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Figure 5. Gyratory compactor
with shear stress measurement.
Figure 4. University of New Hampshire workability
device.
2.6 Phase II Studies
2.5 Revised Preliminary Mixture In Phase II of NCHRP Project 09-43, three studies were con-
Design Procedure ducted to evaluate the revised preliminary procedure. The
The preliminary mixture design procedure was modified Phase II studies included (1) a laboratory mixture design study,
based on the findings of the Phase I studies. These modifica- (2) a field validation study, and (3) a WMA fatigue study. The
tions generally involved substituting tentative criteria devel- sections that follow describe these studies.
oped from the Phase I studies into the appropriate sections of
the preliminary mixture design procedure. The criteria that Table 12. Mixture used in the
were developed are discussed in Chapter 3. No modifications workability study.
were made to the mixture analysis portion of the procedure.
Property
Value
Sieve Size
Table 11. Screening study for workability tests. 3/4 in 100.00
1/2 in 99.00
Factor Levels Details 3/8 in 86.00
Mixtures 1 12.5 mm #4 57.00
Gradation
PG 64-28 control #8 40.00
(% Passing)
Binders 3 PG 64-28 with Sasobit #16 28.00
PG 64-28 with Advera #30 20.00
UMass Prototype (auger) #50 12.00
Workability Modified Nynäs #100 6.00
5
Tests Gyratory Shear Stress #200 3.20
University of New Hampshire Asphalt Content, % 5.40
300°F Ndesign 75.00
Temperatures 3 245°F Design Air Voids, % 3.70
190°F Design VMA, % 14.60
Replicates 2 -- Design VFA, % 74.50
Note. -- = No qualifying details for replicates. Fines to Effective Asphalt Ratio 0.69
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2.6.1 Laboratory Mixture Design Study where
The objective of the laboratory mixture design study was to WMA = population mean for WMA mixtures,
test the engineering reasonableness, sensitivity, and practicality HMA = population mean for HMA mixtures,
of the revised preliminary mixture design and analysis proce- d = average of the differences between WMA and HMA
dure for WMA. The study was designed to compare properties mixtures,
of WMA mixtures designed according to the revised prelimi- sd = standard deviation of the differences, and
nary procedure with those of corresponding HMA mixtures n = number of mixtures compared.
designed according to AASHTO R 35. As previously mentioned, Table 13 presents the experimental design for the laboratory
the underlying principle for the mixture design procedure for mix design study. In this study, various properties for WMA
WMA is to produce mixtures with strength and performance and corresponding HMA mixtures were evaluated using paired
properties similar to those of HMA. The experimental design difference comparisons. Comparisons were made for Advera,
for the mix design study was a paired difference experiment. Evotherm, and Sasobit. For the WMA processes, two mixing
This design is commonly used to compare population means-- and compaction temperatures were used: one above the prelim-
in this case, the properties of properly designed WMA and inary grade bumping temperature from the Phase I binder
HMA mixtures for the same traffic level, using the same aggre- grade study and one below. The HMA mixtures and the WMA
gates with the same gradation. In this design, differences mixtures above the grade bumping temperature were made
between the properties for WMA and HMA are computed for with PG 64-22 binder. Also, the WMA mixtures with RAP and
each mixture included in the experiment. If the two design Sasobit below the grade bumping temperature were made with
procedures produce mixtures with the same properties, then PG 64-22 because both RAP and Sasobit increase the high-
the average of the differences will not be significantly different temperature grade of the binder. The Advera and Evotherm
from zero. The difference for an individual mixture may be WMA mixtures below the grade bumping temperature were
positive or negative, but the average difference over several made with PG 70-22 binder. All mixtures were short-term con-
mixtures should be zero. A t-test is used to assess the statistical ditioned for 2 h at the compaction temperature. The six mix-
significance of the average difference as summarized below. tures were selected to provide a range of gyratory compaction
levels and aggregate absorptions. One half of the mixtures
included RAP at 25 percent. A total of 24 mixture designs were
Null hypothesis: WMA - HMA = 0 prepared using either AASHTO R 35 for HMA mixtures or the
Alternative hypothesis: WMA - HMA > 0 or WMA - HMA < 0 revised preliminary WMA mixture design procedure.
(as appropriate) For the experimental design in Table 13, separate compar-
isons were made between the properties of HMA and each of
d
Test statistic : t= the WMA processes. Comparisons were made for the follow-
sd ing properties:
n
Rejection region: Reject the null hypothesis and accept · Design air voids, vol %
the alternative hypothesis if t > t for · Design VMA, vol %
n - 1 degrees of freedom. · Effective binder content (VBE), vol %
Table 13. Mix design experiment.1
Mixture Identification Process
No. Evotherm
Aggregate Advera Sasobit
Ndesign RAP2 HMA G3
Absorption WMA WMA
WMA
1 50 High3 Yes 320/3104 225/215 225/215 270/260
2 50 Low5 No 320/310 270/260 270/260 225/215
3 75 Low Yes 320/310 270/260 225/215 270/260
4 75 High No 320/310 225/215 270/260 225/215
5 100 High Yes 320/310 270/260 270/260 225/215
6 100 Low No 320/310 225/215 225/215 270/260
1
Low-temperature Advera and Evotherm WMA use PG 70-22; all other mixtures use PG 64-22.
All mixtures short-term conditioned 2 h at the compaction temperature.
2
RAP content 25 percent in all mixtures containing RAP.
3
High absorption > 2.0 percent.
4
XXX/XXX, e.g., 320/310, denotes mixing/compaction temperatures, °F.
5
Low absorption < 1.0 percent.
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· Binder absorption, wt % were composed of gravel and limestone from Pennsylvania. The
· Design binder content, wt % gravel material in these mixtures was selected for its historically
· Effective binder content, wt % high absorption, but the material supplied had lower absorp-
· Coating tion than expected, which resulted in lower water absorptions
· Gyrations to 8% air voids at the compaction temperature for the planned high-absorption mixtures. For the 50 and
· Gyrations to 8% air voids at the compaction temperature 75 gyration designs, the high-absorption mixtures have approx-
minus 54°F (30°C) imately twice the water absorption of the low-absorption
· Density at Nmax mixtures. For the 100 gyration design, the planned low- and
· Dry tensile strength high-absorption mixtures have approximately the same water
· Conditioned tensile strength absorption. This difference was taken into account when per-
· Tensile strength ratio forming statistical analysis of the experiment results. The same
· Flow number RAP was used in the three mixtures that incorporated RAP.
· Rutting resistance Table 15 presents the gradation and binder content of the RAP
material that was used. The RAP binder had a continuous per-
These properties are all obtained as part of the WMA mix- formance grading of PG 95.9 (33.9) -13.1. The RAP was
ture design process. The HMA mixtures required design in obtained from Loudoun County Asphalt in Leesburg, VA. All
accordance with AASHTO R 35, flow number testing, and of the RAP mixtures used 25 percent RAP, which resulted in
assessment of compactability at the lower temperature as pro- an RAP binder contribution of approximately 1.1 percent by
posed in the WMA mixture design procedure. weight. NuStar Asphalt Refining, LLC, provided the binders for
Table 14 presents the six mixtures that were included in the this study from their Paulsboro, NJ, refinery. The dosage rate of
mix design study. The volumetric properties presented for these the Sasobit was 1.5 percent by weight of the total binder (virgin
mixtures are those obtained from conducting an HMA mixture plus RAP) in the mixture. The dosage rate of the Advera was
design in accordance with AASHTO R 35 and AASHTO M 323. 0.25 percent by total mix weight. Binders containing the
The low-absorption mixtures were composed of limestone or Evotherm G3 were provided premixed by NuStar Asphalt
diabase aggregate from Virginia. The high-absorption mixtures Refining, LLC, and the Evotherm dosage rate was not adjusted
Table 14. Mixtures used in the mix design experiment.
Mix Number 1 2 3 4 5 6
Design Gyrations 50 50 75 75 100 100
Aggregate Water Absorption, % 1.5 0.8 1.0 1.6 1.2 1.3
RAP Yes No Yes No Yes No
NMAS1 9.5 mm 9.5 mm 9.5 mm 9.5 mm 9.5 mm 9.5 mm
PA Gr avel VA Diabase PA Gravel
Coarse VA Limestone PA Gravel VA Diabase
RAP RAP RAP
Aggregate PA Limestone VA Diabase
PA Limestone PA Limestone VA Diabase
Sources Fine PA Gr avel VA Limestone Natural Sand
PA Gravel RAP Natural Sand
RAP RAP
RAP LCA, Leesburg, VA None LCA, Leesburg, VA None LCA, Leesburg, VA None
Sieve Size, mm
12.5 100 100 100 100 100 100
9.5 97 94 94 98 97 98
4.75 61 50 54 63 63 53
2.36 43 32 38 44 41 40
Gradation
1.18 32 22 28 32 26 31
0.6 25 14 21 22 17 22
0.3 13 10 12 12 11 12
0.15 6 7 8 5 7 7
0.075 3.8 5.4 5.2 3.0 4.6 4.8
FAA 44.1 45.8 46.1 43.5 45.4 48.3
Aggregate CAA2 98/95 100/100 100/99 98/95 98/95 100/100
Properties Flat & Elongated 4.5 1.6 2.7 7.4 4.4 7.6
Sand Equivalent 93.2 75.0 59.4 80.2 91.9 76.7
Binder Content, wt % 6.4 6.8 5.5 6.3 6.0 5.7
Effective Binder Content, wt % 5.6 6.1 4.8 5.3 5.4 4.7
Air Voids, vol % 3.6 4.0 3.9 4.3 4.0 3.7
Voids in Mineral Aggregate, vol % 16.4 18.0 15.9 16.3 16.4 15.1
Effective Binder Content, vol % 12.8 14.0 12.0 12.0 12.4 11.4
Voids Filled With Asphalt, % 78.0 77.8 75.5 73.6 75.6 75.5
Dust to Effective Asphalt Ratio 0.7 0.9 1.1 0.6 0.9 1.0
1 NMAS = Nominal maximum aggregate size.
2 CAA = Coarse aggregate angularity.
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Table 15. Properties of RAP used in the mixture and analysis procedure. The parts of the revised preliminary
design experiment. procedure addressed by the validation included the following:
Property
Sieve Size Value · Binder grade selection
(mm) · RAP
12.5 100 · Short-term oven conditioning
9.5 92
· Specimen fabrication and compactability
4.75 63
Gradation 2.36 44 · Moisture sensitivity
(% Passing)
1.18 32 · Rutting resistance
0.6 24
0.3 17
Table 16 summarizes the mixtures that were included in the
0.15 11
0.075 7.8 validation study. Materials from a total of 16 mixtures from
Asphalt Content, wt % 4.4 six projects were sampled. The validation mixtures included a
Continuous Performance Grade PG 95.9 (33.9) -13.1 wide range of processes. Four mixtures were HMA control;
Aggregate Bulk Specific Gravity 2.877
three mixtures used the Advera WMA process; two mixtures
Aggregate Water Absorption, % 1.01
Fine Aggregate Angularity, % 44.4 used the Evotherm WMA process; two mixtures used the LEA
Crushed Aggregate Fractured Faces (1 Face), % 99.3 process; two mixtures used plant foaming processes; and three
Crushed Aggregate Fractured Faces (2 Faces), % 94.3 mixtures used Sasobit. The WMA production temperatures
Flat and Elongated Particles, % 0.5
ranged from 210°F to 275°F (99°C to 135°C), and the WMA
compaction temperatures ranged from 195°F to 250°F (90°C
for the RAP binder in the Evotherm RAP mixtures. The mix- to 121°C). Most of the WMA mixtures were produced around
tures incorporating gravel required an anti-strip additive. Akzo- 250°F (121°C) and compacted around 230°F (121°C). The
Nobel WETFIX 312 was used in the HMA, Sasobit, and Advera mixes included PG 58 and PG 64 binders. Only one mixture
mixtures. The dosage rate for the anti-strip additive was included RAP.
0.25 percent by weight of the total binder in the mixture. Rep- Table 17 summarizes the analyses that were completed in
resentatives of Evotherm recommended that the anti-strip not the validation study. Initial validation of the findings from the
be added when using the Evotherm G3 additive. Phase I binder grade study was completed using recovered
binder grading and estimates of rutting from the MEPDG rut-
ting model using measured dynamic moduli from plant mix-
2.6.2 Field Validation Study
tures (1). Recovered binder grading data were collected on all
The objective of the field validation study was to use prop- of the 16 validation mixtures. Rutting estimates were made
erties of laboratory- and field-produced WMA to validate only for the mixtures included in the Colorado I-70, Yellow-
selected parts of the revised preliminary WMA mixture design stone National Park, and New York Route 11 projects.
Table 16. Field validation mixtures.
Temperature
Project Process (°F) Mix Type
Production Compaction
HMA Control 280 260 9.5 mm, PG 58-28,
Colorado I-70 Advera 250 230 75 gyrations
Evotherm DAT 250 230
Sasobit 250 230
HMA Control 325 315
Yellowstone 19 mm, PG 58-34,
Advera 275 250
National Park Hveem
Sasobit 275 245
9.5 mm, PG 64-22,
NY Route 11 LEA 210 205
65 gyrations
PA SR2007 HMA Control 320 300 9.5 mm, PG 64-22,
Evotherm DAT 250 230 50 gyrations
HMA 310 275
PA SR2006 Advera 250 230 9.5 mm, PG 64-22,
and PA Gencor Ultrafoam GX 250 230 75 gyrations
SR2012 LEA 210 195
Sasobit 250 230
9.5 mm, PG 64-22
Monroe, North Astec Double Barrel
275 260 with 30% RAP,
Carolina Green
75 gyrations
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Table 17. Summary of validation study analyses.
Component Phase I Study Validation Analyses
Recovered binder grading.
Binder Grade Selection Binder Grade Selection Estimated rutting using MEPDG
rutting model.
Mixing of RAP and New Mixing analysis of plant-produced
RAP Study
Binders WMA with RAP.
Compare maximum specific gravity
Short-Term
Short-Term Conditioning and tensile strength of plant mixtures
Conditioning Study
with laboratory mixtures.
Volumetric properties of WMA
Process-Specific Specimen- Literature Review and mixtures.
Fabrication Procedures Research in Progress WMA mixture design for plant
foaming processes.
Compare compactability of field
Compactability Workability Study
mixtures to reported workability.
Compare moisture sensitivity results
Literature Review and
Moisture Sensitivity for HMA control and WMA
Research in Progress
mixtures.
Literature Review and Compare flow numbers for HMA
Rutting Resistance
Research in Progress control and WMA mixtures.
A binder mixing analysis using dynamic modulus and WMA mixture design was completed using a Wirtgen WLB-10
recovered binder testing on plant mix from the North Carolina laboratory foaming plant to assess the practicality of using this
project was used to validate that RAP and new binders mix at type of equipment for mixture design work. The compactabil-
WMA process temperatures. The North Carolina project was ity of the HMA and WMA mixtures from the field validation
the only project in the field validation study that included RAP. study was used to validate the tentative compactability criteria
The short-term oven conditioning process recommended in developed in the Phase I workability study.
the Phase I short-term oven conditioning study was validated Finally, specimens of WMA and HMA prepared from labo-
by comparing the maximum specific gravity of plant mixtures ratory mixtures were subjected to moisture sensitivity and flow
with laboratory-prepared mixtures and comparing the ten- number testing as required by the preliminary WMA mixture
sile strength of plant-mixed, laboratory-compacted samples design procedure. A comparison was made between the results
with the tensile strength of laboratory-mixed, laboratory- of the HMA control and the results of the WMA mixture for
compacted samples. Fifteen of the 16 validation mixtures were each project.
included in the analysis. The New York Route 11 LEA mixture
was not included because the LEA additive used on the project
2.6.3 Fatigue Study
was not available.
The process-specific specimen-fabrication procedures for One of the potential benefits of WMA mixtures is improved
WMA contained in the preliminary WMA mixture design pro- fatigue characteristics compared to HMA mixtures due to the
cedure and the compactability criteria developed in the Phase I reduced aging that occurs during plant mixing at the lower
workability study were validated by preparing laboratory WMA WMA process temperatures. Phase II included a brief study to
mixtures replicating the field mixtures. Volumetric properties evaluate the fatigue resistance of WMA compared to HMA.
of the laboratory-prepared specimens were used to validate the The experimental design for this study is presented in Table 18.
process-specific specimen-fabrication procedures. Addition- Two of the mixtures from the mix design experiment were
ally, for the two projects that used plant foaming processes, a used in this study. Continuum damage fatigue tests were
Table 18. Experimental design for the WMA fatigue study.1
Mixture Identification Process
No. Ndesign Aggregate RAP HMA WMA WMA WMA
Absorption Organic Foam Chemical
4 75 High No 320/3102 250/240 250/240 250/240
6 100 Low No 320/310 250/240 250/240 250/240
1
Mixtures from Table 14. All mixtures use PG 64-22 binder.
All mixtures short-term conditioned 2 h at the compaction temperature. All mixtures
long-term conditioned 120 h at 185°F.
2
XXX/XXX, e.g., 320/310, denotes mixing/compaction temperatures, °F.
