

Asphalt binder type Mean (mm) N Std deviation Std error mean T Df SigTest temperature minus 12degCNeat +CR 36009 3289 215842 03764 6054 3288 0001Neat +CR+ SO 32363 3289 185615 03237Test temperature minus 18degCNeat +CR 19971 2027 113464 002520 8061 2026 0001Neat +CR+ SO 19999 2027 114478 002543Test temperature minus 24degCNeat +CR 22378 1553 114058 002894 minus 83146 1552 0001Neat +CR+ SO 15337 1553 087921 002231

12

10

8

6

4

2

0

Neat + CR + SO ndashnotched

Neat + CR + SO ndashunnotched

Frac

ture

toug

hnes

s (kP

a m0

5)

ndash12degC

ndash18degC

ndash24degC

494

646

83

703

100

1

120

(g)

16

14

12

10

8

6

4

2

0

Neat + CR + SO ndashnotched

Neat + CR + SO ndashunnotched

Frac

ture

toug

hnes

s (kP

a m0

5)

ndash12degC

ndash18degC

ndash24degC

607

79

101

666

119

3

139

1

(h)

Figure 5 Low-temperature performance of crumb rubber asphalt considering influence of precracked and uncracked notches Load-displacement curves at (a) minus 12degC (b) minus 18degC and (c) minus 24degC (d) Stiffness modulus of asphalt binders (e) Fracture energy of binders (f )Fracture energy of binders (g) Fracture toughness of binders (h) Fracture toughness of binders

Advances in Materials Science and Engineering 9

laboratory test results before and after silicone oil treat-ment to crumb rubber asphalt were compared e resultsfound that standard error at three temperatures was notmore than 000602 as shown in Table 6 Since a smallervalue of the standard error of the mean indicates a moreprecise estimate of the population mean the results wereconsidered valid

7 Conclusion

In this paper the effect of silicone oil on dispersion and low-temperature fracture performance of crumb rubber binderwas investigated based on SENB AFM and FM testsMaterialcharacterization was analysed by performing the FTIR teste research was driven by the notion that although CR hassucceeded in improving low-temperature performance ofasphalt pavements compatibility between asphalt and crumbrubber still remains a challenge to be solved As part of aneffort to solve the problem and develop sustainable materialssilicone oil was used to improve both rubber particle dis-persion in asphalt and low-temperature fracture perfor-mance is study led to following conclusions

(1) e analysis of molecular structure of siliconeconfirmed that the material was vinyl silicone oilFurther the analysis of asphalt modified with sili-cone oil resulted in generation of new absorptionpeaks with the main peak having Si-O-Si bond isbond indicates that silicone oil is a highly hydro-phobic material (water repellent) and also has

chemical durability which ensures that the siliconeoil is applied in asphalt

(2) e morphological images from the FM test revealedthat the addition of silicone oil improves the dispersionof crumb rubber particles in asphalt binder matrix

(3) e atomic force microscopy results suggested thatsurface roughness increases with the addition ofsilicone oil which implied that there was a change inmicrostructure of the sample Moreover the increasein roughness of the surface implied that bonding ofasphalt with rubber particles was enhanced therebyresulting in improved distribution of rubber particlesin asphalt

(4) e addition of crumb rubber to asphalt generallydecreased the stiffness of the material at low tem-peratures In addition the study concluded thataddition of silicone oil to crumb rubber asphaltresulted in a further decrease of stiffness therebyimproving low-temperature crack resistance evalues of fracture toughness as well as fracture energyindicated that crumb rubber asphalt binders con-taining silicone oil had superior crack resistance thanthe one without silicone oil modification

(5) Analysis of variance and t test results confirmed thatthe influence of silicone oil on displacement wasstatistically significant is means that low-tem-perature performance of a crumb rubber modifiedasphalt is strongly influenced by the addition of thesilicone oil

Table 6 Paired sample test results of displacement at different test temperatures for notched samples

Asphalt binder type N Mean (mm) Std deviation Std error mean99 CI

t Df Sig (2 tailed)Lower Upper

Test temperature minus 12degCNeat +CR 3289 minus 036459 034538 000602 minus 03812 minus 034907 minus 60540 3288 0001Neat +CR+ SOTest temperature minus 18degCNeat +CR 2027 000272 001520 000034 000185 000359 8061 2026 0001Neat +CR+ SOTest temperature minus 24degCNeat +CR 2667 002056 002075 000040 001952 002159 51163 2666 0001Neat +CR+ SO

Table 5 ANOVA test results of displacement at different test temperatures

Displacement Sum of squares Df Mean square F SigTest temperature minus 12degCBetween groups 15196637 3144 4834 5732 276e minus 30Within groups 121428 144 0843Total 15318064 3288Test temperature minus 18degCBetween groups 18759285 3730 5029 2763 976e minus 15Within groups 291212 160 1820Total 19050497 3890Test temperature minus 24degCBetween groups 5993014 2628 2280 2662 0000174Within groups 32556 38 0857Total 6025570 2666

10 Advances in Materials Science and Engineering

(6) Furthermore this study concluded that the im-provement in low-temperature performance ofcrumb rubber modified with silicone oil can becaptured from two perspectives Firstly as indicatedby the analysis of stiffness in FTIR and FM thesilicone oil softened the modified crumb rubberasphalt and enhanced the dispersion of rubberparticles in the binder Softening of asphalt improvescrack resistance Secondly as seen in IR spectrumthe Si-O bond in silicone oil makes it highly hy-drophobic (water repellent) and thus could delay thewater penetration and subsequent freezing of asphaltbinder during water conditioning of samples at lowtemperature resulting in lower stiffness

(7) e comparison between the notched andunnotched samples indicated that the modulus of thenotched binders was lower than that of theunnotched one In addition the unnotched asphaltbinders containing silicone oil did not break at minus 12degCwhich confirmed the great influence of silicone oil onrubberised asphalt low-temperature performance

In spite of results obtained in this study it should bementioned that the research had the following limitationsthe low-temperature performance of crumb rubber con-taining SO was limited to SENB test No BBR test wasconducted Future research can incorporate the BBR test andother techniques to better understand the behaviour ofasphalt modified with silicone oil

Data Availability

e data used to support the findings of this study are in-cluded within the article

Conflicts of Interest

e authors declare that there are no conflicts of interestregarding the publication of this article

Acknowledgments

e authors would like to express their gratitude to theHarbin Institute of Technology for providing laboratoryequipment and materials for experiments is research wasfunded by the National Natural Science Foundation of Chinawith Grant nos 51478152 and 51478154 Furthermore thefees relating to the publication of the manuscript was fundedby the Copperbelt University in Zambia

References

[1] M Marasteanu W Buttlar H Bahia et al Investigation ofLow Temperature Cracking in Asphalt Pavements NationalPooled Fund StudyndashPhase II Minnesota Department ofTransportation Saint Paul MN USA 2012 httphdlhandlenet11299135177

[2] R Velasquez and H Bahia ldquoCritical factors affecting thermalcracking of asphalt pavements towards a comprehensivespecificationrdquo Road Materials and Pavement Design vol 14no sup1 pp 187ndash200 2013

[3] E V Dave H Benjamin H Chelsea M Jared and J LukeldquoImplementation of laboratory testing to predict low tem-perature cracking performance of asphalt pavementsrdquo in 8thRILEM International Symposium on Testing and Character-ization of Sustainable and Innovative Bituminous MaterialsSpringer Berlin Germany 2016

[4] H U Bahia and A Davies ldquoEffect of crumb rubber modifiers(CRM) on performance related properties of asphalt bindersrdquoJournal of Association of Asphalt Paving Technology vol 63pp 414ndash449 1994

[5] T R Hoare and S A M Hesp ldquoLow-temperature fracturetesting of asphalt binders regular and modified systemsrdquoTransportation Research Record Journal of the TransportationResearch Board vol 1728 no 1 pp 36ndash42 2000

[6] P E Sebaaly V T Gopal and J A Epps ldquoLow temperatureproperties of crumb rubber modified bindersrdquo RoadMaterialsand Pavement Design vol 4 no 1 pp 29ndash49 2003

[7] S-S Kim Z D Wysong and J Kovach ldquoLow-temperaturethermal cracking of asphalt binder by asphalt binder crackingdevicerdquo Transportation Research Record Transportation Re-search Record Journal of the Transportation Research Boardvol 1962 no 1 pp 28ndash35 2006

[8] A Zofka and A Braham ldquoComparison of low-temperaturefield performance and laboratory testing of 10 test sections inthe midwestern United Statesrdquo Transportation Research Re-cord Journal of the Transportation Research Board vol 2127no 1 pp 107ndash114 2009

[9] M Pszczoła J Mariusz S Cezary J Jozef and D BohdanldquoEvaluation of low temperature properties of rubberized as-phalt mixturesrdquo Procedia Engineering vol 172 pp 897ndash9042017

[10] P S Wulandari and D Tjandra ldquoUse of crumb rubber as anadditive in asphalt concrete mixturerdquo Procedia Engineeringvol 171 pp 1384ndash1389 2017

[11] M Mull M A Stuart and K Yehia ldquoFracture resistancecharacterization of chemically modified crumb rubber asphaltpavementrdquo Journal of Materials Science vol 37 no 3pp 557ndash566 2002

[12] A Hussain and S A Elmasry ldquoChemically modified crumbrubber effects on rubberized asphalt propertiesrdquo InternationalJournal of Environmental Sciences vol 2 no 4 pp 158ndash1622013

[13] S Zhihao Z-J Wang and G Y Xie ldquoPreparation andperformances of silicone modified asphaltrdquo Fine and SpecialChemical vol 11 2017

[14] Y Li Y Zhang and Y Zhang ldquoMechanical properties ofhigh-density polyethylenescrap rubber composites modifiedwith ethylene-propylene-diene terpolymer dicumyl peroxideand silicone oilrdquo Journal of Applied Polymer Science vol 88no 8 pp 2020ndash2027 2003

[15] C Peng H Zhang Y Zhanping et al ldquoPreparation and anti-icing properties of a superhydrophobic silicone coating onasphalt mixturerdquo Construction and Building Materialsvol 189 pp 227ndash235 2018

[16] C Gorkem and S Burak ldquoPredicting stripping and moistureinduced damage of asphalt concrete prepared with polymermodified bitumen and hydrated limerdquo Construction andBuilding Materials vol 23 no 6 pp 2227ndash2236 2009

[17] J Lin C Meizhu W Shaopeng et al ldquoUtilization of siliconemaintenance materials to improve the moisture sensitivity ofasphalt mixturesrdquo Construction and Building Materialsvol 33 pp 1ndash6 2012

[18] R Zhang Y Zhanping W Hainian Y Mingxiao K Y Yokeand S Chundi ldquoe impact of bio-oil as rejuvenator for aged

Advances in Materials Science and Engineering 11

(a) (b)

Figure 3 FM images of crumb rubber asphalt (with and without waste silicone oil) (a) Neat +CRndashFM images (b) Neat +CR+ SOndashFMimages

ndash12degCndashneat + CRndash12degCndashneat + CR + SOndash18degCndashneat + CRndash18degCndashneat + CR + SOndash24degCndashneat + CRndash24degCndashneat + CR + SO

0

2000

4000

6000

8000

10000

12000

14000

16000

0 1 2 3 4 5 6 7Displacement (mm)

Forc

e (m

N)

(a)

35 30

162

102

179

151

020406080

100120140160180200220240

Neat + CR Neat + CR + SOAsphalt binder

Stiff

ness

mod

ulus

(kPa

)

ndash12degC

ndash18degC

ndash24degC

(b)

400

600

200

580

150

475

0

100

200

300

400

500

600

700

800

900

Neat + CR Neat + CR + SOAsphalt binder

Frac

ture

ener

gy (J

m2 )

ndash12degC

ndash18degC

ndash24degC

(c)

45 6

65 7

982

101

0

2

4

6

8

10

12

14

16

Neat + CR Neat + CR + SOAsphalt binder

Frac

ture

toug

hnes

s (kP

a m0

5)

ndash12degC

ndash18degC

ndash24degC

(d)

Figure 4 (a) Force-displacement curves (b) Change Detection to Stiffness modulus (c) Fracture energy (d) Fracture toughness plots

Advances in Materials Science and Engineering 7

14000

12000

10000

8000

6000

4000

2000

00 1 2 3 4 5 6 7

Forc

e (m

N)

Displacement (mm)

ndash12degC neat + CR ndash notchedndash12degC neat + CR ndash unnotchedndash12degC neat + CR + SO ndash notchedndash12degC neat + CR + SO ndash unnotched

(a)

18000

16000

14000

12000

10000

8000

6000

4000

2000

00 1 2 3 4 5 6 7

Forc

e (m

N)

Displacement (mm)

ndash18degCndashneat + CR ndash notchedndash18degCndashneat + CR ndash unnotchedndash18degCndashneat + CR + SO ndash notchedndash18degCndashneat + CR + SO ndash unnotched

(b)

18000

16000

14000

12000

10000

8000

6000

4000

2000

0

22000

20000

0 1 2 3 4 5 6 7

Forc

e (m

N)

Displacement (mm)

ndash24degCndashneat + CR ndash notchedndash24degCndashneat + CR ndash unnotchedndash24degCndashneat + CR + SO ndash notchedndash24degCndashneat + CR + SO ndash unnotched

(c)

025

020

015

010

005

000

Stiff

ness

mod

ulus

(MPa

)

Neat + CR + SO ndashnotched

Neat + CR + SO ndashunnotched

ndash12degC

ndash18degC

ndash24degC

004

009

016

005

5

011

3

021

5

(d)800

700

600

500

400

300

200

100

0Neat + CR ndash notched Neat + CR ndash unnotched

Frac

ture

ener

gy (J

m2 )

ndash12degC

ndash18degC

ndash24degC

407

17

195

64

136

94

662

58

461

27

283

24

(e)

1200

1000

800

600

400

200

0Neat + CR + SO ndash

notchedNeat + CR + SO ndash

unnotched

Frac

ture

ener

gy (J

m2 )

ndash12degC

ndash18degC

ndash24degC

600

978

575

02

506

07

998

64

970

99

700

2

(f )

Figure 5 Continued

8 Advances in Materials Science and Engineering

for unnotched samples than for notched samples In generala study found that unnotched binders are more resistant tolow-temperature cracking than notched binders In addi-tion examining the tested samples it was observed that forunmodified samples cracks initiated from the bottom of thesample under the load Whereas for notched samples crackspropagated from the preexisted cracks upwards

66 Statistical Analysis of Displacement in Asphalt BindersSeveral studies have used the analysis of variance(ANOVA) statistic test to determine the significance oflaboratory based experimental results [27 28] In thisstudy the ANOVA test was conducted for purposes ofdetermining whether or not there was a statistically sig-nificant difference on low-temperature performance ofcrumb rubber asphalt binders modified with and withoutsilicone oil Since asphalt binders having lower deflection(uf ) at fracture performed very poorly in the field as regardsthermal cracking [4] this study used load-deflection valuesfrom SENB test in statistical analysis e higher the de-flection values the better the low temperature crackingresistance SPSS statistical software was utilized to aid the

statistical computations at three temperatures minus 12degCminus 18degC and minus 24degC respectively by applying one-wayANOVA and a t-test and the results of which are presentedin Tables 4 and 5 respectively

Table 4 indicates that the amount of displacement atminus 12degC was T (6054) 0001 Plt 001 whereas at minus 18degC thedisplacement was T (8061) 0001 Plt 001 and at minus 24degCdisplacement was T (minus 83146) 0001 (Plt 001) Since P

values lt001 significance level the influence of silicone oil ondisplacement of asphalt samples at different temperatureswas found to be statistically significant

Table 5 indicates that the displacement analysis result atminus 12degC was F (5732) 276e minus 30 (Plt 001) whereas thatdisplacement result at minus 18degC was F (2763) 976e minus 15(Plt 001) Finally displacement result at minus 24degC was F(2662) 0000174 (Plt 001) Since all P values are signifi-cant at lt001 level the influence of silicone oil on low-temperature performance of crumb rubber asphalt is foundto be statistically significant

Standard error (SE) is the estimated standard deviationfor the distribution of sample means for an infinite pop-ulation e SE values of the estimates of displacement inSENB test were calculated by performing a paired t teste

Table 4 T test results of displacement at different test temperature

Asphalt binder type Mean (mm) N Std deviation Std error mean T Df SigTest temperature minus 12degCNeat +CR 36009 3289 215842 03764 6054 3288 0001Neat +CR+ SO 32363 3289 185615 03237Test temperature minus 18degCNeat +CR 19971 2027 113464 002520 8061 2026 0001Neat +CR+ SO 19999 2027 114478 002543Test temperature minus 24degCNeat +CR 22378 1553 114058 002894 minus 83146 1552 0001Neat +CR+ SO 15337 1553 087921 002231

12

10

8

6

4

2

0

Neat + CR + SO ndashnotched

Neat + CR + SO ndashunnotched

Frac

ture

toug

hnes

s (kP

a m0

5)

ndash12degC

ndash18degC

ndash24degC

494

646

83

703

100

1

120

(g)

16

14

12

10

8

6

4

2

0

Neat + CR + SO ndashnotched

Neat + CR + SO ndashunnotched

Frac

ture

toug

hnes

s (kP

a m0

5)

ndash12degC

ndash18degC

ndash24degC

607

79

101

666

119

3

139

1

(h)

Figure 5 Low-temperature performance of crumb rubber asphalt considering influence of precracked and uncracked notches Load-displacement curves at (a) minus 12degC (b) minus 18degC and (c) minus 24degC (d) Stiffness modulus of asphalt binders (e) Fracture energy of binders (f )Fracture energy of binders (g) Fracture toughness of binders (h) Fracture toughness of binders

Advances in Materials Science and Engineering 9

laboratory test results before and after silicone oil treat-ment to crumb rubber asphalt were compared e resultsfound that standard error at three temperatures was notmore than 000602 as shown in Table 6 Since a smallervalue of the standard error of the mean indicates a moreprecise estimate of the population mean the results wereconsidered valid

7 Conclusion

In this paper the effect of silicone oil on dispersion and low-temperature fracture performance of crumb rubber binderwas investigated based on SENB AFM and FM testsMaterialcharacterization was analysed by performing the FTIR teste research was driven by the notion that although CR hassucceeded in improving low-temperature performance ofasphalt pavements compatibility between asphalt and crumbrubber still remains a challenge to be solved As part of aneffort to solve the problem and develop sustainable materialssilicone oil was used to improve both rubber particle dis-persion in asphalt and low-temperature fracture perfor-mance is study led to following conclusions

(1) e analysis of molecular structure of siliconeconfirmed that the material was vinyl silicone oilFurther the analysis of asphalt modified with sili-cone oil resulted in generation of new absorptionpeaks with the main peak having Si-O-Si bond isbond indicates that silicone oil is a highly hydro-phobic material (water repellent) and also has

chemical durability which ensures that the siliconeoil is applied in asphalt

(2) e morphological images from the FM test revealedthat the addition of silicone oil improves the dispersionof crumb rubber particles in asphalt binder matrix

(3) e atomic force microscopy results suggested thatsurface roughness increases with the addition ofsilicone oil which implied that there was a change inmicrostructure of the sample Moreover the increasein roughness of the surface implied that bonding ofasphalt with rubber particles was enhanced therebyresulting in improved distribution of rubber particlesin asphalt

(4) e addition of crumb rubber to asphalt generallydecreased the stiffness of the material at low tem-peratures In addition the study concluded thataddition of silicone oil to crumb rubber asphaltresulted in a further decrease of stiffness therebyimproving low-temperature crack resistance evalues of fracture toughness as well as fracture energyindicated that crumb rubber asphalt binders con-taining silicone oil had superior crack resistance thanthe one without silicone oil modification

(5) Analysis of variance and t test results confirmed thatthe influence of silicone oil on displacement wasstatistically significant is means that low-tem-perature performance of a crumb rubber modifiedasphalt is strongly influenced by the addition of thesilicone oil

Table 6 Paired sample test results of displacement at different test temperatures for notched samples

Asphalt binder type N Mean (mm) Std deviation Std error mean99 CI

t Df Sig (2 tailed)Lower Upper

Test temperature minus 12degCNeat +CR 3289 minus 036459 034538 000602 minus 03812 minus 034907 minus 60540 3288 0001Neat +CR+ SOTest temperature minus 18degCNeat +CR 2027 000272 001520 000034 000185 000359 8061 2026 0001Neat +CR+ SOTest temperature minus 24degCNeat +CR 2667 002056 002075 000040 001952 002159 51163 2666 0001Neat +CR+ SO

Table 5 ANOVA test results of displacement at different test temperatures

Displacement Sum of squares Df Mean square F SigTest temperature minus 12degCBetween groups 15196637 3144 4834 5732 276e minus 30Within groups 121428 144 0843Total 15318064 3288Test temperature minus 18degCBetween groups 18759285 3730 5029 2763 976e minus 15Within groups 291212 160 1820Total 19050497 3890Test temperature minus 24degCBetween groups 5993014 2628 2280 2662 0000174Within groups 32556 38 0857Total 6025570 2666

10 Advances in Materials Science and Engineering

(6) Furthermore this study concluded that the im-provement in low-temperature performance ofcrumb rubber modified with silicone oil can becaptured from two perspectives Firstly as indicatedby the analysis of stiffness in FTIR and FM thesilicone oil softened the modified crumb rubberasphalt and enhanced the dispersion of rubberparticles in the binder Softening of asphalt improvescrack resistance Secondly as seen in IR spectrumthe Si-O bond in silicone oil makes it highly hy-drophobic (water repellent) and thus could delay thewater penetration and subsequent freezing of asphaltbinder during water conditioning of samples at lowtemperature resulting in lower stiffness

(7) e comparison between the notched andunnotched samples indicated that the modulus of thenotched binders was lower than that of theunnotched one In addition the unnotched asphaltbinders containing silicone oil did not break at minus 12degCwhich confirmed the great influence of silicone oil onrubberised asphalt low-temperature performance

In spite of results obtained in this study it should bementioned that the research had the following limitationsthe low-temperature performance of crumb rubber con-taining SO was limited to SENB test No BBR test wasconducted Future research can incorporate the BBR test andother techniques to better understand the behaviour ofasphalt modified with silicone oil

Data Availability

e data used to support the findings of this study are in-cluded within the article

Conflicts of Interest

e authors declare that there are no conflicts of interestregarding the publication of this article

Acknowledgments

e authors would like to express their gratitude to theHarbin Institute of Technology for providing laboratoryequipment and materials for experiments is research wasfunded by the National Natural Science Foundation of Chinawith Grant nos 51478152 and 51478154 Furthermore thefees relating to the publication of the manuscript was fundedby the Copperbelt University in Zambia

References

[1] M Marasteanu W Buttlar H Bahia et al Investigation ofLow Temperature Cracking in Asphalt Pavements NationalPooled Fund StudyndashPhase II Minnesota Department ofTransportation Saint Paul MN USA 2012 httphdlhandlenet11299135177

[2] R Velasquez and H Bahia ldquoCritical factors affecting thermalcracking of asphalt pavements towards a comprehensivespecificationrdquo Road Materials and Pavement Design vol 14no sup1 pp 187ndash200 2013

[3] E V Dave H Benjamin H Chelsea M Jared and J LukeldquoImplementation of laboratory testing to predict low tem-perature cracking performance of asphalt pavementsrdquo in 8thRILEM International Symposium on Testing and Character-ization of Sustainable and Innovative Bituminous MaterialsSpringer Berlin Germany 2016

[4] H U Bahia and A Davies ldquoEffect of crumb rubber modifiers(CRM) on performance related properties of asphalt bindersrdquoJournal of Association of Asphalt Paving Technology vol 63pp 414ndash449 1994

[5] T R Hoare and S A M Hesp ldquoLow-temperature fracturetesting of asphalt binders regular and modified systemsrdquoTransportation Research Record Journal of the TransportationResearch Board vol 1728 no 1 pp 36ndash42 2000

[6] P E Sebaaly V T Gopal and J A Epps ldquoLow temperatureproperties of crumb rubber modified bindersrdquo RoadMaterialsand Pavement Design vol 4 no 1 pp 29ndash49 2003

[7] S-S Kim Z D Wysong and J Kovach ldquoLow-temperaturethermal cracking of asphalt binder by asphalt binder crackingdevicerdquo Transportation Research Record Transportation Re-search Record Journal of the Transportation Research Boardvol 1962 no 1 pp 28ndash35 2006

[8] A Zofka and A Braham ldquoComparison of low-temperaturefield performance and laboratory testing of 10 test sections inthe midwestern United Statesrdquo Transportation Research Re-cord Journal of the Transportation Research Board vol 2127no 1 pp 107ndash114 2009

[9] M Pszczoła J Mariusz S Cezary J Jozef and D BohdanldquoEvaluation of low temperature properties of rubberized as-phalt mixturesrdquo Procedia Engineering vol 172 pp 897ndash9042017

[10] P S Wulandari and D Tjandra ldquoUse of crumb rubber as anadditive in asphalt concrete mixturerdquo Procedia Engineeringvol 171 pp 1384ndash1389 2017

[11] M Mull M A Stuart and K Yehia ldquoFracture resistancecharacterization of chemically modified crumb rubber asphaltpavementrdquo Journal of Materials Science vol 37 no 3pp 557ndash566 2002

[12] A Hussain and S A Elmasry ldquoChemically modified crumbrubber effects on rubberized asphalt propertiesrdquo InternationalJournal of Environmental Sciences vol 2 no 4 pp 158ndash1622013

[13] S Zhihao Z-J Wang and G Y Xie ldquoPreparation andperformances of silicone modified asphaltrdquo Fine and SpecialChemical vol 11 2017

[14] Y Li Y Zhang and Y Zhang ldquoMechanical properties ofhigh-density polyethylenescrap rubber composites modifiedwith ethylene-propylene-diene terpolymer dicumyl peroxideand silicone oilrdquo Journal of Applied Polymer Science vol 88no 8 pp 2020ndash2027 2003

[15] C Peng H Zhang Y Zhanping et al ldquoPreparation and anti-icing properties of a superhydrophobic silicone coating onasphalt mixturerdquo Construction and Building Materialsvol 189 pp 227ndash235 2018

[16] C Gorkem and S Burak ldquoPredicting stripping and moistureinduced damage of asphalt concrete prepared with polymermodified bitumen and hydrated limerdquo Construction andBuilding Materials vol 23 no 6 pp 2227ndash2236 2009

[17] J Lin C Meizhu W Shaopeng et al ldquoUtilization of siliconemaintenance materials to improve the moisture sensitivity ofasphalt mixturesrdquo Construction and Building Materialsvol 33 pp 1ndash6 2012

[18] R Zhang Y Zhanping W Hainian Y Mingxiao K Y Yokeand S Chundi ldquoe impact of bio-oil as rejuvenator for aged

Advances in Materials Science and Engineering 11

14000

12000

10000

8000

6000

4000

2000

00 1 2 3 4 5 6 7

Forc

e (m

N)

Displacement (mm)

ndash12degC neat + CR ndash notchedndash12degC neat + CR ndash unnotchedndash12degC neat + CR + SO ndash notchedndash12degC neat + CR + SO ndash unnotched

(a)

18000

16000

14000

12000

10000

8000

6000

4000

2000

00 1 2 3 4 5 6 7

Forc

e (m

N)

Displacement (mm)

ndash18degCndashneat + CR ndash notchedndash18degCndashneat + CR ndash unnotchedndash18degCndashneat + CR + SO ndash notchedndash18degCndashneat + CR + SO ndash unnotched

(b)

18000

16000

14000

12000

10000

8000

6000

4000

2000

0

22000

20000

0 1 2 3 4 5 6 7

Forc

e (m

N)

Displacement (mm)

ndash24degCndashneat + CR ndash notchedndash24degCndashneat + CR ndash unnotchedndash24degCndashneat + CR + SO ndash notchedndash24degCndashneat + CR + SO ndash unnotched

(c)

025

020

015

010

005

000

Stiff

ness

mod

ulus

(MPa

)

Neat + CR + SO ndashnotched

Neat + CR + SO ndashunnotched

ndash12degC

ndash18degC

ndash24degC

004

009

016

005

5

011

3

021

5

(d)800

700

600

500

400

300

200

100

0Neat + CR ndash notched Neat + CR ndash unnotched

Frac

ture

ener

gy (J

m2 )

ndash12degC

ndash18degC

ndash24degC

407

17

195

64

136

94

662

58

461

27

283

24

(e)

1200

1000

800

600

400

200

0Neat + CR + SO ndash

notchedNeat + CR + SO ndash

unnotched

Frac

ture

ener

gy (J

m2 )

ndash12degC

ndash18degC

ndash24degC

600

978

575

02

506

07

998

64

970

99

700

2

(f )

Figure 5 Continued

8 Advances in Materials Science and Engineering

for unnotched samples than for notched samples In generala study found that unnotched binders are more resistant tolow-temperature cracking than notched binders In addi-tion examining the tested samples it was observed that forunmodified samples cracks initiated from the bottom of thesample under the load Whereas for notched samples crackspropagated from the preexisted cracks upwards

66 Statistical Analysis of Displacement in Asphalt BindersSeveral studies have used the analysis of variance(ANOVA) statistic test to determine the significance oflaboratory based experimental results [27 28] In thisstudy the ANOVA test was conducted for purposes ofdetermining whether or not there was a statistically sig-nificant difference on low-temperature performance ofcrumb rubber asphalt binders modified with and withoutsilicone oil Since asphalt binders having lower deflection(uf ) at fracture performed very poorly in the field as regardsthermal cracking [4] this study used load-deflection valuesfrom SENB test in statistical analysis e higher the de-flection values the better the low temperature crackingresistance SPSS statistical software was utilized to aid the

statistical computations at three temperatures minus 12degCminus 18degC and minus 24degC respectively by applying one-wayANOVA and a t-test and the results of which are presentedin Tables 4 and 5 respectively

Table 4 indicates that the amount of displacement atminus 12degC was T (6054) 0001 Plt 001 whereas at minus 18degC thedisplacement was T (8061) 0001 Plt 001 and at minus 24degCdisplacement was T (minus 83146) 0001 (Plt 001) Since P

values lt001 significance level the influence of silicone oil ondisplacement of asphalt samples at different temperatureswas found to be statistically significant

Table 5 indicates that the displacement analysis result atminus 12degC was F (5732) 276e minus 30 (Plt 001) whereas thatdisplacement result at minus 18degC was F (2763) 976e minus 15(Plt 001) Finally displacement result at minus 24degC was F(2662) 0000174 (Plt 001) Since all P values are signifi-cant at lt001 level the influence of silicone oil on low-temperature performance of crumb rubber asphalt is foundto be statistically significant

Standard error (SE) is the estimated standard deviationfor the distribution of sample means for an infinite pop-ulation e SE values of the estimates of displacement inSENB test were calculated by performing a paired t teste

Table 4 T test results of displacement at different test temperature

Asphalt binder type Mean (mm) N Std deviation Std error mean T Df SigTest temperature minus 12degCNeat +CR 36009 3289 215842 03764 6054 3288 0001Neat +CR+ SO 32363 3289 185615 03237Test temperature minus 18degCNeat +CR 19971 2027 113464 002520 8061 2026 0001Neat +CR+ SO 19999 2027 114478 002543Test temperature minus 24degCNeat +CR 22378 1553 114058 002894 minus 83146 1552 0001Neat +CR+ SO 15337 1553 087921 002231

12

10

8

6

4

2

0

Neat + CR + SO ndashnotched

Neat + CR + SO ndashunnotched

Frac

ture

toug

hnes

s (kP

a m0

5)

ndash12degC

ndash18degC

ndash24degC

494

646

83

703

100

1

120

(g)

16

14

12

10

8

6

4

2

0

Neat + CR + SO ndashnotched

Neat + CR + SO ndashunnotched

Frac

ture

toug

hnes

s (kP

a m0

5)

ndash12degC

ndash18degC

ndash24degC

607

79

101

666

119

3

139

1

(h)

Figure 5 Low-temperature performance of crumb rubber asphalt considering influence of precracked and uncracked notches Load-displacement curves at (a) minus 12degC (b) minus 18degC and (c) minus 24degC (d) Stiffness modulus of asphalt binders (e) Fracture energy of binders (f )Fracture energy of binders (g) Fracture toughness of binders (h) Fracture toughness of binders

Advances in Materials Science and Engineering 9

laboratory test results before and after silicone oil treat-ment to crumb rubber asphalt were compared e resultsfound that standard error at three temperatures was notmore than 000602 as shown in Table 6 Since a smallervalue of the standard error of the mean indicates a moreprecise estimate of the population mean the results wereconsidered valid

7 Conclusion

In this paper the effect of silicone oil on dispersion and low-temperature fracture performance of crumb rubber binderwas investigated based on SENB AFM and FM testsMaterialcharacterization was analysed by performing the FTIR teste research was driven by the notion that although CR hassucceeded in improving low-temperature performance ofasphalt pavements compatibility between asphalt and crumbrubber still remains a challenge to be solved As part of aneffort to solve the problem and develop sustainable materialssilicone oil was used to improve both rubber particle dis-persion in asphalt and low-temperature fracture perfor-mance is study led to following conclusions

(1) e analysis of molecular structure of siliconeconfirmed that the material was vinyl silicone oilFurther the analysis of asphalt modified with sili-cone oil resulted in generation of new absorptionpeaks with the main peak having Si-O-Si bond isbond indicates that silicone oil is a highly hydro-phobic material (water repellent) and also has

chemical durability which ensures that the siliconeoil is applied in asphalt

(2) e morphological images from the FM test revealedthat the addition of silicone oil improves the dispersionof crumb rubber particles in asphalt binder matrix

(3) e atomic force microscopy results suggested thatsurface roughness increases with the addition ofsilicone oil which implied that there was a change inmicrostructure of the sample Moreover the increasein roughness of the surface implied that bonding ofasphalt with rubber particles was enhanced therebyresulting in improved distribution of rubber particlesin asphalt

(4) e addition of crumb rubber to asphalt generallydecreased the stiffness of the material at low tem-peratures In addition the study concluded thataddition of silicone oil to crumb rubber asphaltresulted in a further decrease of stiffness therebyimproving low-temperature crack resistance evalues of fracture toughness as well as fracture energyindicated that crumb rubber asphalt binders con-taining silicone oil had superior crack resistance thanthe one without silicone oil modification

(5) Analysis of variance and t test results confirmed thatthe influence of silicone oil on displacement wasstatistically significant is means that low-tem-perature performance of a crumb rubber modifiedasphalt is strongly influenced by the addition of thesilicone oil

Table 6 Paired sample test results of displacement at different test temperatures for notched samples

Asphalt binder type N Mean (mm) Std deviation Std error mean99 CI

t Df Sig (2 tailed)Lower Upper

Test temperature minus 12degCNeat +CR 3289 minus 036459 034538 000602 minus 03812 minus 034907 minus 60540 3288 0001Neat +CR+ SOTest temperature minus 18degCNeat +CR 2027 000272 001520 000034 000185 000359 8061 2026 0001Neat +CR+ SOTest temperature minus 24degCNeat +CR 2667 002056 002075 000040 001952 002159 51163 2666 0001Neat +CR+ SO

Table 5 ANOVA test results of displacement at different test temperatures

Displacement Sum of squares Df Mean square F SigTest temperature minus 12degCBetween groups 15196637 3144 4834 5732 276e minus 30Within groups 121428 144 0843Total 15318064 3288Test temperature minus 18degCBetween groups 18759285 3730 5029 2763 976e minus 15Within groups 291212 160 1820Total 19050497 3890Test temperature minus 24degCBetween groups 5993014 2628 2280 2662 0000174Within groups 32556 38 0857Total 6025570 2666

10 Advances in Materials Science and Engineering

(6) Furthermore this study concluded that the im-provement in low-temperature performance ofcrumb rubber modified with silicone oil can becaptured from two perspectives Firstly as indicatedby the analysis of stiffness in FTIR and FM thesilicone oil softened the modified crumb rubberasphalt and enhanced the dispersion of rubberparticles in the binder Softening of asphalt improvescrack resistance Secondly as seen in IR spectrumthe Si-O bond in silicone oil makes it highly hy-drophobic (water repellent) and thus could delay thewater penetration and subsequent freezing of asphaltbinder during water conditioning of samples at lowtemperature resulting in lower stiffness

(7) e comparison between the notched andunnotched samples indicated that the modulus of thenotched binders was lower than that of theunnotched one In addition the unnotched asphaltbinders containing silicone oil did not break at minus 12degCwhich confirmed the great influence of silicone oil onrubberised asphalt low-temperature performance

In spite of results obtained in this study it should bementioned that the research had the following limitationsthe low-temperature performance of crumb rubber con-taining SO was limited to SENB test No BBR test wasconducted Future research can incorporate the BBR test andother techniques to better understand the behaviour ofasphalt modified with silicone oil

Data Availability

e data used to support the findings of this study are in-cluded within the article

Conflicts of Interest

e authors declare that there are no conflicts of interestregarding the publication of this article

Acknowledgments

e authors would like to express their gratitude to theHarbin Institute of Technology for providing laboratoryequipment and materials for experiments is research wasfunded by the National Natural Science Foundation of Chinawith Grant nos 51478152 and 51478154 Furthermore thefees relating to the publication of the manuscript was fundedby the Copperbelt University in Zambia

References

[1] M Marasteanu W Buttlar H Bahia et al Investigation ofLow Temperature Cracking in Asphalt Pavements NationalPooled Fund StudyndashPhase II Minnesota Department ofTransportation Saint Paul MN USA 2012 httphdlhandlenet11299135177

[2] R Velasquez and H Bahia ldquoCritical factors affecting thermalcracking of asphalt pavements towards a comprehensivespecificationrdquo Road Materials and Pavement Design vol 14no sup1 pp 187ndash200 2013

[3] E V Dave H Benjamin H Chelsea M Jared and J LukeldquoImplementation of laboratory testing to predict low tem-perature cracking performance of asphalt pavementsrdquo in 8thRILEM International Symposium on Testing and Character-ization of Sustainable and Innovative Bituminous MaterialsSpringer Berlin Germany 2016

[4] H U Bahia and A Davies ldquoEffect of crumb rubber modifiers(CRM) on performance related properties of asphalt bindersrdquoJournal of Association of Asphalt Paving Technology vol 63pp 414ndash449 1994

[5] T R Hoare and S A M Hesp ldquoLow-temperature fracturetesting of asphalt binders regular and modified systemsrdquoTransportation Research Record Journal of the TransportationResearch Board vol 1728 no 1 pp 36ndash42 2000

[6] P E Sebaaly V T Gopal and J A Epps ldquoLow temperatureproperties of crumb rubber modified bindersrdquo RoadMaterialsand Pavement Design vol 4 no 1 pp 29ndash49 2003

[7] S-S Kim Z D Wysong and J Kovach ldquoLow-temperaturethermal cracking of asphalt binder by asphalt binder crackingdevicerdquo Transportation Research Record Transportation Re-search Record Journal of the Transportation Research Boardvol 1962 no 1 pp 28ndash35 2006

[8] A Zofka and A Braham ldquoComparison of low-temperaturefield performance and laboratory testing of 10 test sections inthe midwestern United Statesrdquo Transportation Research Re-cord Journal of the Transportation Research Board vol 2127no 1 pp 107ndash114 2009

[9] M Pszczoła J Mariusz S Cezary J Jozef and D BohdanldquoEvaluation of low temperature properties of rubberized as-phalt mixturesrdquo Procedia Engineering vol 172 pp 897ndash9042017

[10] P S Wulandari and D Tjandra ldquoUse of crumb rubber as anadditive in asphalt concrete mixturerdquo Procedia Engineeringvol 171 pp 1384ndash1389 2017

[11] M Mull M A Stuart and K Yehia ldquoFracture resistancecharacterization of chemically modified crumb rubber asphaltpavementrdquo Journal of Materials Science vol 37 no 3pp 557ndash566 2002

[12] A Hussain and S A Elmasry ldquoChemically modified crumbrubber effects on rubberized asphalt propertiesrdquo InternationalJournal of Environmental Sciences vol 2 no 4 pp 158ndash1622013

[13] S Zhihao Z-J Wang and G Y Xie ldquoPreparation andperformances of silicone modified asphaltrdquo Fine and SpecialChemical vol 11 2017

[14] Y Li Y Zhang and Y Zhang ldquoMechanical properties ofhigh-density polyethylenescrap rubber composites modifiedwith ethylene-propylene-diene terpolymer dicumyl peroxideand silicone oilrdquo Journal of Applied Polymer Science vol 88no 8 pp 2020ndash2027 2003

[15] C Peng H Zhang Y Zhanping et al ldquoPreparation and anti-icing properties of a superhydrophobic silicone coating onasphalt mixturerdquo Construction and Building Materialsvol 189 pp 227ndash235 2018

[16] C Gorkem and S Burak ldquoPredicting stripping and moistureinduced damage of asphalt concrete prepared with polymermodified bitumen and hydrated limerdquo Construction andBuilding Materials vol 23 no 6 pp 2227ndash2236 2009

[17] J Lin C Meizhu W Shaopeng et al ldquoUtilization of siliconemaintenance materials to improve the moisture sensitivity ofasphalt mixturesrdquo Construction and Building Materialsvol 33 pp 1ndash6 2012

[18] R Zhang Y Zhanping W Hainian Y Mingxiao K Y Yokeand S Chundi ldquoe impact of bio-oil as rejuvenator for aged

Advances in Materials Science and Engineering 11

for unnotched samples than for notched samples In generala study found that unnotched binders are more resistant tolow-temperature cracking than notched binders In addi-tion examining the tested samples it was observed that forunmodified samples cracks initiated from the bottom of thesample under the load Whereas for notched samples crackspropagated from the preexisted cracks upwards

66 Statistical Analysis of Displacement in Asphalt BindersSeveral studies have used the analysis of variance(ANOVA) statistic test to determine the significance oflaboratory based experimental results [27 28] In thisstudy the ANOVA test was conducted for purposes ofdetermining whether or not there was a statistically sig-nificant difference on low-temperature performance ofcrumb rubber asphalt binders modified with and withoutsilicone oil Since asphalt binders having lower deflection(uf ) at fracture performed very poorly in the field as regardsthermal cracking [4] this study used load-deflection valuesfrom SENB test in statistical analysis e higher the de-flection values the better the low temperature crackingresistance SPSS statistical software was utilized to aid the

statistical computations at three temperatures minus 12degCminus 18degC and minus 24degC respectively by applying one-wayANOVA and a t-test and the results of which are presentedin Tables 4 and 5 respectively

Table 4 indicates that the amount of displacement atminus 12degC was T (6054) 0001 Plt 001 whereas at minus 18degC thedisplacement was T (8061) 0001 Plt 001 and at minus 24degCdisplacement was T (minus 83146) 0001 (Plt 001) Since P

values lt001 significance level the influence of silicone oil ondisplacement of asphalt samples at different temperatureswas found to be statistically significant

Table 5 indicates that the displacement analysis result atminus 12degC was F (5732) 276e minus 30 (Plt 001) whereas thatdisplacement result at minus 18degC was F (2763) 976e minus 15(Plt 001) Finally displacement result at minus 24degC was F(2662) 0000174 (Plt 001) Since all P values are signifi-cant at lt001 level the influence of silicone oil on low-temperature performance of crumb rubber asphalt is foundto be statistically significant

Standard error (SE) is the estimated standard deviationfor the distribution of sample means for an infinite pop-ulation e SE values of the estimates of displacement inSENB test were calculated by performing a paired t teste

Table 4 T test results of displacement at different test temperature

Asphalt binder type Mean (mm) N Std deviation Std error mean T Df SigTest temperature minus 12degCNeat +CR 36009 3289 215842 03764 6054 3288 0001Neat +CR+ SO 32363 3289 185615 03237Test temperature minus 18degCNeat +CR 19971 2027 113464 002520 8061 2026 0001Neat +CR+ SO 19999 2027 114478 002543Test temperature minus 24degCNeat +CR 22378 1553 114058 002894 minus 83146 1552 0001Neat +CR+ SO 15337 1553 087921 002231

12

10

8

6

4

2

0

Neat + CR + SO ndashnotched

Neat + CR + SO ndashunnotched

Frac

ture

toug

hnes

s (kP

a m0

5)

ndash12degC

ndash18degC

ndash24degC

494

646

83

703

100

1

120

(g)

16

14

12

10

8

6

4

2

0

Neat + CR + SO ndashnotched

Neat + CR + SO ndashunnotched

Frac

ture

toug

hnes

s (kP

a m0

5)

ndash12degC

ndash18degC

ndash24degC

607

79

101

666

119

3

139

1

(h)

Figure 5 Low-temperature performance of crumb rubber asphalt considering influence of precracked and uncracked notches Load-displacement curves at (a) minus 12degC (b) minus 18degC and (c) minus 24degC (d) Stiffness modulus of asphalt binders (e) Fracture energy of binders (f )Fracture energy of binders (g) Fracture toughness of binders (h) Fracture toughness of binders

Advances in Materials Science and Engineering 9

laboratory test results before and after silicone oil treat-ment to crumb rubber asphalt were compared e resultsfound that standard error at three temperatures was notmore than 000602 as shown in Table 6 Since a smallervalue of the standard error of the mean indicates a moreprecise estimate of the population mean the results wereconsidered valid

7 Conclusion

In this paper the effect of silicone oil on dispersion and low-temperature fracture performance of crumb rubber binderwas investigated based on SENB AFM and FM testsMaterialcharacterization was analysed by performing the FTIR teste research was driven by the notion that although CR hassucceeded in improving low-temperature performance ofasphalt pavements compatibility between asphalt and crumbrubber still remains a challenge to be solved As part of aneffort to solve the problem and develop sustainable materialssilicone oil was used to improve both rubber particle dis-persion in asphalt and low-temperature fracture perfor-mance is study led to following conclusions

(1) e analysis of molecular structure of siliconeconfirmed that the material was vinyl silicone oilFurther the analysis of asphalt modified with sili-cone oil resulted in generation of new absorptionpeaks with the main peak having Si-O-Si bond isbond indicates that silicone oil is a highly hydro-phobic material (water repellent) and also has

chemical durability which ensures that the siliconeoil is applied in asphalt

(2) e morphological images from the FM test revealedthat the addition of silicone oil improves the dispersionof crumb rubber particles in asphalt binder matrix

(3) e atomic force microscopy results suggested thatsurface roughness increases with the addition ofsilicone oil which implied that there was a change inmicrostructure of the sample Moreover the increasein roughness of the surface implied that bonding ofasphalt with rubber particles was enhanced therebyresulting in improved distribution of rubber particlesin asphalt

(4) e addition of crumb rubber to asphalt generallydecreased the stiffness of the material at low tem-peratures In addition the study concluded thataddition of silicone oil to crumb rubber asphaltresulted in a further decrease of stiffness therebyimproving low-temperature crack resistance evalues of fracture toughness as well as fracture energyindicated that crumb rubber asphalt binders con-taining silicone oil had superior crack resistance thanthe one without silicone oil modification

(5) Analysis of variance and t test results confirmed thatthe influence of silicone oil on displacement wasstatistically significant is means that low-tem-perature performance of a crumb rubber modifiedasphalt is strongly influenced by the addition of thesilicone oil

Table 6 Paired sample test results of displacement at different test temperatures for notched samples

Asphalt binder type N Mean (mm) Std deviation Std error mean99 CI

t Df Sig (2 tailed)Lower Upper

Test temperature minus 12degCNeat +CR 3289 minus 036459 034538 000602 minus 03812 minus 034907 minus 60540 3288 0001Neat +CR+ SOTest temperature minus 18degCNeat +CR 2027 000272 001520 000034 000185 000359 8061 2026 0001Neat +CR+ SOTest temperature minus 24degCNeat +CR 2667 002056 002075 000040 001952 002159 51163 2666 0001Neat +CR+ SO

Table 5 ANOVA test results of displacement at different test temperatures

Displacement Sum of squares Df Mean square F SigTest temperature minus 12degCBetween groups 15196637 3144 4834 5732 276e minus 30Within groups 121428 144 0843Total 15318064 3288Test temperature minus 18degCBetween groups 18759285 3730 5029 2763 976e minus 15Within groups 291212 160 1820Total 19050497 3890Test temperature minus 24degCBetween groups 5993014 2628 2280 2662 0000174Within groups 32556 38 0857Total 6025570 2666

10 Advances in Materials Science and Engineering

(6) Furthermore this study concluded that the im-provement in low-temperature performance ofcrumb rubber modified with silicone oil can becaptured from two perspectives Firstly as indicatedby the analysis of stiffness in FTIR and FM thesilicone oil softened the modified crumb rubberasphalt and enhanced the dispersion of rubberparticles in the binder Softening of asphalt improvescrack resistance Secondly as seen in IR spectrumthe Si-O bond in silicone oil makes it highly hy-drophobic (water repellent) and thus could delay thewater penetration and subsequent freezing of asphaltbinder during water conditioning of samples at lowtemperature resulting in lower stiffness

(7) e comparison between the notched andunnotched samples indicated that the modulus of thenotched binders was lower than that of theunnotched one In addition the unnotched asphaltbinders containing silicone oil did not break at minus 12degCwhich confirmed the great influence of silicone oil onrubberised asphalt low-temperature performance

In spite of results obtained in this study it should bementioned that the research had the following limitationsthe low-temperature performance of crumb rubber con-taining SO was limited to SENB test No BBR test wasconducted Future research can incorporate the BBR test andother techniques to better understand the behaviour ofasphalt modified with silicone oil

Data Availability

e data used to support the findings of this study are in-cluded within the article

Conflicts of Interest

e authors declare that there are no conflicts of interestregarding the publication of this article

Acknowledgments

e authors would like to express their gratitude to theHarbin Institute of Technology for providing laboratoryequipment and materials for experiments is research wasfunded by the National Natural Science Foundation of Chinawith Grant nos 51478152 and 51478154 Furthermore thefees relating to the publication of the manuscript was fundedby the Copperbelt University in Zambia

References

[1] M Marasteanu W Buttlar H Bahia et al Investigation ofLow Temperature Cracking in Asphalt Pavements NationalPooled Fund StudyndashPhase II Minnesota Department ofTransportation Saint Paul MN USA 2012 httphdlhandlenet11299135177

[2] R Velasquez and H Bahia ldquoCritical factors affecting thermalcracking of asphalt pavements towards a comprehensivespecificationrdquo Road Materials and Pavement Design vol 14no sup1 pp 187ndash200 2013

[3] E V Dave H Benjamin H Chelsea M Jared and J LukeldquoImplementation of laboratory testing to predict low tem-perature cracking performance of asphalt pavementsrdquo in 8thRILEM International Symposium on Testing and Character-ization of Sustainable and Innovative Bituminous MaterialsSpringer Berlin Germany 2016

[4] H U Bahia and A Davies ldquoEffect of crumb rubber modifiers(CRM) on performance related properties of asphalt bindersrdquoJournal of Association of Asphalt Paving Technology vol 63pp 414ndash449 1994

[5] T R Hoare and S A M Hesp ldquoLow-temperature fracturetesting of asphalt binders regular and modified systemsrdquoTransportation Research Record Journal of the TransportationResearch Board vol 1728 no 1 pp 36ndash42 2000

[6] P E Sebaaly V T Gopal and J A Epps ldquoLow temperatureproperties of crumb rubber modified bindersrdquo RoadMaterialsand Pavement Design vol 4 no 1 pp 29ndash49 2003

[7] S-S Kim Z D Wysong and J Kovach ldquoLow-temperaturethermal cracking of asphalt binder by asphalt binder crackingdevicerdquo Transportation Research Record Transportation Re-search Record Journal of the Transportation Research Boardvol 1962 no 1 pp 28ndash35 2006

[8] A Zofka and A Braham ldquoComparison of low-temperaturefield performance and laboratory testing of 10 test sections inthe midwestern United Statesrdquo Transportation Research Re-cord Journal of the Transportation Research Board vol 2127no 1 pp 107ndash114 2009

[9] M Pszczoła J Mariusz S Cezary J Jozef and D BohdanldquoEvaluation of low temperature properties of rubberized as-phalt mixturesrdquo Procedia Engineering vol 172 pp 897ndash9042017

[10] P S Wulandari and D Tjandra ldquoUse of crumb rubber as anadditive in asphalt concrete mixturerdquo Procedia Engineeringvol 171 pp 1384ndash1389 2017

[11] M Mull M A Stuart and K Yehia ldquoFracture resistancecharacterization of chemically modified crumb rubber asphaltpavementrdquo Journal of Materials Science vol 37 no 3pp 557ndash566 2002

[12] A Hussain and S A Elmasry ldquoChemically modified crumbrubber effects on rubberized asphalt propertiesrdquo InternationalJournal of Environmental Sciences vol 2 no 4 pp 158ndash1622013

[13] S Zhihao Z-J Wang and G Y Xie ldquoPreparation andperformances of silicone modified asphaltrdquo Fine and SpecialChemical vol 11 2017

[14] Y Li Y Zhang and Y Zhang ldquoMechanical properties ofhigh-density polyethylenescrap rubber composites modifiedwith ethylene-propylene-diene terpolymer dicumyl peroxideand silicone oilrdquo Journal of Applied Polymer Science vol 88no 8 pp 2020ndash2027 2003

[15] C Peng H Zhang Y Zhanping et al ldquoPreparation and anti-icing properties of a superhydrophobic silicone coating onasphalt mixturerdquo Construction and Building Materialsvol 189 pp 227ndash235 2018

[16] C Gorkem and S Burak ldquoPredicting stripping and moistureinduced damage of asphalt concrete prepared with polymermodified bitumen and hydrated limerdquo Construction andBuilding Materials vol 23 no 6 pp 2227ndash2236 2009

[17] J Lin C Meizhu W Shaopeng et al ldquoUtilization of siliconemaintenance materials to improve the moisture sensitivity ofasphalt mixturesrdquo Construction and Building Materialsvol 33 pp 1ndash6 2012

[18] R Zhang Y Zhanping W Hainian Y Mingxiao K Y Yokeand S Chundi ldquoe impact of bio-oil as rejuvenator for aged

Advances in Materials Science and Engineering 11

laboratory test results before and after silicone oil treat-ment to crumb rubber asphalt were compared e resultsfound that standard error at three temperatures was notmore than 000602 as shown in Table 6 Since a smallervalue of the standard error of the mean indicates a moreprecise estimate of the population mean the results wereconsidered valid

7 Conclusion

In this paper the effect of silicone oil on dispersion and low-temperature fracture performance of crumb rubber binderwas investigated based on SENB AFM and FM testsMaterialcharacterization was analysed by performing the FTIR teste research was driven by the notion that although CR hassucceeded in improving low-temperature performance ofasphalt pavements compatibility between asphalt and crumbrubber still remains a challenge to be solved As part of aneffort to solve the problem and develop sustainable materialssilicone oil was used to improve both rubber particle dis-persion in asphalt and low-temperature fracture perfor-mance is study led to following conclusions

(1) e analysis of molecular structure of siliconeconfirmed that the material was vinyl silicone oilFurther the analysis of asphalt modified with sili-cone oil resulted in generation of new absorptionpeaks with the main peak having Si-O-Si bond isbond indicates that silicone oil is a highly hydro-phobic material (water repellent) and also has

chemical durability which ensures that the siliconeoil is applied in asphalt

(2) e morphological images from the FM test revealedthat the addition of silicone oil improves the dispersionof crumb rubber particles in asphalt binder matrix

(3) e atomic force microscopy results suggested thatsurface roughness increases with the addition ofsilicone oil which implied that there was a change inmicrostructure of the sample Moreover the increasein roughness of the surface implied that bonding ofasphalt with rubber particles was enhanced therebyresulting in improved distribution of rubber particlesin asphalt

(4) e addition of crumb rubber to asphalt generallydecreased the stiffness of the material at low tem-peratures In addition the study concluded thataddition of silicone oil to crumb rubber asphaltresulted in a further decrease of stiffness therebyimproving low-temperature crack resistance evalues of fracture toughness as well as fracture energyindicated that crumb rubber asphalt binders con-taining silicone oil had superior crack resistance thanthe one without silicone oil modification

(5) Analysis of variance and t test results confirmed thatthe influence of silicone oil on displacement wasstatistically significant is means that low-tem-perature performance of a crumb rubber modifiedasphalt is strongly influenced by the addition of thesilicone oil

Table 6 Paired sample test results of displacement at different test temperatures for notched samples

Asphalt binder type N Mean (mm) Std deviation Std error mean99 CI

t Df Sig (2 tailed)Lower Upper

Test temperature minus 12degCNeat +CR 3289 minus 036459 034538 000602 minus 03812 minus 034907 minus 60540 3288 0001Neat +CR+ SOTest temperature minus 18degCNeat +CR 2027 000272 001520 000034 000185 000359 8061 2026 0001Neat +CR+ SOTest temperature minus 24degCNeat +CR 2667 002056 002075 000040 001952 002159 51163 2666 0001Neat +CR+ SO

Table 5 ANOVA test results of displacement at different test temperatures

Displacement Sum of squares Df Mean square F SigTest temperature minus 12degCBetween groups 15196637 3144 4834 5732 276e minus 30Within groups 121428 144 0843Total 15318064 3288Test temperature minus 18degCBetween groups 18759285 3730 5029 2763 976e minus 15Within groups 291212 160 1820Total 19050497 3890Test temperature minus 24degCBetween groups 5993014 2628 2280 2662 0000174Within groups 32556 38 0857Total 6025570 2666

10 Advances in Materials Science and Engineering

(6) Furthermore this study concluded that the im-provement in low-temperature performance ofcrumb rubber modified with silicone oil can becaptured from two perspectives Firstly as indicatedby the analysis of stiffness in FTIR and FM thesilicone oil softened the modified crumb rubberasphalt and enhanced the dispersion of rubberparticles in the binder Softening of asphalt improvescrack resistance Secondly as seen in IR spectrumthe Si-O bond in silicone oil makes it highly hy-drophobic (water repellent) and thus could delay thewater penetration and subsequent freezing of asphaltbinder during water conditioning of samples at lowtemperature resulting in lower stiffness

(7) e comparison between the notched andunnotched samples indicated that the modulus of thenotched binders was lower than that of theunnotched one In addition the unnotched asphaltbinders containing silicone oil did not break at minus 12degCwhich confirmed the great influence of silicone oil onrubberised asphalt low-temperature performance

In spite of results obtained in this study it should bementioned that the research had the following limitationsthe low-temperature performance of crumb rubber con-taining SO was limited to SENB test No BBR test wasconducted Future research can incorporate the BBR test andother techniques to better understand the behaviour ofasphalt modified with silicone oil

Data Availability

e data used to support the findings of this study are in-cluded within the article

Conflicts of Interest

e authors declare that there are no conflicts of interestregarding the publication of this article

Acknowledgments

e authors would like to express their gratitude to theHarbin Institute of Technology for providing laboratoryequipment and materials for experiments is research wasfunded by the National Natural Science Foundation of Chinawith Grant nos 51478152 and 51478154 Furthermore thefees relating to the publication of the manuscript was fundedby the Copperbelt University in Zambia

References

[1] M Marasteanu W Buttlar H Bahia et al Investigation ofLow Temperature Cracking in Asphalt Pavements NationalPooled Fund StudyndashPhase II Minnesota Department ofTransportation Saint Paul MN USA 2012 httphdlhandlenet11299135177

[2] R Velasquez and H Bahia ldquoCritical factors affecting thermalcracking of asphalt pavements towards a comprehensivespecificationrdquo Road Materials and Pavement Design vol 14no sup1 pp 187ndash200 2013

[3] E V Dave H Benjamin H Chelsea M Jared and J LukeldquoImplementation of laboratory testing to predict low tem-perature cracking performance of asphalt pavementsrdquo in 8thRILEM International Symposium on Testing and Character-ization of Sustainable and Innovative Bituminous MaterialsSpringer Berlin Germany 2016

[4] H U Bahia and A Davies ldquoEffect of crumb rubber modifiers(CRM) on performance related properties of asphalt bindersrdquoJournal of Association of Asphalt Paving Technology vol 63pp 414ndash449 1994

[5] T R Hoare and S A M Hesp ldquoLow-temperature fracturetesting of asphalt binders regular and modified systemsrdquoTransportation Research Record Journal of the TransportationResearch Board vol 1728 no 1 pp 36ndash42 2000

[6] P E Sebaaly V T Gopal and J A Epps ldquoLow temperatureproperties of crumb rubber modified bindersrdquo RoadMaterialsand Pavement Design vol 4 no 1 pp 29ndash49 2003

[7] S-S Kim Z D Wysong and J Kovach ldquoLow-temperaturethermal cracking of asphalt binder by asphalt binder crackingdevicerdquo Transportation Research Record Transportation Re-search Record Journal of the Transportation Research Boardvol 1962 no 1 pp 28ndash35 2006

[8] A Zofka and A Braham ldquoComparison of low-temperaturefield performance and laboratory testing of 10 test sections inthe midwestern United Statesrdquo Transportation Research Re-cord Journal of the Transportation Research Board vol 2127no 1 pp 107ndash114 2009

[9] M Pszczoła J Mariusz S Cezary J Jozef and D BohdanldquoEvaluation of low temperature properties of rubberized as-phalt mixturesrdquo Procedia Engineering vol 172 pp 897ndash9042017

[10] P S Wulandari and D Tjandra ldquoUse of crumb rubber as anadditive in asphalt concrete mixturerdquo Procedia Engineeringvol 171 pp 1384ndash1389 2017

[11] M Mull M A Stuart and K Yehia ldquoFracture resistancecharacterization of chemically modified crumb rubber asphaltpavementrdquo Journal of Materials Science vol 37 no 3pp 557ndash566 2002

[12] A Hussain and S A Elmasry ldquoChemically modified crumbrubber effects on rubberized asphalt propertiesrdquo InternationalJournal of Environmental Sciences vol 2 no 4 pp 158ndash1622013

[13] S Zhihao Z-J Wang and G Y Xie ldquoPreparation andperformances of silicone modified asphaltrdquo Fine and SpecialChemical vol 11 2017

[14] Y Li Y Zhang and Y Zhang ldquoMechanical properties ofhigh-density polyethylenescrap rubber composites modifiedwith ethylene-propylene-diene terpolymer dicumyl peroxideand silicone oilrdquo Journal of Applied Polymer Science vol 88no 8 pp 2020ndash2027 2003

[15] C Peng H Zhang Y Zhanping et al ldquoPreparation and anti-icing properties of a superhydrophobic silicone coating onasphalt mixturerdquo Construction and Building Materialsvol 189 pp 227ndash235 2018

[16] C Gorkem and S Burak ldquoPredicting stripping and moistureinduced damage of asphalt concrete prepared with polymermodified bitumen and hydrated limerdquo Construction andBuilding Materials vol 23 no 6 pp 2227ndash2236 2009

[17] J Lin C Meizhu W Shaopeng et al ldquoUtilization of siliconemaintenance materials to improve the moisture sensitivity ofasphalt mixturesrdquo Construction and Building Materialsvol 33 pp 1ndash6 2012

[18] R Zhang Y Zhanping W Hainian Y Mingxiao K Y Yokeand S Chundi ldquoe impact of bio-oil as rejuvenator for aged

Advances in Materials Science and Engineering 11

(6) Furthermore this study concluded that the im-provement in low-temperature performance ofcrumb rubber modified with silicone oil can becaptured from two perspectives Firstly as indicatedby the analysis of stiffness in FTIR and FM thesilicone oil softened the modified crumb rubberasphalt and enhanced the dispersion of rubberparticles in the binder Softening of asphalt improvescrack resistance Secondly as seen in IR spectrumthe Si-O bond in silicone oil makes it highly hy-drophobic (water repellent) and thus could delay thewater penetration and subsequent freezing of asphaltbinder during water conditioning of samples at lowtemperature resulting in lower stiffness

(7) e comparison between the notched andunnotched samples indicated that the modulus of thenotched binders was lower than that of theunnotched one In addition the unnotched asphaltbinders containing silicone oil did not break at minus 12degCwhich confirmed the great influence of silicone oil onrubberised asphalt low-temperature performance

In spite of results obtained in this study it should bementioned that the research had the following limitationsthe low-temperature performance of crumb rubber con-taining SO was limited to SENB test No BBR test wasconducted Future research can incorporate the BBR test andother techniques to better understand the behaviour ofasphalt modified with silicone oil

Data Availability

e data used to support the findings of this study are in-cluded within the article

Conflicts of Interest

e authors declare that there are no conflicts of interestregarding the publication of this article

Acknowledgments

e authors would like to express their gratitude to theHarbin Institute of Technology for providing laboratoryequipment and materials for experiments is research wasfunded by the National Natural Science Foundation of Chinawith Grant nos 51478152 and 51478154 Furthermore thefees relating to the publication of the manuscript was fundedby the Copperbelt University in Zambia

References

[1] M Marasteanu W Buttlar H Bahia et al Investigation ofLow Temperature Cracking in Asphalt Pavements NationalPooled Fund StudyndashPhase II Minnesota Department ofTransportation Saint Paul MN USA 2012 httphdlhandlenet11299135177

[2] R Velasquez and H Bahia ldquoCritical factors affecting thermalcracking of asphalt pavements towards a comprehensivespecificationrdquo Road Materials and Pavement Design vol 14no sup1 pp 187ndash200 2013

[3] E V Dave H Benjamin H Chelsea M Jared and J LukeldquoImplementation of laboratory testing to predict low tem-perature cracking performance of asphalt pavementsrdquo in 8thRILEM International Symposium on Testing and Character-ization of Sustainable and Innovative Bituminous MaterialsSpringer Berlin Germany 2016

[4] H U Bahia and A Davies ldquoEffect of crumb rubber modifiers(CRM) on performance related properties of asphalt bindersrdquoJournal of Association of Asphalt Paving Technology vol 63pp 414ndash449 1994

[5] T R Hoare and S A M Hesp ldquoLow-temperature fracturetesting of asphalt binders regular and modified systemsrdquoTransportation Research Record Journal of the TransportationResearch Board vol 1728 no 1 pp 36ndash42 2000

[6] P E Sebaaly V T Gopal and J A Epps ldquoLow temperatureproperties of crumb rubber modified bindersrdquo RoadMaterialsand Pavement Design vol 4 no 1 pp 29ndash49 2003

[7] S-S Kim Z D Wysong and J Kovach ldquoLow-temperaturethermal cracking of asphalt binder by asphalt binder crackingdevicerdquo Transportation Research Record Transportation Re-search Record Journal of the Transportation Research Boardvol 1962 no 1 pp 28ndash35 2006

[8] A Zofka and A Braham ldquoComparison of low-temperaturefield performance and laboratory testing of 10 test sections inthe midwestern United Statesrdquo Transportation Research Re-cord Journal of the Transportation Research Board vol 2127no 1 pp 107ndash114 2009

[9] M Pszczoła J Mariusz S Cezary J Jozef and D BohdanldquoEvaluation of low temperature properties of rubberized as-phalt mixturesrdquo Procedia Engineering vol 172 pp 897ndash9042017

[10] P S Wulandari and D Tjandra ldquoUse of crumb rubber as anadditive in asphalt concrete mixturerdquo Procedia Engineeringvol 171 pp 1384ndash1389 2017

[11] M Mull M A Stuart and K Yehia ldquoFracture resistancecharacterization of chemically modified crumb rubber asphaltpavementrdquo Journal of Materials Science vol 37 no 3pp 557ndash566 2002

[12] A Hussain and S A Elmasry ldquoChemically modified crumbrubber effects on rubberized asphalt propertiesrdquo InternationalJournal of Environmental Sciences vol 2 no 4 pp 158ndash1622013

[13] S Zhihao Z-J Wang and G Y Xie ldquoPreparation andperformances of silicone modified asphaltrdquo Fine and SpecialChemical vol 11 2017

[14] Y Li Y Zhang and Y Zhang ldquoMechanical properties ofhigh-density polyethylenescrap rubber composites modifiedwith ethylene-propylene-diene terpolymer dicumyl peroxideand silicone oilrdquo Journal of Applied Polymer Science vol 88no 8 pp 2020ndash2027 2003

[15] C Peng H Zhang Y Zhanping et al ldquoPreparation and anti-icing properties of a superhydrophobic silicone coating onasphalt mixturerdquo Construction and Building Materialsvol 189 pp 227ndash235 2018

[16] C Gorkem and S Burak ldquoPredicting stripping and moistureinduced damage of asphalt concrete prepared with polymermodified bitumen and hydrated limerdquo Construction andBuilding Materials vol 23 no 6 pp 2227ndash2236 2009

[17] J Lin C Meizhu W Shaopeng et al ldquoUtilization of siliconemaintenance materials to improve the moisture sensitivity ofasphalt mixturesrdquo Construction and Building Materialsvol 33 pp 1ndash6 2012

[18] R Zhang Y Zhanping W Hainian Y Mingxiao K Y Yokeand S Chundi ldquoe impact of bio-oil as rejuvenator for aged

Advances in Materials Science and Engineering 11

asphalt binderrdquo Construction and Building Materials vol 196pp 134ndash143 2019

[19] W H Daly Relationship between Chemical Makeup of Bindersand Engineering Performance (No Project 20-015 (Topic 47-13))Atomic Force Microscopy (AFM) 2017

[20] S Iliuta A M H Simon O MMihai M Tony and K T KaildquoField validation study of low-temperature performancegrading tests for asphalt bindersrdquo Transportation ResearchRecord Journal of Transportation Board vol 1875 no 1pp 14ndash21 2004

[21] H Bahia R Velasquez H Tabatabaee and S Puchalski ldquoerole of asphalt binder fracture properties in thermal crackingperformance of mixtures and pavementsrdquo in Proceedings ofthe CTAA Annual Conference Vancouver Canada November2012

[22] A Groza A Surmeian and M Ganciu ldquoInfrared spectralinvestigation of organosilicon compounds under coronacharge injection in air at atmospheric pressurerdquo Journal ofOptoelectronics and Advanced Materials vol 7 no 5pp 2545ndash2548 2005

[23] Q F An K Guo M T Li and L X Huang ldquoSynthesis andcharacterization of polyether-b-polysiloxane and its appli-cation in antifoaming agentrdquo Silicone Material vol 6 2008

[24] Q Yang and X Li ldquoMechanism and effectiveness of a silicone-based warm mix additiverdquo Journal of Materials in Civil En-gineering vol 31 no 1 Article ID 04018336 2019

[25] A Kanabar ldquoPhysical and chemical aging behavior of asphaltcements from two northern Ontario pavement trialsrdquo Doctoraldissertation Queenrsquos University Kingston Canada 2010

[26] K W Kim J K Seung S D Young and T-S Park ldquoFracturetoughness of polymer-modified asphalt concrete at lowtemperaturesrdquo Canadian Journal of Civil Engineering vol 30no 2 pp 406ndash413 2003

[27] T Gandhi ldquoEffects of warm asphalt additives on asphaltbinder and mixture propertiesrdquo Doctoral thesis ClemsonUniversity Clemson SC USA 2008httpstigerprintsclemsoneduall_dissertations203

[28] C Akisetty F Xiao T Gandhi and S Amirkhanian ldquoEsti-mating correlations between rheological and engineeringproperties of rubberized asphalt concrete mixtures containingwarm mix asphalt additiverdquo Construction and Building Ma-terials vol 25 no 2 pp 950ndash956 2011

12 Advances in Materials Science and Engineering

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