the structure of polymer modified binders and corresponding

Danish Road InstituteReport 921999

0LQLVWU\�RI�7UDQVSRUW��'HQPDUN

The Structure of PolymerModified Binders andCorresponding AsphaltMixtures

Title: The Structure of Polymer Modified Binders andCorresponding Asphalt Mixtures

Author: Vibeke Wegan, Bernard BrûléPhoto: Vibeke WeganDated: May 1999Copyright: Road Directorate, All rights reservedPrinting:Number printed: 300Published by: Road Directorate, Danish Road InstituteISBN: 87-90145-56-9ISSN: 0909-1386

Road DirectorateDanish Road InstituteElisagaardsvej 5P.O. Box 235DK-4000 RoskildeDenmarkTelephone: +45 46 30 70 00Telefax: +45 46 30 71 05

11

Danish Road InstituteReport 921999

The Structure of PolymerModified Binders andCorresponding AsphaltMixtures

Vibeke Wegan, Danish Road Institute

Bernard Brûlé, Jean Lefebvre, France

33

Contents

Preface 4Abstracts 15Introduction 17New Development 10Experimental Details 12

Preparation of thin and plane sections for investigation of thestructure of the polymer modified binder 12

Preparation of binder specimens for investigation of thestructure of the pure polymer modified binder 13

Microscopie Analyses 14

Materials 15

Results and Discussion 17The structure of the pure polymer modified binder comparedwith the structure of the polymer modified binderin asphalt mixtures 17The structure of SBS compared with the structure of EVA in theasphalt mixtures 19

The structure of the polymer modified binder compared indense graded asphalt concrete and in SMA 21

The structure of the polymer modified binder in asphalt mixturesproduced with binders from different origin 21

Increasing polymer content compared to the structure ofthe polymer modified binder 21

The structure of the polymer modified binder in thin sectioncompared to plane sections 22

Conclusion 24Acknowledgement 25References 26

44

Preface

This report contains a reprint of a paper written and presented at the 75thAnnual Business Meeting and Technical Sessions for the Association of AsphaltPaving Technologists (AAPT), held in Chicago, March 8-10, 1999. The paper waspresented by Vibeke Wegan in session I: “Binder/Mastic Rheology” having GeraldHuber as president.

The Association of Asphalt Paving Technologists is today an association with 821members residing on every continent in the world. Its journal now consists of 67volumes, is a widely referenced source of literature in the field of asphalt pavingtechnology. This paper will be a part of 68th volume, which is expected to beprinted in the beginning of 2000. Beside the paper, the journal also contains asummary of the discussion held after the presentation of the paper.

55

Abstract

As a part of the Strategic Highway Research Program (SHRP), the Danish RoadInstitute has developed an optical method for evaluation of asphalt mixtures bymicroscopy of thin and plane sections. The method is based on the techniqueused to examine and characterize the microstructure of Portland CementConcrete.

In this study, the preparation technique has been modified, making it possible toexamine the structure of the polymer modified binder directly in the asphalt mix-ture. The structure is observed under a microscope with UV-light by illuminatingthe surface of cut and polished specimens of the asphalt mixture prepared as thinor plane sections. The polymers used were SBS and EVA type polymers.

It is important to be able to examine the structure of the polymer modified binderin the asphalt mixture since the chemical interaction and structural build-up ofthe polymer phase is influenced by several factors. It is well known thatmechanical treatment and mixing temperature affect the quality of the polymermodified binder. In addition, the cooling rate influences how the polymerstructurizes in the binder during placement and compaction of the final asphaltpavement.

The polymer modified binder will be subjected to oxidation and degradationduring mixing, storage and transportation of the hot mix asphalt. This, togetherwith chemical interactions of the polymer phase and the surface of the mineralaggregates, will greatly affect the structure of the polymer modified binder andfinally the performance of the asphalt mixture. This effect is impossible to predictby only looking at the structure of the pure polymer modified binder.

Consequently, it is not sufficient to know the structure of the pure polymermodified binder before mixing with aggregates. It is also necessary to know thestructure of the polymer modified binder in the final asphalt mixture, since eachmixture has undergone its own special mechanical treatment, mixing temperatureand cooling rate, thereby resulting in a specific structure of the polymer modifiedbinder.

The main conclusion from the microscopic investigation of 25 laboratoryproduced asphalt mixtures is that the structure of the pure polymer modifiedbinder in most cases has shown not to be the same as the structure of the poly-mer modified binder in the asphalt mixture. In the asphalt mixtures, the polymerphase is observed as small spots or as smaller or larger irregular globules in acontinuous asphalt phase. For EVA modified asphalt mixtures, the EVA phase canin addition be observed as a film around the surface of the mineral aggregates.

66

The EVA phase obviously has an affinity to the coarse aggregate, which seems tobe influenced by the amount of mineral filler. For SBS modified binders thisaffinity to the mineral aggregates has not been observed.

The study has shown that an interaction exists between the polymer phase andthe aggregates in the asphalt mixture, indicating that it is very difficult toestablish performance based specifications for polymer modified binders. Henceit would be most sensible to evaluate the performance of the polymer modifiedasphalt mixture from tests on the actual asphalt mixture.

77

Introduction

In the period from 1989 to 1992, as a part of the Strategic Highway ResearchProgram (SHRP), the Danish Road Institute has developed an optical method foruse as an analytical tool in the evaluation of asphalt mixtures (1, 2 and 3). Themethod is based on the optical technique used to examine and characterize themicrostructure of Portland Cement Concrete.

The SHRP project has shown that it is possible to prepare plane and thin sectionsfrom asphalt mixtures for microscopical examination without damaging theinternal structure. When preparing the plane and thin sections, all cavities in theasphalt mixture are by impregnation filled with an epoxy resin containing afluorescent dye, whereby air voids and cracks are visualized when illuminatedwith UV-light.

The plane sections are primarily used to characterize air voids in compacted asp-halt mixtures by content, size, forms and distributions using automatic imageanalysis. Information and characterization of crack formation in the binder/fillermatrix, cracks in the aggregates or water induced damages such as stripping ordisintegration of the asphalt matrix can be observed.

In figure 1, three examples of plane sections prepared during the SHRPCompaction Study can be seen. The plane sections are prepared from densegraded asphalt concrete composed by basaltic mineral aggregates added naturalsand and 1.5 percent lime stone filler. The asphalt content is 4.6 percent AC-20by weight of the total mix. The asphalt mix is compacted by either the AmericanRolling Wheel Compactor (Exxon), the SHRP Gyratory Compactor or thespecimen is cored from a road test section.

The first plane section is prepared from the specimen compacted by the RollingWheel Compactor. There is a very low void content in this mixture, concentratedin the top of the sample. Air voids can be seen as yellow features (black/white:white features). The void content is measured to 1.3 volume-percent by imageanalysis (4 and 5); SHRP has reported the air void content to 1.6 percent.

The second plane section is prepared from the specimen compacted by the SHRPGyratory Compactor. The air voids are small and homogeneously distributed inthe binder/filler matrix, despite one larger air inclusion in the middle. The voidcontent is measured to 9.8 volume-percent by image analysis; SHRP has reportedthe void content to 9.5 percent. The third plane section is prepared from aspecimen cored from a road. The air voids are small and homogeneouslydistributed in the binder/filler matrix and the void content is measured to

88

8.4 volume-percent by image analysis; SHRP has reported the void content to8.6 percent.

Despite the fact that plane sections determine the void contents, the planesection has the additional advantage that they can be used to determine the sizeand distribution of the void structure, which is very important for theperformance of the asphalt mixture.

Figure 1. Plane sections of dense graded asphaltconcrete compacted by Rolling Wheel, SHRP Gyratoryor cored at site. Section size 50 x 100 mm.

Plane sections vertical through a pavement core can be seen in figure 2. The firstphoto is taken in normal daylight and the second photo is taken in UV-light. Thepavement consists of three layers, a wearing course of approximately 3 cm, abinder course of approximately 5.5 cm and a base course of approximately11.5 cm. In the photo with the UV illuminated section, all cavities can be seenwith a yellow color (black/white: white color). There is a low void content in thewearing and binder course. A main vertical crack can be seen going through thewearing and binder course and other “secondary” cracks can be seen in thebinder course only. Visualization of cracks in asphalt concrete mixes has also beenstudied by Eugene Shin et al (6) using a high-speed camera or a ScanningElectron Microscope.

99

Figure 2. Plane section vertical through a pavement core in daylight and in UV-light,90 x 205 mm.

Thin sections are used to characterize microscopical features in the asphalt mix-ture using polarizing and fluorescent microscopy. Information can be obtainedabout the asphalt mixture, such as aggregate and filler mineralogy, signs ofaggregate degradation, filler distribution, homogeneity of asphalt/filler matrix,presence of special filler types such as fly ash and fibers, adhesion betweenaggregates and binder, signs of stripping, binder intrusion in porous aggregateparticles, location and size of cracks etc.

1010

New Development

The optical method developed for evaluation of asphalt mixtures with plane andthin sections was modified in a Brite-EuRam project: “Quality Analysis of PolymerModified Bitumens and Bitumen Products by Image Analysis with FluorescentLight (MIAF)“, whereby it is possible to investigate the structure of the polymermodified binder directly in an asphalt mixture. Observation of the structure of thepolymer modified binder in an asphalt mixture has been reported by F. Durrieuand M. Baille (7) not to be the same as in the pure modified binder.

The objective of the MIAF project was to develop an optical method for charac-terization of the structure of the polymer modified binder and to investigate ifthis structure could be correlated to physical properties of the binder or asphaltmixture (8). The sample preparation technique already developed in the SHRPproject and used by Durrieu and Baille (7) however demanded new procedures toget an undisturbed picture of the structure of the polymer modified binder in theasphalt mixture.

Observation of the structure of the pure polymer modified binder is a well knowntechnique (9) used in many countries today for quality control and researchpurposes (10), and experience from this was used in modifying the preparationtechnique for thin and plane sections.

The chemical interaction and structural build-up of the polymer phase in a poly-mer modified binder is influenced by several factors. It is well known that themechanical treatment and mixing temperature affect the quality of the polymermodified binder. In addition, the cooling rate influences how the polymerstructurizes in the binder during placement and compaction of the final asphaltpavement (11).

The polymer modified binder will be subjected to oxidation and degradationduring mixing, storage and transportation of the hot mix asphalt. This, togetherwith chemical interactions of the polymer phase and the surface of the mineralaggregates, will greatly affect the structure of the polymer modified binder andfinally the performance of the asphalt mixture. This effect is impossible to predictby only looking at the structure of the pure polymer modified binder.

Consequently, it is not sufficient to know the structure of the pure polymermodified binder before mixing with aggregates. It is also necessary to know thestructure of the polymer modified binder in the final asphalt mixture, since eachmixture has undergone its own special mechanical treatment, mixing tempera-ture and cooling rate, thereby resulting in a specific structure of the polymermodified binder.

1111

Observation and investigation of the structure of the polymer modified binder inan asphalt mixture is hence a very effective tool in the process of evaluating thepolymer modification, since it is this structure that should be correlated to thefinal performance characteristics of the asphalt pavement or with results frommechanical testing of the asphalt mixture.

1212

Experimental Details

Preparation of thin and plane sections for investigation ofthe structure of the polymer modified binder

In order to prepare a thin section (figure 3), an asphalt mixture specimen is cutwith a diamond saw (3.3 mm blade thickness) from a laboratory producedsample or a core from a road. A smaller asphalt mixture specimen is cut,approximately 30 x 45 mm and 10 – 20 mm in thickness, by means of a thinnersaw (1.3 mm blade thickness) using a thin section apparatus. The specimen isglued onto a plane glass slide, which helps to attach the specimen, and thensawed so that the specimen is plane with the glass slide and the thickness of thespecimen and the glass slide is approximately 14 mm.

The specimen is impregnated under vacuum with a colorless epoxy resin, whichafter curing helps to stabilize the specimen during further preparation procedure.The surface is sawed very close to the impregnated surface, ground to levelnessby diamond coated rollers and polished by a rotating pellet disc (the polishingshould be leafed out, if the asphalt mixture is highly polymer modified, morethan 6 percent by weight).

An object glass is glued to the surface of the specimen, which is the first finishedside of the thin section. The specimen is cut with the small saw close to theobject glass, and then ground by diamond coated rollers and polished to a finalthickness of 20 µm.

Throughout the preparation procedures the specimen and equipment isconstantly cooled to approximately -5°C and ice cooled water is sprayed on thespecimen during all sawing, grinding and polishing to avoid smearing the poly-mer phase.

A plane section of an asphalt mixture is produced in a similar manner to the thinsection, but the grinding is done with diamond coated pads and the specimen isonly impregnated with epoxy resin if the asphalt mixture is very open or the bin-der is very brittle. A plane section is typically 1 cm thick and 10 x 10 cm in dimen-sion.

Detailed preparation procedures for thin and plane sections and a supplementaryvideo instruction have been produced by the Danish Road Institute (12, 13, 14,15 and 16).

1313

Figure 3. Thin section of an asphaltmixture, 30 x 40 mm and 20 µm inthickness.

Preparation of binder specimens for investigation of thestructure of the pure polymer modified binder

The polymer modified binder is reheated in an oil bath to 180°C andhomogenized with a mechanical agitator for 10 minutes without mixing air intothe binder. During the heating and homogenizing, the binder is covered with alid to reduce oxidation of the binder to a minimum. After the homogenization,the polymer modified binder is poured into a mould with the dimension 30 x 30x 50 mm. The mould is also preheated to 180°C. The mould with the binder isallowed to cool naturally to room temperature.

When the sample has the ambient temperature, a crack initiator is made at thetop of the sample, by making a scratch perpendicular to the longest side with aknife or a similar device. Then the sample is cooled further by placing it in solidCO2, until the polymer modified binder is brittle. After this, the sample is brokeninto two samples by bending it along the crack initiator.

The cracked surface is immediately examined under the microscope. If a moreregular surface is needed, the surface is smoothed by cutting of thin slices at thesurface with a microtome, after the binder has been cooled in solid CO2. Thesurface is only investigated 10 mm from each edge, to avoid any edge effect.

1414

Microscope Analyses

The structure of the polymer modified binder in the thin and plane sections andin the binder specimens is investigated under a Leitz Medilux microscope withincident UV-light. The light source comes from a high-pressure Xenon lamp,75 W. The microscope is equipped with a three filter system; an excitation filter(BP 420/490), a beam splitter filter (RKP 510) and a barrier filter (LP 515).

Figure 4a. Incident UV-light on a thin section,0.5 x 0.7 mm.

Figure 4b. As figure 4a, but transmitted light.

Figure 4c. As figure 4a, but crossed nicols andgypsum filter.

Figure 5. Thin section of an unmodifiedasphalt concrete, 0.5 x 0.7 mm.

AGGREGATE POL.PHA.

AIR AGGREGATE

AGGREGATE POL.PHA.

AIR AGGREGATE

AGGREGATE POL.PHA.

AIR AGGREGATE

AGGREGATE

AGGRE-GATE

BINDER/FILLER

1515

From the light source, the light falls on the excitation filter, which transmits lightfrom 420 – 490 nm. Light with this wavelength falls then on the surface of thespecimen. Unabsorbed exciting light and emitted light is then reflected to thechromatic beam splitter filter, which reflects light shorter than 510 nm andtransmits light of longer wavelength. According to Stokes’ Law, emitted light willhave a longer wavelength than its exciting light, hence the beam splitter filtereffectively reflects exciting light and transmits emitted light, in this wayseparating the two. To eliminate any residual exciting light, the emitted/transmitted light with wavelengths longer than 510 nm finally falls on the barrierfilter, which has a high transmission for wavelengths longer than 515 nm.

The specimens are typically examined with magnifications of 25 – 500.

When the thin and plane sections and the binder specimens are illuminated withthe UV-light, the polymer phase (POL.PHA.), swollen by a part of the maltenesfrom the asphalt, emits yellow light. The fine and coarse aggregates often appeargreen and the asphalt phase is black or brown. Air or cracks appear with ayellow-green color (figure 4a). If it is difficult to distinguish between the differentphases, the thin sections can be analyzed under a polarization microscope. Thethin section from figure 4a, can in figure 4b be seen under a polarizationmicroscope (Leitz Laborlux, 12 Pol) with transmitted light and parallel nicols.Under these conditions, the polymer is orange and air is white. With crossednicols and a gypsum filter (figure 4c), the polymer is red, the air is pink and theaggregate has many colors, which change when the specimen is rotated on ahorizontal plane. In figure 5, a thin section of an unmodified asphalt mixture canbe seen under the microscope with UV-light. The aggregate is still green, but theasphalt can be seen with a slightly yellow fluorescent color, due to the poly-aromatic structures in the maltenes.

Materials

In the study, asphalt mixtures produced in the laboratory were examined underthe microscope. The study included dense graded asphalt concrete, gab gradedasphalt concrete and Stone Mastic Asphalt (SMA) which are produced withbinders modified with Styrene-Butadiene-Styrene (SBS) or Ethylene-Vinyl-Acetate(EVA). Russian and Venezuelan asphalts are modified with 3, 5 and 7 percentSBS, while Middle East, Russian and Venezuelan asphalts are modified with 5 and7 percent EVA.

Physical properties of the pure modified binders are listed in Table 1 and 2.

1616

Unit Middle East Russian Venezuelan

5 % 7 % 5 % 7 % 5 % 7 %

Softening Point, Ring and Ball (17) C 61.0 69.5 66.5 69.0 64.0 69.0

Penetration, 25C, 100 g, 5 sec. (18) dmm 43 37 51 47 58 53

Penetration Index (19) - 0.9 2.0 2.3 2.5 2.2 2.9

Breaking Point Fraass (20) C -12 -11 -13 -13 -14 -10

Ductility, 10C, 5 cm/min (21) cm 8 5 20 19 10 12

Viscosity, 135C (23) Pas 1.38 2.05 0.90 1.44 1.16 1.97

Viscosity 180C (23) Pas 0.21 0.31 0.16 0.24 0.18 0.30

Table 1. Physical Properties of the SBS Modified Binders.

Table 2. Physical Properties of the EVA Modified Binders.

The results obtained from the physical characterization of the polymer modifiedbinders confirm common knowledge of polymer modified binder:

• Modification with SBS polymers results in a considerable increase in the Ringand Ball temperature and also in an increase in the elastic recovery (in theorder of 70 percent at 10°C with only 3 percent of SBS). The breaking pointFraass temperature is relatively low (in the order of -14°C to -18°C), butcuriously it gets higher with the increase of polymer content.

• The EVA modified binders have, despite a relatively high modification level(7 percent) zero elastic recovery (the ductility at 20°C has to be at least 20cm), a moderate ring and ball temperature (in the order of 70°C) and arelatively low Fraass temperature (in the order of -10°C through -14°C).

Unit Russian Venezuelan

3 % 5 % 7 % 3 % 5 % 7 %

Softening Point, Ring and Ball (17) C 52.5 78.0 95.0 52.0 74.0 88.0

Penetration, 25C, 100 g, 5 sec. (18) dmm 63 57 50 63 54 49

Penetration Index (19) - 0.0 4.4 6.1 -0.1 3.7 5.3

Breaking Point Fraass (20) C -16 -15 -14 -18 -16 -14

Ductility, 10C, 5 cm/min (21) cm 95 99 101 81 90 81

Elastic Recovery, 10C (22) % 68 76 81 71 78 80

Viscosity, 135C (23) Pas 0.74 1.10 1.71 0.86 1.39 2.12

Viscosity 180C (23) Pas 0.13 0.19 0.30 0.13 0.21 0.30

1717

Results and discussion

The structure of the pure polymer modified bindercompared with the structure of the polymer modifiedbinder in asphalt mixtures

Twenty-five asphalt mixtures were produced from 12 different polymer modifiedbinders. A comparison of the structure of the polymer modified binder wascarried out between the binder and the corresponding asphalt mixtures. In mostcases it is seen that the structure of the pure modified binder is completelydifferent from the structure of the polymer modified binder in the asphalt mix-ture.

Where a continuous network of the polymer phase could be observed in thebinder, no continuous network of the polymer phase could be detected in theasphalt mixture. The 7 percent EVA modified Venezuelan binder has a continuousnetwork of the polymer phase (figure 6). When asphalt mixtures are producedfrom this binder, no continuous network of the polymer phase could be observedin the mixes (figures 7 through 9). The same observation is valid for the Russianbinder modified with 7 percent SBS (figure 10 and 11).

Where the polymer in the binder can be seen as globules with more or lessirregular shapes in a continuous asphalt phase, the polymer globules are oftensmaller in the asphalt mixture produced from these binders. This observation isvalid for the Middle East binder modified with 7 percent EVA (figure 12) andSMA (figure 13) produced from this binder. It is also valid for the Venezuelanbinder modified with 5 or 7 percent SBS (figures 19 or 21) and the SMAproduced from these binders (figures 20 or 22).

The same structure of the polymer phase in the binder and in the asphalt mixtureproduced with the same binder has only been observed for low polymer content(3 percent), as it can be seen for the Venezuelan binder modified with 3 percentSBS (figure 17) and the SMA produced with this binder (figure 18).

1818

Figure 6. Venezuelan binder modified with 7percent EVA, cracked surface, 0.5 x 0.7 mm.

Figure 7. SMA produced from the binder infigure 6, thin section, 0.5 x 0.7 mm.


Figure 9. Gab graded asphalt concreteproduced from the binder in figure 6, thinsection, 0.5 x 0.7 mm.

Figure 10. Russian binder modified with7 percent SBS, cracked surface, 0.5 x 0.7 mm.

Figure 11. SMA produced from the binder infigure 10, plane section, 0.5 x 0.7 mm.

POL.PHA.

AGGREGATE

POL.PHA.

AGGREGATE

AGGREGATE

POL.PHA.

POL.PHA. 100 µm

20 µm

1919

Figure 12. Middle East binder modified with7 percent EVA, cracked surface, 0.5 x 0.7 mm.


The structure of SBS compared with the structure of EVA inthe asphalt mixtures

In all asphalt mixtures produced with SBS modified binders, the SBS can be seenas small spots or as smaller or larger irregular globules in a continuous asphaltphase. The globules are swelled by the maltenes from the asphalt, and a networkof the SBS phase can be seen inside some of the globules. In figure 11, globulesof SBS can be seen in the SMA produced from the Russian binder modified with7 percent SBS.

The EVA phase is in the asphalt mixtures observed as smaller or larger globuleswith more or less irregular shapes in a continuous asphalt phase, but in additionthe EVA can also be observed as a film around the surfaces of the aggregates(figures 8 and 9) or a few mm from the surface of the aggregates (figure 7). TheEVA seems to have an affinity to the aggregates.

The phenomena with the EVA film around or close to the surface of theaggregates can be explained by the polarity of the different components in theasphalt mixture. If the EVA phase, swollen by a part of the maltenes, has a highersolubility parameter compared to the asphalt phase, the EVA phase will, atequilibrium, surround the aggregates, which has many polar groups. Where theEVA film is seen a few mm from the aggregate, it is a possibility that a part of themost polar asphaltenes surrounds the aggregate.

The EVA film in the SMA produced with the Venezuelan binder modified with7 percent EVA is in one position in the asphalt core seen a few µm from thesurface of the aggregate, with an average thickness of approximately 35 µm(figure 7). The EVA film is in another position in the same asphalt mixture incontact with the surface of the aggregate (figure 8), thus indicating that thesame binder in the same asphalt mixture can provide close but not exactly thesame structure of the polymer modified binder.

2020

The film thickness of EVA has in the SMA been measured as ranging from 10 to70 µm, with an average of approximately 20 µm (figures 7 and 8). In the gabgraded asphalt concrete, containing only 3 percent filler, produced with the samebinder, the EVA film is much thicker (figure 9) compared to the film observed inthe SMA containing 10 percent filler. The EVA film in the gab graded asphaltconcrete is on average measured to approximately 175 µm.

If there is a high content of filler in the binder phase, the affinity between thestone and the EVA is probably disturbed by the affinity between the filler and theEVA, since the specific surface of the filler is large compared to the specific sur-face of the stones. Study of the structure of the polymer modified binder in the7 percent modified Venezuelan binder blended with respectively 10, 50 and70 percent of lime stone filler has shown that the EVA structure is influenced bythe filler. Comparing the pure binder (figure 6) with the binder blended with10 percent lime stone filler (figure 14), no large difference in the EVA structure isobserved. Adding 50 percent filler (figure 15) or 70 percent filler (figure 16) tothe binder, influences the EVA structure. In the SMA, containing 10 percent fillerand 6 percent binder, the filler content in the filler-binder-matrix is 63 percentand is hereby most comparable with figure 16.

Figure 14. Venezuelan binder modified with7 percent EVA blended with 10 percent limestone filler, cracked surface, 0.5 x 0.7 mm.

Figure 15. Venezuelan binder modified with7 percent EVA blended with 50 percent limestone filler, cracked surface, 0.5 x 0.7 mm.

Figure 16. Venezuelan binder modifiedwith 7 percent EVA blended with70 percent lime stone filler, crackedsurface, 0.5 x 0.7 mm.

2121

The EVA film around the aggregates has been observed with the Venezuelanbinder modified with 5 and 7 percent EVA in dense graded asphalt concrete, gabgraded asphalt concrete and SMA, produced with either Granite or Diorite asaggregate. It has also been observed with the Middle East binder and Russianbinder modified with 5 and 7 percent EVA in dense graded asphalt concrete andSMA, produced with the same two types of aggregate.

The structure of the polymer modified binder compared indense graded asphalt concrete and in SMA

When comparing the structure of the polymer modified binder in dense gradedasphalt concrete and SMA produced with the same EVA-modified binder, nosignificant difference could be observed. The dense graded asphalt concrete andthe SMA produced with the same SBS-modified binder have identical structuresof the polymer modified binder. The mix design thus does not seem to haveinfluence on the structure of the polymer modified binder in the asphalt mixture.

The structure of the polymer modified binder in asphaltmixtures produced with binders from different origin

Despite the fact that there is a large difference between the structure of thepolymer modified binder in the Venezuelan (figure 6) and the Middle East (figure12) EVA modified binders, no significant difference could be observed in theasphalt mixtures produced from these binders (figures 7, 8 and 13). A continuousnetwork of the EVA phase is observed in the Venezuelan binder and a continuousasphalt phase is observed in the Middle East binder. In all asphalt mixtures, theEVA phase could be seen as more or less irregular globules and as a film aroundthe aggregates. This illustrates that binders with a completely inverse structure ofthe polymer phase may result in asphalt mixtures with the same structure of thepolymer modified binder.

In the same way, there is no significant difference observed between thestructure of the SBS phase in the asphalt mixtures produced by either themodified Venezuelan or the modified Russian binder. This is despite the fact thatthe SBS phase forms a continuous network in the Russian binder (figure 10)compared to the Venezuelan binder, where it is the asphalt, which forms thecontinuous phase (figure 21). In all asphalt mixtures, the SBS is observed as smal-ler or larger globules with more or less irregular shapes in a continuous asphaltphase.

Increasing polymer content compared to the structure of thepolymer modified binder

The Venezuelan binder containing 3, 5 and 7 percent SBS and the Russian bindercontaining 3, 5 and 7 percent SBS were investigated in SMA and dense graded

2222

asphalt concrete. No continuous network of the SBS phase could be observed inthe twelve asphalt mixtures. A continuous network in the asphalt mixture mighthave been expected from examination of the pure binder, since in the case of7 percent SBS, there is a continuous network of the SBS phase in one of thebinders.

The increase in the SBS content is, however, clearly visible in the SMA producedboth with the modified Venezuelan (figures 18, 20 and 22) and the modifiedRussian binder. In the asphalt mixtures produced with the binder containing7 percent SBS, the polymer phase is almost able to form a continuous network(figures 11 and 22). However, it has not been investigated, whether the polymerphase in theory can form a continuous network in three dimensions (percolationtheory could be applied).

In the twelve asphalt mixtures investigated it is observed that the SBS polymerphase does not stick to the aggregates.

The structure of the polymer modified binder in thin sectioncompared to plane sections

A plane section of an asphalt mixture can be easily and quickly produced,especially if it is not necessary to impregnate the specimen to fix the structure(a section can be produced within two and a half hours). Due to the thickness ofthe specimen, it is easier to keep the specimen cold during the preparation,compared to preparation of the thin sections. This also means that it is easier todo the grinding and polishing without disturbing the polymer phase.

A thin section gets warm more quickly during grinding and polishing procedure,whereby it is necessary to be very careful not to smear the polymer phase andtherefore repeated cooling of the specimen is necessary.

The structure of the polymer modified binder is normally clearly visible in theplane section, but thin sections are needed if it is difficult to distinguish betweenthe polymer and the filler or aggregate. In a polarization microscope withtransmitted light a thin section can be analyzed with parallel nicols and crossednicols together with a gypsum filter. Here it is possible to distinguish the polymer,the filler or aggregate and air since the phases appear in different colors.

Thin sections also have the advantage that the specimen can be investigated athigher magnification. This makes it possible to obtain further information aboutthe asphalt mixture, such as aggregate and filler mineralogy, signs of aggregatedegradation, filler distribution, homogeneity of binder/filler mastic, presence ofspecial fillers such as fly ash and fibers, adhesion between aggregate and binderincluding signs of stripping, binder intrusion in porous aggregate particles andlocation and size of cracks etc.

2323

Figure 17. Venezuelan binder modified with3 percent SBS, cracked surface, 0.5 x 0.7 mm.





Figure 22. SMA produced from the binder infigure 21, plane section, 0.5 x 0.7 mm.

2424

Plane sections are recommended for observation and investigation of thestructure of the polymer modified binder for quality control. For scientific re-search or development, thin sections or plane sections can be used forinvestigation of the structure of the polymer modified binder in an asphalt mix-ture.

2525

Conclusion

This study has shown that it is possible to prepare thin and plane sections fromasphalt mixtures for microscopical investigation of the polymer modified binderwithout damaging the structure. This is a very efficient tool in the process ofevaluating the benefits from the polymer modification and a unique opportunityto investigate the polymer phase in contact with the coarse and fine aggregates.

The study has confirmed an earlier study made by Durrieu and Baille [7]concluding that the structure of the polymer phase observed in the puremodified binders in most cases is not comparable to the structure of the polymermodified binder in the asphalt mixtures. Where a continuous network of thepolymer phase can be seen in the binder, no continuous network of polymerphase could be seen in the asphalt mixture. Where the polymer phase in the purebinder is observed as smaller or larger globules in a continuous asphalt phase, theglobules are often smaller in the asphalt mixture. The same structure of the purepolymer modified binder and the modified binder in the asphalt mixture has onlybeen observed for low polymer content (3 percent).

The SBS polymer phase is in the asphalt mixtures observed as spots or as smalleror larger irregular globules in a continuous asphalt phase. On the other hand, theEVA polymer phase primarily seems to concentrate/stick against the aggregate inthe asphalt mixtures, but it can also be observed as smaller or larger globules inthe continuous asphalt phase.

The observed structure of the polymer phase may not have been investigated at astage of equilibrium. More study is therefore needed to investigate the influenceof mixing time and mixing temperature of the asphalt mixture on the structure ofthe polymer phase.

The observations made in this study raise the problem of the relationship be-tween the characterization of the polymer modified binder and the performancecharacteristics of the polymer modified asphalt mixture and after that the pro-blem of specifications for polymer modified asphalt. Specification for polymermodified asphalt implies that there is a simple uncomplicated relationshipbetween the binder characteristics and the performance of the asphalt mixtureand hereby no interactions between the aggregate and the modified binder. Thisstudy however clearly shows that there exists a specific interaction between onetype of polymer used for modification of the binder and the aggregate in theasphalt mixture. This indicates that it would be very difficult, if not impossible, toestablish general relationships between properties of a modified binder and theperformance of an asphalt mixture, which would not depend on the type/natureof the polymer.

2626

Thus it would be very difficult to establish performance based specifications formodified binders, leading to the conclusion that the most sensible would be toevaluate the performance on the polymer modified asphalt mixture.

AcknowledgementThis research has been carried out as a part of the Brite-EuRam project: “QualityAnalysis of Polymer Modified Bitumens and Bitumen Products by Image Analysiswith Fluorescent Light (MIAF)”. The project acknowledges the support of theEuropean Communities, Brite-EuRam II Programme, project no. P-7426/BRE2-0951 and the MIAF Consortium: Rambøll, Dansk Vejteknologi (H. C. Korsgaard,J. Sundahl, J. Blumensen), Rambøll, G. M. Idorn Consult (N. Thaulow, L. Palbøl),Centre Scientifique et Technique du Bâtiment - CSTB (J. C. Marechal),Jean Lefebvre (B. Brûlé, M. Mazé), Ooms Avenhorn (A. Srivastava. R. v. Rooijen),University of Nottingham (S. Brown, G. Airey) and the Danish Road Institute(H. J. Ertman Larsen, V. Wegan).

2727

References

1. K. Eriksen and A. Neidel (1990): “Thin sections of asphalt concretepreparation techniques”. Strategic Highway Research Program, Contractno: SHRP-88-AIIR-13, Phase 1, Subtask 1.1-1, p 15.

2. K. Eriksen, V. Wegan and J. Krarup. (1992): “Air void content and other aircharacteristics of asphalt concrete by image analysis”. Strategic HighwayResearch Program, Contract no: SHRP-88-AIIR-13, Phase 2, p 35.

3. K. Eriksen (1992): “Air void characteristics in asphalt concrete samples fromthe compaction study”. Strategic Highway Research Program, Contract no:SHRP-88-AIIR-13, Phase 3a, p 20.

4. K. Eriksen and V. Wegan (1993): “Optical Methods for the Evaluation ofAsphalt Concrete and Polymer-Modified Bituminous Binders”. 5thEurobitume Congress, pp 705-708, Stockholm.

5. K. Eriksen (1993): “Microscopical Analysis of Asphalt-Aggregate MixturesRelated to Pavement Performance”. Danish Road Institute, Note 245, p 17.

6. E. Eugene Shin et al. (1996): “Microstructure, Morphology and FailureModes of Polymer-Modified Asphalts”. Transportation Research Record, No.1535, Materials and Construction, pp 61-73.

7. F. Durrieu, M. Baille. (1993): “Observation microscopique d’enrobes à basede bitumes-polymères”. 5th Eurobitume Congress, pp 86-90, Stockholm.

8. H.C. Korsgaard and J. Sundahl (1997): “Quality Analysis with FluorescentLight”. European Asphalt Magazine, 1, pp 22-25.

9. B. Brûlé and M. Druon (1975): “La microscopie de fluorescence appliquée àl’observation de bitumes thermoplastiques”. Bull. Liaison Labo. P. et Ch., Vol.79, pp 11-14.

10. B. Brûlé, Y. Brion and A. Tanguy (1988): “Paving asphalt polymer blends:Relationships between composition, structure and properties”. Proceedingsof the Association of Asphalt Paving Technologists, pp 41-64, Williamsburg,Virginia.

11. A. Dony and F. Durrieu (1990): “Influence de la nature du bitume sur lespropriétés et la stabilité des liants bitumes-polyméres”. Bull. liaison Labo. P. etCh. Vol. 168, pp 57 – 63.

12. “Plane Sections of Polymer Modified Asphalt Mixtures”. Danish RoadInstitute, Test procedure 30-15, February 1998.

13. “Thin Sections of Polymer Modified Asphalt Mixtures”. Danish Road Institute,Test procedure 30-16, February 1998.

14. “Microscopic Analysis of Asphalt Concrete Mixtures. Preparation Techniquesfor Plane Sections. Preparation Techniques for Thin Sections”. Danish RoadInstitute, Information Guide, p 13.

15. Video: “Thin Sections of Asphalt Concrete. Preparation Techniques”. DanishRoad Institute.

2828

16. Video: “Plane Sections of Asphalt Concrete. Preparation Techniques”. DanishRoad Institute.

17. European Standard, Draft prEN 1427, “Petroleum products - Bitumen andbituminous binders - Determination of softening point - Ring and ballmethod”, May 1994.

18. European Standard, Draft prEN 1426, “Petroleum products - Bitumen andbituminous binders - Determination of needle penetration”, May 1994.

19. J. Ph. Pfeiffer, and P. M. van Doormaal: “The rheological properties of asphaltic bitumens”. Journal of the Institute of Petroleum, Vol. 22, pp 414-440,1936.

20. European Standard, Draft prEN QQQ, “Determination of the Fraass BreakingPoint”, November 1994.

21. “Ductility Test Specification NF T 66-006”, Jean Lefebvre, 1995.22. European Standard, Draft prEN FFF, “Petroleum products - Bitumen and

bitumen binders - Elastic recovery”, August 1994.23. “Round Robin” Testing Protocol For Rotational Viscometer”, Nottingham

University, 1995.

the structure of polymer modified binders and corresponding

Documents