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TH-23 Base SMA Overlay US-280 Base, InitialUS-280 Base, Supp.
16
GPR Air Voids, percent
14
12
10
8
6
4
2
0
100 200 300 400 500 600 700
PSPA Seismic Modulus, ksi
Figure 44. PSPA modulus versus GPR air voids.
ments. This finding is applicable to all the NDT devices used the unbound base layer had already been compacted by the
to test the HMA mixtures. contractor, and the instrumented roller was only used to test
the surface. The contractor did not want to take the risk of
potentially disturbing the aggregate base, requiring it to be re-
2.5 Supplemental Comparisons
compacted and tested. Figures 46 through 48 present some of
This section provides an overview of three areas of supple- the IC roller data, as related to HMA densities measured with
mentary information and data that were collected during other devices. Overall, the densities and stiffness measured
the Part B field evaluation projects: (1) modulus and density with other devices correlated well with the output from the
growth relationships for monitoring the rolling operations, instrumented rollers in the areas without localized anomalies.
(2) multiple operators and NDT devices, and (3) agency and The instrumented rollers did not identify differences caused
contractor use of NDT devices. by localized anomalies (i.e., anomalies significantly less than
the width of the roller).
Different NDT devices were also used to monitor the
2.5.1 Modulus and Density-Growth
compaction operation of HMA and unbound layers to
Relationships for Monitoring
demonstrate the value of these devices in real time. The
the Rolling Operation
PSPA, DSPA, GeoGauge, and PaveTracker devices were used
Instrumented rollers were used on projects to monitor the on some of the Part A and most of the Part B field evaluation
increase in density and stiffness of the unbound and HMA projects. The following subsection contains important
layers, where the rollers could be scheduled for use. In a observations from the use of selected NDT devices for con-
couple of cases, Asphalt Manager was on the project site, but trolling the placement and compaction of both unbound
it exhibited hardware or software problems. In other cases, and HMA layers in real time.
TH-23 Base SMA Overlay US-280 Base, InitialUS-280 Base, Supp.
165
160
PQI Density, pcf
155
150
145
140
135
130
100 200 300 400 500 600 700
PSPA Seismic Modulus, ksi
Figure 45. PSPA modulus versus PQI density of HMA mixtures.
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68
U.S. 280 19.0 mm NMAS
160
y = 0.0819x + 131.94
155
R2 = 0.47
Nuclear Density, lb/ft^3
150
145
140
135
130
0 50 100 150 200 250 300
Evib * 100, psi
Figure 46. Comparison of the nuclear density gauge readings to the
Evib values measured with the IC roller.
2.5.1.1 Unbound Materials and Layers to determine the increase in material modulus with com-
paction. The DCP was used along this project because it was
Overall, the GeoGauge, DCP, and DSPA were successful in
on a private facility, and delaying the compaction of this base
monitoring the build up of modulus with the number of material was not an issue. Both devices found an increase in
roller passes for the unbound materials placed within the field modulus with an increasing number of roller passes.
evaluation, and they were beneficial in assisting the contractor · Figure 50 presents data collected during the compaction of
in making decisions on the compaction operation used along a Missouri crushed limestone base material. The first roller
the project. Some examples follow. pass within this figure is after the material had been pre-
liminarily compacted from other construction equipment
· Figure 49 presents data collected on a caliche base material and roller passes. The maximum modulus for this material
placed along an entrance roadway from County Road 103 was achieved at about eight passes of the roller over a spe-
near Pecos, Texas. Both the GeoGauge and DCP were used cific area. The number of passes obviously is dependent on
U.S. 280 19.0 mm NMAS
150
y = 0.0328x + 134.31
145
R2 = 0.24
PQI Density, lb/ft^3
140
135
130
125
120
0 50 100 150 200 250 300
Evib * 100, psi
Figure 47. Comparison of the PQI density readings to the Evib values
measured with the IC roller.
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Location 3
160 300
155 250
150 200
Density, lb/ft^3
145 150
140 100
135 50
130 0
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
Roller Passes
Density Site 6 Density Site 7 Evib Site 6 Evib Site 7
Figure 48. Example of a density growth curve prepared from the
IC roller demonstration and NDT results.
the water content of the in-place material; for the Missouri shows the benefit and advantage of using the GeoGauge or
crushed limestone, the in-place water content was just DSPA to make decisions in real time.
below the optimum value.
· Figure 51 presents data collected during the compaction These examples show the benefit of developing modulus-
of a South Carolina crushed granite base material. This growth curves using the DSPA or GeoGauge during con-
crushed granite base material was difficult to compact with struction for monitoring and optimizing the rolling pattern.
the roller on the project site when compaction was initi-
ated. In addition, the water content of this base material 2.5.1.2 HMA Mixtures and Layers
was well below the optimum value. Both the DSPA and the
GeoGauge modulus values did not increase with the num- Overall, the PSPA and PaveTracker were successful in
ber of roller passes. A nuclear density gauge was also used monitoring the build up of modulus and density with the
along the project, and it also showed no increase in density number of roller passes for the HMA layers placed within the
with the number of roller passes. Thus, rather than waste field evaluation projects. Some examples follow.
additional compaction effort, the contractor had to use
a heavier roller and had to increase the water content of · Figure 52 presents data collected along the Missouri widen-
the material to obtain the specified density. This example ing project (US-47) for two different areas. Figure 52(a)
compares the densities measured using the contractor's
nuclear density gauge on site for QC to those values mea-
DCP GeoGauge Log. (GeoGauge) Log. (DCP) sured with the PaveTracker. The densities from the nuclear
gauge were related to the non-nuclear density gauge values
Resilient Modulus from
30
with mixture specific calibration values. The contractor
NDT Devices, ksi
25 was using one-test point readings with the nuclear gauge,
20 while four readings at a test point were made with the
15 PaveTracker within the same time.
10 The contractor was using the cold-side pinch method
5 for compacting the longitudinal joint adjacent to the old
0 2 4 6 8 10 12 pavement. This HMA was tender based on visual observa-
Number of Roller Passes tions of its behavior under the roller--shoving of the mat
Figure 49. Modulus-growth relationships for a caliche was observed in front of, as well as across, the roller's
base along an entrance roadway to a facility from direction. Rollers marks were also present after the last
County Road 103 near Pecos, Texas. pass of the finish roller. The HMA was being pushed away
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Missouri Crushed Limestone Base
28
GeoGauge Modulus, ksi
26
24
22
20
18
16
14
12
10
0 1 2 3 4 5 6 7 8 9 10 11 12
Number of Roller Passes
DSPA Modulus GeoGauge Modulus
90 30
80
GeoGauge Modulus,
DSPA Modulus, ksi
25
70
60 20
50
ksi
15
40
30 10
20
5
10
0 0
0 2 4 6 8 10 12
Number of Roller Passes
Figure 50. Modulus-growth relationships for a Missouri
crushed limestone base material for two different areas.
DSPA Modulus GeoGauge Modulus
70 11
DSPA Modulus, ksi
65 10
60
9
55
8
50
45 7
40 6
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
Number of Roller Passes
South Carolina Crushed Granite
10
GeoGauge Modulus, ksi
9
8
7
6
5
0 2 4 6 8 10 12 14
Number of Roller Passes
Figure 51. Modulus-growth relationships for a South Car-
olina crushed granite base material for two different areas.
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from the confined longitudinal joint, rather than being this temperature sensitivity under the rollers. Selecting
pushed down into the joint. Joint densities were made HMA mixtures that checked and tore for the field evalua-
with both the nuclear and non-nuclear density gauges tion was not planned.
along the joint, and the densities were found to be very · The I-75 Michigan overlay project was another project
low--about 5 to 10 pcf below the densities measured where a HMA mixture was rolled within its temperature
within the center of the mat. The contractor was asked to sensitive zone. With three passes of a SAKAI vibratory
change the rolling pattern for the confined longitudinal roller in the primary roller position, the HMA mixture
joint using the hot-side method. With this method, the density was greater than the specified value (see Figure 54).
first pass of the roller is along the confined longitudinal However, an intermediate roller continued to roll the mix,
joint, with about a 6-in. overhang off the hot mat. Densi- and was followed by two additional rollers. The use of the
ties were measured with both devices after changing the PaveTracker determined that the contractor was rolling
rolling pattern. Figure 52(b) shows the densities along the in the temperature sensitive zone--the density began to
longitudinal joint, as compared to those in the center of decrease. By monitoring the density of the mat during
the mat. The densities significantly increased after elimi- rolling, the result was that the contractor could eliminate
nating the roller pass on the cold side of the joint. Thus, two of the rollers and use fewer passes to obtain the required
the contractor was able to use the non-nuclear density density, as long as the rollers stayed out of the temperature
gauge in real time to significantly increase the joint den- sensitive zone.
sity by slightly revising the rolling pattern of the joint. · Figure 55 shows an example for polymer modified asphalt
The PSPA was also used along this project, but the results (PMA) and conventional neat asphalt mixtures. These mix-
were erratic during or immediately after compaction of tures were placed during the same time period. The conven-
the mat--the wave form was not consistent with HMA tional neat asphalt mixture exhibited the traditional checking
mixtures. The mixture was found to be too tender to obtain and tearing of the mat when it was rolled within the temper-
reliable readings, until the mix cooled below about 150°F. ature sensitive zone, while the PMA mixture did not exhibit
This HMA mixture was being used as the base for the tearing or checking. After pass 3 for the neat asphalt mix and
shoulder or in a non-critical area. It was initially believed after pass 5 for the PMA mix, the densities decreased. The
that the PSPA had been damaged in transport, but that mix tearing and checking was observed under the roller to
was found to be incorrect from latter testing of the HMA confirm that the mix was rolled within the temperature zone.
after it had cooled down. At lower temperatures, the PSPA Thus, the mat had to be rolled much more to increase den-
provided reasonable results. Thus, its use would have been sity to the specified value for both mixtures.
a benefit in identifying a tender mix, if this mix had been
used in a critical area under heavy traffic. Attempts were Similar to the benefit for unbound layers, the non-nuclear
made to use the PSPA on a couple of other projects, but the density gauges provide significant benefit to a contractor to
temperature of those mixtures was too high to obtain reli- optimize the rolling pattern within the center of the mat, as
able results. Mix temperature is a limitation on testing well as along longitudinal joints. The non-nuclear gauges can
HMA mixtures during rolling. also be used to determine when the rollers are being operated
· Figure 53 presents density data collected on a Missouri within the temperature sensitive zone, so a contractor does
HMA base mixture that was not tender, but was rolled not waste compaction effort or time and does not tear or
within the temperature sensitive zone. The first pass of the damage the HMA mix by operating the rollers within the
rubber-tired roller increased the density, but additional temperature sensitive zone.
passes of that roller significantly decreased the density of
the mat. The nuclear density gauge being used on site for
2.5.2 Multiple Operators and NDT Gauges
QC gave the same results. The nuclear gauge, however, was
not being used after each roller pass. This mixture did not For most of the Part B projects, multiple GeoGauges and
exhibit the traditional mix "checking" or tearing under the PaveTrackers were used by different operators to determine the
rollers, but the non-nuclear density gauge did identify the effects of multiple operators on the variability of the devices.
detrimental effect of rolling within the temperature sensi- Figure 56 compares the measured responses from the two
tive zone. More roller passes were required to regain the GeoGauges that were used for testing unbound materials,
density that was lost by rolling within the temperature sen- while Figure 57 compares the measured densities from the two
sitive zone. Many of the other HMA mixtures that were PaveTracker devices used to monitor HMA mixtures. At the
included within the field evaluation projects also exhibited end of the field evaluation testing for each project, one of each
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PaveTracker Density Nuclear Gauge Density Temperature
154 250
152
HMA Mat Density, pcf
Mat Temperature, °F
150 200
148
150
146
144
100
142
140 50
138
136 0
0 1 2 3 4 5
Number of Roller Passes
(a) PaveTracker versus nuclear gauge density measurements.
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
(b) PaveTracker density measurements made along a confined joint and within the center of the mat.
Figure 52. Typical density-growth curve measured with PaveTracker and nuclear density
gauge for the Missouri US-47 project.
Compaction Operation:
Missouri HMA Mixture
Pass 1-2; Vibratory Roller
Pass 3-4; Static Steel Wheel
150 Pass 5-6; Vibratory Roller
Density Measured with
149 Pass 7-11; Rubber Tired
148
PaveTracker, pcf
Pass 12-14; Finish Roller
147
146
145
144
143
142
141
140
0 2 4 6 8 10 12 14 16
Number of Roller Passes
Figure 53. Density-growth relationship for an HMA base mixture from Missouri.
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Density Temperature
158.0 260
156.0 250
PaveTracker, pcf
Temperature of
Measured with
Density of Mat
Mixture, °F
154.0 240
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
SAKAI Vibratory SAKAI Pneumatic & Other Rollers
Temperature
154.0 270
260
PaveTracker, pcf
152.0
Temperature of
Measured with
Density of Mat
Mixture, °F
150.0 250
148.0 240
146.0 230
144.0 220
142.0 210
0 2 4 6 8 10 12
Number of Roller Passes
Vibratory Intermediate &
Breakdown Finish Rollers
Roller
Figure 54. Density-growth curves for the Michigan mixture
measured with PaveTracker and effects of rolling within the
temperature sensitive zone; two different areas.
device was left with the agency and contractor personnel. The 2.5.3 Agency and Contractor Use
following are observations from this comparative testing. of NDT Devices
· Use of different GeoGauges and operators resulted in some During Part B of the field evaluation, one of the multiple
bias that was modulus dependent for some materials; more gauges being used on a project was left with agency and
bias was exhibited for the higher modulus values or stiffer contractor construction personnel for continued use on a
material. Material specific calibration or adjustment factors day-to-day QA basis. Those NDT devices left with the con-
should be determined and used for each material tested struction personnel included the GeoGauge, PSPA, and
(see Table 24). This material specific calibration with a PaveTracker. Data from this additional use were included
sufficient number of replicate tests should minimize the in the comparison of multiple operators and devices at spe-
bias between the different gauges. The variability between cific project sites. This information was used in the evalua-
different gauges, however, will still exist. tion described in Chapter 3, in determining the parameters
· Use of different PaveTrackers and operators resulted in needed to set up control and acceptance plans when using
almost no bias between the two gauges, with the exception these NDT devices.
of dense or high specific gravity mixtures. Material specific The projects where construction personnel continued to
adjustments should be determined for these devices for use the devices included Missouri, North Dakota, and
each mixture tested. The mixture specific factors should Texas. The NDT devices were going to be left at the Michi-
minimize bias, but the variability between different gauges gan I-75 project, but issues with the HMA mixture resulted
will still exist. in the project being stopped for a short term, so the con-
