NDT Technology for Quality Assurance of HMA Pavement Construction (2009)

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This appendix contains the Volume 1—Procedural Manual for NCHRP Project 10-65. A P P E N D I X B Volume 1—Procedural Manual 87

88 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

89 NCHRP 10-65—Part 1: Procedural Manual June 2008 Final Report 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).

90 NCHRP 10-65—Part 1: Procedural Manual June 2008 Final Report 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

91 NCHRP 10-65—Part 1: Procedural Manual June 2008 Final Report 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. Carriage case recently developed for facilitating the use of the PSPA & DSPA in data collection.

92 NCHRP 10-65—Part 1: Procedural Manual June 2008 Final Report Figure 3. Humboldt GeoGauge Figure 4. Non-Nuclear Density Gauge, PaveTracker

93 NCHRP 10-65—Part 1: Procedural Manual June 2008 Final Report 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. s LSLXQL ................................................................................................................ (1) s XUSLQL ................................................................................................................ (2) Where: LQ = Lower quality index. UQ = 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. 100UL PWLPWLPWL ......................................................................................... (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.

94 NCHRP 10-65—Part 1: Procedural Manual June 2008 Final Report 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. sAXUCL X 3 ........................................................................................................ (4) sAXLCL X 3 ........................................................................................................ (5) Where: X UCL = Upper control limit for the sample means. X LCL = 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.

95 NCHRP 10-65—Part 1: Procedural Manual June 2008 Final Report 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. sBUCL s 3 ................................................................................................................ (6) sBLCL s 4 ................................................................................................................ (7) RDUCL R 3 .............................................................................................................. (8) RDLCL R 4 .............................................................................................................. (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.

96 NCHRP 10-65—Part 1: Procedural Manual June 2008 Final Report 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.

97 NCHRP 10-65—Part 1: Procedural Manual June 2008 Final Report 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. Figure 5. HMA Dynamic Moduli, Measured in the Laboratory or Calculated Using MEPDG Regression Equation Dynamic Modulus Regression Equation 0.1 1 10 100 0.1 1 10 100 Frequency, Hz. D yn am ic M od ul us , E x 1 05 ps i 70 F 90 F 110 130 150 Dynamic Modulus Regression Equation 0.1 1 10 100 60 70 80 90 100 110 120 130 140 150 160 Temperature, F D yn am ic M od ul us , E x 1 05 ps i 0.5 1 5 10 25 `

98 NCHRP 10-65—Part 1: Procedural Manual June 2008 Final Report Step 4: Measure Laboratory Seismic Modulus on Plant Produced Mixture The seismic modulus should be measured in accordance with ASTM D 5345. The seismic modulus can be measured on those test specimens that were prepared for the mixture verification process (see step 2), as long as they were compacted to the expected or specified in-place target density or air void level. The seismic modulus is measured on test specimens for each temperature selected under step 3 using a device, known as a V-meter, containing a pulse generator and a timing circuit, coupled with piezoelectric transmitting and receiving transducers (see Figure 6). The timing circuit digitally displays the time needed for a wave to travel through the test specimen. The measured travel time, the dimensions, and the mass of the test specimen are used to calculate the modulus. The free-free resonant column (FFRC) test is a laboratory test to measure the modulus of the HMA mixture during the mixture design and field verification process. A cylindrical specimen is subjected to an impulse load at one end. Seismic energy over a large range of frequencies will propagate within the specimen. Depending on the dimensions and the stiffness of the specimen, energy associated with one or more frequencies are trapped and magnified (resonate) as they propagate within the specimen. The goal with this test is to determine these resonant frequencies. Since the dimensions of the specimen are known, if one can determine the frequencies that are resonating (i.e., the resonant frequencies), one can readily calculate the modulus of the test specimen. Figure 6. Equipment for Measuring the Seismic Modulus of Laboratory Compacted Test Specimens

99 NCHRP 10-65—Part 1: Procedural Manual June 2008 Final Report The seismic modulus should be translated into a design modulus (see Figure 7). This step is necessary because seismic moduli are low-strain, high-strain-rate values, whereas the design moduli are based on low-strain, low-strain-rate values. The method of calculating the design modulus is to develop a master curve based on the recommendations of NCHRP Report 465, "Simple Performance Test for Superpave Mix Design," or in accordance with the NCHRP Project 9-33 mixture design procedure. Figure 7. Graphical Illustration for Shifting the Seismic Moduli to the Dynamic Moduli for a Specific Load Frequency Using the Mixture Master Curve Select the mat temperatures that are expected during the acceptance testing (see step 3). Typical values that can be used include 90, 110, 130, and 150 °F. The seismic shift factor is determined using Equation 10. TTc TTc aLog o o T 2 1 (10) Where: c1 = Regression coefficient determined from the dynamic modulus tests or calculations (for neat mixtures this value has been reported to be 19 and for polymer modified asphalt mixtures the value is 17.44). 1 10 100 1000 1E-02 1 Seismic Design Frequency Design Modulus 10000 1E-04 1E+02 Frequency (Hz) M o du lu s (k si) 1E+06 1E+081E+04 Step 5: Determine Seismic Shift Factor to Translate the Seismic Modulus into the Design Modulus

100 NCHRP 10-65—Part 1: Procedural Manual June 2008 Final Report c2 = Regression coefficient determined from the dynamic modulus tests or calculations (for neat mixtures this value has been reported to be 92, while for polymer modified mixtures this value is 51.6). To = Reference temperature, which should be the median value expected during acceptance testing. T = Test temperature. Equation 10 is used to translate the PSPA seismic moduli measured at varying surface temperatures during acceptance testing to the design modulus at the reference temperature and frequency. The reference temperature should be the approximate mid-range temperature during acceptance testing. Using the mid-range temperature should reduce or minimize potential bias that could be present if always translating to a higher or lower temperature. The seismic shift factors are entered in the PSPA software to adjust the seismic values to the design frequency selected (see Figure 7). It is recommended that a load frequency of 5 Hz be used to determine the design modulus. However, the agency can select other frequencies to be consistent with the posted speed limit of the project—an input to the MEPDG. Step 6: Determine the Field Adjustment Factor (Adjusting Field to Laboratory Conditions) This step is to determine the field ratio for adjusting the design moduli to laboratory conditions. In other words, that ratio should be used to adjust the design moduli measured with the PSPA to laboratory conditions. a. Select 8 to 10 random locations within the control strip or first day’s production and measure the PSPA modulus and surface temperatures in accordance with step 7. b. Drill and recover cores at a minimum of three locations. One core should be recovered from a location where the higher seismic modulus was measured, one at the location of the lowest seismic modulus, and the third at the median modulus value. c. Measure the bulk specific gravity (Gmb) of each core from the HMA mat in accordance with AASHTO T 166. d. Measure the maximum specific gravity (Gmm) of each core in accordance with AASHTO T 209. e. Calculate the air void level (Va) of each core in accordance with AASHTO T 269 and determine the percent compaction using Equation 11. aVCompaction 100% (11) f. Calculate or measure the dynamic modulus of the mixture using the average air void level measured from the three field cores.

101 NCHRP 10-65—Part 1: Procedural Manual June 2008 Final Report g. Determine the specific adjustment ratio for the mixture in accordance with Equation 12. Design Lab E E R * (12) h. 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 HMA mixtures. It is expected that the ratio should be within three standard deviations. If the field ratio is outside three standard deviations from the mean value, it is expected that a significant change has occurred to the mixture between field verification and production. If the values are outside three standard deviations from those listed in Table 1, the mixture should be evaluated in more detail to ensure that the values are correct. Field Adjustment Ratios HMA Mixture Type Mean StandardDeviation High binder content mixtures that exhibit tenderness, including SMA type mixtures 0.89 0.153 Harsh mixtures, coarse-graded mixtures including PMA 1.34 0.231 Table 1. Summary of the Average Ratios That Have Been Measured on Other HMA Mixtures Step 7: Acceptance Testing with the PSPA for Measuring Modulus of HMA Mixtures a. Allow the mixture to cool prior to using the PSPA. Elevated temperatures can cause the rubber pads on the tips of the receivers to melt. The test should be performed on areas with surface temperatures less than 200°F. The PSPA test should be performed in accordance with the manufacturer’s recommendations. b. Remove any loose material on the surface. The receivers or sensors should be in direct contact with the test surface. c. Place the PSPA on the HMA surface. Align the sensor bar parallel to the direction of the paver and rollers. Slightly push the sensor bar to ensure that the receivers are in good contact with the surface. If mat tears or checking is observed in the test area, the PSPA should not be moved; the test should be conducted on that area, regardless of the surface condition. d. After seating the PSPA, activate the software. Enter the type of surface tested and the mat thickness into the software. Inspect the graphical display of the load response and receivers on the screen of the laptop. If the load pulse has an irregular shape, repeat the test. One of the receivers may not be in good contact with the surface.

102 NCHRP 10-65—Part 1: Procedural Manual June 2008 Final Report 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. Gauge CoreDCF or )( )( Gaugemb Coremb G G γ γ (13)

103 NCHRP 10-65—Part 1: Procedural Manual June 2008 Final Report 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.

104 NCHRP 10-65—Part 1: Procedural Manual June 2008 Final Report 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. 145 147 149 151 153 155 157 159 161 163 165 0 1 2 3 4 5 Number of Roller Passes D en si ty M ea su re d w ith P av eT ra ck er , p cf 170 180 190 200 210 220 230 Te m pe ra tu re o f M ix tu re , F Mat Density Joint Density Mat Temperature Joint Temperature 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.

105 NCHRP 10-65—Part 1: Procedural Manual June 2008 Final Report Pooled Standard Deviation for Density = 2.5 pcf 146.0 148.0 150.0 152.0 154.0 156.0 158.0 0 2 4 6 8 10 12 Number of Passes of the Rollers D en si ty o f M at M ea su re d w ith Pa ve Tr ac ke r, pc f 200 210 220 230 240 250 260 Te m pe ra tu re o f M ix tu re , F Density Temperature 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

106 NCHRP 10-65—Part 1: Procedural Manual June 2008 Final Report 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. Layer & Material Type Confinement, psi Repeated Stress, psi Total Vertical Stress, psi Subgrade; Fine-Gained Soils with Plasticity 2 2 4 Embankment; Soil-Aggregate Mixture 4 4 8 Crushed Aggregate Base 6 6 12 Table 2. Option A—Measure Resilient Modulus Figure 10. Resilient Modulus Measured in the Laboratory for a Crushed Stone Base Material 10000 30000 50000 70000 90000 110000 130000 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 R es ili en t M od ul us , p si Confinement = 3 psi Confinement = 6 psi Confinement = 10 psi Confinement = 15 psi Confinement = 20 psi

107 NCHRP 10-65—Part 1: Procedural Manual June 2008 Final Report 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. 32 11 k a oct k a aR pp pkM θ θ θ τ τ τ σ σ σ σ σ σ σ σ σ σ (14) Where: = Bulk Stress, psi 321 15) = Octahedral shear stress, psi 3 5.02 13 2 32 2 21 ( (16) ap = Atmospheric pressure, 14.7 psi. 3,2,1 = Principal stress, psi. 3,2,1k = Regression constants from laboratory resilient modulus test results. 10 20 30 40 50 60 70 80 90 0 10 20 30 40 50 60 70 80 90 100 Bulk Stress, psi R es ili en t M od ul us , k si Confinement = 3 psi Confinement = 6 psi Confinement = 10 psi Confinement = 15 psi Confinement = 20 psi

108 NCHRP 10-65—Part 1: Procedural Manual June 2008 Final Report 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: dryswLL γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ Pk 0001.0037.00088.0008.07632.0 8/31 (17) 40# 2 8/32 00000024.00006.0 038.00008.00016.02159.2 P wLLPk dry dry s (18) dryswLLk 0005.00014.00082.01720.13 (19) Embankments, Soil-Aggregate Mixture, Coarse-Grained 40# 2 200#4#8/31 00000082.0 3932.06456.10426.00000016.0 0149.00027.00174.00130.05856.0 P w w w PIPPPk Max Max s Max dry SMax (20) 40# 2 200#2 00000027.0 1483.00001.00081.00060.07833.0 P w w PIPk dry opt s Max (21) 40# 2 200#3 00000081.00026.01906.0 P Pk opt (22) Embankments, Soil-Aggregate Mixture, Fine-Grained Max dry optw LLPPk 179.1051.0 0030.00128.00051.07668.0 200#4#1 (23) Max dryPPk 3941.10061.00141.04951.0 200#4#2 (24) Max dryLLPk 8903.30036.00293.09303.0 8/33 (25)

109 NCHRP 10-65—Part 1: Procedural Manual June 2008 Final Report Fine-Grained Clay Soil swClayk 0437.00106.03577.11 (26) swLL PPPk 0049.00030.0 0027.00095.00073.05193.0 200#40#4#2 (27) opt s dryopt w w wLL γ γ SiltPPPk 6055.00025.00026.00672.00535.0 025.00521.00303.00288.04258.1 max 200#40#4#3 (28) 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. DesignM LabM R R R Resilient Modulus (29) 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

110 NCHRP 10-65—Part 1: Procedural Manual June 2008 Final Report 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 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 5 10 15 20 25 30 0 2 4 6 8 10 12 Number of Roller Passes R es ili en t M od ul us fr om N D T D ev ic es , k si DCP GeoGauge Log. (GeoGauge) Log. (DCP)

111 NCHRP 10-65—Part 1: Procedural Manual June 2008 Final Report 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.

112 NCHRP 10-65—Part 1: Procedural Manual June 2008 Final Report 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