تاریخ انتشار: دوشنبه 31 شهریور 1393

  Evaluation of rutting properties of high density polyethylene

ORIGINAL ARTICLE

Evaluation of rutting properties of high density polyethylene

modified binders

Fereydoon Moghadas Nejad Mohsen Gholami

Koorosh Naderi Mohammad Rahi

Received: 1 February 2014 / Accepted: 4 August 2014

_ RILEM 2014

Abstract Rutting in asphalt pavements may reduce

service life and endanger the safety of highway users. In

this regard, high density polyethylene (HDPE) is one of

the plastomers which can be used to modify asphalt

binders and to reduce permanent deformation. However

storage stability is a major problem for polyethylenemodified

asphalt binders. The objective of this research

is to measure the rutting potential of bitumen modified

with HDPE while addressing the storage stability issue

by using HDPE with low molecular weight. Superpave’s

rutting criteria (G*/sin d), Shenoy’s proposed

rutting parameter (G*/(1 –(1/(tg sin d)))), zero shear

viscosity, non-recoverable compliance (Jnr) and recovery

parameter(R) are used to characterize the complex

rutting behavior ofHDPE-modified binders. The results

of the storage stability test showed that melt flow index

has a significant impact on the increase of the solubility

of HDPE which may contribute to a better storage

stability of HDPE-modified binders. The results from

different rutting parameters indicate that the addition of

a 7 % HDPE (by weight) to neat binder, increases the

complex modulus significantly and decreases the nonrecoverable

compliance which results in more rutting

resistance.

Keywords Rutting _ Zero shear viscosity (ZSV) _

Multiple stress creep recovery (MSCR) _ HDPE

modified binder

1 Introduction

Rutting is known to be one of the major distresses in

asphalt pavements and there have been many studies on

asphalt pavement’s rutting potential in recent years. In

hot climates and where asphalt pavements are subject to

heavy loads, rutting occurs due to the accumulated

plastic deformation in upper layers of asphalt pavement

[3]. It is suggested that this distress is caused by the

combination of densification and shear deformation

along the longitudinal axis of the road and in vehicle

wheel path [30]. Many other factors contribute to the

occurrence of rutting, such as environmental conditions

(e.g. temperature, humidity and aging), vehicle speed,

contact pressure of the wheel and binder type [34].

Many researchers believe that the use of polymermodified

binders can reduce the potential occurrence of

this type of distress [16, 18].

High density polyethylene (HDPE) is one of the

plastomers which can be used to modify asphalt

F. Moghadas Nejad _ K. Naderi

Department of Civil and Environmental Engineering,

Amirkabir University of Technology, Tehran, Iran

M. Gholami (&)

Department of Road and Transportation, Science and

Research Branch, Islamic Azad University, Tehran, Iran

e-mail: mhsngholami@gmail.com

M. Rahi

R&D Department, Pasargad Oil Company,

Tehran 1879913111, Iran

Materials and Structures

DOI 10.1617/s11527-014-0399-z

binders and reduce permanent deformation under

traffic load [10]. Hisonghlou et al. [14, 24] showed

that a 2 % HDPE reduces permanent strains up to

34 %. Also, Yeh et al. [31] used Superpave’s parameter

(G*/sin d) to measure the rutting potential of

HDPE- modified binders and found that adding 5 %

polyethylene by the weight of asphalt binder increases

G*/sin d’ considerably .

Modification of asphalt binder using polyethylene

produces amulti-phase system with complex rheological

behaviors such as delayed elasticity and stress sensitivity

[9]. However, Superpave’s performance grading method

is not sufficient considering these complexities in

rheological properties of polyethylene-modified binder.

On the other hand, zero shear viscosity (ZSV) is sensitive

to the molecular weight of additives and multiple stress

creep and recovery method can consider the non-linear

viscoelastic behavior and stress sensitivity of the modified

binders [6, 8]. Thus it is expected that the evaluation

of rutting properties of HDPE modified binders through

ZSVand MSCR methodsmay providemore information

about these materials.

Polyethylene is one of the semi crystalline polymers,

which is produced by ethylene polymerization

(C2 H4). It is chemically identical to saturate components

of asphalt binder. It swells by the absorption of

Maltenes when added to asphalt and gets several times

larger than its original size. However, due to its nonpolar

nature and tendency to become crystalline,

polyethylene has a minimal tendency to interact with

asphalt binder [7, 21, 24].

Storage stability is a major problem for polyethylene-

modified asphalt binders and a considerable

amount of research has been conducted to overcome

this issue. It is suggested that when there is no mixing

force, the polyethylene modified asphalt binder may

become unstable, and due to weak van der Waals’

forces, the asphalt binder and polyethylene phases

become separated. Numerous methods have been

proposed to improve the storage stability of polyethylene

modified asphalt binders such as using acids (e.g.

PPA) as crosslinking agents [5, 27, 28], decreasing the

density difference between polymer and asphalt via

adding silica and carbon black [20, 29], equalizing the

polarity difference between asphalt and polymer using

epoxy functions or silica [17, 20], using polyethylene

with lower molecular weight and wider molecular

weight distribution [15] and adding maltene-like

materials into the polymer modified bitumen [11].

Among all these methods, using polyethylene with

lower molecular weight may be the easiest way to

ensure the storage stability of modified binders. Melt

flow index (MFI), as an indirect measure of molecular

weight, can be used to distinguish between different

grades of polyethylene. Since a high flow rate corresponds

to a low molecular weight, using a polyethylene

with higher values of MFI may result in improved

storage stability of modified binders. Melt Flow Index

of polyethylene is the mass in grams flowing in 10 min

through a capillary of a specific diameter and length by

a pressure applied via 2.16 kg weight which is

measured at 190 _C. The results are expressed in

grams per 10 min of the total time of the test [1, 32].

However, the downside with using polyethylene

with lower molecular weight is decreased effect of this

polymer on rutting properties of the modified binder.

The objective of this research is to measure the rutting

potential of bitumen modified with HDPE while

addressing the storage stability issue by using HDPE

with low molecular weight. Effectiveness of using a

polyethylene with high values of MFI in improving

storage stability will be evaluated. ZSV, multiple stress

creep recovery, Shenoy’s proposed rutting parameter

(G*/(1 –(1/(tg sin d)))) and Superpave rutting criteria

will be used to investigate the effect of polyethylene on

rutting properties of the modified binder.

2 Experimental work

2.1 Materials

85/100 Penetration grade neat binder from Pasargad

refinery was selected as the base binder. Five different

grades of polyethylene from Maroon Petrochemical

Company were used in this study. So as to prepare the

samples, 3 and 7 % HDPE by weight of the asphalt

binder were mixed at 180 _C using high shear mixer

with shear speed of 5,500 rpm for 1 h [2, 12, 24]. To

consider the effect of aging on the rutting properties of

the binders, all the samples were exposed to short-term

aging in RTFO according to ASTM D 2872.

2.2 Storage stability test

In order to consider the storage stability of HDPEmodified

binders, the difference in the softening point

between the upper and the lower parts of the samples

Materials and Structures

was measured by the tube test [17, 20, 33] and the

results of which are presented in Table 1. The results

indicate that MFI parameter has a significant impact

on the compatibility of polyethylene and asphalt

binder, As MFI parameter increases, the nonpolar part

of polyethylene gets smaller and solubility increases.

This causes polyethylene to bond more easily with the

polar parts of the asphalt binder. It should be noted that

as the MFI value for HDPE increases the effect of this

polymer on high temperature properties of modified

binder decreases. Thus using HDPE with a very large

MFI will result in a less pronounced effect of

modification in the asphalt binder.

Based on the results shown in Table 1, in comparison

to other grades, EX 1 S shows a better compatibility

and it is expected that high temperature

properties of the resulting modified binder using this

polymer will not be sacrificed. As a result, this

polymer was selected for the modification of asphalt

binder and further tests were performed for the

evaluation of the rutting resistance of asphalt binders

modified with EX 1 S high density polyethylene.

2.3 Methods

Physical properties of neat and polyethylene-modified

binders, softening point, penetration (25 _C), ductility

and elastic recovery were determined for un-aged

samples according to ASTM D-36, ASTM D-5,

ASTM D-133 and ASTM D-6084 respectively and

the results are presented in Table 2.

Strain sweep, frequency sweep, and MSCR tests

using Anton Paar Smartpave dynamic shear rheometer

were carried out on all the binder samples in both unaged

and RTFO-aged conditions.

Prior to the frequency sweep test and in order to

determine the linear viscoelastic limit, strain sweep

test was performed at 0.1 and 10 Hz at the temperatures

of 52, 64 and 76 _C [3]. Frequency sweep test

was then performed on all the samples at the same

temperatures according to ASTM D 7175 so as to

determine the Superpave’s rutting criteria, Shenoy’s

proposed rutting parameter and ZSV.

To determine the ZSV of the binders, Cross/

Williamson, Cross/Sybilski and Carreau models were

fitted to the results of g_ master curves at the reference

temperature of 64 _C. Next, the viscosity values at

zero shear-rate were extrapolated from the results of

calibrated models. These models are represented and

their respective parameters are introduced below [4].

Cross/Williamson Model’s:

g_ ¼

g0 _ g1

1 ًKxقm g1 ً 1ق

Cross/Sybilski Model’s:

g_ ¼

g0

1 ًKxقm ً 2ق

Carreau Model’s:

g_ ¼

g0 _ g1

ً 1 Kxق 2 _ _m=2 g1 ً 3ق

In these relations, g_ is the complex viscosity, g0 is

the Newtonian viscosity or ZSV, g1 is the infinite

shear viscosity, x is the frequency in radians per

second, k is related to the type of materials with the

Table 1 Characteristics of various HDPE grades used in this study and the results of tube test

HDPE

grade

Density

(g/cm3)

MFI (2.16 kg g/

10 min)

HDPE Content

(% by weight)

Softening point difference

between top and

bottom of tube (_C)

EX 3-80 S 0.954 4 3 6

EX 3-80 S 0.954 4 7 18

EX 5 HS 0.95 7.5 3 4

EX 5 HS 0.95 7.5 7 11

EX 3-80 0.945 12 3 2

EX 3-80 0.945 12 7 5.5

EX 1 S 0.944 21 3 0.5

EX 1 S 0.944 21 7 2

EX 7C 0.946 63 3 0.5

EX 7C 0.946 63 7 1

Materials and Structures

Table 2 The studied

binders in this research and

their physical properties

Sample Polymer

content (%)

Softening

point (_C)

Penetration

(0.1 mm)

Ductility (cm) Elastic

recovery (%)

BU 0 45.8 92–94 ?100 5

HU3 3 48.5 67–68 46.5 15

HU7 7 72 35–37 21 35

Table 3 Linear limit of

stress, strain and phase

angle at different testing

conditions for unaged and

RTFO binders

Sample Temp

(_C)

Frequency

(Hz)

Stress

(Pa)

Strain

(%)

Phase

angle

(deg)

Polymer

content

(% by weight)

Aging

condition

BU 52 0.1 ?188 ?100 ?88.2 0 Un-aged

64 ?39.3 ?100 ?89

76 ?28.87 ?100 ?89.8

BU 52 10 769 17.28 85.7 0 Un-aged

64 728 27.25 88.3

76 307 40.04 89.1

BR 52 0.1 412.3 ?100 88.4 0 RTFO-aged

64 ?67.2 ?100 ?88.9

76 ?44.1 ?100 ?89.5

BR 52 10 3,577 2.15 82.9 0 RTFO-aged

64 1,014 12.11 86.7

76 350 21.6 88.8

HU3 52 0.1 67 17.11 87.3 3 Un-aged

64 23 28.4 87.7

76 15 72.97 88.8

HU3 52 10 657 1.81 83.9 3 Un-aged

64 452 8.64 84.4

76 171 8.84 84.8

HR3 52 0.1 70 4.69 80.9 3 RTFO-aged

64 25 10.86 84.6

76 19 17.2 85.2

HR3 52 10 1,686 2.15 80.1 3 RTFO-aged

64 657 3.16 83.8

76 298 8.56 85.1

HU7 52 0.1 49 0.46 61 7 Un-aged

64 17.3 0.52 66.7

76 8.2 2.31 68.7

HU7 52 10 354 0.27 42.9 7 Un-aged

64 95 0.32 47.9

76 44 0.42 51.5

HR7 52 0.1 68 0.46 72 7 RTFO-aged

64 17.5 0.5 74

76 9 1.28 74.2

HR7 52 10 377 0.21 49 7 RTFO-aged

64 145 0.3 56

76 81 0.4 61.6

Materials and Structures

dimension of time, and m is a dimensionless material

constant [4].

The MSCR test was performed according to ASTM

D 7405 to determine Jnr and R on all the samples at

temperatures of 52, 64 and 76 _C.

3 Results

3.1 Strain sweep test

According to SHRP, linear viscoelastic limit during

strain sweep test is the strain where the complex

modulus reaches 95 % of its initial value which is the

zero strain [22, 23]. The results are presented in

Table 3. As it can be seen, for neat binders in un-aged

and RTFO conditions at 0.1 Hz, and at temperatures of

64 and 76 _C, the strain value is more than 100 %, and

since measuring its exact value was beyond the

capacity of the machine, the value is shown with a

‘‘?’’ sign. Based on the results of Table 3, 0.1 %strain

was selected to make sure that frequency sweep test is

performed within the linear viscoelastic limit.

3.2 Superpave’s rutting criteria and Shenoy’s

proposed rutting parameter

Superpave’s rutting criteria and Shenoy’s proposed

rutting parameter [25, 26] at 64 _C are calculated and

presented in Fig. 1. As it can be seen from Fig. 1, as

the HDPE content goes up the complex modulus value

of the binders increases while at the same time the

phase angle values decrease which in turn increases

the value of ‘G*/ sin d’. Moreover, it can be observed

that RTFO conditioning increases both‘G*/ sin d’and

‘(G*/(1 –(1/(tg sin d))))’, indicating that short-term

aging improves rutting resistance. The results of

Shoney’s proposed rutting parameter at 64 _C

(Fig. 1), follow the same trend as Superpave’s rutting

criteria.

In order to compare these two parameters and

distinguish their differences, the increase in the values

of‘G*/ sin d’ and ‘(G*/(1 –(1/(tg sin d)))), which was

of course due to HDPE addition, was evaluated in

comparison to each other at 64 _C. The ratio of each

rutting parameter for binders containing i (i = 3 and

7) percent HDPE to those containing j (j = 0 and 3)

percent HDPE is calculated and the results are

presented in Table 4. The results for both of the

parameters show that the addition of 3 % HDPE to the

base binder slightly alters the two parameters and in

fact the two parameters show similar results.

Nonetheless, the increase in the HDPE content from

3 to 7 % and from 0 to 7 % shows that the changes in

the values of ‘G*/ sin d’are less pronounced compared

to ‘(G*/(1 –(1/(tg sin d))))’in both aged and RTFO

conditions. This implies that Shenoy’s proposed

rutting parameter is more sensitive to the changes in

binder’s structure, which helps it render a more

accurate description of the non-recoverable strains,

compared to Superpave’s rutting criteria.

Superpave’s rutting criteria and Shenoy’s proposed

rutting parameter at 76 _C are calculated and presented

in Fig. 2. According to Fig. 2, it is observed

that for a 7 % HDPE-modified binder, the resulted

values for Shenoy’s parameter at 76 _C are negative.

This is due to the fact that this parameter yields

negative values for phase angles smaller than 52

Fig. 1 Comparison of

Superpave’s rutting criteria

with shenoy’s proposed

rutting parameter in 64 _C

Materials and Structures

degrees. It can be inferred that this parameter is not

suitable for highly polymer-modified asphalt binders.

3.3 Zero shear viscosity

Zero shear viscosities at 64 _C are calculated and

presented in Table 5. The results show that the addition

ofHDPE increases the ZSVvalue. The master curves of

complex viscosity for the binders are presented in

Fig. 3. Adding 3 %HDPE does not change ZSV values

noticeably and the slope of master curve remains

relatively constant. This can be due to the lack of

sufficient interaction between the HDPE and the asphalt

binder and the low sensitivity of ZSV parameter to low

amounts of HDPE. However, it can be observed that

beyond the shear rate of 100 (1/s), for a 7 % HDPEmodified

binder, the slope of master curve changed and

also the ZSV value increased dramatically compared to

the neat binder and the 3 % HDPE-modified binder.

Comparing un-aged samples to RTFO samples

shows an increase in the values of zero shear

viscosities in all the three models upon aging. This

indicates that RTFO aged binders show better

resistance to rutting. It can also be understood from

the results that the type of selected model affects the

resulting ZSV value. As it is shown in Table 5, all

the three models have approximately the same

prediction for neat binder. This also holds true for

the 3 % HDPE-modified binder, but with the 4 %

increase in the HDPE content, the errors resulted

from Cross/Sybilski model increased whereas the

Cross/Williamson and Carreau models had almost

the same prediction. This is because of the incapability

of Cross/Sybilski model to fit the obtained

data in high and low frequency ranges, which leads

to wrong values of ZSV.

As it is shown in Fig. 3, the Cross/Sybilski model

for neat and 3 % binders, managed well to fit the

experiment data, while it predicted a straight line

without any curvature for the7 % HDPE-modified

binder. However, in a similar situation, Carreau model

managed well to fit the data for this binder. The reason

Fig. 2 Superpave’s rutting criteria and shenoy’s proposed rutting parameter at 76 _C

Table 4 The effect of HDPE content on the values of SHRP. The ratio of rutting parameter of i percent HDPE modified binder to

that of modified with j percent HDPE

i and j indices Unaged RTFO

G_=sindi

G_=sindj

G_=ً 1_ً 1=ًtgd sin dقi

G_=ً 1_ً 1=ًtgd sin dقj

G_=sindi

G_=sindj

G_=ً 1_ً 1=ًtgd sin dقi

G_=ً 1_ً 1=ًtgd sin dقj

i = 3, j = 0 1.89 1.92 2.09 2.5

i = 7, j = 3 9.59 156.69 9.78 73.74

i = 7, j = 0 18.17 302 20.51 184.60

Materials and Structures

can be the lack of infinite shear viscosity parameter in

Cross/Sybilski model. Thus, it can be deduced that all

the three models provide similar predictions for the

neat and slightly modified binders, whereas for high

contents of modifiers, Cross/Sybilski model cannot

predict ZSV precisely, Carreau and Cross/Williamson

models having relatively similar results. However, in

some cases like BU and HU7, Carreau model resulted

in smaller error values and could better match the

experiment data compared to Cross/Williamson

model, which consequently led to a more accurate

estimation of ZSV.

Furthermore, the results indicate that many factors

such as the content of modifier, the type of selected

model and the frequency range of experimental data

influence the amount of obtained ZSV and make it

difficult to determine a definite estimation. Moreover,

it is impossible to measure the sensitivity of the

behavior of these binders to the stress level using this

method.

3.4 MSCR test

The results of the multiple stress creep and recovery

test are presented in Fig. 4 and Table 6. Figure 4

shows that the compliance (J) in stress levels of both

Fig. 3 The complex

viscosity master curves of

the binders in 64 _C and the

fitted models

Table 5 The results of

ZSV of the binders

calculated by the Cross/

Williamson, Cross/Sybilski

and Carreau models in

64 _C

Sample ZSV’s value (Pa) Error (%)

Cross/

Williamson

model

Cross/

Sybilski

model

Carreau

model

Cross/

Williamson

model

Cross/

Sybilski

model

Carreau

model

BU 6.69E1 6.69E1 7.17E1 0.73 0.73 0.36

BR 1.13E2 1.13E2 1.13E2 0.56 0.56 0.56

HU3 1.49E3 4.66E2 5.77E2 0.64 1.83 0.64

HR3 5.95E4 1.57E3 1.55E5 1.06 1.06 1.06

HU7 1.62E7 4.22E7 2.37E7 2.24 25.58 1.52

HR7 7.43E8 8.00E7 1.09E9 2.59 34.25 2.59

Table 6 Results of MSCR test at 100 and 3,200 Pa stress level

Binder

type

MSCR in 64 _C

100 Pa stress level 3,200 Pa stress level

Jnr (1/

Pa)

Recovery

(%)

Jnr (1/

Pa)

Recovery

(%)

BU 0.0157 -33.60 0.0194 -278.60

BR 0.0096 -19.00 0.0114 -234.20

HU3 0.0074 0.70 0.0092 -2.20

HR3 0.0034 1.20 0.0041 -1.57

HU7 0.0002 29.60 0.0008 6.20

HU7 0.000 39.50 0.0003 9.20

Materials and Structures

100 and 3,200 Pa, decreased as the HDPE content

increased. Also, the RTFO binders show smaller

values of compliance in comparison to un-aged

binders, which confirms the positive effect of aging

on resistance to rutting.

The average amounts of Jnr and R over ten cycles in

both stress levels are provided in Table 6. As it was

expected, the compliance of neat binder is significantly

higher than the modified binders. Also the strain

recovery is insignificant for neat binders during

unloading indicating their improper resistance to

rutting. However, the results show that the addition

of the 7 % HDPE decreases Jnr and this suggests the

ability of HDPE to reduce permanent deformations

and improve the resistance to rutting.

The results of the percentage of recovery for the

base binder under 100 and 3,200 Pa stress levels and

for the 3 % binder under 3,200 stress level are

negative. The negative recovery can be due to the

low stiffness and the low elastic behavior of the

samples, and instrumental inertia. More recovery

suggests more elastic behavior for the binder. Thus

the binder with more recovery is more capable of

recovering the permanent deformations. As it can be

observed, the base binder has no recovery in any of the

stress levels. For the 3 % HDPE-modified binder,

under 100 Pa stress, the recovery value is insignificant

and no deformation is recovered under 3,200 Pa. The

reason can be the lack of HDPE content as well as the

insufficient interaction of HDPE parcels with asphalt

binder molecules. However, the 7 % HDPE modified

binder shows more recovery in both stress levels.

The amount of the sensitivity of the binder behavior

to the imposed stress level, a parameter which was not

measurable in previous methods, can be evaluated

using Jnr_diff .

Jnr_diff ¼

Jnr@3;200 Pa _ Jnr@100 Pa

Jnr@3;200 Pa

_ 100 ً 5ق

where Jnr@100 Pa and Jnr@3;200 Pa are non-recoverable

compliances under 100 and 3,200 Pa respectively.

This parameter was calculated and the results are

shown in Fig. 5. The results indicate that Jnr parameter

is highly sensitive to the stress level and this sensitivity

is dependent on the HDPE content. As can be

observed, Jnr did not show any significant sensitivity

for the 3 % HDPE-modified binder, unlike the 7 %

HDPE-modified binder.

As it can be observed in Fig. 6, after 9 s of

recovery, the unloading curves for the 7 % HPDEmodified

did not become horizontal in any of the stress

levels. This behavior shows that more deformation

could be recovered if the recovery time were higher.

However because of the small unloading time during

MSCR test, the binder is not capable of recovering

more deformation and this can lead to a wrong

estimation of Jnr and Recovery values as it was

mentioned by other researchers [13, 19].

4 Summary of the results and conclusion

The results of the storage stability test showed that

MFI parameter has a significant impact on the increase

Fig. 4 MSCR creep

compliance of binders at 100

and 3,200 Pa in 64 _C

Materials and Structures

of the solubility of HDPE which may contribute to a

better storage stability of HDPE-modified binders.

Based on the results of Superpave’s rutting criteria

and Shenoy’s proposed rutting parameter, low contents

of HDPE could not significantly improve the

rutting performance of the neat binder, whereas the

results of adding higher contents of HDPE (7 %)

increased the rutting resistance noticeably. On the

other hand, the results revealed that aging has a

noticeable impact on increasing the resistance of the

binders to rutting and decreasing permanent deformations.

However, negative values of Shenoy’s parameter

for 7 % HDPE modified binders suggests this

parameter’s inability to measure rutting potential for

highly modified binders.

Despite the complications in the determination of

ZSV for these binders, the results suggests noticeable

increase in rutting performance of 7 % HDPE

modified binder compared to the base binder. The

results from MSCR tests indicate stress sensitivity of

7 % HDPE-modified binder is significant while modified

binder with 3 % HDPE is not susceptible to the

change in the stress level.

A comparison of different methods and parameters

for the determination of the rutting properties of

HDPE-modified binders suggested that although all

these different parameters result in the superior

rutting behavior of highly HDPE-modified binders,

complications can be observed estimating these

parameters. Negative values of Shenoy’s parameter,

difficult and time-consuming determination of ZSV

and inaccurate values of non-recoverable compliance

and Recovery for MSCR test are among these

complications for highly modified binders. multiple

stress creep and recovery test is easier to perform

and provide more information compared to these

Fig. 5 Percent difference

values of Jnr in 64 _C

0.0

0.1

0.1

0.2

0.2

0.3

0.3

0 20 40 60 80 100

J @ 100 pa and 64 (1/Pa)

Time,(s)

HU7

HR7

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

100 120 140 160 180 200

J @ 3200 Pa and 64(1/Pa) Time,(s)

HU7

HR7

(a) 100 Pa (b) 3200 Pa

Fig. 6 MSCR creep

compliance of 7 % HDPE

modified binder at 100 and

3,200 Pa in 64 _C

Materials and Structures

other tests, however modification to this method

(e.g. prolonged unloading times) should be considered

to improve the evaluation of the rutting

properties of highly modified binders.

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