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Influence of Reduced Production Temperatureson the Adhesive Properties of Aggregates andLaboratory Performance of Fine Aggregate-AsphaltMixturesKamilla L. Vasconcelos a , Amit Bhasin b & Dallas N. Little aa Zachry Department of Civil Engineering , Texas Transportation Institute Texas A&MUniversity , MS 3135, College Station, TX, 77843, USA E-mail:b The University of Texas at Austin , 1 University Station C1761, Austin, TX, 78712, USAE-mail:Published online: 19 Sep 2011.
To cite this article: Kamilla L. Vasconcelos , Amit Bhasin & Dallas N. Little (2010) Influence of Reduced ProductionTemperatures on the Adhesive Properties of Aggregates and Laboratory Performance of Fine Aggregate-Asphalt Mixtures,Road Materials and Pavement Design, 11:1, 47-64, DOI: 10.1080/14680629.2010.9690259
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RMPD – 11/2010. Asphalt Pavements and Environment, pages 47 to 64
Influence of Reduced Production
Temperatures on the Adhesive Propertiesof Aggregates and Laboratory Performanceof Fine Aggregate-Asphalt Mixtures
Kamilla L. Vasconcelos* — Amit Bhasin** — Dallas N. Little*
* Zachry Department of Civil Engineering and Texas Transportation Institute
Texas A&M University MS 3135
College Station, TX 77843, USA
** The University of Texas at Austin
1 University Station C1761
Austin, TX 78712, USA
ABSTRACT. Several new technologies have made production of hot mix asphalt (HMA) possible
at lower temperatures by reducing binder viscosity and increasing mixture workability. The
asphalt mixture produced using this technology is referred to as warm mix asphalt (WMA). In
this study, three aggregates and two asphalt binders were used with a synthetic zeolite to
produce six different types of Fine Aggregate Matrix (FAM), that were prepared at three
different mixing and compaction temperatures. The first objective of this study was to
evaluate the impact of reducing mixing and compaction temperatures on the mechanical
behavior of these mixtures using the Dynamic Mechanical Analyzer (DMA). Secondly, the
micro calorimeter was used to measure the total energy of adhesion (TEA) between the
asphalt binder and aggregates treated at different temperatures. Results from the DMA
indicate that shear modulus and fatigue cracking resistance of the FAM typically decreased
when the mixing and compaction temperatures were reduced. TEA results indicate that
residual moisture on aggregate surfaces at reduced mixing temperatures does not contribute
significantly to the observed reduction in the mechanical results at lower mixing
temperatures.
KEYWORDS: Warm Mix Asphalt, Zeolite, Dynamic Mechanical Analyzer, Micro Calorimeter.
DOI:10.3166/RMPD.11.47-64 © 2010 Lavoisier, Paris
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48 RMPD – 11/2010. Asphalt Pavements and Environment
1. Introduction
The production of hot mix asphalt (HMA) typically requires heating the asphalt
binder and aggregate to temperatures in the range of 140qC to 160qC. These high
production temperatures generally ensure that: i) the asphalt binder has sufficiently
low viscosity to coat the aggregate surface and ii) the aggregate surface is dried
sufficiently so that a durable bond can be formed between the aggregate and the
asphalt binder. Therefore, selection of the mixing and compaction temperatures is
crucial to ensure proper aggregate coating, matrix stability during production and
transport, ease of placement, acceptable compaction, and ultimately acceptable
performance of the pavement.
Several new techniques have been developed to reduce the temperatures used for
mixing and compaction of hot mix asphalt (HMA). The asphalt mix produced at
lower than conventional mixing and compaction temperature using any of these
techniques is referred to as warm mix asphalt (WMA). Development of the WMA
technology was initiated by the German Bitumen Forum in 1997 in response to the
Kyoto agreement. WMA is produced at temperatures that are up to 40qC lower than
the typical HMA production temperatures. Lower production temperatures reduce
emissions, fumes and odors, and hardening of the binder during construction. Lower
production temperatures also offer benefits such as energy savings, ability to open
sites early and pave during cooler periods. Some of the techniques currently being
explored to produce WMA are: (i) production of foaming action within the asphalt
binder at the time of mixing (WAM-Foam�), (ii) use of emulsion to reduce binder
viscosity (Evotherm�), (iii) use of mineral additives to release water during the
mixing process so that binder viscosity is reduced (Aspha-Min� and Advera�), (iv)
use of organic additives to reduce binder viscosity (Sasobit� and Asphaltan B�),
and (v) use of a combination of dry and wet aggregates during mixing to release
water and reduce binder viscosity (low energy asphalt).
Irrespective of the technique used to produce a WMA, one of the concerns of
producing asphalt at reduced mixing and compaction temperatures is inadequate
drying of the aggregate surface and its impact on long term durability of the asphalt
mixture. For example, Hurley and Prowell (2005a, 2005b, 2006) report that in some
cases lower compaction temperatures used to produce WMA increased the potential
for moisture damage. They speculated that incomplete drying of the aggregate at
lower temperatures could have resulted in the reduced durability of the asphalt
mixture.
Several researchers have evaluated the performance of WMA produced using
different techniques under laboratory conditions (Hurley and Prowell, 2005a;
Barthel et al., 2004; Sousa Filho et al., 2006a, 2006b; Wasiuddin et al., 2007). Most
of these studies compare the performance of WMA to a similar HMA. The findings
from these studies enumerate any potential durability and performance related issues
that may be associated with the use of different WMA technologies. A pressing need
exists to individually address each attribute that makes the WMA different from a
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Influence of Temperature on Aggregate and Mixture Properties 49
HMA. These include: i) efficiency of the technique or additive that is used to
improve binder workability, ii) impact of residual moisture in or on the aggregate on
the performance and durability of the mix, and iii) long term impact of the additive
that remains as a part of the mix (after paving and compaction) on its performance
and durability.
The first objective of this study was to evaluate the impact of reduced mixing
and compaction temperatures on the durability and performance of the Fine
Aggregate Matrix (FAM) produced at different mixing and compaction
temperatures. The performance and durability of an asphalt mixture is strongly
related to the performance and durability of its FAM (Kim and Little, 2004;
Arambula et al., 2007). Previous research studies have evaluated the fatigue
cracking and moisture damage resistance of the FAM portion of several different
asphalt mixtures (Arambula et al., 2007; Masad et al., 2006; Caro et al., 2008). The
FAM used in this study was comprised of aggregate finer than 1.18 mm and asphalt
binder. For each combination of asphalt and aggregate, FAM specimens were
produced at three different mixing and compaction temperatures. The mechanical
behavior of the FAM was evaluated using a Dynamic Mechanical Analyzer (DMA).
A zeolite (type A) based additive was used to produce FAM specimens at
reduced temperatures. The choice of zeolite rather than other additives was based on
the following rationale. One group of specimens was prepared at reduced mixing
and compaction temperatures using hydrated zeolite particles as filler. Addition of
hydrated zeolite particles causes foaming which in turn reduces binder viscosity and
allows for the production of FAM specimens at reduced temperatures. During
mixing and compaction the zeolite particles dehydrate and are retained in the
specimen as a filler. A second group of specimens was prepared at conventional
mixing and production temperatures. In this case dehydrated zeolite particles were
added as a filler to the mix. Use of dehydrated zeolite will not cause foaming and
consequently will not affect the workability of the mix at conventional mixing and
production temperatures. Based on this logic, one is able to produce two groups of
mixtures that are identical composition but that are produced at conventional and
reduced mixing and production temperatures. This cannot be achieved with the wax
based or emulsion based additives.
The second objective of this study was to isolate and evaluate the impact of
reduced mixing temperatures on the residual moisture retained on aggregate
surfaces. Residual moisture retained on the aggregate surface can reduce the bond
strength between the asphalt binder and the aggregate as well as the wettability of
the asphalt binder to the aggregate. Wettability and the bond strength between the
binder and the aggregate are strongly correlated to the performance and durability of
the composite (FAM or asphalt mixture) (Bhasin et al., 2007). A micro calorimeter
was used to measure the total energy of adhesion between the asphalt binder and
aggregates pretreated at different temperatures. The test method was devised such
that the measured total energy of adhesion was only affected by the pretreatment
temperatures of the aggregate.
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50 RMPD – 11/2010. Asphalt Pavements and Environment
2. Materials and methods
Three aggregates with different mineralogies were selected from the Strategic
Highway Research Program (SHRP) Materials Reference Library (MRL): Basalt
(RK), Gravel (RL), and Limestone (RD) (Robl et al., 1991). Two asphalt binders,
AAB and AAD, were also selected from the SHRP MRL. Binder AAB is a PG 58-
22 grade from Wyoming and AAD is a PG 58-28 grade California Coastal product
(Jones IV, 1993). The selection of softer grade asphalt binders renders the
mechanical performance of the mixture more sensitive to the aggregate properties at
test temperatures (around 25°C).
Two test methods were used in this study: (i) the dynamic mechanical analyzer
(DMA) to measure the mechanical properties and damage resistance of the FAM,
and (ii) the micro calorimeter, to measure of the total energy of adhesion between
asphalts and aggregates subjected to different pre-treatment temperatures.
2.1. Dynamic Mechanical Analyzer (DMA)
2.1.1. Materials and specimen preparation
The mixture design for the Fine Aggregate Matrix (FAM) follows the method
described in Zollinger (2005). Fine aggregate particles smaller than 1.18 mm in size
(passing ASTM sieve #16) were used in the mixture design. The fine aggregates
were separated into different size fractions and recombined to match the gradation of
a typical dense graded mixture. The fine aggregates were oven dried for four hours
at the selected mixing temperature prior to use. The aggregates were then mixed
with the asphalt binder and aged for a period of two hours at the selected compaction
temperature.
Each combination of asphalt binder and aggregate was prepared at three different
mixing and compaction temperatures. The first mix was prepared using a mixing and
compaction temperature representative of conventional hot mix asphalt (according to
ASTM D 2493). The other two mixtures were prepared at 20°C and 40°C below
conventional mixing and compaction temperatures. These two mixtures are
representative of WMA. Zeolite was added at the rate of 0.3% by weight of the total
mixture during the preparation of each of the three mixtures. As described
previously, the most important difference was that for the conventional hot mix, the
zeolite was dehydrated by heating it to the same temperature as the aggregate prior
to mixing. Since dehydrated zeolite does not release water during mixing it can be
treated as mineral filler that is incorporated in the FAM. For the mixes prepared at
reduced temperatures, hydrated zeolite stored at room temperatures was added to the
aggregates along with the asphalt binder during mixing. In this case, hydrated zeolite
particles come into contact with the binder, which exists at relatively higher
temperature, and release moisture under these conditions. This causes the zeolite
particles to release their moisture and the binder to foam simultaneously improving
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Influence of Temperature on Aggregate and Mixture Properties 51
the workability of the mixture. After mixing and short term aging, the dehydrated
zeolite particles can be considered to remain in the mix as mineral filler.
The Superpave Gyratory Compactor (SGC) was used to compact the mix and
fabricate samples approximately 80 mm height in a 150 mm diameter mold. The
compaction was set to stop at 87% of the maximum specific gravity (Gmm). The
ends of the 150 mm diameter sample were sawed to achieve the target height of 50
mm. Following this, 12 mm diameter specimens were obtained by coring the 150
mm diameter SGC specimen. The bulk specific gravity of the DMA specimens was
determined and the average air void content of the samples was 15% (+/- 1.5%). The
specimens were then glued using epoxy to metallic holders for testing with the
DMA.
2.1.2. Test procedure
All tests using the DMA were run in the controlled-strain mode. A torsion load
was applied following a sinusoidal wave form at a constant frequency (10 Hz) and
temperature (24oC) for all the tests. The test was performed in two steps: (i) a low
strain amplitude (0.0065%) was applied to obtain the linear viscoelastic properties of
the material; and (ii) a high strain amplitude (0.15%) was applied to induce damage
in the specimens. The progression of damage during the cyclic loading process was
monitored to determine the fatigue damage resistance of the FAM. Both steps were
conducted on at least four replicate specimens for each of the eighteen mixtures, and
at least four more replicates were tested following moisture conditioning. Moisture
conditioning was carried out by partially saturating the specimens (65 - 80%) using a
vacuum pump, and leaving the specimens under water at room temperature for a
period of 12 hours.
2.1.3. Analysis method
At high strain amplitudes, the apparent or measured shear modulus of the
specimen gradually decreases as the number of load cycles increases until the
specimen fails. The results from the DMA were analyzed to obtain three different
measures of FAM performance: (i) the initial state of the FAM quantified based on
its shear modulus (G*) measured at 1200 cycles at a low strain amplitude, and (ii)
the fatigue damage resistance of the FAM determined based on a dissipated strain
energy parameter. Dissipated energy was used as a measure of fatigue life as it
typically has much lower variability compared to the number of load cycles to
failure (Castelo Branco et al., 2008). This was also confirmed based on the data
from this study. In addition, the moisture damage resistance of the FAM was
quantified by comparing the above parameters for moisture conditioned specimens
to the same parameters for unconditioned specimens.
The following dissipated strain energy parameter was used to characterize the
fatigue cracking resistance of the FAM specimens.
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52 RMPD – 11/2010. Asphalt Pavements and Environment
� �**2
02
1NfVE GGW � J [1]
where, *
VEG is the shear modulus of the FAM specimen in its initial state determined
using the low strain amplitude (0.0065%), *
NfG is the shear modulus just before
specimen failure when subjected to the cyclic test at the high strain amplitude
(0.15%), and 0J is the target constant strain amplitude during the fatigue test (0.15%
in this case). In addition to W from Equation [1], other dissipated energy parameters
may also be used to characterize fatigue damage in the FAM specimens. Masad et
al. (2007) present the use of other parameters such as the crack growth index to
characterize the fatigue cracking life of FAM specimens. In the context of this study,
the material properties required to compute the crack growth index could not be
readily determined for specimens produced at the different temperatures.
Furthermore, since the objective of this study was to evaluate the impact of mixing
and compaction temperature on the mechanical behavior of FAM specimens, the
parameter based on Equation [1] was considered to be adequate to characterize the
fatigue cracking resistance.
2.2. Micro calorimeter
The differential isothermal micro calorimeter used in this study was
manufactured by OmniCal Inc., USA. It was used to measure the total energy of
adhesion (TEA) between an asphalt binder solution and an aggregate. The results of
this test are influenced by two main properties: (i) the specific surface area (SSA) of
the aggregates (the higher the SSA, the higher the energy released), and (ii) the
surface free energy of the materials involved in the adhesion process. The SSA of
the aggregates in question was determined using a nitrogen adsorption method with
BET equations (Gregg and Sing, 1967). The following procedure was used for
sample preparation, testing and analysis. More detailed information can be found in
Vasconcelos et al. (2008).
2.2.1. Sample preparation
One of two methods may be used to mix asphalt binder with aggregates in a
calorimetric cell and record the TEA. The first is to measure the TEA at elevated
temperatures when the binder has a very low viscosity and can easily coat the
aggregates. An alternative method is to measure the TEA at room temperatures by
using the asphalt binder in the form of a solution. The latter was used in this study
since the same binder solution could be used at a constant test temperature with only
the aggregates being treated at different temperatures. This method allows one to
isolate the impact of change in aggregate properties on the TEA as a function of the
aggregate treatment temperature.
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Influence of Temperature on Aggregate and Mixture Properties 53
Stock solutions for different asphalt binders were prepared using 1.5 g of asphalt
dissolved in 11 mL of HPLC grade toluene. Previous studies conducted at the
Western Research Institute indicate that asphalt binder in a toluene solution does not
compromise the physio-chemical characteristics of the bitumen. Also, the bitumen
molecules in a toluene solution have similar kinetics to those of molecules in liquid
bitumen at elevated temperatures (WRI, 2001).
Aggregates passing ASTM sieve #100 and retained on ASTM sieve #200 were
used for this test. The aggregates were washed with distilled water to remove dust
particles from surfaces, and then left overnight in the oven. Two vials were used for
each test, one empty (reference) and the other with 8 g r 0.01 g of the aggregate
(sample). Both vials were subjected to the same conditioning procedure. The
aggregates were treated at four different temperatures (90oC, 110oC, 130oC, and
150oC). The heat treatment was carried out by placing the sample and the reference
vials on top of an electronically controlled heating surface. The vials were heated
with open caps for a period of three hours at the specified temperature. Immediately
after removal from the heater, the vials were closed using a poly-propylene cap with
air tight silicone septa. The vials were then allowed to cool down to room
temperature. This procedure allowed the aggregate sample in the vial to retain its
surface characteristics, which were representative of different mixing temperatures.
In addition to the four treatment temperatures, samples of each aggregate type were
prepared at 150°C under vacuum for three hours, and at room temperature (referred
to as no heat). High temperature and vacuum were used together in an attempt to
create an ideal dry aggregate surface.
2.2.2. Test procedure and analysis
The micro calorimeter was used with proprietary data acquisition and analysis
software to record heat flow during the test and to compute the total heat of
immersion. The vial with the aggregate sample was placed in the reaction cell and
the empty vial was placed in the reference cell of the micro calorimeter. Four
syringes of 2 ml capacity each were used to draw the asphalt solution. Two of these
syringes were positioned on top of the reaction vial and two on top of the reference
vial. Heat flow between the sample and reference cell was recorded using the
software that accompanied the micro calorimeter. The cells were allowed to reach
thermal equilibrium. Equilibrium was confirmed as the point when the heat flow
ceased to change over time. After reaching thermal equilibrium, the asphalt binder
solution was injected into the vials. The asphalt binder molecules preferentially
adhere to the aggregate surface reducing the total energy of the system and
producing heat. The heat flow from the reaction cell was recorded over time and the
system was allowed to return to thermal equilibrium. The area under the heat flow
curve over time was integrated to obtain the TEA (or enthalpy of immersion,
immH' ). The magnitude of the TEA is proportional to the bond strength between
the binder and the aggregate surface. A correction in the integrated value is
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54 RMPD – 11/2010. Asphalt Pavements and Environment
necessary due to the difference in free volumes inside the reaction and reference
cells, vHG' . The corrected enthalpy of immersion is determined as follows:
RT
pHHHHH s
vapmeasvmeasimm
0QG '�' '�' ' [2]
where, sQ is the volume occupied by aggregates in the vacuum sealed reaction cell,
0p is the saturation vapor pressure of the toluene at the test temperature, R is the
universal gas constant, T is the test temperature, and vapH' is the change in
enthalpy due to vaporization or heat of vaporization per mole of toluene. A
minimum of three replicates were tested for each of the 36 combinations of two
asphalt binder, three aggregates and six treatment conditions. Figure 1 illustrates the
main steps described above.
Figure 1. Schematic of the micro calorimeter test procedure
3. Results
3.1. Shear Modulus (G*)
In the first step of the DMA test, shear modulus of the FAM specimens was
determined by applying 1200 load cycles in torsion at the low strain amplitude.
Figure 2 illustrates the average and the standard deviation of the mixtures prepared
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Influence of Temperature on Aggregate and Mixture Properties 55
at different mixing temperatures; results were obtained on three or more replicates
for each material.
0.E+00
1.E+08
2.E+08
3.E+08
4.E+08
5.E+08
6.E+08
7.E+08
SH
EA
R M
OD
UL
US
(P
a)
-D
RY
155C
135C
115C
RKAAB RKAAD RLAAB RLAAD RDAAB RDAAD
AGG/ ASPHALT COMBINATIONS
Figure 2. Average and r one standard deviation of the shear modulus at the low
strain amplitude for the different temperatures
3.2. Dissipated Energy (W)
In the second step of the DMA test, fatigue cracking resistance of the FAM
specimens was determined by applying cyclic loading at a higher strain amplitude
until failure occurred. The dissipated energy parameter W was computed for all
replicates of the 18 mixtures using Equation [1]. Figure 3 illustrates the results for
the average and the ± one standard deviation of the dissipated energy parameter, W.
A higher value of this parameter indicates better fatigue cracking resistance.
0.E+00
1.E+02
2.E+02
3.E+02
4.E+02
5.E+02
6.E+02
W -
DR
Y
155C
135C
115C
RKAAB RKAAD RLAAB RLAAD RDAAB RDAAD
AGG/ ASPHALT COMBINATIONS
Figure 3. Average and r one standard deviation of W used as a measure of fatigue
cracking life
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56 RMPD – 11/2010. Asphalt Pavements and Environment
3.3. Moisture damage
To determine the moisture damage resistance of the mixtures, the specimens
were partially vacuum saturated (65-80%) and left under water for a period of 12
hours at room temperature. After removal from the water, the specimens were tested
again using the same strain amplitude, temperature, and frequency as the
unconditioned specimens. The shear modulus at low strain amplitude and the
dissipated energy parameter, W, at high strain amplitude were determined as before.
For each material combination, the values of the shear modulus, G*, and dissipated
energy parameter, W, were normalized with respect to results from the
unconditioned mix prepared at 155°C. This facilitated the comparison of both
factors (production temperature and moisture conditioning) on a common scale. In
other words, for each material combination the normalized values of G* or W
indicate the relative change in the parameter due to the reduction in mixing
temperature and/or moisture conditioning with respect to the unconditioned mix
prepared at 155°C. Figures 4 and 5 illustrate the impact of mixing temperature and
moisture conditioning on G* and W, normalized for each of the six different
material combinations.
115
135
155
115
135
155
115
135
155
115
135
155
115
135
155
115
135
155
DRY
WET
0%
20%
40%
60%
80%
100%
120%
RKAABRKAAD
RLAABRLAAD
RDAABRDAAD
No
rmali
zed
valu
es f
or
Sh
ear
Mo
du
lus
Figure 4. Normalized values for shear modulus
DRY
WET
0%
20%
40%
60%
80%
100%
120%
No
rmali
zed
valu
es f
or
W
RKAABRKAAD
RLAABRLAAD
RDAAB
RDAAD
RKAABRKAAD
RLAABRLAAD
RDAAB
RDAAD
Mixing Temperatures (qC)
Figure 5. Normalized values for W
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Influence of Temperature on Aggregate and Mixture Properties 57
3.4. Total Energy of Adhesion (TEA)
The two asphalt binders (AAB and AAD) were combined with the three
aggregates (RK, RL and RD) treated using six different conditions: at ambient
conditions with no heat treatment, heated to 90qC, 110qC, 130qC, and 150qC, and
heated at 150qC under vacuum. The TEA was measured using three or more
replicates for each of the aforementioned 36 combinations. The SSA of the
aggregates was determined using the multi-point BET method with nitrogen as
adsorbate, and with an outgas temperature of 150qC. The SSAs obtained for RK,
RL, and RD were: 11.292; 3.803; and 0.906 m2/g, respectively.
The results obtained by the integration of the heat flow curve were divided by the
weight of the aggregate after the pre-conditioning state, and then divided by its SSA.
Figure 6 illustrates the final results in ergs/cm2.
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0
50
100
150
200
250
300
350
400
1
To
tal E
ne
rgy o
f A
dh
es
ion
(e
rgs/c
m2
)
NO HEAT
90 Cxxxxxxxxxxxxxxxx 110 C
130 Cxxxxxxxxxxxxxxxx 150 C
150 C + VACUUM
RKAAB RKAAD RLAAB RLAAD RDAAB RDAAD
AGG/ASPHALT COMBINATIONS
Temperature rangecomparable with the
DMA results
Figure 6. Total energy of adhesion between asphalt solution and aggregate
4. Discussion
4.1. Mechanical response of FAM at lower mixing temperatures
The mechanical properties of the unconditioned FAM specimens, as determined
using the DMA, either decreased with a decrease in the mixing temperature or did
not change significantly (Figures 2 and 4). One or more of the following contributed
to the reduction in the stiffness of the FAM at lower mixing temperatures:
1) reduced workability of the asphalt binder (despite addition of the warm mix
additive),
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2) incomplete dehydration or presence of residual moisture in the zeolite
particles, and
3) increase in residual moisture on the aggregate surface resulting in poor
bonding with the asphalt binder.
The interaction of the binder with the WMA additive, in this case the zeolite
particles, could not by itself be the cause of the observed differences in the
properties. This is because the zeolite particles were added to all mixtures, WMA as
well as those produced at conventional mixing and compaction temperatures.
Additional tests were conducted to further evaluate the contribution of causes (ii)
and (iii) to the reduction in the mechanical properties with mixing temperatures.
Sections 4.2 and 4.3 discuss the findings from these tests.
4.2. Residual moisture in zeolite particles at lower mixing temperatures
The Differential Scanning Calorimeter/Thermo Gravimetric Analyzer
(DSC/TGA) was used to determine the amount of water released by the zeolite
particles at different temperatures. A high ramp rate (20°C/minute) was used to
achieve the required temperature followed by a 180 minute isotherm. The reduction
in mass of the zeolite sample was recorded over time. This reduction in mass is due
to the release of water molecules bonded to the zeolite structure. The rapid
temperature ramp was intended to simulate the increase in temperature experienced
by the zeolite particles after coming into contact with the asphalt binder at mixing
temperatures. Different target temperatures of 90°C, 110°C, 130°C, and 150°C were
developed. Table 2 presents the percentage loss in mass of the zeolite (amount of
water released) and the time required for the mass to reach equilibrium from the start
of the temperature ramp (also illustrated in Figure 7). The time required for the mass
of the zeolite sample to reach equilibrium indicates the duration over which the
zeolite particles release moisture before reaching equilibrium.
Table 2. DSC/TGA analysis of zeolite sample
Target Temperature
(°C)
Mass lost (% of hydrated
weight)
Time required for mass to
reach equilibrium from start
of test (minutes)
90 6 65
110 9 115
130 13 100
150 15 55
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Influence of Temperature on Aggregate and Mixture Properties 59
Results from Table 2 clearly indicate that the level of dehydration of the zeolite
particles depends on the mixing temperature. Therefore, zeolite particles in a
mixture prepared at 115°C are likely to contain more residual moisture compared to
the zeolite particles in a mix prepared at 155°C. Consequently, it is likely that
incomplete dehydration of zeolite at lower mixing temperatures resulted in reduced
shear modulus observed using the DMA.
80
84
88
92
96
100
0 50 100 150 200
Time (min)
Wei
ght
(%)
90C
110C
130C
150C
Figure 7. DSC/TGA analysis of zeolite sample
4.3. Interfacial adhesion between the aggregate and binder at lower mixing
temperatures
One of the objectives of this study was to isolate the impact of reduced mixing
temperatures on the residual moisture on aggregate surfaces. This was addressed by
determining the TEA between asphalt binders and aggregates pretreated at different
temperatures. Results indicate that the TEA between the asphalt binder and the
aggregate either decreases slightly or is not significantly affected by the treatment
temperature of the aggregate within the temperature range of 90°C to 150°C (which
is of interest for the production of WMA). The TEA between the asphalt binder and
aggregate was also determined for aggregates that were not subjected to any heat
treatment. In this case, the TEA was significantly lower compared to aggregates
treated between 90°C to 150°C. This was as expected, since aggregates that are not
heated retain substantial amounts of surface adsorbed moisture and result in reduced
adhesion with the asphalt binder. The conclusion would then, in summary, be that
the TEA is substantially different for aggregates that are not heated before mixing
with asphalt binder and aggregates that are heated before mixing with asphalt binder.
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60 RMPD – 11/2010. Asphalt Pavements and Environment
However, the difference in TEA (for aggregates mixed with asphalt binder) when
the aggregates are heated to between 90oC and 150oC before mixing with asphalt
binder is not significant.
A significant increase in the TEA was observed for the limestone aggregate
when the aggregate were treated at 150°C under vacuum as compared to when it was
treated at the same temperature without vacuum. This increase was not substantial
for the other predominantly siliceous aggregates.
The results from this study were compared to the findings from other similar
studies on different types of silicate minerals. Ligner et al. (1989) presented the
variation in the dispersive components of the surface energies for different silicates
(amorphous and crystalline) as a function of thermal treatment. A decrease in the
dispersive component of the aggregate surface energy will reduce its bond strength
with any given asphalt binder. Consequently this should result in a lower TEA when
measured using the micro calorimeter. The results reported by Linger et al. (1989)
for crystalline and amorphous silicates suggest that the TEA (at least for the
siliceous aggregates) should not change significantly for the temperature range used
in this study (90 to 150qC) (Figure 8). This was consistent with the results based on
the TEA measured using the micro calorimeter.
60
65
70
75
80
85
90
95
100
105
50 150 250 350 450 550 650 750
P
G
A
L1
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Silica Pretreatment Temperature (qC)
Figure 8. Variation in D
SJ of amorphous silica [(A) aerosol, (P) precipitated, (G)
gel], and crystalline silica (L1) heat-treated at increasing temperatures, shaded
area reflects 90 to 150qC range (Adopted from Ligner et al., 1989)
4.4. Moisture damage resistance of FAM at lower mixing temperatures
For most given combinations of materials and mixing temperatures, moisture
conditioning resulted in a reduced value of G* and W as compared to the
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Influence of Temperature on Aggregate and Mixture Properties 61
unconditioned specimens. In most cases, the response of the moisture conditioned
specimens prepared at different mixing temperatures followed the same trend as that
of the unconditioned specimens. Another observation was that, for any given mixing
temperature, the FAM prepared using asphalt binder AAD showed better or similar
resistance to moisture induced damage compared to asphalt binder AAB. This is
contradictory to findings from previous studies that indicate that asphalt binder AAD
has poor resistance to moisture induced damage (Little and Bhasin, 2006). The
anomalous moisture resistance of materials with the binder AAD may be explained
as follows.
Addition of divalent cations to the asphalt binder has been shown to result in the
formation of water insoluble salts with carboxylic acids within the mastic. This
promotes the migration of other functional groups such as pyridines, ketones, and
sulfoxides to the aggregate surface in order to form more durable, moisture resistant
adhesive bonds. The above mechanism has been used to explain the improved
moisture damage resistance of certain asphalt binders with the addition of hydrated
lime (Little and Petersen, 2005). Asphalt binders with more polar and asphaltene
content are generally most responsive to the action of the hydrated lime (Plancher
and Petersen, 1976; Petersen et al., 1987). Since the asphalt binder AAD has high
asphaltene content and polar functional groups (Jones IV, 1993), and the zeolite that
was used in this study was rich in calcium ions, the authors hypothesize that the high
moisture damage resistance of binder AAD may be due to the mechanisms described
above.
5. Summary and conclusions
The use of warm mix asphalt has several benefits such as energy savings and
reduced emissions. Several research studies have compared the performance of
HMA to a similar WMA produced using different additives and techniques. While
these comparisons are typically made on a holistic basis, there is a need to
individually assess the source and impact of the various factors that differentiate a
WMA from a HMA. The objectives of this study were to evaluate the impact of
reducing mixing temperatures on the: i) mechanical behavior of the fine aggregate
matrix (FAM) portion of an asphalt mixture, and ii) residual moisture on aggregate
surfaces and concomitant adhesive bond strength with the asphalt binder. In this
study, a calcium based synthetic zeolite was used to prepare FAMs produced over a
range of mixing and compaction temperatures. The key findings from this study are
as follows:
– Results based on the dynamic mechanical analysis of the FAM specimens
indicate that for a given material combination, shear modulus and fatigue cracking
resistance of the FAM typically decreased when mixing and compaction
temperatures decreased.
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– Results based on the micro calorimeter demonstrate that for the non-porous
aggregates used in this study, lower aggregate pretreatment temperatures (within the
range of 90oC to 150oC) did not significantly impact TEA. From this the researchers
infer that residual moisture on the aggregate surfaces at reduced mixing
temperatures (within the range of 90oC to 150oC) did not significantly contribute to
the observed reduction in the shear modulus and fatigue cracking resistance at lower
mixing temperatures.
– A link between the diminished mechanical properties of the FAMs based on
DMA measurements and the reduction in pretreatment temperatures of the aggregate
and the rate of dehydration of the zeolite filler was established. Moisture egress from
zeolite was determined to be slower at lower treatment temperatures, and this could
have resulted in the potential for more residual moisture in mixtures prepared at
lower temperatures. The higher residual moisture content of the FAMs prepared at
lower temperatures is consistent with inferior mechanical properties.
– Based on historical performance data of the binders used in this study, it
appears that the use of a synthetic zeolite rich in calcium ions may help improve the
moisture damage resistance of certain asphalt binders.
An important consideration related to the above findings is that these are
restricted to aggregates with low porosity. For porous aggregates, such as certain
types of limestone, lowering the mixing temperature may influence the moisture
absorbed within the aggregate bulk and consequently contribute to the adverse
performance of mixtures. The authors are conducting further research on the impact
of using porous aggregates with WMA.
Acknowledgements
The authors thank the Federal Highway Administration (contract number
DTFH61-06-C-0021), ICAR for the financial support. Portions of the test methods
on TEA were developed as a part of the Asphalt Research Consortium.
6. References
Arambula E., Masad E., and Epps Martin A., “Moisture Susceptibility of Asphalt Mixtures
with Known Field Performance Using Dynamic Analysis and Crack Growth Model”, 86th
Transportation Research Board, Washington, D.C. 2007.
Bhasin A., Little D.N., Vasconcelos K.L., and Masad E., “Surface Free Energy to Identify
Moisture Sensitivity of Materials for Asphalt Mixes”, Transportation Research Record:
Journal of the Transportation Research Board, No. 2001, Transportation Research Board
of the National Academies, Washington, D.C., 2007, p. 37-45.
Barthel W., Marchand J. P., von Devivere M., “Warm Asphalt Mixes by Adding a Synthetic
Zeolite”, 3rd Eurasphalt & Eurobitume Congress, Vienna, 2004, p. 1241-1249.
Caro S., Masad E., Airey G., Bhasin A., Little D.N., “Probabilistic Analysis of Fracture in
Asphalt Mixtures Caused by Moisture Damage. In: Transportation Research Record:
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ity]
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201
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Influence of Temperature on Aggregate and Mixture Properties 63
Journal of the Transportation Research Board, No. 2057, Transportation Research Board
of the National Academies, Washington, D.C., 2008, p.28-36.
Castelo Branco V.T.F., Masad E., Bhasin A., Little D.N., “Fatigue Analysis of Asphalt
Mixtures Independent of Mode of Loading”, Transportation Research Record: Journal of
the Transportation Research Board, No. 2057, Transportation Research Board of the
National Academies, Washington, D.C., 2008, p.149-156.
Gregg S.J, and Sing K.S.W., Adsorption, Surface Area and Porosity, London, New York,
Academic Press, 1967.
Hurley G.C., Prowell B.D., Evaluation of Aspha-Min Zeolite for Use in Warm Mix Asphalt,
Final Report, NCAT 05-04, Auburn, 2005a.
Hurley G.C., Prowell B.D., Evaluation of Sasobit for Use in Warm Mix Asphalt. Final Report,
NCAT 05-06, Auburn, 2005b.
Hurley G.C., Prowell B.D., Evaluation of Evotherm for Use in Warm Mix Asphalt. Final
Report, NCAT 06-02, Auburn, 2006.
Jones IV, D.R., “SHRP Materials Reference Library: Asphalt Cements: A Concise Data
Compilation”, Strategic Highway Research Program, Report SHRP-A-645, Contract A-
001, National Research Council, Washington, DC, 1993.
Kim Y.-R., Mechanistic Fatigue Characterization and Damage Modeling of Asphalt
Mixtures. PhD Dissertation, Texas A&M University, College Station, Texas, 2003.
Kim, Y.-R., and Little D.N., “Linear Viscoelastic Analysis of Asphalt Mastics”, Journal of
Materials in Civil Engineering (ASCE), Vol. 16, No. 2, 2004, p. 122-132.
Little D.N., and Petersen J.C., “Unique Effects of Hydrated Lime on the Performance Related
Properties of Asphalt Cements: Physical and Chemical Interactions Revisited”, Journal of
Materials in Civil Engineering (ASCE), Vol. 17, No. 2, 2005, p. 207-218.
Little D.N., and Bhasin A., “Using Surface Energy Measurements to Select Materials for
Asphalt Pavement”, Final Report, National Cooperative Highway Research Program,
NCHRP 9-37, 2006.
Ligner G., Vidal A., Balard H., and Papirer E., “London Component of the Surface Energy oh
Heat-Treated Silicas”, Journal of Colloid and Interface Science, Vol. 133, No. 1,
November 1989, p. 200-210.
Masad E., Zollinger C., Bulut R., Little D.N., and Lytton R., “Characterization of HMA
Moisture Damage Using Surface Energy and Fracture Properties”, Proc., Association of
Asphalt Paving Technologists, Vol. 75, 2006, p. 712-754.
Masad E., Castelo Branco V.T.F., Little D., Lytton R., “A Unified Method for the Analysis of
Controlled-Strain and Controlled-Stress Fatigue Testing, International Journal of
Pavement Engineering (In Press). ISSN: 1029-8436. Published in iFIRST, DOI:
10.1080/10298430701551219, 2007.
Plancher H., Petersen J.C., “Reduction of Oxidative Hardening of Asphalts by Treatment with
Hydrated Lime. A Mechanistic Study”, Proc., Association of Asphalt Paving
Technologists, Vol. 45, 1976, p. 1-24.
Petersen J.C., Plancher, H., and Harnsberger P.M., “Lime Treatment of Asphalts to Reduce
Age Hardening and Improve Flow Properties”, Proc., Association of Asphalt Paving
Technologists, Vol. 56, 1987, p. 632-653.
Dow
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by [
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ity]
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Robl T.L., Milburn D., Thomas G., Groppo J., O’Hara K., The SHRP Materials Reference
Library Aggregates: Chemical, Mineralogical, and Sorption Analyses, Report No. SHRP-
A/UIR-91-509." Strategic Highway Research Program, 1991.
Sousa Filho A.C., Silveira L.E.M., Sant’ana H.B., Soares J.B., “Produção de Misturas
Asfálticas a Temperaturas Intermediárias Pela Inserção de Zeólitas” (Asphalt Mixes
Production at Intermediate Temperatures by Addition of Zeolite). 18º Encontro de
Asfalto, Instituto Brasileiro de Petróleo e Gás (18th Asphalt Meeting, Brazilian Institute of
Oil Gas) – IBP, Rio de Janeiro, 2006a.
Sousa Filho A.C., Silveira L.E.M., Sant’ana H.B., Soares J.B., “Avaliação da Infuência de
Zeólitas Sobre as Propriedades Volumétricas de Misturas Asfálticas Produzidas a
Temperaturas Intermediárias” (Volumetric Properties Evaluation of Asphalt Mixes
Produced at Intermediate Temperatures)”. In: XX Congresso da Associação Nacional de
Ensino e Pesquisa em Transportes (XX Conference from the National Association of
Research and Teaching in Transportation), Brasília, Vol. II., 2006b, p. 1057-1068.
Vasconcelos K.L., Bhasin A., Little D.N., “Calorimetric Measurement of Adhesion between
Bitumen and Aggregate used in Asphalt Mixtures”, International ISAP Symposium on
Asphalt Pavements and Environment. Zurich, Switzerland, August, 2008.
Wasiuddin N.M., Selvamohan S., Zaman M.M., Geugan M.L.T.A., “A Comparative
Laboratory Study of Sasobit and Aspha-Min in Warm Mix Asphalt”, 86th Transportation
Research Board, Washington, D.C. 2007.
Western Research Institute (WRI) Fundamental Properties of Asphalts and Modified
Asphalts, Volume I: Interpretive Report. FHWA-RD-99-212, Western Research Institute,
Laramie, WY, 2001.
Zollinger C., Application of Surface Energy Measurements to Evaluate Moisture
Susceptibility of Asphalt and Aggregates, Ph.D. Thesis in Civil Engineering, Texas A&M
University, College Station, Texas, 2005.
Received: 4 February 2009
Accepted: 15 February 2010
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