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I. Special Mixture Design Considerations and Methods for Warm Mix Asphalt (WMA) 21
Table 14. Flow number
criteria for WMA mixtures.
Traffic Level, Minimum Flow
Million ESALs Number
<3 NA
3 to < 10 30
10 to < 30 105
30 415
1. Specimens compacted to 7.0 ± 0.5% air voids,
2. Test temperature equal to the 50% reliability, 7-day maximum pavement temperature as
determined using LTPPBind version 3.1. For surface courses, compute the test temperature
at a depth of 20 mm. For intermediate and base courses, compute the test temperature at the
top of the layer.
3. Unconfined testing with a repeated deviator stress of 87 psi (600 kPa) and a contact deviator
stress of 4.4 psi (30 kPa).
Lower criteria are used for WMA compared with HMA because of the reduced short-term con-
ditioning. Recall that HMA used in making specimens for performance testing is conditioned for
4 hours at 275°F (135°C) while WMA used for making specimens for performance testing is con-
ditioned for only 2 hours at the planned compaction temperature, which is usually lower than 275°F
(135°C). The shorter conditioning time and lower condition temperature result in less aging for the
binder in the WMA specimens. The WMA flow number criteria are listed in Table 14.
The rutting resistance of WMA mixtures can be improved using the same adjustments
described in Chapter 8 for HMA. These include
· Increasing the binder high-temperature grade
· Adding RAP to the mixture
· If the binder is not modified, considering using a polymer-modified binder of the same grade
or one high-temperature grade lower
· If the binder is polymer-modified, trying a different type of modified binder
· Increasing the amount of mineral filler in the mix and adjusting the aggregate gradation if
necessary to maintain adequate VMA
· Decreasing the design VMA value, if possible, by adjusting the aggregate gradation
· Replacing part or all of the aggregate (fine or coarse or both) with a material or materials having
improved angularity
If a different asphalt binder is used in the mix, the volumetric composition should not
change. However, if other aspects of the mix design are changed, the volumetric composition
might change significantly which will require further refinement of the mix prior to further
rut resistance testing.
Step 11. Compile Mix Design Report
The mix design report is compiled in the same manner as described for HMA. In many states,
standard forms must be filled out by producers and submitted to the appropriate state agency
or office for approval. In some cases, engineers or technicians may wish to develop their own
mix design reports, for internal purposes or for use on private jobs. In such cases, the following
information should be included in the report:
· The organization that performed the mix design
· The name of the technician or engineer responsible for developing the mix design

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22 Special Mixture Design Considerations and Methods for Warm Mix Asphalt
· The date the mix design was completed
· The name of the client for which the mix design was developed
· The name of the project for which the mix design was developed (if applicable)
· General mix design information, including the type of mix (surface course, intermediate
course, base course), the nominal maximum aggregate size, the design traffic level, the Ndesign
value, and any special requirements
· Complete aggregate information, including for each aggregate the producer, the size designation
of the aggregate, gradation, specific gravity, and all applicable specification properties
· Binder information, including the binder PG grade and the name of the supplier
· Composition of the mixture, including the design air void content, the design VMA, the
design VBE, the mineral filler content, the target dust/binder ratio and the estimated unit
weight for the mix
· The planned production and compaction temperatures
· The results of the evaluation of coating
· The results of the compactability analysis
· The results of moisture resistance testing
· The results of rut resistance testing, if applicable (generally for mixtures designed for traffic
levels of 3 million ESALs and over)
HMA Tools includes a comprehensive mix design report that contains all of this information
and additional information on the results of trial mixtures evaluated during the mix design
process. This HMA Tools report might be useful to some engineers and technicians for internal
purposes and might also serve as a template for those wishing to develop their own customized
mix design reports.
Example WMA Mix Design
A 12.5-mm WMA mix is to be designed, using a foaming process. The gradation of the aggregates
to be used is listed in Table 15; the table includes the gradation of the RAP to be included in the
mix design. Other test properties for the four aggregates are listed in Table 16. The RAP was
separated into fine and coarse fractions for testing, and the results are also included in Table 16.
The specified binder grade is PG 64-22, while the grade of the binder extracted from the RAP is
PG 76-16. Binder test data are given in Table 17. The binder content of the RAP is 5.2% by total
weight. The design traffic level is 6 million ESALs.
Referring to Table 1, the steps in a WMA mix design are as follows:
1. Gather information
2. Select asphalt binder
Table 15. Aggregate gradations for WMA example.
% Passing by Weight
Sieve No. 67
Size Stone 1B Stone Screenings Sand RAP
(mm)
19.000 100.0 100.0 100.0 100.0 100.0
12.500 72.0 91.0 100.0 100.0 100.0
9.500 48.0 48.0 100.0 100.0 95.0
4.750 8.0 10.0 81.0 100.0 76.0
2.360 6.0 5.0 45.0 91.0 56.0
1.180 4.0 3.0 30.0 48.0 42.0
0.600 4.0 3.0 20.0 36.0 28.0
0.300 3.0 3.0 16.0 21.0 19.0
0.150 3.0 2.8 8.0 12.0 14.0
0.075 2.6 2.2 5.8 7.1 11.4

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I. Special Mixture Design Considerations and Methods for Warm Mix Asphalt (WMA) 23
Table 16. Aggregate test properties for WMA example.
No. 67 1B RAP, RAP,
Property Stone stone Screenings Sand Fine Coarse
Bulk Specific Gravity 2.635 2.639 2.771 2.630 2.631 2.605
Apparent Specific 2.699 2.702 2.856 2.760 2.682 2.694
Gravity
Water Absorption 0.90 0.88 1.07 1.79 0.72 1.27
CAFF, One Fractured 96.0 96.0 N/A N/A N/A 100.0
Face, %
CAFF, Two Fractured 91.0 93.0 N/A N/A N/A 95.0
Faces, %
Flat & Elongated, % 0.8 0.0 N/A N/A N/A 1.5
FAA, Uncompacted N/A N/A 48.0 43.0 44.2 N/A
Voids
Sand Equivalent N/A N/A 58.0 89.0 N/A N/A
Table 17. Binder properties for WMA example.
Property PG 64-22 Binder RAP Binder
Specific Gravity 1.030 1.030
Continuous high-temperature grade, °C 59.0 81.4
Continuous intermediate-temperature grade, °C 13.0 27.4
Continuous low-temperature grade, °C -30.1 -19.7
3. Determine compaction level
4. Select nominal maximum aggregate size
5. Determine target VMA and air voids values
6. Calculate target binder content
7. Calculate aggregate content
8. Proportion aggregate blends for trial mixtures
9. Calculate trial mix proportions by weight and check dust/binder ratio
10. Evaluate and refine trial mixtures
11. Compile mix design report
In this example, much of Steps 1, 2, and 4 have been completed and the pertinent infor-
mation listed above. The purpose of this example is to illustrate those parts of the mix design
process that differ from normal HMA mix design as outlined in Chapter 8 of this manual.
Therefore, those steps in the mix design that do not differ from standard HMA mix design
practice are not discussed in detail in this example; readers uncertain of these steps should
review Chapter 8.
One of the important differences in the WMA mix design process is the limits on production
and compaction temperatures. In this case, these limits have been established by the producer:
132°C for production and 124°C for compaction. In order to ensure proper compaction, the
high-temperature grade of the RAP binder (81.4°C) must be less than the specified WMA com-
paction temperature--124°C in this case, so the RAP binder is acceptable. The mix design in this
example requires the use of two liquid additives in the mix design: an antistrip additive and a
recycling agent. The antistrip additive has a specific gravity of 1.030 and is to be added at 0.50%
by binder weight. The recycling additive has a specific gravity of 1.020 and is to be added at 1.00%
by total mix weight.
After entering the binder grading data in HMA Tools, the blended binder grade is given as a
PG 64-22, with an intermediate grading temperature of 25°C. This meets the specified require-
ment. Note that HMA Tools includes the low-temperature grade adjustment as described in

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24 Special Mixture Design Considerations and Methods for Warm Mix Asphalt
Table 18. Aggregate
proportions of WMA example.
Aggregate Wt. % in
Aggregate Blend
No. 67 Stone 20
1B Stone 25
Screenings 10
Manufactured Sand 15
RAP (aggregate only) 30
Table 3. Details on the calculations used to estimate blended binder grades for HMA and WMA
containing RAP are given in AASHTO M 323.
At a traffic level of 6 million ESALs, Ndesign is 100 gyrations (Table 8-2). Given the NMAS
of 12.5 mm, the minimum VMA is 15.0% and the maximum 17.0%; therefore, a target VMA
of 16.0% is selected. A target air void content of 4.0% is also selected for the mix design. For
this example, an aggregate gradation somewhat below maximum density is selected, with
aggregate proportions as shown in Table 18. Calculation of the volumetric composition for
the trial blend is complicated by the use of liquid additives. The suggested procedure involves
working through the known composition by volume, and then working back and forth
between weight and volume calculations until the total binder volume and weight can be
calculated. Then, the weights of the additives can be calculated. The various steps are shown
in Table 19.
The volume compositions in Table 19 are given in percents, which are equivalent to cm3 per
100 cm3 total volume. The weights are then calculated simply by multiplying this volume by the
appropriate specific gravity. (Note that the component weights are not percentages but are in units
Table 19. Calculation of volume percentages and weights
for WMA example.
Step Calculation Formula Result
1. VMA Given 16.00
2. Volume % of air voids (VA) Given 4.00
3. Binder effective volume % (VBE) VBE=VMAVA 12.00
4. Volume % of aggregate (VS) VS=100 VMA 84.00
5. Weight of aggregate (Ps), g/100 cm3 Ps = VS Gsb 222.06
6. Weight of RAP aggregate (Psr), Psr = Ps % RAP in 66.62
g/100 cm3 Aggregate Blend
7. Weight of RAP binder (Pbr), Pbr = Psr RAP binder 3.46
g/100 cm3 content
8. Volume % RAP binder (VBR) VBR=Pbr/RAP binder 3.36
specific gravity
9. Volume % of effective new binder and VBEN=VBE-VBR 8.64
liquid additives (VBEN)
10. Approximate weight of effective new Pben=VBA/specific gravity 8.86
binder and liquid additives (Pben), of new binder
g/100 cm3
11. Weight of absorbed binder (Pba), Pba=Ps water absorption 1.09
g/100 cm3 of aggregate 0.45
12. Weight of new binder, RAP binder and Pb=Pbr+Pben+Pba 13.42
liquid additives (Pb), g/100 cm3
13. Total weight of mix (Ptot), g/100 cm3 Sum all weights 235.47
14. Weight of antistrip additive, g/100 cm3 = (0.50/100) Pb 0.066
15. Weight of recycling additive, g/100 cm3 = (1.0/100) Ptot 2.309
16. Weight % of various components =Wt. in g/100 cm3 / Ptot Varies
100 %

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I. Special Mixture Design Considerations and Methods for Warm Mix Asphalt (WMA) 25
of g/100 cm3 volume.) In the final step (Step 16), these weights are converted to percentages by divid-
ing by the total mix weight and multiplying by 100%. In order to simplify calculations, the volume
and weight of new binder and liquid additives are lumped together and assumed to have the same
specific gravity--that of the new binder. Because the amount of liquid additives should be very small
and their specific gravity values close to that of the binder, the error in this assumption is quite small.
Note that in the calculation of absorbed asphalt (Step 11), the water absorption is multiplied
by 0.45 to estimate the asphalt binder absorption; in HMA designs, water absorption is mul-
tiplied by 0.50 rather than 0.45. The last step in this procedure is calculation of composition
in weight percent, which is done by dividing the weight of the various components by the
total mix weight. The final volumetric composition of the trial mixture is summarized
in Table 20. Although this procedure appears complicated, it can be performed using HMA
Tools (or other similar spreadsheet programs), simplifying the calculations and reducing the
chance for errors.
In preparing laboratory specimens, parts of the procedure are similar to those for HMA
practice. Batch weights are calculated in the same way. Because this is a foamed asphalt, a
laboratory foaming unit is used to foam the binder (with antistrip additive) prior to mix-
ing it with the hot aggregate and RAP. In this case, the recycling additive is added to the hot
aggregate and RAP and mixed for a few seconds prior to the addition of the foamed asphalt
binder. The mixed WMA is short-term oven conditioned for 2 hours at the planned com-
paction temperature, 124°C. It is then compacted in the Superpave gyratory compactor for
100 gyrations.
Provided the volumetrics of the trial mix are acceptable, the WMA, just as for HMA, must be
evaluated for moisture resistance according to AASHTO T 283. However, the WMA must also be
evaluated for coating and compactability. For the particle coating test (ASTM T 195), some of the
freshly mixed WMA is set aside and spread out on a metal pan to cool. The coarse aggregate par-
ticles are then separated out and the degree of coating determined. The number of completely
coated, partially coated, and uncoated particles is counted. In this case, there are 145 completely
coated particles, 6 particles that are partially coated, and none that are completely uncoated. The
percentage of coated particles is then 145/(145 + 6) × 100% = 96%. Since this is greater than 95%,
this WMA passes the coating test.
Calculations for the compactability test are shown in Table 21. As explained previously,
four specimens are compacted--two at the planned compaction temperature of 124°C and
two at a temperature 30°C below this, 94°C. Then, the relative density and height and Ndesign are
Table 20. WMA mix composition by weight
percentage from volume percentage and specific
gravity values.
Percent by Bulk Percent by Percent by
Total Mix Specific Aggregate Total Mix
Mix Component Volume Gravity Weight Weight
Air 4.00 --- --- ---
New Asphalt Binder 7.34 1.026 --- 3.19
RAP Asphalt Binder 3.37 1.030 --- 1.47
Liquid Antistrip Additive 0.066 1.020 --- 0.028
Recycling Additive 2.31 1.030 --- 1.00
No. 67 Stone 16.67 2.635 20 18.86
1B Stone 20.81 2.639 25 23.58
Screenings 7.90 2.771 10 9.43
Manufactured Sand 12.36 2.630 15 14.15
RAP Aggregate 25.13 2.619 30 28.29
Note: Calculations may not agree exactly because of rounding.

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26 Special Mixture Design Considerations and Methods for Warm Mix Asphalt
Table 21. Calculation of gyration ratio for compactability test.
124 C 94 C
Property Specimen 1 Specimen 2 Specimen 3 Specimen 4
Density @ Ndesign 96.0 95.9 96.1 96.0
Height @ Ndesign, mm 116.7 115.3 114.1 113.0
Height @ Relative Density = 121.8 120.2 119.2 117.9
92%
Gyrations at 92% Relative 33 38 42 39
Density
Gyration Ratio 1.14 < 1.25 Pass
determined for each specimen. Then, Equation 9 is used to calculate the height at a relative den-
sity of 92%. The gyratory output files are then examined to determine the number of gyrations
required to reach a relative density of 92%, N92. The gyration ratio is then calculated as the ratio
of N92 at TC-30/TC:
( 42 + 39)
Gyration Ratio = 2 = 1.14 (11)
(33 + 38)
2
In this example, the gyration ratio is 1.14, which is below the maximum allowable value of
1.25 so the mix passes this test.
Because the design traffic level in this case--6 million ESALs--is greater than or equal
to 3 million ESALs, performance testing using the AMPT is required as a final step in the
mix design. After short-term oven conditioning for 2 hours at 116°C, two gyratory specimens
are prepared and tested for flow number. In this example, the 7-day maximum pavement
temperature at a depth of 20 mm and at 50% reliability is determined to be 58.5°C. The
two specimens are tested at this temperature and produce flow number values of 27 and
29, giving an average value of 28. Unfortunately, this is below the minimum required value
of 30 (Table 14). The mix must be adjusted to provide better rut resistance. A second
trial mix design is made, increasing the RAP content from 30% to 40%; given that the
asphalt binder in RAP is relatively stiff, this should increase the rut resistance of the mix. The
resulting mix meets all requirements for volumetric composition, moisture resistance,
coating, and compactability. Performance testing results in an average flow number of 33,
meeting the minimum requirements. The laboratory mix design is completed and a report
prepared.
A Note on Using HMA Tools to Perform WMA Mix Designs
HMA Tools has several features designed specifically for use in designing WMA. In work-
sheet "General," there is a section for entering information generally required for WMA, such
as production and compaction temperature, and whether or not to allow adjustment in the
low-temperature grade of the virgin binder. If allowed, HMA Tools will make this adjustment
automatically. There is also a worksheet for recording data from the two mixture tests
required for WMA--the coating and compactability tests. The worksheet on liquid additives,
although not exclusively for use in designing WMA, allows for rigorous inclusion of such
materials in the volumetric analyses performed in HMA Tools.