Evaluation and optimization of the engineering properties of polymer-modified asphalt

75Practical Failure Analysis Volume 2(3) June 2002

Evaluation and Optimization of the EngineeringProperties of Polymer-Modified Asphalt

J.-S. Chen, M.-C. Liao, and H.-H. Tsai

(Submitted 3 December 2001; in revised form 21 February 2002)

Polymers are increasingly being used to modify asphalt and enhance highway pavement performance.This paper reports the development of a procedure to evaluate and optimize a polymer-modified asphalt(PMA). Two asphalt cements and two styrene-butadiene-styrene (SBS) copolymers were mixed at tenconcentration levels. The engineering properties and morphologies of the binders were investigated usinga dynamic shear rheometer, scanning electron microscopy (SEM), and other rheological techniques. Themorphology of the PMA was characterized by the SBS concentration and the microstructure of thecopolymer. Polymer modification increased the elastic responses and dynamic moduli of asphalt binders.As the SBS concentration increased, the copolymer gradually became the dominant phase, accompaniedby a change in engineering properties. Results from SEM demonstrated that, up to 6% concentration,good compatibility exists between SBS and asphalt binder. The modified binders show either a continuousasphalt phase with dispersed SBS particles or a continuous polymer phase with dispersed asphalt globules,or two interlocked continuous phases. The optimum SBS content was determined based on the formationof a critical network between asphalt and polymer.

J.-S. Chen, M.-C. Liao, and H.-H. Tsai, National Cheng Kung University, Department of Civil Engineering, Tainan 70101, Taiwan,R.O.C. Contact e-mail: [email protected].

Keywords: polymer-modified asphalt, styrene-butadiene-styrene, compatibility

PFANF8 (2002) 3:75-83 © ASM International

IntroductionOne of the primary uses for asphalt is in highway

construction. A typical highway pavement containsstone aggregate surrounded by a matrix of asphaltbinder. The performance of such highway pavementsis controlled by the properties of the asphalt cement,because asphalt is the continuous matrix and theonly deformable component. At high temperatures(40 to 60 °C), asphalt exhibits a viscoelastic behavior.Pavements made of asphalt may show distress whenexposed to high temperatures. At elevated temper-atures, permanent deformation (rutting) occurs and

leads to channels in the direction of travel. This isattributed to the viscous flow of the asphalt matrixin paving mixtures, which retains strains inducedby traffic. Therefore, pavement performance isstrongly associated with the rheological propertiesof asphalt cement.

Increased traffic factors such as heavier loads,higher traffic volume, and higher tire pressure de-mand higher performance pavements. A high per-formance pavement requires asphalt cement that isless susceptible to high temperature rutting or lowtemperature cracking and has excellent adherenceto stone aggregates. Mixing a polymer with theasphalt has potential for addressing the distressproblems that exist in today’s highways. Polymer-modified asphalt (PMA) binders are, however,poorly understood scientifically. Significant researchis needed to better understand the relationshipbetween the compositions and properties of PMAs.

A limited number of polymers have been favored,including homopolymers (low density polyethylene[LDPE], high density polyethylene [HDPE],ethylene-propylene-diene [EPDM], and ataticpolypropylenes [APP]), random copolymers

Note from peer reviewer:This report is not failure analysis. It may be, how-

ever, considered failure avoidance. This reviewer hashad the privilege, over the past few months, of travel-ing extensively in the United States, from the PacificOcean to the Atlantic Ocean and from the Gulf ofMexico to the Great Lakes. Although there are manyfine roads, there are also several, especially in areaswhere temperature variations are large, that couldbenefit from the pavement enhancement suggested inthis report.

Evaluation and Optimization of the Engineering Properties of Asphalt (continued)

76 Practical Failure AnalysisVolume 2(3) June 2002

(styrene-butadiene random [SBR] copolymers andethylene-vinyl acetate [EVA] copolymers), andtriblock copolymers (styrene-butadiene-styrene[SBS], styrene-isoprene-styrene [SIS], and theirhydrogenated forms).[1–11] The high cost of thesepolymers makes the commercial use of modifiedasphalt only attractive for road construction if theamount of polymer needed to significantly improvepavement performance is relatively small. The majorgoal in this study is to optimize the polymer contentto a level that satisfactorily improves asphalt proper-ties at a minimum cost.

Styrene-butadiene-styrene (SBS), one of the mostpromising polymers for asphalt modification,[1–3,

6–7, 12–15] was selected for use in this study. In priorstudies of the compatibility of triblock copolymerswith asphalt through property changes, SBS hasusually been added to bitumen in small quan-tities.[12–16] These studies do not provide details ofthe immiscibility of the polymer with asphaltcomponents. Furthermore, PMA may separate intopolymer-rich and asphalt-rich phases during hotstorage. Highway agencies state that there is anurgent need to monitor the stability of PMA; how-ever, no specification is established to regulate thephase separation in PMA. In this investigation,rheological tests and scanning electron microscopy(SEM) are used to evaluate the interactions ofasphalt with SBS by monitoring changes in blendmicrostructures.

MaterialsMaterials Selection

The selected asphalts were viscosity graded AC-

10 and AC-20 provided by the China Petroleumand Chemical Corporation (Beijing, China). Table1 lists the basic properties of typical paving gradeasphalts used in Taiwan. Asphalt consists of threemain constituents: oil, resin, and asphaltene. Oilsin asphalt have the lowest molecular weight(24–800 g/mol), a large number of saturated sidechains, and few rings. Resins are the intermediatemolecular weight compounds (800–2000 g/mol).Asphaltenes are the highest molecular weightcompounds (1800–8000 g/mol), with aromatic ringstructures, few side chains, and functional groupsthat may react with potential polymer modifiers.The average asphaltene content of the samples was15%, while the oil and the resin constituted 62and 23% of the samples, respectively. This com-position was believed to have a desirable com-patibility with polymers.

Two types of SBS (SBS-l and SBS-r) were selectedfor this investigation. Chie-Mei Enterprise Co. Ltd.(Taipei Hsien, Taiwan) supplied the SBS in theform of a graded ground crumb mixture with amaximum size of about 1 mm diameter. This poly-mer is a high molecular weight, random block co-polymer consisting of approximately 30% styreneand 70% butadiene. Table 2 lists the basic propertiesof the two SBS copolymers.

PreparationSBS-modified asphalt was prepared by melt

blending. The SBS materials, supplied in the formof a fine uniform powder, were suitable for mixingwith asphalt due to the high surface area of theparticles. Mixing was performed using a TokyoKikakikae mixer model Eyel 4 (Kikakikae Company,

Table 2 Properties of Styrene-Butadiene-Styrene (SBS) Copolymer

Styrene-Butadiene Tensile Strength, Number Avg, MolecularCopolymer Structure Ratio Specific Gravity MPa Mn Weight, Mw

SBS-l linear 31.5/68.5 0.95 1.5 130,000 145,000SBS-r radial 30/70 0.95 0.6 320,000 460,000

Table 1 Basic Properties of Asphalts

Penetration Softening Viscosity Weight Avg,Grade 25 °C (dmm) Point, °C 60°C (poise) Asphaltenes, % Oils, % Resins, % Mw

AC-10 93 31 962 12.1 70.1 17.8 1280

AC-20 62 43 1856 18.3 54.8 26.9 1580


Tokyo, Japan). The SBS copolymer was mixed withasphalt binders using a preparation methoddeveloped in the laboratory that maximized therheological properties while minimizing asphaltdegradation. The mixer was operated at a constantmixing speed of 150 rpm to ensure that no voidswere created in the mixtures. An x-shaped propellerwas used to stir the polymer-modified asphalt. Allpolymers were blended with the asphalt cement atten different concentration levels. The SBS contentsused were 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9% (by weight)of the blend. A total of 40 mixes were prepared.

Six hundred grams of the asphalt were heated tofluid condition and poured into a 2000 ml sphericalflask, which was then placed in a heating mantle.To avoid the adverse effects of excessive heat,temperature was carefully monitored throughoutmixing using two thermocouple probes. The firstprobe, which was installed between the beaker andheating mantle, controlled the power input. Thesecond probe directly measured the temperature ofthe binder inside the beaker. Upon reaching 180°C, a weighed amount of polymer was added to theasphalt (slowly, to prevent the polymer particles frompossible agglomeration). Mixing was then continuedat 180 °C for 2 h to produce homogeneous mixtures.After completion, the SBS-modified asphalt wasremoved from the flask and divided into small con-tainers. The blend was cooled to room temperature,sealed with aluminum foil, and stored for furthertesting. The process for preparing the modifiedbinders exposed the asphalt to high temperature andair for an extended time, which led to hardening ofthe bitumen. To assure an accurate evaluation ofpolymer effects, the base asphalt was also subjectedto the same treatments as the polymer-bitumenblends.

Test Methods

Softening Point TestSoftening points were used to determine the temp-

erature at which a phase change occurs in the binder.A steel ball weighing 3.5 g was placed on a disk ofasphalt sample contained in a horizontal, verticallysupported, 20 cm diameter metal ring. The assemblywas heated in an ethylene glycol bath at 5 °C/min.The softening point was taken as the temperatureat which the sample became soft enough to allowthe ball, enveloped in the sample material, to fall a

distance of 25.4 mm. This was recorded as the ring-and-ball softening temperature (Tr+b).

ViscosityThe viscosity at 60 °C was used for grading the

consistency of the asphalt cement. Under closelycontrolled conditions, the time required for a fixedvolume of the asphalt to be drawn up through acapillary tube by means of vacuum (300 ± 0.5 mmHg vacuum) was measured. The viscosity in poisewas calculated by multiplying the flow time inseconds by the viscometer calibration factor.

Storage Stability TestThe possible separation of the constituents of the

PMA during storage was evaluated using a heatedoven in the laboratory. Samples were held verticallyin aluminum tubes (25.4 mm, or 1 in., diameter by139.7 mm, or 5.5 in., long) in an oven heated to165 °C for 1, 2, 3, and 7 days. The selection ofthese times was based on expected highway con-struction delays caused by rain. Due to the lowerdensity of the SBS, the dispersed phase might floatupward and change concentrations. At the end ofthe test period, samples were placed in a freezer at–10 °C for 4 h to solidify the PMA completely.Upon removing the tubes from the freezer, eachsample was cut with a spatula and hammered intothree portions of equal length. The top and bottomsamples from the same tube were prepared forfurther tests.

Dynamic Shear Rheometer (DSR)The rheological properties of asphalt were

measured with an AR-500 model DSR (Carri-MedCorporation, now TA Instruments, New Castle,DE) over a broad range of temperatures. All testswere performed in the linear viscoelastic range. Fortests at 40 °C and higher, a 1 mm gap and a 25 mmdiameter plate were used. For tests below 40 °C, a2 mm gap and an 8 mm diameter plate were used.About 1 g of binder was applied to the bottom plate,covering the entire surface. After heating to thedesired test temperature, the top plate was broughtinto contact with the sample and the sample wastrimmed. An actuator then applied a sinusoidalstrain. Viscoelastic properties at different temp-eratures and frequencies were obtained. A specificstrain level was determined at each testing temp-erature to assure that the strain was kept low enough,



within the linear viscoelastic range. The actual strainand torque were measured and used as input for acomputer program that calculates various viscoelasticparameters, including complex modulus (G∗) andphase angle (δ). The G∗ value is a measure of thetotal resistance of a material to deformation whenrepeatedly sheared. The δ value is an indicator ofthe relative amount of recoverable and non-recoverable deformation.

Toughness and Tenacity TestA toughness and tenacity test was used to monitor

the tensile strength properties of PMA binder.Samples were imbedded in a container with ahemispherical tension head and allowed to cool to25 °C. The head was then pulled at a rate of 50 cm/min to produce a load-deformation curve accordingto ASTM D 5801.[17] A typical tensile strengthload deflection curve is shown in Fig. 1. The tenacityis defined as the area of B, and the toughness is thetotal area under the curve, A+B.

Wheel-Tracking TestA wheel-tracking test, which simulates the effect

of traffic on pavements, was performed to evaluatePMA susceptibility to permanent deformation.Samples of different asphalts were carefully preparedto have the same binder content, air void content,

gradation, and aggregate type as those used in thefield. The aggregate used in preparing the pavingmixture is described in Table 3. The wheel-trackingtest was conducted at the mean highest weeklyaverage temperature (60 °C) under dry conditions.A smooth, solid steel wheel traveling at a speed of1.4 km/h was used to correlate rutting. Rut depthswere measured after every 200 wheel passes on 300by 300 by 70 mm samples with a simulated tirepressure of 540 kPa (80 psi).

Scanning Electron Microscopy (SEM)Scanning electron microscopy facilitated the direct

observation of PMA structure. A preparationmethod was used to leach out the oil phase with asolvent without disturbing the binder. The deoiledsamples were placed on filter paper and weremetallized and then observed with a Hitachi ModelS-2500 SEM (Taipei, Taiwan). The accelerationvoltage of the electron beam was 5 kV. Fissurechanges in PMA were visible, and the main struc-ture was observed. This technique reveals thedispersed polymer-rich phase as bright, while thecontinuous asphaltene-rich phase remains dark.Previous researchers also found SEM preferablebecause it provides a clear view of material in theraw state.[9, 18–20]

Fig. 1 Typical results from toughness and tenacity testFig. 2 Traditional properties of SBS modified with asphalt

AC-10

Table 3 Aggregate Gradation

Sieve Size (mm) 37.5 25 12.5 10 4.75 2.5 0.63 0.3 0.075Percent Passing 100 94.4 64.4 53.3 39.9 26.9 13.9 9.24 5.12


Results and Discussion

Traditional Properties of PMAThe traditional properties of the binders mixed

with different SBS concentrations are presented inFig. 2. The viscosity and the softening pointtemperature increase with increasing polymerconcentration. There is limited increase in viscosityat a concentration of 1% because the SBS only actsas a dispersed polymer. At 2 to 3% concentration,the viscosity increases by a factor of two because theSBS begins to form a localized network structure.The radial SBS tends to have higher values than alinear one due to the higher molecular weight.

At concentrations greater than 3%, the localnetworks begin to interact to form a continuousnetwork throughout the binder. The formationresults in a linear increase in the viscosity withincreasing SBS content. The network acts as a sup-port structure reinforcing the asphalt and resistingdeformation. Once 6% SBS is added to the asphaltbinder, there is a dramatic increase in the viscosity,as shown in Fig. 2. The addition of at least 6% SBSappears to provide the viscosity necessary to enhanceasphalt properties.

The ring-and-ball softening point temperature(Tr+b) is another important performance criterionfor bituminous materials. The Tr+b increases rapidlyabove a 5 to 6% addition of SBS (Fig. 2). After thispoint the elastomeric phase in SBS becomescontinuous, thus contributing to the steady increasein the Tr+b. The magnitude of the achievable increasein Tr+b is a function of polymer type and con-centration. The SBS content needs to be at least 6%

to have Tr+b reach 60 °C, which is the maximumtemperature generally measured in pavements.

Figure 3 shows the toughness and tenacity of thesamples at various SBS concentrations. Toughnessis the total work required to completely separate thetension hand from the sample under the specifictest conditions. Tenacity is a measure of the in-creasing force as the sample is stretched past theinitial peak. Figure 3 demonstrates that the higherthe SBS content, the more work is required to stretchPMA. The properties of base asphalts also affectthe toughness and tenacity, indicating that mixingdifferent bitumens with SBS could result in differentengineering properties. Both toughness and tenacityreach the maximum values at 6% SBS. The gradualdecrease in the toughness and tenacity after the peakpoint indicates that adding more than 6% SBS maylead to morphological discontinuity between SBSand asphalt. This type of discontinuity is related tothe compatibility between SBS and asphalt. Stifferbase AC-20 asphalt provides higher strength thanthe softer AC-10 (Fig. 3). The toughness andtenacity test has proven to be a good method forevaluating PMA strength.

Compatibility Between Asphalt and PolymerCompatibility was studied using SEM by charac-

terizing the nature of the continuous phase and thefineness of the dispersion of the discontinuous phase.The morphology of the SBS/asphalt blends isdisplayed in Fig. 4, in which the SBS content isincreased from 3 to 9%. At a low polymer contentof 3% SBS, the small polymer spheres swollen byasphalt compatible fractions (e.g., aromatic oils) arespread homogeneously in a continuous bitumenphase under a magnification of 2000×. In this case,the asphalt is the continuous phase of the system,and the polymer phase is dispersed through it (Fig.4a). The light phase in the picture represents theswollen polymer, and the dark phase is the asphalt.With its lowered oil content, the asphalt phase hasa correlatively higher asphaltene content. As a re-sult, cohesion and elasticity are both enhanced. Inaddition, the polymer phase is dispersed throughthe asphalt matrix. At higher service temperatures,the stiffness modulus of the polymer phase is higherthan that of the matrix. These reinforcing propertiesof the polymer phase improve the mechanicalperformance of the binder. At low temperatures, thestiffness modulus of the dispersed phase is lower

Fig. 3 Toughness and tenacity of linear SBS mixing with twoasphalts



than that of the matrix, which reduces its brittleness.Consequently, the dispersed polymer phase enhancesthe properties of the binder at both high and lowservice temperatures.

Microstructure appears to be forming at 5% SBSwhere the two phases are continuous and interlocked,as illustrated in Fig. 4(b). At this concentration theSBS phase gradually becomes the matrix of thesystem, and the PMA starts the phase inversion.This phase inversion results when the oils swell theSBS copolymer and the asphalt is enriched inasphaltenes that contain virtually no polymer. TheSBS copolymers represent a triblock structure inwhich polystrene is the thermoplastic end block andpolybutadiene is the rubbery midblock. Within thepolymer-rich phase there are two microphases—swollen polybutadiene and essentially pure poly-styrene domains—that act as physical crosslink sitesand form a network. When the polymer-rich phaseforms the continuum as shown Fig. 4(b), the SBS-modified asphalt displays rubber-like elasticity. Suchsystems are generally difficult to control and posestability problems. Their micromorphology andproperties often depend on temperature history. Testresults from viscosity and Tr+b in Fig. 2 confirm thephase inversion in PMA with relatively low (<5%)concentrations of SBS.

Better dispersion of the polymer is obtained at6% SBS (Fig. 4c). A continuous polymer phasestabilizes the network between asphalt and polymer.The stabilization at 6% SBS explains why the PMAreaches peak values on toughness and tenacity (Fig.3). The minimum percentage of polymer needed toensure formation of a continuous phase depends, toa greater extent, on the base asphalt rather than onthe polymer. In this case, the polymer content issufficiently high for the polymer phase to be thematrix of the system.

The SBS becomes the dominant phase at 9% (Fig.4d). The large polymer domains in the morphologysuggest a large degree of incompatibility. This in-compatibility leads to decrease in engineeringproperties such as toughness and tenacity (Fig. 3).Because of differences in molecular weight, polarity,and structure, there is a chemical dissimilaritybetween asphalt and SBS. The morphology is theresult of the mutual interaction of SBS and asphaltand, consequently, is influenced by asphalt com-position and polymer nature and content. Obser-vations of PMA microstructure agree well with thetest results, as shown in Fig. 3.

Stability of PMABecause of delays such as rain, the storage ability

of modified asphalt binders is an important char-acteristic during actual highway construction. It isnot unusual for the polymer to be blended with theasphalt and stored for several days at a time beforebeing applied. The effect of storage time on uni-formity at higher temperature was studied by keep-ing the binder in a vertical position in an aluminumtube at 165 °C for up to seven days. The difference

Fig. 4 Microstructures of SBS-modified asphalt observed bySEM. (a) 3% SBS, (b) 5% SBS, (c) 6% SBS, (d) 9% SBS

a b

c d

Fig. 5 Difference in softening point between top and bottomsections in terms of SBS weight concentration


in Tr+b between the top and bottom sections of thesamples was used to evaluate the stability of thePMA according to ASTM D 5892.[21] A low Tr+b

difference is observed up to the addition of 6% SBS(Fig. 5). Therefore, the uniformity of the PMA isnot likely to be affected by storage time, as long asthe SBS content is =6%.

A significant difference in Tr+b occurs after anaddition of 7% SBS. Due to the chemical dis-similarity between asphalt and polymer, the SBS-modified binders were determined to bethermodynamically immiscible. Consequently,storage stability of polymer-modified binders isassociated with the compatibility between asphaltand polymer.

Figure 6 shows that the Tr+b difference can becontrolled within 2 °C and the PMA can beproperly stored. At higher polymer concentrations,segregation becomes evident between top andbottom samples because the Tr+b difference is higher

than 4 °C. Thus, as a monitor of PMA stability, thehighway engineers in Taiwan selected 2 °C as themaximum Tr+b difference.

Rheological Properties of PMAThe stress relaxation technique was used to eval-

uate the elastic nature of the base and PMAs. Thechanges in stress are expressed in the form of complexmodulus, G∗, for different concentrations of SBS-modified asphalt (Fig. 7). For clarity, curves of otherblends are not plotted, but they all lie between theupper and lower extreme curves in this figure. TheSBS-modified asphalt blends were thoroughlymixed before being tested, and no segregation wasobserved. Increasing polymer contents lead to anincrease in complex modulus. At concentration levelsfrom 5 to 6%, adding SBS modifier results in amarked increase in G∗ (Fig. 7). This significantimprovement in G∗ at 6% SBS confirms theformation of a polymer network in the binder. Thehigher the G∗ value is at high temperatures, thelower the temperature susceptibility of the PMA.

Figure 8 shows the tan δ (the ratio of G″ to G′,where G″ and G′ are the storage and loss modulus,respectively) trends for PMA and base asphalt. Theparameter, tan δ, is one of the key elements inpredicting binder performance. Results obtainedfrom the dynamic shear rheometer show that thetan δ value of SBS does not increase significantly asthe temperature increases, as compared to pureasphalt. A wide difference between the asphalt andPMA is observed particularly at temperatures above30 °C. After this point the viscous behavior of thepure asphalt, generally considered as a Newtonianfluid, is characterized by the higher tan δ value.

Fig. 6 Difference in softening point between top and bottomsections in terms of storage time

Fig. 7 Complex shear modulus curves at 60 °C for SBS-lmixed with AC-20

Fig. 8 Rheological parameter tan δ versus temperature curve at6% concentration



PMA is promising because of its smaller tan δ,indicating that SBS behaves as an elastic network inPMA.

Performance Evaluation of PMAThe wheel-tracking test was conducted to evaluate

the effect of polymer content on the performanceof hot mix asphalt (HMA) mixtures. Rut depthdecreases with increasing polymer percentages, asindicated in Fig. 9. The most significant reductionof rutting occurs at the addition of 6% SBS, andthis observation of improvement corresponds wellwith the previous discussion. Adding more than 6%SBS may not be economically feasible, however,because of the limited effect on rutting reduction.

Good correlation is observed between rut depthof the mixture and the rheological parameter of thebinder, G∗/sin δ (Fig. 10). For permanentdeformation, the correlation between wheel trackingand parameter G∗/sin δ appears reasonable. Thisgood correlation suggests that rutting is dependenton shear deformation of the binder when theaggregate type and gradation are controlled. Thecombined effects of a higher G∗ and lower δvalues make PMA more resistant to permanentdeformation.

ConclusionsIn this study, SBS was shown to improve the

rheological properties of the asphalt binder due tothe formation of a polymer network in the binder.This network forms in two stages: at low polymerconcentrations, the SBS acts as a dispersed polymerand does not significantly affect properties; at higherconcentrations, local SBS networks begin to formand are accompanied by a sharp increase in thecomplex modulus, softening point temperatures,

and toughness. This two-stage formation is im-portant to the determination of the optimal amountof SBS. After the critical network begins to form,increases in polymer content are accompanied byless significant property increases. This suggests thatthe optimum content for SBS modification is theone required for the formation of a network. AddingSBS to asphalt was shown to improve all aspects ofpavement performance. The optimum SBS contentmay also depend on asphalt and polymer sources.The difference in softening point temperature at 2°C was found to be suitable as a monitor of thestability of a polymer-modified asphalt.

AcknowledgmentsThe authors are grateful to the National Science

Council (NSC89-2218-E-006-119) and theMinistry of Transport and Communication(MOTC-STAO-90-013) for their support, whichmade the completion of this work possible.

References1. T.S. Shuler, D.L. Hanson, and R.G. McKeen: “Design and

Construction of Asphalt Concrete Using Polymer ModifiedAsphalt Binders,” Polymer Modified Asphalt Binders, ASTMSTP1108, ASTM, W. Conshohocken, PA, 1992, pp. 97–128.

2. F.S. Choquet and E.J. Ista: “The Determination of SBS,EVA and APP Polymers in Modified Bitumens,” PolymerModified Asphalt Binders, ASTM STP1108, ASTM, W.Conshohocken, PA, 1992, pp. 35–49.

3. L.H. Lewandowski: “Polymer Modification of PavingAsphalt Binders,” Rubber Chem. Technol., 1994, 67, pp. 447–80.

4. F. Bonemazzi, V. Braga, R. Corrieri, C. Giavarini, and F.Sartori: “Characteristics of Polymers and Polymer-Modified

Fig. 9 Rut depth obtained from the wheel-tracking testFig. 10 Relationship between rut depth and rheological

parameter G∗/sin δ


Binders,” Transportation Research Record 1535, 1996, pp.36–47.

5. S. Maccarrone, G. Holleran, and G.P. Gnanaseelan:“Properties of Polymer Modified Binders and Relationshipto Mix and Pavement Performance,” J. Assoc. Asphalt PavingTechnol., 1996, 64, pp. 209–40.

6. G. Hernandez, R. Rodriguez, R. Blanco, and V.M. Castano:“Mechanical Properties of the Composite Asphalt-Styrene-Butadiene Copolymer,” Inter. J. Polym. Mater., 1997, 35,pp. 129–44.

7. H.I. Al-Dubabe, W. Al-Abdul, I.M. Asi, and M.F. Ali:“Polymer Modification of Arab Asphalt,” J. Mater. CivilEng., 1998, 10, pp. 161–7.

8. M.J. Khattak and G.Y. Baladi: “Engineering Properties ofPolymer-Modified Asphalt Mixture,” TransportationResearch Record 1638, 1998, pp. 12–21.

9. D. Lesueur, J.F. Gerard, P. Letoffe, J.M. Letoffe, D. Martin,and J.P. Planche: “Polymer Modified Asphalts as ViscoelasticEmulsions,” J. Rheol., 1998, 42, pp. 1059–74.

10. U. Isacsson and X. Lu: “Laboratory Investigation of PolymerModified Bitumens,” J. Assoc. Asphalt Paving Technol., 1999,68, pp. 35–63.

11. M. Panda and M. Mazumdar: Engineering Properties ofEVA-Modified Bitumen Binder for Paving Mixes, J. Mater.Civil Eng., 1999, 11, pp. 131–7.

12. K.W. McKay, W.A. Gros, and C.F. Diehl: “The Influenceof Styrene-Butadiene Diblock Copolymer and Styrene-Butadiene-Styrene Triblock Copolymer Properties andProduct Performance,” J. Appl. Polym. Sci., 1995, 56, pp.947–58.

13. R. Blanco, R. Rodriguez, M. Garcia-Garduno, and V.M.Castano: “Morphology and Tensile Properties of Styrene-Butadiene Copolymer Reinforced Asphalt,” J. Appl. Polym.Sci., 1995, 56, pp. 57–64.

14. Adedeji, T. Grunfelder, F.S. Battes, C.W. Macosko, M.Stroup-Gardiner, and D.E. Newcomb: “Asphalt Modifiedby SBS Triblock Copolymer: Structures and Properties,”Polym. Eng. Sci., 1996, 36, pp. 1701–23.

15. X. Lu, U. Isacsson, and J. Ekblad: “Phase Separation of SBSPolymer Modified Bitumens,” J. Mater. Civil Eng., 1999,11, pp. 51–7.

16. G. Kraus: “Modification of Asphalt by Block Polymers ofButadiene and Styrene,” Rubber Chem. Technol., 1982, 55,pp. 1389–402.

17. Anon.: “Standard Test Method for Toughness and Tenacityof Bituminous Materials,” ASTM D 5801, Annual Book ofASTM Standards, vol. 04.03, ASTM, W. Conshohocken,PA, 1999.

18. G.H. Michler: “Electron Microscopic Investigations ofMorphology and Structure Formation of Polymers,” J.Macromol. Sci.,1996, 35, pp. 329–55.

19. R.L Schalek and L.T. Drzal: “Characterization of AdvancedMaterials Using SEM,” J. Adv. Mater., 2000, 2, pp. 32–8.

20. L. Loeber, O. Sutton, J. Morel, J.M. Valleton, and G. Muller:“New Direction Observations of Asphalts and AsphaltBinders by Scanning Electron Microscopy,” J. Microsc., 1996,182, pp. 32–9.

21. Anon.: “Standard Specification for Type IV Polymer-Modified Asphalt Cement for Use in PavementConstruction,” ASTM D 5892, Annual Book of ASTMStandards, vol. 04.03, ASTM, W. Conshohocken, PA,1999.

Documents

Evaluation and optimization of the engineering properties of polymer-modified asphalt