Evaluation of Low-temperature Performance of Porous Asphalt Mixture

Journal of Highway and Transportation Research and Development Vol.4,No.2(2009)33

Evaluation of Low-temperature Performance of Porous Asphalt Mixture*

MAXiang(^r$3)** ,NI Fujian (i^fi) ,CHEN Rongsheng ($^£) ,WANG Yan (itfe)

(School of Transportation,Southeast University,Nanjing Jiangsu 2100%, China J

Abstract: To analyze influencing factors and evaluation method of low-temperature performance of porous asphalt mixture, first, three kinds

of modified binder were chosen as original, thin film aging and pressure aging samples for customary index test and bending beam rheome-

ter (BBR) test at - 12 T to evaluate low-temperature performance of these modified binders. Then, evaluation of the low-temperature

anti-cracking performance of different kinds of porous asphalt mixture was made by thermal stress restrained sample test (TSRST) . At the

same time, the result of abovementibned TSRST were compared with the TSRST result of samples of the porous asphalt mixtures after long

-term aging to evaluate the influence of aging on low-temperature performance of porous asphalt mixtures. The results show that (1)

TSRST result of porous asphalt mixtures coincides with creep stiffnesses of BBR test of modified binders; (2) the fracture temperatures of

the porous asphalt mixtures increase and their fracture stresses decrease after aging; (3) the fracture stresses of porous asphalt mixtures

are just one-third of those of dense-gradation asphalt mixtures while the fracture temperatures almost the same, which indicates that their

low-temperature performances are almost the same.

Key words: road engineering; low-temperature performance; thermal stress restrained sample test; porous asphalt mixture; creep stiff -

0 Introduction

The low-temperature cracking of asphalt concrete is one

of the major damage on asphalt pavement. There are many

influencing factors for the low-temperature cracking, includ-

ing material, surrounding and pavement structure, etc. The

aging of pavement is the surrounding factor influencing pave-

ment low-temperature cracking. The cracks result from the

tensile stress in the bottom of the pavement when the temper-

ature decreases. When the tensile stress reaches the limit

value of the pavement intensity, fissure will appear and de-

velop under the effect of low-temperature or low-temperature

circulation.

Domestic researches on the low - temperature perfor-

mance of asphalt mixture are laying emphasis on the evalua-

tion indexes of asphalt binder . Some researchers are al-

so making research on the low-temperature performance of

asphalt mixture ~ . However, these researches are based

on dense-gradation asphalt mixture. Now porous asphalt mix-

tures which have well surface performance properties are

spreading gradually, but the researches on the low-tempera-

ture performance of this kind of mixture are lacking. Ref.

[6] made an evaluation on the low-temperature performance

of porous asphalt mixture with different gradations and differ-

ent binders by - 10 t bending experiment. The results

showed that the breaking strain of porous asphalt mixture

could not meet the requirements of Chinese current specifi-

cations on dense-gradation asphalt concrete. There are some

limitations of the low-temperature bending experiment of tra-

becula itself, so it may not be useful to evaluate the low-tem-

perature performance of porous asphalt mixture. After syn-

thesizing the experiment methods of low-temperature cracking

for kinds of asphalt concrete, SHRP research plan chose

thermal stress restrained sample test (TSRST) to evaluate

and forecast low-temperature cracking-resistance performance

of the pavement. Therefore, this paper adopts TSRST which

could simulate the actual temperature-decreasing process on

the basis of considering the aging of asphalt mixture. Mean-

while , it analyzes the correlation between the low-temperature

performance of porous asphalt mixture and the low-tempera-

ture performance of binders.

Manuscript received May 6,2008

* Supported by Chinese National Natural Science Foundation( No. 60472120)

E-mail address: [email protected]

J. Highway Transp. Res. Dev. (English Ed.) 2010.4:33-37.

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34 Journal of Highway and Transportation Research and Development

1 Experiment scheme

The main purpose of this research is to make a research

on the low-temperature performance of porous asphalt mix-

ture, and consider the influence of aging on that perfor-

mance. Binder is the key influencing factor to the porous as-

phalt mixture performance. The research of SHRP and other

researches at home and abroad have indicated that the results

of asphalt direct tension test ( DTT) and bending beam

rheometer (BBR) test have a good correlation with the low-

temperature performance of the asphalt mixture. Some re-

searches have indicated that the two experiments correlate

with each other well, so it is unnecessary to make the two ex-

periments at the same time. In order to analyze the influenc-

ing factors of the low-temperature performance of porous as-

phalt mixture, evaluation on low-temperature performance in-

dexes of the binder is necessary.

Therefore, first, three kinds of modified asphalt (high

viscosity modified asphalt, high viscosity modified asphalt +

additive and SBS modified asphalt) are chosen for thin film

oven test ( TFOT) and pressure aging vessel ( PAV) test.

The original and aging samples are used for general tests and

bending beam rheometer (BBR) test at - 12 °C. Then after

determining the optimum asphalt - aggregate ratio of the

porous asphalt mixture, rutting board is divided into trabecu-

las of 200 mm x 30 mm x 35 mm. The samples with error of

over 2 mm are abandoned. The samples which needs aging

are dealt by the method in Standard Test Methods of Bitumen

and Bituminous Mixtures for Highway Engineering (JTJ 052-

2000) . Besides, in order to compare the low-temperature

cracking-resistance performance between porous asphalt mix-

ture and dense-gradation asphalt mixture, AC-13 dense-gra-

dation asphalt mixture with SBS modified asphalt is chosen to

make parallel research with PAC-13 asphalt mixture. After

the preparation of the samples, the voids is measured. Then

TSRST is performed. Combined with the test results of as-

phalt binder, the low-temperature performance of porous as-

phalt mixture is analyzed and used to compare with the per-

formance of dense-gradation asphalt mixture.

2 Asphalt experiments

2.1 General test For modified asphalt, the current domestic specification

adopts penetration index and 5 °C ductility to evaluate the

low-temperature cracking-resistance performance of asphalt,

and adopts mass - loss of asphalt after TFOT aging, 25 X.

penetration ratio and 5 °C ductility ratio to evaluate the

aging-resistance performance of asphalt. Therefore, the tests

on three general indexes are made of the original samples,

TFOT aging samples and PAV aging samples of the three

kinds of asphalt at first. The result is shown as follows:

Tab. 1 Result of general indexes of different kinds of bitumen

Bi tumen type

id indexes Original

1T0T(5 h) PAV

at Value Ratio* Value Ratio*

High

25 X penetration

( X 0.1 mm) 51 41 0.80 36 0.71

viscosity

modified

Softening

point (X) 94.8 82.0 0.86 80.8 0.85

asphalt 5 X

Ductility( cm) 38.4 28.5 0.74 1.0 0.03

High

viscosity

25 X penetration

( xO.l mm) 42 38 0.90 28 0.67

Softening modified 97.5 100.0 1.03 94.2 0.97

point (X,) asphalt 5<CDucti]ity

additive (cm) 22.6 18.5 0.82 1.0 0.04

SBS

modified

251 penetration

( X 0.1 mm) 54 43 0.80 36 0.67

Softening

point (X) 62.5 68.0 1.09 64.4 1.03

asphalt 5 X. Ductility

(cm) 35.0 23.0 0.66 1.0 0.03

Noat: * The ratio indicates the experimental value in bitumen state to the o-

riginal sample value.

From the data above it can be seen that additive can

obviously increase the softening point of the high viscosity

modified asphalt but it decreased the 5 °C ductility. From

the ratios of three general indexes in different aging states it

can be seen that with the increase of the aging,25 °C pene-

tration and 5 t ductility decrease gradually, and softening

point changes irregularly. After aging the softening point of

SBS modified asphalt increased, but it has no coherence with

the aging degree. For high viscosity asphalt it decreases first

then increases with the different stage of aging, while for high

viscosity asphalt + additive it first increases then decreases.

Therefore, softening point could not be used as the evaluation

index for aging-resistance performance of modified asphalt.

In addition, 5 °C ductilities of the three kinds of asphalt after

PAV aging are closed to 0, so it is no need to compare them.

Therefore,it is advised that the evaluation temperature after

PAV aging should be set as 10 t.

2.2 Bending beam rheometer (BBR) test


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MA Xiang, et al: Evaluation of Low-temperature Performance of Porous Asphalt Mixture 35

In the criterion of asphalt in American SHRP plan, it is

determined that in order to get the low-temperature perfor-

mance of asphalt, BBR is taken to do trabecular bending

creep test to measure stiffness S and stiffness curve slope

m. Also it is stipulated that the value of creep stiffness of

the asphalt sample after aging at the test temperature should

be no more than 300 MPa, and the value of m no less than

0.3. Several kinds of asphalt are used to take BBR test, and

the results are as follows.

Tab. 2 Result of bending beam rheometer test

High viscosity High viscosity asphalt SBS modified asphalt

Asphalt state asphalt + additive

m S(MPa) m S(MPa) m S(MPa)

Original 0.450 51.1 0.398 66.9 0.442 73.8

TFOT(5 h) 0.447 60.5 0.357 75.0 0.418 76.8

PAV 0.375 76.7 0.333 94.1 0.388 108.5

From Tab. 2 it can be seen that the two indexes which

are used to evaluate the low-temperature performance of as-

phalt in the BBR test result do not match well. Moreover, for

asphalt after PAV aging the stiffness of high viscosity asphalt

is lower than that of SBS modified asphalt, and so does its m

value. Therefore, the two indexes could be used to evaluate

the low-temperature performance of asphalt at the same time.

It is needed to combine with the test results of asphalt mix-

ture to make a synthetical evaluation.

3 Composition of asphalt mixture

The target voids of the porous asphalt mixture (PAO

13) in the research is 20% . According to the exsiting re-

search results , the target gradation in Tab. 3 is adopted.

For AC-13 the gradation takes the median of criterion.

Tab. 3 Gradation of asphalt mixtures

Sieve size

(mm) 16 13.2 9.5 4.75 2.36 1.18 0.6 0.3 0.015 0.075

PA013 pass

rate( % ) 100 94.0 77.6 20.6 13.4 11.9 10.4 8.9 7.5 6.1

AC-13 pass

rate( %) 100 95.0 76.5 53.0 37.0 26.5 19.0 13.5 10.0 6.0

In order to determine the optimum asphalt-aggregate ra-

tio of porous asphalt mixture, leakage test, dispersion test and

Marshall stability test are taken at first. Then the asphalt

dosage range is determined according to leakage test and dis-

persion test. Based on the result of Marshall stability test,

the optimum asphalt dosages of several kinds of porous as-

phalt mixtures are fixed. Considering all these test results,

take the same asphalt-aggregate ratio for the mixtures in this

research. The result of Marshall test is listed as follows:

Tab. 4 Experimental result of asphalt mixtures

made of different kinds of asphalt

Asphalt type

Asphalt-

aggregate

ratio( % )

Voids

(*) Stability

(kN)

Loss in Loss in the

the Leakage dispersion

test( % ) test( % )

High viscosity asphalt 4.8 19.7 5.78 0.18 9.3

High viscosity asphalt

+ additive 4.8 19.2 6.22 0.25 10.2

SBS modified asphalt

AC-13 asphalt mixture

4.8

4.8

20.3

4.4

5.31

15.7

0.22 12.9

4 Thermal stress restrained sample test (TSRST)

4.1 Introduction Thermal stress restrained sample test (TSRST) was

raised by Monismitlr . The exterior structure of TSRST e-

quipment is shown in Ref. [5] . In the process of test, first

take trabecular sample which is prepared before the test to

stick with the clamps with AB glue,and then assemble them

into the environmental chamber after 24 h putting at room

temperature. Set the initial temperature and cooling rate and

other parameters before the test. When test begins, take the

method of injection of liquid nitrogen into the environmental

chamber to reach the rapid cooling. TSRST has five temper-

ature sensors, four of them are used to measure the surface

temperature of the sample, the other one measures the envi-

ronmental chamber' s temperature. When the sample con-

tracts in the process of cooling, the samples are stretched by

stepper motor in the TSRST equipment controlled by comput- •

er to take it back to original length.

Typical TSRST curve is shown in Fig. 1. With the de-

crease of temperature, thermal stress increases gradually until

the sample breaks up. At the breaking temperature, thermal

stress gets the maximum value, which is breaking strength of

the sample. The slope of stress-temperature curve AS /AT

increases gradually until maximum, then AS/AT keeps as a

constant value, and stress-temperature curve becomes nearly

a straight line at this time. Transition temperature divides

stress-temperature curve into two parts-with relaxation and

without relaxation. When it reaches the transition tempera-

ture, sample gets harder; when the temperature is lower than

this value,sample would have no relaxation in itself. When

the sample is closed to breakage, the slope might decrease,


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36 Journal of Highway and Transportation Research and Development

which is related to the change of the modulus of the sample

or the development of micro cracks. Transition temperature

and slope dS/dT may play an important role in evaluating

the rheological behaviour of the asphalt mixture at the low

temperature . Therefore, SHRP suggested that the follow-

ing indexes should be taken to evaluate the low-temperature

cracking-resistance performance of asphalt mixture: transi-

tion temperature, slope, breaking temperature and breaking

strength.

4 r Freezing-oflf stress

OH

Freezihg-ofF temperature

-35

g 1 " Transiti an temperature

-25 -20 -15 Temperature(°C)

4.2 Fig. 1 Typical TSRST curve

Test results

In order to weaken the influence of sample molding on

the test results, the voids of the sample is measured before

the test. The samples with similar voids are chosen for tests.

After aging, the voids of porous asphalt mixture increases, so

the voids of chosen sample is a little larger than that of origi-

nal sample. The initial analysis of test results indicates that

the transition temperature in this test is not definite due to

the heterogeneity and the non-uniform cooling rate of the

sample. Therefore, this paper tries to evaluate the low-tem-

perature performance of several kinds of asphalt mixture by

freezing-off temperature and freezing-off stress. The test re-

sults are shown as Tab. 5, Fig. 2, Fig. 3, Fig. 4 and Fig.

5.

Tab. 5 TSRST results of several kinds of asphalt mixture

Gradation Asphalt type Aged or

not

Voids

(%)

Freezing-off

temperature

CO

Freezing-off

stress

(MPa)

PA013 High viscosity asphalt

PA013 High viscosity asphalt

No

Yes

18.4

19.3

-30.38

-25.30

7.07

6.40(3.83) *

High viscosity PAC-13

asphalt + additive No 18.3 -24.24 3.24

High viscosity PAC-13

asphalt + additive Yes 19.6 -21.63 3.14

PAC-13 SBS modified asphalt

PAC-13 SBS modified asphalt

AC-13 SBS modified asphalt

No

Yes

No

18.6

19.5

3.8

-22.36

-19.64

-22.82

2.03

1.90

8.06(5.76) *

Noat: * Thermal stress at the freezing-off point has a mutation, and the

thermal stress at the critical point is shown in the bracket.

~ 10 cd

s 8

P. 6 "

■ High viscosity asphalt - High viscosity asphalt+additive ■ SBS modified asphalt

Fig. 2

£ 10 S 8

OJ 4

1 2 D. 0 6

-PAC-13 (original) -PAC-13 (aged) -AC-13

0 -10 -20 Temperature(°C)

0 -10 -20 -30

Temperature(°C)

40

-10 -20 Temperature(°C)

Temperature-stress curves of three

kinds of original PAC

—O-Original -Aged

0 -10 -20 Temperature(°C)

Fig. 3 Temperature-stress curves of

SBS modified asphalt mixtures


high viscosity asphalt mixtures


high viscosity asphalt mixtures + additive

Analysis of the test results are as follows:

(1) From comparison of the three kinds of porous as-

phalt mixture it can be seen that the sequence of the low-

temperature cracking - resistance performance of the three

kinds of asphalt mixtures is: High viscosity asphalt mixture

> High viscosity asphalt mixture + additive > SBS modi-

fied asphalt mixture. The temperature-stress curve of high

viscosity asphalt mixture and that of high viscosity asphalt

mixture + additive are nearly in coincidence. The additive

doesn t change the temperature-stress relationship of asphalt

mixture, but weakens the freezing-off strength of porous as-

phalt mixture. This can be reflected in 5 t ductility test

and sticky toughness test (in these tests the asphalt with ad-

ditive is brittle and less in sticky toughness) , the additive re-

duces the low - temperature performance of porous asphalt

mixture with high viscosity asphalt.


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MA Xiang, et al: Evaluation of Low-temperature Performance of Porous Asphalt Mixture 37

(2) The sequence of low-temperature cracking-resis

tance performance of asphalt mixtures after aging is the same

as that of original asphalt mixtures. Freezing-off temperature

of the porous asphalt mixture increases after aging, while

freezing- off stress decreases. So it can be seen that aging

could reduce the low-temperature performance of porous as

phalt mixture . From Fig. 3 - Fig . 5 it can be seen that un

der the same temperature-cooling range, the thermal stress of

aged asphalt mixture is a little larger than that of original

one, because aging increases the creep stiffness of porous as

phalt mixture.

(3) Compare TSRST results with indexes in Tab. 1

and Tab. 2, it can be seen that asphalt indexes after TFOT

aging and PA V aging and m value in BBR test which are

used to evaluate the low- temperature performance of asphalt

binder are not the same as TSRST test results . The creep

stiffness in BBR test could evaluate the low-temperature per

formance of aged porous asphalt mixture well, and the origi

nal mixture accords with it. Therefore, creep stiffness of BBR

test is a reasonable index to evaluate the low - temperature

performance of asphalt binder.

(4) From Fig . 3 it can be seen clearly that under al

most the same temperature dropping, thermal stress of dense

gradation asphalt mixture is 3 times as that of porous asphalt

mixture. However, the freezing- off temperatures of the two

kinds of asphalt mixtures are close to each other. According

to the calculation equations of asphalt concrete temperature

shrinkage stress raised by Hills and Brienl lO ] ,it can be ex

plained that on one hand porous asphalt mixture has larger

voids thus has smaller linear expansion coefficient; on the

other hand, porous asphalt mixture has smaller low-tempera

ture stiffness. Though the strength of porous asphalt mixture

is smaller, its temperature shrinkage stress is smaller as well.

So the low- temperature cracking- resistance performance of

porous asphalt mixtures composed by the same binder is no

worse than that of dense-gradation asphalt mixtures.

5 Conclusion

Based on considering aged asphalt and asphalt mixture,

after performing TSRST test to evaluate porous asphalt mix

ture' s low- temperature performance and comparing the test

results with low- temperature evaluation indexes of asphalt,

this paper achieves conclusions as follows:

( 1) The low - temperature cracking - resistance perfor

mance of porous asphalt mixtures with the same asphalt

binder is close to that of the dense- gradation asphalt mix

ture. The low-temperature cracking-resistance performance of

porous asphalt mixture with high viscosity asphalt is obvious

ly better than that of dense - gradation asphalt mixture with

SBS modified asphalt.

(2) Mter aging, the stiffness of porous asphalt mixture

increases, thus brings larger thermal stress, which raises

freezing-off temperature and reduces freezing-off stress.

(3) Among general evaluation indexes of low-tempera

ture performance of asphalt binder, creep stiffness in BBR

test is in good agreement with TSRST test results of porous

asphalt mixture.

(4) The quantitative relationship between freezing-off

temperature of porous asphalt mixture and BBR test results

needs further research.

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Documents

Evaluation of Low-temperature Performance of Porous Asphalt Mixture