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7956+00.4 7957+00 7958+00 7959+00 7959+99.4
170
Density (pcf) 160
150
140
130
120
110
200.0 300.0 400.0 500.0 600.0
7962+00.5 7963+02.1 7964+02.5 7965+04 7966+04.2
170
160
Density (pcf)
150
140
130
120
110
800.0 900.0 1000.0 1100.0 1200.0
7971+23.3 7972+23.4 7973+22.3 7974+21.9 7975+21.9
170
160
150
Depth (in.)
140
130
120
110
1800.0 1900.0 2000.0 2100.0
Distance from S Catch Basin (ft.)
TH23 - Spicer, MN
Base Sections - Base Density
Moisture Content Assumed Constant at 4.12% Analyzed by: GLM Date: 10/21/04
Checked by: KRM Date: 10/22/04
GPS Stations INFRASENSE, Inc.
Arlington, MA 02476
Sheet: 1 of 1
Figure 29. Density profiles generated from the GPR test results for the crushed aggregate base layer
placed along the TH-23 reconstruction project.
information is grouped into two areas--those NDT devices oratory conditions with the adjustment ratios listed in
with an acceptable to excellent success rate and those with Table 24. Figure 34(a) includes a comparison of the indi-
poor success rates in identifying material/layer differences. vidual test points, while Figure 34(b) compares the data on
a project basis. Figure 33 compared the adjusted PSPA and
FWD modulus for the HMA layers using the adjustment
2.4 Comparison of Results Between
ratios listed in Table 25.
NDT Technologies
The adjustment procedure reduced the bias between the
This section provides a brief evaluation and comparison of different devices, but not the dispersion. Thus, any of these
the test results between different technologies to determine NDT modulus estimating devices can be used to estimate the
the reasons for the low success rates of the DCP, LWD, GPR, resilient modulus of the material with proper calibration at
and EDG. the beginning of the project, with some exceptions.
· Deflection-Based Devices: The calculated modulus values
2.4.1 NDT Modulus Comparisons
from the deflection-based devices can be affected greatly by
Figure 34 compares the NDT modulus values used to the underlying materials and soils. For example, the crushed
identify areas with physical differences in the unbound lay- stone base material placed in area 4 along US-280 near
ers, except that the NDT values have been adjusted to lab- Opelika, Alabama, is a stiff and dense material, even though
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58
Geo., Fine-Grained Geo., Coarse-Grained Line of Equality
DSPA, Fine-Grained DSPA, Coarse-Grained
60
Adjusted Elastic Modulus
from NDT Devices, ksi
50
40
30
20
10
0
0 10 20 30 40 50 60
Laboratory Resilient Modulus, ksi
(a) DSPA and the GeoGauge.
DCP, Fine-Grained DCP, Coarse-Grained Line of Equality
LWD, Fine-Grained LWD, Coarse-Grained
60
Adjusted Elastic Modulus
from NDT Devices, ksi
50
40
30
20
10
0
0 10 20 30 40 50 60
Laboratory Resilient Modulus, ksi
(b) Deflection-Based and DCP methods.
Figure 30. Laboratory resilient modulus versus adjusted NDT
modulus.
GeoGauge DSPA Zero Residual DCP LWD Zero Residual
25
Residual from Target Value,
15
Residual from Target Value,
20
10
15
5 10
ksi
ksi
0 5
0
-5
-5
-10 -10
-15 -15
0 10 20 30 40 50 60 0 10 20 30 40 50 60
Laboratory Resilient Modulus,Target Value, ksi Laboratory Resilient Modulus, Target Value, ksi
(a) GeoGauge and DSPA. (b) DCP and LWD.
Figure 31. Residuals (laboratory minus NDT modulus values) versus adjusted NDT modulus.
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Table 30. Tabulation of the mean of the residuals Table 31. Tabulation of the mean of the residuals
and standard error for NDT devices. and standard error for NDT devices from the
expected laboratory value.
NDT Device GeoGauge DSPA DCP LWD
Mean Residual, ksi -0.117 0.149 -0.078 0.614 NDT Device PSPA FWD
Standard Error, ksi 2.419 4.486 3.768 5.884 Mean Residual, ksi 13.5 39.0
Standard Error, ksi 76 87
the deflection-based devices found it to be weaker than the
other areas tested with a value less than 20 ksi. All other modulus of the entire layer. In fact, the surface of this
NDT devices estimated the modulus for area 4 to be about material actually exhibited radial cracks during the seating
35 ksi or higher. An in-place modulus of 20 ksi for this drop of the DCP. Figure 35 shows the estimated modulus
material is too low. Thus, variations in the subsurface layers with depth from the DCP.
or materials/soils can incorrectly result in significant bias in
the resilient modulus.
· DSPA: The DSPA can significantly overestimate the labo- 2.4.2 NDT Volumetric Property Comparisons
ratory measured resilient modulus values. The US-280
2.4.2.1 Unbound Layers
crushed stone base was dry or significantly below the opti-
mum water content during testing in some areas. It is The EDG and GPR were used to estimate the volumetric
believed that the surface of this dense, dry crushed stone is properties of the unbound materials. The following list pro-
responding like a bound layer--resulting in a much higher vides a summary of the response measurements to the dry
FWD PQI GPR Line of Equality
35
Coefficient of Variation,
Other Devices, percent
30
25
20
15
10
5
0
0 5 10 15 20 25 30 35
PSPA Coefficient of Variation, percent
Figure 32. Comparison of coefficients of variation of
different NDT devices.
Adjusted to Laboratory Conditions Line of Equality
700
Adjusted Elastic Modulus,
600
500
FWD, ksi
400
300
200
100
100 200 300 400 500 600 700
Adjusted Seismic Modulus, PSPA, ksi
Figure 33. Comparison of the PSPA and FWD modulus values
adjusted to laboratory conditions.
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Table 32. NDT device and technology variability analysis; standard error.
Material/Layer Property
NDT Structural Volumetric
Material
DevicesThickness, Modulus, Density, Air Fluids
in. ksi pcf Voids, % Content
NDT Devices with Good Success Rates Based on Modulus or Volumetric Properties; see Section 2.1.1
GeoGauge NA 2.5 NA NA NA
Fine-Grained Soils
DSPA NA 4.5 NA NA NA
Coarse-Grained Soils GeoGauge NA 2.5 NA NA NA
& Aggregate Base DSPA NA 4.5 NA NA NA
PSPA NA 76 NA NA NA
HMA Mixtures
PQI & PT NA NA 1.7 NA NA
NDT Devices with Poor Success Rates Based on Modulus or Volumetric Properties; see Section 2.1.2
DCP NA 3.8 NA NA NA
LWD NA 5.9 NA NA NA
Fine-Grained Soils
GPR NA NA NA NA NA
EDG NA NA 0.8 NA 0.2
DCP NA 3.8 NA NA NA
Coarse-Grained Soils LWD NA 5.9 NA NA NA
& Aggregate Base GPR 0.8 NA 3.4 NA NA
EDG NA NA 1.0 NA 0.2
FWD NA 87 NA NA NA
GPR; Single 0.25 NA NA 0.40 NA
HMA
GPR;
0.27 NA 1.6 0.22 0.18
Multiple
NOTES:
1. The standard error for the modulus estimating devices is based on the adjusted modulus values that have been
adjusted to laboratory conditions.
2. The US-280 project with the PATB was removed for the GPR (single antenna) thickness data--it was the only
site that resulted in a significant bias of layer thickness and the only one with a PATB layer directly beneath the
layer tested.
Table 33. NDT device and technology variability analysis; 95 percent
precision tolerance.
Material/Layer Property
NDT Structural Volumetric
Material
DevicesThickness, Modulus, Density, Air Fluids
in. ksi pcf Voids, % Content
NDT Devices with Good Success Rates Based on Modulus or Volumetric Properties; see Section 2.1.1
GeoGauge NA 4.9 NA NA NA
Fine-Grained Soils
DSPA NA 8.8 NA NA NA
Coarse-Grained Soils GeoGauge NA 4.9 NA NA NA
& Aggregate Base DSPA NA 8.8 NA NA NA
PSPA NA 150 NA NA NA
HMA Mixtures
PQI & PT NA NA 3.4 NA NA
NDT Devices with Poor Success Rates Based on Modulus or Volumetric Properties; see Section 2.1.2
DCP NA 7.4 NA NA NA
LWD NA 11.6 NA NA NA
Fine-Grained Soils
GPR NA NA NA NA NA
EDG NA NA 1.6 NA 0.4
DCP NA 7.4 NA NA NA
Coarse-Grained Soils LWD NA 11.6 NA NA NA
& Aggregate Base GPR 1.5 NA 6.7 NA NA
EDG NA NA 2.0 NA 0.4
FWD NA 170.5 NA NA NA
GPR; Single 0.49 NA NA 0.8 NA
HMA
GPR;
0.55 NA 3.1 0.4 0.36
Multiple
NOTES:
1. The precision tolerance for the modulus estimating devices is based on the adjusted modulus values that have
been adjusted to laboratory conditions.
2. The US-280 project with the PATB was removed for the GPR (single antenna) thickness data--it was the only
site that resulted in a significant bias of layer thickness and the only one with a PATB layer directly beneath the
layer tested.
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Table 34. NDT device and technology variability analysis; combined or pooled
standard deviation.
Material/Layer Property
StructuralNDT Volumetric
Material
Thickness, Devices
Modulus, Density, Air Fluids
in. ksi pcf Voids, % Content
NDT Devices with Good Success Rates Based on Modulus or Volumetric Properties; see Section 2.1.1
GeoGauge NA 1.1 NA NA NA
Fine-Grained Soils
DSPA NA 1.2 NA NA NA
Coarse-Grained Soils GeoGauge NA 1.8 NA NA NA
& Aggregate Base DSPA NA 1.5 NA NA NA
PSPA NA 56 NA NA NA
HMA Mixtures PQI &
NA NA 2.5 NA NA
PaveTracker
NDT Devices with Poor Success Rates Based on Modulus or Volumetric Properties; see Section 2.1.2
DCP NA 1.9 NA NA NA
LWD NA 2.0 NA NA NA
Fine-Grained Soils
GPR NA NA 4.2 NA NA
EDG NA NA 0.7 NA 0.5
DCP NA 5.3 NA NA NA
Coarse-Grained Soils LWD NA 2.0 NA NA NA
& Aggregate Base GPR 0.6 NA 3.0 NA NA
EDG NA NA 0.8 NA 0.6
FWD NA 55 NA NA NA
GPR; Single 0.3 NA NA 2.1 NA
HMA
GPR;
NA NA NA NA NA
Multiple
NOTES:
1. The pooled standard deviations for the modulus estimating devices are based on the adjusted modulus values that
have been adjusted to laboratory conditions.
2. The US-280 project with the PATB was removed for the GPR (single antenna) thickness data--it was the only
site that resulted in a significant bias of layer thickness and the only one with a PATB layer directly beneath the
layer tested.
DSPA DCP LWD Line of Equality
60
Other NDT Devices, ksi
Elastic Modulus from
50
40
30
20
10
0
0 10 20 30 40 50 60
Elastic Modulus, GeoGauge, ksi
(b) Comparison of adjusted modulus values on a project basis.
DCP DSPA LWD Line of Equality
100
Elastic Modulus from Other
90
80
NDT Devices, ksi
70
60
50
40
30
20
10
0
0 10 20 30 40 50 60
Elastic Modulus, GeoGauge, ksi
(a) Comparison of adjusted modulus values on a point-by-point basis.
Figure 34. Comparison of adjusted modulus values determined
from different NDT devices.
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US-280 Base; Area 1-C US-280; Area 1-A
60
Resilient Modulus Estimated
from the DCP Penetration
50
40
Rate, ksi
30
20
10
0
0 2 4 6 8 10 12
Depth Below the Surface, inches
Figure 35. Modulus gradient measured with the DCP for the
US-280 crushed stone base material.
densities obtained from construction records and traditional decreased, but across significantly different materials.
volumetric tests. Changes in material density along the same project were
poorly correlated to changes in the dielectric value.
· Figure 36 compares the dielectric values to the dry densities · Figure 38 compares the dry densities measured with the
measured with the EDG. No good correlation was found EDG to those measured with a traditional nuclear den-
between the different materials tested. In addition, no sity gauge. There are two definite groups of data--one
defined relationship was found between the two response for fine-grained soils and the other for crushed aggregate
measurements for the same material. This observation base materials. As the dry density increased between dif-
suggests that there are different properties affecting the ferent materials, the density from the EDG also increased.
EDG and GPR results--none of which could identify the Within each group, however, no reasonable relationship
physical differences at a reasonable success rate. was found.
· Figure 37 compares the GPR dielectric values to the dry
density measured with different devices--the EDG, nuclear
2.4.2.2 HMA Layers
density gauges, and sand-cone tests. No good correlation
was found; only a trend was identified between the GPR Figure 39 compares the air voids measured with the GPR to
results and the densities obtained from construction records. the results from other devices and methods. Figure 39(a) com-
As the dry density increased, the GPR dielectric values pares the densities measured directly with the nuclear density
I-85 Embankment TH-23 Embankment SH-130 Subgrade
TH-23 Base US-280 Base
50
Dielectric Values, GPR
40
30
20
10
0
100 110 120 130 140 150
Dry Density, EDG, pcf
Figure 36. GPR dielectric values versus the EDG dry densities
measured along different projects.
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Electrical Density Gauge Nuclear Density Gauge
Power (Nuclear Density Gauge)
150
140
Dry Density, pcf
130
120
110
100
90
0 10 20 30 40 50
GPR Dielectric Values
Figure 37. GPR dielectric values versus dry densities measured
with nuclear and non-nuclear density gauges.
gauge and PQI. There is a general trend between the air void 2.4.3 Volumetric--Modulus Comparisons
measurements and densities--as air voids increase, the density
decreases, but any correlation is poor. There are significant dif- 2.4.3.1 Unbound Layers
ferences between the volumetric properties measured with The in-place modulus of the unbound materials is depen-
these different devices. Figure 39(b) compares the air voids cal- dent on its density. The FHWA-LTPP study reported that the
culated from the maximum theoretical density provided for laboratory resilient modulus was dependent on dry density
each mixture to the air voids estimated from the GPR dielec- for all unbound materials (Yau and Von Quintus). In fact,
tric values. As shown, no correlation exists between the devices density and water content are two volumetric properties that
from the field evaluation projects included in this study. have a significant affect on the modulus of the material. Thus,
Figure 40 compares the densities measured with the it follows that the NDT devices resulting in a material modu-
nuclear density gauge and the PQI along the longitudinal lus should be related to the density and/or water content of
joints and in areas with localized segregation. These densities the material. Dry densities and water contents were extracted
are compared with the values measured away from the joints from the QA reports for the different projects included in the
and outside any noticeable segregation. There is a greater field evaluation.
variation in density measured with the nuclear device than Figure 41 compares the average modulus values esti-
with the PQI. However, the wet surface may have affected the mated from the different NDT devices and dry densities
PQI readings when the measurements were recorded. reported by the individual agencies during construction.
Series1 Line of Equality
140
Dry Density, Nuclear Density
135
130
125
120
Gauge
115
110
105
100
95
90
90 95 100 105 110 115 120 125 130 135 140
Dry Density, EDG, pcf
Figure 38. Dry densities measured with the EDG and nuclear
density gauges.
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PQI - TH-23 Base PQI - SMA Overlay PQI - US-280 Base
PQI - US-280 Base Nuclear - SMA Overlay Nuclear - US-280 Base
170
160
Density, pcf 150
140
130
4 6 8 10 12 14 16
Air Voids, GPR, percent
(a) Density measured with the different devices.
PQI, TH-23 PQI, SMA Nuclear, SMA PQI, US-280
Nuclear, US-280 PQI, US-280 Line of Equality
14
Air Voids, Other Devices,
12
10
percent
8
6
4
2
0
0 2 4 6 8 10 12 14
Air Voids, GPR, percent
(b) Air voids calculated from the maximum theoretical density for the mixture.
Figure 39. Air voids measured with the GPR versus densities
measured with the PQI and nuclear density gauges for
different HMA mixtures.
Joint Readings Segregated Areas HMA Mixture Line of Equality
170
160
Density, PQI, pcf
150
140
130
120
120 130 140 150 160 170
Density, nuclear, pcf
Figure 40. Nuclear density gauge measurements compared
to the PQI values along longitudinal joints and in areas
with segregation.
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GeoGauge DCP LWD Poly. (DCP) Poly. (GeoGauge)
60
Modulus from NDT Tests,
50
Unadjusted, ksi
40
30
20
10
0
100 110 120 130 140 150 160
Dry Density, QA Records, pcf
(a) Unadjusted modulus values.
GeoGauge DCP LWD
DSPA Poly. (GeoGauge) Poly. (DCP)
60
Adjusted Modulus from
50
NDT Tests, ksi
40
30
20
10
0
100 110 120 130 140 150 160
Dry Density, QA Records, pcf
(b) Modulus values adjusted to laboratory conditions.
Figure 41. Dry density versus NDT adjusted modulus values
for different materials.
The important observation from this comparison is that The dry density and water contents from the QA records
there is a good relationship between dry density and the were fairly dispersed and were not taken at each NDT test
DCP estimated modulus, prior to adjusting the modulus location or individual area. As such, the QA data can only be
values to laboratory conditions (Figure 41[a]). The resilient used to evaluate the results for different types of materials,
modulus from the GeoGauge is also related to the dry den- rather than actual density variations within a project or lot.
sity of the material, but appears to become insensitive to The EDG was used to measure the density and water content
dry density for less dense, fine-grained soils with high water at specific test locations for the other NDT devices.
content. The resilient modulus from the LWD is related to Figure 42 compares the dry densities measured with the
dry density but has the greatest variation because of the EDG and modulus values estimated from the GeoGauge and
influence of the underlying materials. DCP. The NDT modulus increases with increasing dry density
Figure 41(b) graphically presents the same comparison over a wide range of material types, which is consistent with
included in Figure 40(a), but using the adjusted modulus previous experience. However, there are clusters of data for
values. The GeoGauge and DSPA have similar relationships the EDG that correspond to similar unbound materials that
to dry density for both conditions. The relationship for the were tested. Within each data cluster, the correspondence
DCP becomes less defined and it is improved for the LWD. between dry density and NDT modulus is poor for both
Overall, the modulus values resulting from each NDT device devices.
are related to the dry density across a wide range material. This observation suggests that there are other factors that
The GeoGauge has the better correlation to dry density using impact the modulus within a specific area; for example,
the adjusted values, followed by the DSPA and DCP. Thus, the water content and amount of coarse aggregate varying
GeoGauge was the primary device used in comparing the within each data cluster. The EDG did not measure large
elastic modulus to the EDG and GPR results. variations in water content within each area. In summary,
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GeoGauge DCP Poly. (DCP)
Adjusted Elastic Modulus, ksi
80
70
60
50
40
30
20
10
0
100 110 120 130 140 150 160
Dry Density, EDG, pcf
Figure 42. NDT modulus values versus dry density measured
by the EDG.
the within-project area variation of the modulus values air voids and increasing PSPA modulus, but no good corre-
appears to be more dependent on properties other than dry lation. All NDT devices did correctly identify the difference
density (e.g., water content, gradation)--assuming that the between the US-280 initial and supplemental sections, with
EDG is providing an accurate estimate of the in-place dry the exception of the PQI. This difference was not planned but
density. That assumption is questionable based on the data was confirmed through the use of laboratory dynamic mod-
accumulated to date. ulus tests. The state agency's and contractor's QA data did
Figure 43 compares the GeoGauge modulus to the GPR not identify any difference between these two areas or time
dielectric values. No clear correspondence was found between periods.
the dielectric values and modulus values. Specifically, a wide Figure 45 compares the PSPA modulus and the PQI den-
range of dielectric values and moduli were measured, but no sity. A general trend exists for a specific mixture, but no cor-
consistent relationship was found between the two properties. relation exists between these devices that can be used in
Thus, material/layer properties that affect modulus within an day-to-day construction operations for control or accept-
area have little effect on the dielectric values. ance. A more important observation is that the volumetric
measuring devices are not being influenced by those proper-
ties that affect the modulus measuring NDT devices. As an
2.4.3.2 HMA Layers
example, changes in the asphalt content and gradation in
Figure 44 compares the PSPA modulus and the GPR air relation to density, air voids, and stiffness changes do not
voids. There is a general trend within this data set--decreasing affect density measurements as they do modulus measure-
60
Resilient Modulus, GeoGauge,
50
40
ksi
30
20
10
0
0 10 20 30 40 50
GPR Dielectric Values
Figure 43. GPR dielectric values versus the GeoGauge
modulus.
