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APPENDIX B
Volume 1--Procedural Manual
This appendix contains the Volume 1--Procedural Manual for NCHRP Project 10-65.
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Project No. 10-65
NONDESTRUCTIVE TESTING TECHNOLOGY FOR
QUALITY CONTROL AND ACCEPTANCE OF FLEXIBLE
PAVEMENT CONSTRUCTION
FINAL REPORT
VOLUME 1--PROCEDURAL MANUAL
Prepared for:
National Cooperative Highway Research Program
Transportation Research Board
National Research Council
Of National Academies
Prepared By:
Harold L. Von Quintus, P.E., ARA (Principal Investigator)
Chetana Rao, PhD., ARA (Project Manager)
Robert E. Minchin, Jr., PhD., P.E., UFL, Gainesville
Kenneth R. Maser, PhD., P.E., Infrasense, Inc.
Soheil Nazarian, PhD., P.E., UT, El Paso
Brian Prowell, P.E., NCAT
Submitted by
Applied Research Associates, Inc.
100 Trade Centre Drive, Suite 200
Champaign, Illinois 61820-7233
July 2008
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Volume I--Procedural Manual
Judging the Quality of and Accepting Flexible Pavement
Construction Using NDT Methods
1.1 INTRODUCTION
Key properties that are needed to predict the performance of flexible pavements and hot mix
asphalt (HMA) overlays are modulus, thickness, and density--called quality characteristics.
Transportation Research Circular Number E-C037 defines a quality characteristic as (TRB
2005): "That characteristic of a unit or product that is actually measured to determine
conformance with a given requirement. When the quality characteristic is measured for
acceptance purposes, it is an acceptance quality characteristic (AQC)." Agencies and
contractors have been using density as a quality characteristic for many years. Density is
normally measured using nuclear density gauges for control, while cores are almost always
used for acceptance of HMA layers. Modulus is not included in the acceptance plan of any
agency but is a required input for structural design. Modulus is also becoming a material
property for selecting and designing materials.
Using the same mixture properties for accepting the pavement layer as those used for
structural and mixture design allows an agency to more precisely estimate the impact that
deficient and superior materials or construction quality have on performance. This direct
relationship to the mixture and structural design methods is especially important when
developing and implementing performance-related specifications (PRS). The Guide for the
Mechanistic-Empirical Design of New and Rehabilitated Pavements developed under
NCHRP Project 1-37A and 1-40D (MEPDG1) as well as the simple performance tests
developed under NCHRP Project 9-19 in support of the Superpave volumetric mixture design
procedure use modulus and other fundamental engineering properties for characterizing the
materials.
Nondestructive testing and evaluation offers a high production method of determining the
structural and volumetric properties of pavement layers that are required for both mixture and
structural design. This document provides a procedure for including the material modulus as
a quality characteristic in controlling and accepting flexible pavements and HMA overlays.
2.1 SCOPE OF MANUAL
The manual provides guidelines for implementing the selected NDT technologies in routine
quality control and acceptance (QC/QA) procedures of an agency's quality assurance
program (QA). The manual contains 5 sections. The first section covers the introduction to
using NDT for QA of flexible pavement construction, and discusses the basis for selecting
NDT technologies for implementation; the second section summarizes the scope of this
manual. The third section provides a description of the devices that are recommended for use
in QC/QA and also refers to the procedures used in developing quality control and quality
1
The product from NCHRP 1-37A project is also alluded to in industry as the Mechanistic-Empirical Pavement
Design Guide (MEPDG).
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acceptance plans for agencies. The recommended QA procedures using NDT devices are
covered in the fourth and fifth sections for HMA mixtures and unbound materials,
respectively. Each of these two sections is further divided into two subsections that list the
step-by-step procedures for including material modulus in quality control and acceptance
(QC/QA) plans.
3.1 SUMMARY OF EQUIPMENT TO MEASURE QUALITY
CHARACTERISTICS
The procedures presented herein use the dynamic modulus for HMA mixtures and resilient
modulus for all unbound materials. The dynamic modulus is estimated with the Portable
Seismic Pavement Analyzer (PSPA), while the resilient modulus is estimated with the
GeoGauge. The PSPA uses ultrasonic methods, and the GeoGauge uses steady-state
vibratory methods. Adjustment ratios have to be developed or determined for the specific
material being evaluated to relate field to laboratory conditions. Both the PSPA and
GeoGauge can be used for controlling and accepting HMA mixtures and unbound materials,
respectively.
The PSPA is designed to determine the average modulus of an in-place HMA layer (see
Figures 1 and 2). The PSPA consists of two receivers (accelerometers) and a source
packaged into a hand-portable system, which can perform high frequency seismic tests. The
device measures the velocity or propagation of surface waves that is used to determine the
material's modulus. A software program that controls the testing comes with the device and
keeps record of all measurements taken.
Figure 1. PSPA, Carrying Case, and Laptop
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Carriage case recently developed
for facilitating the use of the
PSPA & DSPA in data collection.
Figure 2. PSPA for Testing HMA Layers
The GeoGauge measures the impedance at the surface of an unbound layer (see Figure 3). It
imposes small displacements and stresses to the surface of a layer and uses 25 steady-state
frequencies between 100 to 196 Hz. The resulting surface velocity is measured as a function
of time. This device also has a built-in data acquisition system to keep a record of the test
results.
The other device that is recommended for use in the control of HMA layers is the non-
nuclear density gauge--specifically, PaveTracker (see Figure 4). This is an electromagnetic
sensing device that contains software and a built-in reference plate that takes the density
readings and keeps a record of them. The non-nuclear density gauges for unbound layers are
not recommended for QC/QA at this point in time. Future updates and improvements will
likely result in the use of these devices for process control.
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Figure 3. Humboldt GeoGauge
Figure 4. Non-Nuclear Density Gauge, PaveTracker
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3.1.1 Acceptance Plan
Different acceptance procedures are used in judging whether the pavement material meets the
required specifications. Two methods used by most agencies are Percent Within Limits
(PWL) and Average Absolute Deviation (AAD). This document uses PWL for determining
acceptance and specification compliance. AASHTO R 9-03, Acceptance Sampling Plans for
Highway Construction, is recommended for use in preparing practical but effective
procedures that agencies can use in deciding whether the product meets their specifications
(AASHTO 2003). AASHTO R 9-03 should be followed in determining the number of tests
per lot, lot size, and other specifics of the acceptance sampling plan.
The upper and lower quality indices are calculated in accordance with Equations 1 and 2,
respectively.
X LSL
QL ................................................................................................................ (1)
s
USL X
QL ................................................................................................................ (2)
s
Where:
QL = Lower quality index.
QU = Upper quality index.
USL = Upper specification limit.
LSL = Lower specification limit.
s = Sample standard deviation of the lot.
X = Sample mean of a lot.
The upper and lower quality indices are used to determine the total PWL for each lot of
material using Equation 3. The upper and lower PWL values are then determined from the
Q-tables provided in the AASHTO QC/QA Guide Specification.
PWL PWLL PWLU 100 ......................................................................................... (3)
Where:
PWL = Percent Within Limits.
PWLL = Percent Within Limits from the lower specification limit.
PWLU = Percent Within Limits from the upper specification limit.
Determine the Combined Variability for HMA Mixtures
The combined variability includes the within-process variability and the target-miss
variability or the precision of the target value. A reasonable combined variability for the
initial use in setting the specification is provided for both HMA and crushed aggregate base
layers in latter parts of this document. The combined variability is expected to be dependent
on the target stiffness of the material.
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Agencies should develop agency-specific values based on reasonable standard care and
workmanship of producing, placing, and compacting HMA layers. A minimum of 10 projects
should be used to determine the combined variability for a range of mixtures. The within-
process and center or target-miss variability should exclude areas with anomalies or
construction defects.
Determine Specification Limits for an HMA Mixture
Establishing the specification limits for a specific mixture requires that the acceptable and
unacceptable (defined as rejectable material) be defined. The acceptance and rejectable
quality levels are dependent on the within-process variability. These all become engineering
decisions of the agency and are used to determine the PWL for the different materials.
3.2.1 Quality Control Plan
Of the many process control procedures that can be used in highway construction, process
control charts, particularly statistical control charts, are commonly used by contractors and
material producers for verifying that their process is under control. Although there are
different approaches that can be taken in implementing NDT technologies to verify that the
process is in control, statistical control charts are being used within this document. The
ASTM Manual on Presentation of Data and Control Chart Analysis was used for preparing
practical procedures that contractors can use in deciding whether their process is in control
(ASTM 1992).
The upper and lower control or action limits for the sample means are calculated in
accordance with Equations 4 and 5.
UCL X X A3 s ........................................................................................................ (4)
LCL X X A3 s ........................................................................................................ (5)
Where:
UCL X = Upper control limit for the sample means.
LCL X = Lower control limit for the sample means.
X = Target value for a project.
s = Pooled standard deviation that represents the process variance.
A3 = Factor for computing control chart limits and dependent on the number of
observations in the sample.
The target value of the control chart for each material is the average modulus measured in the
laboratory. Both action and warning limits are normally included on the statistical control
charts. The upper and lower action limits are set at three standard deviations from the target
value, while the warning limits are set at two standard deviations from the target.
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The upper and lower control limits for the sample standard deviations are calculated in
accordance with Equations 6 and 7, while Equations 8 and 9 are the limits when the range
( R ) is used.
UCLs B3 s ................................................................................................................ (6)
LCLs B4 s ................................................................................................................ (7)
UCLR D3 R .............................................................................................................. (8)
LCL R D4 R .............................................................................................................. (9)
Where:
B3,4 = Factors for computing control chart limits based on sample standard
deviations and dependent on the number of observations in the sample.
D3,4 = Factors for computing control chart limits based on the range within the
sample and dependent on the number of observations in the sample.
4.1 HMA MIXTURES AND LAYERS
4.1.1 Acceptance Testing of HMA Mixtures and Layers
The dynamic moduli measured in the laboratory and the moduli measured with the PSPA
were found to have a normal distribution, excluding areas with construction defects. Thus,
the assumption of normality is applicable but should be checked, especially for harsh and
tender HMA mixtures.
Step 1: Determine JMF and Target Mixture Properties
A master curve for each HMA mixture included in the design strategy (new construction or
rehabilitation with HMA overlays) is normally assumed for structural design. This assumed
master curve or specific modulus values are used within the mixture design process for
determining the job mix formula (JMF) to ensure that the mixture design satisfies the
structural design assumptions. The materials selection and mixture design should be
completed in accordance with NCHRP Project 9-33.
Step 2: Verify the JMF with Plant Produced Mixture
The HMA mixture JMF should be verified with a plant produced mixture. If minor revisions
are needed to satisfy the design criteria, those revisions should be completed and confirmed
prior to determining the target modulus value for acceptance. The procedures recommended
within NCHRP Project 9-33 should be followed for making any revisions to the JMF to
ensure that the assumptions used for structural design have been met.
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Step 3: Determine Target Dynamic Modulus for HMA Mixture
a. After the HMA mixture design has been verified from plant produced material, dynamic
moduli should be determined for the mixture compacted to the target density specified for
the in-place mixture (93 to 94 percent compaction or percent maximum theoretical
density). The target density or percent compaction should be established by the agency.
These dynamic moduli are used to determine the seismic shift factor. The purpose of the
seismic shift factor is to translate the seismic modulus into a design modulus (see step 5).
The test temperatures should include those that are expected during the acceptance testing
of the mixture. The recommended temperatures include 90, 110, 130, and 150 °F (see
Figure 5). Higher temperatures may need to be used if the acceptance testing is
completed the same day of paving. The load frequencies used during testing should
include 0.1, 0.5, 1.0, 5.0, and 10.0 Hz. If an approved master curve was already measured
from the mixture plant verification process, it is not necessary to redo the test. The results
from the earlier testing can be used.
Not all agencies have the laboratory equipment in their district or field laboratories for
HMA mixtures. Two options are provided: one for the case where the equipment is
available for measuring the dynamic moduli and the second for the case where that
equipment is unavailable.
Option A--Measure Dynamic Modulus
Sample plant produced mixture from the control strip or at the beginning of the
project and compact three test specimens using a Superpave gyratory compactor to
the density or air void level targeted or specified. Dynamic moduli are measured on
the approved, plant verified JMF in accordance with AASHTO TP 62 over the range
of temperatures expected during acceptance testing.
Option B--Calculate Dynamic Modulus of HMA Mixture with Regression
Equations
Calculate the dynamic modulus over the range of frequencies and temperatures
selected in accordance with NCHRP Project 9-33 or NCHRP Report 465 (see Figure
5). Use of regression equations is considered permissible because adjustments need to
be made for the specific mixture.
b. The target dynamic modulus is determined for a specific or reference frequency (5 Hz is
suggested) and temperature (the mid-range temperature expected during acceptance
testing is suggested). See step 5 for additional discussion on the reference frequency and
temperature. The target dynamic moduli should be compared to the value used for
structural design. If the measured or calculated modulus is significantly different than the
assumed value at the same frequency and temperature, revisions should be made to the
mixture or structural designs.
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c. The test specimens used to verify the JMF and prepared for dynamic modulus testing are
also used in step 4 for measuring the seismic modulus of the mixture at different
temperatures.
Dynamic Modulus Regression Equation
100
Dynamic Modulus, E x 105 psi
10
70 F
90 F
110
130
150
1
0.1
0.1 1 10 100
Frequency, Hz.
Dynamic Modulus Regression Equation
100
Dynamic Modulus, E x 105 psi
10
0.5
1
` 5
10
25
1
0.1
60 70 80 90 100 110 120 130 140 150 160
Temperature, F
Figure 5. HMA Dynamic Moduli, Measured in the Laboratory or Calculated Using
MEPDG Regression Equation
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e. Record the seismic-design modulus and surface temperature reported by the PSPA.
f. Lift and rotate the PSPA 90° to the first direction of testing and repeat steps b to d.
g. Lift and rotate the PSPA by 45° between the first two readings and repeat steps b to d.
Step 8: Determine the Combined Variability for Setting the Specification Limits
The specification limits are defined by the combined variability for the HMA. Most agencies
will have insufficient data to date for estimating this value in terms of setting the
specification limits. Based on multiple operators and gauges, the following provides the
recommended combined variability for dense-graded HMA mixtures to be used until
sufficient data become available (based on the number of tests recommended above).
Dynamic Modulus Combined Variability = 95 ksi
The target dynamic modulus for the specifications was defined under step 3.
Step 9: Determine Quality Indices and PWL for a Lot
The upper and lower quality indices are calculated in accordance with Equations 1 and 2,
respectively, and used to determine the total PWL for each lot of material using Equation 3.
The upper and lower PWL values are then determined from the Q-tables provided in the
AASHTO QC/QA Guide Specification.
4.2.1 Quality Control Testing of HMA Mixtures and Layers
The quality control plan uses the non-nuclear density gauges. The PaveTracker gauge was
specifically used to determine the control limits and other required information; that gauge is
referred to specifically within this document, but other non-nuclear density gauges can be
used if found to be acceptable.
Step 1: Determine the Density Correction Factor for the Non-Nuclear Density Gauge Used
for Process Control
a. The density of the HMA mat should be measured with the PaveTracker device at each
of the 8 to 10 locations selected for seismic testing within the control strip of the first
day's production (see Acceptance Testing).
b. Determine the average density correction factor (DCF) between the PaveTracker
density values and the densities (bulk specific gravities) measured on the field cores.
Core Gmb ( Core )
DCF or (13)
Gauge Gmb ( Gauge )
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It is recommended that a contractor take a total of five cores at the beginning to
increase the sample size for determining the average density correction factor. As the
contractor becomes more familiar with the non-nuclear density gauges, that number
for the control strips can be reduced to three for most mixtures. In addition, make sure
that the surface is dry when establishing the DCF.
c. The densities measured with the PaveTracker or other non-nuclear density gauges are
multiplied by the DCF to obtain the in-place density.
Step 2: Establish Density-Growth Curve and Temperature Sensitive Zone
a. At the beginning of the paving process, it is recommended that a density-growth
curve be developed for the specific mixture and compaction train being used.
b. Measure the density after each pass of the roller over a specific point, in at least two
locations or test points. Two readings should be taken at each point, and the average
value recorded and used to determine the DCF. The surface temperature should also
be recorded after each pass of the roller used in the compaction train--including the
finish roller(s). The reason for reducing the number of density measurements in
developing the density-growth curve is avoid delaying the compaction operation of
the rollers. If time permits between each roller pass over a specific point, a minimum
of three readings should be taken and the average value used.
c. A density-growth curve should be prepared for each test point used during the control
strip or first day's production (see Figure 8). This testing is recommended for two
reasons:
To determine the number of passes of each roller for obtaining the target or
specified density level.
To determine whether the rollers will be operating within the temperature
sensitive zone, and if so, to determine the temperature range through which the
rollers should be restricted from rolling the mat (see Figure 9). Rolling within the
temperature sensitive zone can significantly reduce the density of the HMA mat
and cause the mat to check and tear. If this condition occurs, the owner agency
will likely require that the mat be removed and replaced.
Step 3: Process Control Testing with Non-Nuclear Density Gauges
a. The non-nuclear density gauge should be operated according to the manufacturer's
recommendations.
b. If the surface is wet (free water or water ponded on the surface), all free water should
be removed and the surface allowed to dry in the area of the test prior to taking any
readings.
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c. Determine the number of test points per lot and sublot for controlling the HMA
compaction. As a minimum, it is recommended that three test points per sublot be
used for process control. The lot should be determined based on other tests being used
by the contractor for process control (i.e., sampling the mixture for volumetric
property determination using the gyratory compactor in the field or plant laboratory).
d. Identify or mark the area to be tested within each sublot.
e. Take four readings around the sides of each test point or test location. The gauge
should be oriented in the same direction for each reading--in the direction of the
paver and rollers is recommended. After the first reading, lift the gauge and move it
to the next consecutive or adjacent side of the test point. Repeat until all sides of the
test point have been taken. All four readings should be taken within a 1- to 2-foot
square area.
f. Record all four readings and the surface temperature at each test point, and average
the values for the test point.
Mat Density Joint Density Mat Temperature Joint Temperature
165 230
163
Density Measured with PaveTracker, pcf
220
161
Temperature of Mixture, F
159
210
157
155 200
153
190
151
149
180
147
145 170
0 1 2 3 4 5
Number of Roller Passes
Figure 8. Density-Growth Curve Measured with the PaveTracker
Step 4: Determine the Combined Variability for Setting the Control Limits
The control limits are defined by the contractor's within-process variability of density for
HMA. Most contractors should have sufficient data for estimating this value in terms of
setting the action and warning limits for the statistical control charts. Based on multiple
operators and gauges, the following provides the recommended pooled standard deviation for
density of the non-nuclear density gauges (PaveTracker), excluding all areas with anomalies
and those areas where mat checking and tearing were exhibited.
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Pooled Standard Deviation for Density = 2.5 pcf
Density Temperature
158.0 260
156.0 250
PaveTracker, pcf
Temperature of
Density of Mat
Measured with
154.0 240
Mixture, F
152.0 230
150.0 220
148.0 210
146.0 200
0 2 4 6 8 10 12
Number of Passes of the Rollers
Figure 9. Density-Growth Curve Showing the Effects of Rolling within the
Temperature Sensitive Zone
5.1 UNBOUND MATERIALS AND LAYERS
5.1.1 Acceptance Testing for Unbound Materials and Layers
The resilient moduli measured in the laboratory and the moduli measured with the GeoGauge
were found to have a normal distribution, excluding areas with construction defects.
Step 1: Determine the Moisture-Density Relationship of the Soil and Material
Determine the moisture-density (M-D) relationship of the unbound material or soil in
accordance with AASHTO T 180. The optimum water content and maximum dry density are
the target values for determining the resilient modulus of the unbound layer.
Step 2: Determine Target Resilient Modulus
The target value for acceptance should be the average resilient modulus used as the input to
the MEPDG. This value may have been determined from other physical properties and may
or may not relate to the optimum water content and maximum dry unit weight of the
material.
The resilient modulus, however, should be determined in the laboratory on test specimens
prepared and compacted to the target density specified for the in-place mixture (100 percent
of the maximum dry density as determined by AASHTO T 180). The target density should be
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established by the agency. The resilient modulus determined for the specified density and
water content is the target resilient modulus for process control (see Figures 10 and 11). This
target resilient modulus may or may not be the target value for acceptance.
Not all agencies have the laboratory equipment in their district or field laboratories for
measuring the resilient modulus of the unbound layers. Thus, two options are provided: one
for the case where the repeated load resilient modulus measuring equipment is available and
the second for the case where that equipment is unavailable.
Option A--Measure Resilient Modulus
Sample the unbound materials from the stockpiles or from the control strip and
compact three test specimens. Measure the resilient modulus of the unbound material
over the range of stress states in accordance with AASHTO T 307. Determine the
target resilient modulus at a low confining pressure and repeated vertical stress
suggested below.
Confinement, Repeated Total Vertical
Layer & Material Type
psi Stress, psi Stress, psi
Subgrade; Fine-Gained Soils with
2 2 4
Plasticity
Embankment; Soil-Aggregate
4 4 8
Mixture
Crushed Aggregate Base 6 6 12
Table 2. Option A--Measure Resilient Modulus
Confinement = 3 psi Confinement = 6 psi Confinement = 10 psi
Confinement = 15 psi Confinement = 20 psi
130000
Resilient Modulus, psi
110000
90000
70000
50000
30000
10000
0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0 90.0 100.0
Bulk Stress, psi
Figure 10. Resilient Modulus Measured in the Laboratory for a Crushed Stone Base
Material
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Confinement = 3 psi Confinement = 6 psi Confinement = 10 psi
Confinement = 15 psi Confinement = 20 psi
90
80
70
Resilient Modulus, ksi
60
50
40
30
20
10
0 10 20 30 40 50 60 70 80 90 100
Bulk Stress, psi
Figure 11. Resilient Modulus Measured in the Laboratory for a Crushed Stone or
Aggregate Base Material
Option B--Calculate Resilient Modulus of the Unbound Material with
Regression Equations
Calculate the resilient modulus for the stress states listed above in accordance with
one of the regression equations from the Federal Highway Administration (FHWA)
Long Term Pavement Performance (LTPP) program. These regression equations are
shown below. Use of the regression equations is considered permissible because
adjustments need to be made for the specific material.
k2 k3
oct
MR k1 p a 1 (14)
pa pa
Where:
= Bulk Stress, psi
1 2 3 (15)
= Octahedral shear stress, psi
2 2 2 0.5
3 1
3 1 2 2
(16)
3
pa = Atmospheric pressure, 14.7 psi.
1, 2,3 = Principal stress, psi.
k1, 2,3 = Regression constants from laboratory resilient modulus test results.
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The k regression constants are material specific. The following defines the regression
constants for the different materials that were tested within the field evaluation projects.
These relationships for these regression constants were developed from the FHWA-LTPP
study (Von Quintus and Killingsworth 1998)
Crushed Stone Base Materials:
k1 0.7632 0.008 P3 / 8 0.0088 LL 0.037 ws 0.0001 dry (17)
k2 2.2159 0.0016 P3 / 8 0.0008 LL 0.038 ws
dry
2
(18)
0.0006 dry 0.00000024
P# 40
k3 1.1720 0.0082 LL 0.0014 ws 0.0005 dry (19)
Embankments, Soil-Aggregate Mixture, Coarse-Grained
k1 0.5856 0.0130 P3 / 8 0.0174 P# 4 0.0027 P# 200 0.0149 PI
dry ws
0.0000016 Max 0.0426 wS 1.6456 0.3932 (20)
Max wMax
Max
2
0.00000082
P# 40
ws
k2 0.7833 0.0060 P# 200 0.0081 PI 0.0001 Max 0.1483
wopt
(21)
dry
2
0.00000027
P# 40
opt
2
k3 0.1906 0.0026 P# 200 0.00000081 (22)
P# 40
Embankments, Soil-Aggregate Mixture, Fine-Grained
k1 0.7668 0.0051 P# 4 0.0128 P# 200 0.0030 LL
dry (23)
0.051 wopt 1.179
Max
dry
k2 0.4951 0.0141 P# 4 0.0061 P# 200 1.3941 (24)
Max
dry
k3 0.9303 0.0293 P3 / 8 0.0036 LL 3.8903 (25)
Max
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Fine-Grained Clay Soil
k1 1.3577 0.0106 Clay 0.0437 ws (26)
k 2 0.5193 0.0073 P# 4 0.0095 P# 40 0.0027 P# 200
(27)
0.0030 LL 0.0049 ws
k 3 1.4258 0.0288 P# 4 0.0303 P# 40 0.0521 P# 200 0.025 Silt
ws (28)
0.0535 LL 0.0672 wopt 0.0026 max 0.0025 dry 0.6055
wopt
Step 3: Determine the Field Adjustment Factor (Adjusting Field to Laboratory Conditions)
The GeoGauge results in a field modulus and needs be adjusted to be consistent with the
structural design assumptions based on laboratory resilient modulus. This step is to determine
the field ratio for adjusting the GeoGauge measurements to laboratory conditions. Once this
field ratio or factor is determined, that ratio should be used to adjust the GeoGauge modulus
to laboratory conditions for all readings.
a. At a minimum of two locations within the control strip or first day's production, use
the GeoGauge to measure the increase in modulus of the material under the roller. In
other words, develop a modulus-growth curve (see Figure 12). The number of passes
of the roller should be increased until the modulus remains the same.
b. Select 8 to 10 random locations within the control strip or first day's production and
measure the GeoGauge modulus in accordance with step 7.
c. Measure the density and moisture content at three of these locations using the sand-
cone test to ensure that the material has been compacted to the dry density established
by the agency's specifications.
d. Calculate or measure the resilient modulus of the in-place material using the average
density and moisture contents measured from the sand-cone tests.
e. Determine the specific field ratio for the layer in accordance with the following
equation.
M R Lab
RResilient Modulus (29)
M R Design
f. Determine if the field ratio deviates significantly from values near unity. The
following provides a summary of the average ratios that have been measured on other
unbound materials. It is expected that the ratio should be within three standard
deviations. If the adjustment ratio is outside three standard deviations from the mean
value, it is expected that a significant change has occurred to the material between
field calibration and production. If the values are outside three standard deviations
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from those listed below, the material should be evaluated in more detail to ensure that
the values are correct.
Field Adjustment Ratios for Aggregate Base Materials and Soil-Aggregate
Mixtures for Embankments:
Mean Value = 1.031
Standard Deviation = 0.370
DCP GeoGauge Log. (GeoGauge) Log. (DCP)
Resilient Modulus from
30
NDT Devices, ksi
25
20
15
10
5
0 2 4 6 8 10 12
Number of Roller Passes
Figure 12. Modulus-Growth Curve Measured with the GeoGauge
Step 4: Use GeoGauge for Measuring Modulus of Unbound Layers for Acceptance and
Conformance
a. The material modulus should be measured on the in-place material using the
GeoGauge in accordance with the manufacturer's recommendations.
b. Remove any loose material on the surface, being careful not to disturb or remove an
excessive amount of material. Figure 3 shows the tools that can be used to clean the
test surface.
c. Place the moist sand on the test surface and pad it into place to fill any surface voids.
The layer of moist sand should just cover the test surface and be sufficient in area so
that three different readings of the GeoGauge can be made within this test area. This
area should be about 1 to 2 square feet in size. This thin, moist sand layer is to ensure
that the bottom ring of the GeoGauge is in contact with the surface for at least 75
percent of it surface area.
d. Place the GeoGauge on the surface of the sand. Lightly twist the GeoGauge, but do
not push the GeoGauge into the test material. The bottom plate of the GeoGauge (not
the bottom of the ring) must not be in contact with the material being tested. After the
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test, the surface of the layer should be inspected to ensure that it was not in contact
with the GeoGauge.
e. Take a reading of the GeoGauge and record the modulus displayed. These readings
can be stored in the device and downloaded at the end of the lot testing.
f. Adjust the readings externally to determine the laboratory equivalent resilient
modulus values read by the GeoGauge.
g. Lift the GeoGauge and observe the surface of the thin layer of sand and test area. The
thin layer of sand or test surface should not be indented by the gauge such that the
bottom of the GeoGauge was in contact with the surface. If that was the case, the test
result should be so noted and not used in the acceptance testing and the test repeated
in a different area of the test area.
h. Move it to a different area with the sand layer and repeat steps d to g.
i. Lift the GeoGauge and move it to a third location and repeat steps d to g.
Step 5: Determine the Combined Variability for Setting the Specification Limits
The specification limits are defined by the combined variability for the unbound layers. Most
agencies will have insufficient data to date for estimating this value in terms of setting the
specification limits. Based on multiple operators and gauges, the following provides the
recommended combined variability for dense-graded crushed stone base layers to be used
until sufficient data become available (based on the number of tests recommended above).
Resilient Modulus Combined Variability = 3.10 ksi
The target resilient modulus for the specifications was defined under step 2 and is the value
assumed and used as an input to the MEPDG.
Step 6: Determine Quality Indices and PWL for a Lot
The upper and lower quality indices are calculated in accordance with equations 1 and 2,
respectively, and used to determine the total PWL for each lot of material using equation 3.
The upper and lower PWL values are then determined from the Q-tables provided in the
AASHTO QC/QA Guide Specification.
5.2.1 Quality Control Testing of Unbound Materials and Layers
The quality control plan uses the GeoGauge to determine the control limits and other
required information. The non-nuclear electrical density gauges require future improvements
for use in process control. Thus, most of the steps included for acceptance testing also apply
to process control, with the following exceptions.
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The target value of the control chart for the unbound layers is the average value
measured in the laboratory in accordance with AASHTO T 307 and compacted to the
specified density and water content specified by the agency.
Both action and warning limits are normally included on the statistical control charts.
The upper and lower action limits are set at three standard deviations from the target
value, while the warning limits are set at two standard deviations from the target. The
pooled standard deviation used to set the control limits will be contractor and material
specific. The following provides the overall pooled standard deviation until
contractors develop sufficient information and data for setting their own control
limits.
Overall pooled standard deviation for setting the limits of statistical control
charts for process control = 3.10 ksi
