review article a review on using crumb rubber in

Review ArticleA Review on Using Crumb Rubber in Reinforcement ofAsphalt Pavement

Nuha Salim Mashaan Asim Hassan Ali Mohamed Rehan Karim and Mahrez Abdelaziz

Center for Transportation Research Faculty of Engineering University of Malaya 50603 Kuala Lumpur Malaysia

Correspondence should be addressed to Nuha Salim Mashaan nuhamashaansiswaumedumy

Received 28 August 2013 Accepted 22 October 2013 Published 30 January 2014

Academic Editors T H D Flores-Sahagun and Q Ma

Copyright copy 2014 Nuha Salim Mashaan et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

An immense problem affecting environmental pollution is the increase of waste tyre vehicles In an attempt to decrease the magni-tude of this issue crumb rubber modifier (CRM) obtained fromwaste tyre rubber has gained interest in asphalt reinforcementTheuse of crumb rubber in the reinforcement of asphalt is considered as a smart solution for sustainable development by reusing wastematerials and it is believed that crumb rubber modifier (CRM) could be an alternative polymer material in improving hot mixasphalt performance properties In this paper a critical review on the use of crumb rubber in reinforcement of asphalt pavementwill be presented and discussed It will also include a review on the effects of CRM on the stiffness rutting and fatigue resistanceof road pavement construction

1 Introduction

Roadways are an integral aspect of transportation infrastruc-ture Road construction engineers must consider the primaryuserrsquos requirements of safety as well as the economy Toachieve this goal designers should take into account threefundamental requirements which include environmental fac-tors traffic flow and asphalt mixtures materials [1ndash3] Inasphalt concrete (AC) bitumen as a binder serves two majorfunctions in road pavement first to hold the aggregatesfirmly and second to act as a sealant against water Howeverdue to some distresses like fatigue failure the performanceand durability of bitumen are highly affected by changeswith time in terms of its characteristics which can lead tothe cracking of pavement [2] In general road pavementdistresses are related to asphalt binder (bitumen) and asphaltmixture properties Rutting and fatigue cracking are amongthe major distresses that lead to permanent failure of thepavement surface The dynamic properties and durability ofconventional asphalt however are deficient in resisting pave-ment distresses Hence the task of current asphalt researchersand engineers is to look for different kinds of polymer mod-ified asphalt such as crumb rubber [3] The term reinforced

pavements refers to the use of one or more reinforcing layerswithin the pavement structure Another application of pave-ment reinforcement is the use of reinforcement elements inasphalt overlays to provide an adequate tensile strength tothe asphalt layer and to prevent failures of the pavement suchas reflection cracking Thus the difference between the twoapplications is that the first application is used as measure toovercome the distress failure which already occurred in thepavement while the second application is used as measure toprevent the existence of such failure Modificationreinforce-ment of asphalt binder is possible during different stages of itsusage either in between binder production andmix processesor before paving mix production [4] According to Larsenet al [5] the bitumen modification provides binders with

(i) sufficient increase in consistency at the highest tem-perature in pavements to prevent plastic deformation

(ii) an increase in flexibility and elasticity of binders at lowtemperature to avoid crack deformations and loss ofchippings

(iii) an improvement of adhesion to the bitumen intoaggregates

Hindawi Publishing Corporatione Scientific World JournalVolume 2014 Article ID 214612 21 pageshttpdxdoiorg1011552014214612

2 The Scientific World Journal

(iv) improved homogeneity high thermo stability andaging resistance which helps reduce the hardeningand initial aging of the binders during mixing andconstruction

Worldwide there are many additives used as reinforcingmaterial into the asphalt mixes among these additives usedis the CRM [3 4] In this paper asphalt pavement designcriteria will be displayed and a considerable review on theuse of crumb rubber in asphalt pavement reinforcement willbe presented and discussed It also includes a review on theeffects of CRM on the stiffness rutting and fatigue resistanceof road pavement In order to understand the asphalt-rubberreinforcement technology asphalt properties and crumbrubber characteristics will be illustrated

2 Asphalt Pavement Design

The design of asphalt mixture involves the selection andproportioning of materials to obtain the desired propertiesin the finished product Asphalt concrete (AC) is designed toresist rutting fatigue low temperatures cracking and otherdistressesThe serious distresses associatedwith asphalt pave-ments are cracking which occurs at intermediate and lowtemperatures and permanent deformation which occurs athigh temperaturesThese distresses reduce the services life ofthe pavement and elevate the maintenance costs [6] Asphaltcement binds the aggregate particles together enhancing thestability of the mixture and providing resistance to deforma-tion under induced tensile compressive and shear stressesThe performance of asphalt mixture is a function of asphaltcement aggregate and its volumetric properties In recentyears there has been a rapid increase in using additives inasphalt concrete mixtures to improve its properties Asphaltroad pavements are defined as asphalt layers built boundover a granular base Due to this the total pavement structuredeflects due to traffic loads thus these types of pavements areknown as flexible pavements A flexible pavement structureis composed of various layers of materials Basically thepavement structure is divided into three layers namely bitu-minous surfacing (surface course) road base (base course)and subbase [6] as shown in Figure 1

Flexible pavements could have one of the three typicalcross section geometries as shown in Figure 2 At the pave-ment edge between the pavement edge and adjacent soil twoforces exist which are vertical friction 119865 and lateral passivepressure119875The friction force (119865) relies on relativemovementcoefficient of friction and the lateral passive pressure Lateralpassive pressure (119875) varies depending on soil type and weightof the soil subjected to the pavement As illustrated inFigure 2(a) the soil wedge is small and the two forces (119865and 119875) can be ignored On the other hand as shown inFigures 2(b) and 2(c) the friction and passive forces maybe significant and the pavement edge can move laterally andvertically [7]

Asphalt concrete (AC) should have high stiffness to beable to resist permanent deformation On the other hand themixtures should have enough tensile stress at the bottom ofthe asphalt layer to resist fatigue cracking after many load

Surface courseBase course

Subbase course

Figure 1 Typical flexible pavement structure

applications Figure 3 presents the orientation of principalstresses with respect to position of rolling wheel load [8]

The overall objective for the design of asphalt pavingmixes is to determine an economical blend and gradation aswell as asphalt binder that will yield a mix having sufficientbinder to ensure a durable pavement sufficient stabilitysufficient voids in the total compactedmix to allow for a slightamount of additional compaction under traffic loading with-out flushing and sufficient workability to permit efficientplacement of the mix without segregation [9]

The increased demand on highway roads might reduceits strength properties and make roads more susceptibleto permanent distresses and failure In general pavementperformance properties are affected by the bitumen binderproperties it is known that the conventional bitumen has alimited range of rheological properties and durability that arenot sufficient enough to resist pavement distressesThereforebitumen researchers and engineers are looking for differenttypes of bitumenmodifiersThere aremanymodification pro-cesses and additives that are currently used in bitumen mod-ifications such as styrene butadiene styrene (SBS) styrene-butadiene rubber (SBR) ethylene vinyl acetate (EVA) andcrumb rubber modifier (CRM) The use of commercialpolymers such as SBS and SBR in road and pavement con-structionwill increase the construction cost as they are highlyexpensive materials However with the use of alternativematerials such as crumb rubber modifier (CRM) it willdefinitely be environmentally beneficial and not only it canimprove the bitumen binder properties and durability but ithas also a potential to be cost effective [10ndash12]

3 Historical Experiment of Using CrumbRubber in Pavement

In 1840s the earliest experiments had involved incorporatingnatural rubber into asphalt binder to increase its engineeringperformance properties The process of asphalt modificationinvolving natural and synthetic rubber was introduced asearly as 1843 [13] In 1923 natural and synthetic rubbermodifications in asphalt were further improved [14 15]According toYildirim [15] the development of asphalt-rubbermaterials being used as joint sealers patches andmembranesbegan in the late 1930s The first attempt to modify asphaltbinders by adding rubber was made in 1898 by Gauedmbergwho patented a process for manufacturing asphalt rubberFrance was then given credit for installing the first road witha crumb rubber modified asphalt surfacing material [2]

The Scientific World Journal 3

156Flexible pavement

156 F

P

Sub-grade

(a) Full cross section


156 F

P

Sub-grade

(b) At grade cross section

156 156Flexible pavement

F

P

Sub-grade

(c) Cut cross section

Figure 2 Flexible pavement typical cross section geometries [7]

1205901

1205901

1205901

1205901

1205901

1205901

12059021205902

1205902

12059021205902

1205902

120590y120590y

120590y120590y

120590y

120590y

120590x120590x120590x 120590x 120590x 120590x

120591xy

120591xy

120591xy

120591xy

Shear stress

Stre

ss

Time

Vertical stress

Horizontal stress

After wheel load Before wheel load

Figure 3 Stress beneath a rolling wheel load [8]

In 1950 the use of scrap tyre in asphalt was reported [16]In the early 1960s CharlesMcDonald working as headMate-rial Engineer for the city of Phoenix Arizona found thatafter completing the mixing of crumb rubber with the virginasphalt cement and allowing it to blend for mix duration of45ndash60minutes there were newmaterial properties producedThere was swelling in the size of the rubber particles at highertemperatures allowing for higher concentrations of liquidasphalt contents in pavement mixes [17] The application ofrubber-modified asphalt pavement started in Alaska in 1979Placement of seven rubberised pavements totalling 4 lane kmusing the Plus Ride dry process between 1979 and 1981 wasreported The performance of these sections in relation to

mixing compaction durability fatigue stability and flow andtyre traction and skid resistance were described Asphalt rub-ber using the wet process was first applied in Alaska in 1988[18] Around 1983 in the Republic of South Africa asphalt-rubber seals were first introduced Over 150 000 tons ofasphalt were paved over the first 10 years From the evalua-tion it was concluded that the asphalt rubber stress absorbingmembrane interlayers (SAMIs) and asphalt performed aboveexpectations The asphalt rubber overlays out-performed thevirgin asphalt under identical conditions by a large marginAsphalt-rubber and SAMIs are especially suited for highlytrafficked roads with pavements in structural distress andwhere overlays will eliminate reworking options in congested


traffic situations [19] Lundy et al [20] presented three casestudies using crumb rubberwith both thewet process and dryprocess at Mt St Helens Project Oregon Dot and PortlandOregonThe results showed that even after a decade of servicecrumb rubber products have excellent resistance to thermalcracking Although asphalt-rubber mixtures can be builtsuccessfully quality control ought to be maintained for goodperformance Rubber Pavement Association found that usingtyre rubber in open-graded mixture binder could decreasetyre noise by approximately 50 Also in spray applicationsrubber particles ofmultiple sizes had better sound absorption[21] Moreover another advantage of using asphalt rubberis to increase the life span of the pavement However rec-ommendations were made to assess the cost effectiveness ofasphalt rubber [22]The benefits of using crumb rubbermod-ified bitumen are lower susceptibility to varying temperatureon a daily basis more resistance to deformation at higherpavement temperature proved age resistance propertieshigher fatigue life for mixes and better adhesion betweenaggregate and binder Ever since then the use of crumb rub-ber has gained interest in pavement modification as it isevident that crumb tyre rubber can improve the bitumenperformance properties [23ndash26]

In Malaysia the use of rubber as an additive for roadpavement construction supposedly started in the 1940s butthere has not been any official record of such practices Thefirst recorded trial using rubberised bitumen technology wasreported in 1988 the wet mix process was used with the mixof rubber additives in the form of latex into bitumen binder[27] In 1993 another rubberised road trial using waste glovesand natural rubber latex was carried out in Negeri Sembilan[28]

4 Interaction Mechanism ofAsphalt Rubber Elements

Previous researchers found that when incorporating the rub-ber powder into asphalt cement the rubber will degrade andits effectiveness is reduced on prolonged storage at elevatedtemperatures [2]The improvements effected in the engineer-ing properties of Asphalt Rubber (AR) depend largely on theparticle dispersion the molecular level dissolution and thephysical interaction of rubber with asphalt Temperature andtime of digestion are highly important factors affecting thedegree of dispersion for slightly vulcanized and vulcanizednatural rubber For instance the optimum digestion time fora slightly vulcanized rubber powder is 30 minutes at 180∘Cand 8 h at 140∘C [29] On the other hand vulcanized rubberpowder requires merely 10 minutes digestion time at 160∘C toachieve the same resultsThe easy dispersion of unvulcanisedpowder is because of the state of the rubber and fineness ofthe powder (95 percent passing 02mm sieve) Vulcanisedpowders are harder to disperse because they are coarser(about 30 percent retained on 0715mm sieve and 70 percentretained on 02mm sieve) and also due to vulcanizationAccording to Jensen and Abdelrahman [30] there are threestages of interaction that have been evaluated with regard toasphalt rubber binder (i) an early stage that occurs imme-diately after mixing crumb rubber with bitumen (ii) an

Aromatics

80

80

80

60

60

60

40

40

40

20

20

20Saturates Polar compounds(R + A + PA)

Figure 4 Compositional representation on ternary diagram of 640different crudes [36]

intermediate storage stage during which the binder is heldat elevated temperatures for up to a few hours beforemixing with aggregate (iii) an extended (storage) stagewhen bitumen-rubber blends are stored for extended periodsbefore mixing with aggregate Miknis and Michon [31]investigated the application of nuclear magnetic resonanceimaging to rubberised bitumen binder The application ofthis technology led to investigating the different interactionbetween crumb rubber and asphalt such as swelling by asphaltmolecules possible dissolution of rubber components inasphalt and devolatitisation and crosskicking in rubber Theoutcome of this study is swelling of rubber particles whichmay depend on asphalt molecules According to Shen et al[32] the factors which affect the digestion process of theasphalt and rubbers blends are rubber content rubber gra-dations binder viscosity binder source and blending con-ditions of time and temperature

5 Key Factors That Influence the Properties ofAsphalt Rubber

51 Asphalt Properties Asphalt is a dark black semisolidmaterial obtained from the atmospheric and vacuum distil-lation of crude oil during petroleum refining which is thensubjected to various other processes [33] It is considered asa thermoplastic viscoelastic adhesive which is used for roadand highway pavement engineering primarily because of itsgood cementing power and waterproof properties [34] Theanalysis of bitumen indicates that the mix is approximately8ndash11 hydrogen 82ndash86 carbon 0ndash2 oxygen and 0ndash6 sulphur by weight with minimal amounts of nitrogenvanadium nickel and iron In addition it is a complexmixture of awide variety ofmolecules paraffinic naphthenicand aromatics including heteroatoms [34] Most producersuse atmospheric or vacuum distillation to refine the asphaltcement While there is some solvent refining and air blowingutilised they are clearly of secondary importance [35] Basedon chemical analysis crude oil may be predominantly paraf-finic naphthenic or aromatic with of paraffinic and naph-thenic combinations being most commonThere are approx-imately 1500 different crudes produced globally Accordingto the yield and quality of the resultant product only a few ofthese presented in Figure 4 (compositions are in percentageof weight and represent the +210∘C fraction) are consid-ered appropriate for the manufacture of bitumen [36 37]

The Scientific World Journal 5M

olar

mas

s-pa

raffi

ne C

nH

2n+2

0

142

292

422

0

5

10

15

20

25

30Ca

rbon

num

ber

minus18

0 200 400 600 800 1000 1200 1400∘F760∘C64953931520493 427

Atmospheric equivalent boiling point

nC10

nC14

nC16

nC18

nC20

nC22

nC24

nC26

nC11

nC6

Polar polyfunctionalcompounds

Figure 5 Evolution of molecular weights and structures as afunction of the boiling point [38]

The most commonly used method and probably the oldestmethod is the atmospheric vacuum distillation of suitablecrudes which produce straight-run residual asphalt The airblowing process is done to give oxidized or semiblown prod-ucts which are inherently upgrades of low-grade asphaltCrude heavy fractions are defined as molecules containingmore than 25 carbon atoms (C25) which increases with theboiling point (Figure 5) as well as the molecular weight thedensity the viscosity the refractive index (aromaticity) andthe polarity (contents of heteroatoms and metals) [38 39]These fractions are enriched in highly polar compounds suchas resins and asphaltenes When compared to the crude orlighter fractions the highly polar compounds are composedof various chemical species of different aromaticity func-tional heteroatoms and metal contents [38 39]

511 Asphalt Chemical Components The chemical compo-nent of asphalt cement can be identified as asphaltenes andmaltenes The maltenes can be further subdivided into threegroups of saturated aromatic and resins The polar natureof the resins provides the asphalt its adhesive propertiesThey also act as dispersing agents for the asphaltenes Resinsprovide adhesion properties and ductility for the asphaltmaterials The viscous-elastic properties of asphalt and itsproperties as a paving binder are determined by the differingpercentages between asphaltenes and maltenes fraction [40ndash42] Figure 6 shows the representative structures of fourgeneric groups (SARA) saturated aromatic resins (which areform the maltene fraction) and asphaltenes This model isbased on the colloidalmodel [43 44]The complexity contentof heteroatom aromatic and increase of molecular weightare in the order of S lt A lt R lt A (saturates lt aromatics ltresins lt asphaltenes) [45] A study by Loeber et al [46] illus-trated the rheological properties related to asphalt colloidalbehaviour Also it possesses a strong temperature depen-dence on rheological properties organised by the interactionof individual constitution (asphaltenes resins aromaticsand saturates) Loeber et al [46] reported that an increasein one of these constitutions would change the structureand rheological behaviour of asphalt cement Thus asphaltwith high asphaltenesresins ratio would lead to a network

structure with more rigidity and elasticity (low in phaseangle and high in complex shear modulus) unlike the caseof asphalt with high resinsasphaltenes ratio which leads tohigh viscous behaviour higher softening points and lowerpenetrations

Resins are an intermediate weight semisolid fractionformed of aromatic rings with side chains Also resinsare polar molecules that act as peptizing agents to preventasphaltenesmolecules fromcoagulatingThe lightestmolecu-lar weight materials are the nonpolar oils Oils generally havea high proportion of chains as compared to the number ofrings From the literature the resins and oils are referred tocollectively as maltenes In general asphaltenes produce thebulk of the bitumen while resins contribute to adhesion andductility and oils influence flow and viscosity properties [47]According to the microstructure and the colloidal systemasphaltenes are diffused into an oily matrix of maltenesencased by a shell of resins whereby its thickness varies withthe temperature that is being tested [48] Thus bitumencomposition and temperatures are strongly dependent on themechanical properties andmicrostructure of bitumen and onthe degree of aromatisation of the maltenes and the concen-tration of asphaltenes [48 49]

512 Asphalt Polarity and Morphology Asphalt has anotherimportant property which is polarity which is the separationof charge within a molecule Polarity is an important factorsystem because it refers to molecules managing themselvesinto preferred orientations According to Robertson [50]most of the naturally occurring heteroatoms nitrogen sulfuroxygen andmetals are strongly dependent on polarity withinthese molecules Also oxidation products upon aging arepolar and further contribute to the polarity of the entire sys-temThe physicochemical properties have an obvious signifi-cant effect on asphalt and each reflects the nature of the crudeoil used to prepare it Pfeiffer and Saal [51] suggested thatasphalt cement dispersed phases are composed of an aromaticcore surrounded by layers of less aromatic molecules and dis-persed in a relatively aliphatic solvent phase However theydo not point out that there are distinct boundaries betweendispersed and solvent phases as found in soapmicelles How-ever they suggest that it ranges from low to high aromaticitythat is from the solvent phase to the centres of the entitiesconstituting the dispersed phase as shown in Figure 7

According to Robertson [50] themost consistent descrip-tion or model of petroleum asphalt polarity is as fol-lows Asphalt cement is a collection of polar and nonpolarmolecules (i) the polar molecules are associated strongly toform organised structures and represent a more stable ther-modynamic state (ii) The nonpolar model has the ability todissociate the organised structure but again there are possiblevariations from asphalt sources and its viscous behaviours arehighly dependent on the temperature

Using current day technology the morphology of asphalthas been studied in order to verify the asphalt structureThusFigure 8 presents the topographic atomic force microscopy(AFM) images of two different grades of asphalt cementshowing a flat background where another phase is dispersed[52]


S

SS

S

NN

OH

Saturates(paraffins)

Resins

Bitumen

Aromatics

Asphaltenes

Figure 6 Representative structures of asphalt fractions [43]

In the image of the left side of Figure 8 the dispersedphase displays a range of pale and dark lines frequentlyregarded as ldquobeesrdquo or ldquobee structuresrdquo However with theimage on the right side where the bee-like structures arenot independent of one another they are substituted byldquomultiarm star-shapesrdquo [52] A dispersed phase with a ldquobee-likerdquo appearance as presented in Figure 8 is attributed toasphaltenes which is also supported by Pauli et al [53]However no correlation was found between the atomic forcemicroscopy morphology and the composition made up ofasphaltenes polar aromatics naphthene aromatics and sat-urates [52]

52 Crumb Rubber Properties The use of rubber crumbsinstead of polymer depends on the desired properties of themodified bitumen for a particular application However thechoice is also determined to a certain extent by the cost ofmodification and the availability of the modifier [2] Therequired properties are preferably obtained with minimalcost The growth of vehicle productions year by year hasgenerated wasted tyres Due to limitation of disposal area andenvironmental problem the recycling of these vehicles tyres asindustrial wastes has been encouraged and the production ofrubber crumbs from it has found it suitable for use asmodifierinto bitumen Also it offers other benefits such as using withless complicated blending equipment and minimal require-ment to modify the asphalt Comparing the use of polymeras a modifier taking the two fundamental points cited abovethe cost using polymer is much higher than using rubbercrumbs and its availability is less compared to rubber crumbsEven though the properties of using polymers may be betterthey are comparable to those of rubberised asphalt

521 Crumb Rubber Constitutions and ConcentrationCrumb rubber or waste tyre rubber is a blend of syntheticrubber natural rubber carbon black antioxidants fillersand extender type of oils which are soluble in hot pavinggrade Asphalt rubber is obtained by the incorporation ofcrumb rubber from ground tyres in asphalt binder at certainconditions of time and temperature using either dry process(method that adds granulated or crumb rubber modifier(CRM) from scrap tires as a substitute for a percentage of theaggregate in the asphalt concrete mixture not as part of theasphalt binder) or wet processes (method of modifying theasphalt binder with CRM from scrap tires before the binderis added to form the asphalt concrete mixture) There aretwo different methods in the use of tyre rubber in asphaltbinders first one is by dissolving crumb rubber in the asphaltas binder modifier Second one is by substituting a portion offine aggregates with ground rubber that does not completelyreact with bitumen [22]

According to laboratory binder tests [10ndash12] it is clearthat rubber crumb content played a main role in influencingsignificantly the performance and rheological properties ofrubberised bitumen binders It could enhance the perfor-mance properties of asphalt pavement resistance againstdeformation during construction and road services Theincrease in rubber crumb content was from 4 to 20 thusindicating a liner increase in softening point ductility elasticrecovery viscosity complex shear modulus and rutting fac-tor This phenomenon could be explained by the absorptionof rubber particles with lighter fraction oil of bitumen lead-ing to increase in rubber particles during swelling during theblending process The increase in rubber content by 16 and20 showed a corresponding increase in Brookfield viscosityvalue that is higher than SHRP specification limits (3 Pa)


(a) (Sol-type) (b) Flocculated asphaltene micelles

(c) Gel structure of an asphaltic

Figure 7 Asphalt colloidal model [51]

These make the two stated percentages unacceptable for fieldconstruction during asphalt pavement mixture construction

Regarding the low temperature performance an investi-gationwith 18ndash22of rubber content showed change thatwaslittle significance within this range in affecting the tensile andfracture performance of the bitumen compared to varying thebinder content between 6 and 9 by bitumen weight [22 54]A study byKhalid [55] found that higher binder content led tolonger fatigue life of rubberised bitumen mixture and betterresistance to rutting as well as results showing good resistanceto fracture and fatigue cracking Liu et al [56] found thatcontent of crumb rubber is the most significant affectingfactor followed by crumb rubber type and lastly the size ofthe particle

522 Crumb Rubber Grinding Process and Particle SizeCrumb rubber is made by shredding scrap tyre which is aparticular material free of fibre and steel The rubber particle

is graded and found in many sizes and shapes as shown inFigure 9 To produce crumb rubber initially it is importantto reduce the size of the tyres There are two techniques toproduce crumb rubber ambient grinding and the cryogenicprocess [57] In the crumb rubber market there are threemain classes based on particle size

(a) type 1 or grade A 10-mesh coarse crumb rubber(b) type 2 or grade B 14- to 20-mesh crumb rubber(c) type 3 30-mesh crumb rubber

Mesh size designation indicates the first sieve with anupper range specification between 5 and 10 of materialretained Ambient grinding process can be divided into twomethods granulation and cracker mills Ambient describesthe temperature when the waste tyres rubber size is reducedThe material is loaded inside the crack mill or granulatorat ambient temperature Whereas cryogenic tyre grinding


(a) (b)

Figure 8 Topographic AFM images of two types of asphalt [52]

6mm rubber

(a)

Minus 20ndash30 mesh

(b)

20 mesh rubber

(c)

10 mesh rubber

(d)

Figure 9 Different type of crumb rubber based on particle size

consists of freezing the scrap tyre rubber using liquid nitrogenuntil it becomes brittle and then cracking the frozen rubberinto smaller particles with a hammer mill The resultingmaterial is composed of smooth clean flat particlesThe highcost of this process is considered a disadvantage due to theadded cost of liquid nitrogen [3]

The particles size disruption of crumb rubber influencedthe physical properties of asphalt-rubber blend In generalsmall difference in the particles size has no significant effectson blend properties However the crumb rubber size cancertainlymake a big difference A study [58] reported that theparticle size effects of CRM on high temperature properties


of rubberised bitumen binders was an influential factor onviscoelastic properties Also coarser rubber produced amod-ified binder with high shear modules and an increased con-tent of the crumb rubber decreased the creep stiffness whichin tandem displayed better thermal cracking resistance

In summary the primarymechanism of the interaction isswelling of the rubber particles caused by the absorption oflight fractions into these particles and stiffening of the resid-ual binder phase [58ndash61]The rubber particles are constrictedin their movement into the binder matrix to move about dueto the swelling process which limits the free space betweenthe rubber particles Compared to the coarser particles thefiner particles swell easily thus developing higher bindermodification [58 59]The swelling capacity of rubber particleis linked to the penetration grade of the binder crude sourceand the nature of the crumb rubber modifier [60]

53 Interaction Process Variables Interaction process vari-ables consist of curing profile of temperature and durationand mixing shear energy [12 58 59 62] A study [63] studiedthe effect of the mixing types on the properties of rubberisedasphalt An ordinary propeller-type mixer and the highspeed shear mixer were used The study indicated that theresultant binder produced using the high-speed shear mixerappears to have slightly superior properties as comparedto that produced using the propeller-type mixer It showedthat the viscosity and softening point of the rubberisedasphalt produced using the high-speed shearmixer producedhigher agitation level and shearing action that can chop theswollen rubber particles within a certain volume of binderThus the absorbent of the lighter oily fraction was increaseddue to the large amount of the small rubber particles A studyby Thodesen et al [64] indicated that processing procedureand tyre type play an important role in the determinationof rubberised bitumen viscosity Interaction between crumbrubber and bitumen binders is referred to as a physical inter-action where the crumb rubber through diffusion absorbsthe aromatic fraction of the bitumen binders which leads toswelling of the crumb rubber particles This particle swellingcompounded with reduction in the oily fraction of the binderresults in increased viscosity in the rubberised bitumenbinder In general the bitumen binder and ground tyre rub-ber are mixed together and blended at elevated temperaturesfor differing periods of time prior to using them as a pavingbinder These two factors work together to evaluate the per-formance properties of rubberised bitumen binder throughblending process of asphalt rubber interactionThis variationin mixing time and temperature results due to the normalactivities which are related to bitumen paving construction[2] Nevertheless the consistency of asphalt rubber can beaffected by the time and temperature used to combine thecomponents and thus must be cautiously used for its opti-mum potential to be achieved The increase in blending timeshowed insignificant difference on rubberised asphalt prop-erties in the case of 30 and 60 minutes whereas the increasein blending temperature corresponded to the increase inBrookfield viscosity softening point ductility elastic recov-ery and complex shear modulus [10ndash12] Several studies [6265ndash67] showed that longer reaction time for production of

the asphalt rubber apparently caused increased viscosity dueto the increased rubber mass through binder absorption Onthe other hand [12 61 68ndash70] reported that the reaction timehas no significant effect on the selection of the optimal bindercontent In addition there was no difference in the molecularsize variation between the control binder and the asphalt rub-ber binders Also blending time had insignificant differenceon asphalt rubber physical and rheological properties anda rather slight influence on the performance properties ofrubberised asphalt

54 Elasticity of Tyre Rubber Themain characteristics of rub-ber is its property of high elasticity which allows it to undergolarge deformations from which almost complete instanta-neous recovery is achieved when the load is removed [71]This property of high elasticity derives from the molecularstructure of rubber Rubber belongs to the class of materialsknown as polymers and is also referred to as an elastomerThe properties of an elastomer rubber are as follows (a) themolecules are very long and are able to rotate freely aboutthe bonds joining neighbouring molecular units (b) Themolecules are joined either chemically or mechanically at anumber of sites to form a three-dimensional network Thesejoints are termed cross-linked (c) Apart from being cross-linked themolecules are able tomove freely past one anotherthat is the Van der Waalrsquos forces are small

Similar to asphalt rubber is a thermoplastic visco-elasticmaterial whose deformation response under load is related toboth temperature and rate of strain However the deforma-tion of rubber is relatively incentive to temperature changewhere at both low rates of strain and at temperature wellabove the ambient the material remains elastic The widerrange of elastic behaviour of rubber compared to that of bitu-men largely results from the cross-linking of the long rubbermolecules Rubber is alsomuchmore ductile than bitumen atlow temperatures and high loading rates [2 3]

6 Rheological and Physical Characteristics ofAsphalt Rubber

61 Temperature Susceptibility (Newtonian Behaviour) Thetemperature susceptibility was defined as a ratio of Newto-nian viscosities at 25∘C and 60∘C [72] The binder contentin the asphaltic mix is usually less than 7 but it plays avery significant role in the overall properties of the compositematerial It strongly affects both the load spreading capabilityand resistance to distortion under heavy traffic The defor-mation response of a binder in a mix under load depends onits temperature sensitivity the temperature range is subjectedto rate of strain and the geometry of binder between theaggregate particlesTherefore it is logical to use a binder withlower temperature susceptibility particularly when the rangeof working temperatures is very high [2] The concept of thepenetration index (PI) was introduced by Pfeiffer and VanDoormaal [73] to measure both the binderrsquos temperaturesusceptibility and in particular its rheological type in terms


Appl

ied

stres

s (120590

)

t0 t1

Stra

in (120576

)

Time-t

Time-t

(a) Elastic response

Stra

in (120576

)

Time-t

(b) Viscous response

Strain (120576)

Instantaneous

Instantaneous

elasticity

Creep underconstant stress

Delayedrecovery

recovery

Permanentdeformation

Time-t

(c) Viscoelastic response

Figure 10 General behaviour of elastic viscous and viscoelastic material under constant stress loading [75]

of deviation from Newtonian behaviour PI is obtained fromthe relationship

119889 log pen119889119879=(20 minus PI10 + PI)50

(1)

Normal road paving asphalt has a PI value betweenminus1 and+1 Asphalt with PI below minus2 is substantially Newtonian andcharacterised by brittleness at low temperature Asphalt withPI above +2 is far less temperature susceptible is less brittleat low temperature indicates marked time dependent elasticproperties and shows deviations fromNewtonian behaviourespecially at large strain rates [74]The coefficients of temper-ature susceptibility (CTS) based on viscosity measurementsin the temperature range 60∘ndash80∘C were used to assess thebehaviour of rubberised asphalt binder with temperatureCTS is obtains from (2) as shown in

CTS =log (log 120578

1198791

log 1205781198792

)

log (11987921198791) (2)

where 119879 is Temp ∘F and 1205781198791

and 1205781198792

are viscosities measuredat temperatures 119879

1and 119879

2

In 1984 a research study found that 4 rubber is effectivein reducing the temperature susceptibility of virgin binders by

a factor of at least two Hence asphalt rubber ismore resistantto rapid changes in temperature [74]

Mashaan and Karim [12] investigated a good correlationbetween temperature susceptibility and rheological proper-ties of crumb rubbermodified asphalt in termof elasticity andsoftening point data

62 Viscoelastic Behaviour (Dynamic Shear) Asphalt cementbinders are referred to as viscoelastic materials becausethey exhibit combined behaviour (properties) of elastic andviscousmaterial as presented in Figure 10(a) with the removalof the applied stress from the material there is a completerecovery to the original position Figure 10(b) explains thebehaviour of a viscous material in case the strain of the mate-rial increases through time under stable stress Figure 10(c)illustrates the behaviour of a viscoelasticmaterial when stablestress increases the strain over a long period of time andwhen the applied stress is removed the material loses itsability in attaining its original position resulting in permanentdeformation According to Van der Poel [75] generally thestiffness modulus of bitumen binders can be defined by

119878 (119905) =120590

120576 (119905) (3)


where 119878(119905) is dependent stiffness modulus (Pa) (119905) is loadingtime (s) 120590 is the applied constant uniaxial stress (Pa) and120576(119905) refers to uniaxial strain at time 119905 (mm) Since asphaltis a viscoelastic material its rheological properties are verysensitive to temperature as well as to the rate of loadingWithrespect to temperature the most frequent problems of roadpavement are rutting fatigue cracking and thermal crackingDynamic shear rheometer (DSR) was used to measure anddetermine the rheological properties of the asphalt binder atdifferent stresstemperature sweep and various frequenciesDSR testing included parameters of complex shear modulus(119866lowast) storage modulus (1198661015840) loss modulus (11986610158401015840) and phaseangle (120575) The formula to calculate the 119866lowast 1198661015840 and 11986610158401015840 as wellas 120575 in (4) respectively is demonstrated as follows

119866lowast

= (120591

120574)

1198661015840

= cos (120575) (120591120574)

11986610158401015840

= sin (120575) (120591120574)

120575 =119866

11986610158401015840

(4)

where 119866lowast is the complex shear modulus 120591 is the shear stress120574 is the shear strain 1198661015840 is the storage modulus 11986610158401015840 is the lossmodulus and 120575 is the phase angle

Navarro et al [40] studied the rheological characteristicsof ground tire rubber-modified asphalt The experiment wasperformed in a controlled-stress Haake RS150 rheometerThe study aimed at comparing the viscoelastic behaviour offive ground tyres rubber modified with unmodified asphaltand polymer-modified (SBS) asphalt The study displayedthat rubber-modified asphalt improved viscoelastic charac-teristics and therefore has higher viscosity than unmodifiedbinders Thus the asphalt rubber is expected to betterenhance resistance to permanent deformation or rutting andlow temperature cracking The study also found that theviscoelastic properties of rubber-modified asphalt with 9weight are very similar to SBS-modified bitumen having 3weight SBS at minus10∘C and 7 weight at 75∘C

Mashaan and Karim [12] investigated the rheologicalproperties of asphalt rubber for various combination factorsof crumb rubber content and blending conditions Thedynamic shear rheometer (DSR) test was conducted toevaluate the engineering properties of asphalt binder rein-forced with crumb rubber at 76∘C Specification testing wasperformed at a test frequency of 10 rads which is equivalentto the car speed of 90 kmh Test specimens of 1mm thickby 25mm in diameter were formed between parallel metalplates The study displays increases in 119866lowast 1198661015840 and 11986610158401015840 anddecrease in phase angle (120575) Thus the modified asphaltbecame less susceptible to deformation after stress removalsThe study also presented a considerable relationship betweenrheological parameters (119866lowast 1198661015840 11986610158401015840 and 120575) and softeningpoint in terms of predicting physical-mechanical propertiesregardless of blending conditions

Natu and Tayebali [76] observed that the unmodifiedand crumb rubber modified binders with the same hightemperature PG rating do not show similar viscoelasticbehaviour over a range of frequencies It was also concludedthat the unmodified and crumb rubber modified mixturescontaining binders with the same high temperature PG ratingdo not show similar viscoelastic behaviour over a range offrequencies Mixtures containing the same PG rated bindersperformed similarly if their performance was evaluated ata frequency and temperature at which the binder hightemperature PG rating was determined

The loss tangent (Tan 120575) of the binder was not observedto be directly related to the loss tangent of the mixture sincethe loss tangent of the mixture was much lower perhaps dueto the aggregate effects than the loss tangent of the binder Itwas also noted that the loss tangent of the mixture increasedwhen the temperature was decreased A similar observationwas alsomade for the influence of frequencyWith increasingfrequency the loss tangent increased to a peak value and thendecreasedwith further increase in frequencyThe loss tangentof the binder increased appreciablywhen the temperaturewasincreased [2] Mixture stiffness by itself does not appear toprovide a measure for assessing the propensity for rutting inmixtures containingmodified bindersHigher dynamicmod-ulus (119866lowast) are not necessarily associatedwith lower permanentdeformation With respect to binder type the dynamicmodulus is lower for the mixtures containing modifiedbinders as compared to the mixture containing conventionalbinder [2]

At high service temperatures rutting resistance tests weremeasured as a function of some binder parameters (vis-cosity ductility recovery nonrecoverable creep compliancecomplex shear modulus 119866lowast and parameter specified bySHRP 119866lowastsin 120575) It was concluded that of the parametersconsidered for this range of binders only the SHRP119866lowastsin 120575gives the most reliable prediction of rut resistanceThe SHRPrecommended frequency (16Hz) was found to correspondclosely to the frequency of the wheel tracking test used forrutting resistance experiments This parameter includes botha measure of the stiffness of the binder (its ability to resistdeformation when a load is applied) and its ability to recoverany deformation when the load is removed The frequencyselected for the binder measurements has been found to havea significant impact on the quality of the correlation obtainedand should be as possible to the frequency of loading appliedto the mix [2] At intermediate pavement service tempera-tures a reasonable correlation was found between one aspectof mix fatigue performance (120576) and the binder loss modulus(119866lowast sin 120575) again measured under the same temperature andloading as the mix testing However above certain binderstiffness the variation in measured fatigue life was smalldue to machine compliance becoming significant at high mixstiffness It is unlikely that binder rheology alone will besufficient to accurately predict and explainmix fatigue life [2]

63 Viscosity Property (Flow Resistance) Viscosity refers tothe fluid property of the asphalt cement and it is a gauge


of flow-resistance At the application temperature viscositygreatly influences the potential of the resulting pavingmixes During compaction or mixing low viscosity has beenobserved to resulting in lower stability values and betterworkability of asphalt mixture

Nair et al [77] used a Haake rotational viscometer tomeasure the viscosity of the soft asphalt samples while theviscosity of the blown asphalt samples is measured on a cap-illary rheometer The tests were conducted to study the flowbehaviour on the modification of asphalt with liquid naturalrubber (LNR) The findings are as follows for soft asphaltthe temperature dependence on viscosity is prominent up to100∘C and subsequently marginal The addition of 20 LNRresults in themaximumviscosity Activation energy of flow ofsoft bitumen increased while that of blown asphalt decreasedon addition of LNR

Zaman et al [78] found that the viscosity of asphaltcement increases with the addition of rubber and rubber-modified asphalt-cement samples show a more uniform andhigher resistance against loading as the amount of rub-ber increased The degrees of shear-thickening and shear-thinning behaviour decreased by increasing the amounts ofrubber in asphalt cement The liner dynamic viscosity wasincreased by increasing the amount of rubber in asphaltcement Piggott et al [79] mentioned that the vulcanizedrubber had a large effect on the viscosity of the asphaltcementThe viscosity measured at 95∘C increased by a factorof more than 20 when 30 vulcanized rubber was added tothe mixture In contrast the devulcanized rubber had only avery small effect The viscosity test also showed that there isno danger of gel formation when rubber is mixed with hotasphalt cement

64 Physical Behaviour and Stiffness Performance Mahrez[2] investigated the properties of asphalt rubber binderprepared by physical blending of asphalt 80100 penetrationgrade with different crumb rubber content and various agingphases The results of penetration values decreased over theaging as well as before aging by increasing the rubber contentin the mix Also the modified binders showed lower pene-tration values than unmodified binders Another study [80]on penetration change was conducted using asphalt 80100and 70100 penetration grade mixes with different crumbrubber percentage The results showed a significant decreasein the penetration values of modified binder due to highcrumb rubber content in the binders According to Jensenand Abdelrahman [30] elastic recovery property is veryimportant in both fatigue and rutting resistance selection andevaluation Elastic recovery is a property that indicates thequality of polymer components in asphalt binders Oliver[81] concluded from his study that the elastic recovery ofasphalt rubber binders leads to an increase as the rubberparticle size decreases It was found that rubber types couldaffect the force ductility properties at 4∘C [82] Asphalt rubbermodification resulted in a better rutting resistance and higherductility However the modified binder was susceptible todecomposition and oxygen absorption There were problemsof low compatibility because of the high molecular weightFurthermore it was found that recycled tyre rubber decreases

reflective cracking which in turn increases durability Duringcompaction or mixing low viscosity has been observed toresulting in lower stability values Softening point refers to thetemperature at which the asphalt attains a particular degree ofsoftening [3] Mahrez and Rehan [83] claimed that there is aconsistent relationship between viscosity and softening pointat different aging phases of asphalt rubber binder Also it isreported that the higher crumb rubber content leads to higherviscosity and softening point

Mashaan andKarim [12] reported that the softening pointvalue increases as crumb tuber content increases in the mixThe increase of rubber content in the mix could be corelatedto the increase in the asphaltenesresins ratio which probablyenhanced the stiffening properties making the modifiedbinder less susceptible to temperature changes According toLiu et al [56] the main factor in the increase in softeningpoint can be attributed to crumb rubber content regardlessof type and size The increase in softening point led to a stiffbinder that has the ability to enhance its recovery after elasticdeformation According toMashaan et al [11] the rubberisedasphalt binder was evaluated in terms of binder elasticityand rutting resistance at high temperatureThe higher crumbrubber content appears to dramatically increase the elasticrecovery and ductility According to a study [71] the ductilitytest conducted at low temperature was found to be a usefulindicator of brittle behaviour of bitumen Latex contents inthe range from 3 to 5 were found to result in nonbrittlebehaviour in the ductility test at 5∘C whereas the unmodifiedbitumen failed by brittle fracture in the same test Nair et al[77] found that the ductility decreased in the case of softbitumen with increasing concentration of liquid naturalrubber while some improvement was noticed in the case ofblown bitumen at 10 loading The ductility is measuredat 27∘C and pulled apart at a rate of 50mmmin Modifiedbitumen binders showed a significant enhancement on theelastic recovery and in contrast the ductility decreased withrespect to unmodified binders [84]

7 Durability and Aging of Asphalt Rubber

In the paving design mixture the general practice is toarrive at a balanced design among a number of desirablemix properties one of which is durability Durability is thedegree of resistance to change in physicochemical propertiesof pavement surface materials with time under the action ofweather and traffic The life of a road surfacing will dependprimarily on the performance of the binder provider the mixdesign and construction techniques [2] Asphalt hardeningcan lead to cracking and disintegration of the pavement sur-face The rate of hardening is a good indicator of the relativedurability Many factors might contribute to this harden-ing of the asphalt cement such as oxidation volatilisationpolymerization and thixotropy This is because asphalt is anorganic compound capable of reacting with oxygen foundin the environment The asphalt composite changes with thereaction of oxidation developing a rather brittle structureThis reaction is referred to as age hardening or oxidative hard-ening [85] Volatilisation occurswhen the lighter componentsof the asphalt evaporate In general this is related to elevated


temperatures that are found firstly during the hot mix asphaltproduction process Polymerisationis the means by whichresins are assumed to combine into asphaltenes resultingin an increase in the brittleness of the asphalt along with atendency toward non-Newtonian behaviour At the end ofthe reaction thixotropy or an increase in viscosity over timealso contributes to the aging phenomenon in asphalt [85]However the most important factors in the aging processof asphalt binder seem to be oxidation and volatilisationThe occurrence of steric hardening and the time-dependentreversible molecular association have affected the binderproperties but this is not considered as aging Steric hard-ening is only a factor at intermediate temperatures at hightemperatures excess kinetic energy in the system prevents theassociation and at low temperatures the rate of association isfound to be slower due to the binderrsquos high viscosity [85]

Bahia and Anderson [86] studied the mechanism bywhich binder properties may change at low temperatureThis mechanism which is called physical hardening occursat temperatures next to or lower than the glass transitiontemperature and causes significant hardening of the asphaltbinderThe rate and magnitude of the hardening phenomenahave been observed to increase with decreasing temperaturesand is reported to be similar to the phenomena called physicalaging on amorphous solids [87] The physical hardening canbe explained using the free volume theory which introducedthe relationship between temperature and molecular mobil-ity The free volume theory includes the molecular mobilitydependent on the equivalent volume ofmolecules present perunit of free space or free volume Based on the free volumetheory when amorphous material is cooled from a tempera-ture above its glass transition temperature molecular adjust-ments and the collapse of free volume rapidly show a drop intemperature At that temperature the structural state of thematerial is frozen-in and deviates from thermal equilibriumdue to the continuous drop in kinetic energy Hence it hasbeen postulated that in order for physical hardening tohappen in binders temperatures must be higher than theglass transition temperature

Many durability tests are based on the evaluation ofresistance to asphalt hardening Mahrez and Rehan [83]investigated ageing effects on viscoelastic properties of rub-berised asphalt using the Dynamic Shear Rheometer (DSR)The binders were aged with theThin FilmOven Test (TFOT)the Rolling Film Oven Test (RFOT) and the Pressure AgeingVessel (PAV) This research found that ageing influences therheology of rubberised asphalt The mechanical propertiesof aged binder improved by increased complex modulus anddecreased phase angle The aged samples were characterizedby higher stiffness and elasticity due to an increase in theelastic (storage) modulus 1198661015840 The high value of 1198661015840 is anadvantage since it improved further the rutting resistanceduring service Natu and Tayebali [76] carried out compre-hensive research study which evaluated high temperatureperformance characteristics of unmodified and crumb rub-ber modified asphalt binders and mixtures The researchshowed that the effect of RFTO aging on binder rutting factorwas increased at low frequencies andor high temperaturesThe improvement in the rutting factor diminished with

an increase in frequency and at very high frequencies (lowtemperatures) the rutting factors for unaged and RFTOaged binders were nearly the same The increase in binderrutting factor of crumb rubber modified asphalt bindersat low frequencies suggested that the binder resistance topermanent deformation has improved Ali et al [88] studiedthe influence of the physical and rheological properties ofaged rubberised asphalt The results indicate that the use ofrubberised binder reduces the aging effect on physical andrheological properties of the modified binder as illustratedthrough lower aging index of viscosity (AIV) lower agingindex of 119866lowastsin 120575 lower softening point increment (Δ119878) lesspenetration aging ratio (PAR) and an increase in Tan 120575 withcrumb rubber modifier content increasing indicating thatthe crumb rubber might improve the aging resistance ofrubberised binder

8 Failure of Road Pavement Cracking andPermanent Deformation

Two kinds of loading are of specific importance in tandemwith the performance of bituminous surfacing One is due tovehicles loads passing over the road surfacing while the sec-ond is due to thermal contraction in relation to temperaturechanges [81] Vehicle loading can lead to distress at either endof the range of pavement surface temperatures At increasedpavement temperatures the binder can be extremely fluidand probably will not resist the plucking and shearing actionof vehicle tyres At low pavement temperatures the bindercan be so hard (particularly after a long period of service)that vehicle loading causes brittle fracture of the binder filmsThe explanation to this phenomenon is thought to be dueto the theory of ldquoNormal Stressesrdquo (Wiesenberger effect)which applies to viscoelasticmaterial such as a bitumenscraprubber mixture This theory covers normal stress differenceswhich are forces that developnormally (that is perpendicular)to the direction of shear [81]

According to the theory a viscoelastic material forcedthrough an open tube expands normally to the axis of the tubeon leaving the tube In a cracked pavement the vertical loadsare applied by the vehicle wheels which compel the bitumenbinder to expand normally to the applied vertical load(horizontally) and thus fill up the cracks Another reason isthat if this bitumenrsquos mixture is stirred while being hot with astick in a container thematerial will climb up the stick ratherthan forming a vortex as found in Newtonian type fluids [81]

81 Correlation between Rheological Properties of AsphaltBinder and Performance of Asphalt Mixture As extensiveresearch program conducted [89] to investigate the benefitsof using fundamental binder rheological measurements topredict asphalt pavement performance included

(i) pavement deformation (rutting) at high service tem-peratures

(ii) fatigue at intermediate service temperatures

(iii) brittle fracture at low service temperatures


At high service temperatures rutting resistance tests weremeasured as a function of some binder parameters (viscosityductility recovery nonrecoverable creep compliance com-plex shear modulus 119866lowast and parameter specified by SHRP119866lowastsin 120575) It was concluded from the parameters considered

that for this range of binders only the SHRP 119866lowastsin 120575 givesthe most reliable prediction of rut resistance The SHRPrecommended frequency (16Hz) was found to correspondclosely to the frequency of the wheel tracking test used forrutting resistance experiments This parameter includes botha measure of the stiffness of the binder (its ability to resistdeformation when a load is applied) and its ability to recoverany deformation with the removal of the loadThe frequencyselected for the bindermeasurementswas to have a significantimpact on the quality of the correlation obtained and shouldbemaintained close to the frequency of loading applied to themix [89]

At intermediate pavement service temperatures a reason-able correlation was found between one aspect of mix fatigueperformance (120576) and the binder loss modulus (119866lowastsin 120575)again measured under the same temperature and loadingas the mix testing However above certain binder stiffnessdue to machine compliance being significant at high mixstiffness the variation in measured fatigue life was minimalBinder rheology alone is not adequate to accurately predictand explain mix fatigue life At low pavement service tem-peratures a binder limiting stiffness temperature (LST) inthis case based on 119866lowast = 300Mpa at 1000 s provides a goodindicator of the fracture temperature of the mix [89]

82 Fatigue Resistance of Asphalt Rubber Bahia and Davies[90] used the rheological properties as indicators for thepavement performance At high temperature the rheolog-ical properties were related to the rutting performance ofpavements The rheology at intermediate temperatures hadan impact on the fatigue cracking of pavements The lowtemperature properties of the binder are related to the low-temperature thermal cracking of the pavement Temperatureadditionally is a vital factor that is correlated with the rate ofloading At elevated temperatures or slow rates of loadingbitumen becomes a viscous material

However at decreased temperatures or higher rates ofloading bitumen then becomes a highly elastic material Infact at intermediate temperatures bitumen has two differentcharacteristics that is an elastic solid and a viscous fluid [75]

Aflaki and Memarzadeh [91] investigated the effects ofrheological properties of crumb rubber on fatigue crackingat low and intermediate temperatures using different shearmethodsThe results showed that the high shear blending hasmore effect on improvement at low temperatures than the lowshear blend

Bahia and Anderson [92] presented a description of thepurpose and scope of the dynamic shear rheometer testThe dynamic shear rheometer (DSR) was used to charac-terise the viscoelastic behaviour of bituminous material atintermediate and high service temperatures Stress-strainbehaviour defines the response of materials to load Asphaltbinders exhibit aspects of both elastic and viscous behaviourshence they are referred to as viscoelastic materials Bahia and

Figure 11 Fatigue cracking

Anderson [86] conducted a time sweep test using dynamicshear rheometer The test is a simple method of applyingrepeated cycles of stress or strain loading at selected temper-atures and loading frequencyThe initial data under repeatedloading in shear showed that the time sweeps are effective inmeasuring binder damage behaviour One of the advantagesof the time sweep test is that it can be used to calculatefatigue life of asphalt binder based on dissipated energyapproaches Fatigue is one of most important distresses inasphalt pavement structure due to repeated load of heavy traf-fic serviceswhich occur at intermediate and low temperaturesas shown in Figure 11 The use of crumb rubber modifiedwith bitumen binder seems to enhance the fatigue resistanceas illustrated in a number of studies [3 6 18 88 91 93ndash95]The improved performance of bitumen-rubber pavementscompared with conventional bitumen pavements has partlyresulted from improved rheological properties of the rub-berised bitumen binder

Cracking is normally considered to be low temperaturephenomena while permanent deformation is consideredthe predominant mode of failure at elevated temperaturesCracking is mainly categorised into thermal cracking andload-associated fatigue cracking Large temperature changesthat occur in pavement usually result in thermal crackingThis type of failure occurs when the thermally induced tensilestress together with stresses caused by traffic exceeds thetensile strength of the materials It is often characterised bytransverse cracking along the highway at certain intervalsLoad-associated fatigue cracking is the phenomenon of frac-ture as a result of repeated or fluctuated stresses brought aboutby traffic loading Traffic loads can cause a pavement structureto flex and the maximum tensile strain will occur at the baseof the bituminous layer If this structure is inadequate for theimposed loading conditions the tensile strength of thematerials will be exceeded and cracks are likely to initiatewhich will be manifested as cracks on the surface of thepavement [9]

This resistance of bituminous mixtures to cracking isessentially dependent upon its tensile strength and extensibil-ity characteristicsThese can be achieved by simply increasingthe bitumen content of the mix However such an attemptmay have an adverse effect on the mix stability The use ofsofter bitumen can also improve the mix flexibility but this


Mode 1 Mode 2 Mode 3(opening) (tearing)(sliding)

y

x

z

Figure 12 Modes of crack displacement [79]

can only be achieved at the expense of the tensile strengthand stability of the mix [9]

In the fracture mechanics approach fatigue crackingprocess of pavement systems is considered to develop in twodistinct phases involving different mechanismsThese phasesconsist of crack initiation and crack propagation before thematerial experiences failure or rupture Crack initiation canbe described as a combination of microcracks within the mixforming a macrocrack as a result of repeated tensile strainsThis occurrence usually creates gradual weakening of thestructural component [96] These microcracks become morevisible as the stress concentrations at the tip of the crackincrease and cause further crack propagation Crack propa-gation is the growth of the macrocrack through the materialunder additional application of tensile strains The actualmechanism of crack initiation and propagation involvesfracture of the overlay when the tensile stresses exceed thetensile strength under the particular conditions [9] For anaccurate determination of the crack propagation the magni-tude of the stress intensity factors over the overlay thicknessshould be available for each fracture mode In general themechanisms of cracking propagation can follow one or moreof the three fracture modes which are directly related to thetype of displacement induced [97]This is shown in Figure 12

(i) Mode I loading (opening mode) results from loadapplied normally to the crack plane (normal tension)This mode is associated with traffic loading and in thecase of thermally induced displacement

(ii) Mode II loading (sliding mode) results from inplanenormal shear loading which leads to crackfaces sliding against each other normal to the leadingedge of the crackThismode is usually associatedwithtraffic loading or differential volume changes

(iii) Mode III loading (tearing mode) results from outof plane shear (parallel shear) loading which causessliding of the crack faces parallel to the crack loadingedge This mode may occur under lateral displace-ment due to instability if the crack plane is not normalto the direction of traffic

83 Rutting Resistance of Asphalt Rubber There are variouslaboratory methods for studying distortion or rutting TheTRRL Wheel Tracking Test appears to be the most suitablein stimulating the field conditions as closely as possible Thetest was conducted for 24 hours in temperature controlledcabinet at 60∘C From the indents made on the slab thedepth of tracking was recorded at the mid-point of its lengthAfter about 6 hours a steady state of tracking was observedFrom the deformationtime curve the rate of increase in trackdepth is determined in mm per hour once the steady state isreached [19]

According to Shin et al [98] addition of crumb rubberand SBR increases the rutting resistance of asphalt pavingmixtures The results from laboratory study showed that theCR-modified and SBR-modified asphalt had higher stiffnessat 60∘C than the modified mixtures The modified asphaltmixtures also had higher gyratory shear strengths and lowerrut depths in the Loaded Wheel tests than the unmodifiedmixtures

Tayfur et al [99] claimed that after the initial densifica-tion the permanent deformation of the bituminous mixturehappens due to shear loads which take place close to thepavement surface which in fact is the contact area betweenthe tyre and the pavement These efforts increase without thevolume variations in the bituminous mixture They are theprimary mechanisms in the development of rutting duringthe life span of the pavement design

Increased permanent deformation or rutting has beenrelated to the increase in truck tyre pressures axle loads andvolume of traffic [100] A study [2] claimed that the use ofrubberised bitumen binder has a significant effect on improv-ing the mixture resistance to rutting deformation Rutting inflexible pavement can be divided into two types consolida-tion rutting which happens with excessive consolidation ofthe pavement along the wheel path caused by decreased airvoids in the asphalt concrete layer as shown in Figure 13or the permanent deformation of the base or subgradeInstability rutting is due to the asphalt mixture propertiesand is an occurrence in the range of the top 2 inches of theasphalt concrete layer as shown in Figure 14 [101]

9 Marshall Stability and Rubberised Asphalt

In relation to the plastic behaviour of materials the stabilityof an asphaltic paving mixture is influenced by its inter-nal friction cohesion and inertia The friction componentof stability in turn is governed by size shape gradationand surface roughness of aggregate particles intergranularcontact pressure due to compaction and loading aggregateinterlock caused by angularity and viscosity of the binderThe cohesion depends on variables such as the rheology of thebinder number of contact points density and adhesion [102]


Originalprofile

Weak subgrade or underlying layer Subgradedeformation

Figure 13 Consolidations rutting of flexible pavement [101]

Originalprofile

Shear plane

Figure 14 Instability rutting of flexible pavement [101]

The results of Marshall Test by Samsuri [28] indicated thatincorporation of rubber increases the Marshall stability andquotient The increase varied with the form of rubber usedand the method of incorporating the rubber into bitumenThe Marshall stability for mixes containing rubber powderswas increased more than twofold and the Marshall quo-tient increased by nearly threefold compared to the normalunmodified bituminous mix Mixes produced using bitumenpreblended with fine rubber powders showed the greatestimprovement rather than mixes produced by direct mixingof rubber with bitumen and aggregates Thus preblendingof bitumen with rubber is a necessary step in order toproduce an efficient rubberised bitumen binder probably dueto adequate and efficient rubber dispersions in the bitumenphase The optimum binder content was selected based onMarshallMix designmethod as recommended by theAsphaltInstitute [103] which uses five mix design criteria

(a) lower Marshall stability(b) an acceptable average of Marshall flow(c) an acceptable average of air void(d) percent voids filled with asphalt (VFA)(e) lower value of VMA

91 Influence of Aggregate Gradation on Marshall Test Themineral aggregate is bituminous concrete constituting about95 percent of the mixture on a weight basic and about85 percent on a volume basic Characteristics of aggregatecontributing to the properties of bitumen mixture would begradation particle surface texture particles shape cleanli-ness and chemical composition [104] Investigations showedthat the effect of aggregate maximum size on the modifiedMarshall test results resulted in mixtures with aggregatemaximum size of 19mm leading to higher modifiedMarshallstability values and slightly decreased Marshall flow values

thanmixtures with aggregate maximum size of 38mm How-ever the disparity between the results for the two mixtureswas minimal Also the modified Marshall flow did notpresent any specific trend for the two mixtures [105]

The aggregate maximum size had a marked effect onthe amount of air voids and on the specific gravity of thespecimens Small percentages of air voids and higher valuesof air-cured specific gravity were obtained for mixture with38mmof aggregatemaximum size compared tomixture with19mm of aggregate maximum size [105] On the other handbinder emulsion content showed a significant effect on the airvoids and the specific gravity of the specimens Increasing thebinder emulsion content in themixture filled the voids amongaggregate particles and also allowed for more occurrence ofcompaction due to lubrication [105]

92 Influence of Compaction on Marshall Test The stabilityvalues of the various mixes obtained using gyratory com-paction were two to three times greater than the valuesobtained with Marshall Compaction The flow values of themixes obtained using gyratory compaction correlated withthe stability values where the maximum stability occurredthe lowest with regard to the flow while those obtained usingthe Marshall compaction were not consistent in this respect[106]

10 Asphalt Mixtures Testing

Different tests and approaches have been used to evaluateasphalt concrete mixtures properties Several material prop-erties can be obtained from fundamental mechanistic teststhat can be used as input parameters for asphalt concreteperformancemodelsThemain aspects which can be charac-terised using indirect tensile test are resilient elastic proper-ties fatigue cracking and the properties related to permanentdeformation The elastic stiffness of the asphalt mixtures canbe measured using the indirect tensile test (IDT) [6 107]

101 Indirect Tensile Strength Test The indirect tensilestrength of a sample is calculated from the maximum loadto failure According to Witczak et al [108] the indirecttensile test (IDT) has been extensively used in the structuraldesign of flexible pavements since the 1960s Strategic High-way Research Program (SHRP) [109] recommended indirecttensile test for asphalt concrete mixture characterisationThepopularity of this test is mainly due to the fact that the testcan be done using marshal sample or cores from filed Thistest is easy quick and characterised as less variable Guddatiet al [110] have also indicated that there is good potentialin predicting fatigue cracking using indirect tensile strengthresults A study was conducted to evaluate the performanceof Polyethylene (PE) modified asphaltic mixtures based onphysical and mechanical properties Physical properties wereevaluated in terms of penetration and softening point Themechanical properties were evaluated based on the indirecttensile strength The result presented that PE enhanced bothphysical and mechanical properties of modified binder andmixtures [9]


102 Resilient Modulus Test The dynamic stiffness or ldquoresil-ientmodulusrdquo is ameasure of the load-spreading ability of thebituminous layers it controls the levels of the traffic-inducedtensile strains at the underside of the lowest bituminousbound layer which are responsible for fatigue cracking aswell as the stresses and strains induced in the subgrade thatcan lead to plastic deformations (OrsquoFlaherty 1988) [92] Thedynamic stiffness is computed by indirect tensile modulustest which is a quick and nondestructive method In generalthe higher the stiffness the better its resistance is to perma-nent deformation and rutting [28] Eaton et al [111] showedthat the resilient modulus increased or the mix behaved in astiffer manner (the mix becomes stronger) with a decrease intemperature also as the load time increased and the resilientmodulus decreased or yielded more under a longer loadingtime Indirect tensile resilient modulus test is widely usedas a routine test to evaluate and to characterise pavementmaterials Dallas and Kamyar [112] defined the resilientmodulus as the ratio of the applied stress to the recoverablestrain when a dynamic load is applied In this test a cyclicload of constant magnitude in the form of haversine waveis applied along the diametric axis of a cylindrical specimenfor 01 seconds and has a rest period of 09 seconds thusmaintaining one cycle per second Al-Abdul-Wahhab and Al-Amri [113] conducted a resilient modulus test on unmodifiedand modified asphalt concrete mixtures usingMarshall spec-imen A dynamic load of 68 kg was applied and stopped aftera 100 load repetitionsThe load application and the horizontalelastic deformation were used to compute the resilient mod-ulus value Two temperatures were used 25∘C and 40∘CThemodified asphalt mixtures with 10 percent crumb rubbershowed an improved modulus compared to the unmodifiedasphalt concrete mixtures

103 Indirect Tensile Fatigue Test There are different testmethods used throughout the world to measure fatigue resis-tance for asphalt concrete mixtures Read [114] investigatedthe fatigue life of asphalt concrete mixtures using the indirecttension fatigue test During the indirect tension fatigue thehorizontal deformation was recorded as a function of loadcycle The test specimen was subjected to different levelsof stress in order for a regression analysis on a range ofvaluesThis allows the development of the fatigue relationshipbetween the number of cycles at failure (119873

119891) and initial

tensile strain (120576119905) on a log-log relationship Fatigue life (119873

119891) of

a specimen is number of cycles to failure for asphalt concretemixtures The fatigue life is defined as the number of loadcycling application (cycles) resulting in either disintegrationor a permanent vertical deformation Fatigue test procedureis used to rank the bituminousmixture resistance to fatigue aswell as a guide to evaluate the relative performance of asphaltaggregate mixture to obtain data and input for estimatingthe structural behaviour in the road During the fatigue testmodulus value decreased as indicated in Figure 15 Threephases were distinguished [115]

(i) phase I initially there is a rapid diminution of themodulus value

Phase I Phase II Phase III

Mod

ulus

Number of cycles

Figure 15 The three phases of fatigue test [115]

(ii) phase II modulus variation is approximately linear

(iii) phase III rapid decrease of the modulus value

Damage is defined as any loss of strength that takes placein a specimen during a test

A research study [18] investigated the fatigue behaviour ofthe different mixes using controlled-strain third-point flexu-ral beam tests Controlled-strain flexural fatigue testing indi-cated that the incorporation of CRMs in mixes can enhancetheir fatigue resistance The magnitude of improvementappears to depend on the degree and type of rubber mod-ification Multilayer elastic analysis combined with fatiguetest results for typical Alaskan conditions also indicatedthe enhanced fatigue behaviour of CRM mixes Howevercondition surveys at both conventional and CRM sectionsrevealed no longitudinal or alligator type of cracking sug-gesting similar field fatigue performance for both materials

11 Conclusion

Today a serious problem that leads to environment pollutionis the abundance and increase of waste tyre disposal Largeamounts of rubber are used as tyres for cars and trucks andso forth Although rubber as a polymer is a thermosettingmaterial cross-linked to processing and moulding it cannotbe softened or remoulded by reheating unlike other types ofthermoplastics polymer which can be softened and reshapedwhen heated Due to an increase in service traffic densityaxle loading and low maintenance services road structureshave deteriorated and are therefore subjected to failuremore rapidly To minimize the damage of pavement such asresistance to rutting and fatigue cracking asphalt mixturemodification is required Virgin polymer offers the possibilityof producing mixtures that can resist both rutting andcrackingThus using recycled polymer such as crumb rubberis a good alternative and inexpensive Also it is consideredas sustainable technology that is ldquogreening asphaltrdquo whichwould transform unwanted residue into a new bituminousmixture highly resistant to failure Thus utilising crumbrubber obtained from scrap automobile tyre is not only bene-ficial in terms of cost reduction but also has less ecologicalimpact in keeping the environment clean and to achievebetter balance of natural resources


Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

References

[1] E J F Peralta Study of the interaction between bitumen andrubber [MS thesis] Faculty of Engineering University ofMinho 2009

[2] A Mahrez Properties of rubberised bitumen binder and its effecton the bituminous mix [MS thesis] Faculty of EngineeringUniversity of Malaya Kuala Lumpur Malaysia 1999

[3] N S Mashaan The effect of crumb rubber modifier to theproperties and rheological behaviour of asphalt binder [MSthesis] University of Malaya Kuala Lumpur Malaysia 2012

[4] R Richard andT BentRoad Engineering forDevelopment SponPress London UK 2nd edition 2004

[5] H J E Larsen C J Wohlk and B A Hall ldquoModified bitumenrdquoin Proceedings of the 14th Australian Road Research BoardConference (ARRB rsquo88) Canberra Australia 1988

[6] F K M Hamed Evaluation of fatigue resistance for modifiedasphalt concrete mixture based on dissipate energy concept[PhD thesis] Technische Universitat Darmstadt DarmstadtGermany 2010

[7] H Wang Z You J Mills-Beale and P Hao ldquoLaboratory evalu-ation on high temperature viscosity and low temperature stiff-ness of asphalt binder with high percent scrap tire rubberrdquoConstruction and Building Materials vol 26 no 1 pp 583ndash5902012

[8] P S Shaw Stress-strain relationships for granular materialsunder repeated loading [PhD thesis] Department of CivilEngineering University of NottinghamNottinghamUK 1980

[9] A Mahrez Properties and performance of stone mastic asphaltreinforced with glass fibre [PhD thesis] Faculty of EngineeringUniversity of Malaya Kuala Lumpur Malaysia 2008

[10] N SMashaan AHAliM R Karim andMAbdelaziz ldquoEffectof crumb rubber concentration on the physical and rheologicalproperties of rubberised bitumen bindersrdquo International Jour-nal of Physical Sciences vol 6 no 4 pp 684ndash690 2011

[11] N SMashaan AHAliM R Karim andMAbdelaziz ldquoEffectof blending time and crumb rubber content on properties ofcrumb rubber modified asphalt binderrdquo International Journal ofPhysical Sciences vol 6 no 9 pp 2189ndash2193 2011

[12] N S Mashaan and M R Karim ldquoInvestigating the rheologicalproperties of crumb rubber modified bitumen and its correla-tionwith temperature susceptibilityrdquoMaterials Research vol 16no 1 pp 116ndash127 2013

[13] D C Thompson and A J Hoiberg Eds Bituminous MaterialsAsphalt Tars and Pitches Krieger Publishing Co NewYork NYUSA 1979

[14] U Isacsson and X Lu ldquoCharacterization of bitumens modifiedwith SEBS EVA and EBA polymersrdquo Journal of MaterialsScience vol 34 no 15 pp 3737ndash3745 1999

[15] Y Yildirim ldquoPolymer modified asphalt bindersrdquo Constructionand Building Materials vol 21 no 1 pp 66ndash72 2007

[16] D IHansonK Y Foo E R Brown andRDenson ldquoEvaluationand characterization of a rubber-modified hot mix asphaltpavementrdquo Transportation Research Record no 1436 pp 98ndash107 1994

[17] J E Huffman ldquoSahuaro concept of asphalt-rubber bindersrdquo inProceedings of the 1st Asphalt Rubber User Producer WorkshopScottsdale Ariz USA 1980

[18] L Raad and S Saboundjian ldquoFatigue behavior of rubber-modified pavementsrdquo Transportation Research Record no 1639pp 73ndash82 1998

[19] H Y Katman Effects of rubberised bitumen on properties ofporous mixes [MS thesis] University ofMalaya Kuala LumpurMalaysia 2006

[20] J R Lundy R G Hicks and H Zhou ldquoGround rubber tires inasphalt-concrete mixturesmdashthree case historiesrdquo ASTM SpecialTechnical Publication STP1193 pp 262ndash275 1993

[21] H Zhu and D D Carlson ldquoA spray based crumb rubbertechnology in highway noise reduction applicationrdquo Journal ofSolid Waste Technology and Management vol 27 no 1 pp 27ndash32 2001

[22] Y Huang R N Bird and O Heidrich ldquoA review of the use ofrecycled solid waste materials in asphalt pavementsrdquo ResourcesConservation and Recycling vol 52 no 1 pp 58ndash73 2007

[23] D R Brown D Jared C Jones andDWatson ldquoGeorgiarsquos expe-rience with crumb rubber in hot-mix asphaltrdquo TransportationResearch Record no 1583 pp 45ndash51 1997

[24] G W Maupin Jr ldquoHot mix asphalt rubber applications inVirginiardquo Transportation Research Record no 1530 pp 18ndash241996

[25] E Charania J O Cano and R H Schnormeier ldquoTwenty-year study of asphalt rubber pavement in Phoenix ArizonardquoTransportation Research Record no 1307 pp 29ndash38 1991

[26] B Adhikari D De and S Maiti ldquoReclamation and recyclingof waste rubberrdquo Progress in Polymer Science vol 25 no 7 pp909ndash948 2000

[27] Z Sufian and M S Mustafa ldquoProspects of rubberised bitumenpavement Malaysia roads and highwaysrdquo in Proceedings of theConference on the Use of Rubberised Bitumen in the RoadConstruction Selangor Malaysia 1997

[28] A Samsuri ldquoProperties of rubberised bitumen from reclaimedrubberrdquo in Proceedings of the Conference on the Use of Rub-berised Bitumen in the Road Construction pp 15ndash23 SelangorMalaysia 1997

[29] C A OrsquoFlaherty Highway Engineering Textbook EdwardArnold London UK 3rd edition 1988

[30] W Jensen and M Abdelrahman ldquoCrumb rubber in perfor-mance-graded asphalt binderrdquo Final Report SPR-0105Nebraska Department of Roads University of Nebraska-Lincoln 2006

[31] F P Miknis and L C Michon ldquoSome applications ofnuclearmagnetic resonance imaging to crumb rubbermodifiedasphaltsrdquo Fuel vol 77 no 5 pp 393ndash397 1998

[32] J Shen S Amirkhanian F Xiao and B Tang ldquoInfluence ofsurface area and size of crumb rubber on high temperatureproperties of crumb rubber modified bindersrdquo Constructionand Building Materials vol 23 no 1 pp 304ndash310 2009

[33] D Croney and P Croney The Design and Performance of RoadPavement McGraw-Hill Book Co London UK 2nd edition1992

[34] S J Rozeveld E Shin A Bhurke L France and L Drzal ldquoNet-work morphology of straight and polymer modified asphaltcementsrdquoMicroscopy Research and Technique vol 38 no 5 pp529ndash543 1997

[35] J S Youtcheff and D R Jones IV Guideline for Asphalt Refinersand Suppliers Strategic Highway Research Program NationalResearch Council Washington DC USA 1994


[36] J D McLean and P K Kilpatrick ldquoComparison of precipitationand extrography in the fractionation of crude oil residuardquoEnergy and Fuels vol 11 no 3 pp 570ndash585 1997

[37] J M Read and C D Whiteoak The Shell Bitumen HandbookThomas Telford Publishing London UK 5th edition 2003

[38] K H Altgelt andMM BoduszynskiComposition and Analysisof Heavy Petroleum Fractions Marcel Dekker New York NYUSA 1994

[39] I Merdrignac and D Espinat ldquoPhysicochemical characteriza-tion of petroleum fractions the state of the artrdquo Oil and GasScience and Technology vol 62 no 1 pp 7ndash32 2007

[40] F J Navarro P Partal F Martınez-Boza C Valencia and CGallegos ldquoRheological characteristics of ground tire rubber-modified bitumensrdquo Chemical Engineering Journal vol 89 no1ndash3 pp 53ndash61 2002

[41] L H Lewandowski ldquoPolymer modification of paving asphaltbindersrdquo Rubber Chemistry and Technology vol 67 no 3 pp447ndash480 1994

[42] R Dongre J Youtcheff and D Anderson ldquoMit Rheologie zubesseren strassenrdquo Rheology Hannover vol 6 no 2 pp 75ndash821996

[43] J F Masson T Price and P Collins ldquoDynamics of bitumenfractions by thin-layer chromatographyflame ionization detec-tionrdquo Energy and Fuels vol 15 no 4 pp 955ndash960 2001

[44] F J Nellensteyn ldquoThe Constitution of asphaltrdquo Journal of theInstitute of Petroleum Technology vol 10 pp 311ndash325 1924

[45] P Claudy J M Letoffe G N King J P Planche and B BruleldquoCharacterization of paving asphalts by Differential ScanningCalorimetryrdquo Fuel Science and Technology International vol 9no 1 pp 71ndash92 1991

[46] L LoeberGMuller JMorel andO Sutton ldquoBitumen in colloidscience a chemical structural and rheological approachrdquo Fuelvol 77 no 13 pp 1443ndash1450 1998

[47] R D Krebs and R DWalkerHighwayMaterials McGraw-HillNew York NY USA 1971

[48] F J Navarro P Partal M Garcıa-Morales et al ldquoBitumenmod-ification with reactive and non-reactive (virgin and recycled)polymers a comparative analysisrdquo Journal of Industrial andEngineering Chemistry vol 15 no 4 pp 458ndash464 2009

[49] I Widyatmoko and R Elliott ldquoCharacteristics of elastomericand plastomeric binders in contact with natural asphaltsrdquoConstruction and Building Materials vol 22 no 3 pp 239ndash2492008

[50] R E Robertson ldquoChemical properties of asphalts and their rela-tionship to pavement performancerdquo Tech Rep SHRP-AUWP-91-510 Strategic Highway Research Program Washington DCUSA 1991 httponlinepubstrborgonlinepubsshrpSHRP-91-510pdf

[51] J P Pfeiffer and R N J Saal ldquoAsphaltic bitumen as colloidsystemrdquo Journal of Physical Chemistry vol 44 no 2 pp 139ndash149 1940

[52] J F Masson V Leblond and J Margeson ldquoBitumenmorpholo-gies by phase-detection atomic force microscopyrdquo Journal ofMicroscopy vol 221 no 1 pp 17ndash29 2006

[53] A T Pauli J F Branthaver R E Robertson W Grimes and CM Eggleston ldquoAtomic force microscopy investigation of SHRPasphaltsrdquo inHeavy Oil and Resid Compatibility and Stability pp110ndash114 Division of Petroleum Chemistry American ChemicalSociety San Diego Calif USA 2001

[54] M Hossain S Swartz and E Hoque ldquoFracture and tensilecharacteristics of asphalt-rubber concreterdquo Journal of Materialsin Civil Engineering vol 11 no 4 pp 287ndash294 1999

[55] H A Khalid ldquoRecent research on use of rubber in asphaltrdquo inProceedings of the WRAP Rubber in Roads Seminar Universityof Liverpool Liverpool UK 2005

[56] S Liu W Cao J Fang and S Shang ldquoVariance analysis andperformance evaluation of different crumb rubber modified(CRM) asphaltrdquo Construction and Building Materials vol 23no 7 pp 2701ndash2708 2009

[57] Y Becker M P Mendez and Y Rodrıguez ldquoPolymer modifiedasphaltrdquo Vision Tecnologica vol 9 no 1 pp 39ndash50 2001


[59] M A Abdelrahman and S H Carpenter ldquoMechanism of inter-action of asphalt cement with crumb rubber modifierrdquo Trans-portation Research Record no 1661 pp 106ndash113 1999

[60] G D Airey M M Rahman and A C Collop ldquoAbsorption ofbitumen into crumb rubber using the basket drainage methodrdquoInternational Journal of Pavement Engineering vol 4 no 2 pp105ndash119 2003

[61] J Shen and S Amirkhanian ldquoThe influence of crumb rubbermodifier (CRM) microstructures on the high temperatureproperties of CRM bindersrdquo International Journal of PavementEngineering vol 6 no 4 pp 265ndash271 2005

[62] K D Jeong S J Lee S N Amirkhanian and K W KimldquoInteraction effects of crumb rubber modified asphalt bindersrdquoConstruction and Building Materials vol 24 no 5 pp 824ndash8312010

[63] H Y Katman M R Karim M R Ibrahim and A MahrezldquoEffect of mixing type on performance of rubberized porousasphaltrdquo in Proceedings of the 6th International Conference ofEastern Asia Society for Transportation Studies (EASTS rsquo05)Bangkok Thailand September 2005

[64] C Thodesen K Shatanawi and S Amirkhanian ldquoEffect ofcrumb rubber characteristics on crumb rubber modified(CRM) binder viscosityrdquo Construction and Building Materialsvol 23 no 1 pp 295ndash303 2009

[65] S J Lee S N Amirkhanian and K Shatanawi ldquoEffect ofreaction time on physical and chemical properties of rubber-modified bindersrdquo in Proceedings of the International RubberConference Compendium of Papers CD-Rom Lyon FranceMay 2006

[66] S J Lee C K Akisetty and S N Amirkhanian ldquoThe effect ofcrumb rubber modifier (CRM) on the performance propertiesof rubberized binders in HMA pavementsrdquo Construction andBuilding Materials vol 22 no 7 pp 1368ndash1376 2008

[67] F Xiao S N Ameirkhanian and B J Putman ldquoLaboratoryinvestigation of dimensional changes of crumb rubber reactingwith asphalt binderrdquo in Proceedings of the Asphalt Rubber 2006Conference Palms spring Calif USA 2006

[68] F MorenoM C Rubio andM J Martinez-Echevarria ldquoAnaly-sis of digestion time and the crumb rubber percentage in dry-process crumb rubber modified hot bituminous mixesrdquo Con-struction and Building Materials vol 25 no 5 pp 2323ndash23342011

[69] B J Putman J U Thompson and S N Amirkhanian ldquoHightemperature properties of crumb rubber modified bindersrdquoin Proceedings of the Mairepav 4 International SymposiumMaintenance and Rehabilitation of Pavements and TechnologicalControl (iSMARTi rsquo05) Belfast Northern Ireland August 2005

[70] A P Paulo and C P Jorge ldquoLaboratory optimization of con-tinuous blend asphalt rubberrdquo in Proceedings of 3rd European


Pavement and Asset Management Conference (EPAM rsquo08)Coimbra Portugal July 2008

[71] AN S Beaty ldquoLatex-modified bitumen for improved resistanceto brittle fracturerdquo Highways and Transportation vol 39 no 9pp 32ndash41 1992

[72] A K Doolittle ldquoStudies in newtonian flow II the dependenceof the viscosity of liquids on free-spacerdquo Journal of AppliedPhysics vol 22 no 12 pp 1471ndash1475 1951

[73] J P Pfeiffer and P M Van Doormaal ldquoThe rheological proper-ties of asphaltic bitumenrdquo Journal of the Institute of PetroleumTechnologists vol 22 pp 414ndash440 1936

[74] M J Fernando and H R Guriguis ldquoNatural rubber forimproved surfacingrdquo in Proceedings of the 12th Australian RoadResearch Board Conference (ARRB rsquo84) vol 12 part 2 pp 121ndash129 August 1984

[75] C Van der Poel ldquoA general system describing the viscoelasticproperties of bitumen and its relation to routine test datardquoJournal of Applied Chemistry vol 4 pp 221ndash236 1954

[76] G S Natu and A A Tayebali ldquoMixture design and acceleratedlaboratory performance evaluation of unmodified and crumbrubber modified mixturesrdquo Association of Asphalt Paving Tech-nologists vol 68 pp 192ndash221 1999

[77] N R Nair N M Mathew S Thomas P Chatterjee and MA Siddiqui ldquoPhysical and rheological characteristics of liquidnatural rubber modified bitumenrdquo Journal of Applied PolymerScience vol 68 no 1 pp 53ndash61 1998

[78] A A Zaman A L Fricke and C L Beatty ldquoRheological prop-erties of rubber-modified asphaltrdquo Journal of TransportationEngineering vol 121 no 6 pp 461ndash467 1995

[79] C J Piggott D E Sadler and E M Villiers ldquoBitumen rubberasphalt experiences in the RSArdquo in Proceedings of the 7thConference on Asphalt Pavement for Southern Africa 1977

[80] P Kumar H C Mehndiratta and K L Singh ldquoRheologicalproperties of crumb rubber modified bitumenmdasha lab studyrdquoJournal of Scientific and Industrial Research vol 68 no 9 pp812ndash816 2009

[81] J W H Oliver ldquoModification of paving asphalts by digestionwith scrap rubberrdquo Transportation Research Record no 821 pp37ndash44 1981

[82] J C Rosner and J G Chehovits ldquoChemical and physicalproperties of asphalt-rubber mixtures Part III vol 4 physicalproperties of field-mixed asphalt-rubber mixtures and com-parisons of lab and field-mixed asphalt-rubbersrdquo Tech RepFHWAAZ-821594 Arizona Department of Transportation1982

[83] A Mahrez and M Rehan ldquoRheological evaluation of agingproperties of crumb rubber-modified bitumenrdquo Journal of theEastern Asia Society for Transportation Studied vol 5 pp 820ndash833 2003

[84] GMartinez B Caicedo L Celis andDGonzalez ldquoRheologicalbehaviour of asphalt with crumb rubber and other modifiersrdquoin Proceedings of the Asphalt Rubber 2006 Conference PalmsSpring Calif USA 2006

[85] J C Peterson ldquoChemical composition of asphalt as relatedto asphalt durability state of the artrdquo Transportation ResearchRecord no 999 pp 13ndash30 1984

[86] H U Bahia and D A Anderson ldquoGlass transition behavior andphysical hardening of asphalt bindersrdquo Journal of theAssociationof Asphalt Paving Technologists vol 62 pp 93ndash129 1993

[87] L C E Struik Physical Aging in Amorphous Polymers andOtherMaterials Elsevier Scientific Publisher New York NY USA1978

[88] A H Ali N S Mashaan and M R Karim ldquoInvestigationsof physical and rheological properties of aged rubberisedbitumenrdquo Advances in Materials Science and Engineering vol2013 Article ID 239036 7 pages 2013

[89] M Claxton J Lesage and L Planc ldquoThe use of binder rheo-logical properties to predict the perfprmance of asphalt mixesrdquoin Proceedings of the Australian Road Research Board Conference(ARRB rsquo96) Part 2 pp 311ndash326 1996

[90] H U Bahia and R Davies ldquoEffect of crumb rubber modifiers(CRM) on performance-related properties of asphalt bindersrdquoJournal of the Association of Asphalt Paving Technologists vol63 pp 414ndash449 1994

[91] S Aflaki and M Memarzadeh ldquoUsing two-way ANOVAand hypothesis test in evaluating crumb rubber modification(CRM) agitation effects on rheological properties of bitumenrdquoConstruction and Building Materials vol 25 no 4 pp 2094ndash2106 2011

[92] H U Bahia and D A Anderson ldquoStrategic highway researchprogram binder rheological parameters background and com-parison with conventional propertiesrdquo Transportation ResearchRecord no 1488 pp 32ndash39 1995

[93] H R Soleymani H Zhai and H Bahia ldquoRole of modifiedbinders in rheology and damage resistance behavior of asphaltmixturesrdquo Transportation Research Record no 1875 pp 70ndash792004

[94] R B McGennis ldquoEvaluation of physical properties of finecrumb rubber-modified asphalt bindersrdquo TransportationResearch Record no 1488 pp 62ndash71 1995

[95] T C Billiter R R Davison C J Glover and J A Bullin ldquoPhys-ical properties of asphalt-rubber binderrdquo Petroleum Science andTechnology vol 15 no 3-4 pp 205ndash236 1997

[96] KMajidzadeh G J Ilves andM S Luther ldquoReflection crackingmodels review and laboratory evaluation of engineering fab-ricsrdquo Transportation Research Record no 916 pp 18ndash25 1983

[97] P E Joseph R Hass W A Phang and L Rothenburg ldquoLowtemperature reflecting cracking through asphalt overlaysrdquo inProceeding 6th International Conference on Structural Design ofAsphalt Pavements vol 1 pp 13ndash17 1987

[98] C T Shin M Tia and B E Ruth ldquoEvaluation of the effectof crumb rubber and SBR on rutting resistance of asphaltconcreterdquo American Chemical Society Division Fuel Chemistryvol 41 no 4 pp 1227ndash1231 1996

[99] S Tayfur H Ozen and A Aksoy ldquoInvestigation of rutting per-formance of asphalt mixtures containing polymer modifiersrdquoConstruction and Building Materials vol 21 no 2 pp 328ndash3372007

[100] E R Brown and S A Cross ldquoA national study of rutting inasphalt pavementrdquo Journal of the Association of Asphalt PavingTechnologists vol 61 pp 535ndash583 1992

[101] J Harvey S Weissman F Long and C Monismith ldquoTeststo evaluate the stiffness and permanent deformation charac-teristics of asphaltbinder-aggregate mixes and their use inmix design and analysisrdquo in Proceedings of the Asphalt PavingTechnology pp 572ndash604 March 2001

[102] M J Fernando andM S Mesdary ldquoEffect of rubberised asphalton Portland cement coated aggregates in road constructionunder severe conditions of traffic and climaterdquo in Proceedingsof the 14th Australian Road Research Board Conference (ARRBrsquo88) vol 14 pp 78ndash86 1988

[103] Asphalt InstituteMix Design Methods for Asphalt Concrete andOtherHotMix Types Asphalt InstituteManual Series no 2 (MS-2) 1990


[104] L K Wayne and F L Roberts ldquoPerliminary framework fora rotational bituminous mix design to mitigate pavementfailuresrdquo in Proceedings of the 14th Australian Road ResearchBoard Conference (ARRB rsquo88) vol 14 pp 45ndash53 1988

[105] L E Wood andM S Mamlouk ldquoEffect of aggregate top size onasphalt emulsion mixture propertiesrdquo Transportation ResearchRecord no 821 pp 44ndash49 1981

[106] M Brennen M Tia A Altshaeffl and L E Wood ldquoLaboratoryinvestigation of the use of foamed asphalt for recycled bitumi-nous pavementsrdquo Transportation Research Record no 911 pp80ndash87 1983

[107] W Hadley W Hudson and T W Kennedy ldquoA method ofestimating tensile properties of materials tested in indirecttensionrdquo Summary Report 7-98 Center for Highway ResearchAustin Tex USA 1970

[108] M W Witczak K E Kaloush T Pellinen M El-Basyounyand H Von Quintus ldquoSimple performance test for superpavemix designrdquo National Cooperation Highway Research Program(NCHRP) Report 465 Arizona State University 2002

[109] SHRP ldquoStandard method for the test of determining of fatiguelife of compacted bituminous mixture subjected to repeatedflexural bendingrdquo SHRP Designation M-009 1994

[110] M N Guddati Z Feng and R Kim ldquoToward a micromechan-ics-based procedure to characterize fatigue performance ofasphalt concreterdquo Transportation Research Record no 1789 pp121ndash128 2002

[111] R A Eaton R J Roberts and R R Blackburn ldquoUse of scraprubber in asphalt pavement surfacesrdquo Special Report 91-27US Army Corps of Engineers Cold Regions Research andEngineering Laboratory 1991

[112] N L Dallas and M Kamyar ldquoOverview of a rational asphaltconcretemixture design for Texasrdquo Journal of the TransportationResearch Board no 1269 pp 125ndash132 1990

[113] H Al-Abdul-Wahhab and G Al-Amri ldquoLaboratory evaluationof reclaimed rubber asphaltic concrete mixesrdquo Journal of Mate-rials in Civil Engineering vol 3 no 3 pp 189ndash203 1991

[114] J M Read Fatigue cracking of bituminous paving mixtures[PhD thesis] Department of Civil Engineering University ofNottingham Nottingham UK 1996

[115] M Castro and J A Sanchez ldquoEstimation of asphalt concretefatigue curvesmdasha damage theory approachrdquo Construction andBuilding Materials vol 22 no 6 pp 1232ndash1238 2008

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of



CeramicsJournal of


CompositesJournal of

NanoparticlesJournal of



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Biomaterials


NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

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NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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MetallurgyJournal of


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MaterialsJournal of


Nano

materials


Journal ofNanomaterials


(iv) improved homogeneity high thermo stability andaging resistance which helps reduce the hardeningand initial aging of the binders during mixing andconstruction

Worldwide there are many additives used as reinforcingmaterial into the asphalt mixes among these additives usedis the CRM [3 4] In this paper asphalt pavement designcriteria will be displayed and a considerable review on theuse of crumb rubber in asphalt pavement reinforcement willbe presented and discussed It also includes a review on theeffects of CRM on the stiffness rutting and fatigue resistanceof road pavement In order to understand the asphalt-rubberreinforcement technology asphalt properties and crumbrubber characteristics will be illustrated

2 Asphalt Pavement Design

The design of asphalt mixture involves the selection andproportioning of materials to obtain the desired propertiesin the finished product Asphalt concrete (AC) is designed toresist rutting fatigue low temperatures cracking and otherdistressesThe serious distresses associatedwith asphalt pave-ments are cracking which occurs at intermediate and lowtemperatures and permanent deformation which occurs athigh temperaturesThese distresses reduce the services life ofthe pavement and elevate the maintenance costs [6] Asphaltcement binds the aggregate particles together enhancing thestability of the mixture and providing resistance to deforma-tion under induced tensile compressive and shear stressesThe performance of asphalt mixture is a function of asphaltcement aggregate and its volumetric properties In recentyears there has been a rapid increase in using additives inasphalt concrete mixtures to improve its properties Asphaltroad pavements are defined as asphalt layers built boundover a granular base Due to this the total pavement structuredeflects due to traffic loads thus these types of pavements areknown as flexible pavements A flexible pavement structureis composed of various layers of materials Basically thepavement structure is divided into three layers namely bitu-minous surfacing (surface course) road base (base course)and subbase [6] as shown in Figure 1

Flexible pavements could have one of the three typicalcross section geometries as shown in Figure 2 At the pave-ment edge between the pavement edge and adjacent soil twoforces exist which are vertical friction 119865 and lateral passivepressure119875The friction force (119865) relies on relativemovementcoefficient of friction and the lateral passive pressure Lateralpassive pressure (119875) varies depending on soil type and weightof the soil subjected to the pavement As illustrated inFigure 2(a) the soil wedge is small and the two forces (119865and 119875) can be ignored On the other hand as shown inFigures 2(b) and 2(c) the friction and passive forces maybe significant and the pavement edge can move laterally andvertically [7]

Asphalt concrete (AC) should have high stiffness to beable to resist permanent deformation On the other hand themixtures should have enough tensile stress at the bottom ofthe asphalt layer to resist fatigue cracking after many load

Surface courseBase course

Subbase course

Figure 1 Typical flexible pavement structure

applications Figure 3 presents the orientation of principalstresses with respect to position of rolling wheel load [8]

The overall objective for the design of asphalt pavingmixes is to determine an economical blend and gradation aswell as asphalt binder that will yield a mix having sufficientbinder to ensure a durable pavement sufficient stabilitysufficient voids in the total compactedmix to allow for a slightamount of additional compaction under traffic loading with-out flushing and sufficient workability to permit efficientplacement of the mix without segregation [9]

The increased demand on highway roads might reduceits strength properties and make roads more susceptibleto permanent distresses and failure In general pavementperformance properties are affected by the bitumen binderproperties it is known that the conventional bitumen has alimited range of rheological properties and durability that arenot sufficient enough to resist pavement distressesThereforebitumen researchers and engineers are looking for differenttypes of bitumenmodifiersThere aremanymodification pro-cesses and additives that are currently used in bitumen mod-ifications such as styrene butadiene styrene (SBS) styrene-butadiene rubber (SBR) ethylene vinyl acetate (EVA) andcrumb rubber modifier (CRM) The use of commercialpolymers such as SBS and SBR in road and pavement con-structionwill increase the construction cost as they are highlyexpensive materials However with the use of alternativematerials such as crumb rubber modifier (CRM) it willdefinitely be environmentally beneficial and not only it canimprove the bitumen binder properties and durability but ithas also a potential to be cost effective [10ndash12]

3 Historical Experiment of Using CrumbRubber in Pavement

In 1840s the earliest experiments had involved incorporatingnatural rubber into asphalt binder to increase its engineeringperformance properties The process of asphalt modificationinvolving natural and synthetic rubber was introduced asearly as 1843 [13] In 1923 natural and synthetic rubbermodifications in asphalt were further improved [14 15]According toYildirim [15] the development of asphalt-rubbermaterials being used as joint sealers patches andmembranesbegan in the late 1930s The first attempt to modify asphaltbinders by adding rubber was made in 1898 by Gauedmbergwho patented a process for manufacturing asphalt rubberFrance was then given credit for installing the first road witha crumb rubber modified asphalt surfacing material [2]



156 F

P

Sub-grade



156 F

P

Sub-grade



F

P

Sub-grade



1205901

1205901

1205901

1205901

1205901

1205901

12059021205902

1205902

12059021205902

1205902

120590y120590y

120590y120590y

120590y

120590y

120590x120590x120590x 120590x 120590x 120590x

120591xy

120591xy

120591xy

120591xy

Shear stress

Stre

ss

Time

Vertical stress

Horizontal stress










Aromatics

80

80

80

60

60

60

40

40

40

20

20







olar

mas

s-pa

raffi

ne C

nH

2n+2

0

142

292

422

0

5

10

15

20

25

30Ca

rbon

num

ber

minus18

0 200 400 600 800 1000 1200 1400∘F760∘C64953931520493 427


nC10

nC14

nC16

nC18

nC20

nC22

nC24

nC26

nC11

nC6











S

SS

S

NN

OH


Resins

Bitumen

Aromatics

Asphaltenes

















(a) (b)


6mm rubber

(a)


(b)

20 mesh rubber

(c)

10 mesh rubber

(d)














Appl

ied

stres

s (120590

)

t0 t1

Stra

in (120576

)

Time-t

Time-t


Stra

in (120576

)

Time-t


Strain (120576)

Instantaneous

Instantaneous

elasticity


Delayedrecovery

recovery


Time-t





(1)



1198791

log 1205781198792

)

log (11987921198791) (2)


and 1205781198792


1and 119879

2





119878 (119905) =120590

120576 (119905) (3)



119866lowast

= (120591

120574)

1198661015840

= cos (120575) (120591120574)

11986610158401015840

= sin (120575) (120591120574)

120575 =119866

11986610158401015840

(4)











































y

x

z














Originalprofile



Originalprofile

Shear plane














119891) and initial


119891) of




Mod

ulus

Number of cycles






11 Conclusion





References































































































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials





156 F

P

Sub-grade



156 F

P

Sub-grade



F

P

Sub-grade



1205901

1205901

1205901

1205901

1205901

1205901

12059021205902

1205902

12059021205902

1205902

120590y120590y

120590y120590y

120590y

120590y

120590x120590x120590x 120590x 120590x 120590x

120591xy

120591xy

120591xy

120591xy

Shear stress

Stre

ss

Time

Vertical stress

Horizontal stress










Aromatics

80

80

80

60

60

60

40

40

40

20

20







olar

mas

s-pa

raffi

ne C

nH

2n+2

0

142

292

422

0

5

10

15

20

25

30Ca

rbon

num

ber

minus18

0 200 400 600 800 1000 1200 1400∘F760∘C64953931520493 427


nC10

nC14

nC16

nC18

nC20

nC22

nC24

nC26

nC11

nC6











S

SS

S

NN

OH


Resins

Bitumen

Aromatics

Asphaltenes

















(a) (b)


6mm rubber

(a)


(b)

20 mesh rubber

(c)

10 mesh rubber

(d)














Appl

ied

stres

s (120590

)

t0 t1

Stra

in (120576

)

Time-t

Time-t


Stra

in (120576

)

Time-t


Strain (120576)

Instantaneous

Instantaneous

elasticity


Delayedrecovery

recovery


Time-t





(1)



1198791

log 1205781198792

)

log (11987921198791) (2)


and 1205781198792


1and 119879

2





119878 (119905) =120590

120576 (119905) (3)



119866lowast

= (120591

120574)

1198661015840

= cos (120575) (120591120574)

11986610158401015840

= sin (120575) (120591120574)

120575 =119866

11986610158401015840

(4)











































y

x

z














Originalprofile



Originalprofile

Shear plane














119891) and initial


119891) of




Mod

ulus

Number of cycles






11 Conclusion





References































































































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials








Aromatics

80

80

80

60

60

60

40

40

40

20

20







olar

mas

s-pa

raffi

ne C

nH

2n+2

0

142

292

422

0

5

10

15

20

25

30Ca

rbon

num

ber

minus18

0 200 400 600 800 1000 1200 1400∘F760∘C64953931520493 427


nC10

nC14

nC16

nC18

nC20

nC22

nC24

nC26

nC11

nC6











S

SS

S

NN

OH


Resins

Bitumen

Aromatics

Asphaltenes

















(a) (b)


6mm rubber

(a)


(b)

20 mesh rubber

(c)

10 mesh rubber

(d)














Appl

ied

stres

s (120590

)

t0 t1

Stra

in (120576

)

Time-t

Time-t


Stra

in (120576

)

Time-t


Strain (120576)

Instantaneous

Instantaneous

elasticity


Delayedrecovery

recovery


Time-t





(1)



1198791

log 1205781198792

)

log (11987921198791) (2)


and 1205781198792


1and 119879

2





119878 (119905) =120590

120576 (119905) (3)



119866lowast

= (120591

120574)

1198661015840

= cos (120575) (120591120574)

11986610158401015840

= sin (120575) (120591120574)

120575 =119866

11986610158401015840

(4)











































y

x

z














Originalprofile



Originalprofile

Shear plane














119891) and initial


119891) of




Mod

ulus

Number of cycles






11 Conclusion





References































































































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




olar

mas

s-pa

raffi

ne C

nH

2n+2

0

142

292

422

0

5

10

15

20

25

30Ca

rbon

num

ber

minus18

0 200 400 600 800 1000 1200 1400∘F760∘C64953931520493 427


nC10

nC14

nC16

nC18

nC20

nC22

nC24

nC26

nC11

nC6











S

SS

S

NN

OH


Resins

Bitumen

Aromatics

Asphaltenes

















(a) (b)


6mm rubber

(a)


(b)

20 mesh rubber

(c)

10 mesh rubber

(d)














Appl

ied

stres

s (120590

)

t0 t1

Stra

in (120576

)

Time-t

Time-t


Stra

in (120576

)

Time-t


Strain (120576)

Instantaneous

Instantaneous

elasticity


Delayedrecovery

recovery


Time-t





(1)



1198791

log 1205781198792

)

log (11987921198791) (2)


and 1205781198792


1and 119879

2





119878 (119905) =120590

120576 (119905) (3)



119866lowast

= (120591

120574)

1198661015840

= cos (120575) (120591120574)

11986610158401015840

= sin (120575) (120591120574)

120575 =119866

11986610158401015840

(4)











































y

x

z














Originalprofile



Originalprofile

Shear plane














119891) and initial


119891) of




Mod

ulus

Number of cycles






11 Conclusion





References































































































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




S

SS

S

NN

OH


Resins

Bitumen

Aromatics

Asphaltenes

















(a) (b)


6mm rubber

(a)


(b)

20 mesh rubber

(c)

10 mesh rubber

(d)














Appl

ied

stres

s (120590

)

t0 t1

Stra

in (120576

)

Time-t

Time-t


Stra

in (120576

)

Time-t


Strain (120576)

Instantaneous

Instantaneous

elasticity


Delayedrecovery

recovery


Time-t





(1)



1198791

log 1205781198792

)

log (11987921198791) (2)


and 1205781198792


1and 119879

2





119878 (119905) =120590

120576 (119905) (3)



119866lowast

= (120591

120574)

1198661015840

= cos (120575) (120591120574)

11986610158401015840

= sin (120575) (120591120574)

120575 =119866

11986610158401015840

(4)











































y

x

z














Originalprofile



Originalprofile

Shear plane














119891) and initial


119891) of




Mod

ulus

Number of cycles






11 Conclusion





References































































































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials














(a) (b)


6mm rubber

(a)


(b)

20 mesh rubber

(c)

10 mesh rubber

(d)














Appl

ied

stres

s (120590

)

t0 t1

Stra

in (120576

)

Time-t

Time-t


Stra

in (120576

)

Time-t


Strain (120576)

Instantaneous

Instantaneous

elasticity


Delayedrecovery

recovery


Time-t





(1)



1198791

log 1205781198792

)

log (11987921198791) (2)


and 1205781198792


1and 119879

2





119878 (119905) =120590

120576 (119905) (3)



119866lowast

= (120591

120574)

1198661015840

= cos (120575) (120591120574)

11986610158401015840

= sin (120575) (120591120574)

120575 =119866

11986610158401015840

(4)











































y

x

z














Originalprofile



Originalprofile

Shear plane














119891) and initial


119891) of




Mod

ulus

Number of cycles






11 Conclusion





References































































































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials













Appl

ied

stres

s (120590

)

t0 t1

Stra

in (120576

)

Time-t

Time-t


Stra

in (120576

)

Time-t


Strain (120576)

Instantaneous

Instantaneous

elasticity


Delayedrecovery

recovery


Time-t





(1)



1198791

log 1205781198792

)

log (11987921198791) (2)


and 1205781198792


1and 119879

2





119878 (119905) =120590

120576 (119905) (3)



119866lowast

= (120591

120574)

1198661015840

= cos (120575) (120591120574)

11986610158401015840

= sin (120575) (120591120574)

120575 =119866

11986610158401015840

(4)











































y

x

z














Originalprofile



Originalprofile

Shear plane














119891) and initial


119891) of




Mod

ulus

Number of cycles






11 Conclusion





References































































































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials





119866lowast

= (120591

120574)

1198661015840

= cos (120575) (120591120574)

11986610158401015840

= sin (120575) (120591120574)

120575 =119866

11986610158401015840

(4)











































y

x

z














Originalprofile



Originalprofile

Shear plane














119891) and initial


119891) of




Mod

ulus

Number of cycles






11 Conclusion





References































































































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






































y

x

z














Originalprofile



Originalprofile

Shear plane














119891) and initial


119891) of




Mod

ulus

Number of cycles






11 Conclusion





References































































































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




Originalprofile



Originalprofile

Shear plane














119891) and initial


119891) of




Mod

ulus

Number of cycles






11 Conclusion





References































































































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






119891) and initial


119891) of




Mod

ulus

Number of cycles






11 Conclusion





References































































































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






References































































































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






























































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



review article a review on using crumb rubber in

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