evaluation of elastomer modified bitumens using shrp binder specifications

Eurasphalt & Eurobitume Congress 1996 1 E&E.5.121

EVALUATION OF ELASTOMER MODIFIED BITUMENS USING SHRP BINDERSPECIFICATIONS

Jean-Pascal PLANCHE : Research Chemist at Centre de Recherche ELF Solaize, FRANCEDidier LESUEUR : PhD Student at Laboratoire des Matériaux Macromoléculaires, URA CNRS 507, INSA Lyon,FRANCEMichael L. HINES, Gayle N. KING : Research Engineers at Terre Haute KOCH Materials Laboratory, USA

FRANCE

Summary

In this study, binder test methods developed by the Strategic Highway Research Program (SHRP) were usedto evaluate elastomer modified bitumens and grade them according to their expected performance in rutting andthermal cracking. The binders were manufactured by reacting 3-6% Styrene-Butadiene block copolymer intobitumens using a proprietary in-situ cross-linking process. Bitumens of varying penetration grades from several crudesources were used. The modified binders showed a significant improvement at both high and low ends of thetemperature scale, suggesting the temperature dependency markedly decreases as the amount of elastomer isincreased. Another series of modified bitumens (including reacted SB and EVA) have been classified according totheir SHRP performance grade (e.g. PG ??-??), and then compared in field trials under measured traffic and climaticconditions on Pennsylvania Route 11. Good agreement was found between laboratory dynamic shear rheometer testresults and the observed rutting on the pavement test sections, but not as good in case of cracking.

In another study, elastomers were compared to plastomers and other non-polymer modifiers, including EVAand partially air-blown bitumens. Although the plastomeric and oxidized bitumens exhibited PG grades similar to theelastomer modified binder, there was a noticeable shift in the relationship between the m-value (slope of the stiffnessversus loading time creep curve) and the stiffness (S) from Bending Beam Rheometer measurements after PressureAging Vessel aging. Studies of reflective cracking suggest that problems may occur when the S and m-value reachtheir respective specification limits at significantly different temperatures. Greatest problems seem to occur when m-values are well below 0.30 when the stiffness reaches 300 MPa, even though both may be within specification for therequired low temperature. To better understand this cracking phenomenon, (thought to be shear-related), fracturemechanics tests were performed on mixes made from different types of binders. Crack propagation studies in notchedspecimens showed significant differences between classes of modifiers. These tests are meant to evaluate the fractureproperties of binders in the linear region, and therefore should relate to fatigue cracking resistance. Although theviscoelastic properties (particularly the SHRP parameter - G”) of many binders look almost identical at intermediatetemperatures, results from fracture mechanics tests suggest that elastomer modification of bitumen can lead tosignificantly better cracking resistance than other forms of bitumen modification. Some early results from field trialsappear to support this conclusion. Additionally, the concept of relating dissipated energy to fatigue, which led to theselection of G” as a binder specification test parameter, has not been validated by further mixture testing. More fieldtrials are planned to understand how various modified bitumens manufactured to the same PG grade will perform.

In conclusion, SHRP "performance grading " appears to be a promising tool for the specification ofconventional and modified binders when ranking materials for thermal cracking or rutting resistance. Howeverdurability issues, such as shear induced crack initiation and propagation, or the modifiers contribution to moisturesensitivity, have not yet been correctly defined and specified. Further work is needed to identify the fundamentalmechanical properties of bituminous binders which define performance, particularly in the field of fracturemechanics.


EVALUATION DE BITUMES ELASTOMERES SELON LES SPECIFICATIONS SHRPSUR LES LIANTS

Résumé

Dans cette étude, des bitumes modifiés par des élastomères ont été évalués selon les méthodes développéespar le Strategic Highway Research Program (SHRP) pour les liants hydrocarbonés, et classés selon leursperformances attendues en orniérage et fissuration thermique. Les liants ont été préparés en faisant réagir de 3 à 6%de copolymère à bloc styrène-butadiène dans du bitume selon un procédé breveté de réticulation in situ. Les bitumesde base étaient de plusieurs classes de pénétration et de bruts d'origine variée. Leurs propriétés rhéologiques ont éténettement améliorées sur toute la gamme de température par cette modification, présentant une susceptibilitéthermique très diminuée en fonction de la teneur en polymère. Dans une autre série, des liants modifiés SB réagis etEVA ont été classifiés selon les grades de performance SHRP (PG ??-??), puis comparés en service sur la Route 11 enPennsylvanie, sous des conditions climatiques et de trafic contrôlées. Les résultats des tests de cisaillementdynamique sur les liants sont en bon accord avec les observations d'orniérage sur le terrain, mais moins avec celles defissuration.

Dans une autre étude, des élastomères ont été comparés à des plastomères (EVA) et d'autres agents demodification (bitumes semi soufflés). Bien que les bitumes plastomères et oxydés soient de même grade SHRP queles liants élastomères, leurs courbes de fluage à froid mesurées au "Bending Beam Rheometer" après vieillissementau "Pressure Aging Vessel", diffèrent beaucoup au niveau de la relation entre la valeur m (pente de la rigidité enfonction du temps de charge) et la rigidité S. Des études ont montré que lorsque m et S atteignent leurs valeurs limitesde spécification à des températures très différentes, des problèmes peuvent apparaître notamment en réflexion defissures. Les risques sont plus grands quand m est très en dessous de 0.3 lorsque S vaut 300 MPa, même si les deuxparamètres respectent les spécifications aux températures limites du grade considéré. Pour mieux comprendre cephénomène de fissuration (que l'on pense lié au cisaillement), des tests de mécanique de la rupture ont été réalisés surdes enrobés faits avec les mêmes granulats et différents liants. L'étude de la propagation des fissures sur deséchantillons pré-entaillés a montré des différences très significatives selon les bitumes modifiés. Ces tests quipermettent d'évaluer les propriétés de fracture des liants dans le domaine linéaire, devraient donc être reliés à larésistance à la fissuration de fatigue. Bien que de nombreux liants aient des propriétés viscoélastiques, dont le modulevisqueux G", très proches aux températures intermédiaires, leur comportement en mécanique de la rupture diffèrenettement. Ainsi, cet essai montre une meilleure résistance à la fissuration pour les bitumes modifiés par lesélastomères, que confirment des relevés préliminaires sur sites. De plus, le concept de l'énergie dissipée, qui avaitconduit à sélectionner G" comme paramètre de fatigue dans les spécifications sur les liants, n'est pas encore validécomplètement par des tests sur les enrobés. Des études sont prévues pour analyser le comportement en service debitumes modifiés au même grade SHRP.

En conclusion, les spécifications SHRP basées sur les performances semblent prometteuses pour classifier lesbitumes modifiés ou conventionnels vis à vis de la résistance à l'ornièrage et à la fissuration thermique. Par contre,des aspects importants de la durabilité, tels que l'initiation et la propagation des fissures ou le rôle des agents demodification par rapport à la sensibilité à l'eau, n'ont pas encore été correctement définis et spécifiés. Des travauxcomplémentaires sont nécessaires en particulier dans le domaine de la mécanique de la rupture pour identifier lespropriétés mécaniques des liants bitumineux qui définissent les performances.


BEWERTUNG VON ELASTOMERMODIFIZIERTEN BITUMEN NACH DEN SHRP-SPEZIFIKATIONEN

Zusammenfassung

In dieser Untersuchung werden Bindemittel-Prüfverfahren, die im SHRP-Programm entwickelt wurden, zurBeurteilung und Bewertung von elastomermodifizierten Bitumen und ihr voraussichtliches Verhalten im Hinblick aufSpurverformung und Kälterißbildung herangezogen. Die Bindemittel wurden durch Reaktion von 3-6 Gew. % Styrol-Butadien-Block-Copolymer mit Bitumen nach einem patentierten Verfahren erhalten. Es wurden dabei Bitumenunterschiedlicher Penetration und aus unterschiedlichen Ausgangsrohölen eingesetzt. Die modifizierten Bindemittelzeigten deutliche Verbesserungen im unteren und oberen Bereich der Gebrauchstemperaturspane wobei sichabnehmende Temperaturfindlichkeit mit steigendem Polymergehalt feststellen ließ. Eine weitere Serie vonmodifizierten Bitumen (darunter vernetzte SB und EVA) wurden nach den SHRP-Kriterien klassifiziert (PG??-??)und dann mit dem Verhalten von Versuchstraßen unter Berücksichtigung der Verkehrsmengen- undKlimabeanspruchung auf der Pennsylvania Route 11 verglichen. Gute Übereinstimmung wurde zwischen den Wertender im Labor ermittelten dynamischen Scherviskosität (DSR) und den beobachteten Vermungswerten in denFahrspuren gefunden, weniger gute Beziehungen existierten zu den Rißbildungswerten.

In einer weiteren Untersuchung wurden Elastomere mit Plastomeren (EVA) und anderen nicht polymerenModifizierungsverfahren (Semiblown-Verfahren) verglichen. Obwohl die plastomermodifizierten und anoxidiertenBitumen ähnliche PG-Klassifizierungen erreichten wie die elastomermodifizierten Bitumen, trat eine bemerkenswerteVerschiebung zwischen dem Verhältnis von m-Wert (Neigung der Steifigkeit gegenüber Belastungszeit/Kriechkurve)und der Steifigkeit (S) aus dem Biegebalkenrheometer nach simulierter Straßenalterung im Drucktopf statt.Untersuchungen aus Reflexionsrißbereichen zeigen, daß Probleme auftreten können, wenn S- und m-Werte ihreSpezifikationsgrenzwerte bei deutlich unterschiedlichen Temperaturen erreichen. Die größten Probleme scheinenaufzutreten, wenn die m-Werte deutlich unter 0.3 sind wenn S 300 MPa erreicht, obwohl beide Werte dieSpezifikationsgrenzen einhalten. Zum besseren Verständnis dieses Rißphänomens (vermutlich Scherabhängigkeit)wurden bruchmechanische Untersuchungen an Asphalt-Mischungen mit verschiedenen Bindemitteltypen ausgeführt.Diese Untersuchungen sollten die Brucheigenschaften der Bindemittel im linearen Bereich ermitteln und dadurchzum Ermüdungswiderstand in Beziehung gesetzt werden.

Obwohl die viskoelastischen Eigenschaften (besonders der SHRP-Parameter G") vieler Bindemittel immittleren Temperaturbereich praktisch gleich aussehen, zeigen die mechanischen Bruchteste, daßelastomermodifizierten Bitumen eindeutig zu besseren Kälterißwiderständen führen können als andere Formen derBitumenmodifizierung. Einige vorläufige Ergebnisse aus den Feldversuchen scheinen diese Erkenntnisse zubestätigen. Das Konzept der dissipierten (vereinfacht: verbrauchten) Energie, das zur Auswahl von G" alsBindemittel-Test-Parameter fuhrte, ist bisher leider nicht mit weiteren Mischgut-Test-Verfahren auf Gültigkeitüberprüft worden. Es sind weitere Feldversuche geplant, um herauszufinden wie verschiedene modifizierte Bitumendes gleichen PG-Grades sich in der Praxis verhalten.

Zusammenfassend kann gesagt werden, daß "Performance grading" nach SHRP ein vielversprechendesInstrument zur Beurteilung von konventionellen und modifizierten Bindemitteln hinsichtlich thermisch induzierterRißbildung und Spurverformung zu sein scheint. Dauerhaftigkeitsfragen wie scherungsabhängige Rißentwicklungoder der Beitrag des Polymers zur Wasserempfindlichkeit, sind bisher nicht richtig definiert und spezifiziert. Es sindweitere Arbeiten nötig, um die fundamentalen mechanischen Eigenschaften, die die Performance bestimmenherauszufinden, besonders im Bereich der Bruchmechanik.


EVALUATION OF ELASTOMER MODIFIED BITUMENS USING SHRP BINDERSPECIFICATIONS

J.P. Planche(1), D. Lesueur(2), Mickey Hines(3), G.N. King(3)

(1) : Centre de Recherche ELF Solaize - BP 22 - 69360 Solaize - France,(2) : Laboratoire des Matériaux Macromoléculaires URA CNRS No 507 - INSA Bat 403,

20 Avenue A. Einstein - 69621 Villeurbanne Cedex - France,(3): Koch Materials Company - 400 N 10th Street - P.O. Box 1507 - Terre Haute, IN 47802 - USA,

1. IntroductionThe task of characterizing performance of binders has become increasingly complicated with the growing

use of modified bitumens, which address problems associated with binder-related pavement failures. Polymers are themost common modifiers currently being used to improve bitumen viscoelastic properties. The polymers increase thetemperature range over which a binder resists both rutting and thermal cracking, as well as lengthening the timebefore fatigue failure. While conventional methods such as penetration, viscosity, ductility, and ring and ballsoftening point may still adequately compare pure bitumens, they are not accurate enough in predicting relativeperformances of modified materials.

The Strategic Highway Research Program (SHRP) has developed test methods and specifications that areintended to more accurately predict field behavior of all binders, regardless of how they are manufactured [1], [2].SHRP has chosen the Dynamic Oscillatory Shear Rheometer (DSR) to characterize viscoelastic behavior at high andintermediate pavement temperatures. A minimum binder modulus is needed at the highest pavement temperature forrut resistance and a maximum modulus is specified in an intermediate temperature range where load-induced fatiguedamage is most likely to occur. The Bending Beam Rheometer (BBR) predicts the low temperature at which thebinder reaches some limiting stiffness and becomes sensitive to thermally induced cracking [3]. The Direct Tension(DT) simulates fracture under low pavement temperature conditions where the binder has insufficient tensile straintolerance to withstand movement within or under the pavement section.

In this study, the binder test methods developed by SHRP were used to evaluate elastomer modifiedbitumens and grade their expected resistance to rutting and thermal cracking. A plastomer modified bitumen andsome partially air blown bitumens were also evaluated and graded. Some of these binders were then compared in afield trial under specific traffic and climatic conditions.

2. ExperimentalThree laboratories were involved in this international research project including the Elf Research Center at

Solaize, France and the Koch Materials Company laboratories from Terre Haute, IN and Pennsauken, NJ, USA.

2.1 ProductsIn the first part of the study two different crudes, A and B, were vacuum distilled at Elf Refineries to produce

three straight-run penetration grade bitumens (35/50, 50/70, and 70/100). These 6 grades of bitumen were thenmodified respectively with 0, 3, 6 (crude A) and 0, 3.5, 5 (crude B) percent styrene-butadiene block copolymerchemically reacted in-situ using a proprietary process [4].

The second part of this study was performed in the USA. The four binders prepared at Koch Materials Petty'sIsland Plant in Pennsauken, NJ included two straight run bitumens, an AC-20 and an AC-40, and two PMB's, an AC-10 with 5 percent EVA and a 50/70 penetration bitumen with 4 percent styrene-butadiene block copolymerchemically reacted in-situ through the same process. The four bitumen bases all represent different crude sources.

Finally, a vacuum residue from crude C was partially air blown to manufacture oxidized bitumens ofdifferent melt points.

2.2 Test methods and definitionsThe binders were tested according to the SHRP recommended protocol, i.e., before and after Rolling Thin

Film Oven Test (RTFOT) and Pressure Aging Vessel (PAV) aging. The PAV was run using the oven developed byApplied Test System [5]. RTFOT is intended to simulate hot mix plant aging; the PAV simulates aging long term in-service oxidation.The rheological properties of both aged and unaged binders were measured:· viscosity at 135°C with a Brookfield rheometer.· complex modulus, G*, and phase angle, δ, as a function of the temperature and the frequency with a Dynamic

Shear Rheometer RDA II from Rheometrics, equipped with 25 and 8 mm parallel plate geometry [6],


· creep stiffness and m-value (slope of the log stiffness versus log loading time creep curve or the relaxation rate)at low temperature with a Bending Beam Rheometer BBR from Cannon [7].

· stress and strain binder low temperature tensile properties with the Tensile Testing Device from SATEC [8].The following criteria were calculated to determine the SHRP PG grade of each binder [9]:· SHRP stiffness criteria at high (G*/sin δ) and intermediate (G*.sin δ) temperatures,· the limiting stiffness temperature (LST) at high temperature (the high LST is the lower of the two temperatures

at which G*/sin δ is equal to 1.0 kPa before RTFOT and 2.2 kPa after RTFOT) ,· the limiting stiffness temperature (LST) at low temperature (the low LST is the temperature at which S, the BBR

creep stiffness, is equal to 300000 kPa after RTFOT and PAV aging),· the limiting m-value temperature (LmT) at low temperature (the temperature at which BBR m-value is equal to

0.3 after RTFOT and PAV aging),· the SHRP temperature span between high and low temperatures at failure criteria, i.e., high LST - min. (low

LST, LmT) + 10°C.· the physical hardening ratio (PHR) from BBR measurement after 24 hours conditioning at low temperature. PHR

= (S24hr/S1hr)^(m1hr/m24hr) (draft 8E).

Black space curves obtained from the Dynamic Oscillatory Shear Rheometer measurements were also usedto study the rheology of the binders on a more fundamental level. In this representation, the phase angle δ is plottedagainst the complex modulus G*. This is of particular interest because actual experimental data are used without theshifting allowed by SHRP following the time-temperature superposition principle. The shifting may be questionablein cases of highly structured bitumens and PMB's [10], [11]. Therefore, Black space plots cannot be erroneouslyshifted by "black box" computer treatment.

Additionally, classical testing, such as the ring and ball softening point, the penetration at 25°C and theFraass Brittle point [12] were run on some of the binders.

The chemical compositions of the saturates, aromatics, resins and asphaltenes in bitumens from crudes A andB were also analyzed by using an Iatroscan apparatus. Finally, the amount of crystallized fraction of these binderswas determined by Differential Scanning Calorimetry as described elsewhere [13].

2.3 Field test sectionThis paper also gives results from a field project performed in July of 1992 by the Pennsylvania Department

of Transportation (DOT) on Pennsylvania Route 11, in Cumberland County between Carlisle and Mechanicsburg,west of Harrisburg, Pennsylvania, USA. This field project involved a bituminous overlay on Portland cement concrete(PCC).

A limestone was used in the binder mix and a sandstone was used in the surface course. This is a four lanearterial with a center "turn" lane divider. Both ends of the project are heavily trafficked highways: the PennsylvaniaTurnpike and Interstate I-81 are at one end, and I-83 is at the other end. There are six major trucking companyterminals that are accessed by this seven mile (11,2 km) section of Rt. 11. This results in a high (approximately3000) average daily ESAL count. The overall project called for milling out two inches (5 cm) of old material andreplacing it with the same thickness of Pennsylvania ID-3-WC heavy duty mix. The experimental section was a 3800yard area at the north end of the job. In this section, the old pavement was milled to a depth of approximately 4inches. On the south end of the section, this was down to the old Portland cement concrete (PCC), however as thenorth end, approximately four inches (10 cm) of old bituminous mix was left over the PCC. The test section wasdivided and laid out so that the south half utilized the 1/2 inch maximum surface mix (ID-2-WC) and the north a 1inch maximum surface mix (ID-3-WC). The plan was to use only one travel lane for each of the different bitumenbinders (i.e., the AC-20, AC-40 EVAMB and SBMB described above). The targeted thickness was 1.5 inch (3.75 cm)for the ID-2 and 2 inches (5 cm) for the ID-3. The targeted air void content was 5.1% for the ID-2 mix and 4.7 for theID-3. The binder content was 4.0 % for the ID-2 and 4.8% for the ID-3. See Table 1 for design and actual values.

Both modified materials were placed on the passing lane, while neat bitumens were used for the travel lanes.The SHRP properties of those binders were determined, and the field performance of these test sections has beenclosely monitored. More details about this job, including aggregate gradations, were presented elsewhere [14].


3. Results and discussion

3.1 SHRP properties of Elastomer Modified BindersThe chemical composition of the pure bitumens from crudes A and B are given in Table 2. Their physical

properties, including those of the related modified binders, are listed in Tables 3 and 4. Figures 1 and 2 display someof the PMB's rheological Black space curves. In terms of classical testing, the polymer modification results in the expected significant increase in ring andball softening point (R&B) and slight decrease in Fraass brittle point. Both improvements impart a wider plasticityinterval, traditionally meaning a lower temperature susceptibility.

From a rheological standpoint, the effect of increased polymer content is evident in the Black space wherethe curves are shifted toward lower phase angles. This means PMB's are more elastic at a given temperature orfrequency, especially in the high temperature range. This phenomenon is much more prevalent for the high polymercontent (5 - 6%) PMB's, where their micro structure borders the polymer phase inversion. Moreover, curve wavesappear as the polymer content increases, confirming the time-temperature superposition principle does not apply tohighly modified products.

The materials were also compared in terms of temperatures where the SHRP failure criteria are met. Figures3 and 4 illustrate LST's and LmT's for each of the 14 materials. As a general pattern, PMB's have higher stiffness(G*/sin δ) at high temperature (whatever the aging), and lower stiffness and higher m-value at low temperature afterPAV and RTFOT aging. As a result they exhibit higher LST at high temperature and lower LST and LmT at lowtemperature. The limiting strain temperature from tensile testing, despite the limited amount of data, seems to be amore severe criterion than the stiffness and the m-value. It also shows more significant improvement from thepolymer modification. However this criterion, which is no longer mandatory in the latest draft of SHRPspecifications, was not considered in determining the LST. The criterion at intermediate temperature appears veryeasy to meet, having no effect on the grading of any binders from this study. Moreover, the concept of relatingdissipated energy to fatigue, which led to the selection of G” as a binder specification test parameter, has not beenvalidated by further mixture testing and is currently being widely questioned [15], [16], [17], so it will not beconsidered in the paper any further.

Additionally, The PMB's overall temperature span is significantly increased, which means that these bindersshould perform well over a much wider service temperature range. As a result their grading is also enhanced, butmore particularly in the high temperature end (one grade average for 3% polymer). Their effect at low temperature ispositive, but not as pronounced, because the grading is divided in 6°C increments.

On the basis of these results, elastomer modified binders should display better rutting resistance and betterthermal cracking resistance than their base bitumens. They should also allow production of performance grades notpossible with unmodified bitumens.

3.2 Field test results- Binder evaluation : Table 5 and Figure 5 show the physical properties and SHRP gradation of the binders

that were used in the Pennsylvania Route 11 test section. Both PMB's exhibit better high temperature properties thanthe AC-20, and are a little above the AC-40. At low temperature the EVAMB has the best LST but also by far theworst LmT. The SBMB ranks the best at low temperature with only a minor difference between LST and LmT.Consequently, its temperature span is also the widest.

- Field observations : the field project was designed to produce asphalt mixes which would resist prematurepermanent deformations. However since it involved bituminous overlay on Portland cement concrete, reflectivecracking was also a consideration.

Rutting was minor for all binders through three summers after job construction. The modified binder lanesare performing slightly better than the conventional AC's considering they are on the passing lanes with a muchhigher number of ESALs (see Table 1). Rutting was the primary concern with this test section due to its locationbetween two major interstate highways with very heavy truck traffic caused by several truck facilities along the road.Thus these results are very encouraging. They help validate the relevance of the SHRP stiffness criterion to predictrutting resistance. More results on the rutting performance were presented elsewhere [14], showing good agreementwith earlier laboratory validation studies involving "torture testing"[18], [19].

On the other hand, at the beginning of the first winter in December 1992, early transverse cracks appeared onthe EVAMB mix lane, with all other lanes were still performing well (Figure 6.a). A year later, in September 1993,the EVA lane was even more cracked, some of these cracks propagating into the next AC-40 lane (see Figure 6.b).The pattern in the EVA lane suggests more than reflective cracking. Thermal cracking is probably involved as well. Ifthis is true, then the m-value in the SHRP specification would appear very significant. Since the EVAMB showedvery low creep stiffness (low LST), it was only the m-value (or the LmT) which would have indicated a potentialproblem. Since the cracks stop at the AC-40 lane, which has a little better m-value but a much higher creep stiffness,both parameters may need to be considered.


More binder rheological testing was done to better understand the cracking failure of the EVAMB:- Since the cracks happened at an early stage, tensile testing was run at -15 °C on the RTFOT aged materials

(see Table 5). Both modifiers including the EVA, performed significantly better (both higher stress and strain) thanthe regular AC's that did not crack, so these results could not account for the distress seen in the field.

- Physical hardening that appears with time when a binder is stored at low temperature [20], was alsodetermined by running BBR experiments after 24 hours conditioning at -15°C. The physical hardening ratios of allbinders were equivalent, so they did not yield any significant indications in this case. The only criterion that lookedsignificantly worse for the EVAMB is the LmT. Since the m-value is known to relate to the phase angle and to theglass transition temperature [21], it is not surprising that a binder with high LmT would crack earlier than others withLmT’s lower by 5 to 10 degrees.

This field observation appears to validate the relevance of the m-value criterion. In the meantime it showssome limitation of the performance prediction power of creep stiffness and direct tension criteria. Although DT wasrecently emphasized in the literature [22] (but showing results on unaged materials), SHRP experts currentlyrecognize it still lacks measurement precision (how to measure strain as low as 1% and to achieve 1 mm/mnelongation rate?) [23]. At any rate, DT results cannot be simply related to any basic low temperature intrinsicparameter such as the glass transition temperature [21], as can the m-value.

3.3 SHRP Properties of other modifiersTable 6 and Figure 8 illustrate the physical properties and SHRP gradation of air blown bitumens. As

expected from the ring and ball softening points, highly oxidized binders exhibit tremendous high temperature LST(above the highest SHRP PG grading) which means they should have a very good rutting resistance.

On the other hand, they have incredibly poor m-values, which suggests disastrous thermal crackingresistance. This problem is not picked up by the creep stiffness criterion, that remains almost constant whatever theair blowing level. Similarly to EVA modified bitumens, the m-value of air blown bitumens is the controllingparameter for low temperature failure. These results bring more evidence that LST alone cannot be used to controlcracking, or the specifications would favor highly blown bitumens that are not allowed by current practice.

4. Fracture Mechanics and SHRP Specifications.Fatigue cracking damage in asphalt pavements is often simulated in the laboratory. These tests generally

report the number of controlled loading cycles a specimen can withstand before cracking or weakening [25]. Anotherapproach is to measure the rate of crack growth during controlled loading. Texas A&M University’s TexasTransportation Institute has demonstrated that polymer-modified bitumens slow crack growth rates in asphaltconcrete in varying amounts. Crack growth rates were reduced by 42 times with SBMB and 15 times with EVAMB[26]. It is unlikely that the SHRP binder specification identifies this behavior.

The SHRP mix design system “SUPERPAVE Levels II and III” does consider fracture mechanics in servicelife modelling. The 1994 version of SUPERPAVE software makes calculations of crack growth rates using the Parisequation from fracture mechanics. However, the program does not allow the user to input the coefficients of the Parislaw equation. Rather, it predicts the coefficients from creep compliance data measured on the mixture. Therelationship between creep compliance and fracture mechanics has not been verified for polymer modified asphalts[27]. Fortunately, the U.S. FHWA has funded further work on the SUPERPAVE software, so this issue is still openfor discussion.

5. ConclusionIn this study, in-situ chemically crosslinked styrene-butadiene copolymer modified bitumens were evaluated

through the SHRP protocol and graded according to the SHRP specifications. Rheological properties of the modifiedbinders showed a significant improvement at both high and low temperatures, suggesting their temperaturedependency markedly decreases as the amount of elastomer increases. However the polymer modification impact ismore pronounced at high temperature. These promising results appear to be relatively independent of the crudesource, showing the flexibility of the process to achieve a wide variety of PG grades from different base bitumens.

Another set of modified bitumens, including reacted SB as well as EVA from different base bitumens wasclassified according to the SHRP performance grading system, and then compared in a field trial under three years’measured traffic and climatic conditions on Pennsylvania Route 11. The EVA product lead to early cracks the firstwinter, while the elastomer product performed very well. None of the binders showed any serious sign of rutting after3 summers, as anticipated by the limiting stiffness temperature. Only minor rutting was observed for this high numberof ESALs. The early cracking of the EVA mix can be attributed to both reflective cracking from the Portland CementConcrete subcourse and thermal cracking. The cracking validates the very poor BBR limiting m-value temperature ofthe related binder. However, the early cracking was not explained by the low temperature creep stiffness and thedirect tension strain tolerance. One can interpret the m-value as an indication of relaxation rate. Therefore, it appearsthat "m" is more relevant to cracking resistance because the pavement can relax before failure stresses are reached.


In another study, partially air-blown bitumens showed very good high temperature properties. On the otherhand, although those oxidized bitumens exhibited low temperature stiffness similar to the elastomer modified binder,their m-values noticeably worsened through air-blowing. This result suggests very poor thermal cracking resistance,which agrees with the common wisdom using oxidized binders in paving applications.

In conclusion, SHRP "performance grading" appears to be a promising tool for the evaluation and theprediction of modified binders’ performance in terms of thermal cracking and rutting. It clearly shows the benefit ofany modification, including polymer and air blowing. It also confirms that the overall cracking resistance of a mix ishighly binder dependent and that it depends upon the BBR m-value after aging. On the other hand, low temperaturestiffness can be misleading when there is a large difference between LST and LmT. Earlier low temperaturelaboratory testing studies were not entirely confirmed, but they did not involve such a wide variety of binders [24].Moreover, since DSR is being questioned about its capability to pick up potential fatigue related distresses, morework is undoubtedly needed in the field of fatigue cracking. Fracture mechanics could provide one way to addressthis problem. Within the scope of this study, the elastomer modified binders gave the best results in both binderproperties and field data.

AcknowledgmentsThe authors gratefully acknowledge the contributions of many people to this research study, especially F. Fee whoconducted the field study, and all the Elf and Koch personnel from labs in France and in the USA for their help andsweat.References[1] D.R. Jones, T.W. Kennedy, Towards an Understanding of the Relationships Between Asphalt Chemistry andPavement Performance: The SHRP Program, Proceedings, Symposium on Chemistry of Bitumens, Rome, Italy, 5-8/06, 1991[2] D. A. Anderson, D.W. Christensen, H.U. Bahia, Physical Properties of Asphalt Cement and the Development ofPerformance -Related Specifications, Proceedings AAPT, 60, pp. 437-475, 1991.[3] H.U. Bahia, D. A. Anderson, D.W. Christensen, The Bending Beam Rheometer: A simple Device for MeasuringLow Temperature Rheology of Asphalt Binders, Proceedings AAPT, 61, 1992.[4] G.N. King, H.W. Muncy, J.B. Prudhomme, Polymer Modification: Binder's effect on Mix Properties, Proceedings,AAPT, 28, pp. 519-540, 1986.[5] AASHTO Designation PP1, Edition 1A, Standard Practice for Accelerated Aging of Asphalt Binder Using aPressurized Aging Vessel (PAV), AASHTO Provisional Standard, September 1993[6] AASHTO Designation TP5, Edition 1A, Standard Test Method For Determining the Rheological Properties ofAsphalt Binder Using a Dynamic Shear Rheometer (DSR), AASHTO Provisional Standard, August 1993[7] AASHTO Designation TP1, Edition 1A, Standard Test Method For Determining the Flexural Creep Stiffness ofAsphalt Binder Using The Bending Beam Rheometer (BBR), AASHTO Provisional Standard, September 1993[8] AASHTO Designation TP3, Edition 1A, Standard Test Method For Determining the Fracture Properties ofAsphalt Binder in Direct Tension (DT), AASHTO Provisional Standard, September 1993[9] AASHTO Designation MP1, Edition 1A, Standard Specification For Performance Graded Asphalt Binder,AASHTO Provisional Standard, September 1993[10] G.N. King, H.W. King, D. Lesueur, J.P. Planche, SHRP Test Evaluation of High Float and Polymer ModifiedBitumen Emulsions, Vol. 3, Proceedings, First World Congress on Emulsion, Paris, October 1993[11] J.M. Buisine, G. Joly, A. Eladlani, C. Such, F. Farcas, G. Ramond, P. Claudy, J.M. Létoffé, G.N. King, J.P.Planche, L. Germanaud, Thermodynamic Behavior and Physicochemical Analysis of eight SHRP Bitumens,Transportation Research Record 1386, Proceedings, Transportation Research Board 1993[12] NF T 66-026, Détermination du Point de Fragilité Fraass.[13] P. Claudy, J.M. Létoffé, G.N. King, B. Brulé, J.P. Planche, Caractérisation des bitumes routiers par AnalyseCalorimétrique Différentielle, Bulletin de Liaison des Ponts et Chaussées, 165, pp. 85 - 92, 1990.[14] F. Fee, Relationship of SHRP Binder Tests to Field Performance, Transportation Research Board, 1994.[15] R. Reese, J. Goodrich, California Desert Test Road - A step closer to Performance Based Specifications,Proceedings AAPT 62, 1993.[16] D. Lesueur, D.L. Dekker, J.P. Planche, Fatigue Resistance: What's Wrong with Dissipated Energy as Measuredby Rheology?, Proceedings The Rheology of Bituminous Binders European Workshop, 5-7 April 1995.[17] G.N. King, H.W. King, How Do Modified Asphalts Fit Within the SHRP PG Binder Grading System?, SHRPConference, Reno, Nevada, October, 1994[18] G. N. King, H.W. King, O. Harders, P. Chaverot, J.P. Planche, Influence of Asphalt Grade and PolymerConcentration on the High Temperature Performance of Polymer Modified Asphalt, Proceedings AAPT, 61, 1992[19] G. N. King, H.W. King, P. Chaverot, J.P. Planche, O. Harders, Using European Wheel-Tracking and Restrainedtensile tests to Validate SHRP Performance Graded Binder Specifications for Polymer modified Asphalt Cement, 5thEurobitume Congress, Proceedings, p51, Stockholm, Sweden, 16-18 June, 1993


[20] H.U. Bahia, D. A. Anderson, Isothermal Low-Temperature Physical Hardening of Asphalt Cement, Proceedings,International Symposium on Chemistry of Bitumens, Rome, Italy, June 5-8, 1991[21] J.P. Planche, D. Martin, P. Claudy, J.M. Létoffé, G.N. King, Evaluation of the Low Properties of BituminousBinders Using Calorimetry and Rheology, Proceedings, The Rheology of Bituminous Binders European Workshop, 5-7/04 1995.[22] B. Brûlé, M. Mazé, Application of SHRP Developed Tests to the Characterization of Polymer ModifiedBitumens, Preprints AAPT, 1995.[23] D. A. Anderson, Mechanical Properties of Asphalt Cements and the Relationships to Performance, PetersenAsphalt Research Conference at Laramie, Wyoming, USA, 10-12 July, 1995.[24] G.N. King, H.W. King, O. Harders, W. Arand, P. Chaverot, J.P. Planche, Influence of Asphalt Grade andPolymer Concentration on the Low Temperature Performance of Polymer Modified Asphalt, Proceedings AAPT, 62,1993[25] R. Tangella, J. Craus, J.A. Deacon, C.L. Monismith, Summary Report on the Fatigue Life of Asphalt Mixtures,University of California, Berkeley Report A-003A-89-3.[26] C.K. Estakhri, J.W. Button, Evaluation of STYRELF 13 in Hot-Mixed Asphalt Concrete, Texas TransportationInstitute, Research Report 0355, May 1988.[27] R.J. Cominsky, The Superpave Mix design Manual for New Construction and Overlays, SHRP Report A-407,1994.


Figure 1 : Black space diagram of Polymer Modified Bitumen A65

55

60

65

70

75

80

85

90

1,00E+01 1,00E+02 1,00E+03 1,00E+04 1,00E+05 1,00E+06

log G* (log Pa)

phas

e an

gle

(°)

A65

A65-3

A65-6

Figure 2 : Black space diagram of Polymer Modified Bitumen B65

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65

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1,00E+01 1,00E+02 1,00E+03 1,00E+04 1,00E+05 1,00E+06

log G* (log Pa)

Pha

se A

ngle

(°)

B65

B65-3.5

B65-5


Figure 3 : Elastomer Modified Bitumen A vs SHRP Specs

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-15

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105

A45 A45-3 A65 A65-3 A65-6 A85 A85-3

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Unaged Hi Temp RTFO T Hi Temp PAV Int Temp PAV S Lo Temp PAV m-value Lo Temp SHRP Temp Span

Figure 4 : Elastomer Modified Bitumen B vs SHRP Specs

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B45 B45-3,5 B65 B65-3,5 B65-5 B85 B85-3,5

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Unaged Hi Temp RTFOT Hi Temp PAV Int TempPAV S Lo Temp PAV m-value Lo Temp SHRP Temp Span


Figure 5 : PA Route 11 Binders vs SHRP Specs

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AC-20 AC-40 EVAMB SBMB

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Unaged Hi Temp RTFO T Hi Temp PAV Int TempPAV Lo Temp S PAV Lo Temp m-value SHRP Temp Span

Figure 7 : Air Blown Bitumen C vs SHRP Specs

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AB1 AB2 AB3 AB4 AB5

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Table 1: Field Data on PA Route 11 Mixes

Mix Binders Target AC-20 AC-40 EVAMB SBMBLane Number 2 3 4 1Average ESAL's / day 44,2 114, 2652, 2957Polymer Nature None None EVA SB

Cores Plant Field Plant Field Plant Field Plant FieldID-2 Wearing Course mixAir Voids (%) 5,1 5,4 9 4,8 8,7 6,1 8,5 5,7 9,3Binder Content (%) 6 5,8 5,6 6 5,9Average Core Thickness (in) 1,5 2,02 1,74 1,56 1,75ID-3 Wearing Course mixAir Voids (%) 4,7 5,3 9,3 6,6 8,1 6,7 7,9 7,2 9Binder Content (%) 4,8 4,6 4,5 4,9 4,5Average Core Thickness (in) 2 2,19 2,27 2,2 2,16ID-2 Binder Course mixAir Voids (%) 5 4,8 5,1 6,3 6,3 3,7 5,8 5,4 5,3Binder Content (%) 4 4 4,1 4 4Average Core Thickness (in) 2,5 3,28 2,86 2,59 2,73

Table 2 : Chemical Composition of Bitumens from Crudes A and B

Materials A45 A65 A85 B45 B65 B85Bitumen Grade 35/50 50/70 70/100 35/50 50/70 70/100

Saturates (%) 11,9 13,2 15,5 4,4 4,4 5,0Aromatics (%) 53,4 53,6 51,3 64,4 65,7 67,8Resins (%) 18,7 19,3 19,9 18,8 19,2 18,2Asphaltenes (%) 16,0 13,9 13,4 12,4 10,7 9,0

Crystallizable Fraction (%) 0,3 0,3 0,1 2,7 3,5 4,3

Table 3 : Physical Properties of Polymer Modified Bitumens from Crude A

Materials A45 A45-3 A65 A65-3 A65-6 A85 A85-3

Bitumen Grade 35/50 35/50 50/70 50/70 50/70 70/100 70/100% SB copolymer 0 3 0 3 6 0 3

Penetration, 25°C, 1/10 mm 40 35 60 49 50 79 69R & B Softening Point, °C 56 65 51 57 73 48 54Fraass, °C -9 -12 -14 -14 -16 -16 -18

SHRP Tests on unaged materialBrookfield Viscosity @ 135°C, mPa.s 765 1930 510 1300 3860 400 910T. @ G*/sin d = 1.0 kPa @ 10 rad/s, °C 76 80 69 78 84 67 73SHRP Tests on RTFOT aged materialT. @ G*/sin d = 2.2 kPa @ 10 rad/s,°C 75 77 70 74 79 66 71T@ Failure Strain = 1% -13 -15 -14 -16 -19 -16 -18SHRP Tests on PAV aged materialT. @ G*.sin d = 5000 kPa @ 10 rad/s,°C 29 25 25 21 18 16 17T. @ BBR Stiffness = 300 MPa @ 60 s,°C -14 -17 -15 -18 -21 -17 -19T. @ BBR slope = 0.3 @ 60 s, °C -13 -17 -15 -18 -21 -18 -21Plasticity Interval, °C 65 77 65 71 89 64 72SHRP Temperature span, °C 98 104 94 101 110 93 101SHRP PG Grade 70-22 76-22 64-22 70-22 76-28 64-22 70-28


Table 4 : Physical Properties of Polymer Modified Bitumens from Crude B

Materials B45 B45-3,5 B65 B65-3,5 B65-5 B85 B85-3,5Bitumen Grade 35/50 35/50 50/70 50/70 50/70 70/100 70/100% SB copolymer 0 3,5 0 3,5 5 0 3,5

Penetration, 25°C, 1/10 mm 45 41 63 54 49 88 70R & B, °C 53 62 50 58 68 46 56Fraass, °C -13 -17 -16 -19 -20 -19 -21

SHRP Tests on unaged material :Brookfield Viscosity @ 135°C, mPa.s 590 1630 480 1310 1900 340 1030T. @ G*/sin delta = 1.0 kPa @ 10 rad/s, °C 71 80 68 77 82 62 75SHRP Tests on RTFOT aged material :T @ G*/sin d = 2.2 kPa @ 10 rad/s, °C 71 79 67 75 79 60 70SHRP Tests on PAV aged material :T. @ G*. sin d = 5000 kPa @ 10 rad/s, °C 22 17 20 18 19 17 15T. @ BBR Stiffness = 300 MPa @ 60 s,°C -17 -19 -18 -21 -23 -21 -22T. @ BBR slope = 0.3 @ 60 s, °C -15 -17 -18 -19 -20 -21 -21T@ Failure Strain = 1% -9 -15 -17Plasticity Interval, °C 66 79 65 77 88 65 77SHRP Temperature span, °C 96 106 94 103 109 91 101SHRP PG Grade 70-22 76-22 64-22 70-28 76-28 58-28 70-28

Table 5 : Physical Properties of PA Route 11 Binders

Materials AC-20 AC-40 EVAMB SBMBBitumen Grade (vis or pen) AC-20 AC-40 AC-10 50/70Polymer Nature EVA SB% Polymer 0 0 5 4

Penetration at 25°C, 1/10 mm 75 52 65 52Ring and Ball Softening Point, °C 49 54 68 72

SHRP Tests on unaged materialBrookfield Viscosity @ 135°C, mPa.s 1180 1720T. @ G*/sin d = 1.0 kPa @ 10 rad/s, °C 67 72 72 79SHRP Tests on RTFOT aged materialT. @ G*/sin d = 2.2 kPa @ 10 rad/s,°C 68 73 77 78Failure Strain @ -15°C, % 0,5 0,4 >2,6 >2,5Failure Stress @ -15°C, N 15 14 18 25SHRP Tests on PAV aged materialT. @ G*.sin d = 5000 kPa @ 10 rad/s,°C 20 23 8 19T. @ BBR Stiffness = 300 MPa @ 60 s,°C -20 -18 -25 -22T. @ BBR slope = 0.3 @ 60 s, °C -16 -13 -8 -19Physical Hardening Ratio @ -15°C 1,4 1,4 1,2 1,3SHRP Temperature span, °C 93 96 90 107SHRP PG Grade 64-22 70-22 70-16 76-28


Table 6: Physical Properties of Air - Blown Bitumens from Crude C

Materials AB1 AB2 AB3 AB4 AB5Penetration at 25°C, 1/10 mm 102 77 40 30 20Ring & Ball Softening Point, °C 40 52 68 78 96

SHRP Tests on unaged material :T. @ G*/sin delta = 1.0 kPa @ 10 rad/s, °C 56 70 91 100 123SHRP Tests on RTFOT aged material :T @ G*/sin d = 2.2 kPa @ 10 rad/s, °C 59 74 93 101 121SHRP Tests on PAV aged material :T. @ G*. sin d = 5000 kPa @ 10 rad/s, °C 10 12 18 18 23T. @ BBR Stiffness = 300 MPa @ 60 s,°C -27 -26 -26 -25 -26T. @ BBR slope = 0.3 @ 60 s, °C -26 -22 -10 -10 4T@ Failure Strain = 1% -23 -18 -9 -7SHRP Temperature span, °C 92 101 111 120 129SHRP PG Grade 52-34 64-28 "88-16" "100-16" "118-4"


Figure 6A : Research Project N°91-058A SR 0011 Cumberland County 12/1992 Evaluation


Figure 6B : Research Project N°91-058A SR 0011 Cumberland County 09/1993 Evaluation

evaluation of elastomer modified bitumens using shrp binder specifications

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