Key Engineering Materials
ISSN: 1662-9795, Vol. 509, pp 149-154
doi:10.4028/www.scientific.net/KEM.509.149
© 2012 Trans Tech Publications, Switzerland
Online: 2012-04-12
Moisture Sensitivity of Bituminous mixtures with Compound Fly Ash
Modifier
XIE Jun1, a, CAI Jun1, b, WU Shaopeng1, c, PANG Ling1, d
1
State Key Laboratory of Silicate Materials for Architectures, Wuhan University of Technology,
Wuhan 430070, PR China
a
b
email: [email protected];
c
email: [email protected];
email: [email protected];
d
email: [email protected];
Keywords: Gneiss, Granite, Moisture sensitivity, Compound fly ash modifier
Abstract. Bitumen pavement suffers from moisture damage mainly due to loss of durability and
stability in a short span of service life. Filler is known to be capable of increasing the stiffness of
bitumen binder, contributing to improvement of moisture sensitivity of bitumen mixture. In this
paper a new type of filler named ‘Compound Fly Ash Modifier’ (CFAM) was introduced in order to
enhance the bond strength between acidic aggregate with bitumen. The primary object is to
determine the effect of CFAM on the moisture sensitivity of bitumen mixtures prepared by gneiss
and granite respectively, which are termed acidic aggregate. Modified Lottman test and fatigue test
were conducted. The results show that CFAM improves the resistance of mixes to moisture damage
in the increase in indirect tensile strength and the extension of fatigue life. Finally the mechanism of
modified effects for CFAM is discussed.
Introduction
With the development of infrastructure and increasing transportation demands in china, quantities
of pavements have been under construction. By the end of 2010, highway network will be up to
74,000 km in china. However, the service lives of newly built pavements are usually shorter than
that of original designed. Granite and gneiss, which are considered acidic aggregate, are used as
aggregate in an alternative way in some areas where limestone is in poor reserve. Anti-stripping
additives are necessary to utilize in the acidic aggregate mixtures to mitigate water damage. The
additives that are used in practice or tested in the laboratory include: traditional liquid additive,
metal ion surfactants, hydrated lime and quick lime, Portland cement, silane coupling agents and
silicone [1-7]. Their functions on improvement of moisture characteristic in bituminous mixtures
have been proved excellent. However, high expenditure and environmental hostility are still the
concerns of them to apply in practical engineering construction.
Valorization of waste becomes a hot spot in recent years. According to engineering projects, fly
ash is widely applied in bituminous concretes. The effects of fly ash on resistance of bitumen
mixture to moisture have been extensively studied. N. Ali [8]stated that stripping resistance of the
mix was increased by the addition of fly ash. Ibrahim Asi [9] determined that modifying the bitumen
concrete mixes with fly ash improved the mixes resistance to water damages. Li[10] exhibited that
bitumen mix with fly ash maintained its stiffness even after exposure to freeze-thaw cycling during
the first winter after construction. However, there is little application case for fly ash in bituminous
pavement engineering in China for its poor cementitious properties. The limited effect of fly ash in
China might be caused by the different essential properties of fly ash after coal combustion.
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Green Building Materials III
In this paper a new type of filler named ‘Compound Fly Ash Modifier’ (CFAM) was introduced
in order to enhance the bond strength between acidic aggregate with bitumen. The objective of this
paper is to determine the effect CFAM in acid aggregate mixtures on moisture sensitivity and
fatigue properties.
Materials characterization
Gneiss and granite were used as aggregate. Their specifications were within the limits of
corresponding Chinese norm. The bitumen was 60/80 penetration graded as AH70, which was
procured from Guochuang Co., Ltd, in China. The specification of aggregate and bitmen were
shown in Table 1 and 2. CFAM was prepared in laboratory. Dry fly ash was added to silane
coupling agent solution in 50 ml dry toluene. The weight of coupling agent was 5% of mixed fly
ash. After 5 h mix at room temperature, the slurry was washed with toluene and dried in an oven at
105 ℃ for 24 h. Mineral powder (LP) was selected as reference filler. Table.3 shows the basic
properties of selected fillers.
Table 1 Physical properties of selected aggregates
Properties
Gneiss
Granite
-3
Coarse aggregate bulk specific gravity [g.cm ]
2.719
2.669
-3
Fine aggregate bulk specific gravity [g.cm ]
2.744
2.679
Abrasion loss (Los Angeles) [%]
13.6
12.5
Frost action (with Na2SO4) [%]
4.2
3.9
Polishing value
47.5
46.8
Requirements
>2.6
>2.7
<30
≤ 12
>42
Table 2 Physical properties of bitumen
Properties
Measured values
Standards
-3
Specific gravity [g.cm ]
1.032
ASTM D70-76 (ASTM 1976b)
o
Penetration at 25 C [0.1mm]
68
ASTM D5-73 (ASTM 1973)
o
Ductility,5cm/min,15 C [cm]
≥150
ASTM D113-79 (ASTM 1979a)
o
Softening point [ C]
48
ASTM D36-76 (ASTM 1976a)
o
Flash point [ C]
320
ASTM D92-78 (ASTM 1976)
o
Viscosity at 60 C [Pa·s]
198
ASTM D92-78 (ASTM 1976)
Loss on heating [%]
+0.02
ASTM D6-80 (ASTM 1980)
Table 1 Basic properties of selected filler
Properties
Limestone powder
-3
Specific gravity[g.cm ]
2.704
Absorption [%]
0.9
Hydrophilic coefficient
0.67
0.6 mm
100
Percent passing [%]
0.15 mm
93
0.075 mm
85.9
CFAM
2.521
0.6
0.36
100
93.1
89.6
Requirements
>2.50
<1.00
100
90-100
80-100
Key Engineering Materials Vol. 509
151
Experiment methods
Mixtures with 19 mm nominal maximum aggregate size were designed by using standard Marshall
method. It is well known that a suitable gradation is of great importance to determine the
engineering performance of bituminous mixture. Therefore three gradations were designed in forms
of coarse, mediate and fine type for each aggregate. The criteria including Marshall stability, air
void, void in coarse aggregate, etc were set for the selection of the optimizing gradation. In addition,
the optimum bitumen contents were also determined after the measurement of volumetric properties
of samples. The gradations for each aggregate were finally determined, as shown in Fig. 1 . Notably
3 percent of filler was incorporated in the designed bituminous mixture. And the optimum bitumen
content was determined to be 4.8% for gneiss mixtures and 4.5% for granite, by weight of
aggregate.
100
Passing percent /%
80
Upper limit
Lower limit
Gneiss
Granite
60
40
20
0
0.01
0.1
1
Sieves size /mm
10
100
Fig. 1 Selected gradation curves
In modified Lottman test, totally 24 Marshall samples of 7.0±1 percent air voids were prepared
on the same conditions. The samples were divided into 6 groups. Except group 1(the controlled
group), the rest subjected to its related cycles of frost-thaw treatment from 1 to 5 cycles. All the
samples were tested for indirect tensile strength (ITS) by loading the specimens at a constant rate
(50 mm/min vertical deformation at 25 oC) and the force required to break the specimen was
measured.
. Indirect tensile fatigue test was conducted to evaluate the fatigue sensitivity of bituminous mixture
in presence of water with stress controlled mode. Cylindrical specimens (100mm in diameter,
60mm in thickness) at appropriately 7% air void were prepared prior to testing in Universal Testing
Maching (UTM-25) at 20 ℃.
Results and discussion
Modified Lottman test. Indirect tensile strength test coupled with five frost-thawing cycles test are
conducted and the results were displayed graphically in Fig. 3 . Through the frost-thawing test, the
bitumen performance decrease as well as the adhesive bond is destructed eventually by the intrusion
of water. The loss of strength of mixtures with CFAM is not as high as that with LP. In particular,
the tensile strength ratio (TSR) of gneiss mixture with LP is 65.3%, which fails to meet the standard
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Green Building Materials III
requirement. On the other hand 87.2 percent TSR value is achieved with the involvement of CFAM.
Approximately 33.8 %improvement of TSR is obtained. Additionally for the mixture with granite,
the TSR value of CFAM prepared mixture is 85.2%, 4.9% higher than LP prepared mixture.
1.6
Gneiss-LP
1.4
Gneiss-CFAM
Granite-LP
Granite-CFAM
ITS /MPa
1.2
1
0.8
0.6
0.4
0.2
0
1
2
3
4
Cycles / times
5
Fig. 2 Indirect tensile strength (ITS) of mixtures
1
Gneiss-LP
Gneiss-CFAM
Granite-LP
Granite-CFAM
0.9
ITSR /%
0.8
0.7
0.6
0.5
0.4
0.3
1
2
3
4
Cycles / times
5
Fig. 3 Indirect tensile strength ratios through frost-thaw
Fatigue test. Fig.4 shows the fatigue properties of bituminous mixtures. Fatigue life of mix is the
cycle number to failure with repeated load. The mixes with CFAM show a better sensitivity to
fatigue failure. Subsequently the result leads to the conclusion that CFAM is capable of improving
the fatigue properties of mixes. The regression lines of fatigue formula were also drawn in Fig.4.
The slope was also considered an indication of bearing capacity of mixes subjecting to load. A
larger slope means a better durability of mixes while stress increases over time. It is shown that the
slope of regression line for the granite mix with CFAM is the biggest among the four types of
mixes.
Key Engineering Materials Vol. 509
153
100000
Fatigue life (Cycle)
10000
Granite+LP
Granite+CFAM
1000
Gneiss+LP
Gneiss+CFAM
100
0.1
1.0
Stress ratio
Fig. 4 Fatigue properties of bituminous mixtures
Mechanism analysis. There is a remarkable improvement of engineering properties of bituminous
mixture in terms of resistance to moisture damage and fatigue failure. The basic mechanism is the
enhanced bond between bitumen and aggregate. An improved bond is able to resist moisture
intrusion from the bitumen-aggregate interface and decrease cracking possibility. The improving
effects attribute to the addition of CFAM for filler is the only variable during the experiment
elaboration. A probable reaction between fly ash, silane coupling agent and bitumen was shown in
Fig.5.
Si
OH
O
Si
+
O
Si
OEt
OH
OEt +
R
C
OH
OEt
H2N
Bitumen
Silane coupling agent
Surface of fly ash
Si
O
O
OEt
H
O
Si
N
C
R +
C2H5OH
OEt
Si
Fig. 5 Reactions between fly ash, coupling agent and bitumen
Conclusions
The primary object is to determine the effect of CFAM on the moisture sensitivity of bitumen
mixtures prepared by gneiss and granite respectively, which are termed acidic aggregate. According
to the obtained result, several conclusions can be drawn as following.
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Green Building Materials III
1.
The mixtures prepared with CFAM exhibits great moisture sensitivity than the ones with
limestone powder. It is concluded that a significant improvement on bond strength between
bitumen and aggregate was achieved attributing to the addition of CFAM.
2. The distinctions in fatigue lives of mixtures with and without CFAM indicate the benefit of
CFAM on improvement of fatigue properties of bituminous mixtures.
3. As filler, CFAM can be considered as the extension of bitumen. It provide multifunctional
profits in bituminous mixture.
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Green Building Materials III
10.4028/www.scientific.net/KEM.509
Moisture Sensitivity of Bituminous Mixtures with Compound Fly Ash Modifier
10.4028/www.scientific.net/KEM.509.149
DOI References
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