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74 Compaction Operation: Florida PMA Base Mix Pass 1-4; Vibratory Roller Pass 5; Static Steel Drum 144 Pass 6-8; Vibratory Roller Density Measured with 142 Pass 9; Finish Roller PaveTracker, pcf 140 138 136 134 132 0 2 4 6 8 10 Number of Roller Passes (b) PMA Mixture Compaction Operation: Florida Neat Base Mix Pass 1-4; Static Steel Drum Pass 5-7; Rubber Tired Roller 144 Pass 8-10; Finish Roller Density Measured with 142 PaveTracker, pcf 140 138 136 134 132 0 2 4 6 8 10 12 (a) Conventional Neat HMA Number of Roller Passes Mixture Figure 55. Density-growth curves for two Florida mixtures measured with PaveTracker and effects of rolling within the temperature sensitive zone. struction personnel did not actually use the devices. For the 2.6.1 NDT Devices for Unbound Layers Missouri project, weather delays resulted in the contractor and Materials moving to a different project so the devices were not used The DSPA and GeoGauge devices had the highest success on the same project, as that included in the Part B field rates for identifying an area with anomalies, rates of 86 and evaluation. The devices were used for more than 2 weeks on 79 percent, respectively. The DCP and LWD identified the North Dakota and Texas projects. In actuality, the con- about two-thirds of the anomalies, while the GPR and tractor had already been using the PaveTracker and PSPA EDG had unacceptable rates, below 50 percent. on the Texas I-20 project. The PaveTracker was a part of the Three to five repeat measurements were made at each test contractor's standard or day-to-day QC plan, while the point with the NDT devices, with the exception of the DCP. PSPA had been used on a research basis. -- The LWD exhibited low standard deviations that were less dependent on material stiffness with a pooled stan- dard deviation less than 0.5 ksi. One reason for the low 2.6 Summary of Evaluations values is that the moduli were less than for the other In summary, the steady-state vibratory (GeoGauge) and devices. The COV, however, was higher. It is expected seismic (DSPA) technologies are suggested for use in judging that the supporting layers had an effect on the results the quality of unbound layers, while the seismic (PSPA) and by reducing the modulus. non-nuclear density gauges (the PaveTracker was used in -- The GeoGauge had a standard deviation for repeatabil- Part B) are suggested for use on HMA layers. The GPR is sug- ity measurements varying from 0.3 to 3.5 ksi and were gested for layer thickness acceptance, while the IC rollers are material dependent. suggested for use on a control basis for compacting unbound -- The DSPA had the lowest repeatability with a stan- and HMA layers. The following sections provide some of the dard deviation varying from 1.5 to 21.5 ksi. The rea- reasons for these determinations. son for this higher variation in repeat readings is that

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75 Comparison between GeoGauge B 24C and B 25C (All Part B test data) Comparison of GeoGauge B 24C and B 25C (By Section) 45 28 27 40 26 GeoGauge, B 25C; Modulus, ksi y = 0.9025x + 1.6607 GeoGauge, B 25C; Modulus, ksi 35 25 R2 = 0.7615 24 30 23 25 22 20 21 20 15 19 10 18 17 5 16 0 15 0 5 10 15 20 25 30 35 40 45 15 16 17 18 19 20 21 22 23 24 25 26 27 28 GeoGauge, B 24C; Modulus, ksi GeoGauge, B 24C; Modulus, ksi (a) Comparison on a point-by-point basis. (b) Comparison on a project basis. Comparison between GeoGauge B 24C and B 25C (Modulus, ksi) 45 ND US-2 Base 40 NCAT, Missouri N10, Base NCAT, Oklahoma, N8&N9, Subgrade OH, SR-53, Base 35 GeoGauge, B25C; Modulus, ksi Linear (ND US-2 Base) Linear (NCAT, Missouri N10, Base) 30 Linear (NCAT, Oklahoma, N8&N9, Subgrade) Linear (OH,SR-53, Base) 25 20 15 10 5 5 10 15 20 25 30 35 40 45 GeoGauge, B 24C; Modulus, ksi (c) Comparison on a material basis. Figure 56. Comparison of modulus measurement with two independent GeoGauges. the DSPA sensor bar was rotated relative to the direc- Triplicate runs of the GPR were made over the same tion of the roller, while the other devices were kept area or sublot. For comparison to the other NDT devices, stationary or did not have the capability to detect the values measured at a specific point, as close as possi- anisotropic conditions. No significant difference was ble, were used. Use of point specific values from succes- found relative to the direction of testing for fine- sive runs could be a reason for the lower repeatability, grained soils, but there was a slight bias for the stiffer which were probably driver specific. One driver was coarse-grained materials. used for all testing with the GPR. -- The EDG was highly repeatable with a standard deviation The COV was used to compare the normalized dispersion in density measurements less than 1 pcf, while the GPR measured with different NDT devices. The EDG consis- had poor repeatability--based on point measurements. tently had the lowest COV with values less than 1 percent.

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76 Comparison between PaveTracker 10232 and 10233 (All Density Data) Comparison of PaveTracker 10232 and 10233 (Average Density, pcf) 170 170 y = 0.9506x + 7.1232 165 y = 1.1315x - 17.635 R2 = 0.9179 PaveTracker 10233; Density, pcf PaveTracker 10233; Density, pcf 160 2 R = 0.2007 160 155 150 150 140 145 140 130 135 130 120 125 110 120 110 120 130 140 150 160 170 120 130 140 150 160 170 PaveTracker 10232; Density, pcf PaveTracker 10232; Density, pcf (a) Comparison on a point-by-point basis. (b) Comparison on a project basis. Comparison between PaveTracker 10232 and 10233 (Density, pcf) 170 PaveTracker 10233; Density, pcf 160 150 140 130 120 110 110 120 130 140 150 160 170 PaveTracker 10232; Density, pcf MI I-75 Surface MO US-47 Surface ND US-2 Surface OH SR-53 Base OH SR-53 Surface (c) Comparison on a material or mixture basis. Figure 57. Comparison of the density measurements with two non-nuclear PaveTracker devices used within the Part B field evaluation. The GeoGauge had a value of 15 percent, followed by the fine-grained, less stiff soils, the ratio was about 0.5. After DSPA, LWD, DCP, and GPR. The GPR and EDG are adjusting for laboratory conditions, all NDT devices that dependent on the accuracy of other tests in estimating vol- estimate resilient modulus resulted in low residuals (labo- umetric properties (density and moisture contents). Any ratory resilient modulus minus the NDT elastic modulus). error in the calibration of these devices for the specific However, the GeoGauge and DCP resulted in the lowest material is directly reflected in the resulting values. This standard error. The LWD had the highest residuals and could be a probable reason why the GPR and EDG devices standard error. did not consistently identify the areas with anomalies or The DSPA and DCP measured responses represent the physical differences. specific material being tested. The DCP, however, can Repeated load resilient modulus tests were performed in be significantly affected by the varying amounts of aggregate the laboratory for characterizing and determining the particles in fine-grained soils and the size of the aggregate target resilient modulus for each material. Adjustment in coarse-grained soils. The GeoGauge measured responses ratios were determined based on uniform conditions. are minimally affected by the supporting materials, while The overall average ratio for the GeoGauge for the stiffer the LWD can be significantly affected by the supporting coarse-grained materials was near unity (1.05). For the materials and thickness of the layer being tested. Thickness

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77 deviations and variable supporting layers are reasons that The PSPA moduli were comparable to the dynamic moduli the LWD had a low success rate in identifying areas with measured in the laboratory on test specimens compacted anomalies or physical differences. to the in-place density at a loading frequency of 5 Hz and No good or reasonable correlation was found between the the in-place mixture temperature, with the exception of NDT devices that estimate modulus and those devices that one mixture--the US-280 supplemental mixture. In fact, estimate volumetric properties. the overall average ratio or adjustment factor for the PSPA The instrumented rollers were used on too few projects for was close to unity (1.1). This was not the case for the FWD. a detailed comparison to the other NDT devices. The rollers Without making any corrections for volumetric differ- were used to monitor the increase in density and stiffness ences to the laboratory dynamic modulus values, the stan- with an increasing number of roller passes. One potential dard error for the PSPA was 76 ksi (laboratory values disadvantage with these rollers is that they may bridge local- assumed to be the target values). The PSPA was used on ized soft areas. However, based on the results obtained, HMA surfaces after compaction and the day following their ability of provide uniform compaction was verified placement. The PSPA modulus values measured immedi- and these rollers are believed to be worth future investment ately following compaction were found to be similar to the in monitoring the compaction of unbound materials. values 1 or 2 days after placement--making proper tem- The GPR resulted in reasonably accurate estimates to the perature corrections in accordance with the master curves thickness of aggregate base layers. None of the other NDT measured in the laboratory. devices had the capability or same accuracy to determine A measure of the mixture density or air voids is required to the thickness of the unbound layer. judge the acceptability of the modulus value from a dura- bility standpoint. The non-nuclear gauges were found to be acceptable, assuming that the gauges had been properly 2.6.2 NDT Devices for HMA Mixtures calibrated to the specific mixture--as for the PSPA. and Layers Use of the GPR single antenna method, even with mixture The PSPA had the highest success rate for identifying an calibration, requires assumptions on specific volumetric area with anomalies, 93 percent. The PQI identified about properties that do vary along a project. As the mixture three-fourths of the anomalies, while the FWD and GPR properties change, the dielectric values may or may not be identified about one-half of those areas. The seismic and affected. Use of the proprietary GPR analysis method on non-nuclear gauges were the only technologies that consis- other projects was found to be acceptable for the air void or tently identified differences between the areas with and relative compaction method. This proprietary and multiple without segregation. These two technologies also consis- antenna system, however, was not used within Part A of the tently found differences between the longitudinal joint and field evaluation to determine its success rate in identifying interior of the mat. localized anomalies and physical differences between differ- The non-nuclear density gauges (PaveTracker) were able ent areas. Both GPR systems were found to be very good for to identify and measure the detrimental effect of rolling the measuring layer thickness along the roadway. HMA mat within the temperature sensitive zone. This Water can have a definite affect on the HMA density mea- technology was beneficial on some of the Part B projects sured with the non-nuclear density gauges (PQI). The man- for optimizing the rolling pattern initially used by the ufacturer's recommendation is to measure the density contractor. immediately after compaction, before allowing any traffic Three to four repeat measurements were made at each test on the HMA surface. Within this project, the effect of water point with the NDT devices. was observed on the PQI readings, as compared to dry sur- -- The PSPA had a repeatability value, a median or pooled faces. The measured density of wet surfaces did increase, standard deviation, of about 30 ksi for most mixtures, compared to dry surfaces. From the limited testing com- with the exception of the US-280 supplemental mix- pleted with wet and dry surfaces, the PaveTracker was less ture, which was much higher. affected by surface conditions. However, wet versus dry -- The FWD resulted in comparable value for the SMA surfaces were not included in the field evaluation plan for mixture (55 ksi), but had a higher value for the US-280 different devices. Based on the data collected within the mixture (275 ksi). field evaluation, wet surfaces did result in a bias of the den- -- The non-nuclear density gauges had repeatability values sity measurements with this technology. similar to nuclear density gauges, a value less than 1.5 pcf. Another important condition is the effect of time and vary- -- The repeatability for the GPR device was found to be ing water content on the properties of the HMA mixture good and repeatable, with values of 0.5 percent for air during construction. There have been various studies com- voids and 0.05 in. for thickness. pleted on using the PSPA to detect stripping and moisture

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78 damage in HMA mixtures. For example, Hammons et al. has been improved and its reliability has increased. The (2005) used the PSPA (in combination with GPR) to locate technology is suggested for use on a control basis but areas with stripping along selected interstate highways in not for acceptance. Georgia. The testing completed within this study also sup- Ultrasonic technology (PSPA) for HMA layers and materi- ports the use of the seismic-based technology to identify als is suggested for use in control and acceptance plans. such anomalies. -- Test temperature is the main boundary condition for The instrumented rollers used to establish the increase in the use of the PSPA. Elevated temperatures during mix stiffness with number of passes was correlated to the placement can result in erratic response measurements. increases in density, as measured by different devices. Thus, the gauge may not provide reliable responses for These rollers were used on too few projects to develop or monitoring the compaction of HMA layers or for confirm any correlation between the NDT response and determining when the rollers are operating within the the instrumented roller's response. One issue that will temperature sensitive zone for the specific mixture. need to be addressed is the effect of decreasing temperature -- These gauges need to be calibrated to the specific mix- on the stiffness of the mixture and how the IC roller per- ture being tested. However, this technology can be used ceives that increase in stiffness related to increases in den- in the laboratory to measure the seismic modulus on test sity of the mat. A potential disadvantage with these rollers specimens during mixture design or verification prior to is that they will bridge segregated areas and may not accu- measuring the dynamic modulus in the laboratory. rately identify cold spots in the HMA mat. However, based -- A limitation of this technology is that the results on the results obtained, the ability to provide uniform (material moduli) do not provide an indication on the compaction was verified, and the rollers are believed to be durability of the HMA mixture. Density or air void mea- worth future investments in monitoring the compaction of surements are needed to define durability estimates. HMA mixtures. -- The DSPA for testing unbound layers is influenced by the condition of the surface. High modulus values near the surface of the layer will increase the modulus esti- 2.6.3 Limitations and Boundary Conditions mated with the DSPA. Thus, the DSPA also needs to be The following lists the limitations and boundary conditions calibrated to the specific material being evaluated. observed during the field evaluation for the NDT devices Steady-state vibratory technology (GeoGauge) for unbound suggested for QA application on an immediate, effective, and layers and materials is suggested for use in control and practical basis. acceptance plans. -- This technology or device should be used with caution All NDT devices suggested for QA application, with the when testing fine-grained soils with high water con- exception of the GPR and IC rollers, are point-specific tests. tents. In addition, it should not be used to test well- Point-specific tests are considered a limitation because of graded, non-cohesive sands that are dry. the number of samples required to identify localized anom- -- The condition of the surface of the layer is important alies that deviate from the population distribution. and should be free of loose particles. A layer of moist -- Ultrasonic scanners are currently under development. sand should also be placed to fill the surface voids and Relatively continuous measurements can be made with ensure that the gauge's ring is in contact with about this technology. These scanners are still considered to be 75 percent of the material's surface. Placing this thin in the research and development stage and are not ready layer of moist sand takes time and increases the time for immediate and practical use in a QA program. needed for testing. -- GPR technology to estimate the volumetric properties -- These gauges need to be calibrated to the specific material of HMA mixtures is available for use on a commercial being evaluated. They are influenced by the underlying basis, but the proprietary system has only had limited layer when testing layers that are less than 8 in. thick. verification of its potential use in QA applications and -- These gauges are not applicable for use in the labora- validation of all volumetric properties determined with tory during the preparation of M-D relationships that the system. will be used for monitoring compaction. The DSPA -- Similarly, the IC rollers take continuous measurements technology is applicable for laboratory use to test the of density or stiffness of the material being compacted. samples used to determine the M-D relationship. During the field evaluation, some of these rollers had -- A relative calibration process is available for use on a both hardware and software problems. Thus, these day-to-day basis. However, if the gauge does go out of devices were not considered immediately ready for use calibration, it must be returned to the manufacturer for in a day-to-day QA program. The equipment, however, internal adjustments and calibration.

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79 -- These gauges do not determine the density and water -- Use of this technology, even to estimate layer thickness, content of the material. The water content and density should be used with caution when measuring the thick- of the unbound layer should be measured with other ness of the first lift placed above PATB layers. devices. -- GPR can be used to estimate the volumetric properties Non-nuclear density gauges (electric technology) for HMA of HMA mats, but that technology has yet to be verified layers and materials are suggested for use in control and on a global basis. acceptance plans. -- Measurements using this technology and associated -- The results from these non-nuclear density gauges can be devices cannot be calibrated using laboratory data. dependent on the condition of the layer's surface--wet IC rollers are suggested for use in a control plan, but not in versus dry conditions. It is recommended that the gauges an acceptance plan. be used on relatively dry surfaces until additional data -- The instrumented rollers may not identify localized become available relative to this limitation. Free water anomalies in the layer being evaluated. These rollers should be removed from the surface to minimize any can bridge some defects, that is, they lack the level of affect on the density readings. However, water penetrat- sensitivity required to identify defects that are confined ing the surface voids in segregated areas will probably to local areas. affect the readings--incorrect or high density readings, -- Temperature is an issue with the use of IC rollers for compared with the actual density from a core. The PSPA compacting HMA layers. Although most of these rollers was able to identify areas with segregation. have the capability to measure the surface temperature -- These gauges need to be calibrated to the specific material of the mat, the effect of temperature on the mat stiffness under evaluation. is an issue--as temperature decreases, the mat stiffness GPR technology for thickness determination of HMA and will increase, not necessarily because of an increase in unbound layers is suggested for use in acceptance plans. the density of the mat. Delaying the compaction would -- The data analysis or interpretation is a limitation of increase the stiffness of the mat measured under the this technology. The GPR data requires some time to rollers because of the decrease in temperature. estimate the material property--the time for layer -- The instrumented rollers also did not properly identify thickness estimates is much less than those for other when checking and tearing of the mat occurred during layer properties. rolling. The non-nuclear density gauges (PaveTracker) -- This technology requires the use of cores for calibration did identify this detrimental condition. purposes. Cores need to be taken periodically to confirm -- Measurements using this technology and associated the calibration factors used to estimate the properties. devices cannot be calibrated using laboratory data.