45
Sustainability on materials and resources
ABSTRACT: Stripping is one of typical distresses
of asphalt pavement. Once stripping occurs, it is
difficult to repair the asphalt pavement because
asphalt and aggregates would be separated after
stripping. The stripping depends generally upon
the type of aggregates used in asphalt mixture.
Aggregates in which Silicon Dioxide (SiO2) is
contained at higher ratio, like Granite, Andesite and
so on, have the risk that stripping would arise easily.
So the solution which focuses on characteristic of
aggregates used in asphalt mixture would become
more important.
Therefore, we tried to create polarity to asphalt by
using anti-stripping agent, “Tough Fix” or “Tough
Fix Hyper”. As a result, it is clarified that these have
strong chemical bonding between surface potential
of aggregates and asphalt to which polarity was
given. In this paper, the improvement effects to
anti-stripping performance by using “Tough Fix”
or “Tough Fix Hyper” to aggregates, in which SiO2
is contained at high ratio, are introduced through
the test results of Modified Lottoman Test and
Residual Marshal Stability Test.
KEYWORDS: Stripping, SiO2, anti-stripping agent,
modified lottoman test, residual marshal stability test.
nHIROKI IMAI(1) Engineering Research Laboratory of Taiyu Kensetsu Co., LTD. Nagoya, Japan
nNGUYEN QUANG PHUC(2) University of Transport and Communications, Hanoi, Vietnam
nHIROMITSU NAKANISHI(3); TOMOHIRO ANDO(4) Global Business Team of Taiyu Kensetsu Co., LTD. Nagoya, Japan
Email: imai-hiro@taiyu.co.jp(1); nguyenquangphuc@utc.edu.vn(2); nakanishi@taiyu.co.jp(3); andou-tomo@taiyu.co.jp(4)
Anti-Stripping Agent for Hot Mix Asphalt Pavement
1. INTRODUCTION
One of serious distress of asphalt pavement is the
stripping of asphalt mixture as shown in Photo. 1.1. This
stripping is aected by the aggregates using asphalt
mixture, would arise easily, in the case of using aggregates
in which Silicon Dioxide (SiO
2
) is contained at higher ratio,
like Granite, Andesite, and so on. Therefore, the solution
which focuses on characteristic of aggregates used in
asphalt mixture would become more important.
Photo. 1.1: Stripping of Asphalt Mixture
On the other hand, there has been the solution
which focuses on the characteristic of the aggregates.
It is the way in which anti-stripping agent is used with
asphalt. However, conventional anti-stripping agent
tends to soften the base asphalt. In the case of using
such anti-stripping agent, there has been a concern that
rutting problem would arise.
Therefore, this study focused on chemical
constitution of aggregates, and tried to create polarity to
asphalt by using polarity surfactant compound, “Tough
Fix” or “Tough Fix Hyper” as anti-stripping agents to form
strong chemical bonding between surface potential of
aggregates and asphalt.
In this paper, the improvement eects to anti-
stripping and the eect to anti-rutting by using “Tough
Fix” or “Tough Fix Hyper” are described.
2. MECHANISM OF STRIPPING IN ASPHALT
MIXTURE
The aggregates in which SiO
2
is contained, tend to
be charged negatively because Oxygen with the negative
charge is located on surface side of the aggregate. Therefore,
if asphalt mixture using the aggregates containing SiO
2
is
immersed in water, Hydrogen of H
2
O adhered to surface of
aggregates due to electronegativity of Oxygen. As the result,
asphalt is stripped from the aggregates since Hydrogen
bonding is stronger than the intermolecular forces between
asphalt and aggregate as shown in Fig. 2.1 [1].
Therefore, this study tried to create polarity to
base asphalt, and forming the strong chemical bonding
between asphalt and the aggregates as shown in Fig. 2.2.
As the result, stripping problem by Hydrogen bonding
would be able to be resolved.
3. MATERIALS FOR EXPERIMENT AND
EVALUATION METHOD
3.1. Materials
3.1.1. Aggregate
Focusing on the characteristics of aggregates, we used
the dierent types of aggregates which contain SiO
2
in order
to evaluate the relative eects regarding the resistance to
stripping. Coarse aggregates (Andesite, Granite, Limestone)
used for this study are shown in Photo. 3.1.
Photo. 3.1: Aggregate for Experiment
Si-O
2
Si-O
2
Si-O
2
Si-O
2
Si-O
2
aggregate
intermolecular force < hydrogen bonding hydrogen bonding < chemical bonding
Fig. 2.1: Mechanism
of Stripping Fig. 2.2: Creating Polarity
to Asphalt
(Andesite) (Granite) (Limestone)
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Sustainability on materials and resources
3.1.2. Asphalt
Straight asphalt with penetration grade 60 - 80
was used. That is because, it is thought to be dicult
to evaluate accurately the resistance by anti-stripping
agent in case of using modied asphalt due to its eect
on improvement of the water resistance.
3.1.3. Anti-Stripping Agent
We are convinced of the thought that the
resistance to stripping of asphalt mixture is improved
by creating polarity to asphalt and forming chemical
bonding between aggregates and asphalt. In this
study, “Tough Fix”, which gives polarity to asphalt,
and then “Tough Fix Hyper”, which has furthermore
improved the anti-stripping performance, have been
adopted. Two types of anti-stripping agent are shown
in Photo. 3.2 with their characteristics shown in Table
3.1. These agents have great adhesive properties to
various types of aggregates because both of them are
polarity surfactants.
As shown in Table 3.1, both anti-stripping agents can
be dissolved easily into asphalt. Therefore, it is possible
to put these agents into the mixer of an asphalt plant.
Furthermore, adding these agents in a tank truck and an
asphalt tank does not cause any problem with storage
since both agents have excellent storage stability without
separation and deterioration.
Photo. 3.2: Anti-Stripping Agent
Table 3.1. Properties of Anti-Stripping Agents
3.2. Evaluation Method of the Resistance to
Stripping
The evaluation of the resistance to stripping is
carried out by testing the asphalt binder and asphalt
mixture which contains 0,1 to 0,3% by weight of “Tough
Fix” or “Tough Fix Hyper” in mix ratio. Moreover, three
types of dense graded asphalt mixture (13mm top size)
using dierent type of aggregates are adopted.
Three mix gradations of asphalt mixture are shown
in Table 3.2. As shown in Table 3.2, the optimum asphalt
content for each gradation is dierent with the range
from 5,3 to 5,9%.
Table 3.2. Mix Gradation of Three Types of Dense
Graded Asphalt Mixture
Regarding evaluation methods, three methods of
(1) Static Stripping Test, (2) Residual Marshall Stability
Test and (3) Modied Lottman Test are adopted. They
were selected to conrm the eect of two types of anti-
stripping agent including their dierent behavior.
4. TEST RESULT OF ASPHALT BINDER
4.1. General Asphalt Properties
Asphalt properties of straight asphalt with
penetration grade 60 - 80, in which two types of anti-
stripping agent are added, are shown in Table 4.1. As
shown in Table 4.1, the anti-stripping agents used
in this study do not give an adverse eect to asphalt
properties of base asphalt because Softening Point and
Ductility are not changed, even though anti-stripping
agents are added.
Table 4.1. Properties of Asphalt Binder with Anti-Stripping Agent
4.2. Static Stripping Test
Static Stripping Test was carried out in order to
evaluate the resistance of coarse aggregate to stripping
when aggregates coated with asphalt were immersed in
hot water.
4.2.1. Procedure of the test
- Mix 100g of coarse aggregate (9,5 - 13,2mm) and
with 5,5g of asphalt at 160
0
C. The mixing time is 1,0 to
1,5 minutes.
- Spread coarse aggregate coated with asphalt on a
glass plate and cool it at room temperature for one hour.
- Immerse the coarse aggregate on the glass plate in
hot water tank at 80
0
C.
- Take the glass plate out of the hot water tank after
immersing for 30 minutes, and put into cool water tank at
room temperature.
- Observe the stripping state of the coarse aggregate,
calculate stripping area ratio by visual.
4.2.2. Test Result
Test results of Static Stripping test for three types of
coarse aggregates are shown in Table 4.2. As shown in Table
4.2, granite with higher ratio of contained SiO
2
has larger
stripping area ratio than the others. However, by adding
anti-stripping agent, stripping area ratio decreases. This
means the resistance to stripping has improved obviously.
And also, results of adding anti-stripping agents are
excellent in the resistance to stripping without dierence
of their eects.
Table 4.2. Test Result of Static Stripping Test
(Tough
Fix)
(Tough
Fix
Hyper)
Properties Tough Fix Tough Fix Hyper
Melting Point C 70 125
Flash Point C 199 286
pH 3.0 9.6
Not separated Not separated
Not deteriorate Not deteriorate
Strage Stability
Base case : Straight asphalt without agent
Case-1 : Straight asphalt with T ough Fix
Case-2 : Straight asphalt with T ough Fix Hyper
Andes ite Granite Limestone
uppe r : Tough Fix 0.1% uppe r : Tough Fix 0.1% upper : Tough Fix 0.1%
lower : Tough Fix Hyper 0.1% lower : Tough Fix Hyper 0.1% lower : Tough Fix H ype r 0.1%
Original Original Original
25% 30% 5%
0% 0% 0%
0% 0% 0%
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Sustainability on materials and resources
The numeric values shown in Table 4.2 show the
stripping area ratio when the additive amount is 0% and
0,1%. In the cases of the higher additive amount of 0,2%
and 0,3%, the excellent stripping resistance is always
obtained with stripping area ratio of 0,0%.
5. TEST RESULT OF ASPHALT MIXTURE
5.1. Residual Marshall Stability Test (ASTM
D1559)
Residual Marshall Stability Test was carried out
in order to evaluate resistance to stripping of asphalt
mixture. Residual Stability is shown by the percentage of
the Marshall Stability after water immersion against the
Marshall Stability at the normal condition.
5.1.1. Procedure of the Test
Procedure of Residual Stability Test is shown in Fig.
5.1 with test arrangement in Fig. 5.2.
Fig. 5.1: Procedure of Residual Stability Test
Photo. 5.1: Test Arrangement
5.1.2. Test Results
Test results of three types of dense graded asphalt
mixture (13mm top size) in which “Tough Fix” or “Tough
Fix Hyper” is added are shown in Fig. 5.2. As shown in Fig.
5.2, the following ndings were obtained.
- By the addition of anti-stripping agent, the value of
Residual Stability increased by about 10 points to 85% to
90% with “Tough Fix” and increased by about 20 points
to about 95% with “Tough Fix Hyper”. From these eects,
the resistance to stripping was signicantly improved.
- Even if the aggregate Granite in which SiO
2
is
contained at high ratio or Limestone mainly composes
of Ca, the resistance to stripping is improved regardless
of type of aggregates by giving polarity of positive and
negative to asphalt.
- The standard of Residual Marshal Stability in Japan
is 75% or more. According to the result, the Residual
Stability with “Tough Fix” or “Tough Fix Hyper” shows
85% or more. Therefore, it claries that these agents give
excellent resistance to stripping to asphalt mixture.
Fig. 5.2: Test Results of Residual Stability Test
5.2. Modied Lottoman Test (AASHTO T283)
Modied Lottoman Test is a kind of Indirect Tensile
Test, the test is applied to compare curing conditions
of normal curing and accelerated stripping curing. And
then, Indirect Tensile Strength Ratio is obtained by
each Indirect Tensile Strength. It should be noted that
a vacuum pump is used to immerse water forcibly for
obtaining the Indirect Tensile Strength on the accelerated
stripping condition [2].
5.2.1. Procedure of the Test
Procedure of Modied Lottoman Test is shown in Fig.
5.3 with test arrangement in Photo. 5.2.
Fig. 5.3: Procedure of Modified Lottoman Test
Photo. 5.2: Test Arrangement
5.2.2. Test Results
Test results of three types of dense graded asphalt
mixture (13) in which “Tough Fix” or “Tough Fix Hyper”
is added are shown in Fig. 5.4. As shown in Fig. 5.4, the
following ndings were obtained.
- By the addition of anti-stripping agent, the value
of Indirect Tensile Strength Ratio increased by about 20
Fabrication of Marshall Specimen
Immersion Curing in Water
(60 C, 30-40 minutes)
Marshall Test
Measurement of Density
immersion Curing in water
(60 C, 48 hours)
MarshallTest
Calculation of Residual Stability
*1
(Normal Curing) (immersed Curing)
*1 (Fomula.1)
70
75
80
85
90
95
100
0 0.1 0.2 0.3
Residual stability (%)
Mix ratio of agent (%)
Tough Fix
Andesite
Granite
LimeStone
][
70
75
80
85
90
95
100
0 0.1 0.2 0.3
Residual stability (%)
Mix ratio of agent (%)
Tough Fix Hyper
Andesite
Granite
LimeStone
][
Fabrication of Marshall Specimen
Immersion Curing in Water
(25 C, 20 minutes)
Indirect Tensile Test
Measurement of Density
Forced Immersion in Water
(using vacuum pump)
Indirect Tensile Test
Calculation of Indirect Tensile Strength Ratio
*2
Immersion Curing in Water
(60 C, 24 hours)
Immersion Curing in Water
(25 C, 1 hours)
(Normal Curing) (Accelerated Stripping Curing)
*2 (Fomula.2)
48
Sustainability on materials and resources
points with “Tough Fix” and increased by about 30 points
with “Tough Fix Hyper”. From these eects, the resistance
to stripping was signicantly improved.
- The resistance to stripping regardless of type of
aggregates was improved by giving polarity of positive
and negative to asphalt as well as the results of the
Residual Stability.
- Fig. 5.5 shows the relation between Residual
Stability and Indirect Tensile Strength Ratio. There is a
high correlation between Residual Stability and Indirect
Tensile Strength Ratio. According to Fig. 5.5, Indirect
Tensile Strength Ratio needs about 55% or more to meet
75% or more with Residual Stability which is Japanese
standard. Therefore, the resistance to stripping is
obtained by additive amount of 0,1% or more in Modied
Lottoman Test.
Fig. 5.4: Test results of Modified Lottoman Test
Fig. 5.5: Correlation of Characteristics
5.3. Wheel Tracking Test
Wheel Tracking Test is carried out to evaluate the
resistance to rutting of asphalt mixture, the test is unique
to JAPAN.
5.3.1. Procedure of the Test
This test is normally carried out in order to evaluate
the rutting resistance, Dynamic Stability “DS”, of asphalt
mixtures in Japan. The test method and calculation
method of DS are shown in Photo. 5.3.
5.3.2. Test Results
Test results of three types of dense graded asphalt
mixture (13mm top size) in which “Tough Fix” or “Tough
Fix Hyper” is added are shown in Fig. 5.6. As shown in
Fig. 5.6, it is claried that adding the anti-stripping agent
does not have adverse eects of the resistance to rutting
since the Dynamic Stability would not decrease.
Photo. 5.3: Test Arrangement
Fig. 5.6: Test Results of Wheel Tracking Test
6. CONCLUSION
The ndings in this study are as follows:
- The resistance to stripping of asphalt mixture
can be signicantly improved by adding “Tough Fix” or
“Tough Fix Hyper” as anti-stripping agent.
- The eect of the resistance to stripping is obtained
by adding “Tough Fix” or “Tough Fix Hyper” with the
amount of 0,1% or more by dry weight.
- Therefore, it is possible to adjust additive amount
to 0,1% or more in accordance with target property
because those agents are suitable for “Plant Mix”.
- Adding “Tough Fix” or “Tough Fix Hyper” does not
take adverse eect on reduction of resistance to rutting.
References
[1]. A. Hanyu (1996), Adhesion-Improved Modied
Asphalt for Bridge Pavement, ASPHALT.
[2]. S. Higashi (2004), A Study on the Evaluate Method
for the Resistance to Stripping of Asphalt Mixture, JRCA’s
magazine.
20
30
40
50
60
70
80
90
100
0 0.1 0.2 0.3
Indirect tensile strength ratio (%)
Mix ratio of agent (%)
Tough Fix
Andesite
Granite
LimeStone
][
20
30
40
50
60
70
80
90
100
0 0.1 0.2 0.3
Indirect tensile strength ratio (%)
Mix ratio of agent (%)
Tough Fix Hyper
Andesite
Granite
LimeStone
][
R² = 0.8382
20
30
40
50
60
70
80
90
100
40 50 60 70 80 90 100 110 120
Indirect tensile strength ratio (%)
Residual stability (%)
10 100 1,000 10,000
Tough Fix Hyper 0.2
Tough Fix 0.2%
Original
Tough Fix Hyper 0.2
Tough Fix 0.2%
Original
Tough Fix Hyper 0.2
Tough Fix 0.2%
Original
Limestone Granite Andesite
Dynamic stability (pass/mm)
(Test conditions)
Test temperature: 60
o
C
Tracking speed: 42pass/min
Contact pressure: 686N
(Fomula.3)
