National Academies Press: OpenBook
« Previous: Front Matter
Page 1
Suggested Citation:"Summary." National Academies of Sciences, Engineering, and Medicine. 2009. NDT Technology for Quality Assurance of HMA Pavement Construction. Washington, DC: The National Academies Press. doi: 10.17226/14272.
×
Page 1
Page 2
Suggested Citation:"Summary." National Academies of Sciences, Engineering, and Medicine. 2009. NDT Technology for Quality Assurance of HMA Pavement Construction. Washington, DC: The National Academies Press. doi: 10.17226/14272.
×
Page 2
Page 3
Suggested Citation:"Summary." National Academies of Sciences, Engineering, and Medicine. 2009. NDT Technology for Quality Assurance of HMA Pavement Construction. Washington, DC: The National Academies Press. doi: 10.17226/14272.
×
Page 3
Page 4
Suggested Citation:"Summary." National Academies of Sciences, Engineering, and Medicine. 2009. NDT Technology for Quality Assurance of HMA Pavement Construction. Washington, DC: The National Academies Press. doi: 10.17226/14272.
×
Page 4
Page 5
Suggested Citation:"Summary." National Academies of Sciences, Engineering, and Medicine. 2009. NDT Technology for Quality Assurance of HMA Pavement Construction. Washington, DC: The National Academies Press. doi: 10.17226/14272.
×
Page 5
Page 6
Suggested Citation:"Summary." National Academies of Sciences, Engineering, and Medicine. 2009. NDT Technology for Quality Assurance of HMA Pavement Construction. Washington, DC: The National Academies Press. doi: 10.17226/14272.
×
Page 6
Page 7
Suggested Citation:"Summary." National Academies of Sciences, Engineering, and Medicine. 2009. NDT Technology for Quality Assurance of HMA Pavement Construction. Washington, DC: The National Academies Press. doi: 10.17226/14272.
×
Page 7
Page 8
Suggested Citation:"Summary." National Academies of Sciences, Engineering, and Medicine. 2009. NDT Technology for Quality Assurance of HMA Pavement Construction. Washington, DC: The National Academies Press. doi: 10.17226/14272.
×
Page 8
Page 9
Suggested Citation:"Summary." National Academies of Sciences, Engineering, and Medicine. 2009. NDT Technology for Quality Assurance of HMA Pavement Construction. Washington, DC: The National Academies Press. doi: 10.17226/14272.
×
Page 9
Page 10
Suggested Citation:"Summary." National Academies of Sciences, Engineering, and Medicine. 2009. NDT Technology for Quality Assurance of HMA Pavement Construction. Washington, DC: The National Academies Press. doi: 10.17226/14272.
×
Page 10
Page 11
Suggested Citation:"Summary." National Academies of Sciences, Engineering, and Medicine. 2009. NDT Technology for Quality Assurance of HMA Pavement Construction. Washington, DC: The National Academies Press. doi: 10.17226/14272.
×
Page 11
Page 12
Suggested Citation:"Summary." National Academies of Sciences, Engineering, and Medicine. 2009. NDT Technology for Quality Assurance of HMA Pavement Construction. Washington, DC: The National Academies Press. doi: 10.17226/14272.
×
Page 12
Page 13
Suggested Citation:"Summary." National Academies of Sciences, Engineering, and Medicine. 2009. NDT Technology for Quality Assurance of HMA Pavement Construction. Washington, DC: The National Academies Press. doi: 10.17226/14272.
×
Page 13
Page 14
Suggested Citation:"Summary." National Academies of Sciences, Engineering, and Medicine. 2009. NDT Technology for Quality Assurance of HMA Pavement Construction. Washington, DC: The National Academies Press. doi: 10.17226/14272.
×
Page 14
Page 15
Suggested Citation:"Summary." National Academies of Sciences, Engineering, and Medicine. 2009. NDT Technology for Quality Assurance of HMA Pavement Construction. Washington, DC: The National Academies Press. doi: 10.17226/14272.
×
Page 15
Page 16
Suggested Citation:"Summary." National Academies of Sciences, Engineering, and Medicine. 2009. NDT Technology for Quality Assurance of HMA Pavement Construction. Washington, DC: The National Academies Press. doi: 10.17226/14272.
×
Page 16
Page 17
Suggested Citation:"Summary." National Academies of Sciences, Engineering, and Medicine. 2009. NDT Technology for Quality Assurance of HMA Pavement Construction. Washington, DC: The National Academies Press. doi: 10.17226/14272.
×
Page 17
Page 18
Suggested Citation:"Summary." National Academies of Sciences, Engineering, and Medicine. 2009. NDT Technology for Quality Assurance of HMA Pavement Construction. Washington, DC: The National Academies Press. doi: 10.17226/14272.
×
Page 18
Page 19
Suggested Citation:"Summary." National Academies of Sciences, Engineering, and Medicine. 2009. NDT Technology for Quality Assurance of HMA Pavement Construction. Washington, DC: The National Academies Press. doi: 10.17226/14272.
×
Page 19
Page 20
Suggested Citation:"Summary." National Academies of Sciences, Engineering, and Medicine. 2009. NDT Technology for Quality Assurance of HMA Pavement Construction. Washington, DC: The National Academies Press. doi: 10.17226/14272.
×
Page 20
Page 21
Suggested Citation:"Summary." National Academies of Sciences, Engineering, and Medicine. 2009. NDT Technology for Quality Assurance of HMA Pavement Construction. Washington, DC: The National Academies Press. doi: 10.17226/14272.
×
Page 21
Page 22
Suggested Citation:"Summary." National Academies of Sciences, Engineering, and Medicine. 2009. NDT Technology for Quality Assurance of HMA Pavement Construction. Washington, DC: The National Academies Press. doi: 10.17226/14272.
×
Page 22

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

S U M M A R Y Introduction Quality assurance (QA) programs provide the owner and contractor a means to ensure that the desired results are obtained to produce high-quality, long-life pavements. Desired results are those that meet or exceed the specifications and design requirements. Traditional pavement construction quality control and quality acceptance (QC/QA) procedures include a variety of laboratory and field test methods that measure volumetric and surface properties of pavement materials. The test methods to measure the volumetric properties have changed little within the past couple of decades. More recently, nondestructive testing (NDT) methods, including lasers, ground-penetrating radar (GPR), falling weight deflectometers (FWD), penetrometers, and infrared and seismic technologies have been improved significantly and have shown potential for use in the QC/QA of flexible pavement construction. Furthermore, the new Mechanistic-Empirical Pavement Design Guide (MEPDG) uses layer modulus as a key material property. This should lead to increased measurement of layer moduli—a material property that can be estimated through NDT tests, which is not included, at present, in the acceptance plan. This research study investigated the application of existing NDT technologies for measuring the quality of flexible pavements. Promising NDT technologies were assessed on actual field projects for their ability to evaluate the quality of pavement layers during or immediately after placement or to accept the entire pavement at its completion. The results from this project identified NDT technologies ready and appropriate for implementation in routine, practical QC/QA operations. Objectives The overall objective of NCHRP Project 10-65 was to identify NDT technologies that have immediate application for routine, practical QA operations to assist agency and contractor personnel in judging the quality of hot mix asphalt (HMA) overlays and flexible pavement construction. This objective was divided into two parts: 1. Conduct a field evaluation of selected NDT technologies to determine their effectiveness and practicality for QC/QA of flexible pavement construction. 2. Recommend appropriate test protocols based on the field evaluation and test results. Effectiveness and practicality are key words in the first part of the objective. The field evaluation plan was developed to determine the effectiveness and practicality of different NDT Technology for Quality Assurance of HMA Pavement Construction 1

2NDT technologies for use in QA programs. These terms are defined as follows for NCHRP Project 10-65: • Effectiveness of NDT Technology—Ability or capability of the technology and device to detect changes in unbound materials or HMA mixtures that affect the performance and design life of flexible pavements and HMA overlays. • Practicality of NDT Technology—Capability of the technology and device to collect and interpret data on a real-time basis to assist project construction personnel (QC/QA) in making accurate decisions in controlling and accepting the final product. Integration of Structural Design, Mixture Design, and Quality Assurance The approach taken for this project was to use fundamental properties that are needed for both mixture and structural design for both control and acceptance of flexible pavements and HMA overlays. Figure 1 illustrates this integration or systems approach. The material or layer properties were grouped into three areas—volumetric, structural, and functional—and the NDT technologies were evaluated for their ability to estimate these properties accurately. Using the same mixture properties for accepting the pavement layer that were used for structural and mix- ture design allows the agency to more precisely estimate the impact that deficient materials and pavement layers have on performance. The material tests that are needed for structural and mixture design using the newer procedures are listed in Table 1. Two structural properties that are needed to predict the performance of flexible pavements and HMA overlays are modulus and thickness. These are called “quality characteristics,” and they are defined in Transportation Research Circular E-C037 as “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).” Products The final deliverables for NCHRP Project 10-65 were divided into three volumes. Volume 1 is the procedural manual for implementing the NDT methods for QA application. It is included herein as Appendix B. It contains some of the examples for application of the modulus values for controlling and accepting flexible pavements. Volume 2 is the standard NCHRP final report. Part 3 of Volume 2 is the main body of NCHRP Report 626. Volume 3 includes the appendices for the other two volumes. It is not published herein. The appendices in Volume 3 also include the data generated from this project. The complete three volumes are presented in NCHRP Web-Only Document 133. NDT Devices Included in the Field Evaluation A large number of NDT technologies and devices have been used for pavement evaluation and forensic studies. Table 2 summarizes the technologies and methods that have been used to mea- sure different properties and features of flexible pavements. As tabulated, GPR has been used for estimating many more volumetric properties and features than any other NDT technology, while the deflection and ultrasonic-based technologies have been used more for estimating structural properties and features. To narrow the list of NDT devices that have potential for QA application, several highway agencies were contacted to collect information on their practices and experiences. Research

reports of several agencies were also reviewed. These agencies include Arizona, California, Connecticut, Florida, Georgia, Illinois, Maryland, New Hampshire, Minnesota, Mississippi, Missouri, Nevada, Ohio, Oklahoma, Pennsylvania, Texas, Virginia, Washington, and Wisconsin Departments of Transportation (DOTs), the Federal Aviation Administration (FAA), Federal Highway Administration (FHWA), Eastern Federal Lands Division, Central Federal Lands Division, U.S. Air Force, U.S. Army Corps of Engineers Engineer Research and Development Center, Loughborogh University, Nottingham Trent University, Transport Research Laboratory 3 Select Strategy: Trial cross-sections for pavement structural design or rehabilitation. Complete structural design using mixture specifications; Select structural properties to minimize distress. Material selection & certification; Source approval. Material Specifications: Aggregate, Asphalt Binder, Additives, etc. Volumetric Mixture Design; Superpave Gyratory Compactor Feedback from monitoring pavement performance, NCHRP Project 9-30 Confirmation – Adjustment of volumetric mixture design. Prepare specimens over range of volumetric conditions. Perform NDT QA tests on laboratory test specimens. Mix Design Tests, NCHRP Project 9-33 QA Tests; NCHRP Project 10-65 Select final mixture design & measure E* master curve. Field Verification of Mixture Design Select/Establish QA criteria for measuring quality; determine seismic design modulus. Agency Acceptance Plan & Specifications Contractor Quality Control Plan Pavement Management: Monitoring projects – Functional, Structural, Volumetric Properties & Surface Distress. Confirmation of structural design assumptions & performance expectations Perform torture test(s) (APA, Hamburg, etc.) or Dynamic modulus, fracture, permanent deformation tests, etc.; NCHRP Project 9-19. Site Features & Inputs: Climate Traffic Foundation Structural Design, NCHRP Project 1- 37A Calibrate NDT QA tests; control strips, NCHRP Project 10-65. PRS, NCHRP Project 9- 22 Figure 1. Example flow chart for the systems approach for specifying, designing, and placing quality HMA mixtures.

4(formerly known as the Transport and Road Research Laboratory [TRRL]) University of Illinois, University of Mississippi, Louisiana State University, Worcester Polytechnic Institute, and Texas Transportation Institute. Some of the equipment manufacturers and suppliers were also con- tacted to obtain specific information and data on the different NDT devices and technologies. The manufacturers contacted include Olson Engineering; Blackhawk; Geophysical Survey Systems; Inc. (GSSI); TransTech Systems, Inc.; Dynatest; Carl Bro, and others. The following list identifies the factors used to evaluate specific NDT devices that have rea- sonable success of being included in a QA program: • Accuracy and precision of the test equipment and protocols in measuring a specific material property—one of the difficulties of this category is defining the target value of some properties for nonlinear and viscoelastic materials. The accuracy and precision of the technology is also tied to the data interpretation procedures. • Data collection guidelines and interpretation procedures—this category examines whether there are generalized guidelines and procedures available for performing the tests and analyzing the data to estimate the material properties and/or features. • Availability of standardized test procedures (test protocols)—this category verifies if there is a test standard available for use in collecting NDT data to estimate the required material prop- erties and features. • Data collection—production rate of the NDT equipment in collecting the data. • Data interpretation—time and ancillary equipment/software required to analyze and interpret the data for estimating the specific layer property. • Cost of the equipment—this category considers the initial cost of the test equipment, addi- tional software and hardware requirements necessary to perform the test, and the operational and maintenance costs, including calibration. Property Needed for: Pavement Layer Material-Layer Property Structural Design Mixture Design Acceptance Density – Air Voids at Construction Yes Yes Voids in Mineral Aggregate Yes Yes Effective Asphalt Binder Content Yes Yes Voids Filled with Asphalt Yes Gradation Yes Yes Asphalt Binder Properties Yes Yes IDT Strength and Creep Compliance Yes Yes Dynamic Modulus Yes Yes Flow Time or Flow Number Yes HMA Layers; Dense-Graded Mixtures Smoothness, Initial Yes Density Yes Yes Water Content Yes Yes Gradation Yes Yes Minus 200 Material Yes Yes Plasticity Index (Atterberg Limits) Yes Yes Resilient Modulus Yes Yes CBR or R-Value Yes Yes Unbound Layers; Dense Graded Granular Base, Embankment Soils Strength DCP; Penetration Rate Yes IDT – Indirect Tensile CBR – California Bearing Ratio DCP – Dynamic Cone Penetrometer Table 1. Summary of material and layer properties used for design and acceptance of flexible pavements and HMA overlays.

5• Complexity of the equipment or personnel training requirements. • Ability of the test method and procedure to quantify the material properties needed for QA, mixture design, and structural design (see Figure 1). In other words, is the NDT test result applicable to mixture and structural design? • Relationship between the test result and other traditional and advanced tests used in mixture design and structural design. NDT Technologies and Methods Type of Property or Feature HMA Layers Unbound Aggregate Base and Soil Layers Density GPR Non-Nuclear Gauges; PQI, PaveTracker GPR Non-Nuclear Gauges; EDG, Purdue TDR Air Voids or Percent Compaction GPR Infrared Tomography Acoustic Emissions Roller-Mounted Density Devices GPR Roller-Mounted Density Devices Fluids Content GPR GPR Non-Nuclear Gauges; EDG, Purdue TDR Gradation; Segregation GPR Infrared Tomography ROSAN NA Volumetric Voids in Mineral Aggregate GPR (Proprietary Method) NA Thickness GPR Ultrasonic; Impact Echo, SPA, SASW Magnetic Tomography GPR Ultrasonic; SASW, SPA Modulus; Dynamic or Resilient Ultrasonic; PSPA, SASW Deflection-Based; FWD, LWD, Roller-Mounted Response Systems; Asphalt Manager Impact/Penetration; DCP, Clegg Hammer Ultrasonic; DSPA, SPA, SASW Deflection-Based; FWD, LWD Steady-State Vibratory; GeoGauge Roller-Mounted Response Systems Structural Bond/Adhesion Between Lifts Ultrasonic; SASW, Impulse Response Infrared Tomography NA Profile; IRI Profilograph, Profilometer, Inertial Profilers NA Noise Noise Trailers NAFunctional Friction CT Meter, ROSAN NA SPA – Seismic Pavement Analyzer PSPA – Portable Seismic Pavement Analyzer SASW – Spectral Analysis of Surface Waves LWD – Light Weight Deflectometer ROSAN - ROad Surface ANalyzer EDG – Electrical Density Gauge TDR – Time Domain Reflectometry DSPA – Dirt Seismic Pavement Analyzer PQI – Pavement Quality Indicator DCP – Dynamic Cone Penetrometer CT – Circular Texture FWD – Falling Weight Deflectometer Table 2. NDT methods used to measure properties and features of flexible pavements in place.

6NDT Devices Included in the Field Evaluation The following list contains, in no particular order, the NDT technologies and devices that were selected for use in the field study: • Deflection Based Technologies—The FWD and LWD were selected because of the large number of devices that are being used in the United States and the large database that has been created under the FHWA Long Term Pavement Performance (LTPP) program. The LWD was used to evaluate individual layers, especially unbound layers, while the FWD was used to evaluate the entire pavement structure at completion to ensure that the flexible pavement structure or HMA overlay met the overall strength requirements used in the structural design process. Deflection measuring devices are readily available within most agencies for immedi- ate use in QA. • Dynamic Cone Penetrometer—The DCP was selected because of its current use in QA oper- ations in selected agencies and its ability to estimate the in-place strength of unbound layers and materials. In addition, the DCP does not require extensive support software for evaluating the test results. DCP equipment is being manufactured and marketed by various organizations, making it readily available. • Ground Penetrating Radar—GPR was selected because of its current use in pavement foren- sic and evaluation studies for rehabilitation design and for estimating both the thickness and air voids of pavement layers. If proven successful, this will be one of the more important devices used for acceptance of the final product by agencies, assuming that the interpretation of the data can become more readily available on a commercial basis. The GPR air-coupled antenna was used successfully within the FHWA-LTPP program to measure the layer thickness within many of the 500-ft test sections. • Seismic Pavement Analyzer—Both the PSPA and DSPA were selected because they provide a measure of the layer modulus and can be used to test both thin and thick layers during and shortly after placement. This technology can also be used in the laboratory to test both HMA and unbound materials compacted to various conditions (e.g., different water contents for unbound materials and soils or temperature and asphalt content for HMA to evaluate the effect of fluids and temperature). • GeoGauge—The GeoGauge has had mixed results in testing unbound pavement layers in the past. It was selected for this study because it is simple to use and provides a measure of the resilient modulus of unbound pavement layers and embankment soils and can be used to test typical lift thicknesses. • Non-Nuclear Electric Gauges; Non-Roller-Mounted Devices—Non-nuclear density gauges have a definite advantage over the nuclear devices simply from a safety standpoint. These gauges have been used on many projects but with varying results. They were selected for the current study because the devices have been significantly improved since their previous eval- uations. Moreover, many agencies are allowing their use by contractors for QC, and some agencies are beginning to use the contractor QC results for acceptance. They also represent the baseline comparison to the results from the nuclear gauges for measuring density for use in acceptance procedures. Thus, non-nuclear density gauges that provide location-specific results were selected for evaluation under this study. The gauges selected for initial use were the PQI and PaveTracker for HMA mixtures, while the EDG was selected for unbound materials. NDT Devices Excluded from the Field Evaluation The following list contains NDT technologies and devices that were excluded from the field evaluation study. It also contains explanations for the exclusion.

7• Roller-Mounted-Density/Stiffness Devices—Non-nuclear density and stiffness monitoring devices attached to the rollers (for example, the BOMAG Varicontrol and Onboard Measur- ing System) were excluded because these devices have not been extensively used for QC, few agencies are evaluating this technology for possible use in the future, and there are a limited number of these rollers available for contractor use. Although the roller-mounted devices were excluded from the field evaluation, the roller manufacturers were contacted to determine their availability for use on selected projects. • Surface Condition Systems—None of the surface condition measuring systems or devices was suggested for further evaluation under NCHRP Project 10-65. Although the initial Interna- tional Roughness Index (IRI) is an input to the MEPDG, the smoothness measuring devices used for acceptance of the wearing surface are already included in the QA programs of many agencies. In addition, none of the devices provides an estimate of the volumetric and struc- tural properties of the wearing surface. • Noise and Friction Methods—Noise and friction measuring devices were excluded from further consideration because these properties are not needed in the MEPDG or any other structural design procedure, and no agency is considering their use for acceptance. • Infrared Tomography—Infrared cameras and sensors were excluded from the field evaluation because their output only provides supplemental information to current acceptance plans. In other words, the devices are used to identify “cold spots” or temperature anomalies. Other test methods are still used to determine whether the contractor has met the density specification. This statement does not imply that this technology should be abandoned or not used—the infrared cameras and sensors do provide good information and data on the consistency of the HMA being placed by the contractor. However, they do not provide information that is required for QA programs. • Other Ultrasonic Test Methods—Impact echo and impulse response methods, as well as the ultrasonic scanners, were excluded because they are perceived to have a high risk of implementation into practical and effective QA operations. • Continuous Deflection-Based Devices—Rolling wheel deflectometers that are under devel- opment were also excluded from the field evaluation. These devices are considered to be in the research and development stage and are not ready for immediate application into a QA program. Projects and Materials Included in the Field Evaluation The field evaluation was divided into two parts, referred to as Parts A and B. The primary purpose of the Part A field evaluation was to accept or reject the null hypothesis that a given NDT technology or device can accurately identify construction anomalies or physical differ- ences along a project. A secondary purpose of this part of the field evaluation was to confirm that the NDT device can be readily and effectively implemented into routine QA programs for flexible pavement construction and HMA overlays—an impact assessment. Part B of the field evaluation was to use those NDT technologies and devices selected from Part A and refine the test protocols and data interpretation procedures for judging the quality of flexible pavement construction. Part B also included identifying limitations and boundary conditions of selected NDT test methods. Table 3 lists the projects and materials included in the field evaluation, while Table 4 lists those defects and layer differences that should have an impact on the quality characteristics measured by the QA tests. Table 5 contains the anomalies and differences of unbound material sections placed along each project. Likewise, Table 6 lists the anomalies and differences of HMA layers. None of the NDT operators were advised of these anomalies or physical differences.

8Field Evaluation of NDT Devices Identifying Anomalies and Physical Differences A standard t-test and the Student-Newman-Keuls (SNK) mean separation procedure using a 95 percent confidence level were used to determine whether the areas with anomalies or physical differences were significantly different from the other areas tested. Table 7 lists identification of the physical differences of the unbound and HMA layers within a project. The DSPA and GeoGauge are considered acceptable in identifying localized differences in the physical condition of unbound materials, while the PSPA and PQI were considered acceptable for the HMA layers. Part Project Identification & Location Layer/Material Evaluated HMA Dense-Graded Base Mixture Granular Base Class 6, Crushed Aggregate A 1 TH-23 Reconstruction Project; Wilmar/Spicer Minnesota Class 5 Embankment Low Plasticity, Improved Soil with Gravel & Large Aggregate Particles A 2 I-85 Overlay Project; Auburn, Alabama HMA 12.5 mm Stone Matrix Asphalt Mix; PG76- 22 HMA Coarse-Graded Base Mixture; PG67-22 Granular Base Crushed Limestone Base A 3 US-280 Reconstruction Project; Opelika, Alabama Embankment Improved Soil; Aggregate-Soil Mix A 4 I-85 Ramp Construction Project; Auburn, Alabama Embankment Low Plasticity, Fine-Grained Soil HMA Coarse-Graded 19 mm Base Mixture; PG64-22A 5 SH-130 New Construction Project; Georgetown, Texas Embankment Coarse-Grained Aggregate/Soil; Improved Soil A 6 SH-21 Widening Project; Caldwell, Texas Subgrade High Plasticity Fine-Grained Soil with Gravel HMA Coarse-Graded Base Mixture B 7 US-47 Widening Project; St. Clair, Missouri HMA Fine-Graded Wearing Surface B 8 I-75 Rehabilitation Project, Rubblization; Saginaw, Michigan HMA Dense-Graded Binder Mixture; Type 3C HMA Coarse-Graded Base Mix; PG58-28 Granular Base Crushed Gravel with Surface Treatment; Class 5 B 9 US-2 New Construction; North Dakota Embankment Soil-Aggregate Mixture HMA Coarse-Graded Binder Mixture B 10 US-53 New Construction; Toledo, Ohio Granular Base Crushed Aggregate; Type 304 B 11 I-20 Overlay; Odessa, Texas HMA Coarse-Graded Mixture; CMHB B 12 County Road 103; Pecos, Texas Granular Base Caliche, Aggregate Base NCAT; Alabama Overlay, Section E-5, Opelika, Alabama HMA Wearing Surface with 45% RAP; PG67, no modifiers used. NCAT; Alabama Overlay, Section E-6, Opelika, Alabama HMA Wearing Surface with 45% RAP; PG76 with SBS. B 13 NCAT; Alabama Overlay, Section E-7, Opelika, Alabama HMA Wearing Surface with 45% RAP; PG76 with Sasobit. HMA PMA Mixture with SBS; PG76 HMA Neat Asphalt Binder Mix; PG67 B 14 NCAT; Florida; Structural Test Sections N-1 & N-2 Granular Base Limerock Base HMA Polymer Modified Asphalt Mix; PG76 (SBS) HMA Neat Asphalt Binder Mix; PG64 B 15 NCAT; Missouri; Structural Test Section N-10 Granular Base Crushed Limestone B 16 NCAT; Oklahoma; Structural Test Sections N-8 & N-9 Subgrade Soil High Plasticity Clay with Chert Aggregate HMA Coarse-Graded Base Mix; PG67; Limestone B 17 NCAT; Alabama; Structural Test Section S-11 Granular Base Crushed Granite Base CMHB – Coarse Matrix, High Binder Content (mixture type term used by the Texas DOT specifications) PG – Performance Grade PMA – Polymer Modified Asphalt RAP – Recycled Asphalt Pavement Table 3. Projects and material types included in the field evaluation.

9Estimating Laboratory Measured Moduli Laboratory measured modulus of a material is an input parameter for all layers in mechanistic- empirical (M-E) pavement structural design procedures, including the MEPDG. Resilient mod- ulus is the input for unbound layers and soils, while the dynamic modulus is used for all HMA layers. The values determined by each NDT modulus estimating device (DCP, DSPA, PSPA, GeoGauge, and deflection-based devices) were compared to the moduli measured in the labo- ratory on test specimens compacted to the density of the in-place layer. Different stress states were used for determining the resilient modulus of unbound layers, while different frequencies at the in-place mat temperature were used to determine the dynamic modulus of the HMA layers. None of the NDT devices accurately predicted the modulus values that were measured in the laboratory for the unbound materials and HMA mixtures. However, all of the modulus estimat- ing NDT devices did show a trend of increasing moduli with increasing laboratory measured moduli. Unbound Materials and Layers; Embankments All projects No construction defect was observed in any of the Parts A and B projects. As listed in Table 5, however, there were differences in the condition of the base materials and embankments that were planned to ensure that the NDT devices would identify those differences. HMA Mixtures US-280 HMA Base Truck-to-truck segregation observed in some areas. Cores were taken in these areas, but some of the cores disintegrated during the wet coring process. In addition, a significant difference in dynamic modulus was found between the initial and supplemental sections included in the test program. The supplemental section was found to have much higher dynamic modulus values. This difference was not planned. I-85 SMA Overlay No defects noted. TH-23 HMA Base No defects noted. SH-130 HMA Base No defects noted during the time of testing, but there was controversy on the mixture because it had been exhibiting checking during the compaction process. Changes were made to the mixture during production. The change made and the time that the change was made were unclear relative to the time of the NDT evaluation. US-47 HMA Base The mixture was tender; and shoved under the rollers. US-47 Wearing Surface Portions of this mixture were rejected by the agency in other areas of the project. I-75 HMA Base, Type 3-C No defects noted, but mixture placed along the shoulder was tender. I-75 HMA, Type E3 & E10 No defects noted, but portions of this mixture were rejected by the agency in other areas of the project. US-2 HMA Base Checking and mat tears observed under the rollers. US-53 HMA Base No defects noted. I-20 HMA CHMB Base No defects noted. NCAT – Alabama HMA RAP; with & without modifiers No defects noted on any of the test sections. NCAT – South Carolina HMA Base No defects noted. NCAT – Missouri HMA Base No defects noted. NCAT Florida – PMA Base No defects noted. NCAT Florida – HMA Base, no modification Checking and mat tears observed under the rollers. Table 4. Construction defects exhibited on some of the field evaluation projects.

10 Project Identification Unbound Sections Description of Differences Along Project Area 2, No IC Rolling No planned difference between the points tested.SH-21 Subgrade, High Plasticity Clay; Caldwell, Texas Area 1, With IC Rolling With intelligent compaction (IC) rolling, the average density should increase; lane C received more roller passes. Lane A of Sections 1 & 2 Prior to IC rolling, Lane A (which is further from I-85) had thicker lifts & a lower density. I-85 Embankment, Low Plasticity Clay; Auburn, Alabama All Sections After IC rolling, the average density should increase & the variability of density measurements should decrease. South Section – Lane C Construction equipment had disturbed this area. In addition, QA records indicate that this area has a lower density—prior to final acceptance. TH-23 Embankment, Silt-Sand-Gravel Mix; Spicer, Minnesota North Section – Lane A Area with the higher density and lower water content—a stronger area. SH-130, Improved Embankment, Granular; Georgetown, Texas All Sections No planned differences between the areas tested. Section 2 (Middle Section) – Lane C Curb and gutter section; lane C was wetter than the other two lanes because of trapped water along the curb from previous rains. The water extended into the underlying layers. TH-23, Crushed Aggregate Base; Spicer, Minnesota Section 1 (South Section) – Lane A Area with a higher density and lower moisture content; a stronger area. US-280, Crushed Stone Base; Opelika, Alabama Section 4 Records indicate that this area was placed with higher water content and is less dense. It is also in an area where water (from previous rains) accumulated. Table 5. Physical differences in the unbound materials and soils placed along some of the projects. Project Identification HMA Sections Description of Differences Along the Project TH-23 HMA Base; Spicer, Minnesota Section 2, Middle or Northeast Section QA records indicate lower asphalt content in this area—asphalt content was still within the specifications, but consistently below target value. Section 2, Middle; All lanes QA records indicate higher asphalt content in this area, but it was still within the specifications. I-85 SMA Overlay; Auburn, Alabama Lane C, All Sections This part or lane was the last area rolled using the rolling pattern set by the contractor, and was adjacent to the traffic lane. Densities lower within this area. Initial Test Sections, defined as A; Section 2, All Lanes Segregation identified in localized areas. In addition, QA records indicate lower asphalt content in this area of the project. Densities lower within this area. Supplemental Test Sections near crushed stone base sections, defined as B. Segregation observed in limited areas. US-280 HMA Base Mixture; Opelika, Alabama IC Roller Compaction Effort Section, Defined as C. Higher compaction effort was used along Lane C. SH-130 HMA Base Mixture; Georgetown, Texas All Sections No differences between the different sections tested. Table 6. Different physical conditions (localized anomalies) of the HMA mixtures placed along projects within Part A.

11 To compensate for differences between the laboratory and field conditions, an adjustment procedure was used to estimate the laboratory resilient modulus from the different NDT tech- nologies for making relative comparisons. The adjustment procedure assumes that the NDT response and modulus of laboratory prepared test specimens are directly related and propor- tional to changes in density and water content of the material. In other words, the adjustment factors are independent of the volumetric properties of the material. Table 8 lists the adjustment ratios for the unbound layers included in the field evaluation (Parts A and B), while Table 9 contains the ratios for the HMA layers. The adjustment ratios Success Rates, % NDT Gauges Included in Field Evaluation Unbound Layers HMA Layers Ultrasonic DSPA & PSPA 86 93 Steady-State Vibratory GeoGauge 79 --- Impact/Penetration DCP 64 --- Deflection-Based LWD & FWD 64 56 Non-Nuclear Density EDG & PQI 25 71 GPR Single Air-Horn Antenna 33 54 Table 7. Success rates of the NDT devices for identifying physical differences or anomalies. Resilient Moduli, ksi Adjustment Ratios RelatingLaboratory Moduli to NDT Values Project Identification Laboratory Measured Value Predicted with LTPP Equations Geo Gauge DSPA DCP LWD Fine-Grained Clay Soils Before IC Rolling 2.5 10.5 0.154 .0751 0.446 0.39 I-85 Low- Plastic Soil After IC Rolling 4.0 13.1 0.223 0.113 0.606 0.39 NCAT; OK High Plastic Clay 6.9 19.7 0.266 0.166 0.802 --- SH-21, TX High Plastic Clay 26.8 19.6 1.170 0.989 3.045 2.78 Average Ratios for Fine-Grained Clay Soils 0.454 0.336 1.225 Embankment Materials; Soil-Aggregate Mixtures South Embankment 16.0 15.7 0.696 0.367 1.053 3.13 TH-23, MN North Embankment 16.4 16.3 0.735 0.459 0.863 3.13 US-2, ND Embankment 19.0 19.5 1.450 0.574 0.856 --- SH-130, TX Improved Soil 35.3 21.9 1.337 1.029 1.657 1.43 Average Ratios for Soil-Aggregate Mixtures; Embankments 1.055 0.607 1.107 Aggregate Base Materials Co. 103, TX Caliche Base --- 32.3 1.214 --- 1.436 --- NCAT, SC Crushed Granite 14.3 36.1 0.947 0.156 --- --- NCAT, MO Crushed Limestone 19.2 40.9 0.747 0.198 --- --- Crushed Stone, Middle 24.0 29.9 0.851 0.303 0.725 1.69 TH-23, MN Crushed Stone, South 26.0 35.6 0.788 0.235 0.560 1.69 US-53, OH Crushed Stone 27.5 38.3 1.170 0.449 0.862 --- NCAT, FL Limerock 28.6 28.1 0.574 0.324 0.619 --- US-2, ND Crushed Aggregate 32.4 39.8 1.884 0.623 1.129 --- US-280, AL Crushed Stone 48.4 49.3 1.010 0.244 0.962 1.04 Average Ratios for Aggregate Base Materials 1.021 0.316 0.899 Overall Average Ratios for Processed Materials 0.942 0.422 1.084 NOTES: 1. The adjustment ratio is determined by dividing the resilient modulus measured in the laboratory at a specific stress state by the NDT estimated modulus. The overall average values listed above exclude those for the fine-grained clay soils. 2. Table 8. Unbound layer adjustment ratios applied to the NDT moduli to represent laboratory conditions or values at low stress states.

12 were determined for the areas without any anomalies or physical differences from the target properties. • Unbound Layers. The GeoGauge and DCP provided a reasonable estimate of the laboratory measured values (average ratios near unity), with the exception of the fine-grained, clay soils. The GeoGauge deviated significantly from the laboratory values for the fine-grained soils. The results also show that both the GeoGauge and DCP over predicted or under predicted the laboratory measured values for the same material, with few exceptions. • HMA Layers. The PSPA average adjustment ratios were found to be relatively close to unity, with the exception of the I-35/SH-130 HMA base mixture. Conversely, the FWD adjustment ratios were significantly different from unity. The FWD over estimated the stone matrix asphalt (SMA) modulus for the overlay project and under estimated the HMA base modulus for the reconstruction projects—suggesting that the calculated values from the deflection basins are being influenced by the supporting materials. Accuracy and Precision of Different NDT Devices Tables 10 through 12 summarize the statistical analyses of the NDT devices included in the field evaluation projects for unbound fine-grained soils, unbound processed materials, and HMA mixtures, respectively. This information is grouped into two areas—those NDT devices with an acceptable to excellent success rate and those with poor success rates in identifying material/layer differences. Summary of Evaluations The steady-state vibratory (GeoGauge) and ultrasonic (DSPA) are the two technologies suggested for use in judging the quality of unbound layers, while the ultrasonic (PSPA) and Ratio or Adjustment Factor Project/Mixture DynamicModulus, ksi PSPA FWD I-85 AL, SMA Overlay 250 1.055 0.556 TH-23 MN, HMA Base 810 1.688 NA US-280 AL, HMA Base; Initial Area 650 1.407 3.939 US-280 AL, HMA Base; Supplemental Area 780 1.398 2.516 I-35/SH-130 TX, HMA Base 1,750 5.117 3.253 I-75 MI, Dense-Graded Type 3-C 400 0.919 NA I-75 MI, Dense-Graded Type E-10 590 0.756 NA US-47 MO, Fine-Graded Surface 530 1.158 NA US-47 MO, Coarse-Graded Base Mix 420 0.694 NA I-20 TX, HMA Base, CMHB 340 0.799 NA US-53 OH, Coarse-Graded Base 850 1.275 NA US-2 ND, Coarse-Graded Base, PG58-28 510 1.482 NA NCAT AL, PG67 Base Mix 410 0.828 NA NCAT FL, PG67 Base Mix 390 0.872 NA NCAT FL, PG76 Base Mix 590 1.240 NA NCAT AL, PG76 with RAP and Sasobit 610 1.3760 NA NCAT AL, PG76 with RAP and SBS 640 1.352 NA NCAT AL, PG67 with RAP 450 0.881 NA Overall Average Ratio 1.128 2.566 NOTES: 1. The adjustment factor or ratio was determined by dividing the dynamic modulus measured in the laboratory for the in-place temperature and at a loading frequency of 5 Hz by the modulus estimated with the NDT device. 2. The laboratory dynamic modulus values listed above are for a test temperature of a loading frequency of 5 Hz at the temperature of the mixture when the NDT was performed. 3. The overall average adjustment factor excludes the SH-130 mixture because it was found to be significantly different than any other mixture tested in the laboratory; which has been shaded. Table 9. HMA layer adjustment ratios applied to NDT modulus values to represent laboratory conditions.

13 Statistical Value Material Property NDT Devices Standard Error 95% Precision Tolerance Pooled Standard Deviation NDT Devices with Good Success Rates Based on Modulus or Volumetric Properties GeoGauge 2.5 4.9 1.1 Modulus, ksi DSPA 4.5 8.8 1.2 StructuralProperties Thickness, in. None NA NA NA Density, pcf None NA NA NA Air Voids, % None NA NA NAVolumetricProperties Structural Properties Volumetric Properties Fluids Content, % None NA NA NA NDT Devices with Poor (or Undefined) Success Rates Based on Modulus or Volumetric Properties DCP 3.8 7.4 1.9 Modulus, ksi LWD/FWD 5.9 11.6 2.0 Thickness, in. GPR, single antenna NA NA NA GPR, single antenna --- --- 4.2 Density, pcf EDG 0.8 1.6 0.7 Water Content, % EDG 0.2 0.4 0.5 Table 10. NDT device and technology variability analysis for the fine-grained clay soils. Statistical Value Material Property NDT Devices Standard Error 95% Precision Tolerance Pooled Standard Deviation NDT Devices with Good Success Rates Based on Modulus or Volumetric Properties GeoGauge 2.5 4.9 1.8 Modulus, ksi DSPA 4.5 8.8 1.5 StructuralProperties Thickness, in. None NA NA NA Density, pcf None NA NA NA Air Voids, % None NA NA NAVolumetric Properties Fluids Content, % None NA NA NA NDT Devices with Poor (or Undefined) Success Rates Based on Modulus or Volumetric Properties DCP 3.8 7.4 5.3 Modulus, ksi LWD/FWD 5.9 11.6 2.0 StructuralProperties Thickness, in. GPR, single antenna 0.80 1.5 0.6 GPR, single antenna 3.4 6.7 3.0 Density, pcf EDG 1.0 2.0 0.8 VolumetricProperties Water Content, % EDG 0.2 0.4 0.6 Table 11. NDT device and technology variability analysis for the processed materials and aggregate base materials. Statistical Value Material Property NDT Devices Standard Error 95% Precision Tolerance Pooled Standard Deviation NDT Devices with Good Success Rates Based on Modulus or Volumetric Properties Structural Properties Modulus, ksi PSPA 76 150 56 Density, pcf PQI & PT 1.7 3.4 2.5 Air Voids, % None NA NA NAVolumetric Properties Structural Properties Volumetric Properties Fluids Content, % None NA NA NA NDT Devices with Poor (or Undefined) Success Rates Based on Modulus or Volumetric Properties Modulus, ksi FWD 87 170.5 55 GPR, single antenna 0.25 0.49 0.3 Thickness, in. GPR, multiple antenna 0.27 0.55 --- Density, pcf GPR, multiple antenna 1.6 3.1 --- Asphalt Content, % GPR, multiple antenna 0.18 0.36 --- GPR, single antenna 0.40 0.8 2.1 Air Voids, % GPR, multiple antenna 0.22 0.4 --- Table 12. NDT device and technology variability analysis for the HMA mixtures.

14 non-nuclear density gauges (the PaveTracker was used in Part B) are the technologies suggested for use of HMA layers. The GPR is suggested for layer thickness acceptance, while the IC rollers are suggested for use on a control basis for compacting unbound and HMA layers. NDT Devices for Unbound Layers and Materials • The DSPA and GeoGauge devices had the highest success rates for identifying an area with anomalies, with rates of 86 and 79 percent, respectively. The DCP and LWD identified about two-thirds of the anomalies, while the GPR and EDG had unacceptable rates below 50 percent. • Three to five repeat measurements were made at each test point with the NDT devices, with the exception of the DCP. – The LWD exhibited low standard deviations that were less dependent on material stiffness with a pooled standard deviation less than 0.5 ksi. One reason for the low values is that the moduli were less than for the other devices. The coefficient of variation (COV), an estimate of the normalized dispersion, however, was higher. It is expected that the supporting layers had an effect on the results. – The GeoGauge had a standard deviation for repeatability measurements varying from 0.3 to 3.5 ksi. This value was found to be material dependent. – The DSPA had the lowest repeatability, with a standard deviation varying from 1.5 to 21.5 ksi. The reason for this higher variation in repeat readings is that the DSPA sensor bar was rotated relative to the direction of the roller, while the other devices were kept stationary or did not have the capability to detect anisotropic conditions. No significant difference was found relative to the direction of testing for fine-grained soils, but there was a slight bias for the stiffer coarse-grained materials. – The EDG was highly repeatable with a standard deviation in density measurements less than 1 pcf, while the GPR had poor repeatability based on point measurements. Triplicate runs of the GPR were made over the same area or sublot. For comparison to the other NDT devices, the values measured at a specific point, as close as possible, were used. Use of point specific values from successive runs could be a reason for the lower repeatability, which are probably driver specific. One driver was used for all testing with the GPR. • The COV was used to compare the normalized dispersion measured with different NDT devices. The EDG consistently had the lowest COV with values less than 1 percent. The GeoGauge had a value of 15 percent, followed by the DSPA, LWD, DCP, and GPR. The GPR and EDG are dependent on the accuracy of other tests in estimating volumetric properties (density and moisture contents). Any error in the calibration of these devices for the specific material is directly reflected in the resulting values, which probably explains why the GPR and EDG devices did not consistently identify the areas with anomalies or physical differences. • Repeated load resilient modulus tests were performed in the laboratory for characterizing and determining the target resilient modulus for each material. Adjustment ratios were deter- mined based on uniform conditions. The overall average ratio for the GeoGauge for the stiffer coarse-grained materials was near unity (1.05). For the fine-grained, less stiff soils, the ratio was about 0.5. After adjusting for laboratory conditions, all NDT devices that estimate resilient modulus resulted in low residuals (laboratory resilient modulus minus the NDT elastic modulus). However, the GeoGauge and DCP resulted in the lowest standard error. The LWD had the highest residuals and standard error. • The DSPA and DCP measured responses represent the specific material being tested. The DCP, however, can be affected significantly by the varying amounts of aggregate particles in fine-grained soils and the size of the aggregate in coarse-grained soils. The GeoGauge measured responses are minimally affected by the supporting materials, while the LWD can be signifi- cantly affected by the supporting materials and thickness of the layer being tested. Thickness

deviations and variable supporting layers are reasons for LWD’s low success rate in identifying areas with anomalies or physical differences. • No good or reasonable correlation was found between the NDT devices that estimate modulus and those devices that estimate volumetric properties. • Instrumented rollers were used on too few projects for a detailed comparison to the other NDT devices. The rollers were used to monitor the increase in density and stiffness with increasing number of roller passes. One potential disadvantage with these rollers is that they may bridge localized soft areas. However, based on the results obtained, their ability of provide uniform compaction was verified and these rollers are believed to be worth future investment in monitoring the compaction of unbound materials. • The GPR resulted in reasonably accurate estimates to the thickness of aggregate base layers. None of the other NDT devices had the capability or same accuracy to determine the thickness of the unbound layer. NDT Devices for HMA Layers and Mixtures • The PSPA had the highest success rate for identifying an area with anomalies with a rate of 93 percent. The PQI identified about three-fourths of the anomalies, while the FWD and GPR identified about one-half of those areas. The seismic and non-nuclear gauges were the only technologies that consistently identified differences between the areas with and without seg- regation. These two technologies also consistently found differences between the longitudinal joint and interior of the mat. • The non-nuclear density gauge (PaveTracker) was able to identify and measure the detrimen- tal effect of rolling the HMA mat within the temperature sensitive zone. This technology was beneficial on some of the Part B projects to optimize the rolling pattern initially used by the contractor. • Three to four repeat measurements were made at each test point with the NDT devices. – The PSPA had a repeatability value, a median or pooled standard deviation, of about 30 ksi for most mixtures, with the exception of the US-280 supplemental mixture that was much higher. – The FWD resulted in a comparable value for the SMA mixture (55 ksi), but a higher value for the US-280 mixture (275 ksi). – The non-nuclear density gauges had repeatability values similar to nuclear density gauges with a value less than 1.5 pcf. – The repeatability for the GPR device was found to be good and repeatable, with a value of 0.5 percent for air voids and 0.05 inches for thickness. • The PSPA moduli were comparable to the dynamic moduli measured in the laboratory on test specimens compacted to the in-place density at a loading frequency of 5 Hz and the in-place mixture temperature, with the exception of one mixture—the US-280 supplemental mixture. In fact, the overall average ratio or adjustment factor for the PSPA was close to unity (1.1). This was not the case for the FWD. Without making any corrections for volumetric differences to the laboratory dynamic modulus values, the standard error for the PSPA was 76 ksi (laboratory values assumed to be the target values). The PSPA was used on HMA surfaces after com- paction and the day following placement. The PSPA modulus values measured immediately following compaction were found to be similar to the values one or two days after placement— when making proper temperature corrections in accordance with the master curves measured in the laboratory. • A measure of the mixture density or air voids is required in judging the acceptability of the modulus value from a durability standpoint. The non-nuclear gauges were found to be acceptable, assuming that the gauges have been properly calibrated to the specific mixture— as for the PSPA. 15

16 • Use of the GPR single antenna method, even with mixture calibration, requires assumptions that specific volumetric properties do vary along a project. As the mixture properties change, the dielectric values may or may not be affected. Use of the proprietary GPR analysis method on other projects was found to be acceptable for the air void or relative compaction method. This proprietary and multiple antenna system, however, was not used within Part A of the field evaluation to determine its success rate in identifying localized anomalies and physical differ- ences between different areas. Both GPR systems were found to be very good for measuring layer thickness along the roadway. • Water can have a definite effect on the HMA density measured with the non-nuclear density gauges (PQI). The manufacturer’s recommendation is to measure the density immediately after compaction, prior to allowing any traffic on the HMA surface. Within this project, the effect of water was observed on the PQI readings, as compared to dry surfaces. The measured density of wet surfaces did increase compared to dry surfaces. From the limited testing completed with wet and dry surfaces, the PaveTracker was less affected by surface condition. However, wet versus dry surfaces was not included in the field evaluation plan for different devices. Based on the data collected within the field evaluation, wet surfaces did result in a bias of the density measurements with this technology. • Another important condition is the effect of time and varying water content on the properties of the HMA mixture during construction. There have been various studies completed using the PSPA to detect stripping and moisture damage in HMA mixtures. For example, Hammons et al. (2005) recently used the PSPA (in combination with GPR) to successfully locate areas with stripping along selected interstate highways in Georgia. The testing completed within this study also supports the use of ultrasonic-based technology to identify such anomalies. • The instrumented rollers used to establish the increase in stiffness with number of passes was correlated to the increases in density, as measured by different devices. These rollers were used on limited projects to develop or confirm any correlation between the NDT response and the instrumented roller’s response. One issue that will need to be addressed is the effect of decreasing temperature on the stiffness of the mixture and how the IC roller perceives that increase in stiffness related to increases in density of the mat and a decrease in mat temperature as it cools. A potential disadvantage with these rollers is that they will bridge segregated areas and may not accurately identify cold spots in the HMA mat. However, based on the results obtained, the ability to provide uniform compaction was verified and the rollers are believed to be worth future investments in monitoring the compaction of HMA mixtures. Limitations and Boundary Conditions • All NDT devices suggested for QA application, with the exception of the GPR and IC rollers, are point specific tests. Point specific tests are considered a limitation because of the number of samples that would be required to identify localized anomalies that deviate from the population. – Ultrasonic scanners are currently under development so that relatively continuous mea- surements can be made with this technology. These scanners are still considered in the research and development stage and are not ready for immediate and practical use in a QA program. – GPR technology to estimate the volumetric properties of HMA mixtures is available for use on a commercial basis, but the proprietary system has only had limited verification of its potential use in QA applications and validation of all volumetric properties determined with the system. – Similarly, the IC rollers take continuous measurements of density or stiffness of the material being compacted. During the field evaluation, some of these rollers had both hardware and

software problems. Thus, these devices were not considered immediately ready for use in a day-to-day QA program. The equipment, however, has been improved and its reliability has increased. The technology is suggested for use on a control basis but not for acceptance. • Ultrasonic technology (PSPA) for HMA layers and materials; suggested for use in control and acceptance plans. – Test temperature is the main boundary condition for the use of the PSPA. Elevated tem- peratures during mix placement can result in erratic response measurements. Thus, the gauge may not provide reliable responses to monitor the compaction of HMA layers or define when the rollers are operating within the temperature sensitive zone for the specific mixture. – These gauges need to be calibrated to the specific mixture being tested. However, this tech- nology can be used in the laboratory to measure the seismic modulus on test specimens during mixture design or verification prior to measuring the dynamic modulus in the laboratory. – A limitation of this technology is that the results (material moduli) do not provide an indication on the durability of the HMA mixture. Density or air void measurements are needed to define durability estimates. – 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 estimated with the DSPA. Thus, the DSPA also needs to be calibrated to the specific material being evaluated. • Steady-state vibratory technology (GeoGauge) for unbound layers and materials; suggested for use in control and acceptance plans. – This technology or device should be used with caution when testing fine-grained soils at high water contents. In addition, it should not be used to test well-graded, non-cohesive sands that are dry (i.e., well below the optimum water content). – The condition of the surface of the layer is important and should be free of loose particles. A layer of moist sand should also be placed underneath the gauge to fill the surface voids and ensure that the gauge’s ring is in contact with about 75 percent of the material’s surface. Placement of this thin, moist layer of sand takes time and does increase the time needed for testing. – These gauges need to be calibrated to the specific material being evaluated and are influenced by the underlying layer when testing layers that are less than 8 in. thick. – These gauges are not applicable for use in the laboratory during the development of moisture- density (M-D) relationships that are used for monitoring compaction. The DSPA technology is applicable for laboratory use to test the samples used to determine the M-D relationship. – A relative calibration process is available for use on a day-to-day basis. However, if the gauge does go out of calibration, then it must be returned to the manufacturer for internal adjustments and calibration. – These gauges do not determine the density and water content of the material. Alternate devices are necessary to measure the water content and density of the unbound layer. • Non-nuclear density gauges (electric technology) for HMA layers and materials; suggested for use in control and acceptance plans. – Results from these gauges can depend on the condition of the layer’s surface—wet versus dry. It is recommended that the gauges be used on relatively dry surfaces until additional data become available pertaining to this limitation. Free water should be removed from the surface to minimize any effect on the density readings. However, water penetrating the surface voids in segregated areas will probably affect the readings (i.e., incorrect or high density compared to actual density from a core). The PSPA was able to identify areas with segregation. – These gauges need to be calibrated to the specific material under evaluation. 17

18 • GPR technology for thickness determination of HMA and unbound layers; suggested for use in acceptance plans. – The data analysis or interpretation is a limitation of this technology. The GPR data require some processing time to estimate the material property. The time for layer thickness esti- mates is much less than for other layer properties. – This technology requires the use of cores for calibration purposes. Cores need to be taken periodically to confirm the calibration factors used to estimate the properties. – Use of this technology, even to estimate layer thickness, should be used with caution when measuring the thickness of the first lift placed above permeable asphalt treated base (PATB) layers. – GPR can be used to estimate the volumetric properties of HMA mats, but that technology has yet to be verified on a global basis. – Measurements using this technology cannot be calibrated using laboratory data. • IC rollers; suggested for use in a control plan, but not within an acceptance plan. – The instrumented rollers may not identify localized anomalies in the layer being evalu- ated. These rollers can bridge some defects (may have insufficient sensitivity to identify defects that are confined to local areas). – Temperature is considered an issue with the use of IC rollers for compacting HMA layers. Although most IC rollers measure the surface temperature of the mat, the effect of temperature on the mat stiffness is an issue—as temperature decreases the mat stiffness will increase, not necessarily because of an increase in density of the mat. Delaying the com- paction would increase the stiffness of the mat measured under the rollers because of the decrease in temperature. – The instrumented rollers also did not properly indicate when checking and tearing of the mat occurred during rolling. The non-nuclear density gauges (PaveTracker) successfully identified this detrimental condition. – Measurements using this technology and associated devices cannot be calibrated using laboratory data. Conclusions Unbound Layers and Materials • The GeoGauge is a self-contained NDT device that can be readily incorporated into a QA program for both control and acceptance testing. This conclusion is based on the following reasons: – It provides an immediate measure of the resilient modulus of the in-place unbound material. – It identified those areas with anomalies at an acceptable success rate (second only to the DSPA). – It adequately ranked the relative order of increasing strength or stiffness of the unbound materials. – It provided resilient modulus values that were correlated to the dry density over a diverse range of material types. – The normalized dispersion is less than for the other NDT devices that provide an estimate of stiffness. – The training and technical requirements for this technology are no different than what is required when using a nuclear density gauge. Two disadvantages of using this device in a QA program are (1) the need for measuring the water content and density using other methods, which is also the case for the DSPA and other

modulus estimating devices and (2) the need to calibrate the test results to the material and site conditions under evaluation. The latter is the more important issue and is discussed in more detail. The GeoGauge should be calibrated to the project materials and conditions to improve on its accuracy, especially when testing fine-grained soils. This calibration issue requires that laboratory repeated load resilient modulus tests be performed on each unbound layer for judging the quality of construction. Most agencies do not routinely perform resilient modu- lus tests for design. Eliminating the laboratory resilient modulus tests from the calibration procedure will reduce its accuracy for confirming the design values, but not for identifying construction defects. For those agencies that do not have access to or the capability to perform resilient modulus tests, use of the FHWA-LTPP regression equations is an option that can be used to calculate the target resilient modulus at the beginning of construction. The target resilient modulus should be the value used in structural design. For the MEPDG, this is the average value measured in the laboratory. • The DSPA is also a self-contained unit that was successful in many of the areas noted for the GeoGauge. It was the device that had the highest success rate in identifying areas with different physical conditions or anomalies. An additional advantage of the DSPA is that the results can be calibrated to the specific unbound material being tested prior to construction, when the M-D relationship is measured in the laboratory. This calibration procedure allows the DSPA to be used to detect volumetric, as well as physical, changes in the materials during construction. In other words, the DSPA modulus is measured on the M-D samples prepared at different water contents and dry densities. In short, the DSPA can be used in day-to-day operations to assist contractor and agency personnel in judging construction and materials quality by itself or in tandem with other geophysical and/or ground truth sampling programs. Two disadvantages of the DSPA are that it consistently resulted in a higher normalized dis- persion measured over a diverse range of conditions and materials, and that it requires more sophisticated training of technicians to correctly interpret the load pulse and responses to ensure that satisfactory data have been collected by the device. • The DCP was also successful in many of the areas noted for the GeoGauge. However, testing takes much more time, especially for stiff materials and layers with large aggregate. In addition, the test results were found to be more dependent on aggregate size than the other NDT devices. The normalized dispersion was also found to be much higher than for the DSPA and GeoGauge. Conversely, the DCP does have the capability to readily estimate the strength of thicker unbound layers and can measure the modulus gradient with depth. In fact, it can be used in conjunction with the GeoGauge and DSPA in adjusting the modulus values from those devices to laboratory conditions for fine-grained soils for agencies that do not have resilient modulus testing capability in the laboratory. Use of the DCP can be considered an option in adjusting the test results for the GeoGauge for those agencies that have no plans to incorporate a resilient modulus testing capability within their design or materials departments. • The GPR (single antenna method) was found to have a poor success rate in identifying anom- alies. It did not provide a measure of modulus or strength of material. In addition, using the single antenna method requires that either the density or water content be assumed and the other parameter calculated. Both vary along the project, resulting in higher variations of the property being calculated. Using an inaccurate value can lead to an incorrect finding. For example, the GPR found some of the areas tested to have the highest density, while most other NDT devices found that area to be the softest and least dense. It was successful, however, in measuring the layer thickness of the unbound materials. Two other disadvantages of this system are in the training requirements for using this technology and the need to calibrate the dielectric values to physical properties of the in-place 19

20 material. Samples need to be recovered and tested to determine the water contents and den- sities of those areas prior to using the results for QC or acceptance. This requires that control strips be used prior to construction, and these calibration factors should be checked periodically during construction. Many agencies are not requiring control strips, or the first day of con- struction is the control strip. Training is another issue; this system requires more sophisticated training for the operator to interpret the measurements taken with the GPR. Thus, with its current limitations, it is not suggested for future use in testing unbound materials to determine the quality characteristics of the in-place material. However, it is suggested that research with the GPR continue because of its continuous coverage and speed of data collection. • Similar to the GPR, the EDG was found to have a poor success rate in identifying areas with anomalies. However, this device is believed to have potential to provide volumetric data on the unbound materials for use in a QA program with continued use. The density estimated from this device is definitely related to resilient modulus across a wide range of unbound materials. However, further improvements in the measurements will require a program to obtain addi- tional data. The variability of the water contents measured with this device was found to be very low. Other agencies are beginning to use this device in their research programs. For example, Texas and Nevada have ongoing programs that could provide improvements to the equipment and procedures in the near future. As a result, further detailed evaluation of this device and technology to improve its accuracy are warranted. • The deflection-based methods (LWD and FWD) were found to have limited potential for QC purposes. The LWD devices have greater mobility than the FWD, which is an advantage for their use over the FWD. These devices have more potential for use in acceptance programs of the final structure and certainly in forensic areas for evaluating the interaction between the pavement layers and foundation. The following summarizes the conclusions reached on these devices: – Technology was unable to consistently identify those areas with anomalies. – The modulus values can be influenced by the underlying layers, resulting in lower or higher and more variable modulus values. – The normalized dispersion was found to be high, relative to the other NDT devices. – The relationship between modulus from this technology and dry density was poor. – Any error in thickness of the layer being tested can result in large errors and more variabil- ity that could lead to wrong decisions being made by the contractor and agency about the construction operation. HMA Mixtures • The PSPA is a self-contained NDT device that can be readily incorporated into a QA program for both control and acceptance testing of HMA mixtures. As noted for unbound materials, an advantage of this technology is that the device can be calibrated to the specific materials being tested during the mixture design stage for HMA mixtures. This calibration procedure allows the PSPA to be used to detect volumetric, as well as physical, changes in the materials during construction. In short, the PSPA can be used in day-to-day operations to assist con- tractor and agency personnel in judging construction and materials quality by itself or in tan- dem with other geophysical and/or ground truth sampling programs. This conclusion is based on the following reasons. – The PSPA is the NDT device found best suited for QA applications because it adequately identified all but one area with anomalies. The PSPA provides a measure of the dynamic modulus that is needed for pavement structural designs, even before adjusting the PSPA modulus for laboratory conditions. The PSPA modulus was found to be correlated to the dynamic modulus at elevated temperatures using the master curve developed from labo- ratory dynamic modulus tests.

– Similar PSPA modulus values were measured at higher temperatures and corrected for temperature using a master curve in comparison to those measured in the laboratory. – An important condition that the NDT device needs to consider is the effect of time and varying moisture content on the properties of the HMA mixture near construction and how those properties will change in service. There have been various studies completed on using the PSPA to detect stripping in HMA mixtures. For example, the PSPA was used in combination with GPR to successfully locate areas with stripping along selected interstate highways in Georgia (Hammons et al. 2005). The test results from the NCHRP 10-65 study support a similar conclusion. However, the PSPA does have some limitations regarding full-scale use in QA programs. Use of the PSPA should be delayed after rolling to allow the mix to cool. Dr. Nazarian’s rec- ommendation is to delay all testing for one day after HMA placement and compaction. If required, this time restriction is considered a disadvantage for use in QA programs. A measure of the mixture density or air voids is also required in judging the acceptability of the modulus value or durability of the HMA mixture. The two devices that deserve further evaluation include the GPR and non-nuclear density gauges. The GPR provides full coverage in a short period of time. • The non-nuclear density gauges are also well suited for QA because they can be readily incor- porated into control programs. Some contractors are already using the non-nuclear density gauges in controlling the compaction operation. This technology was also used to identify anomalies at a reasonable rate and can be used to identify tender mixtures and the effects of rolling in the temperature sensitive zone. Variations in water have a definite effect on the HMA density measured with the PQI. The manufacturer’s recommendation is to measure the density immediately after compaction, prior to allowing any traffic on the HMA surface. This type of time restriction is considered a disadvantage to the use of the PQI in a day-to-day practical QA program. This time effect, however, was not found within the Part A test program, but the moisture effect was observed in Part A of the field evaluation. Use of other non-nuclear density gauges (PaveTracker) did not exhibit this moisture sensitivity. However, the effect of water on these gauges was not included in the field evaluation as a primary variable. Measurements were taken after heavy rains in areas where the readings were previously taken prior to the thunderstorms. The same density values were measured after removing and drying all free water at the surface. This potential bias of free water on the surface is not considered a limitation but must be considered in taking measurements for control purposes. • Use of the GPR technology using the single antenna method, even with mixture calibration, requires assumptions on specific volumetric properties that do vary along a project. Using the multi-antenna method is expected to improve on the measurement of the volumetric prop- erties and identification of areas with deficiencies or anomalies. Thus, the GPR is suggested for continued research studies, especially with the multiple antenna system, which is a propri- etary analysis system. The proprietary system needs additional validation prior to full-scale implementation into a QA program. • The FWD is not suggested for use in QA programs, because this technology was unable to identify some of the anomalies. In addition, the FWD has high variation in elastic modulus values, and those values are influenced by the strength of the underlying materials and layers. Recommendations The research team’s recommendations are based on the evaluation of NDT devices for imme- diate and practical use in QA programs. Thus the GeoGauge can be used for estimating the modulus of unbound layers, while the PSPA is the device suitable for use with HMA layers. 21

22 The PaveTracker can be used in establishing and confirming the rolling pattern for HMA mix- tures. Other NDT devices may provide useful data for pavement and materials testing purposes. Each has its own benefits and advantages for evaluating and designing pavements. The IC or instrumented rollers can be valuable to a contractor in terms of controlling the com- paction operation. These rollers that operated without problems were used on too few projects to suggest their immediate inclusion in QA programs. Nonetheless, they can assist the contractor in optimizing the compaction of the material. Their disadvantage for HMA layers is the temper- ature of the mat issue. Decreases in temperature will cause the stiffness of the mat to increase. Thus, other devices still need to be used with the IC rollers for control. The use of IC rollers for acceptance is not suggested at this time. Research with the multi-antenna GPR device and proprietary data interpretation system should not be abandoned and should be validated in future studies. This system definitely shows promise in providing the volumetric properties for HMA mixtures. The data can be collected at highway speeds, and the proprietary data interpretation system can provide results on a real-time basis. The disadvantage of this system is that it also needs field cores for calibrating the method to project specific conditions. These cores should be taken periodically to confirm the calibra- tion factors being used in estimating the volumetric properties.

Next: Data Interpretation and Application »
NDT Technology for Quality Assurance of HMA Pavement Construction Get This Book
×
MyNAP members save 10% online.
Login or Register to save!
Download Free PDF

TRB's National Cooperative Highway Research Program (NCHRP) Report 626: NDT Technology for Quality Assurance of HMA Pavement Construction explores the application of nondestructive testing (NDT) technologies in the quality assurance of hot-mix asphalt (HMA) pavement construction. Supplementary material to NCHRP Report 626 was published as NCHRP Web-Only Document 133: Supporting Materials for NCHRP Report 626

  1. ×

    Welcome to OpenBook!

    You're looking at OpenBook, NAP.edu's online reading room since 1999. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.

    Do you want to take a quick tour of the OpenBook's features?

    No Thanks Take a Tour »
  2. ×

    Show this book's table of contents, where you can jump to any chapter by name.

    « Back Next »
  3. ×

    ...or use these buttons to go back to the previous chapter or skip to the next one.

    « Back Next »
  4. ×

    Jump up to the previous page or down to the next one. Also, you can type in a page number and press Enter to go directly to that page in the book.

    « Back Next »
  5. ×

    To search the entire text of this book, type in your search term here and press Enter.

    « Back Next »
  6. ×

    Share a link to this book page on your preferred social network or via email.

    « Back Next »
  7. ×

    View our suggested citation for this chapter.

    « Back Next »
  8. ×

    Ready to take your reading offline? Click here to buy this book in print or download it as a free PDF, if available.

    « Back Next »
Stay Connected!