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Journal of Highway and Transportation Research and Development Vol. 2, No. 2(2007)35
Experimental Research on Fatigue Performance of Asphalt-treated Base Mixtures*
ZHU Hong-zhou (%tWMY* * ,HE Zhao-yi (fa^)1,
HUANG Xiao-ming (M^MY,WU Guo-xiong (^@^|)1
(1. School of Civil Engineering Architecture and Construction, Chongqing Jiaotong University .Chongqing 400074,China:
2.School of Transportation,Southeast University,Nanjing Jaingsu 210096,China)
Abstract: Flexible base asphalt pavements have been used widely in high grade roads in China. The fatigue performance is one of the most
important properties for asphalt-treated base mixtures. Firstly, five kinds of asphalt mixtures were tested with the third-point flexure fatigue
test under strain controlled mode with the effects of aggregate gradation, asphalt content, asphalt property and test temperature on fatigue
performance of asphalt-treated base was analyzed, which can be considered in asphalt-treated base mixtures design.The result shows that
the fatigue performance of suspend-dense mixtures is better than framework-dense mixtures. Fatigue life is improved markedly by the in-
crease of bitumen content and the optimal asphalt content (OAC) determined by Marshall method is less than the OAC with best fatigue
performance. Fatigue life of asphalt mixture in higher temperature is longer than in lower temperature. The asphalt mixture with modified
asphalt is better than ordinary asphalt mixture in terms of fatigue performance.
Key WOrdSrroad engineering;asphalt-treated base;flexure fatigue test;fatigue performance
In recent years, premature failure of semi-rigid base as-
phalt pavement has been paid more attention by road builde-
rs and managers.Investigation indicates that, flexible base
asphalt pavement consisting of bituminous stabilized macad-
am and unbound granular materials has better performance
and longer life than semi - rigid base asphalt pavement
. Therefore, flexible base asphalt pavement is widely used in
high-grade road in China, and researches on performance of
it are becoming more and more deeply.
In flexible base asphalt pavement, asphalt-treated base
has higher modulus than unbound granular materials or sub-
grade soils.Thus, tensile stress and tensile strain are pro-
duced at the bottom of asphalt-treated layer. Under repeated
vehicle loadings, crack usually starts from the bottom of the
asphalt-treated base and propagates up to the surface, lead-
ing to strength of whole pavement failure .Experience of
many years shows that fatigue failure is one of primary failure
mode of flexible base asphalt pavement. Therefore, the fatigue
resistance property of asphalt - treated base affects life of
pavement directly which must be considered as an important
aspect in asphalt-treated base mixtures design.
In this paper, five kinds of asphalt mixtures were tested
with the third-point flexure fatigue test under strain con-
trolled mode. Effects of aggregate gradation, asphalt content,
asphalt property and test temperature on fatigue performance
of asphalt-treated aggregate were analyzed.The study result
can be referenced in design of asphalt-treated base mixtures.
1 Materials for experiment
1.1 Asphalt Two type of asphalt (70 ) heavy traffic asphalt and
MAC modified asphalt) were chosen, and following are main
technology properties of them.
Tab.l Technology properties of asphalt
Items 70# MAC
Penetration(25,100 g,5 s)(0.01 mm) 64 55
Ductility(15 t)(cm) >100 41
Softening point( X,) 51.2 90
Density(g/cm ) 1.025 1.02
1.2 Aggregate The aggregates used in the mixtures are limestone. De-
nsities of coarse and fine aggregate are shown respectively in
Tab.2 and Tab. 3.
Manuscript received November 14,2005
* Supported by the Chongqing Science & Technology Commission( 2004-8367) ;and the Chongqing Municipal Education Commission( KJ060401)
E- mail address : zhuhongzhouchina @ 126. com
J. Highway Transp. Res. Dev. (English Ed.) 2007.2:35-38.
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36 Journal of Highway and Transportation Research and Development
Tab.2 Density of coarse aggregate
Mash size( mm ) 31. 5 26.5 19 16 13.2 9.5 4.75
Density( g/cnr ) 2.710 2.706 2.708 2.700 2.697 2.704 2.677
Tab.3 Density of fii ne aggregate
Mash size( mm) 2.36 1.18 0.6 0.3 0.15 0.075 <0.075
Density (g/cm' ) 2.718 2.700 2.692 2.693 2.691 2.686 2.800
Five types of aggregate gradations for asphalt-treated
base were selected (Tab. 4), in which LSM30 I and LSM30
II are two kinds of large crushed stone asphalt mix gradation
with different airvoid ratios.
Tab.4 Aggregate gradation of asphalt mixtures
Aggregate Quality percent( % )through the following mesh(square mesh(mm))
types 31.5 26.5 19.0 16.0 13.2 9.5 4.75 2.36 1.18 0.6 0.3 0.15 0.075
AC20
ATB25
ATB30
LSAM30 I
LSAM30U
100 100 97.5
100 95.0 70
95.0 80.0 62.5
93.8 75 53.2
94.2 76.6 56.2
82.5 71.0 62.0 48.0 37.0 27.0 21.0 15.0 10.0 6.0
58.0 52.0 42.0 30.0 23.5 17.5 13.0 9.5 6.5 5.0
55.0 49.5 41.0 30.0 23.5 17.5 13.0 9.5 6.5 5.0
43.8 36.9 26.3 19.5 15.4 11.6 8.8 6.7 4.S 3.8
47.5 41.0 31.1 22.8 17.8 13.3 9.9 7.2 10.0 6.0
2 Optimum asphalt content
Standard Marshall design procedure was used to deter-
mine the optimal asphalt content of asphalt mixture. Optimum
bitumen aggregate ratio was estimated on the base of criterion
and practice experience. Then let the estimated bitumen ag-
gregate ratio as median, and adopted five different ratios by
making increment of 0.5% .For example, five bitumen ag-
gregate ratios of ATB30 are 2.5% , 3% , 3.5% , 4% , and
4.5%.Six spesimens were prepared for each asphalt cont-
ent.
Mixing and compacting conditions for asphalt mixture as
follows:
Mineral powder heating temperature: 163 t; Asphalt
heating temperature: 145 °C (70* ), 180 t (MAC); Mixing
pot heating temperature: 145 °C ; Mixing time: 3 min; Speci-
men end-compacting temperature: 135 X..
Five type asphalt mixture' s optimum bitumen contents
and volume parameters are shown in Tab.5.
Tab. 5 Marshall test result of asphalt mixtures
(in^ss Theoretical Gradation . . W
density density
'"** (g/<W)(&W) (%)
vm (%) (
_ tmtimun' Flow
VFA Stability bitumen (%) (kN) * UC x content
(0'm"l) (%) AC20 2.382 2.529 5.822 14.708 60.418 7.33 23 4.4
ATB25 2.396 2.512 4.609 14.617 68.465 8.27 25 3.4
ATB30 2.414 2.495 3.244 14.392 77.463 10.53 28 3.4
LSM30I 2.406 2.478 2.907 15.073 80.712 9.85 30 3.4
I.SM30II 2.403 2.462 2.390 15.583 84.660 9.05 35 3.4
3 Test equipment and procedure
Test specimens were sawed from slabs of the mixes pre-
pared to the target airvoid contents by rolling wheel compac-
tion . The size of specimens is 380 mm x 65 mm x 50 mm.
Test equipment used in the study was asphalt mixture
test system UTM4.The third-point loading flexure fatigue
tests were conducted at temperature of 15 t and 20 °C and
a 10Hz haversine wave was used.The tester control and ac-
quisition software collects load and deformation data at pre-
defined cycles spaced at logarithmic intervals. The initial
stiffness is determined from the load at approximately 50 rep-
etitions. Controlled-strain test was conducted and failure was
defined at 50 percent of reduction in initial stiffness '.
Fig. 1 UTM4 multifunctional material test system
4 Test results and analysis
4.1 Fatigue performances of different aggregate gra- dations
Fig.3 shows the fatigue curves of AC20 I, ATB25,
ATB30,LSM30I and LSM30II .As shown in Fig.3,five type
asphalt-treated base mixtures' curves are almost parallel. In
other words, the parameter n of Ni = K (e, )" has little
change from - 3.2 to -4.0, which coincides with previous
J. Highway Transp. Res. Dev. (English Ed.) 2007.2:35-38.
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ZHU Hong-zhou, et al: Experimental Research on Fatigue Performance of Asphalt-treated Base Mixtures 37
I I 118.5 118.5 118.5
355.5
Bending stress
Fig. 2 Schematic of third-point flexure
fatigue testing(unit:mm)
1 000
100
AC20I lgAfel4.68-3.991g e(Ave) ATB25 lgAM3.78-3.751g e(Ave) ATB30 lgAtl3.3l-3.60lg s(Ave) LSM30I lgAfel3.56-3.731g e. (Ave) LSM30I1 lgAfel3.40-3.701g «(Ave)
lo1 HI1 10'
N (time s) ID"
Fig.3 Fatigue curves of different asphalt mixtures
study. For example, in American Al design method n is -
3.291 ,and n is - 4.0 in Shell design method" • .The K val-
ues represent the position of fatigue curves, so the value re-
flects different asphalt mixtures fatigue performance level
intuitively. According to Fig. 3, fatigue performance level of
five asphalt mixtures can be arranged from good to bad as:
AC20 I—ATB25—ATB30— LSM30I—LSM30II.
As asphalt - treated base materials, ATB25, ATB30,
LSM30I, and LSM30 II mixtures are all skeleton structure
mixtures, so there are little difference in fatigue performance
of them. However, AC20 I mixture belongs to suspension -
dense mixtures, and its fatigue performance is better than
skeleton structure mixtures. When strain level is 400 pz, fa-
tigue life of AC20 I mixture is 2.48 times larger than that of
ATB30 mixture.
4.2 The influence of asphalt content VFA of mixture and thickness of asphalt film raise with
the increase of asphalt content, and the fatigue life prolong
for the same aggregate gradation. It can be seen from Fig. 4
that fatigue life of ATB30 asphalt mixture increases 162%
with the asphalt content increases from 2.8% to 4.0%
.3.4% is optimum asphalt content determined by Marshall
design method, and obviously it is not the optimum asphalt
content for asphalt mixture fatigue performance.
4.3 The influence of temperature
25 000
20 000
£ 15 000
HI (KM)
5 000
Asphalt content (%)
Fig.4 Effect of asphalt content on fatigue life
15 25 TemperatureCC)
Fig.5 Effect of temperature on fatigue life
Test temperature has a prominent influence on fatigue
life of asphalt mixtures. In controlled stress testing it was
found that fatigue live increases sharply with temperature de-
creases . In controlled strain fatigue testing it was found that,
fatigue life is low temperature dependent when temperature is
lower, but increasing the temperature will increase the fatigue
life. Influence of temperature on fatigue life of asphalt-treated
base can be explained by the change of stiffness of mix-
ture. The stiffness of asphalt mixture increases when tempera-
ture descends within a certain range.In controlled stress
mode of loading the stress is kept constant in all load cycles
and less strain produced with stiffness increases which maybe
prolong the fatigue life.On the other hand, in controlled
strain mode of loading, the strain is kept constant along the
test and more stress is produced from one cycle to the next as
higher stiffness and a shorter fatigue life can be obtained.
Fig.5 is the contrast of fatigue lives at different test
temperatures for ATB30 asphalt mixture. It can be seen that
fatigue life of asphalt mixture in higher temperature is longer
than in lower temperature. The fatigue life of asphalt-treated
base mixture ATB30 at 25 t is 9.36 times than that of 15
X.
Thus, there is little fatigue damage in asphalt pavement
at high temperature. So fatigue performance of asphalt layers
under 30 X. should be mainly considered in pavement struc-
ture designing.This indicates that the fatigue test in con-
trolled strain mode of loading is better to simulate the condi-
J. Highway Transp. Res. Dev. (English Ed.) 2007.2:35-38.
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38 Journal of Highway and Transportation Research and Development
tions of loading in the field than controlled stress
mode. There is little fatigue crack in asphalt pavement in
summer.
4.4 Fatigue perfonnances of different types of asphalt
MAC modified asphalt has higher softening point and
lower ductility compared to ordinary asphalt. Therefore the
mixtures using MAC modified asphalt will have outstanding
high temperature stability performance. As shown in Fig. 6,
ATB30 mixture using MAC modified asphalt has a little im
provement in fatigue perfonnance than using 70 # asphalt. It
results from the better cementation between MAC modified
asphalt and aggregate.
Fig. 6
1000
---*-70#Heavy asphalt _____ MAC Modified asphalt
100 '-----'---..L-LJ-LLLLL--'--'--L.ULLLU_-"---L-L.LLlJLU
1000 10 000 100000 N(times)
1000000
Fatigue curves of mixtures with different types of asphalt
5 Conclusions
Different kinds of asphalt - treated base mixtures were
experimented with the third - point flexure fatigue testing of
control strain mode. Effects of aggregate gradation, asphalt
content, asphalt property and test temperature on fatigue per
fonnance of asphalt-treated base were analyzed. The conclu
sions of this paper can be summarized as follows:
(1 ) A TB25, A TB30, LSM30 I and LSM30 II mixtures
have little difference in fatigue performance as they are all
framework-dense mixtures. While AC20 I mixture belongs to
suspend-dense mixtures, and its fatigue performance is better
than that of framework-dense mixtures.
(2) Fatigue performance of asphalt-treated base is im
proved markedly by the increase of bitumen content. The op
timal asphalt content determined by Marshall method should
be increased properly to get better fatigue perfonnance.
( 3 ) Fatigue life of asphalt mixture in higher temperature
is longer than in lower temperature . Fatigue performance of
asphalt layers under 30"C should be mainly considered in
pavement structure designing. It indicates that the fatigue test
in controlled strain mode of loading is better to simulate the
conditions of loading in the field than in controlled stress
mode.
( 4) Asphalt-treated base mixture using modified asphalt
has a little improvement in fatigue performance than using
70# asphalt. It results from the better cementation between
MAC modified asphalt and aggregate.
References
[ 1 J ZHU Hong- zhou. Research On Flexible Base Asphalt Pavements
Fatigue Perlonnance and Design Method [ D J . Nanjing: Southeast
University,2005.
[2J HUANG Yang-xian.Pavement Analysis and Design[MJ .Transla
ted by YU Ding - yuan, et al. Beijing: China Communications
Press,I998:14-19.
[3J
[4J
ITJ052-2<XXJ, Test Specification of Bitumen and Bitumen Mix
tures for Highway Engineering[ S J .
SHRP- A-312. Fatigue Response of Asphalt Mixtures [ RJ . USA:
N.C. R., 1990.
[5J HUANG Wei,QlAN Zhen-dong.Theory and Methodology of Ad
vanced Asphalt Pavement Design [ M J . Beijing: Science Press,
2001.
[ 6 J SHEN Jin- an. Perlonnance of Bitumen and Bitumen Mixtures
[MJ . Beijing: China Communications Press,2001.
[7J DENG Xue-jun,HUANG Xiao-ming.Principles and Design Methods
of Pavement[MJ . Beijing: Orina Comnrunications Press,::nll.
[8J PElL P S, COPPER K E. The Effect of Testing and Mix Vari
ables on the Fatigue Perlonnance of Bituminous Materials [ cJ II Proceing of the Association of Asphalt Paving Technolo
gists. 1975 ,44:1 - 37.
(Selected from Journal of Highway and Transportation
Research and Development, vol. 24, no. 4, pp. 7-10,2007)
J. Highway Transp. Res. Dev. (English Ed.) 2007.2:35-38.
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