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Petroleum Science and Technology, 28:331350, 2010

Copyright Taylor & Francis Group, LLC

ISSN: 1091-6466 print/1532-2459 online

DOI: 10.1080/10916460802640282

Influence of Asphaltenes on the RheologicalProperties of Blended Paving Asphalts

N. K. RAJAN,1 V. SELVAVATHI,2 B. SAIRAM,2 AND

J. M. KRISHNAN1

1Department of Civil Engineering, Indian Institute of Technology Madras,

Chennai, India2R&D Division, Chennai Petroleum Corporation Limited, Chennai, India

Abstract Some of the refineries in India produce asphalt by blending propane deas-

phalting (PDA) pitch and heavy extract. This investigation reports the rheological andchemical characterization of various blends made with PDA pitch and heavy extract.

The main objective is to develop an understanding on the influence of asphaltenechange on the changes in the rheological properties under all aged conditions. Three

blend proportions were manufactured using three different crude sources, and allthe blends were subjected to short- and long-term aging. All the blends were tested

for steady shear, creep and recovery, and stress relaxation properties. A chemicalcomposition analysis of all the blended asphalt samples was carried out under all three

aging conditions. It was seen that the proportion of PDA pitch considerably controls

the rheological properties and that the kinetics of short-term aging are completelydifferent when compared to long-term aging for blended asphalt.

Keywords asphaltenes, creep and recovery, PDA pitch, stress relaxation

Introduction

Modern traffic, with a large number of trucks and increased tire pressure, offers a seriouschallenge to the design, construction, and maintenance of asphalt pavements throughout

the world. Currently, India has the second-largest road network with 3.3 million-km,

and more than $50 billion is being spent on construction of asphalt pavements (National

Highway Authority of India (NHAI), 2008). The role of asphalt on the performancecharacteristics of asphalt pavement is well known. Taking into account the fact that asphalt

processed in India has been investigated very little, an investigation clearly aimed atdeveloping a fundamental understanding is necessary. This investigation is aimed toward

that goal.

The rheological properties of asphalt depend to a large extent on the chemical

composition of asphalt, and this in turn depends on the crude source. The suitability of

a particular asphalt processing method normally depends on the type and classificationof the crude source. The majority of the crudes processed in India belong to medium

Address correspondence to J. M. Krishnan, Assistant Professor, Room Number: B5B233,Department of Civil Engineering, Indian Institute of Technology Madras, IIT Post Office Chennai,India 600036. E-mail: [email protected]

331

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332 N. K. Rajan et al.

American Petroleum Institute (API) gravity variety. In India, asphalt is produced by

several means. It can be produced by a straight reduction to grade by distillation or can be

air blown. Some of the refineries also follow a blending procedure to manufacture asphalt.

This process involves blending PDA pitch and heavy extract. Propane deasphalting (PDA)

pitch or Propane Precipitated Asphalt (PPA) is a residual material that results after

extraction of heavier oils (also called deasphalted oils) from the vacuum residue in apropane deasphalting unit using propane as the solvent. Typically, the penetration values

of PDA pitch lies between 1 and 5. The other component, heavy extract, is from the

residuum stream (i.e., bright stocks produced from deasphalted oils). Since India follows

viscosity grading, 8788% of PDA pitch is blended with 1213% of heavy extract to get

a viscosity grade-10, and 9192% of PDA pitch is blended with 89% of heavy extractto get a viscosity grade-30. This is achieved by manipulating the feed rate through

a line blending process at a high mixing temperature of 190C200C resulting in a

homogeneous mix.

The recent initiatives of the U.S. Strategic Highway Research Program resulted

in developing a fundamental understanding of asphalt chemistry and the relationshipwith rheology (Petersen et al., 1994). On the other hand, rheological and chemicalinvestigations on blended asphalts and the influence of PDA pitch and its effects on

aging have yet to be investigated in detail, barring few investigations in Russia and Israel.

This investigation involves conducting systematic studies on the changes in the chemical

composition during aging and developing an understanding between the rheology and

chemistry of blended asphalt. For the first time for blended asphalt, systematic tests suchas steady shear, creep and recovery, and stress relaxation are carried out for unaged,

short-term-aged, and long-term-aged conditions. Three crude sources spanning a wide

variety are used. After the literature review, the experimental investigations that were

conducted are detailed. The relationships between rheology and chemical composition

of the samples tested are discussed. A possible hypothesis related to the temperaturesusceptibility and oxidation kinetics is made.

Literature Background

Scant literature exists about blended asphalts. Systematic investigations on the influence

of the proportions of PDA pitch, the effects of blending methods, the influence of

aging, and ultimately the influence of crude source on the rheological and chemicalproperties of blended asphalt are missing. Most of the blending proportions arrived at

are based on the nature of the specifications to be met and these specifications could be

based on penetration or viscosity. The details related to the various blending componentsfor processing road bitumen from crude oils with considerable sulphur content and the

effects of low proportions of oil content in the deasphalted petroleum asphalt resulting

in low frost resistivity was discussed by Akhmetova, Fryazinov, and Torbeeva (1965).Rudenskaya, Gubenko, and Nikiforov (1966) suggested high oxidation of the product of

deasphaltization before diluting with selective purification extracts to achieve the desired

softening point, penetration, and ductility values. The choices of various components in

arriving at blended road asphalt with widely varying physicochemical properties were

discussed by Gun and Biryulina (1969). Lopatinskii and Lopatinskii (1970) discussedthe use of a nomogram for arriving at a specific softening temperature based on the

similar properties of the blended components. Akhmetova and Glozman (1974) usedthe triangular diagram (asphaltene-hydrocarbon-resin) in choosing the blend proportions.

The details related to various operations for blending PDA pitch and the significance

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Rheological Investigations Of Blended Asphalts 333

of oxidation during the blending process with related experimental data were detailed

by Akhmetova, Stepanova, Evdokimova, and Chernobrivenko (1979) and Pushmynstsev,

Gun, Chernysheva, Gureev, and Efanova (1982). Allakhverdiev, Kuliev, and Samedova

(1987) suggested that the quantity of heavy distillates in the mixture of reformulated

asphalt be around 3035% for better performance. Detailed investigations on different

blending components of PPA were done by Ishai and coworkers in three significantpublications (Ishai and Tuffour, 1987; Ishai, 1995; Ishai and Yuval, 2002). These are

some of the detailed studies conducted on reformulated asphalt and asphalt mixtures

manufactured with these blends. Apparent viscosity at 60C was considered as an im-

portant rheological parameter to rank the consistency of reformulated asphalt with the

straight-run control sample by Ishai and Yuval (2002). They also precisely remarkedabout the need to investigate the blends within the purview of SUPERPAVE protocols

for performance graded binders. The use of supercritical fractions as asphalt recycling

agents and aging studies on recycled asphalts was detailed by Chaffin, Liu, Davison,

Glover, and Bullin (1997).

Chemical composition analysis is essential in determining the rhelogical propertiesand performance characteristics of asphalts. Petersen (1984) discussed in detail thechemical composition of asphalt as related to its durability. Detailed investigations were

carried out in the past relating the chemical composition of asphalt to the rheologi-

cal properties by a number of researchers, including Rostler and White (1959); Cor-

bett (1965); Gaestel, Smadja, and Lamminan (1971); Moschopedis and Speight (1977);

Poirier and Sawatzky (1992); Lesueur, Gerard, Letoffe, Planche, and Martin (1996); Liuet al. (1997); Loeber, Muller, Morel, and Sutton (1998); Pauli and Branthaver (1998);

Christopher, Richard, and Charles (1999); Robertson (2000); Leon, Rogel, and Espidel

(2000); Redelius and Soenen (2005); and Oyekunle (2000, 2007). With significance

evidence from the literature, one can conclude that each fraction or combination of

fractions perform separate functions in respect to physical properties, and it is logicalto assume that the overall physical properties of one asphalt are dependent on the

combined effect of these fractions and the proportions in which they are present (Petersen,

1984).

Considerable investigations have been conducted on the changes in the internal and

chemical structure of asphalt as a consequence of aging and the effect of the same on the

rhelogical properties. Some recent references include Robertson, Branthaver, and Petersen(1992); Petersen (1993, 1998); Yang, Cong, and Liao (2003); Gawel and Baginska (2004);

Gao, Xiao, Liao, Cong, and Dai (2006); Liao, Wei, Yan, Cong, and Zhai (2004); and

Qi and Wang (2004). Significant understanding related to aging is due to the work of

Petersen (1993).The chemical compositions of asphalt as well as the hypothesized structure associated

with asphalt are still a matter of various investigations. Also, most of the rheological

investigations clearly are restricted to either a set of empirical tests such as penetration,

softening point test, and ductility or measurement of viscosity. Clearly, the influence of

the viscoelastic nature of asphalt is not taken into account. Each type of mechanical

test elicits a specific microstructure response from the material, and hence it will beincomplete to try and characterize the influence of chemical composition at different

stages of aging on only a specific test such as a viscosity test. This investigation tries

to relate the response of blended asphalt under unaged, short-term-aged, and long-term-

aged conditions with the chemical constitution of asphalt. Specifically, this investigation

focuses on the asphaltene fraction. In addition, the rheological tests are chosen such that

a nonlinear response of the material is elicited.

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Experimental Investigations

Material

Three crude sources identified as Basra Light, Upper Zakum, and Arab Mix were used

in the complete set of investigations. The PDA pitch and heavy extract processed fromthese crudes by Chennai Petroleum Corporation Limited (CPCL) was used to blend the

asphalt. Three asphalt blends 90:10, 85:15, and 75:25 (PDA pitch: heavy extract) of all

the three sources were prepared in a laboratory scale using a pilot plant at CPCL for these

investigations. All the blends were prepared in the laboratory, simulating the regular line

blending process normally followed by CPCL asphalt plant. All the blended samples were

subjected to short-term aging using rolling thin film oven equipment (ASTM D2872-04)and long-term aging using pressurized aging vessel (ASTM D6521-08). The total number

of samples tested includes three crude sources and three blended proportions for each

crude source under unaged, short-term-aged, and long-term-aged conditions. Hence, a

total of 27 samples were tested.

Experiments

All the samples were subjected to three rheological tests, namely steady shear exper-iment, creep and recovery experiment, and stress relaxation experiments. Additionally,

all the samples were subjected to chemical composition analysis. The choice of the test

parameters such as temperature, magnitude of load, and loading period was selected after

repeated trials so that all the samples were tested under identical test conditions. This

effort is needed since the blends used in this investigations vary from a highly viscoelasticfluid material (e.g., a 75:25 Arab mix unaged blend) to a highly viscoelastic solid material

(e.g., a 90:10 Basra Light PAV aged material).

Steady Shear Experiments

The Brookfield HA DV-II rotational viscometer with a thermosel apparatus was used

for conducting steady shear experiments on the material at all the three conditions. Two

fixed temperature levels60C and 135Cwere selected. The apparent viscosity ofall the samples at 60C and 135C were calculated as the average of the three steady

state viscosity values observed at the end of sixth, seventh, and eighth minute of the

experiments as per the ASTM D4402-06 procedure. The shear rate adopted at 135 C

was 70 RPM (65.1 s 1), and the shear rate adopted at 60C was 0.1 RPM (0.093 s1).

However, due to the torque limitations of the Brookfield HA DV-II rotational viscometer,steady shear experiments at 60C for PAV-aged samples of all the blends were conducted

using an Anton-Paar MCR- 301 Dynamic Shear Rheometer (DSR). Enough care was

taken to ensure that the measurements were identical for the same testing conditions

using these two equipments. The repeatability and reproducibility of the test results were

found to be within the limits of 5 and 10%, respectively

Creep and Recovery Experiments

The DSR was used to conduct the creep and recovery experiment. In this experiment,

the material is subjected to a constant load of 20 kPa for 10 seconds at 20

C temperatureand then unloaded. The strain during the loading time of 10 seconds as well as during a

recovery period of 100 seconds is measured. The schematic sketch of this test is shown in

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(a)

(b)

Figure 1. Creep and recovery experiment: (a) stress vs. time and (b) strain vs. time.

Figures 1a and 1b. For the creep and recovery experiment, data was collected every 0.05s during creep and during recovery, the data acquisition interval was varied from 0.05 s to

5 s linearly. Figure 1b depicts the various components of the deformation measured duringthe conduct of experiment. One important objective of this investigation is to develop an

understanding of the stress-strain-time behavior of blended asphalts in relation to their

chemical composition.

Stress Relaxation Experiments

A typical stress relaxation experiment consist of applying a constant strain instantaneously

and monitoring how the stress induced relaxes over a period of time. Consideringthe difficulties associated with applying an instantaneous strain particularly on asphalt

samples, the stress relaxation experiments were conducted in a different manner. Theschematic sketch of the test conducted is shown in Figures 2a and 2b. The stress relaxation

was monitored here after subjecting the material to a constant shear rate such that the

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(a)

(b)

Figure 2. Stress relaxation experiment: (a) strain versus time and (b) stress versus time.

required strain level was achieved. Once the required strain is reached, the DSR is

switched to the displacement control mode and the relaxations of stresses are measured.

The stress relaxation test is conducted at a temperature of 20C, and a strain level of25% was used. The stress relaxation response was monitored for 300 seconds. For the

stress relaxation experiment, the data was collected every 0.005 s during ramping of thestrain; during the relaxation, the data acquisition interval was varied from 0.005 s to 20 s

logarithmically. Figure 2b depicts the typical stress relaxation response. Marked in this

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figure is the time to reach 10% peak stress, an important parameter normally used for

characterizing the stress relaxation behavior.

Results and Discussion

Chemical Composition

One major impediment in relating chemical composition with rheology is the multitude

of test procedures available for chemical composition analysis (Goodrich, Goodrich, and

Kari, 1986). In this investigation, the chemical composition analysis of all the blended

asphalt samples is done under unaged, RTFO-aged, and PAV-aged conditions using thestandard Corbetts separation procedure (ASTM D4124-01); the results are tabulated in

Table 1.

Table 1Chemical composition of blended asphalt

Unaged

Basra Light Upper Zakum Arab MixCrude source

PDA Pitch: Ext. 90:10 85:15 75:25 90:10 85:15 75:25 90:10 85:15 75:25

Saturates, wt% 1.9 2.8 5.7 1.9 2.5 3.3 4.8 4.4 4.0

Naphthene

aromatics,

wt%

49.4 50.5 61.4 48.0 50.2 53.6 56.8 58.1 61.1

Polar aromatics,

wt%

36.7 36.4 23.5 40.0 37.8 35.0 30.5 29.8 28.5

Asphaltenes, wt% 12.0 10.3 9.4 10.1 9.5 8.1 7.9 7.7 6.4

RIFOT aged

Saturates, wt% 1.2 1.4 4.2 1.2 1.5 2.9 3.4 3.1 3.8

Naphthene

aromatics,

wt%

45.6 47.4 52.7 44.6 46.2 48.1 50.7 53.7 49.5

Polar aromatics,wt%

39.5 38.3 32.3 42.8 39.8 37 34.8 32.4 36.6

Asphaltenes, wt% 13.7 12.9 10.8 11.4 12.5 12 11.1 10.8 10.1

PAV aged

Saturates, wt% 1 1.2 3.9 1 1.3 2.7 3.8 3.2 4.5

Naphthenearomatics,

wt%

42.8 45.5 46.7 43.8 45.2 47.2 42.7 47.6 52.5

Polar aromatics,

wt%

34.7 34.1 31.6 35.3 34.7 33.1 35 33.3 28.4

Asphaltenes, wt% 21.5 19.2 17.8 19.9 18.8 17 18.5 15.9 14.6

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This investigation focuses on the influence of asphaltene on the rheological behavior

of blended asphalt. Significant investigations conducted in the past attest to the role of

asphaltene in the overall behavior of the material (see, e.g., some of the major works

related to this aspect: Boduszynski, 1979; Boduszynski, McKay, and Latham, 1980;

Acevedo, Ranaudo, Escobar, Gutierrez, and Gutierrez, 1995; Lin, Lunsford, Glover,

Davison, and Bullin, 1995; and Gokhman, 2000).

135C Apparent Viscosity vs. Asphaltenes

Figures 3a, 3b, and 3c illustrate the relationship between asphaltene content and apparent

viscosity at 135C for all the three blends by crude source and also depict the asphaltene

content change related to the change in the apparent viscosity values at 135C from

unaged to RTFO-aged, and RTFO-aged to PAV-aged conditions. From the figure, onecan observe that with the increase in asphaltene content, the apparent viscosity values

increase for all the blends during various stages of aging. One can also observe the effect

of crude source on the variations in the initial asphaltene content for all the unagedblends and the corresponding changes that occur during various stages of aging. It is

also seen that the Arab Mix blends exhibit the least change in viscosity per unit changein asphaltene, and the Basra light mix blends exhibits the greatest change in viscosity

per unit change in asphaltene. It is also seen that the 75:25 blends for all the crude

sources exhibit a linear trend of viscosity change per unit change of asphaltene. Another

interesting trend is related to 85:15 blends. For all the crude sources and under all aged

conditions, this blends shows significantly higher viscosity increase per unit change in

asphaltenes.

(a)

Figure 3. Percentage asphaltenes vs. viscosity at 135C and 60C: (a) Basra Light, (b) Upper

Zakum, and (c) Arab Mix. (continued)

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(b)

(c)

Figure 3. (Continued).

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60C Apparent Viscosity vs. Asphaltenes

Figures 4a, 4b, and 4c illustrate the relationship between asphaltene content and apparent

viscosity at 60C. It is seen that the response of all the blends exhibited more or less a

similar trend when compared to the viscosity at 135C. It is also seen that the 75:25 blend

showed the least change in viscosity per unit change in asphaltene. Also, the viscosity

(a)

(b)

Figure 4. Percentage asphaltenes vs. viscosity at 135C and 60C: (a) Basra Light, (b) Upper

Zakum, and (c) Arab Mix. (continued)

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(c)


measured at 60C at different stages of aging helped to unravel some of the aging kinetics

of the material. For example, the issues related to aging at high temperature versus low

temperature as well as aging of highly and poorly solvated material are well discussed

for a regular asphalt (Petersen 1993, 1998). On the other hand, very little information

exists in the literature related to blended asphalt, especially the role of PDA pitch as amajor constituent of asphalt. If the viscosity at 60C is used as a main criterion, one

can conclude that blends with a lower proportion of PDA pitch are likely to exhibit very

little change during long-term aging. As asphaltenes are produced in oxidative aging of

asphalt, the addition of more asphaltene (through more PDA pitch) essentially creates

asphalt that is likely to fail much earlier due to cracking. On the other hand, blends withhigher PDA pitch content can withstand the plastic deformation normally expected in the

initial life of the pavement.

Creep and Recovery Experiments

Instantaneous Elastic Jump and Total Strain vs. Asphaltenes. The various measures of

deformation during creep and recovery test such as instantaneous elastic jump duringloading and the total deformation at the end of loading are evaluated with the corre-

sponding change in asphaltenes. Normally, a viscoelastic solid-like material will recover

the strain completely during the strain recovery period, whereas a viscoelastic fluid-like

material will exhibit a residual strain. To illustrate, Figure 5 shows a typical creep and

recovery experiment for 90:10 blends of all the three crude sources at the PAV-agedcondition. From the figure, one can observe relatively larger values of instantaneous

elastic jump and total strain during loading as well as larger values of residual strain afterunloading for a 90:10 Arab mix blend as compared with the other two crudes. Figures 6a,

6b, and 6c illustrate the relationship between the instantaneous elastic jump and the

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Figure 5. Typical creep and recovery plot for 90:10 blends for all three crude sources.

(a)

Figure 6. Elastic jump and total strain in the creep and recovery test vs. percentage asphaltenes:

(a) Basra Light, (b) Upper Zakum, and (c) Arab Mix. (continued)

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(b)

(c)


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asphaltene content. Figures 7a, 7b, and 7c illustrate the relationship of asphaltene with

respect to total strain for all the three blends of the crudes: Basra Light, Upper Zakum,

and Arab Mix from unaged to RTFO-aged, and RTFO-aged to PAV-aged conditions.

Large values of instantaneous elastic jump essentially refer to a material with more fluid-

like characteristics. Aging of the material makes it very stiff, and therefore, for the same

applied load, it is expected that the strain will be considerably reduced. Taking intoaccount the role of asphaltenes as the dispersed phase with a more pronounced solid-like

nature, one can expect an increase in asphaltene content during aging that will lead to

considerable reduction in elastic jump. It is seen from the figures that, except for the

90:10 Basra Light blend, all the other blends and crude sources exhibit a linear change

in elastic jump with the percentage increase of asphaltenes when plotted in a semiloggraph. The 75:25 blends for all the crudes exhibit the greatest change in elastic jump. One

very important observation is related to changes in the elastic jump at the two different

levels of aging. When comparing high-temperature RTFOT aging with low-temperature

PAV aging, it is seen that the change in elastic jump per unit change in asphaltene

is always lower during the low-temperature aging. There is an exception here for theArab Mix crude for the 75:25 and 85:15 blends. Obviously, the 90:10 blends for all thecrude sources show limited flexibility in stiffening during aging characterized here by

the elastic jump. All the above observations hold good for the total strain. Similar to

instantaneous elastic jump, with aging the material exhibits lower total strain levels. The

effect of PDA pitch can also be observed with decrease in total strain levels with an

increase in PDA pitch proportions in the blends from Figure 7. As expected, the ArabMix blends exhibits the highest change in total strain per unit change in asphaltenes for

all the conditions. This is consistent with all the mechanical behavior seen earlier: for

example, the 135C and 60C viscosity.

(a)

Figure 7. Elastic jump and total strain in the creep and recovery test vs. percentage asphaltenes:


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(b)

(c)


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Stress Relaxation Components

10% Stress Relaxation Time vs. Asphaltenes. A typical stress relaxation experiment

consists of applying a constant strain instantaneously and monitoring how the stress

induced relaxes over a period of time. When stress relaxation experiments were conducted

on blended asphalts, it was found that the shear stress induced is much larger for theblend with a higher proportion of PDA pitch in PAV-aged, RTFO-aged, and unaged

conditions. This is expected considering the more solid-like nature of the material. The

time taken for a material to reach 10% of its induced peak stress is normally measured

as 10% stress relaxation time in rheological studies. It is obvious that a viscoelastic

solid material will show more than 10% stress relaxation time than a viscoelastic fluid.

Figure 8 depicts a typical stress relaxation experiment for a 90:10 Basra Light blendunder unaged, RTFO-aged, and PAV-aged conditions. Referring to Figure 8, the shear

stress induced is much larger at the PAV-aged condition as compared to unaged and

RTFO-aged conditions. Figures 9a, 9b, and 9c illustrate the relationship between change

in 10% stress relaxation time and change in asphaltene content due to aging for all

the blend by crude source. One can generally observe that there is increase in 10%stress relaxation time with an increase in asphaltene content. One can also observe the

influence of crude source and the effect of aging from Figure 9. The materials solid-like

behavior with increase in the PDA-pitch content is also evident. The Arab Mix blends

exhibit less change in relaxation time when compared with the blends of Basra Light and

Upper Zakum. This is expected, taking into account the more viscoelastic fluid natureof this blend. This characteristic also compares very well with the viscosity at 60 C and

135C as well as creep and recovery test parameters. However, what is very interesting

to see here is the minor role played by asphaltenes in influencing the stress relaxation

properties. For example, for a 90:10 blend, while the Basra-Light and Upper Zakum

showed a considerably large change for all the tests when compared with Arab Mix

Figure 8. Typical stress relaxation plot for 90:10 Basra Light.

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(a)

(b)

Figure 9. Ten percent stress relaxation time in the stress relaxation test vs. percentage asphaltenes:


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(c)


change, the trends for the stress relaxation test are similar when comparing all the aging

conditions.

The role of the underlying microstructure on the rheological behavior of the material

is pertinent. If one considers asphaltenes as dispersed in maltenes, and if we take intoaccount the compatibility of asphaltene with maltenes in terms of dispersability, it ismuch easier to understand the response of the material under steady shear, creep and

recovery, and stress relaxation. In all the investigations reported here, it is clearly seen

that asphaltenes influence the elastic solid behavior of asphalt. It is also clearly shown

here that Petersens ideas related to the aging of asphalt are quite valid for blended asphalt

(Petersen 1993, 1998).

Summary and Conclusions

This investigation reported significant results related to blended asphalt from three crude

sources under varying aging conditions and blend proportions. The changes in asphaltenesfor changes in various rheological parameters were investigated. The influence of the

PDA pitch, the strong relationship between asphaltene content and the rheological pa-

rameters, and the distinct difference between aging kinetics of low-temperature and high-

temperature aging were also clearly seen. The role of crude source in all the above isunderstandably paramount.

Acknowledgment

This investigation was made possible by the sponsored research project funded by Chen-

nai Petroleum Corporation Limited, Chennai, India. We thank Dr. Abhijit Deshpande,Department of Chemical Engineering, IIT Madras, Chennai, India, for permitting us to

use the dynamic shear rheometer.

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