Fuel 89 (2010) 3330–3339

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Fuel

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Physico-chemical analysis of five hard bitumens: Identification of chemicalspecies and molecular organization before and after artificial aging

M. Le Guern a,*, E. Chailleux a, F. Farcas b, S. Dreessen c, I. Mabille d

a Laboratoire Central des Ponts et Chaussées, Route de Bouaye, BP 4129, 44341 Bouguenais, Franceb Division Physico-chimie des matériaux, Laboratoire Central des Ponts et Chaussées, 58 boulevard Lefebvre, 75732 Paris Cedex 15, Francec Centre de Recherche de TOTAL, BP 22, Chemin du Canal, 69360 Solaize, Franced Laboratoire de Génie des Procédés Plasmas et Traitement de Surfaces, UPMC/ENSCP – EA 3492, Ecole Nationale Supérieure de Chimie de Paris,11 rue Pierre et Marie Curie, 75231 Paris Cedex 05, France

a r t i c l e i n f o a b s t r a c t

Article history:Received 5 January 2010Received in revised form 28 April 2010Accepted 29 April 2010Available online 14 May 2010

Keywords:BitumenSize exclusion chromatographyAsphaltene structure

0016-2361/$ - see front matter � 2010 Elsevier Ltd. Adoi:10.1016/j.fuel.2010.04.035

* Corresponding author.E-mail address: malo.leguern@lcpc.fr (M. Le Guern

The present paper focuses on a physico-chemical analysis of five different types of bitumens, both beforeand after aging. These bitumen samples were chosen based on: the original crude oil (straight-run bitu-mens with different asphaltene and crystallized fraction contents), mode of refining (straight-run vs. half-blown bitumen), and modifier characteristics (straight-run vs. polyphosphoric acid (PPA)-modified bitu-men). The aim of this study is to determine both the aging effect on chemical species and the chemicalorganization as a function of the type of bitumen sample.

In order to obtain information on bitumen chemistry, n-heptane precipitation (Standard NF EN 12591),IATROSCAN chromatography (coupling between a thin-layer liquid chromatography on a silica gel and aflame ionization detector), FTIR spectroscopy and differential scanning calorimetry (DSC) have all beenused. Size exclusion chromatography under ‘‘high-speed” conditions (HS-SEC), which yields informationrelative to asphaltene associations, was also introduced. Several years of road aging were simulatedthrough 25 h of a pressure aging vessel (PAV) test.

The coupling of IATROSCAN chromatography and n-heptane precipitation made it possible to identifyand quantify polar resins.

In accordance with previous studies, the use of HS-SEC combined with IATROSCAN chromatographyindicates that a modification by PPA leads to an increase in asphaltene content and a more dispersedasphaltene structure than that found in pure bitumen. This same conclusion can be drawn from observa-tions of the half-blown bitumen sample. The half-blown bitumen actually contains less asphaltene thanone of the straight-run bitumens in the study; furthermore, its asphaltenes are more highly agglomer-ated. These results demonstrate that asphaltene association does not systematically depend on quantityalone, as its chemical type also enters into play. Moreover, during aging, even though asphaltene contentis increasing for all bitumen samples, its agglomeration is still highly dependent on the type of bitumen.It would therefore appear that the presence of crystallized fractions exerts a major influence on thisprocess.

� 2010 Elsevier Ltd. All rights reserved.

1. Introduction

Bitumen is a complex material produced from crude oil; thiscomplexity is due to the fact that bitumen comprises numeroushydrocarbon species. Depending on the crude source, the natureof this material may be paraffinic, naphthenic or aromatic accord-ing to the predominant chemical species: saturate, cyclic or aro-matic [1]. As an example, a naphthenic source (like Venezuelancrude) yields bitumen with practically no crystallized fractions.Nevertheless, bitumen chemistry relies not just on the crude

ll rights reserved.

).

source but also on the manufacturing process and use of additives.Several manufacturing processes are employed to transform crudeoil into bitumen, with the most common being straight-run distil-lation. This process consists initially of removing the lighter com-ponents with an atmospheric distillation step at 350 �C; then, theatmospheric distillation residue is further refined at 425 �C undera vacuum (1–10 kPa). As a last step, the vacuum residue consti-tutes the given bitumen [1]. Other techniques available for deriv-ing bitumen from residue include: air-blowing, deasphalting andvisbreaking. Air-blowing entails the air oxidation of soft bitumenfor several hours at 200–275 �C with, in some instances, the pres-ence of a catalyst such as copper sulfate, zinc or boric acid [2].Moreover, bitumen can also be modified by additives (e.g.

Table 1Determination of both penetration at 25 �C and softening point.

Penetration beforePAV (1/10 mm)

Penetration afterPAV (1/10 mm)

Softeningpoint beforePAV (�C)

Softeningpoint afterPAV (�C)

Bref 38 16 53.6 66.6Basph 44 17 56.4 75.6Bsfc 40 17 54.0 66.8Bss 36 17 60.7 77.0Bppa 28 12 62.8 87.5

M. Le Guern et al. / Fuel 89 (2010) 3330–3339 3331

polyphosphoric acid, paraffin, polymers). Polyphosphoric acid andpolymers are used to modify bitumen properties, whereas paraffinserves to reduce the coating temperature and/or modify bitumenproperties.

Concerning the chemical structure of bitumen, it has been pro-posed that bitumen displays a colloidal structure, with asphalt-enes being present in the form of micelles [3,4]. This colloidalmodel introduces three types of bitumen: sol bitumen (Newto-nian behavior), gel bitumen (non-Newtonian behavior), and sol–gel bitumen. Along these lines, following X-ray diffraction at bothsmall and large-angle observations, Yen proposed an asphalteneassociation model [5] that explains micelle formation in additionto acknowledging the agglomeration potential of micelles. Recentresearch using atomic force microscopy [6,7] seems to corrobo-rate this model by exposing that bitumen is a multi-phase systemthrough a direct observation of the solid state. A number ofresearchers, however, have discarded the colloidal hypothesisand concluded that bitumen is instead a simple homogeneousfluid [8]; some have labeled this model a dispersed polar fluid(DPF) [9]. More recently, Redelius claimed that asphaltenes inbitumen form a molecular solution defined by the asphaltene sol-ubility parameter [10]. For the time being, however, the colloidalmodel is still the only one able to reasonably explain the uniqueaspects of bitumen properties.

Bitumens are very complex materials that have given rise toseveral mechanical or rheological models [11–14]. As indicatedabove, the combination of structure and chemistry, which de-scribes bitumen mechanical behavior, is a topic of current interestand debate. Since bitumens feature a complex composition, theytend to be separated into chemical families according to sizeand ascending polarity: saturates, aromatics, resins and asphalt-enes (known as SARA fractions). To quantify these species, Cor-bett proposed a method based on elution–adsorption liquidchromatography performed on active alumina, through the useof solvents with increasing polarity and aromaticity [2]. Alterna-tive solvents are currently preferred for reasons of both safetyand convenience [1]. For a better appreciation of the colloidalstructure, Gaestel created a colloidal instability index built fromthe SARA fractions [15]. In contrast, size exclusion chromatogra-phy (SEC) enables separating bitumen families by size [16]. Thismethod, however, is unable to quantify the colloidal structureof bitumen since during chromatographic elution, the Van derWaals bindings between asphaltene micelles are decomposing.Nevertheless, Brûlé developed an original approach to an SECapplication that enabled limiting intermolecular dissociationwhile providing a colloidal image [17]. Bitumen can also be char-acterized by thermal analysis, such as differential scanning calo-rimetry [18], which allows determining two main materialcharacteristics: glass transition and crystallized fractions. Crystal-lized fractions appear by the presence of melting enthalpy (nega-tive enthalpy) in the calorimetric diagram. The composition ofthese crystallized fractions has not been thoroughly defined;some authors consider that crystallized fractions are composedentirely of wax [19], whereas others consider that one portionis made of wax while another is due to SARA fractions [20]. Bitu-men aging can be monitored by means of infrared microscopy(FTIR) and may in fact be characterized by creating oxygenatedfunctions, which in turn are easily detected by FTIR [21]. Manyother techniques also serve to characterize bitumen, including:ultraviolet fluorescence [22], X-ray Raman spectroscopy [23], nu-clear magnetic resonance [24], and small-angle X-ray scattering[25]. Despite the existence of these numerous additional bitumencharacterization techniques, building a model where all compo-nents are assigned a defined place and role remains a difficultstep. This finding has consequently led to exploring other tech-niques, such as atomic force microscopy [7].

This paper will focus on a physico-chemical analysis of five dif-ferent types of bitumens, both before and after aging. The bitumensamples were selected according to: the original type of crude oil(i.e. straight-run bitumens with various contents of asphaltenesand crystallized fractions), mode of refining (straight-run vs. half-blown bitumen), and type of modifier (straight-run vs. polyphos-phoric acid (PPA)-modified bitumen). The aim of the present studyis to better understand the aging effect not only on the chemicalspecies but also on chemical organization, as a function of bitumentype. To determine the chemical species, classical tests will be con-ducted: n-heptane precipitation, thin-layer chromatography withflame ionization detection (IATROSCAN), FTIR spectroscopy, anddifferential scanning calorimetry. The chemical structure will beevaluated by quantifying associated molecules (agglomerates)through the use of an improved technique: high-speed size exclu-sion chromatography (HS-SEC). Special attention will be paid tothe theoretical basis of the chosen technique in order to explainhow associated molecules can be quantified. The bitumen sampleswill be artificially aged in this study by means of a pressure agingvessel (PAV).

2. Materials and methods

2.1. Materials

The physico-chemical study has been conducted on a total offive bitumen samples chosen so as to offer similar consistency.The desired penetration grade was defined with respect to theFrench context. Indeed, 35/50 pen grade bitumens are widely usedin this country, from surface through base courses. Both penetra-tion and softening points, as measured using the EN 12591 andEN 1427 Standard protocol, are presented in Table 1. The five bitu-men samples were chosen in order to study different origins, dif-ferent refining modes and PPA addition, consisting of:

– Three straight-run bitumens from different crude oil origins:o Bref: Standard bitumen;o Basph: Bitumen with an asphaltene content greater than Bref

and a crystallized fraction content similar to Bref;o Bsfc: Bitumen with a crystallized fraction content near zero.

– Bss: A half-blown bitumen.– Bppa: The bitumen Bref modified by adding 1.5% of polyphospho-

ric acid at 105–118%, as supplied by Innophos.

It should be noted that adding PPA to the standard bitumen Bref

leads to a decrease in penetration. The consistency of this modifiedbitumen thus slightly differs from the other samples.

2.2. Aging procedure

The binders were artificially aged by spending 25 h in a pres-surized aging vessel (PAV) at 100 �C and 2.1 MPa, using the PAVsystem 9300 provided by Prentex. According to Migliori andCorte [26], exposure to 25 h of PAV leads to the same chemical

3332 M. Le Guern et al. / Fuel 89 (2010) 3330–3339

state as 5 h of the Rolling Thin Film Oven Test (RFOT), at 163 �C,followed by 20 h of PAV (at 100 �C, 2.1 MPa). This artificial agingprocedure is able to simulate the aging that takes place duringthe hot mixing of asphalt binder with aggregates, followed bythe pavement construction phase and then the in-service life ofasphalt pavement. This conclusion was established by means ofseveral tests conducted on unmodified bitumen, consistingof: penetration at 25 �C, ring and ball softening temperature,asphaltene content, creep rheological testing at low temperaturewith the bending beam rheometer, and complex modulusmeasurements.

Ico ¼Area of the carbonyl band centered around 1700 cm�1

Area of the CH2 band centered around 1455 cm�1 þ Area of the CH3 band centered around 1376 cm�1 ð2Þ

2.3. Chemical characterization

2.3.1. Precipitated asphaltene contentPrecipitated asphaltene contents were determined by n-hep-

tane precipitation according to French Standard NF T60-115. Thistype of asphaltene will be called c7-asphaltenes.

2.3.2. Thin-layer chromatography with flame ionization detection(TLC–FID)

The TLC–FID IATROSCAN was used to separate bitumen intoSARA fractions: saturates, aromatics, resins, and i-asphaltenes. (Re-mark: In this study, a distinction is drawn between c7-asphaltenesand i-asphaltenes). The bitumen solutions were prepared in dichlo-romethane, and 1 ll of the sample solution was spotted on chro-marods. Saturates were eluted in a solution of n-heptane;moreover, a solution of toluene/n-heptane (80/20 by volume)was introduced to elute the aromatics. Resins were determinedby an elution in dichloromethane/methanol (95/5 by volume).The share of eluted bitumen corresponds to asphaltenes. Detailsof this method are provided in the literature [27]. Chromatogramswere recorded and measured using the AZUR 4.6 software devel-oped by Datalys.

Results from the TLC–FID IATROSCAN served to determine thecolloidal instability index (Ic) [14], based on the colloidal modelfirst described by Nellensteyn and enhanced by Pfeiffer to explainthe difference between ‘‘sol” and ‘‘gel” bitumens [3,4]. In betweenthese two extremes, a majority of bitumens were found to displayan intermediate behavior due to a mixed ‘‘sol–gel” structure. Todifferentiate these various bitumen types, the Ic index was intro-duced by Gaestel et al. [15] as:

Ic ¼xasph þ xsat

xaro þ xresð1Þ

where xi is the weight content of the generic family (i = i-asphalten-e, resin, aromatic or saturate). The value of Ic typically ranges from0.5 to 2.7 for road bitumens in current use [15].

2.3.3. FTIR spectroscopyThe use of FTIR spectroscopy allows studying aging effects

through monitoring changes in the resulting spectra. This studywill mainly focus on the characteristic band of carbonyl functionsC@O (centered around 1700 cm�1). Tracking of the C@O bandmakes it possible to monitor oxidation of the entire binder. Duringaging, an evolution in bitumen chemistry is actually taking place;this evolution is due to the creation of polar groups with oxygen-like ketones, acids or anhydrides [28–30].

The bitumen samples, dissolved in dichloromethane (30 g l�1),were laid on a thin potassium bromide (KBr) plate. A measurementbetween 4000 and 400 cm�1 was recorded with the thin KBr plateby itself (as the reference acquisition) and then with the sampleadded.

The C@O band can be monitored either relative to the area ofthe functional bands or by calculating structural indices in orderto avoid the effect of the quantities being analyzed, i.e. film thick-ness [21,31,32].

The carbonyl contents were determined using CO indices asfollows:

2.3.4. Differential scanning calorimetry (DSC)In a DSC analysis, a small-sized sample is exposed to cooling

and heating runs, with thermal effects being recorded. Such effectsare due to: glass transition, melting, dissolution, crystallization/precipitation, re-crystallization, and other state changes. In thisstudy, DSC has been undertaken to determine the amount of crys-tallized fractions. To calculate this amount, a melting enthalpy of200 J/g was applied; this value corresponds to the full content ofcrystallized fractions [33,34]. Previous studies [20,35] revealedthat such a calculation is prone to error due to two factors: theTg from asphaltenes at 40–70 �C and an endotherm from non-crys-talline asphaltenes. As explain by Masson et al. [20], the use of amodulated differential calorimeter would allow to distinguishmore precisely the influence of wax, asphaltene or other fractionson the endothermic peak. In the present study, crystallized fractionis taken as global parameter which could include several chemicalspecies.

The DSC analysis in this study was conducted using a NetzschDSC 204 system. Approximately 30 mg of bitumen sample wereweighed in an open pan and placed in the DSC cell under nitrogenblanket. The sample was heated to +160 �C and then cooled at arate of 10 �C/min to reach 25 �C, to remove all traces of the ther-mal history. Next, the sample was cooled at 1 �C/min to �40 �C toallow the wax and other chemical species to crystallize, subse-quent to which the cooling rate was set at 10 �C/min to reach�100 �C. After a step at 100 �C, the sample was heated to+120 �C at a rate of 10 �C/min. The heating cycle between�100 �C and +120 �C was selected in order to calculate the crys-tallizing fraction amount. To perform this calculation, a baselinebetween the temperature at the end of the glass transition anda 90 �C temperature was established (i.e. the green line abovethe heat flow curve). The area between this baseline and the heatflow curve could then be calculated and compared to the 200 J/gmelting enthalpy so as to derive the crystallized fraction content(see Fig. 1).

2.4. High-speed size exclusion chromatography (HS-SEC)

Size exclusion chromatography is typically conducted to sepa-rate and quantify molecules in a mixture according to size [36].Many authors have used SEC to correlate the molecular size distri-bution of bitumen with viscosity measurements [37–39]. However,since bitumen is composed of weak molecular associations,agglomerates during the chromatographic separation tend tobreak, subsequent to which dissociated molecules move at thespeed of isolated molecules [40].

-0.3

-0.25

-0.2

-0.15

-0.1

-0.05

0-100 -80 -60 -40 -20 0 20 40 60 80 100

Temperature (°C)

Po

wer

(m

W/m

g)

% CF

Tg zone

Fig. 1. Thermal diagram of a bitumen by means of DSC.

Fig. 2. Chromatographic diagram of a bitumen sample in an HS-SEC condition andits colloidal structure [11].

M. Le Guern et al. / Fuel 89 (2010) 3330–3339 3333

In order to highlight molecular associations, Brûlé analyzedbitumen under the specific condition of high-speed size exclusionchromatography (HS-SEC) (with a max. flow rate of 3.5 ml/min anda max. concentration of 30 g/l) [11]. This application of SEC yieldedthe chromatographic image that most closely resembles the as-sumed colloidal structure of bitumens. Each chromatographic peakwas ascribed to a state of molecular association (see Fig. 2). In ourstudy, we have used HS-SEC to determine the agglomerate contentin bitumen. To explain how HS-SEC enables detecting and quanti-fying associated molecules, a brief review of the theoretical back-ground, as developed by Farcas [41], will first be presented.

2.4.1. Theoretical backgroundIn order to understand the chromatographic behavior of bitu-

mens, a kinetic model of the dissociation of molecular associationshas been developed [41]. The assumptions and results of this ki-netic model are summarized below.

The colloidal structure of bitumen has been simplified by con-sidering that in diluted bitumen solutions, equilibrium only occursbetween two kinds of species: agglomerated molecules and iso-lated molecules. The theoretical model of dissociation kinetics isthus based on the four following hypotheses:

1. An injected solution contains only two kinds of species:– same-sized agglomerated molecules;– same-sized isolated molecules.

2. The dissociation equilibrium of agglomerates is completely dis-placed in the direction of isolated molecules.

3. Among the factors influencing dissociation equilibrium, onlythe dissociation due to chromatographic separation is takeninto account (i.e. sample band spreading is neglected).

4. At the end of the chromatographic column, the agglomeratedmolecule concentration in the solution is high enough to main-tain the dissociation process continually displaced in the direc-tion of isolated molecules.

By taking into account the dissociation phenomenon in thechromatographic column and by assuming that the dissociationkinetics of molecular association are slow and of the first order,then the solution of kinetic equations produces an expression ofeach species concentration at each moment of the chromato-graphic analysis (Eqs. (5) and (6)). Establishing the model approachproposed by Farcas [41] will be explained below (Fig. 3).

In the case of a solution where no species is able to dissociate,the variation-in-concentration equation for a compound i as afunction of both the accessible volume x and time t of the analysiscan be written as follows:

@C 0iðx; tÞ@t

þ ui@C 0iðx; tÞ@x

¼ 0 ð3Þ

with ui being the speed of species i.In the case of a solution containing micellar compounds, a disso-

ciable quantity of the species is released; this quantity proves to beproportional to the number of remaining dissociable species, whichin turn results in having to solve the following system of equations:

@C01ðx;tÞ@t þ u1

@C01ðx;tÞ@x ¼ kC02ðx; tÞ

@C02ðx;tÞ@t þ u2

@C02ðx;tÞ@x ¼ kC02ðx; tÞ

8<: ð4Þ

where 1k ¼ s is the characteristic time of the dissociation kinetics of

the dissociable species.The solution of the system (in Eq. (4)) leads to the following

expression for the variation in isolated molecule concentration:

C 01ðx; tÞ ¼ C 01ðx� u1t;0Þ þ C 002 ðe�ktmin � e�ktmax Þ ð5Þ

with:

C01ðx; tÞ: Concentration of isolated molecules, expressed as aratio of the pore volume eluted from the chromatographic col-umn to the total permeation volume of the chromatographiccolumn,C002 ðx; tÞ: Initial concentration of molecules involved in themolecular associations as a ratio of the chromatographic col-umn pore volume,u1: Isolated molecular speed inside a chromatographic column,1k ¼ s: Characteristic time of the dissociation kinetics for disso-ciable species,tmin: Advance of the leading edge of agglomerate moleculesover isolated molecules,tmax: Advance of the trailing edge of agglomerate moleculesover isolated molecules.

Moreover, the concentration of agglomerate molecules is ex-pressed as:

C 02ðx; tÞ ¼ C 02ðx� u2t;0Þe�kt ð6Þ

with:

C02ðx; tÞ: Concentration of molecules involved in molecular asso-ciations as a ratio of the chromatographic column pore volume,u2: Speed of molecules involved in the molecular associationswithin a chromatographic column,1k ¼ s: Characteristic time of the dissociation kinetics of disso-ciable species.

The theoretical chromatogram is illustrated in Fig. 3.

Fig. 3. Theoretical chromatographic diagram derived from the equations in the figure with: ai ¼ V0þai VporesV0

(ai is the proportion of pore volume accessible to species i

(0 6 ai 6 1), where w: spread length of all samples injected at the column head and D: flow rate of the chromatographic analysis.

3334 M. Le Guern et al. / Fuel 89 (2010) 3330–3339

2.4.2. Experimental set-up and results interpretationThe bitumen samples have been analyzed under HS-SEC condi-

tions at a 3% concentration in THF and a flow rate of 3 ml/min, witha 10-lm Waters micro-Styragel column and a pore size of 500 Å.

In order to determine the agglomerate content detected on theHS-SEC chromatographic diagram, a deconvolution program hasbeen developed on the basis of a deconvolution of the chromato-graphic diagram program into three Gaussian expressions (Eq.(7)) and a regression for parameters, using a stepwise nonlinearoptimization routine [42] (Fig. 4).

The deconvolution equation introduced is the following:

wTðtÞ ¼X3

i¼1

wi;max exp�� ðt � tR;iÞ2

2r2i

�ð7Þ

with wi;max: height of the distribution, tR;i: position of the maximum,ri: standard deviation.

According to the colloidal model, each chromatographic peakfrom an HS-SEC diagram can be assigned to a molecular associationstate (Fig. 2). However, only the chromatographic peak ascribed toagglomerates has been clearly defined. Consequently, only theagglomerate content will be determined in our study.

3. Experimental results

The five bitumen samples were studied using the test de-scribed in the previous section. All experiments were performed

Fig. 4. Theoretical chromatographic diagram generated from the above equations.

both before and after aging. The presentation of results in thissection will be divided into two parts. First, the results relativeto chemical species, as identified by n-heptane precipitation,TLC–FID, FTIR and DSC, will be provided. Afterwards, results con-cerning the chemical structure (i.e. agglomerate content) fromHS-SEC will be given.

3.1. Chemical species

3.1.1. Asphaltene contentFig. 5 shows that all of the studied bitumens contain differ-

ent amounts of c7-asphaltene. Among the selected bitumens,Basph has the highest c7-asphaltene content and Bref the lowest.The bitumen ranking relative to c7-asphaltene content wasfound to remain unchanged before and after aging. It shouldbe pointed out that adding polyphosphoric acid (PPA) to bitu-men Bref raises the c7-asphaltene content. Hence, a chemicalreaction may be occurring between PPA and bitumen, as as-sumed by Baumgardner et al. [43]. More recent papers[44–49] have shown that there are reactions between PPA andmolecule functions of asphaltene which lead to a decrease ofasphaltene molar mass. It remains to understand how the molarmass decrease can be consistent with the c7-aspahaltene con-tent increase.

3.1.2. SARA fractionsIATROSCAN results indicate that all bitumens studied have

equal saturate rates (Table 2). As observed with n-heptane precip-itation, the addition of PPA to bitumen Bref increases i-asphaltenecontent.

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

Bref Basph Bsfc Bss Bppa

Asp

hal

ten

e co

nte

nt

(%)

OriginAfter PAV

Fig. 5. Determination of asphaltene content by means of n-heptane precipitation.

Table 2Determination of SARA fractions by means of TLC–FID.

Saturates Aromatics Resins i-Asphaltenes

Original Bref 7.8 ± 0.7 50.3 ± 2.8 24.2 ± 1.8 17.7 ± 1.7Bref after PAV 7.0 ± 0.6 34.8 ± 2.8 38.3 ± 2.7 19.9 ± 1.2Original Basph 6.9 ± 0.6 42.9 ± 1.7 25.1 ± 1.7 25.2 ± 1.2Basph after PAV 7.2 ± 0.5 33.2 ± 2.3 31.4 ± 1.7 28.2 ± 1.2Original Bsfc 6.8 ± 0.5 45.1 ± 1.9 26.8 ± 1.3 21.3 ± 1.5Bsfc after PAV 7.2 ± 0.8 37.4 ± 3.8 34.3 ± 2.2 21.1 ± 2.4Original Bss 6.9 ± 0.7 46.7 ± 1.2 22.2 ± 1.8 24.2 ± 0.6Bss after PAV 7.5 ± 0.4 36.0 ± 2.5 32.6 ± 2.1 23.9 ± 0.7Original Bppa 6.2 ± 0.3 49.3 ± 1.5 23.0 ± 0.8 21.5 ± 1.5Bppa after PAV 6.6 ± 0.9 42.1 ± 2.0 25.8 ± 1.7 25.5 ± 1.2

M. Le Guern et al. / Fuel 89 (2010) 3330–3339 3335

After aging, an assessment of the SARA fractions reveals an evo-lution in bitumen structure, namely:

– stability in saturate content;– decrease in aromatics content;– increase in resin content;– higher i-asphaltene content for Bppa, and stability or slight

increase for the other bitumens.

3.1.3. The carbonyl functionAs an example, FTIR spectra (between 500 and 2000 cm�1) ob-

tained from Bsfc before and after 25 h of PAV aging are presented inFig. 6. Results show that only the half-blown bitumen exhibits car-bonyl functions before artificial PAV aging (Fig. 7). This presence ofcarbonyl functions is due to the blowing process, which consists ofair-oxidizing the bitumen for a few hours at 200–275 �C [50].

PAV aging causes the formation of carbonyl functions on allbitumen samples; let us note that bitumen Bsfc seems to be themost sensitive to oxidation. In effect, this bitumen creates carbonylfunctions at a higher rate than the other samples. Moreover, Bss

created fewer carbonyl functions than the straight-run bitumens,perhaps due to the absence of a reaction site within the chemicalenvironment of the half-blown bitumen. It may be assumed that

0

0.05

0.1

0.15

0.2

0.25

0.3

50070090011001300150017001900

Wave number (cm-1)

Op

tic

den

sity Before PAV

After PAV

C=O

CH3

CH2

Before PAV

After PAV

Fig. 6. FTIR spectra (between 500 and 2000 cm�1) of Bsfc, before and after 25 h ofPAV aging.

012345678

Bref Basph Bsfc Bss Bppa

Car

bo

nyl i

nd

ex (

%)

Origin25h PAV

Fig. 7. Carbonyl index of bitumens, before and after 25 h of PAV aging.

most reaction sites have already oxidized during the air-blowingprocess.

3.1.4. Crystallized fractionsAs another example, the thermal diagrams obtained from both

Bref and Bsfc after PAV are presented in Fig. 8. The results depictedin Fig. 9 show that Bsfc contains a very limited amount of crystal-lized fraction. With the exception of Bsfc, the artificial aging isaccompanied by an increase in the crystallized fraction content.Adding PPA to Bref also leads to an increase in the crystallized frac-tion content. As explained in Section 2.3.4, the crystallizable frac-tions measured by non-modulated DSC could not be attributed tothe wax alone [20,35]. The rise in asphaltene content during agingor with the addition of PPA would thus explain partly this increasein crystallized fraction content.

3.2. Chemical structure by HS-CES

For this section, let us take as an example the HS-SEC chromato-gram obtained from Bsfc before and after 25 h of PAV aging(Fig. 10). In this study, the chemical structure has been character-ized by HS-SEC (see Section 2.4.2 for a description). The half-blownbitumen (Bss) presents a high agglomerate content in comparisonwith the other bitumens studied herein (Fig. 11). This finding isin agreement with previous studies [51,52]. Compared to Bref, themodified bitumen Bppa displays a drop in agglomerate content thatcan be attributed to a dispersion of asphaltene micelles due tobreaking the polar interaction between asphaltene molecules[53]. This effect can be link to molar mass decrease of c7-asphal-tene when PPA is added in bitumen [44–49].

After aging, all bitumen samples show an increase in agglomer-ate content, a finding that underscores the bitumen structuringphenomenon during aging. Among these results, it should beremarked that the evolution in agglomerate content remainsthe same for Bref and Bppa (i.e. +1.7%). Results from n-heptane

-0.3

-0.25

-0.2

-0.15

-0.1

-0.05

0-100 -50 0 50 100

Temperature (°C)

Po

wer

(m

W/m

g) Bref PAV

Bsfc PAV

Fig. 8. Thermal diagrams of Bref and Bsfc after PAV.

0.00.51.01.52.02.53.03.54.04.5

Bref Basph Bsfc Bss BppaCry

stal

lized

fra

ctio

ns

(%)

OriginAfter PAV

Fig. 9. Crystallized fraction content of bitumens, both before and after aging.

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

Bref Basph Bsfc Bss Bppa

Dif

fere

nce

(%

)

Before ageing

After ageing

Fig. 12. Differences in asphaltene content obtained by IATROSCAN chromatographyand n-heptane precipitation (NF EN T60-115).

0

200

400

600

800

1000

0 1 2 3 4 5

Time (min)

Inte

nsi

ty

Before PAVAfter PAV

Fig. 10. HS-SEC chromatogram of Bsfc, before and after 25 h of PAV aging.

0.0

2.0

4.0

6.0

8.0

10.0

Bref Basph Bsfc Bss Bppa

Ag

glo

mer

ate

con

ten

t (%

)

Before ageing

After ageing

Fig. 11. Agglomerate content of bitumens, before and after aging, as obtained byHS-SEC.

3336 M. Le Guern et al. / Fuel 89 (2010) 3330–3339

precipitation in Section 3.1 reported that the increases in c7-asphaltene content were equal for these two bitumens (+7%). Con-sequently, molecular agglomeration during aging seems to becaused by asphaltene properties without any PPA influence. Never-theless, the aging mechanisms involved in both of these bitumensare considered to differ: the varying evolution in SARA fractions of-fers a good case in point. On the other hand, let us note that thebitumen without a crystallizable fraction tends to assemble moreagglomerated molecules during aging than the other samples. Itmust now be determined whether this behavior is solely correlatedwith the low crystallizable fraction content.

4. Discussion – cross-reference analysis

4.1. Asphaltene content as a function of method (polar resin)

Results from both IATROSCAN chromatography and n-heptaneprecipitation (NF T60-115) demonstrate that prior to aging, asphal-tene content differs depending on the method employed (Fig. 12).These differences in asphaltene content might be due to polar res-ins in the i-asphaltene fraction [54]. Polar resins are in fact noteluted with the other resins and can be detected with i-asphaltenesat the bottom of the silica rod. The variation in asphaltene contentbetween these two methods then provides the polar resin contentof all bitumens. In order to verify this hypothesis, an IATROSCANchromatography was performed on the maltene phase of all bitu-mens, after precipitation on n-heptane, in which case polar resinsare detected at the bottom of the silica rod. Except for Basph, thishypothesis has been confirmed by comparing the calculated polarresin values with experimentally determined values (Table 3).

In Table 3, the maltene fractions were determined by means ofthe c7-asphaltene content, i.e.:

%X ¼ %XIATROSCAN100�%ðc7AsphÞ

100

� �ð8Þ

%X: Maltene fraction content to be determined.%XIATROSCAN: Maltene fraction content determined byIATROSCAN.%c7Asph: Asphaltene content determined by n-heptane precip-itation (NF EN T60-115).

After aging, the evolution in asphaltene content, as determinedby n-heptane precipitation, reveals a greater increase than the re-sult using IATROSCAN chromatography. The asphaltene contentaccording to these two methods is indeed similar after aging, eventhough before aging the c7-asphaltene content was less than the i-asphaltene content (approx. 5–6%, see Fig. 12). This difference canbe attributed to an oxidization during aging of the polar resins,which were precipitated by n-heptane without modifying the i-asphaltene content. The aromatic decrease actually correspondsto a rise in resin quantity. These differences can be ascribed tothe oxidization of aromatics or resins in polar resins or c7-asphaltene.

4.2. Relationship between colloidal index and agglomerate content

The colloidal index is typically used to characterize the colloidalstability of bitumen. As explained in Section 2.3.1, the colloidal in-dex is determined through the SARA fraction content, as obtainedby IATROSCAN chromatography. This index was compared to theagglomerate content value determined by HS-SEC (Fig. 13). Let usstart by noting that the average standard deviation of colloidalindices equals approximately 10% of the index value. This remarkunderscores that evolution in the colloidal index of Bsfc, Bss and Bref

during aging is irrelevant. These bitumens, however, show a signif-icant evolution in agglomerate content, hence the concept of sta-bility provided by the colloidal index does not appear to besystemically correlated with agglomerate content.

4.3. Relationship between c7-asphaltene content and associatedmolecules

Fig. 14 shows that before aging, agglomerate content is propor-tional to the c7-asphaltene content for straight-run bitumens (Bref,Basp and Bsfc). As opposed to straight-run bitumen, half-blown bitu-men displays a higher agglomerate/asphaltene ratio, as a result ofthe manufacturing process, which ages the bitumen and thereforeacts to create agglomerates. Regarding PPA-modified bitumen, theresults from n-heptane precipitation and HS-SEC suggest that add-ing PPA to Bref leads to an increase in c7-asphaltene content asso-ciated with a drop in agglomerate content (as already observed byBaumgardner et al. and Orange et al.) [43,53].

During aging, bitumen oxidization leads to higher c7-asphalteneand agglomerate contents. As shown with the carbonyl index, this

0

1

2

3

4

5

6

7

8

9

10

0.3 0.35 0.4 0.45 0.5 0.55 0.6

Colloidal index

Ag

glo

mer

ate

con

ten

t

Bref origin

Basph origin

Bsfc origin

Bss origin

Bref after PAV

Basph after PAV

Bsfc after PAV

Bss after PAV

B

Bref origin

Basph origin

Bsfc origin

Bss origin

Bref after PAV

Basph after PAV

Bsfc after PAV

Bss after PAV

Bref origin

Basph origin

Bsfc origin

Bss origin

Bppa origin

Bref after PAV

Basph after PAV

Bsfc after PAV

Bss after PAV

Bppa after PAV

Fig. 13. Comparison between colloidal index and agglomerate content on bitumens, before and after aging.

0.0

1.02.03.0

4.05.06.0

7.08.09.0

10.0

10.0 15.0 20.0 25.0 30.0

N-heptane asphaltenes content (%)

Ag

glo

mer

ates

co

nte

nt

(%)

Bref origin

Basph origin

Bsfc origin

Bss origin

Bref after PAV

Basph after PAV

Bsfc after PAV

Bss after PAV

B

B

Bref origin

Basph origin

Bsfc origin

Bss origin

Bref after PAV

Basph after PAV

Bsfc after PAV

Bss after PAV

Bref origin

Basph origin

Bsfc origin

Bss origin

Bppa origin

Bref after PAV

Basph after PAV

Bsfc after PAV

Bss after PAV

Bppa after PAV

Fig. 14. Comparison between asphaltene content and agglomerate content for bitumens before and after aging.

Table 3IATROSCAN chromatography of bitumens before and after n-heptane asphaltene precipitation (NF EN T60-115).

% Saturates % Aromatics % Resins % Polar resins % c7-Asphaltenes

Bref Maltenes 8.2 ± 0.7 48.7 ± 1.1 24.0 ± 0.8 7.3 ± 0.5 11.8Bitumen 7.8 ± 0.7 50.3 ± 2.8 24.2 ± 1.8 5.9a ± 1.7

Basph Maltenes 7.9 ± 0.8 45.8 ± 1.6 17.7 ± 1.3 5.3 ± 0.8 23.3Bitumen 6.9 ± 0.6 42.9 ± 1.7 25.1 ± 1.7 1.9a ± 1.2

Bsfc Maltenes 8.4 ± 0.4 47.9 ± 1.0 21.4 ± 1.1 6.2 ± 0.8 16.1Bitumen 6.8 ± 0.5 45.1 ± 1.9 26.8 ± 1.3 5.2a ± 1.5

Bss Maltenes 10.4 ± 1.0 48.3 ± 1.0 18.2 ± 1.1 3.3 ± 0.5 19.7Bitumen 6.9 ± 0.7 46.7 ± 1.2 22.2 ± 1.8 4.5a ± 0.6

Bppa Maltenes 8.3 ± 0.7 49.0 ± 1.5 20.8 ± 1.3 4.8 ± 0.7 17.1Bitumen 6.2 ± 0.3 49.3 ± 1.5 23.0 ± 0.8 4.4a ± 1.5

a % i-Asphaltenes and % c7-asphaltenes.

M. Le Guern et al. / Fuel 89 (2010) 3330–3339 3337

finding is due to the creation of carbonyl functions that raisebitumen polarity and enable the creation of intermolecular hydro-gen links. Even with the addition of PPA, the increase in agglomer-ate/asphaltene ratio for Bref and Bppa is the same. From this result, itmay be deduced that PPA does not stimulate molecular associationduring aging. Let us also point out that after aging, the agglomer-ate/asphaltene ratio changes for all straight-run bitumens. As amatter of fact, this ratio increased more for the bitumen withouta crystallized fraction, i.e. for a given amount of c7-asphaltene cre-

ated, a greater quantity of new agglomerates is found in Bsfc than inthe other bitumen samples. It can be assumed that the absence ofcrystallizable fraction plays a role in this evolution. Confirmingsuch a conclusion requires studying other bitumens containingno crystallized fraction.

All these observations underscore that knowing the c7-asphal-tene rate is not sufficient by itself to determine the colloidal struc-ture of bitumen; considering just the SARA fraction content orc7-asphaltene content when characterizing the colloidal structure

y = 66,804x - 0,8542R2 = 0,969

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0.020 0.030 0.040 0.050 0.060

Carbonyl index evolution during PAV

Ag

glo

mer

ates

co

nte

nt

evo

luti

on

d

uri

ng

PA

V (

%)

Bref

Basph

Bsfc

Bss

Bppa

Fig. 15. Comparison of the evolution in both carbonyl index and agglomerate rateduring PAV aging of bitumen.

3338 M. Le Guern et al. / Fuel 89 (2010) 3330–3339

of bitumen remains too narrow an approach. The chemical envi-ronment (i.e. PPA modification, absence of wax) must also be takeninto count, a step for which HS-SEC seems to offer a useful tool.

4.4. Correlation between associated molecules and carbonyl index

An analysis of HS-SEC and infrared spectroscopy results indi-cates similarities with respect to the evolution during aging. In or-der to verify these initial impressions, the evolution in bothagglomerate content and carbonyl index during aging has beendetermined and compared (Fig. 14).

This comparison reveals a linear correlation between the twocharacteristics. Such a finding appears to be logical given that thecarbonyl index enables tracking polarity increases in bitumen: anincrease in bitumen polarity leads to a rise in the level of molecularassociation, i.e. the greater the number of carbonyl functions, thegreater the quantity of agglomerates. The exact nature of the inter-action between these agglomerates still needs to be determined,although the consistency of results in Fig. 15 for Bppa relative tothe other bitumens would suggest an interaction between newly-formed C@O and existing hydroxyl groups. PPA reacts with amines[46], but not with the hydroxyl groups [47], thus leaving hydroxylgroups to interact freely with carbonyl groups in forming agglom-erates, as measured by HS-SEC.

5. Conclusion

The aim of this study has been to understand the aging effecttaking place on chemical species as well as the chemical organiza-tion with respect to bitumen type. This work has confirmed thatwith IATROSCAN chromatography, polar resins are non-eluted likei-asphaltene. It has also demonstrated that during aging, the rise inresin content is due to aromatics association, while the rise inasphaltene content is due to polar resin association; moreover,the oxidization of aromatics or resins within polar resins orasphaltenes is indeed possible during aging.

This study indicates that high-speed size exclusion chromatog-raphy provides complementary information about chemical orga-nization. Results from HS-SEC, in comparison with classicalphysico-chemical identification steps, have in particular demon-strated that:

– Modification due to PPA lowers agglomerate content andincreases c7-asphaltene content. The higher molecular associa-tion during aging, however, does not seem to be influenced byPPA.

– The reliance on blowing as a manufacturing process implies ahigh agglomerate-to-asphaltene ratio.

– The lack of crystallized fractions might influence agglomerationduring aging.

– The evolution of agglomerates is linearly correlated with theevolution of carbonyl index during aging. The carbonyl indexactually serves to track the polarity increase in bitumen. Anincrease in bitumen polarity also leads to greater molecularassociation.

From a more general perspective, this study has shown thatknowledge of the c7-asphaltene content or SARA fractions is notenough to determine the colloidal structure of bitumen. The colloi-dal image, strongly correlated with agglomerate content, appar-ently depends on many other factors, including type,modification, etc. It remains to be understood how agglomeratesinfluence the mechanical properties of binders, yet the assumptioncan nonetheless be made that this ‘‘heterogeneity” at the macro-molecular scale may be correlated with the cracking propertiesof bitumen. This will be the subject of a future study where crack-ing properties assessed in fatigue and monotonic mode of loadingwill be compared to the physico-chemical parameters determinedhere. This comparison should help designer to choose bituminousbinders in order to improve pavement durability.

References

[1] Speight JG. The chemistry and technology of petroleum. 3rd ed. NewYork: Marcel Dekker; 1999.

[2] Corbett LW. Composition of asphalt based on generic fractionation, usingsolvent deasphaltening, elution–adsorption chromatography and densimetriccharacterization. Anal Chem 1969;41:576–9.

[3] Nellensteyn FJ. The constitution of asphalt. J Inst Petrol Technol1924;10:311–25.

[4] Pfeiffer JP, Saal RNJ. Asphaltic bitumen as colloid systems. J Phys Chem1940;44:139–49.

[5] Yen TF. Present status of the structure of petroleum heavy ends and itssignificance to various technical applications. Preprints of ACS symposium onadvances in analysis of petroleum and its products, vol. 17; 1972. p. 102–14.

[6] Masson J-F, Leblond V, Margeson J. Bitumen morphologies by phase-detectionatomic force microscopy. J Microsc 2006;221:17–29.

[7] Masson J-F, Leblond V, Margeson J, Bundalo-Perc S. Low-temperature bitumenstiffness and viscous paraffinic nano and micro-domains by cryogenic AFM andPDM. J Microsc 2007;227:191–202.

[8] Petersen JC, Robertson RE, Branthaver JF, Harnsberger PM, Duvall JJ, Kim SS,et al. Binder characterization and evaluation, vol. 1. SHRP report A-367.Washington, DC: National Research Council; 1994.

[9] Christensen DW, Anderson DA. Rheological evidence concerning the moleculararchitecture of asphalt cements. In: Proceedings chemistry of bitumen, vol. 2.Rome: 1991. p. 568–95.

[10] Redelius P. The structure of asphaltenes in bitumen. Road Mater Pavement Des2006;143–62 [special issue EATA 2006].

[11] Cheung CY, Cebon D. Deformation mechanisms of pure bitumen. J Mater CivilEng 1997;9:117–29.

[12] Lesueur D, Gérard J-F, Claudy P, Létoffé J-M, Planche J-P, Martin D. A structure-related model to describe asphalt linear viscoelasticity. J Rheol1996;40:813–36.

[13] Krishnan JM, Rajagopal KR. Review of the uses and modeling of bitumen fromancient to modern times. Appl Mech Rev 2003;56:149–214.

[14] Krishnan JM, Rajagopal KR. On the mechanical behavior of asphalt. MechMater 2005;37:1085–100.

[15] Gaestel C, Smadja R, Lamminan KA. Contribution à la connaissance despropriétés des bitumes routiers. Revue Générale des Routes et Aérodromes1971;466:85–97.

[16] Baginska K, Gawel I. Effect of origin and technology on the chemicalcomposition and colloidal stability of bitumens. Fuel Process Technol2004;85:1453–62.

[17] Brûlé B, Ramond G, Such C. Relations composition–structure–propriété desbitumes routiers. Etat des recherches au LCPC. Bulletin de Liaison desLaboratoires des Ponts et Chaussées 1987;148:69–81.

[18] Planche JP, Claudy PM, Létoffé JM, Martin D. Using thermal analysis methodsto better understand asphalt rheology. Thermochim Acta 1998;324:223–7.

[19] Edwards Y, Isacsson U. Wax in bitumen part 2 – characterization and effects.Road Mater Pavement Des 2005;6(4):439–68.

[20] Masson J-F, Polomark GM, Collins P. Time-dependent microstructure ofbitumen and its fractions by modulated differential scanning calorimetry.Energy and Fuels 2002;16:470–6.

M. Le Guern et al. / Fuel 89 (2010) 3330–3339 3339

[21] Lamontagne J, Dumas P, Mouillet V, Kister J. Comparison by FTIR spectroscopyof different ageing techniques: application to road bitumens. Fuel2001;80:483–8.

[22] Pieri N, Planche JP, Kister J. Caractérisation structurale des bitumes routiers parIRTF et fluorescence UV en mode excitation–émission synchrones. Analysis1996;24:113–22.

[23] Bergmann U, Mullins OC, Cramer SP. X-ray Raman spectroscopy of carbon inasphaltene: light element characterization with bulk sensitivity. Anal Chem2000;72:2609–12.

[24] Michon L, Martin D, Planche J-P, Hanquet B. Estimation of average structuralparameters of bitumens by 13C nuclear magnetic resonance spectroscopy.Fuel 1997;76(1):9–15.

[25] Yen TF. The colloidal aspect of a macrostructure of petroleum asphalt. Fuel SciTechnol Int 1992;10:723–33.

[26] Migliori F, Corte J-F. Comparative study of RTFOT and PAV aging simulationlaboratory tests. Transport Res Record 1998;1638:56–63.

[27] Masson J-F, Price T, Collins P. Dynamics of Bitumen fractions by thin-layerchromatography/flame ionization detection. Energy Fuels 2001;15:955–60.

[28] Petersen JC. Quantitative functional group analysis of asphalts usingdifferential infrared spectrometry and selective chemical reactions: theoryand application. Transport Res Record 1986;1096:1–11.

[29] Morgan P, Mulder A. The shell bitumen industrial handbook. Shell Bitumen;1995.

[30] Lu X, Isacsson U. Effect of ageing on bitumen chemistry and rheology.Construct Build Mater 2002;16:15–22.

[31] Pieri N, Planche J-P, Kister J. Caractérisation structurale des bitumes routierspar IRTF et Fluorescence UV en mode excitation–emission synchrones.Analusis 1996;24:113–22.

[32] Mouillet V, Farcas F, Besson S. Ageing by UV radiation of an elastomer modifiedbitumen. Fuel 2008;87:2408–19.

[33] Brûlé B, Planche JP, King GP, Claudy P, Letoffe JM. Relationships betweencharacterization of asphalt cements by differential scanning calorimetry andtheir physical properties, vol. 37. American Chemical Society, Division ofPetroleum Chemistry; 1990. p. 330–7 [Preprints].

[34] Lesueur D, Planche J-P, Dumas P. Détermination de la teneur en paraffines desbitumes. Bulletin des Laboratories des ponts et chaussées 2000;229:3–11.

[35] Masson J-F, Polomark GM, Collins P. Steric hardening and the ordering ofasphaltenes in bitumen. Energy Fuels 2005;19:120–2.

[36] Rosset R, Caude M, Jardy A. Chromatographies en phases liquide etsupercritique. Masson; 1991. p. 632.

[37] Jennings PW. High Pressure liquid chromatography as a method of measuringasphalt composition. Report no. FHWA-MT-7930. Bozeman, Mt.: Dept. ofChemistry, Montana St. Univ.; 1980.

[38] Kim KW, Burati JL. Use of GPC chromatogram to characterize aged asphaltcement. J Mater Civil Eng, ASCE 1993;5:41–52.

[39] Lee Soon-Jae, Amirkhanian Serji N, Kim Kwang W. Laboratory evaluation of theeffects of short-term oven aging on asphalt binders in asphalt mixtures usingHP-GPC. Construct Build Mater 2009.

[40] Coll H. Behavior of micellar solutions in gel permeation chromatography. Atheory based on a simple model. In: Altgelt KH, Segal L, editors. Gel permeationchromatography. Marcel Publisher; 1971. p. 329–37.

[41] Farcas F. Etude d’une méthode de vieillissement sur route des bitumes. Thesisat Paris VI University; 1996.

[42] Broadhurst HA, Rein PW. Deconvolution of GPC chromatograms of sugarsolutions. Zuckerindustrie 2003;128(2):96–9.

[43] Baumgardner GL, Masson J-F, Hardee JR, Menapace AM, Williams AG.Polyphosphoric acid modified asphalt: proposed mechanisms. In:Proceedings of the association of asphalt technologists; 2005. p. 283–305.

[44] Masson J-F. Brief review of the chemistry of polyphosphoric acid (PPA) andbitumen. Energy Fuels 2008;22(4):2637–40 [erratum p. 3560].

[45] Masson J-F, Gagné M. Ionic pairs in polyphosphoric acid (PPA)-modifiedbitumen: insights from model compounds. Energy Fuels 2008;22(5):3390–4.

[46] Masson J-F, Gagné M. Polyphosphoric acid (PPA)-modified bitumen:disruption of the asphaltenes network based on the reaction of nonbasicnitrogen with PPA. Energy Fuels 2008;22(5):3402–6.

[47] Masson J-F, Gagné M, Robertson G, Collins P. Reactions of polyphosphoric acidand bitumen model compounds with oxygenated functional groups: where isthe phosphorylation. Energy Fuels 2008;22(6):4151–7.

[48] Masson J-F, Collins P. FTIR study of the reaction of polyphosphoric acid andmodel bitumen sulfur compounds. Energy Fuels 2009;23(1):440–2.

[49] Masson J-F, Collins P, Woods JR, Bundalo-Perc S, Margeson J. Chemistry andeffects of polyphosphoric acid on the microstructure, molecular mass, glasstransition temperatures and performance grades of asphalts. Journal AAPT2009;78:456–84.

[50] Corbett LW. Manufacture of petroleum asphalt. In: Hoiberg A, editor.Bituminous materials: asphalts, tars and pitches, vol. 2. IntersciencePublishers; 1979. p. 81–122.

[51] Corbett LW, Swarbrick RE. Composition analysis used to explore asphalthardening. Process Assoc Asphalt Paving Technol 1960;29:104–12.

[52] Moschopedis SE, Speight JG. The effect of air blowing on the properties andconstitution of a natural bitumen. J Mater Sci 1977;12:990–8.

[53] Orange G, Dupuis D, Martin JV, Farcas F, Such C, Marcant B. Chemicalmodification of bitumen trough polyphosphoric acid: properties –microstructure relationship. In: Third Eurasphalt and Eurobitume congress,Vienna; 2004.

[54] Torres J, González JM, Peralta X. Correlation between the fractionation ofbitumen according to the methods ASTM D-4124 and IATROSCAN,Eurobitumen, Stockholm; 1993.