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Unbound Materials HMA Mixtures
1. Develop M-D relationships in the laboratory prior to 1. Conduct an HMA mixture design to determine the target
construction for the unbound material to determine the gradation and asphalt content.
maximum dry unit weight.
Select the target density and job mix formula for the project
Select the target density and water content for compacting mixture or lift being tested. The target job mix formula will
the unbound layer. likely be revised based on plant produced and placed
material.
2. Prepare and compact test specimens at the average water 2. Prepare and compact test specimens at the target asphalt
content and dry density expected during construction; based content and the average density expected during
on the project specifications. construction; based on the project specifications.
3. Measure the repeated load resilient modulus in 3. Measure the dynamic modulus in accordance with the
accordance with the agency's procedure (AASHTO T307 or agency's procedure or the test protocol in accordance with
NCHRP 1-28A, as required by the MEPDG). the MEPDG.
Determine the resilient modulus at a selected stress state. Determine the dynamic modulus for the test temperature
The resilient modulus should equal or exceed the value used expected during acceptance testing. Two values should be
during design. extracted from the test results or master curve; one for the
day of paving (an elevated temperature expected after
If the agency does not have a resilient modulus testing compaction) and the other for one or multiple days
capability, the FHWA-LTPP regression equations can be following placement. This target value for one or more days
used to estimate the target value, until the laboratory following placement will need to be adjusted back to a
resilient modulus test has been completed (see Equations 1 standard temperature depending on the actual pavement
through 15). temperature.
4. Define the adjustment factor or ratio for the unbound 4. Define the adjustment factor for the HMA mixtures to
material to laboratory conditions. Low stress states were laboratory conditions. A load frequency of 5 Hz was used in
used in establishing the ratios for this project. establishing the adjustment ratios for this project.
5. Determine the combined or pooled standard deviation of 5. Determine the combined or pooled standard deviation of
the modulus for setting up the control limits of the unbound the seismic modulus for setting up the control limits of the
layer for the contractor (see Section 3.3). HMA mixture for the contractor (see Section 3.3).
Establish the action, as well as warning, limits for the Establish the action, as well as warning limits for the
statistical control charts; upper and lower control limits (see statistical control charts; upper and lower control limits (see
Section 3.2). Section 3.2).
6. Determine the upper and lower specification limits (see 6. Determine the upper and lower specification limits (see
Section 3.3) for the resilient modulus of the unbound Section 3.3) for the dynamic modulus of the HMA mixture.
material. This includes the upper and lower specification This includes the upper and lower specification limits for the
limits for the resilient modulus of the unbound layer. dynamic modulus of the HMA mixture.
7. Prepare the statistical control charts. 7. Prepare the statistical control charts.
8. Determine the PWL criteria for different conditions. 8. Determine the PWL criteria for different conditions.
The target value of the control chart for each material is the Acceptance Sampling Plans for Highway Construction. The
average value measured in the laboratory in accordance with pooled standard deviation was determined for each project
AASHTO T 307 or the test protocol used by the agency. Both and unbound material using the NDT results for the areas
action and warning limits are normally included on the statis- without anomalies or physical differences. The pooled stan-
tical control charts. The upper and lower action limits are set at dard deviations for each project and material are listed in
three standard deviations from the target value, while the warn- Tables 35 and 36 for the unbound and HMA layers, respec-
ing limits are set at two standard deviations from the target. tively. These values were used to determine whether the proj-
ects were in-control or out-of-control, using the action limits:
3.2.1 Target Modulus or Critical Value upper control limits (UCL) and lower control limits (LCL)
provided in Tables 35 and 36.
The target value of the control chart for each material and
project is the modulus measured in the laboratory. This aver-
3.3 Parameters for Determining PWL
age laboratory value should be the same as the input to the
MEPDG for structural design. Tables 35 and 36 list the target 3.3.1 Determining Quality Indices
values for the unbound and HMA layers included in the field
The upper and lower quality indices are calculated in
evaluation projects, respectively.
accordance with Equations 18 and 19, respectively. The upper
and lower specification limits were determined using data
3.2.2 Combined or Pooled
from all projects with similar materials.
Standard Deviation
The pooled standard deviation was calculated in accordance X - LSL
QL = (18)
with the AASHTO R9-03, Standard Recommended Practice for s

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Table 35. Parameters used to prepare statistical control charts for the
unbound layers included in the field evaluation projects.
Project Target Pooled Action Warning
Identification Material Modulus, Standard Limits, ksi
ksi Deviation, ksi UCL LCL
I-85, AL Low Plasticity Clay 4.0 0.8 5.6 2.4
NCAT, OK High Plasticity Clay 6.9 2.0 10.8 3.00
SH-21, TX High Plasticity Clay 26.8 2.5 30.4 23.2
Soil-Aggregate
TH-23, MN 16.4 1.0 17.8 15.0
Embankment
Soil-Aggregate
US-2, ND 19.0 2.6 22.7 15.3
Embankment
Improved Soil
SH-130, TX 35.3 2.8 39.3 31.3
Embankment
NCAT, SC Crushed Granite Base 36.1 2.7 41.4 30.8
NCAT, MO Crushed Limestone Base 19.2 2.7 24.5 13.9
TH-23, MN Crushed Stone Base 24.0 2.6 27.7 20.3
US-53, OH Crushed Stone Base 27.5 1.6 30.6 24.4
NCAT, FL Limerock Base 28.6 3.5 35.4 25.5
US-2, ND Crushed Aggregate Base 32.4 4.5 38.8 26.0
US-280, AL Crushed Limestone Base 48.4 10.0 62.7 33.7
NOTE: The target modulus for the South Carolina crushed granite base was determined using the FHWA-LTPP
regression equation, because the densities were significantly below the maximum dry unit weight of the material
during NDT testing. The pooled standard deviation for this project was assumed to be equal to the Missouri
limestone base because the same contractor placed both materials.
USL - X s = Sample standard deviation of the lot.
QL = (19)
X = Sample mean of a lot.
s
Where: The upper and lower quality indices are used to determine
QL = Lower quality index. the total PWL for each lot of material using Equation 20.
QU = Upper quality index. The upper and lower PWL values are then determined
USL = Upper specification limit. from the Q-tables provided in the AASHTO QC/QA Guide
LSL = Lower specification limit. Specification.
Table 36. Parameters used to prepare statistical control charts for the
HMA layers included in the field evaluation projects.
Pooled Action Warning Limits, ksi
Project Target
Material Standard
Identification Modulus, ksi UCL LCL
Deviation, ksi
I-85, AL SMA 250 14 270 230
TH-23, MN HMA Base 810 35 860 760
US-280, AL HMA Base 650 45 715 585
I-35, TX HMA Base 800 57 910 690
I-75, MI Type 3-C 400 86 520 280
I-75, MI Type E-10 590 86 715 465
US-47, MO Surface Mix 530 60 615 445
US-47, MO Base Mix 420 36 470 370
I-20, TX CMHB Base 340 40 420 260
US-53, OH HMA Base 850 44 915 785
US-2, ND HMA Base 510 33 555 465
NCAT, SC HMA Base 410 58 525 295
NCAT, FL HMA Base 390 40 470 310
NCAT, FL PMA Base 590 45 675 505
NCAT, AL PG76-Sasobit 610 40 690 530
NCAT, AL PG76-SBS 640 45 725 555
NCAT, AL HMA Base 450 50 550 350
NOTE: The Texas SH-130 target modulus was determined from Witczak's regression equation because changes were
made to the mixture just before NDT testing.

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Table 37. Upper and lower specification limits for the unbound layers
and materials included in the field evaluation projects.
Project Median Standard Specification
Material
Identification Deviation, ksi Tolerance, (-) ksi
I-85, AL Low Plasticity Clay
NCAT, OK High Plasticity Clay 2.0 3.3
SH-21, TX High Plasticity Clay
Soil-Aggregate
TH-23, MN
Embankment
Soil-Aggregate
US-2, ND 2.1 3.5
Embankment
Improved Soil
SH-130, TX
Embankment
NCAT, SC Crushed Granite Base
NCAT, MO Crushed Limestone Base
TH-23, MN Crushed Stone Base
US-53, OH Crushed Stone Base 3.0 5.0
NCAT, FL Limerock Base
US-2, ND Crushed Aggregate Base
US-280, AL Crushed Limestone Base
PWL = PWLL + PWLU - 100 (20) 3.3.2 Determining Specification Limits
Where: Tables 37 and 38 list the target values for the unbound and
PWL = Percent within limits. HMA layers included in the field evaluation projects, respec-
PWLL = Percent within limits from the lower specification tively. These values were used to determine the PWL for the
limit. different materials used in the field evaluation projects and
PWLU = Percent within limits from the upper specification were compared to the control limits determined for each
limit. project.
Table 38. Upper and lower specification limits for the HMA layers
and mixtures included in the field evaluation projects.
Project Median Standard Specification
Material
Identification Deviation, ksi Tolerance, + ksi
I-85, AL SMA 15 30
TH-23, MN HMA Base
US-280, AL HMA Base
50 100
I-35, TX HMA Base
I-75, MI Type 3-C
I-75, MI Type E-10
70 140
US-47, MO Surface Mix
US-47, MO Base Mix
I-20, TX CMHB Base
US-53, OH HMA Base
US-2, ND HMA Base 50 100
NCAT, SC HMA Base
NCAT, FL HMA Base
NCAT, FL PMA Base
NCAT, AL PG76-Sasobit
45 90
NCAT, AL PG76-SBS
NCAT, AL HMA Base 50 100