influence of warm mix asphalt additive.pdf
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INFLUENCE OF WARM MIX ASPHALT ADDITIVE AND DOSAGE RATE ON1
CONSTRUCTION AND PERFORMANCE OF BITUMINOUS PAVEMENTS2
3
Ashley Buss4Graduate Research Assistant (Corresponding Author)5
Iowa State University6
Civil Construction and Environmental Engineering Department7
174 Town Engineering Building, Ames, IA 500118Phone: 563-880-80989
abuss@iastate.edu10
11
Yu Kuang12
Graduate Research Assistant, Iowa State University13
Civil Construction and Environmental Engineering Department14
394 Town Engineering Building, Ames, IA 5001115
ykuang@iastate.edu16
17
R. Christopher Williams18Professor, Iowa State University19
490 Town Engineering Building, Ames, IA 5001120
Phone: 515-294-441921 rwilliam@iastate.edu22
23
Jason Bausano24
Research Engineer, MeadWestvaco25
5255 Virginia Avenue, North Charleston, SC 2940626
Phone: 843-740-229227
jason.bausano@mwv.com28
29
Andrew Cascione30Graduate Research Assistant, Iowa State University31
Civil Construction and Environmental Engineering Department32
394 Town Engineering Building, Ames, IA 5001133
Phone: 520-481-412734
aacascio@iastate.edu35
36
Scott Schram37Bituminous Engineer38
Materials Office39
Iowa Department of Transportation40
Ames, IA 5001041
Phone: 515-239-160442
scott.schram@dot.iowa.gov43
44
45
Submitted on: August 1, 201346
47
TEXT: 523748FIGURES and TABLES: 949
TOTAL WORDS: 748750
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ABSTRACT1Warm mix asphalt (WMA) technology is an effective way to reduce emissions and save energy during asphalt2
paving by reducing production temperatures of hot mix asphalt (HMA). As development of WMA additives3
evolve, many owner-agencies do not know the effect WMA dosage rates have on moisture susceptibility, rutting4
resistance, and mixture compaction at different temperatures. The overall influence of time and temperature on5
mixture performance is also important. In this research, two versions of a commonly used WMA additive6
derived from the forest products industry are evaluated for performance during construction and traffic loading.7
Laboratory specimens with different additive contents (0%, 0.5%, and 1.0%) were compacted at different8
temperatures (115C, 130C, and 145C), to evaluate shear capability parameters. Statistical analyses of the9compaction force index (CFI) indicated the stability of asphalt mixtures at various compaction temperatures.10
Evaluation of moisture sensitivity and rutting performance was conducted using the indirect tensile strength test11
and Hamburg wheel tracking test. Improvements were realized at the 0.5% dosage level; therefore, no economic12
benefit is achieved by increasing the dosage level. Findings from the laboratory were tested in the field to13
evaluate the effect of curing time and temperature on WMA compared with HMA. A plant-produced mix14
included HMA and a WMA mixture produced for the same project. The WMA additive used in the plant project15
is the same additive used in the laboratory study. Loose mix was collected in order to evaluate the influence of16
curing time and temperature of a WMA mixture.17
18
Keywords: warm mix asphalt, compaction, anti-strip, rutting19
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INTRODUCTION1WMA technology contributes to the construction of sustainable roadways by reducing plant mixing2
temperatures 20C to 55C (35F to 100F) lower than typical HMA ( 1). This not only reduces the emission of3
greenhouse gases that include carbon dioxide (CO2) and sulfur dioxide (SO2), but also lowers fuel consumption4
which saves energy and production costs. During jobsite placement of WMA, the lower temperatures reduce the5
amount of fumes and odors inherent when asphalt is produced and placed at high temperatures. Producing6
asphalt at lower temperatures also reduces binder oxidation, which can increase asphalt pavement cracking7
resistance and service life (1).8
There are three main types of WMA technologies. These include foaming, organic wax additives, and9chemical processes. According to a recent survey (2), Evotherm, Sasobit and Double Barrel Green are10
widely used WMA additives or processes used in the United States. Evotherm 3G is a chemical based additive.11
Evotherm does not contain any water but is in the form of a liquid additive which includes chemical agents12
derived from the forest products industry. Sasobit, an organic wax WMA additive, is a Fisher-Tropsch wax.13
These are created by the treatment of hot coal with steam in the presence of a catalyst. Double barrel green is an14
asphalt foaming system that uses water to produce foamed WMA. All of the commonly used WMA products are15
designed to improve bitumen coating of aggregates, workability, and aggregate-binder adhesion.16
As use of WMA technology grows, owner/agencies are interested in knowing how the WMA additives17
affect the compactability of the asphalt mixture during lay down as well as the moisture susceptibility of the18
asphalt pavement. The addition of WMA additives will improve compaction of the asphalt mixture at lower19
temperatures but effectiveness as a compaction aid over a range of temperatures or dosage rates has not been20
widely studied. Compactability of WMA using variable dosage rates of Sasobit and Rediset were evaluated21
and compared with a 0.6% dosage rate of Evotherm 3G. Evotherm 3G was found to provide the best22compactability (3). Further study of dosage rates for surfactant-based chemical WMA additives is needed.23
Likewise, little research has been conducted on the dosage rate of WMA additives as it relates to the24
moisture sensitivity of an asphalt mixture as well. Traditionally, the moisture susceptibility of WMA has been a25
concern for pavement engineers due to the lower mixing temperatures, addition of water that is necessary for26
some WMA technologies, or the change in asphalt-water affinity caused by chemicals or waxes. In most27
chemical based WMA additives, the chemical additives are designed to improve aggregate-binder adhesion to28
improve the moisture susceptibility of the asphalt pavement. Moisture susceptibility improvement has been29
experimentally proven (4); however, it is not known whether dosage rate that optimizes the compactability of30
the asphalt mixture is the same dosage rate that optimizes its resistance to moisture damage. Moreover, little31
research has been conducted to determine if different dosage rates of a WMA additive have different effects on32
mixture compactability and performance. Curing time and temperature is also a factor that has shown to33
influence the performance of WMA (5-7). Recent studies have shown that the stiffness of asphalt mixtures is34
sensitive to curing temperature and temperature of WMA (5-7). The effect that the curing time and temperature35 has on the Hamburg Wheel Tracking Device (HWTD) results should be evaluated to determine if the reduced36
reheating temperature and/or curing time will cause mixes to fail the 14,000 stripping inflection point37
requirement for mixes with equivalent single axle load (ESAL) designs greater than 3 million ( 8).38
39
OBJECTIVES40This research addresses three main objectives. The first objective is to evaluate the effectiveness of additives A-41
1 and B-1 as compaction aids by using shear force index parameters obtained from the Superpave Gyratory42
Compactor (SGC). The second objective is to study how effective these two types of additives perform as liquid43
anti-strip agents by conducting the following two moisture sensitivity analyses:44
1.
Evaluate the indirect tensile strength of moisture conditioned and unconditioned specimens by45
following AASHTO T-283 Resistance of Compacted HMA to Moisture-Induced Damage.46
2.
Utilize the HWTD to test the mixtures susceptibility to moisture damage. 47
The third objective is to evaluate B1 additives effect oncuring time and temperature on a plant-produced WMA48
and HMA.49
50
MATERIALS51
The two WMA technologies used in this study are generically referred to as: WMA-A1 and WMA-B1. The52
properties of each material are listed in Table 1. The main difference between the materials is their viscosity53
with WMA-A1 having a higher viscosity than WMA-B1.54
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TABLE 1WMA additive properties1
WMA-B1 WMA-A1
Physical form Dark amber liquid Dark liquid
Specific gravity at 25C (77F) 0.97 0.999
Conductivity at 25C (77F) (S/cm) 2.2 4.3
Dielectric Constant at 25C (77F) 2 - 10 2 - 10
Viscosity (Pa S)
at 27C (80F) 0.280.56 1.051.90at 38C (100F) 0.150.30 0.470.85
at 49C (120F) 0.080.16 0.200.40
2
TABLE 2 Aggregates and combined gradation for lab produced mix and plant produced mix3
Aggregate % in Mix Source Location Gsb %Abs FAA
1/2 Crushed Eagle City 32 Ames Mine/Martin Marietta 2.581 2.65 47.0
3/4 CL Chip Eagle City 5 Ames Mine/Martin Marietta 2.625 1.92 47.0
1/2 X 4 Quartzite 13 Dell Rapids E. Minnehaha Co/Everi. 2.641 0.14 47.5
3/8 CL Chip Lime Creek 8 Ames Mine/Martin Marietta 2.680 0.44 47.0
Manf. Sand Lime Creek 24 Ames Mine/Martin Marietta 2.659 0.78 45.0
Sand 17 Ames South/Hallett Materials Co. 2.594 1.35 40.0
Hydrated Lime 1 commercially produced
1/2 X 4 Quartzite
1/2 ACC Stone
Manf Sand
Concrete Sand
RAP
9.0%
31%
26%
17%
17%
New Ulm Quartzite Quarry
Greene Limestone- Warnholtz
Greene Limestone- Warnholtz
Greene LS- Cedar Acres Resorts
2RAP09-06 (4.63%)
2.620
2.606
2.705
2.606
2.635
0.72
2.45
1.41
0.76
1.65
45.0
45.0
45.0
38.0
42.4
Job Mix Formula- Combined Gradation
1" 3/4" 1/2" 3/8" #4 #8 #16 #30 #50 #100 #200
Upper Tolerance
100 100 100 91 63 43 18 5.0100 100 95 84 56 38 25 14 5.8 3.4 3.0
100 100 88 77 49 33 10 1.0
Lower Tolerance
Upper Tolerance
100 100 100 94 72 53 24 1.0
100 100 95 87 65 48 32 20 8.8 5.8 4.7
100 100 100 94 72 53 24 1.0
Lower Tolerance
4
The A-1 and B-1 additives were each blended with a PG 64-22 asphalt binder at 0%, 0.5%, and 1.0%5
by weight of binder.6A 12.5 mm (0.5 in.) nominal maximum aggregate size (NMAS) was developed using Superpave7
specifications for the 10 million ESAL level. The optimal binder content that met all Superpave volumetric8
criteria was 5.3%. All samples were compacted in the Superpave Gyratory compactor. The non-shaded portion9
of Table 2 shows the combined gradation for the laboratory mixture as well as each aggregate type, bulk specific10
gravity, percent absorption and fine aggregate angularity. The variable factors for the samples are the two types11
of WMA additive, (A1 and B1) with three different dosage contents (0%, 0.5%, 1%). Therefore, one control12
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and four experimental mixes were developed. The mixes are abbreviated as 0%, A1-0.5%, A1-1%, B1-0.5% and1
B1-1% for subsequent discussion.2
The laboratory study was expanded to include a plant produced (field) mixture in order to identify the3
effects of curing time and temperature on WMA compared with HMA. The field mixture included a control4
HMA mix (no additive) and a WMA (additive B1) mixture. The field mixture is a 12.5 mm (0.5 in.) NMAS and5
a 10 million ESAL level design. The shaded portion of Table 2 shows the combined gradation and aggregate6
properties. The mixture was produced in Floyd County Iowa on a section of US 218 near Charles City. Reduced7
plant temperatures were achieved on this project.8
9
TEST METHODOLOGY10To evaluate the performance of additives A1 and B1 as a compaction aid, the samples were compacted using a11
Superpave Gyratory Compactor at three different mixing/compaction temperatures: 160/145C (320/293F),12
145/130C (293/266F), and 130/115C (266/239F), respectively. The selected design number of gyrations13
(Ndes) was 96 and the maximum number of gyrations (Nmax) was 152. Three replicate samples for each14
mixing/compaction temperature combination were compacted to Nmax.15
The Superpave Gyratory Compactor used in this research was equipped with several advanced16
functions that include measurement of the force and shear capability applied to the specimen. From this data,17
resistive effort curves can be constructed to analyze the stability of the asphalt mixtures at the three different18
mixing/compaction temperature combinations. The resistive effort represents the work done by the SGC per19
unit volume per gyration, assuming the material is perfectly viscous or plastic ( 9). From the resistive effort20
curve, the compaction force index (CFI) and the traffic force index (TFI) are developed to estimate the shear21
force effect from compaction and traffic on asphalt pavements.22The resistive effort curve is separated at 92% of the asphalt mixture maximum theoretical specific23
gravity (Gmm) into a construction effect zone and a traffic effect zone. The CFI refers to the construction side24
and relates to the area under the resistive effort curve below 92% Gmm. For the traffic effect zone, the TFI is25
measured by the area between 92% and 98% Gmmunder the resistive effort curve. In essence, low resistive effort26
is desirable for a contractor to easily compact an asphalt pavement, saving compaction time/effort and reducing27
cost. Therefore, asphalt mixtures with lower CFI values are desired for improved constructability. Inversely,28
higher TFI values are desired for asphalt mixtures as they indicate a greater resistance to stress from traffic29
loading and a reduction in pavement rutting, ultimately extending the pavements service life (10).30
31
Moisture Sensitivity32
In order to evaluate the contribution of the WMA additives as an anti-strip and to determine which type has the33
ability to mitigate moisture sensitivity at the optimum dosage rate, Indirect Tensile Strength (IDT) testing and34
HWTD were conducted. For the laboratory produced mixes, six replicate samples for each test were compacted35to 7%0.5 air voids using the Superpave Gyratory Compactor. Dimensions for AASHTO T-283 cylindrical36
samples are 100 mm (4 in.) diameter and 63.2 2.5 mm (2.5.1in.) in height. Mixing and compaction37
temperatures were 155C (311F) and 145C (293F), respectively. Samples for each test were randomly38
assigned into two subsets of three samples. Moisture conditioning of the samples was conducted according to39
AASTHO T-283.40
One of two subsets was randomly selected to be tested under the dry condition. The dry samples were41
conditioned to a temperature of 25 0.5C (771F) for two hours prior to testing. The moisture-conditioned42
specimens underwent vacuum saturation. The degree of saturation was between 70 and 80 percent for the tested43
specimens and they were each wrapped with a plastic film and then placed in a plastic bag which contained 10 44
0.5 ml of water and sealed. Afterwards, the sealed samples were stored in a freezer at a temperature of -18 3C45
(0 5F). After a minimum of 16 hours, all of samples were removed from the freezer, unwrapped, and46
submerged in a water bath at 60 1C (1402F) with 25mm (1in.) of water above their surface for 24 147
hours. For the last step, before testing is same as control group samples as all of conditioned samples were48 placed in a 25 0.5C (771F) water bath for two hours prior to testing.49
The laboratory evaluation of optimum dosage rate and compactability will ultimately be tested in the field50
where moisture susceptibility requirements are important. Therefore, the influence of curing time and51
temperature was studied for a plant-produced/laboratory-compacted mixture. The curing of WMA field samples52
is currently performed at the reduced compaction temperatures. This portion of the study focuses on how HMA53
and WMA performance results in the HWTD change due to different curing times and temperatures. The intent54
is to determine how long curing should take place and at which temperature in order to have comparable test55
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results in the HWTD between HMA and WMA as well as determine which temperature and time combination1
best simulates the field core HWTD test results. The curing durations chosen were 2 and 4 hours with curing2
temperatures of 120C (248F), 135C (275F), and 150C (302F). A curing time of greater than four hours is3
not generally practical in industry. The cured samples were tested in the HWTD. Only WMA samples were4
cured at reduced temperatures. Table 3 shows the Hamburg pairs that were tested. Each X represents a sample5
that was paired and tested in the HWTD. Cores taken from the field two years after construction were also6
tested.7
8
TABLE 3 Plan of study for investigating curing time and temperature in the HWTD9
Mixes120C (248F) 135C (275F) 150C (302F)
2 Hours 4 Hours 2 Hours 4 Hours 2 Hours 4 Hours
Field Mix HMA --* -- -- -- XXXXXX XXXX
Field Mix WMA XXXXXX XX XXXXXX XXXX XXXXXX XX
*-- indicates no samples were tested for this category10
11
Indirect Tensile Strength12The IDT test was conducted according to AASHTO T-283 to evaluate the mixtures resistance to stripping.13
Moisture damage in asphalt can be influenced by the presence of moisture in the asphalt mixture and will result14
in a loss of strength through the weakening of the bond between the asphalt cement and the aggregate (11). The15
loss of strength due to moisture in the asphalt mixture can be reflected from the tensile strength ratio (TSR). The16
TSR is a numerical index that expresses an HMA pavement s resistance to moisture damage as the ratio of17
retained strength after freeze-thaw conditioning to that of its original strength.18
For testing, the samples were placed between steel loading strips in a hydraulic universal testing19
machine (UTM) within an environmental chamber set at 25C (77F). A load was applied to the specimen at a20
constant rate of 50 mm/min (2 in/min). The maximum compressive load was recorded from which the tensile21
strength can be calculated. The average tensile strength of the moisture conditioned subset group was divided by22
the dry subset group to calculate the TSR.23
24
Hamburg Wheel Track Test25The HWTD is one of several wheel tracking tests used in the United States. It was developed in the 1970s by26
Esso A.G of Hamburg, Germany, (12). The HWTD is used to test an asphalt mixtures susceptibility to moisture27
damage and its resistance to permanent deformation.28
AASHTO T-324 followed for specimen preparation and test setup. Mixing and compaction29
temperatures were 155C (311F) and 145C (293F), respectively. Two cylindrical specimens 150 mm (6 in.)30in diameter and 611 mm (2.40.04 in.) in height were butted into molds and placed under water at 50C31
(122F). Two solid steel wheels with 0.73 MPa (145 psi) contact stress were loaded on the samples and repeated32
20,000 times at 1.1km/h wheel passes for about 6.5 hours or until failure. The test ends automatically when 5033
mm (1.6 in.) rut depth occurs or the preset number of 20,000 wheel cycles is reached (11).34
An important indication moisture damage measured by the HWTD is called the stripping inflection35
point (SIP). The SIP is the number of wheel passes at the intersection of the creep slope and the stripping slope.36
After the number of wheel passes at that point, the moisture damage tends to dominate performance. The37
Colorado Department of Transportation (CDOT) points out that any inflection point below 10,000 wheel passes38
is an indication of moisture susceptibility (13). The HWTD rutting result is defined as the rut depth at 20,00039
wheel passes. Currently, there is no AASHTO specification to limit the maximum rut depth for the HWTD40
testing in the U.S.; however, the Texas Department of Transportation (TxDOT) uses 12.5 mm (0.5 in.) after41
10,000 passes for mixes with a PG 64-22 and the Colorado Department of Transportation (CDOT) suggested42
that a rut depth of 10 mm (0.4 in.) after 20,000 passes as the criterion ( 14).4344
TEST RESULTS AND DISCUSSION45Test results were evaluated based upon how the additive types, A1 and B1, contribute to both the stability of the46
asphalt mixtures and the results for IDT and HWTD, while taking into consideration the various additive dosage47
levels as well as the mixing and compaction temperature combinations. Statistical analysis was conducted using48
JMP statistical software (15).49
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Figure 1 displays the average values of the compaction force index (CFI) shown with 95% confidence1
intervals. The error bars in Figure 1 and Figure 2 show little difference between the additive dosage levels for2
both CFI and TFI. ANOVA testing confirmed there are no statistically significant differences in additive type3
and no interaction effects for dosage rate and temperature among additive types A1/B1 at an =0.05 level.4
However, for A1 and B1, there are the same significant differences in temperature when Tukey honestly5
significant difference (HSD) multiple comparison testing was performed. The compaction temperature of 145C6
(293F) is not significantly different with 130C (266F) and 115C (239F), but 115C (239F) is significantly7
different with 130C (266F). The statistical difference between 115C (239F) and 130C (266F) indicates8
the compaction temperature of 115C (239F) may be too low for this mixture and better compaction is9achieved at 130C (266F). The CFI at 115C (239F) also has the highest average for each mixture tested. The10
largest average reduction in the CFI values occurred for B1-1% followed by A1-0.5% but variability in the CFI11
parameter does not allow for statistical conclusions at an -level of 0.05. An ANOVA analysis of CFI data12
confirmed that there are no statistically significant differences in the variable dosage levels and no interaction13
effects between additive type and compaction temperature exist. The ANOVA analysis suggests some statistical14
differences between compaction temperatures but no overall trend applies to all dosage rates and temperatures.15
These differences can be observed by the overlapping of confidence intervals in Figure 1.16
17
18FIGURE 1Effects of different additives and dosage levels on the CFI.19
20
Figure 2 shows the TFI values with error bars that represent 95% confidence interval. The average TFI21
for the control shows the largest sensitivity to temperature, on average. The ANOVA analysis showed no22
significant differences in additive type or dosage level and no significant interactions between factors.23
A comparison between A1-0.5% and B1-0.5%, showed no statistically significant differences in24
additive type and no interactions between additive and temperature. The highest mean TFI was measured at25
115C (239F) compaction temperature and is statistically different from the mean TFI at 130C (266F). On26
average, the control samples had a higher TFI at the lower temperatures of 130C (266F) and 115C (239F).27
Comparing between A1-1% and B1-1% TFI, there are no statistically significant differences in the28
factors of additive type, temperature and the interaction between additive and temperature.29
30
0.0
100.0
200.0
300.0
400.0
500.0
600.0
700.0
800.0
CFI
145 C
130 C
115 C
Control B1- 0.5% B1-1% A1-0.5% A1-1%
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1FIGURE 2Effects of different additives and dosage levels on the TFI.2
3
The TSR and indirect strength values with 95% confidence intervals are shown in Figure 3. The TSR4
ratio was calculated by using the conditioned mix strength with an additive as the numerator and the5 unconditioned mix strength without additive as the denominator. The denominator of the TSR ratio is always the6
dry strength of the 0% additive content mix. By keeping a consistent denominator, the data does not add a7
confounding factor. This method accurately reflects the difference in TSR values.8
All TSR values meet the required 80% minimum. The ANOVA analysis shows no statistical difference9
between additive type and content; however, on average the 0.5% dosage rate has the highest average TSR10
values.11
12
13FIGURE 3Iowa DOT TSR values for the control and treatment conditions.14
15
The mixes were evaluated using the HWTD test using laboratory compacted specimens which contain16
two types of additives (A1, B1) and three content level (0%, 0.5% and 1%) organized as a full factorial design.17
Three replicates were prepared at each combination of factor levels, which required a total of 36 specimens.18
0.0
500.0
1000.0
1500.0
2000.02500.0
3000.0
3500.0
4000.0
4500.0
5000.0
TFI
145 C
130 C
115 C
Control B1- 0.5% B1-1% A1-0.5% A1-1%
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0
200
400
600
800
1000
1200
1400
IowaDOTTSR
IndirectTensileStrength,
kPa
IDT Ratio
IDT Strength
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Mixing and compaction temperatures were 155C (311F) and 145C (293F), respectively. The laboratory mix1
samples were cured for 2 hours at the compaction temperature.2
According to the literature review, it is not inevitable that HWTD results will show all three3
characteristic variables: creep slope, stripping slope and SIP. For the result of the HWTD test, no stripping4
deformation occurred. Therefore, only the creep slope and the maximum rut depth at 20,000 passes were used to5
analyze the data.6
Based on the data comparison, adding either additives, A1 or B1, can reduce the rutting depth when7
mixed and compacted at the same temperature. The mix types with the WMA additive (A1 or B1) present better8
rutting resistance with a reduced creep slope as compared to the HMA samples. The A1-0.5% and A1-1.0%9performed almost same as the B1-0.5% and B1-1%, respectively.10
With respect to the creep slope, the ANOVA analysis indicates statistical differences in additive type11
and dosage rate. The B1 additive has the lowest mean creep slope and is statistically different than A1.12
Moreover, the 0%-control specimens show the highest mean creep slope and is significantly different from other13
mixes containing WMA additives at all dosage rates (0.5%, 1.0%), as shown in Figure 4.14
Figure 4 shows the rut depth at 20,000 passes. By examining the rut depths, a comparison of dosage15
level demonstrates the impact the additives have on rutting performance in the asphalt mixes. The mixes with16
the WMA additive exhibited statistically lower amounts of rutting than the mix with no WMA additive. There17
were no differences in rutting performance between the 0.5% and 1.0% dosage rate or between the A1 and B118
additives. Therefore, adding at least 0.5% of the A1 or B1 additives will improve an asphalt mixtures resistance19
to rutting.20
21
22FIGURE 4Average rut depth at 20,000 passes and creep slope for control and treatment samples.23
24
The curing study was performed on plant produced mixes using the HWTD to investigate the impact of25
time and temperature on the SIP results. The curing times were either 2 or 4 hours and the temperatures were26
120C (248F), 135C (275F) and 150C (302F). All of the mixes included in this study used the same WMA27additive. The HWTD sample dimensions were 150mm (6 in.) diameter and 60.3 mm (2.374 in.) in height.28
Cores were sawn to the test sample height.29
The HWTD test results for the cured-lab compacted samples were compared against the cores taken30
from the roadway. Figure 5 shows the comparisons for all samples including WMA and HMA. The dash lines31
represent only 2 hours of curing. The WMA and HMA cores performed well with no evidence of stripping. The32
HMA mixes are denoted in the graph as red or orange lines. The WMA is shown in blue or green lines. The33
WMA samples with 2 hours of curing at 120C (248F) and 135C (275F) were the poorest performing mixes.34
0.0E+00
2.0E-05
4.0E-05
6.0E-05
8.0E-05
1.0E-04
1.2E-04
1.4E-04
1.6E-04
1.8E-04
0
1
2
3
4
5
6
0% A1-0.5% A1-1% B1-0.5% B1-1%
Cr
eepSlope(mm/pass)
RutDept
hat20000Passes(mm)
Rutting Depth
Creep Slope
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10
HMA and WMA samples cured for 2 hours at 150C (302F) displayed similar test results. Increased1
conditioning time of 4 hours also increased performance in the HWTD. The HMA and WMA both showed2
similar rutting depths when cured at 4 hours at 150C (302F) and this was similar with the rutting depths of the3
tested cores. The data for the WMA samples cured for four hours at 150C (302F) showed some noise in the4
data but there was not significant rutting or signs of stripping. The SIP values are shown in Figure 6. The HMA5
samples cured for 2 hours at 150C (302F) showed similar values to the WMA samples cured for 4 hours at6
120C (248F). Samples conditioned for the two hour curing time at 120C (248F) and 135C (275F) showed7
low stripping inflection points and would not pass the 14,000 SIP requirement for this 10 million ESAL mix but8longer curing times or higher temperatures would increase the SIP values so that the required minimum SIP9
would be met.10
11
12
FIGURE 5Hamburg results comparing curing temperature and time.13
14
15FIGURE 6 SIP comparing HMA/WMA, curing time and temperature.16
17
-16.0
-14.0
-12.0
-10.0
-8.0
-6.0
-4.0
-2.0
0.0
0 5,000 10,000 15,000 20,000
RutDepth
,mm.
Pass Number
WMA Core HMA Core WMA 2 hrs 120CWMA 2 hrs 135C WMA 2 hrs 150C HMA 2 hrs 150WMA 4hrs 120C WMA 4 hrs 135C WMA 4 hrs 150CHMA 4 hrs 150C
0
2000
4000
6000
8000
10000
12000
14000
16000
1800020000
NumberofPasses
TRB 2014 Annual Meeting Paper revised from original submittal
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8/10/2019 influence of warm mix asphalt additive.pdf
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8/10/2019 influence of warm mix asphalt additive.pdf
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TRB 2014 A l M i P i d f i i l b i l
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