Construction and Building Materials 23 (2009) 2636–2640

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Construction and Building Materials

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Effect of organo-montmorillonite on aging properties of asphalt

Jian-Ying Yu *, Peng-Cheng Feng, Heng-Long Zhang, Shao-Peng WuSchool of Materials Science and Engineering, Wuhan University of Technology, Wuhan 430070, PR China

a r t i c l e i n f o

Article history:Received 29 November 2008Received in revised form 9 January 2009Accepted 28 January 2009Available online 3 March 2009

Keywords:AsphaltMontmorilloniteThermo-oxidative agingUltraviolet agingRheology

0950-0618/$ - see front matter � 2009 Elsevier Ltd. Adoi:10.1016/j.conbuildmat.2009.01.007

* Corresponding author. Tel.: +86 27 59735080; faxE-mail address: jyyu@whut.edu.cn (J.-Y. Yu).

a b s t r a c t

Effects of organo-montmorillonite (OMMT) on thermo-oxidative and ultraviolet (UV) aging properties ofasphalt were investigated. The results show that the viscosity aging index (VAI) and softening point incre-ment (DS) of OMMT modified asphalt decrease significantly due to introduction of OMMT, and the duc-tility retention rate of the modified asphalt is also evidently higher than that of the pristine asphalt afterthin-film oven test (TFOT) and pressure aging vessel (PAV) aging. In the meantime, both VAI and DS of themodified asphalt are obviously lower than that of the pristine asphalt after UV aging. Furthermore, com-pared with the pristine asphalt, the results of dynamic shear rheometer (DSR) testing exhibit smallerchanges in rut factor (G*/sind) after TFOT and lower fatigue factor (G*sind) after PAV for the modifiedasphalt, which suggests that the effect of thermo-oxidative aging on dynamic rheological behaviors ofthe modified asphalt is restrained due to introduction of OMMT.

� 2009 Elsevier Ltd. All rights reserved.

1. Introduction

As is well known, asphalt has been preferential choice in pave-ment construction since excellent utility of pavement, however, asother organic substances, it is also subjected to aging phenomenaevolving with time. Asphalt aging is one of the principal factorscausing the deterioration of asphalt pavements. It is prone to gofragile and stiff due to exposing to heat, oxygen, and ultraviolet(UV) light during storage, mixing, transport and laying down, aswell as in service life [1–3]. These aging processes lead to decreaseof asphalt properties such as high-temperature rutting and low-temperature cracking, and shorten the lifetime of pavement [4].Asphalt is composed of asphaltenes, saturates, naphthene aromat-ics and polar aromatics according to the Corbett’s selective adsorp-tion–desorption method [5], the total physical and aging propertiesof an asphalt were determined by the proportions of these frac-tions. The main aging mechanism is an irreversible one, which con-tributes to the oxidation, loss of volatile components andexudation of oily components from the asphalt into the aggregate[6–9]. Those changes eventually lead to the physical hardening ofasphalt during the aging periods [10–12]. The factors affecting as-phalt aging include characteristics of asphalt, mixing conditions ofbinder and environmental conditions of asphalt pavement, and allthese factors operate simultaneously, making the process of as-phalt aging very complex [13].

Field aging of asphalt can be accelerated in the laboratory byusing increased temperature, decreased asphalt film thickness, in-

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creased oxygen pressure, or combinations of these factors [14].Accelerated aging tests have been developed in evaluating theaging properties of asphalt [15], which mainly include thin-filmoven test (TFOT), rolling thin-film oven test (RTFOT), pressureaging vessel (PAV) and UV aging. TFOT or RTFOT was used to sim-ulate aging of asphalt during the plant hot mixing and the laydown process, PAV and UV aging were used to simulate the severeaging that occurs after the binder has served many years in apavement.

Montmorillonite (MMT) has been widely used for the modifica-tion of polymers [16–18]. Polymer chains can intercalate into theinterlayer of MMT, which makes MMT dispersed into the polymermatrix at nanometer-scale. These lead to significant improvementsin the thermal, mechanical and barrier properties of polymers[19,20]. The effects of sodium montmorillonite (Na-MMT) and org-ano-montmorillonite (OMMT) on the physical properties of asphalthave been investigated in our previous work [21]. The resultsshowed that MMT can obviously improve the physical properties,rheological behaviors and the storage stability of asphalts, andthe OMMT exhibited better modified effects to the asphalt thanNa-MMT.

The purpose of this work was to investigate the effect of OMMTon thermo-oxidative and UV aging properties of asphalt by meansof TFOT, PAV and UV light irradiation test.

2. Experimental

2.1. Materials

Asphalt, SK-70 paving asphalt was supported by SK Corp., Korea. The physicalproperties of asphalt were as follows: penetration, 64.6 d mm at 25 �C (ASTMD5); softening point, 48.0 �C (ASTM D36); viscosity, 0.563 Pa s at 135 �C and

1 2 3 4 5 6 7 8 9 10

Rel

ativ

e in

tens

ity

2θ (degree)

a b

Fig. 1. XRD patterns of OMMT and OMMT modified asphalt: (a) OMMT and (b)OMMT modified asphalt.

50

60

70

80

(%)

Pristine asphalt Asphalt with 3wt% OMMT

J.-Y. Yu et al. / Construction and Building Materials 23 (2009) 2636–2640 2637

272 Pa s at 60 �C (ASTM D4402). OMMT, which is made by montmorillonite ex-changed with hexadecyl dimethyl benzyl ammonium ions, was supplied by Feng-hong Clay Chemical Factory, Zhejiang, China.

2.2. Preparation of OMMT modified asphalt

The modified asphalt was prepared using a high shear mixer. Asphalt was firstheated until it becomes well melting fluid at around 150 �C in an iron container.Then 3wt% OMMT was added into asphalt, and the mixture was blended at5000 r/min rotation speed for 60 min to ensure the uniform dispersion of OMMT.The pristine asphalt was also processed under the same conditions in order to com-paring with the OMMT modified asphalt.

2.3. Aging procedure

TFOT was executed in an oven with a plate and axis, and the rotation of platewas carried out around the axis. The asphalt for the TFOT was heated in the ovenfor 5 h at 163 �C according to ASTM D1754. The PAV apparatus consisted of thepressure aging vessel and temperature chamber. A cylinder of dry and clean com-pressed air was provided by a pressure regulator with air pressure. The standardaging procedure of 100 �C, 2.1 MPa and 20 h for the PAV was used according toASTM D 6521. The UV aging was performed in a chamber with an UV lamp of500 W, and the wavelength of UV radiation was 340 nm. The melted asphalt wasplaced on a £15 ± 0.5 mm iron pan which was put on bottom of the chamber,and the thickness of asphalt film was about 2.0 mm. The height from the pan tothe lamp was 500 mm. The working temperature was controlled at 80 �C. The UVaging rate was followed by measuring changes in viscosity and softening pointfor a period from 0 to 18 days.

2.4. X-ray diffraction (XRD) test

XRD graphs were obtained using a Rigaku D/max 2400 diffractometer with CuKa radiation (k = 0.154 nm; 40 kV, 50 mA) at room temperature. The diffractogramswere scanned from 1� to 15� in the 2h range in 0.01� steps and scanning rate was 5deg/min.

2.5. Physical properties test

The physical properties of asphalt, including softening point, penetration (25 �C)and ductility (15 �C), were tested according to ASTM D36, ASTM D5 and ASTMD113-86, respectively.

Brookfield viscometer (Model DV-II+, Brookfield Engineering Inc., USA) was em-ployed to measure the viscosity of the asphalt according to ASTM D4402.

2.6. Dynamic rheological characterization

Dynamic rheological measurements for all samples before and after aging wereperformed in parallel plate mode, in the Dynamic Shear Rheometer (Model AR2000,TA Co., USA). A temperature sweeps with 2 �C increments was applied at a fixed fre-quency of 10 rad/s and at variable strain. In this study, parallel plate diameter, par-allel plate gaps and the relevant testing temperature ranges for samples aged afterTFOT or PAV were listed in Table 1. The sizes of the tested samples were corre-spondingly consistent with diameter and gaps of the used parallel plate. The rheo-logical parameters including rut factor (G*/sind) and fatigue factor (G*sind) weremeasured for calculating viscoelastic parameters such as complex modulus (G*)and phase angle (d).

3. Results and discussion

3.1. Structure of OMMT modified asphalt

The exfoliation degree of silicate layers of OMMT in asphalt wasinvestigated by XRD. The XRD curves for OMMT and OMMT mod-ified asphalt are shown in Fig. 1. As reported in our previous work

Table 1Test parameters of DSR.

Rheologicalparameters

Platediameter(mm)

Gap(mm)

Testtemperature(�C)

Sample

G*/sind 25 1.0 40–70 Residue afterTFOT

G*sind 8 2.0 5–40 Residue afterPAV

[21], any crystalline peak in XRD for the OMMT modified asphaltcould not be observed in the Fig. 1, which indicates that the layerof OMMT has already been peeled off and the OMMT modified as-phalt may form an exfoliated structure.

3.2. Effect of OMMT on physical properties of asphalt after thermo-oxidative aging

3.2.1. Viscosity aging indexViscosity is an important parameter for evaluating the perfor-

mance of asphalt, and the viscosity aging index (VAI) is very impor-tant to evaluate aging resistance property of asphalt. It is computedas Formula (1). The higher the VAI value, the more aged the sampleis [22].

VAI ¼ Aged v iscosity value� Unaged v iscosity valueUnaged viscosity value

� 100 ð1Þ

Fig. 2 shows VAI values of the pristine and OMMT modified as-phalts after TFOT and PAV aging. It exhibits that VAI value of theOMMT modified asphalt is evidently lower than that of the pristineasphalt, which suggests that OMMT can availably improve thethermo-oxidative aging properties of asphalt. The result may bedue to the formation of exfoliated structure in OMMT modified as-phalt. During the oxidative process of the asphalt, the composi-tional changes should imply transition of different fractions, i.e.

VAPTOFT0

10

20

30

40

VAI a

t 135

Fig. 2. VAI of the pristine and OMMT modified asphalts after TFOT and PAV aging.

OMMT modified asphalt Pristine asphalt

Individual silicate layers

Oxygen Oxygen Volatile components Volatile components

Fig. 3. Schematic of anti-aging mechanism of OMMT modified asphalt.

2638 J.-Y. Yu et al. / Construction and Building Materials 23 (2009) 2636–2640

the naphthene aromatics are converted in part to polar aromaticswhich later turned to asphaltenes, and making the viscosity of as-phalt increasingly enhance [4]. However, as shown in Fig. 3, OMMTindividual silicate layers with high aspect ratio which dispersed inasphalt matrix can efficiently hinder permeability of oxygen bymeans of their geometrical constraints. The oxidation of asphalt re-duced remarkably, and the above-mentioned transformation ofgeneric fractions in asphalt was necessarily restrained. On theother hand, the silicate platelet may also obstruct loss of volatilecomponents in asphalt at high temperature. Therefore, those fac-tors eventually lead to decrease in VAI and enhancement in anti-aging capability of asphalt.

3.2.2. Softening point incrementSoftening point increment after aging can also be able to reflect

the susceptive degree of aging. It can be expressed as DS, and it iscomputed as

DS ¼ Aged softening point value

� Unaged softening point value ð2Þ

The effect of OMMT on softening point of asphalt after TFOT andPAV aging is shown in Fig. 4. It should be noted that softening pointof the pristine and OMMT modified asphalts has increased after thetwo different aging, indicating an inherent hardening process ofthe material in aging. According to Fig. 4, compared with the pris-tine asphalt, the OMMT modified asphalt exhibits lower DS, whichmay also be caused by the exfoliation of OMMT layers in asphalt.Generally, the content of fractions with large molecules in asphaltincreases at the expense (oxidation) of the small molecules duringthe aging [8], the physical hardening finally results to increase of

VAPTOFT0

1

2

3

4

5

6

7

8

ΔS

()

Pristine asphalt Asphalt with 3wt% OMMT

Fig. 4. DS of the pristine and OMMT modified asphalts after TFOT and PAV aging.

the DS. But, OMMT individual silicate layers effectively block theoxidation of asphalt, which restricts the hardening process of theasphalt, and endows asphalt the lower DS. Consequently, the resultfurther indicates that the thermo-oxidative aging resistance of as-phalt is improved due to the introduction of OMMT.

3.2.3. Ductility retention rateDuctility retention rate (DRR) can reflect the changes of ductile

property of asphalt during aging, and its calculative formula is ex-pressed as

DRR ¼ Aged ductility valueUnaged ductility value

� 100 ð3Þ

Fig. 5 shows effect of OMMT on the DRR of asphalt after TFOTand PAV aging. It can be seen that ductility of both the pristine as-phalt and the OMMT modified asphalt clearly decrease after thetwo different aging. However, DRR of the OMMT modified asphaltis evidently bigger than that of the pristine asphalt. That impliesthe addition of OMMT in asphalt can reduce deterioration in duc-tile property of asphalt during thermo-oxidative aging. The reasoncan more or less be ascribed to obstruction of OMMT to the hard-ening process of asphalt.

3.3. Effect of OMMT on physical properties of asphalt after UV aging

3.3.1. Viscosity aging indexThe effects of UV irradiation on VAI of the pristine and OMMT

modified asphalts are shown in Fig. 6. It is easily found that VAIof the two asphalts gradually increases with prolonging aging peri-ods. Within the initial 4 days, the VAI of the two asphalts increases

VAPTOFT0

5

10

15

20

25

30

35

40

45

DR

R (%

)

Pristine asphalt Asphalt with 3wt % OMMT

Fig. 5. DRR of the pristine and OMMT modified asphalts after TFOT and PAV aging.

0 2 4 6 8 10 12 14 16 180

200

400

600

800

1000

1200

VAI a

t 135

(%)

Aging time (d)

Pristine asphalt Asphalt with 3wt% OMMT

Fig. 6. Curves of VAI vs. UV aging time for the pristine and modified asphalts.

30 35 40 45 50 55 60 65 70

0

200

400

600

800

1000

G*/s

inδ (

kPa)

Temperature ( )

Pristine asphalt Asphalt with 3wt% OMMT Pristine asphalt after TFOT Asphalt with 3wt% OMMT after TFOT

Fig. 8. Curves of G*/sind vs. temperature for the pristine and OMMT modifiedasphalts after TFOT.

J.-Y. Yu et al. / Construction and Building Materials 23 (2009) 2636–2640 2639

quickly, then the increased extent of that gradually get slow in thenext 4 days. After that, the VAI of both the pristine and OMMTmodified asphalts exhibits significant increase again. However,the VAI of the OMMT modified asphalt shows lower values thanthat of the pristine asphalt during the whole UV aging periods. Thisresult is similarly attribute to formation of the exfoliated structurein OMMT modified asphalt. As the mechanism as the UV aging ofother polymers, UV radiation makes more asphalt molecules reachto its excited states which are easily oxidized in the presence ofoxygen. The primary oxidation products, such as carboxyl and per-oxide groups, are photolytically unstable. They can further acceler-ate the aging of asphalt under the UV irradiation conditions [23].But, after the diffusion of oxygen in asphalt matrix is availablycumbered by individual OMMT silicate layers, the primary oxida-tion products reduce greatly. As a result, the UV aging resistanceof asphalt is markedly improved.

3.3.2. Softening point incrementFig. 7 shows the effects of UV irradiation on DS of the pristine

and OMMT modified asphalts. The increased trend of DS for thetwo asphalts is as similar as that of their VAI. Likewise, DS of themodified asphalt is distinctly lower than that of the pristine as-phalt, which means that the UV aging resistance of asphalt isgreatly dragged on out due to introduction of OMMT. The results

0 2 4 6 8 10 12 14 16 180

10

20

30

40

ΔS

()

Aging time (d)

Pristine asphalt Asphalt with 3wt% OMMT

Fig. 7. Curves of DS vs. UV aging time for the pristine and modified asphalts.

may also be caused by the exfoliated structure of OMMT modifiedasphalt.

3.4. Effects of OMMT on dynamic rheological properties of asphalt afterthermo-oxidative aging

Numerous studies address the rheological properties of thepristine and polymer modified asphalts [24,25], and the changesin viscoelastic parameters of asphalt during aging process has avery large effect on utility of asphalt in pavements [26,27].

In accordance with the strategic highway research program(SHRP) specification, G*/sind at 10 rad/s as the rut factor has beenselected for measuring the contribution of a binder to the perma-nent deformation [28]. Fig. 8 shows the effect of TFOT aging onG*/sind for the pristine and OMMT modified asphalts. It is easilyobserved that there is a great increase in G*/sind for the pristine as-phalt after TFOT. However, the increasing extent of that for OMMTmodified asphalt is very slight, which can be contributed to theimprovement in thermo-oxidative aging resistance of asphalt dueto introduction of OMMT.

The influence of OMMT on G*sind of the pristine and OMMTmodified asphalts after PAV aging is showed in Fig. 9. G*sind at10 rad/s as the fatigue factor according to the SHRP method is used

10 15 20 25 30 35 400

5000

10000

15000

20000

25000

G*s

inδ(

kPa)

Temperature ( )

Pristine asphalt Asphalt with 3wt% OMMT

Fig. 9. Curves of G*sind vs. temperature for the pristine and OMMT modifiedasphalts after PAV.

2640 J.-Y. Yu et al. / Construction and Building Materials 23 (2009) 2636–2640

to measure the contribution of a binder to the fatigue ability resis-tance [28]. The higher the G*sind value, the more quick the shear-ing energy loss under the relative loads, namely, the worse thefatigue ability resistance of bitumen. As shown in Fig. 9, G*sindof the modified asphalt is obviously lower than that of the pristineasphalt at the same temperature, which means that it is well to im-prove the fatigue ability resistance of asphalt as a result of intro-duction of OMMT.

4. Conclusions

OMMT modified asphalt is prepared by melt blending, and theeffects of OMMT on thermo-oxidative aging properties of the pris-tine and OMMT modified asphalts were investigated by TFOT andPAV aging, respectively. Both VAI and DS of the OMMT modifiedasphalt decrease significantly due to introduction of OMMT afterTFOT and PAV aging. Additionally, DRR of the OMMT modified as-phalt is evidently bigger than that of the pristine asphalt after ther-mo-oxidative aging, which means that OMMT can largely improvethe thermo-oxidative aging resistance of asphalt.

The effects of OMMT on UV aging properties of the pristine andmodified asphalts were also investigated. With increasing theaging time, both the viscosity and softening point of the pristineand modified asphalts increase gradually during UV aging. How-ever, compared with the pristine asphalt, the OMMT modified as-phalt shows lower VAI and DS values, which indicates that theUV aging resistance of asphalt is enhanced outstandingly due tothe addition of OMMT.

Moreover, the effect of OMMT on dynamic rheological behav-iors of the modified asphalt after thermo-oxidative aging wasinvestigated. The OMMT modified asphalt exhibits smaller changesin G*/sind after TFOT and lower G*sind after PAV in comparisonwith the pristine asphalt, which suggests that the effect of ther-mo-oxidative aging on dynamic rheological behaviors of the mod-ified asphalt is restrained due to adding the OMMT.

Acknowledgments

This work is part of a research Project 50773061 supported byNational Natural Science Foundation of China. The authors grate-fully acknowledge its financial support.

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