complexsphalts areing on thelectric andturee cure the

Journal of Colloid and Interface Science 280 (2004) 366–373www.elsevier.com/locate/jcis

Rheology of asphalts modified with glycidylmethacrylatefunctionalized polymers

Giovanni Polaccoa,∗, Jiri Stastnab, Dario Biondia, Federico Antonellia, Zora Vlachovicovab,Ludovit Zanzottob

a Dipartimento di Ingegneria Chimica, Università di Pisa, Via Diotisalvi 2, 56126 Pisa, Italyb Department of Civil Engineering, University of Calgary, 2500 University Drive, Calgary, AL T2N 1N4, Canada

Received 9 February 2004; accepted 4 August 2004

Available online 21 September 2004

Abstract

Asphalt is known to be a colloidal suspension in which asphaltenes are covered by a stabilizing phase of polar resins and formmicelles that are dispersed in the oily maltenic phase. In order to enhance its mechanical properties (e.g., in road paving), aoften loaded with polymeric materials, thereby obtaining blends that can have different physical or chemical structures, dependcomposition of the added polymer. Asphalts modified by the addition of reactive ethylene terpolymers were prepared and their dierheological properties were measured both before and after a cure at hightemperature. Even if it is not possible to determine the exact naof the chemical interactions between asphalt and polymer, master curves obtained from dynamic data clearly show that during thmaterial tends to the behavior of a cross-linked network. 2004 Elsevier Inc. All rights reserved.

Keywords:Polymer modified asphalts; Reactive ethylene terpolymers; Gel point; Rheology; Dielectric properties

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1. Introduction

Asphalts are widely used in road paving because of tgood adhesion to mineral aggregates and their viscotic properties. Moreover, asphalts also have applicationroofing membranes and in other waterproofing materialorder to improve their performance, asphalts are often mified by the addition of polymers. With respect to the bmaterial, polymer-modified asphalts (PMA) have reduthermal susceptibility and permanent deformation and henhanced resistance to low-temperature cracking. Asphalwith polymers form multiphase systems, which usually ctain a phase rich in polymer and a phase rich in asphaltnot absorbed by the polymer. The properties of asphpolymer blends depend on the concentration and theof polymer used. The polymer is usually loaded in conc

* Corresponding author. Fax: +39-050511266.E-mail address:g.polacco@ing.unipi.it(G. Polacco).

0021-9797/$ – see front matter 2004 Elsevier Inc. All rights reserved.doi:10.1016/j.jcis.2004.08.043

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trations of about 4–6% by weight with respect to the asphHigher concentrations of polymers are considered to benomically less viable and also may cause other problrelated to the material properties.

Polymers used for asphalt modification can be grouinto three main categories: thermoplastic elastomers, ptomers, and reactive polymers. Thermoplastic elastomare obviously able to confer good elastic properties onmodified binder; while plastomers and reactive polymeare added to improve rigidity and reduce deformationsder load. Belonging to the first category, styrene–butadiestyrene block (SBS) copolymers are probably the mostquently used asphalt modifiers for paving applications[1–5].The molecular architecture of SBS can be either linearadial, and styrene blocks unite to form uniformly distruted domains, leading to the formation of a physically crolinked network[6,7].

Examples of the plastomeric types of polymers studfor asphalt modification are polyethylene (PE), ethyle

G. Polacco et al. / Journal of Colloid and Interface Science 280 (2004) 366–373 367

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vinyl acetate (EVA), and ethylene–butyl acrylate (EBA) random copolymers[8–14]. Due to its low compatibility withasphalt, PE is not widely used for paving applications: eylene copolymers are preferred. Recently, reactive polymhave been introduced as asphalt modifiers: their “reacty” is due to the presence of functional groups supposeable to bond with asphalt molecules. Examples of retive polymers are thermoplastic elastomers functionaliwith maleic anhydride and ethylene-based copolymerstaining epoxy rings. The latter are commercially availaas random terpolymers of ethylene, glycidyl methacry(GMA), and an ester group (usually methyl, ethyl, or buacrylate). Due to their composition, they are often careactive ethylene terpolymers (RET). Thanks to their reactivity, RETs are quite widely used as compatibilizers of dferent polymeric blends like polyethylene and polyamid[15,16], or polyolefins and polyesters[17–19]. The same reactions can be useful for asphalt modification; and, REcan be used either as asphalt modifiers or as compatibilbetween asphalt and conventional polymers[20–25]. Aftermixing with asphalt, a curing at storage temperature is sgested in order to let the epoxy rings react. Accordingthe manufacturers, GMA functionality mainly reacts wcarboxylic groups present in asphaltenes, thus formingester link. This bond should prevent phase separationimprove storage stability. Moreover, if the asphaltene mcule, or micelle, contains more than one carboxylic groa chemical network could theoretically form. Other retions are possible between the GMA group and the futional groups present in asphalts. For example, the epring can be opened by a hydroxyl group to form an etbond or by an amine group. Moreover, once a GMA ringbeen opened by any of the above-mentioned reactionswater molecule, and a hydroxyl group has been formedthe polymer main chain, an intermolecular cross-linkingaction can take place. This would lead to the formationa polymer network not necessarily involving asphalt mocules.

Unfortunately, due to the extremely complex cheminature and composition of asphalts, it is difficult to detthe real nature of chemical bonds formed during the cing period. Considering that the cure is generally carrout for 24 or 48 h at 160–180◦C, it is reasonable to assume that to some extent all the proposed reactions oTo the authors’ knowledge, however, no experimental dhave been reported to clarify this point. As a matter of fawhen an asphalt is modified by RET, the polymer amohas to be chosen very carefully because an excessive qtity leads to the formation of an insoluble, infusible asphgel. Therefore, either by the presence of asphaltene brior by interpolymer reactions, a chemical network can fowhen GMA-functionalized polymers are added to asphFor this reason, RET polymers are added in quantitiesally ranging from 1.5 to 2.5% by weight. Considering tchemical nature of the bonds that are established betwpolymer chains and/or polymer chains and asphalt m

.

-

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cules, RET polymers can only be used if the forming nwork is kept below the “chemical” gel point, i.e., beforeinfinite molecule is formed extending to the whole matevolume. In other words, the reaction must be stopped wthe cross-linking polymer consists of a distribution of cluters, swelled by asphalt but still able to melt or dissolvesolvents.

One of the most critical aspects of asphalt modificatiostorage stability. This point isquite different for nonreactingand reacting polymers. In fact, the nonreacting polymerstially maintain their structure even after mixing with asphaand the above-mentioned multiphase nature of the mixcan evolve to macroscopic phase separation during stoIn contrast, when reactive polymers are used, usuallypolymeric phase is homogeneously dissolved in the asphone. This is due to three reasons: (i) RETs are added inquantity, (ii) RETs have a highly polar nature, which ehances compatibility with asphalts, and, of course, (iii)formation of a chemical bond between polymer and asphelps to prevent phase separation. Moreover, the storagriod coincides with a curing time during which functiongroups of polymer and asphalt are supposed to react.ter storage at high temperatures, the material is supposshow rheomechanical characteristics strongly enhancedrespect to those it possessed just after the mixing, anphase separation is expected tooccur. In this case, the onlsignificant storage problem can be related to gel formatiothe polymer quantity is not calculated properly.

The literature on asphalt modification with RET polymeis quite scarce[26–28], especially with respect to rheologicproperties. Some preliminary data were reported in[29].

In this paper, a rheological characterization of REmodified asphalts is carried out for two different formutions. In the first formulation, an asphalt is modified wan amount of polymer so that no gel formation is poss(even if the material is subjected to a long curing time)the second one, the same base asphalt is loaded with amer content so that it tends to form a gel after a relativshort curing time.

From an experimental point of view, it is quite simpleindividuate the gel point because it can be associated wsolubility limit. Not considering empirical methods such athe tilted test tube method and the falling ball method,first rheological approach suggested that the gel point cadetermined through the appearance of an equilibrium modulusGe or the divergence of steady shear viscosity[30–33].Both methods, and especially the second one, are quiteple; however, they present some disadvantages[34]. Themost significant disadvantage is that the gel point is foby extrapolation.

For end-linking polymers, in conditions where thereno physical contribution to gel point, Chambon, Winter, aco-workers[34–42]proposed a criterion based on measurfrequency-dependent dynamic properties or time-dependerelaxation modulus. They found that, at the gel point,mechanical behavior could be described by the power

368 G. Polacco et al. / Journal of Colloid and Interface Science 280 (2004) 366–373

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form of the relaxation shear modulus:

(1)G(t) = St−n.

In the case of small-amplitude oscillatory shear, the stoG′(ω) and lossG′′(ω) moduli are the Fourier sine and csine transforms, respectively, of the relaxation modulus[43].Hence for Eq.(1) one obtains

G′(ω) = Sπωn

2Γ (n)sin(πn/2),

(2)G′′(ω) = Sπωn

2Γ (n)cos(πn/2)

and

(3)n = 2

πarctan

(G′′

G′

),

whereΓ (n) is the gamma Legendre function. It can be sfrom Eq. (3) that at the gel point, the loss tangent isdependent of frequency but proportional to the relaxatioexponentn.

Therefore, in experiments performed on similar gellsystems under time-sweep conditions, lines of tan(δ) at dif-ferent frequencies intersect at the gel point (thex axis rep-resents the time or the extent of reaction). This methorecognized to be very effective in gel point determinatand permits a significant advantage over extrapolation mods. After the studies of Winter and co-workers, the methas been tested with other end-linking networks[44], ex-tended to different covalently cross-linking systems[45–49],and it was also successfully applied to physical syst[50,51].

2. Materials and methods

2.1. Asphalts

Two different base asphalts were used:

• Asphalt from vacuum distillation of 70/100 Pen gradeRing and Ball temperature= 46◦C (referred to as asphalt A).

• Asphalt from visbreaking of 70/100 Pen grade, Rinand Ball temperature= 47◦C (referred to as asphalt B

2.2. Polymers

Terpolymers ethylene–butylacrylate–glycidylmethaclate:

• Elvaloy AM (butylacrylate 28% by weight, glycidymethacrylate 5.3% by weight),

• Elvaloy EP 4170 (butylacrylate 20% by weight, glcidylmethacrylate 9% by weight)

manufactured by DuPont.

2.3. Polymer-modified asphalts

Aluminum cans of approximately 500-cm3 volume werefilled with 250–260 g of asphalt and put in a thermoeltric heater where the temperature was raised to 180◦C.Then a high shear mixer was dipped into the can andto 3000 rpm. The polymer was added gradually (5 g/min).Temperature was kept within 180± 1◦C during the polymeaddition and subsequent mixing.

At the end of mixing, the material was split into differecans and transferred to an oven at 180◦C, under static conditions and in an oxygen-free environment. After the desperiod of curing, the cans were taken out and the asphalpoured into molds for subsequent rheological testing. Betesting, the samples were cooled at room temperaturestored in a refrigerator at−20◦C.

2.4. Rheometry

Asphalt samples were poured into rubberized moldsfore being used for rheological testing. The rheometerthe Rheometric Scientific ARES A-33A, which operatesder strain control. The test geometries were plate–plateameters 25 and 50 mm) and torsion bar. Viscosity measments were conducted in the temperature range 30–13◦Cand shear-rate range 10−3–103 s−1. In dynamic measurements, the temperature was varied from−30 to 110◦C inorder to construct the master curves of the dynamic maial functions. The maximum strain was kept below the limof the linear viscoelastic region. It should be noted thattemperatures at which the rheological measurements weperformed were lower than the curing temperature, sono significant kinetic effects can start during testing. In fathe highest test temperature was 130◦C, which is 50◦C be-low the curing temperature; moreover, the samples wereat the test temperature for a relatively short period of tiTherefore, at the testing temperature, no kinetic effects werexpected to be present. This guaranteed the reliabilityreproducibility of the measurements.

2.5. Ring and ball temperature

The Ring and Ball temperature (TR&B) was measured according to ASTM D36-76.

2.6. Fluorescence microscopy

The asphalt samples in the molten state were pouredsmall cylindrical molds (1 cm diameter, 2 cm height), kfor 15 min in an oven at 180◦C, and then cooled to roomtemperature and stored at−30◦C. After extraction from thecylindrical mold, the samples were fractured and the fture surfaces were examined under a LEICA DM LB micscope.

G. Polacco et al. / Journal of Colloid and Interface Science 280 (2004) 366–373 369

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2.7. Dielectric properties

The dielectric properties of asphalt were measured onsample in the form of an asphalt circular disc. The acvoltage/current measurement was performed by a femtof the EIS 900 electrochemical impedance system (GaInstruments Inc., Willow Grove, PA). The asphalt samand femtostat were in an electrostatically screened environment. The sample cell was kept in a thermostatic chamcontrolled by a PID programmable controller (±0.1◦C). The0.1-mm gap between capacitor plates was maintained bruby balls that also provided anelectrical insulation of a fieldhomogenizing ring. A special device in the form of a coaxcontainer with a preloaded spring mechanism was usedthe loading of samples into the capacitor to ensure thaprescribed gap was maintained.

3. Results and discussion

Preliminary tests were conducted by modifying the basphalts with small quantities of the two RET polymeThese tests were performed in order to determine (i) thepropriate operating conditions, (ii) the polymer quantitybe added without having problems related to gel formatand (iii) which one of the two base asphalts is more cvenient for modification withethylene reactive terpolymerAfter the preliminary tests, it was decided to mix polymand asphalt for 15 min at 180◦C for all PMA preparations.

TR&B values obtained by adding Elvaloy AM and EPasphalts A and B are reported inTable 1. For asphalt A,no problems of gel formation were observed on the samwhere the polymer with lower GMA content (Elvaloy AMwas added, even after 48 h of curing at 180◦C. Moreover, theTR&B values show that for the lower polymer content, notectable increase was observed after mixing, while a slightincrease can be observed for 2.0 and 2.5% of added p

Table 1TR&B before and after curing

TR&B (◦C)

0 h 24 h 48 h

Asphalt AAM 1.5 46 51 53.5AM 2 48 52 55AM 2.5 52 56 59EP 1.5 47 51 53.6EP 2 49 67.5 GelEP 2.5 51 Gel Gel

Asphalt BAM 1.5 47 51 54AM 1.75 50 53 59AM 2.0 52 54 GelAM 2.5 53 Gel GelEP 1.0 49 52 55EP 1. 5 50 55 GelEP 1.75 52 Gel Gel

t

mer. These low increments confirm that the GMA groudid not react significantly during the 15 min of mixing; andthe low effect onTR&B, if present, was probably due mainto the slight increase in average molecular weight as asequence of the polymer addition. Then, in all three catwo days of curing resulted in an increase of about 7◦C intheTR&B value with respect to theTR&B value shown aftemixing.

When asphalt A is mixed with Elvaloy EP, the only posible addition of the polymer is 1.5% by weight. If 2.02.5% is added, the material becomes a gel after 48 (2.or 24 (2.5%) h of curing. Comparing theTR&B values of un-cured materials obtained from asphalt A and Elvaloy Aor EP, it can be seen that for the same amount of polytheTR&B values were very similar. The differences werethe limit of experimental uncertainty. The fact that the saamount of uncured polymer gave similarTR&B values is fur-ther confirmation that no reaction took place during mixiElvaloy EP, thanks to its higher GMA content with respecElvaloy AM, leads to higher cross-linking via either asphtene groups or interchain mechanisms in network format

Different behavior was found in similar experiments pformed with base asphalt B (Table 1). In this case, the material showed a higher tendency to gelation, even when Elvaloy AM was used. The highest amount of this polymer tcould be added without gel formation was 1.75% by weigwhile 1% was the maximum for Elvaloy EP. The fact ththe use of different asphalts led to different gelation cditions suggests that asphalt molecules played an imporole in network formation. However, there are no reasonexclude that both hypothesizedmechanisms (reactions btween polymer and asphaltenes and interchain reactionsbe present.

For both asphalts A and B, it seems that Elvaloy AM hto be preferred to Elvaloy EP because the former allowebetter balance between polymer quantity and gelationdency. In fact, the highest content of glycidylmethacryl(GMA) groups led to gelation for very small polymer quatities, such that the formation of links and the subsequmolecular weight increase wasnot sufficient to significantlyimprove the binder properties. These experiments sugthat a polymer with an even lower content of GMA grouwould be recommended for asphalt modification. Withspect to comparison between asphalts A and B, it sethat the better combination would be the modificationasphalt B with 1.75% Elvaloy AM, because it allowed thighest ratio betweenTR&B increase and added polymquantity. Therefore, both steady state and dynamic rheologcal tests were performed on this PMA, both before and acuring for 24, 48, and 72 h in an oxygen-free atmospherethe following, the corresponding PMAs will be referred0, 24, 48, and 72 h, respectively.

Results of viscometric measurements on these asphave been described in detail elsewhere[52]. In experimentsconducted under steady conditions, the viscosity was msured in shear rate sweep tests. For all tested tempera

370 G. Polacco et al. / Journal of Colloid and Interface Science 280 (2004) 366–373

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Fig. 1. Viscosity functions at 70◦C for asphalt B modified with 1.75% polymer at different curing times.

Fig. 2. Zero shear viscosities at different temperatures for asphalt B mfied with 1.75% polymer at different curing times.

and different curing times at 180◦C, RET-modified asphaltshowed qualitative behavior similar to that of the unmodifibase. The viscosity curves obtained at 70◦C are reported inFig. 1. At low shear rates, the materials showed Newtonbehavior, with viscosity nearly constant until a critical shrate at which shear thinning begins. With respect to the mnitude, the modified but uncured material has a viscovalue close to that of the unmodified base; however, sigicant differences appear after 24 and 48 h. During the creactions caused the viscosity to increase by about onder of magnitude in each of the first two days. After 48the reaction is almost complete and the third day of cudoes not significantly increase the material stiffness. Zshear viscosity (η0) values were extrapolated from a Netonian plateau and are reported inFig. 2 in a semilog plot asa function of temperature.

From the dynamic data taken in isothermal frequesweep tests, master curves were obtained. InFig. 3, themaster curves of storage and loss moduli for PMA “0and “48 h” are reported. The reference temperature is 0◦C.From the curves, it can be seen that both uncured and cmaterials had a glass transition atω ≈ 102 rad/s, which

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Fig. 3. Storage and loss moduli for PMAs “0 h” and “48 h” (reference temperature 0◦C).

Fig. 4. Loss tangent for asphalt B and PMAs “0 h,” “24 h,” and “48(reference temperature 0◦C).

corresponds to a temperature around−10◦C (calculated byplottingG′′ as a function of temperature at a fixed frequeof 0.5 Hz). Moreover, the two materials had very simiqualitative and quantitative behavior in the high-freque(low-temperature) range. This was expected because asphmodification by polymers is mainly manifested at elevatemperatures, while low-temperature behavior is knowbe less influenced by polymer modifiers[53].

Quite significant differences could be observed inlow-frequency–high-temperature domain, and they shoa different dependence of moduli on frequency. In this cthe modified and cured material had considerably higmoduli (by at least one order of magnitude). For both mrials, moduli were following a power law dependence whthe cured PMA showed a quite similar slope forG′ andG′′,and the base asphaltG′′ curve has a greater slope thanG′.This difference meant that during the cure the loss tanis “losing” its dependence on frequency, and this shouldrelated to the reaction of epoxy groups. The changes intangent can be better appreciated inFig. 4, where the mastecurves of the cured material are compared with those ouncured and unmodified one. In the 1.75% Elvaloy modiasphalt, the polymer quantity was not enough for gelatTherefore, the loss tangent evolution observed inFig. 4 can

G. Polacco et al. / Journal of Colloid and Interface Science 280 (2004) 366–373 371

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Fig. 5. Master curves forε′, ε′′ for PMA “24 h” (reference temperatur40◦C).

Fig. 6. Comparison of shift factors obtained in three different ways (refeence temperature 40◦C) and WLF fit.

be interpreted as that of a material in a pregel region, whwas approaching self-similar limiting behavior.

Dielectric measurements were performed on asphaand PMAs “0 h,” “24 h,” and “48 h,” for which the dielectric permittivityε′ and the dielectric loss factorε′′ wereobtained.

No significant differences were observed in the dieltric properties between the uncured and cured materialsexample, at low temperatures where the effect of electpolarization is weak, the dielectric permittivity and conductivity are both slightly decreasing with the curing time. Siilarly to rheological data, dielectric data could be shifteda single master curve as shown inFig. 5 for dielectric per-mittivity and loss factor of PMA “24 h” (reference temperture 40◦C). As expected, the shifting factors obtained frosteady state viscosity, dynamic data frequency sweep,dielectric measurements are almost identical.Fig. 6 showsthat the shifting factor can be satisfactory described by thWLF relation[43],

(4)log(aT ) = −c1(T − Tr)

c2 + T − Tr.

The same coherence of shifting factors values was obtafor all the tested materials.

Even if such a formulation cannot be useful for practiapplications, in order to better understand how the reac

r

Fig. 7. Storage and loss moduli foruncured PMA obtained by adding 4%Elvaloy AM to asphalt A (reference temperature 0◦C).

Fig. 8. Storage and loss moduli forPMA obtained by adding 4% ElvaloyAM to asphalt B after 10 h of curing (reference temperature 0◦C).

influences the rheological behavior of asphalts, a PMA w4.0% RET was prepared. In this case, it must be emphasthat the polymer content was such that it could be ablpartially segregate and give rise to local semicrystallinemains that can give a physical contribution to the polymenetwork. Some evidence of this behavior has been repoin [52]. However, the fluorescence microscopy showesubstantial homogeneity of all the samples. The polycontent is such that the material became an insoluble, infusible material after approximately 11 h of curing at 180◦Cin an oxygen-free environment. Therefore, the dynamicchanical properties were studied after curing for 0, 2, 6,10 h, respectively.

In Figs. 7 and 8, master curves for the storage and lomoduli of the PMA after 0 and 10 h of curing are report(reference temperature 0◦C). For the uncured material, ithe low-frequency domain the logarithmic plot showed tdistinct power-law regions for the moduli: (i) the first owith G′(ω) ≈ ω1.7 andG′′(ω) ≈ ω where the material behaved in a manner similar to the classical liquid-typesponse (G′(ω) ≈ ω2 andG′′(ω) ≈ ω), showing some analogies to the prediction of both the Rouse and Zimm modfor solutions of linear polymers[43]; (ii) the second onewhere theG′ dependence on frequency changed and tendeto be similar to that ofG′′. The presence of such a tran

372 G. Polacco et al. / Journal of Colloid and Interface Science 280 (2004) 366–373

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e of

witha

f re

ity

atisffre-ela-

d

nceis-

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Fig. 9. Loss tangent at different curing times for PMA obtained by addin4% Elvaloy AM to asphalt B (reference temperature 0◦C).

tion was not easily detectable in previous PMAs, due to tlower polymer content. For the sake of brevity, the curfor 2 and 6 h of curing time are not reported; however, asreaction proceeded, the distinction between the two regiontended to disappear andG′ dependence on frequency tendgradually to power-law with decreasing exponent (G′(ω) ≈ω1.6 for 2 h of curing andG′(ω) ≈ ω1.3 for 6 h of curing).After 10 h of curing, no transition inG′ slope could be foundand the two moduli appeared to be parallel in a wide rangfrequencies whereG′(ω) ≈ G′′(ω) ≈ ω0.85. Again, a plot ofloss tangent clearly shows how the properties evolvedthe reaction (Fig. 9) and how the 10-h-cured material hadconstant value of the tangent over almost six decades oduced frequency.

Complex modulus is related to the complex viscosfunction as

(5)η∗(ω) = G∗(ω)

iω= η′(ω) − iη′′(ω),

whereη∗ is the complex viscosity andη′, η′′ are its realand imaginary parts. In the domain(0.01,100) of reducedfrequencies (and shear rates) the studied materials sthe Cox–Merz rule at the studied temperatures. At lowquencies, the studied asphalts satisfy the following rtion:

(6)limω→0

|η∗| = limω→0

|η′| = η0.

Therefore, from the Cole–Cole plot,η0 can be extrapolateas the intercept between the curve and the real axis.Fig. 10displays such a plot for the four studied materials (referetemperature 0◦C). During the reaction, the zero shear vcosity rapidly increased and curves ofη′ versusη′′ tended tobecome straight lines for the 10-h-cured material, confiing that the latter was in the vicinity of gel point. Moreovtime sweep experiments at different frequencies (1.0, 2.5.0, 7.5, 10.0 Hz) were performed on the cured maals (Fig. 11) from which it can be clearly seen that tan(δ)

showed a tendency to converge to a common value.tan(δ) curves were very close after 10 h of curing, aspected for a material in a precritical gel state.

-

y

Fig. 10. Cole–Cole plot after different periods of curing (reference tempeature 0◦C).

Fig. 11. Loss tangent at different frequencies (Hz) as a function of curintime.

4. Conclusions

Asphalts modified by polymers containing a glycidmethacrylate functionalization were studied, with particuattention to their rheologicalproperties. Thanks to the reativity of the GMA group, RET polymers are widely useddifferent applications. It is not well known how the polyminteracts with asphalt molecules; however, it is believedthe epoxy ring should react with functional groups prelently present in asphaltene micelles. However, the pence of an interpolymer cross-linking reaction cannot becluded. At the end of curing, these systems showed a stincrease in viscosity during the cure. The polymer quanhad to be chosen very carefully in order to avoid the riskformation of an infusible, insoluble asphalt gel.

Two different PMA formulations were prepared. The fione was a composition that was believed to be usefupractical applications in road paving. The second formtion had a very high amount of polymer, so that the effewere more pronounced, and was of scientific interest oRheological and dielectric data showed that, in the invtigated temperature range, all materials satisfied the titemperature superposition principle. Even if it was not p

G. Polacco et al. / Journal of Colloid and Interface Science 280 (2004) 366–373 373

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03)

sible to follow the reaction directly in samples loaded inrheometer, the materials werecharacterized after differencuring times. Therefore, material properties were compaat different degrees of reaction. In both cases, the curingtermined a pronounced increase in viscosity and dynamoduli of the material. Moreover, all collected data incated that the asphalt–polymer systems tended to chemgelation.

During the curing, epoxy rings are involved in cheical reactions and high-molecular-weight clusters form inthe whole material volume. If the polymers’ and functiongroups’ quantity is properly chosen, these clusters swellcluding the low-molecular-weight fractions of asphalt, athe whole material can have strongly enhanced mechcal properties. Moreover, the presence of a chemical bwithin the polymer and asphaltenes strongly reduces theof phase separation. The reaction extent, however, hasmaintained under the limit of the critical liquid–solid tran-sition where viscosity diverges to infinite value. If suchsituation occurs, it would be impossible to use the marial and even its removal from the storage tank wouldimpossible. As a warning to the users of RETs it has tostressed that the enhancement of properties might be ocompared with the effect obtained with similar amountsconventional polymers. Therefore, the reaction can solve thproblem of asphalt–polymer compatibility, but at the satime, it constitutes a limit for the maximum improvementmaterial properties.

Acknowledgments

G.P. gratefully acknowledges the Italian NATO–CNgrant program. The authors express their gratitude toNatural Sciences and Engineering Research CouncCanada and to Husky Energy Inc. for their financial sport of this work.

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