Construction and Building Materials 24 (2010) 410–418

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Construction and Building Materials

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The research for high-performance SBR compound modified asphalt

Feng Zhang *, Jianying YuKey Laboratory of Silicate Materials Science and Engineering of Education Ministry, Wuhan University of Technology, Wuhan 430070, PR China

a r t i c l e i n f o

Article history:Received 24 April 2009Received in revised form 11 September 2009Accepted 15 October 2009Available online 13 November 2009

Keywords:AsphaltPolyphosphoric acidStyrene–butadiene rubberSulfur

0950-0618/$ - see front matter � 2009 Elsevier Ltd. Adoi:10.1016/j.conbuildmat.2009.10.003

* Corresponding author. Tel.: +86 27 62981108; faxE-mail address: wucifanying@163.com (F. Zhang).

a b s t r a c t

The high-performance SBR compound modified asphalt can be made with the addition of polyphosphoricacid (PPA), styrene–butadiene rubber (SBR) and sulfur. The effects of PPA, SBR, sulfur on the physicalproperties, the dynamic rheological properties, the high-temperature storage stabilities, the morpholo-gies and the internal structures of asphalts were studied, respectively. The high-temperature storage sta-bility of SBR-modified asphalt can be improved significantly with the addition of PPA and sulfur by thegelation effect and the dynamical vulcanization. The addition of SBR to the pure PPA modified asphaltimproved the low-temperature physical properties with unfavourable effects on the resistance to rutting.The addition of sulfur to the PPA/SBR-modified asphalt improved the rheological properties and the adhe-sion of modified binders to stone matrix. The optimal proportion of PPA, SBR, sulfur can improve theproperties of asphalt roundly.

� 2009 Elsevier Ltd. All rights reserved.

1. Introduction

Asphalt as the binder of aggregate has been widely used in roadpavement. Unfortunately, high-temperature rutting and low tem-perature cracking of asphalt cement or coating layer, due to severetemperature susceptibility limits its further application [1]. There-fore, it is necessary to modify asphalt. Among the modifiers of as-phalt, styrene–butadiene rubber (SBR) and polyphosphoric acid(PPA) are widely used in road pavement.

SBR has been widely used as an important asphalt modifier[2–4]. An Engineering Brief form 1987 available at the US FederalAviation Administration website [5] describes the benefits ofSBR-modified asphalt in improving the properties of bituminousconcrete pavement and seal coats. Low-temperature ductility isimproved, viscosity is increased, elastic recovery is improved andadhesive and cohesive properties of the pavement are improved.According to Becker et al. SBR latex polymers increase the ductilityof asphalt pavement, which allows the pavement to be more flex-ible and crack resistant at low temperature [6], as found by theFlorida Department of Transportation. Unfortunately the loss oflow-temperature ductility of SBR-modified asphalt is very evidentafter RTFOT ageing. Due to the much butadiene structures contain-ing in SBR molecule, SBR is more easier to be oxidized or decom-posed in short-term ageing [7]. Besides the improvement of SBRon the high-temperature performance of asphalt is very limitedand the poor compatibility between SBR and asphalt made asphaltunstable at high-temperature [7]. Though the addition of SBR canimprove the adhesive and cohesive properties of asphalt to some

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extent, the adhesion of the pure SBR-modified asphalt to stone ma-trix is still not very good, due to the soft characteristics of SBR. Inorder to evaluate the properties of SBR-modified asphalt roundly,toughness and tenacity as two important parameters have beenadopted to measure the adhesion ability of SBR-modified asphaltto stone matrix in many professional standards. According to ASTMD 5801-95, the toughness and the tenacity of SBR-modified asphaltshould be no less than 5.0 N m and 2.5 N m, respectively. Many re-search results have shown the testing for the toughness and thetenacity of SBR-modified asphalt is very helpful for us to evaluateits properties. The toughness shows the holding power to roadstone matrix, the tenacity shows the ability of resisting deforma-tion under different loads and the tenacity is a main consistingelement of the toughness [8]. To improve the toughness and thetenacity of SBR-modified asphalt, some approaches have beenadopted in research, one effective way was to vulcanize SBR.

In 1972, TOSCO (The Oil Shale Company) was the first companythat cited polyphosphoric acid by name as an asphalt modifierwithout air blowing. PPA has since been a way to improve theasphalt binder properties. PPA can improve the high-temperaturePG grade evidently and can be used alone or in conjunction witha polymer [9]. To obtain more better modifying results, mostresearchers begun to modify asphalt by using PPA and some poly-mers together. Since then a large number of patents and papershave been published and presented on the usage of PPA and differ-ent polymers in different types of applications from pavement con-struction to roofing [10]. However most polymers that they haveused together with PPA were SBS [11–17], EVA [18,19], SIS, PE[20,21], APP [22,23], GMA [24,19], ABS [25,26], and so on, theconcrete research for the PPA/SBR-modified asphalt has not beenreported in many publications.

F. Zhang, J. Yu / Construction and Building Materials 24 (2010) 410–418 411

In this content, our purpose is to obtain a high-performance SBRcompound modified asphalt by using three modifiers PPA, SBR, sul-fur and study the effects of modifiers on the physical and the rhe-ological properties of asphalt. On the basis of the optimalproportion of the high-performance SBR compound modified as-phalt (PPA/SBR/sulfur:2/6/0.67) we have investigated the internalstructures, the modification mechanism and the thermal stabilitiesof asphalts containing different ratios of modifiers (2 parts PPA; 2parts PPA, 6 parts SBR; 2 parts PPA, 6 parts SBR 0.67 part sulfur) byusing FTIR, optical microscope and thermal weight experiments.

2. Materials and measurements

2.1. Materials

AH-90 paving asphalt, was obtained from the Lanzhou Petroleum Asphalt Fac-tory, China. The physical properties were as follows: penetration, 90 dmm (0.1 mm,25 �C, ASTM D5); softening point, 46 �C (ASTM D36); viscosity, 0.35 Pa s (135 �C,ASTM D4402). SBR was produced by the Lanzhou Petrochemical Co. Ltd., China. Itwas a star-like SBR, containing 27.3 wt.% styrene, 0.64 wt.% water soluble,0.37 wt.% volatile fraction and viscosity (ML1+4 100 �C) 48–55. Polyphosphoric acidwas purchased from Sinopharm Chemical Reagent Co. Ltd., China. Polyphosphoricacid concentration calculated by P2O5 is no less than 80%. Sulfur precipitated is acommercial product (industrial grade) of Yili Chemical Co. Ltd., China.

2.2. Preparation of samples

The modified asphalts were prepared using a high shear mixer (made by ROSSMachine Co. Ltd., China) Firstly, asphalt (600 g) was heated until it became fluid inan iron container, then upon reaching about 120–130 �C, the SBR (based on 100parts asphalt) and sulfur powder (based on 100 parts SBR) were added. The shear-ing time was 40–50 min [27] and then the PPA (based on 100 parts asphalt) wasadded, heated until reaching about 160–170 �C and sheared 40 min at the shearingspeed of 5000 r/min.

2.3. The ageing of modified asphalt

The ageing of the modified polymer asphalts was performed using the rollingthin film oven test (RTFOT, ASTM D2872) simulates the changes in the propertiesof asphalt during the hot mixing and the lay down process.

2.4. Physical properties test

The physical properties of asphalts, including softening point, penetration,toughness and tenacity, ductility (5 �C), were tested in accordance with ASTMD36, D5, D5801-95 and Chinese specification GB/T 4508, respectively.

2.5. Storage stability test

The storage stability of modified asphalts was measured as follows. The samplewas poured into an aluminum toothpaste tube (32 mm in diameter and 160 mm inheight). The tube was sealed and stored vertically in an oven at 163 �C for 48 h, thentaken out, cooled to room temperature and cut horizontally into three equal sec-tions. The samples taken from the top and bottom sections were used to evaluatethe storage stability of a PMA by measuring their softening points. If the differenceof the softening points between the top and the bottom sections was less than2.5 �C, the sample was considered to have good high-temperature storage stability.If the softening points differed by more than 2.5 �C, the PMA was consideredunstable.

2.6. Rheological characterization

A strain-controlled dynamic shear rheometer (DSR, Bohlin CVO100, UK) withparallel plate geometry (25 mm in diameter), was used to determine the rheologicalbehaviour of asphalts. Temperature sweeps (form 50 to 100 �C) with 2 �C incre-ments were applied at a fixed frequency of 10 rad/s and variable strain. In each test,about 1.0 g of sample was placed on the bottom plate, covering the entire surface,and the plate was then mounted in the rheometer. After the sample was heated tobecome a melt, the top plate was brought into contact with the sample, and thesample was trimmed. The final gap was adjusted to 1.2 mm. The actual strainwas measured to calculate various viscoelastic parameters such as complex modu-lus (G�) and phase angle (d). All tests were performed within the linear viscoelasticrange of the sample.

2.7. Morphology observation

The sample morphology was observed using an optical microscope made byNikkon Co., Japan. Squashed slides of modified binders were prepared using verysmall amounts of the heated sample and viewed under the microscope at a magni-fication of 400.

2.8. Fourier transform infrared (FTIR) spectroscopy

A FTIR spectrometer, infinity 60 AR (Mattson, resolution 0.125 cm�1), was usedto determine the functional characteristics of asphalts in wavenumbers rangingfrom 4000 to 400 cm�1. Bitumen was dissolved in carbon disulfide with 5 wt.% con-centration, then dropped onto KBr table and dried for the FTIR analysis.

2.9. Thermal analysis

The thermal stability of asphalts was evaluated by thermal analysis on a TAInstruments, model SDT 2960, under nitrogen atmosphere, sample mass around5 mg, with heating rate of 10 �C min�1, heated from room temperature to 750 �C.The nitrogen flow during the experiments was 120 ml min�1. The TG experimentswere performed at a constant heating rates 10 �C min�1.

3. Results and discussion

3.1. The preparation of high-performance SBR compound modifiedasphalt

To investigate the effects of PPA and SBR on the physical prop-erties of the base asphalt, the physical properties of the pure PPAmodified asphalts and the pure SBR-modified asphalts were mea-sured and shown in Table 1. For the pure SBR-modified asphalt,as can be seen from Table 1, the low-temperature ductility in-creased evidently when the asphalt/SBR ratio was at 100/3 com-pare with the base asphalt, which implies a good improvementof SBR on the low-temperature properties of the base asphalt.However the loss of the low-temperature ductility was severe afterRTFOT ageing, it can be related to the high butadiene content inSBR. More butadiene structures containing in SBR molecules madeSBR much easier to be oxidized and decomposed in the ageing pro-cess. Therefore the loss of the low-temperature ductility of asphaltwas evident, especially at a low SBR content. As SBR content in-creased, the low-temperature ductility after RTFOT ageing in-creased evidently due to the increasing content of SBR withoutbeing oxidized fully in asphalt. When the asphalt/SBR ratio de-clined to 100/5, the low-temperature ductility after RTFOT ageingwas no less than 200 cm. While the softening point increasedslightly when the asphalt/SBR ratio was not more than 100/3 andthe toughness and the tenacity of the pure SBR-modified asphaltcannot come up to the professional standard of SBR-modified as-phalt (ASTM D 5801-95). The results indicated the improvementof SBR on the high-temperature property of the base asphalt is lim-ited and the adhesion of the pure SBR-modified asphalt to stonematrix is poor. For the pure PPA modified asphalt, with increasingPPA content, the softening point increased evidently and the pen-etration decreased correspondingly, which implied that the high-temperature properties of asphalt would be improved by PPA,however the low-temperature ductilities before and after RTFOTageing were very poor, this can be related to the increasing gela-tion degree of asphalt. In fact the increasing PPA content provideda severe structure shift from sol to gel and made asphalt more likea solid [28] and RTFOT ageing made asphalt brittle further. To re-duce the excessive gelation effect caused by PPA and get an evidentimprovement on the high-temperature property of asphalt, the as-phalt/PPA ratio was fixed at 100/2.

The low-temperature ductility is an important property of apaving asphalt, which indicates the low-temperature resisting-cracking property of pavement [29]. To improve the low-tempera-ture resisting-cracking property of the pure PPA modified asphalt,we made the PPA/SBR-modified asphalts with various SBR

Table 1Effect of PPA, SBR, on the physical properties of the original asphalt.

Softening point Penetration Toughness Tenacity Ductility After RTFOT

�C 25 �C, 0.1 mm N m N m 5 �C, cm

Asphalt/SBR100/0 48 80 – – 6.4 3.7100/3 56 46 1.2 0.5 200 56100/4 58 44 1.4 0.8 200 120100/5 60 42 2.0 1.0 200 200100/6 60.2 41 2.2 1.1 200 200

Asphalt/PPA100/1 62 43 – – 4.3 2.5100/2 75 36 – – 3.7 2.3100/3 92 29 – – 1.4 0.8

Table 2The physical properties of the PPA/SBR-modified asphalt.

Softening point Penetration Toughness Tenacity Ductility After RTFOT

�C 25 �C, 0.1 mm N m N m 5 �C, cm

PPA/SBR2/3 75.4 38 6.0 1.0 137.6 12.12/4 75 40 6.5 1.2 200 190.22/5 75 43 6.7 1.5 200 2002/6 75.1 46 6.6 1.4 200 200

412 F. Zhang, J. Yu / Construction and Building Materials 24 (2010) 410–418

contents, the physical properties were tested and shown in Table 2.It can be seen that with increasing SBR content, the low-tempera-ture ductility of asphalt before and after RTFOT ageing increaseddramatically, which implied the low-temperature resisting-crackproperty of asphalt was improved, the penetration increasedslightly and the softening point did not change evidently. Howeverthe toughness and the tenacity of the PPA/SBR-modified asphaltscannot still come up to the professional standard of SBR-modifiedasphalt.

Toughness and tenacity are two important properties to be con-sidered in the application of SBR-modified asphalt, which show theadhesion ability of modified binder to stone matrix. To improve thetoughness and the tenacity of the PPA/SBR-modified asphalt, wemade the PPA/SBR/sulfur modified asphalts with two sulfur levels,the physical properties of the PPA/SBR/sulfur modified asphaltswere tested and shown in Table 3. It can be seen that the toughnessand the tenacity of the PPA/SBR/sulfur modified asphalt were im-proved to some extent through dynamic vulcanization. Withincreasing sulfur content, the toughness and the tenacity increasedcorrespondingly. When 0.67 part sulfur was added, the toughnessand the tenacity increased evidently and can be fit for the profes-sional standard of SBR-modified asphalt. Though the addition ofsulfur can improve the toughness and the tenacity, the low-tem-perature ductility of asphalt after ageing declined rapidly due tothe increasing crosslinking density and the degradation of SBR

Table 3The physical properties of the PPA/SBR/sulfur modified asphalt.

Softening point Penetration Tou

�C 25 �C,0.1 mm N m

PPA/SBR/sulfur2/3/0.34 75 36 7.52/4/0.34 75.1 38 7.62/5/0.34 75.1 39 7.82/6/0.34 75 40 7.92/3/0.67 75 35 8.92/4/0.67 75.4 38 9.02/5/0.67 75 39 9.12/6/0.67 75 41 9.4

molecules. Fortunately the modified binder with 6 parts SBR stillowned a good low-temperature ductility after ageing. Syntheticallythink about the main properties of SBR compound modified as-phalt including the softening point, the low-temperature ductility,the toughness and the tenacity, we can see the PPA/SBR/sulfur (2/6/0.67) modified asphalt was the best one.

3.2. Storage stability of SBR compound modified asphalts

Due to the difference in the solubility parameter and densitybetween SBR and asphalt, phase separation would take place inSBR-modified asphalts during storage at elevated temperatures.Droplets of the SBR melt dispersed in asphalt are usually accumu-lated and float on the top of asphalt at a high-temperature and sta-tic state. The high-temperature storage stabilities of the pure SBR-modified asphalts, the PPA/SBR-modified asphalts and the PPA/SBR/sulfur modified asphalts were tested and the results were pre-sented in Fig. 1. Obviously, for the pure SBR-modified asphalt, thedifferences of the softening points between the top and bottomsections of the samples were large, indicating that the phase sepa-ration was very serious. The pure SBR-modified asphalt becameunstable at 4 parts SBR. With increasing SBR content, the phaseseparation became more serious. When the SBR content increasedto 6 parts, SBR has seriously separated form the asphalt, the differ-ence in softening points was 17 �C shown in Fig. 1.

ghness Tenacity Ductility After RTFOT

N m 5 �C, cm

1.7 43.6 6.91.9 136.8 9.72.0 190.4 7.12.1 200 1213.0 11.3 5.22.9 50.4 5.93.1 103 7.33.7 200 106

Fig. 1. Storage stabilities of SBR compound modified asphalts.

F. Zhang, J. Yu / Construction and Building Materials 24 (2010) 410–418 413

Storage-stable SBR-modified asphalts can be prepared by reac-tion with PPA and sulfur at high-temperature under high shearmixing. It can seen that the PPA/SBR-modified asphalts with vary-ing SBR contents showed good storage stability. The stability of aPMA is not only linked to the difference of density and viscosity be-tween bitumen and polymer. The molecular weight and structureof the bitumen phase is also important. In fact, polyphosphoric acidprovided the shift from sol to gel structure. The shift form sol to gelstructure made the asphalt more and more similar to a solid mate-rial and therefore affected the stability of PMA. The storage stabil-ity of the PPA/SBR-modified asphalt can be improved further byreaction with sulfur. With the addition of sulfur, the difference inthe softening points of the PPA/SBR/sulfur modified asphaltdeclined further indicating the presence of sulfur improved thecompatibility between asphalt and SBR through a dynamic vulca-nization process. When the sulfur content increased to 0.67 part,the differences in softening points were no more than 0.5 �C.

Fig. 2. The viscoelasticity of SBR

3.3. Rheological properties of SBR compound modified asphalt

3.3.1. Viscoelasticity of SBR compound modified asphaltFig. 2 shows the comparison of rheological properties of the ori-

ginal asphalt, the pure PPA modified asphalt, the PPA/SBR-modifiedasphalt, the PPA/SBR/sulfur modified asphalt. With increasing thetemperature, tand increased and G� decreased for the original as-phalt. The varying trend of tand and G� was slowed down greatlywhen 2 parts PPA was added to the asphalt. Compared with othersamples, the pure PPA modified asphalt owned the highest com-plex modulus and the lowest tand due to the change of asphaltstructure from sol to gel [28]. However, the addition of SBR tothe pure PPA modified asphalt declined the modulus and increasedthe tand to some extent, this was related to the soft characteristicsof SBR powder mainly [30]. The addition of SBR to the hard PPAmodified asphalt increased the flexibility of asphalt and madethe modified binder soft. Therefore the resistance of modified bind-ers to rutting declined. Nevertheless, the addition of sulfur to thePPA/SBR-modified asphalt led to the increase in G� at elevated tem-perature, and the tand curve became flatter over a wide range oftested temperatures. The G�of the PPA/SBR/sulfur modified asphaltwith 0.67 part sulfur was more higher than that of the modifiedbinder with 0.34 part sulfur at high-temperature and the changein tand was also reduced to some extent. It implied that theincreasing sulfur level enhanced the degree of chemical vulcaniza-tion of SBR, by which the dynamic mechanical properties of thePPA/SBR/sulfur modified asphalt were influenced [31]. In accor-dance with the Strategic Highway Research Program (SHRP) meth-od, the temperature of asphalt binders when G�/sind was equal to1000 Pa were 64 �C for the original AH-90 asphalt, 100 �C for themodified asphalt containing 2 parts PPA, 92 �C for the modified as-phalt containing 2 parts PPA, 6 parts SBR, 96 �C for the modified as-phalt containing 2 parts PPA, 6 parts SBR, 0.34 part sulfur, 98 �C forthe modified asphalt containing 2 parts PPA, 6 parts SBR, 0.67 partsulfur, respectively.

3.3.2. The rheological properties of the PPA/SBR-modified asphaltFig. 3 shows the dynamic rheological properties of the PPA/SBR-

modified asphalts with various SBR contents. It can be seen thatwhen 3 parts SBR was added to the pure PPA modified asphalt,the G� of the modified binder declined, the tand increased evidently

compound modified asphalt.

Fig. 3. The rheological properties of the PPA/SBR-modified asphalt.

Table 4Effect of SBR content on the performance grade of PPA modified asphalt.

PPA/SBR The temperature (�C) when G�/sind = 1 KPa

2/0 1002/3 982/4 962/5 942/6 92

414 F. Zhang, J. Yu / Construction and Building Materials 24 (2010) 410–418

at high-temperature. As SBR content increased, the G� of the mod-ified binders declined continuously in the whole temperaturerange, the tand increased correspondingly. It can be related tothe soft characteristic of SBR powder and the increasing SBR con-tent, with increasing SBR content, the modified binder becomemore flexible. We can calculate the temperature of the modifiedbinders when G�/sind was equal to 1 KPa, and relate it to differentSBR contents, as shown in Table 4. The performance grade of themodified binders declined with increasing SBR content.

Fig. 4. Effect of sulfur (0.34 part) on the rheologica

3.3.3. The rheological propeties of the PPA/SBR/sulfur modified asphaltThe rheological properties of the PPA/SBR/sulfur modified as-

phalts with two sulfur levels were shown in Figs. 4 and 5. InFig. 4, it can be seen that when 0.34 part sulfur was added to thePPA/SBR-modified asphalt, the G� of modified binders with variousSBR contents were very near and higher than those of the PPA/SBRmodified binders correspondingly in the whole temperature rangeand the tand declined evidently. As can be seen from Fig. 5, whenthe sulfur content increased to 0.67 part, the differences of the G�

among the modified binders were reduced further and the tand de-clined evidently. The modified binders with the same sulfur con-tent showed the similar rheological behaviours in the wholetemperature range.

When G�/sind was equal to 1 KPa, the temperatures were 96 �Cand 98 �C for the PPA/SBR/sulfur modified asphalt with 0.34 and0.67 parts of sulfur, respectively. It was obvious that the increasingsulfur level enhanced the degree of chemical vulcanization of SBR,by which dynamic mechanical properties of the modified binderswere influenced further.

l properties of the PPA/SBR-modified asphalt.

Fig. 5. Effect of the increasing sulfur level (0.67 part) on the rheological properties of PPA/SBR-modified asphalt.

F. Zhang, J. Yu / Construction and Building Materials 24 (2010) 410–418 415

3.4. Morphology

The compatibility between polymer and asphalt is critical to theproperties of PMAs [32]. The morphology of PMAs was investigatedusing optical microscopy by characterizing the distribution and thefineness of polymer in the asphalt matrix. The morphologies of thebase asphalt and the pure PPA modified asphalt containing 2 partsPPA were shown in Fig. 6. It can be seen in Fig. 6A and B somewhite materials appeared in some areas of asphalt matrix com-pared with the base asphalt, which indicated PPA reacted withsome constituents of asphalt and new complexes have beencaused. This can be related to the presence of charge-transfer com-plexes between phosphorous and aromatic structures of asphalt-enes after adding PPA. As the result of condensation of thecomplexes, the white materials shown by microscopy were formed

Fig. 6. Micrographs of the original asphalt and the pure PPA modified asphalt (optical masphalt (asphalt/PPA:100/2).

[33]. These condensed products were comparable with the mi-celles described by Yen in his colloidal model for the sol–gel struc-ture of a bitumen [34], it may be supposed that their MW was veryhigh, approaching the polymer MW. The decline of the moleculeweight difference between polymer and asphalt improved the dis-persion of polymer in asphalt.

Fig. 7 showed the comparisons among the morphologies of thepure SBR-modified asphalt containing 6 parts SBR, the PPA/SBR (2/6) modified asphalt and the PPA/SBR/sulfur (2/6/0.67) modified as-phalt. The pure SBR-modified asphalt showed the presence of a lotof coarse particles in asphalt matrix shown in Fig. 7C, which im-plied SBR was difficult to disperse into asphalt. This incompatibil-ity suggested that pure SBR-modified asphalt had the poorstability. The morphology of the PPA/SBR-modified asphalt wasshown in Fig. 7D. It can be seen that the SBR particles became

icroscopy) at a magnification of 400 (A) original asphalt (B) the pure PPA modified

Fig. 7. Micrographs of the pure SBR-modified asphalt, the PPA/SBR-modified asphalt, the PPA/SBR/sulfur at a magnification of 400 (C) the pure SBR-modified asphalt (asphalt/SBR:100/6) (D) the PPA/SBR (2/6) modified asphalt (E) the PPA/SBR/sulfur (2/6/0.67) modified asphalt.

416 F. Zhang, J. Yu / Construction and Building Materials 24 (2010) 410–418

dim in asphalt matrix and seemed more smaller than that in thebase asphalt, which implied the good dispersion of SBR in acid-treated asphalt. In the Fig. 7E, we can see the vulcanization ofSBR improved the dispersion of it in asphalt matrix evidently.The evident decrease in polymer size meant the dispersion ofSBR in asphalt was improved further by vulcanization.

Fig. 9. FTIR spectra of the pure PPA modified asphalt (asphalt/PPA:100/2).

3.5. Infrared spectroscopy analysis

The FTIR spectra of the base AH-90 asphalt and PPA were givenin Fig. 8. In the FTIR spectrum of the base asphalt, the strong peakswithin 2850–2960 cm�1 region were typical C–H stretching vibra-tions in aliphatic chains. The peak at 1605.11 cm�1 was attributedto C@C stretching vibrations in aromatics. The C–H asymmetricdeforming in CH2 and CH3, and C–H symmetric deforming in CH3

vibrations were observed at 1458.86 cm�1 and 1375.01 cm�1,respectively. The peak at 1215.15 cm�1 corresponded to the framevibration of (CH3)3–C–R. The small peaks within 650–910 cm�1 re-gion were typical C–H vibrations of benzene ring. In the FTIRspectrum of PPA, the broad and low peak at 2843 cm�1 was attrib-uted to the P–OH stretching vibrations, the peaks were observed at2350 cm�1 corresponding to P–H stretching vibrations; 1645 cm�1

corresponding to the O–H deforming vibrations; 1007.82 cm�1

Fig. 8. FTIR spectra of the original asphalt and PPA.Fig. 10. FTIR spectra of the PPA/SBR (2/6) modified asphalt and the PPA/SBR/sulfur(2/6/0.67) modified asphalt.

Table 5The TG properties results of asphalts.

Samples T0 (�C) Mass loss (%) Residue at 553 �C (%)

AH-90 323 75.14 16.06PPA 364 69.27 22.3PPA/SBR 348 71.13 21.41PPA/SBR/sulfur 330 71.82 19.98

F. Zhang, J. Yu / Construction and Building Materials 24 (2010) 410–418 417

corresponding to the P–O–P stretching vibrations; 925 cm�1 and699.2 cm�1 corresponding to the asymmetric vibrations of P–O–P; 494.3 cm�1 corresponding to the bending vibrations of P–O–P.

The FTIR spectrum of the pure PPA modified asphalt containing2 parts PPA was shown in Fig. 9, it can be seen that new absorptionpeaks appeared at 1007.82 cm�1, 699.2 cm�1, 494.3 cm�1 respec-tively compare with the original asphalt, however these peaks alsocan be found in the FTIR spectra of PPA. Though PPA reacted withsome constituents of asphalt, the absorption peaks of new com-plexes caused can not be found in the FITR spectra of the purePPA modified asphalt due to the overlap of other peaks.

The FTIR spectra of the PPA/SBR (2/6) and the PPA/SBR/sulfur (2/6/0.67) modified asphalts were given in Fig. 10. The new peak at968.58 cm�1 was corresponding to C@C stretching vibrations inSBR molecule. To avoid the effect of asphalt film thickness, thestructural indices Ic@c was used to show the change of SBR contentbefore and after adding sulfur and Ic@c can be calculated by the fol-lowing equation [35,36]:

Ic@c ¼Area of the ethylene band centered around968 cm�1

Area of the CH2 band centered 1458 cm�1 þ Area of theCH3 band centered1375 cm�1 ð1Þ

It can be calculated from Fig. 10 the structural indices Ic@c were0.51 and 0.42 for the PPA/SBR and the PPA/SBR/sulfur modified as-phalts respectively, the PPA/SBR/sulfur modified asphalt showedthe lower structural indices compare with the PPA/SBR modifiedasphalt, indicating the decline of SBR content in asphalt throughdynamic vulcanization.

3.6. Thermal analysis

The thermal stability of bitumens is an important property to beconsidered in the proper application, depending on the property ofthe products. The thermal stabilities of the original asphalt, thepure PPA modified asphalt (2 parts PPA), the PPA/SBR (2/6) modi-fied asphalt, the PPA/SBR/sulfur (2/6/0.67) modified asphalt) andtheir chromatographic fractions were studied by TG experimentsunder a nitrogen atmosphere. The main features of the curves wereobtained, the onset temperatures of the mass loss effects (T0), themass loss in the main decomposition temperature range (350–

Fig. 11. TG curves under nitro

553 �C) and the residue content at 553 �C were calculated, asshown in Table 5 from the TG curves in Fig. 11, respectively.

The thermogravimetric measurements performanced undernitrogen gas flow showed that all samples undergo a mass loss pro-cess. The thermal evolution of four asphalts was similar. The onsettemperature of mass loss process of asphalts indicated that thepure PPA modified asphalt has the highest thermal stability, fol-lowed by the PPA/SBR and the PPA/SBR/sulfur modified asphalts,and the original asphalt was the most instable. The similar conclu-sion can be certified from the mass loss of asphalts in the main

decomposition temperature range. Compare to the residue contentof the PPA/SBR-modified asphalt at 553 �C, the residue content ofthe PPA/SBR/sulfur modified asphalt seemed more smaller show-ing the low thermal stability of C–S bond. The residue content ofthe original asphalt showed the presence of coke.

4. Conclusion

The addition of PPA, SBR, sulfur to the base asphalt, in order toimprove the performance for pavement applications in terms ofphysical and rheological properties had been studied. Due to astructure shift of asphalt from sol to gel, PPA can improve thehigh-temperature physical and rheological properties of asphaltwith an unfavourable effect on the low-temperature ductility.The addition of SBR to the pure PPA modified asphalt can improvethe low-temperature ductility dramatically, however it influencedthe dynamic rheological properties to some extent, this was relatedto the soft characteristics of SBR rubber mainly. The addition of sul-

gen gas flow for asphalts.

418 F. Zhang, J. Yu / Construction and Building Materials 24 (2010) 410–418

fur to the PPA/SBR-modified asphalt improved the high-tempera-ture rheological properties, the adhesion to stone matrix and thecompatibility between asphalt and polymer through dynamicalvulcanization with a small effect on the thermal stability. ThePPA/SBR/sulfur modified asphalts with the same sulfur contentshowed the similar rheological behaviour. The suitable proportionof PPA, SBR, sulfur in asphalt can improve the properties of SBRcompound modified asphalt roundly.

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