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67 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. 126.96.36.199 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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69 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 188.8.131.52 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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70 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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71 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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72 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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73 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-