Nondestructive Testing to Identify Delaminations Between HMA Layers: Phase III–Develop User Guidelines (2014)

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SHRP 2 Renewal Project R06D Nondestructive Testing to Identify Delaminations Between HMA Layers Phase 3—Develop User Guidelines

SHRP 2 Renewal Project R06D Nondestructive Testing to Identify Delaminations Between HMA Layers Phase 3—Develop User Guidelines Michael Heitzman and Nam H. Tran National Center for Asphalt Technology at Auburn University Auburn, Alabama Kenneth Maser Infrasense, Inc. Arlington, Massachusetts TRANSPORTATION RESEARCH BOARD Washington, D.C. 2015 www.TRB.org

© 2015 National Academy of Sciences. All rights reserved. ACKNOWLEDGMENTS This work was sponsored by the Federal Highway Administration in cooperation with the American Association of State Highway and Transportation Officials. It was conducted in the second Strategic Highway Research Program, which is administered by the Transportation Research Board of the National Academies. The project was managed by Monica Starnes and James Bryant, Senior Program Officers, SHRP 2 Renewal. The work of this Phase 3 task was performed by the National Center for Asphalt Technology (NCAT) with support from Infrasense, Inc. Michael Heitzman, NCAT, was the principal investigator. Other authors of this report were Kenneth Maser, Infrasense Inc., and Nam Tran, NCAT. The team recognizes the support of the nondestructive testing (NDT) technology firms that provided input for the development of the guidelines. The companies that supported the project were Geophysical Survey Systems, Inc.; MALA AB; 3d-Radar; IDS; Geomedia Research and Development; and Olson Instruments, Inc. The Phase 3 study could not have been completed without their generous assistance. The team especially recognizes the effort of the staff of 3d-Radar and Olson Instruments, Inc., for improving the capabilities of their NDT technologies to meet the needs of highway agencies and for assisting with pilot workshops. COPYRIGHT INFORMATION Authors herein are responsible for the authenticity of their materials and for obtaining written permissions from publishers or persons who own the copyright to any previously published or copyrighted material used herein. The second Strategic Highway Research Program grants permission to reproduce material in this publication for classroom and not-for-profit purposes. Permission is given with the understanding that none of the material will be used to imply TRB, AASHTO, or FHWA endorsement of a particular product, method, or practice. It is expected that those reproducing material in this document for educational and not-for-profit purposes will give appropriate acknowledgment of the source of any reprinted or reproduced material. For other uses of the material, request permission from SHRP 2.

NOTICE The project that is the subject of this document was a part of the second Strategic Highway Research Program, conducted by the Transportation Research Board with the approval of the Governing Board of the National Research Council. The Transportation Research Board of the National Academies, the National Research Council, and the sponsors of the second Strategic Highway Research Program do not endorse products or manufacturers. Trade or manufacturers’ names appear herein solely because they are considered essential to the object of the report. DISCLAIMER The opinions and conclusions expressed or implied in this document are those of the researchers who performed the research. They are not necessarily those of the second Strategic Highway Research Program, the Transportation Research Board, the National Research Council, or the program sponsors. The information contained in this document was taken directly from the submission of the authors. This material has not been edited by the Transportation Research Board. SPECIAL NOTE: This document IS NOT an official publication of the second Strategic Highway Research Program, the Transportation Research Board, the National Research Council, or the National Academies.

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Contents 1 CHAPTER 1 Background 3 Phase 3 Objective and Work Plan 4 CHAPTER 2 Developing User Guidelines 4 Proposed Specifications 7 Survey of Vendors 8 Identify Target Users 8 Guideline Format 10 CHAPTER 3 Pilot Workshops 11 Workshop Discussion 13 CHAPTER 4 Summary and Conclusions 14 Reference 15 Abbreviations, Acronyms, Initialisms, and Symbols A1 APPENDIX A1 GPR Vendor Survey Responses A8 APPENDIX A2 SASW/IE Vendor Survey Responses B1 APPENDIX B1 GPR User Guidelines B22 APPENDIX B2 GPR Vendors’ Features C1 APPENDIX C1 SASW/IE User Guidelines C17 APPENDIX C2 SASW/IE Vendor Features

CHAPTER 1 Background Several types of surface distress in asphalt pavements, such as longitudinal cracking in the wheel path and tearing in the surface, can be attributed to delamination between hot mix asphalt (HMA) layers. Delamination is primarily due to layer debonding or stripping. Debonding occurs when there is improper tack between asphalt concrete (AC) layers or between an AC overlay and concrete pavement. Stripping develops when the aggregates and asphalt binder are incompatible, adhesion is lost, and water separates the asphalt binder from the aggregate. Delamination is difficult to detect before the surface distress—cracking or tearing— occurs. Currently, coring is often used to measure the depth, type, and severity of delamination after the visual distress appears. This test method is destructive and not suitable for continuous, effective evaluation of long stretches of pavement. Nondestructive testing (NDT) methods are needed to identify the presence, location (depth and area), and severity of delamination in a rapid, effective manner even before the surface distresses occur. They can be applicable to both network-level pavement condition assessment and project-level investigation to select a proper rehabilitation strategy and improve construction quality. Strategic Highway Research Program 2 (SHRP 2) Project R06D was initiated to evaluate NDT technologies that could detect delamination and to further develop the most promising methods to accomplish construction, project-level, and network-level evaluations. NDT for construction quality assurance should have the ability to detect debonding after placement of an AC lift. NDT for project-level investigation should have the ability to provide a detailed identification of the location and severity of delamination. NDT for network-level assessment should have the ability to detect the presence of delamination with the test equipment operating full lane width at a safe highway speed. The SHRP 2 Project R06D was initially conducted in two phases; Phase 3 was added later to the project after the first two phases had been completed. Phase 1 identified potential NDT technologies and prepared research programs for developing and evaluating these technologies. Phase 2 conducted the research programs and refined the best candidate NDT technologies. Detailed results of Phases 1 and 2 were presented in a separate report (1); a summary of the results is provided in the following paragraphs. Phase III developed guidelines and facilitated the implementation of the selected NDT technologies for evaluating delamination in asphalt pavements. Results of Phase 3 are presented later in this report. In Phase 1, through a literature search, meeting with NDT vendors, and discussion with a panel of experts, nine NDT technologies, including three ground-penetrating radars (GPR), two mechanical wave techniques, two infrared thermography devices, and two deflection measurement methods were selected for further evaluation in Phase 2. In Phase 2, the NDT technologies were evaluated in both controlled and uncontrolled conditions. The controlled-condition evaluation was conducted on two delaminated pavement slabs (8 ft × 4 ft × 8 in. thick) in the National Center for Asphalt Technology (NCAT) laboratory 1

and on ten 25-ft intact and delaminated pavement sections constructed on the NCAT Pavement Test Track. The evaluation was performed under warm-dry pavement and cool-wet pavement conditions. Based on the results of the controlled-condition evaluation, the GPR and mechanical wave technologies were identified as most promising for achieving the objectives of the project. A GPR vendor and a mechanical wave vendor agreed to work with the research team through two seed-money agreements to improve their hardware and software before the uncontrolled-condition evaluation. At the time, the GPR vendor already had a lane-width, air- launched antenna array with the software that could process the raw data into a three- dimensional visual array. Hence, the hardware improvement focused on modifying the vehicle attachment for safe and secure transport between testing sites. Software improvements were done to help users examine the GPR measurements in greater detail and streamline the data analysis. During the controlled-condition evaluation, the mechanical wave vendor demonstrated a prototype device with two rolling wheels that could conduct impact echo (IE) and spectral analysis of surface waves (SASW) measurements along a longitudinal path. Further development of the hardware focused on increasing the number of wheels to measure the lane width in a single pass. The software was improved to collect more data when more wheels were used and to better analyze data, particularly for SASW measurements. The improved NDT devices were then evaluated in uncontrolled conditions at delaminated pavement sites in Maine, Kansas, and Florida. Both of the vendors showed significant improvements in their hardware and software. GPR is capable of testing full lane width at moderate testing speed. Mechanical wave methods are limited to testing at less than 5 mph, but this is still a significant improvement over point-test methods. Software is available to analyze data in great detail but requires a trained technician. Further improvement in software is needed to reduce the analysis time. Both technologies can be used to detect discontinuities in asphalt pavements; however, they cannot be used to conclusively distinguish between types of pavement discontinuities. Coring will be needed to confirm the nature of the discontinuity. GPR can be used to identify variations in the pavement, isolate the depth and area of a discontinuity in the pavement, and provide a relative degree of severity. Severe conditions, like stripping, can be observed with conventional analysis software. Detecting debonding between asphalt layers requires a refined analysis methodology. For the mechanical wave methods, IE can identify variations in the pavement below 4-in. depth, and SASW can identify variations in the top 7 in. of the pavement. However, IE should be conducted on cool and stiff asphalt surfaces, and SASW requires a reasonable value for the pavement stiffness for analysis. Both the IE and SASW methods have limited ability to provide the degree of severity and cannot measure pavement condition below the top of the discontinuity. GPR and mechanical wave methods were recommended for implementation as project- level tools used independently or in combination to determine the extent and depth of pavement discontinuity to help select the proper rehabilitation strategy. GPR can be conducted without a lane closure and is appropriate for preliminary assessment of pavement condition. IE and SASW 2

will require a lane closure and can be used to supplement GPR results. In addition, continuing improvement in data analysis software is needed to make NDT a network-level tool for detecting delamination in HMA pavements. Phase 3 Objective and Work Plan The objective of Phase 3 was to develop user guidelines for the NDT technologies selected in Phase 2, that is, GPR and mechanical wave. Phase 3 was added to the project to help implement the advanced NDT technologies for detecting delamination in HMA pavements. The guidelines would be provided to pavement engineers (users) with an interest in applying NDT for pavement evaluation and project development. The Phase 3 objective was later enhanced to include pilot workshops for interested users. 3

CHAPTER 2 Developing User Guidelines The research team developed guidelines for using the NDT technologies improved under SHRP 2 Project R06D to identify delamination between asphalt layers. The guidelines were developed in three steps. First, the research team proposed hardware and software specifications for GPR and mechanical wave methods based on the results of the evaluations in Phase 2 and prepared vendor surveys based on the specifications. Second, the team then sent the specifications and surveys to vendors for review and followed up with a conference call with each vendor to discuss the vendor’s comments and responses. Finally, the guidelines were prepared in a generic NDT technology perspective based on the proposed specifications, the vendors’ survey inputs, and expected target users. A summary of each step follows. Proposed Specifications Proposed Specifications for GPR Based on the Phase 2 evaluation results, GPR is capable of detecting moderate to severe delamination by observing spatially coherent anomalies in the GPR data at specific depths. It could also identify debonding between asphalt lifts if water was present in the seam. This detection capability was implemented using a multi-antenna array distributed across the width of the pavement. The purpose of the array was to collect equally spaced parallel lines of data simultaneously, so that coherent areas of delamination can be identified and mapped for the full width of a 12-ft wide lane. Data are collected continuously while the system is driven along the surface of the pavement. The data collection is typically triggered using a distance measuring instrument (DMI) mounted to the vehicle wheel or to an external distance wheel. Tables 2.1 and 2.2 show proposed specifications for a GPR system that can be used to evaluate delamination in asphalt pavements. 4

Table 2.1 Proposed System Requirements for GPR System Component Specification System type Array of multiple antenna elements lined up transverse to the direction of travel Frequency Range - Impulse radar systems Center frequency of pulse > 2.0 GHz; –10 db limits: 0.5 to 5.0 GHz Frequency Range - Frequency sweep radar systems Frequency range: up to 3.0 GHz Lateral spacing of antenna elements < 1.5 ft Lateral coverage per pass 12 ft (full lane width) Longitudinal data collection rate > 2 scans per foot per antenna element Travel speed during data collection > 20 mph Travel speed during mobilization Posted speed limit Real-time display B-scan for selected antenna elements System monitoring and control From within the survey vehicle Data collection rate Data collection should be triggered on distance using a DMI Spatial reference Vehicle DMI, external distance wheel, or global positioning system (GPS) Detection Depth Range 2 to 12 in. Table 2.2 Proposed Data Output and Display Requirements for GPR Requirements GPR Data Output Output should be a volume of data with amplitude as a function of x (longitudinal distance), y (transverse offset), and z (time) Data Display Field operation and playback software should be capable of the following displays: • Direct time domain waveform (A-scan) • Longitudinal profile for a given transverse offset (B-scan) • Time/depth slice for a given time range • Transverse profile for a given location or station Proposed Specifications for Mechanical Wave Methods Based on this project evaluation results, SASW and IE methods are capable of detecting delamination by observing spatially coherent anomalies in the data at specific depths. The SASW detection capability was implemented using multiple pairs of motion sensors (displacement transducers) with an impact source in an array distributed across the width of the pavement. The automated IE system is an array of measurement units, each consisting of one impact source and one motion sensor. The purpose of the array is to collect equally spaced parallel lines of data simultaneously so that coherent areas of delamination can be identified and mapped for the full lane width of 12 ft. Data are collected incrementally while the system is moved along the surface 5

of the pavement. The data collection is typically triggered using a DMI mounted to the vehicle wheel or to an external distance wheel. Tables 2.3 and 2.4 show proposed specifications. Table 2.3 Proposed System Requirements for SASW and IE System Component SASW Specification IE Specification System type Array of impact sources and pairs of motion sensors, lined up transverse to the direction of travel Array of impact sources and motion sensors lined up transverse to the direction of travel Sensor frequency response Up to 50,000 Hz Up to 50,000 Hz Impact source input frequency Up to 50,000 Hz Up to 50,000 Hz Lateral spacing between sensors 2 ft between center of motion sensor pairs (maximum) 2 ft between motion sensors (maximum) Lateral coverage per pass 6 ft (half lane width) 12 ft (full lane width) Longitudinal data collection rate 1 test per foot (minimum) 1 test per foot (minimum) Travel speed during data collection 1 to 2 mph 1 to 2 mph Travel speed during mobilization Posted speed limit Posted speed limit Real-time display Single sensor pair waveforms in time domain at reduced display rate Waveform and resonant frequency at each sensor System monitoring and control Within or outside the survey vehicle Within or outside the survey vehicle Data collection rate Based on speed and sensor spacing on the sensor array Based on speed and sensor spacing on the sensor array Spatial reference Vehicle DMI, external distance wheel, or GPS Vehicle DMI, external distance wheel, or GPS Table 2.4 Proposed Data Output and Display Requirements for SASW and IE SASW IE Data Output Requirements • Output format should be a volume of data with surface wave velocity as a function of x (longitudinal distance), y (transverse offset), and z (depth) • Output format should be a two- dimensional array of data with thickness as a function of x (longitudinal distance) and y (transverse offset) Data Display Requirements • Direct time domain waveforms from each of the two receivers • Dispersion curve for each sensor pair • Waterfall plot of dispersion curves collected versus distance covered for each sensor pair • Direct time domain waveforms from each source-receiver pair • Running amplitude/thickness plot, or equivalent B-scan, for each sensor pair 6

Survey of Vendors The proposed NDT system specifications along with questionnaires were sent to GPR vendors and mechanical wave equipment manufacturers. Four GPR vendors and two mechanical wave equipment manufacturers responded. The research team then had a conference call with each vendor to discuss the specification and survey. The questions used in the survey are listed below. The same set of questions were used for both NDT technologies but referred to the applicable NDT technology specification described in the previous section of this report. The vendor responses are summarized in Appendix A. Question 1 Do you currently supply equipment that can be configured to meet the proposed requirements? Question 1a If yes, please describe the components that you would use, and how they would be configured to meet these requirements. Question 1b What type of carrying/mounting assembly would you use to meet the target testing speed? Question 1c Also, if yes, can you exceed the proposed requirements, and to what degree? Question 1d If not, do you have plans to offer equipment that would meet these requirements? When would this equipment become available? Question 1e If no, what changes in the requirements would need to be made in order for your equipment to comply? Question 2 What would be the approximate cost range for the system that you would propose in answer to question 1? Question 3 Are there modifications to the proposed requirements that you would recommend based on your perception of the overall objectives of this system? Question 4 Based on your experience, who are the probable buyers for this equipment? Question 5 Based on your experience, how frequently do you anticipate this system would need to be upgraded, and what would be the cost implications? Question 6 What are the features of your process that supports data transfer and analysis? Question 7 What are the features of your analysis software that supports our pavement evaluation objectives? Question 8 How do you analyze the data and report delamination conditions? Question 9 What is the level of expertise needed to operate the equipment and analyze the data? Question 10 What do you consider to be the unique strength of your system in meeting the proposed objectives? Question 11 Similarly, what do you consider to be potential limitations of your system? Question 12 What are the weather and pavement condition limitations for your equipment? Question 13 (GPR only) Has the equipment that you propose been approved by the Federal Communications Commission (FCC)? If not, is the equipment going through the approval process, and if so, what is the status of this process? Are there any regulatory restrictions to the use of your equipment, and, if so, what are they? 7

Identify Target Users Determining the target audience for the guidelines is an important step that precedes preparation of the document. The target audience must have a need for the equipment, funding to purchase the equipment, and a level of technical expertise to operate and analyze the data. An obvious target audience would be the pavement design engineers of state highway agencies. State highway agencies are responsible for most of the moderate- to high-volume routes and are most likely to have resources to purchase NDT equipment. The second likely group is the pavement management engineers responsible for measuring and monitoring the condition of the pavements. The third group would be the consulting engineering firms that provide pavement assessment and design services. Each of the three groups has individuals who operate and maintain testing equipment and individuals who process and analyze pavement data. Vendor Survey Question 4 asked the vendors about anticipated target users who might purchase the equipment. Their responses confirmed the previous target list. The vendors also identified factors that would influence potential users. Two additional factors are the ability to use the equipment for multiple purposes (such as pavements and bridge decks) and resistance to purchase a device that requires a “black box” to collect and analyze the data. Guideline Format The format for the guidelines is based on the research team’s experience from Phases 1 and 2, the information collected from the vendor survey, and knowledge of the target users. The document is intended to be a concise user guide, not a detailed user operation manual. As a tool to foster NDT implementation, the guideline needs to follow a logical sequence of topics. For example, a discussion of the data analysis should follow the discussion of data collection. The research team elected to prepare separate guidelines for GPR and the mechanical wave technologies. While the general purpose of the equipment is the same (detect delamination in asphalt pavements), the features and operation of each device are unique. The format needs to conform to the scope and objectives of SHRP 2 R06D while recognizing there are multiple vendors. To accomplish this, the format for the body of the guidelines is generic and an additional appendix is included for each vendor to highlight their equipment’s capabilities. The user guidelines for GPR are found in Appendix B1. The user guidelines for SASW/IE are found in Appendix C1. Both the GPR and mechanical wave guidelines use the following format. 1. General Theory 2. Equipment Specifications 3. Proposed Data Output and Display Requirements 4. Equipment Calibration and Verification 5. Pavement and Climate Conditions for Testing 6. Testing Modes and Required Settings 7. Test Output Data Formats 8

8. Test Output Data Quality Control Check 9. Data Analysis 10. Test Reporting 9

CHAPTER 3 Pilot Workshops The original scope of this Phase 3 implementation effort included a focus on a pilot workshop effort by FHWA. Later, the scope was expanded to have the research team coordinate with FHWA and key NDT vendors (3d-Radar and Olson Engineering) to identify interested users and pilot the NDT capabilities with those users. Each pilot workshop included a presentation of the NDT capability to the user’s engineers and pilot testing with the equipment, when the equipment was available, on a field site selected by the user. The following bullets highlight the results of each pilot workshop. • FHWA Measures NCAT Pavement Test Track SHRP 2 R06D Research Sections On June 21, 2012, FHWA Turner Fairbanks Highway Research Center travelled to the NCAT Pavement Test Track facility to measure the SHRP 2 delamination test sections with their GPR and MIRA equipment. Results of their measurements and analysis have not been shared with the SHRP 2 research team. • NCAT Regional Pilot for Southeast Highway Agencies On December 3, 2012, the research team, with cooperation of 3d-Radar and Olson Engineering, hosted a pilot workshop at the NCAT Pavement Test Track. Ten agencies in the southeast region were invited to attend the half-day program. Twelve representatives from four agencies were able to attend (one representative from the FHWA Resource Center in Atlanta, one representative from the Georgia Department of Transportation [DOT], two representatives from the Florida DOT, and eight representatives from the Alabama DOT). The program included presentations by Dr. Heitzman and Mr. Olson on SASW and IE technologies and presentations by Dr. Maser and Mr. Stevens on GPR technology. After lunch, 3d-Radar and Olson Engineering operated their NDT equipment on the NCAT Pavement Test Track for the participants to observe NDT measurements of test track sections. • TRB Vendor and User Contacts During the TRB annual meeting, the research team, Olson Engineering and 3d-Radar, used the opportunity provided by the vendor exhibit hall to solicit additional interest for pilot workshops. A specific conversation was held with Minnesota DOT recognizing the diverse pavement research sections available at the MnROAD Research Facility. Potential dates in April were considered. • Minnesota Regional Pilot for North Central Highway Agencies On April 19, 2013, the research team, with cooperation of the Minnesota Department of Transportation, 3d-Radar, and Olson Engineering, hosted a pilot workshop at the MnROAD Research Facility. Five agencies in the north-central region were invited to attend the half-day program. Nine representatives from two agencies were able to attend (one representative from FHWA and eight representatives from the Minnesota DOT). 10

Poor weather conditions restricted representatives from other DOTs from attending. The program included presentations by Dr. Heitzman and Mr. Olson on SASW and IE technologies and presentations by Dr. Maser and Mr. Stevens on GPR technology. After lunch, 3d-Radar and Olson Engineering operated their NDT equipment on MnROAD Test Sections for the participants to observe NDT measurements of research sections. • Indiana Regional Pilot for North Central Highway Agencies Indiana expressed an interest in hosting a pilot but was unable to establish an acceptable date. • Connecticut DOT Regional Pilot for North East Highway Agencies Connecticut expressed an interest in hosting a pilot in the northeast region, but was unable to establish an acceptable date. Workshop Discussion The participants at the workshop expressed a number of key questions and comments. A summary of those discussions is given below. Question: Why were these technologies recommended? Response: Numerous NDT technologies were examined in Phase 1 and 2 of the SHRP2 study. The study reviewed literature on each technology, performed theoretical modeling, and tested each technology against known delamination built into test sections on the NCAT Pavement Test Track. GPR and SASW/IE were the only technologies that demonstrated reasonable potential to meet the SHRP2 study objectives. Question: The SHRP2 study is recommending both devices. Why are both devices needed? Response: These NDT technologies use different methods for measuring changes in the pavement. They each have strengths and weaknesses. GPR can assess a large area of pavement very quickly, but the measurement is sensitive to distress severity and the presence of moisture. SASW/IE is not as rapid as GPR and is sensitive to the temperature of the pavement. Question: What are the differences between the vendors for this equipment? Response: Each vendor manufactures a uniquely different device. The NDT technology applied is similar, but the features of each device are different. For GPR, three major differences are (1) air-coupled versus ground-coupled antenna configurations, (2) antenna signal frequency, and (3) single antenna units versus units with an array of antennas. For SASW/IE the primary difference is manual point-to-point testing versus automated testing. Question: How many tests can each device perform? Response: The density (spatial distribution) of tests is dependent on a number of factors. For GPR, the frequency of testing is an input for the device and influences the speed of testing. If individual antennas are used, then the density of tests is also controlled by the number of passes 11

made by the device. When an antenna array is used, the density of tests (rows of data) will likely be much larger. For SASW/IE, the density of testing is established by the test grid for manual point-by-point measurements. For the automated SASW/IE device, the density of testing is controlled by the automated frequency in the longitudinal direction and the spacing between the units in the transverse direction. Question: Is either NDT technology cost-effective to own and operate? Response: Both technologies can be a valuable tool for pavement forensic evaluations. The cost- effectiveness of each technology depends on the amount of use and the ability to expand the use these NDT technologies for other applications. For example, GPR can be used for numerous types of subsurface evaluations involving soils and drainage. SASW/IE is also used for bridge deck delamination evaluations. Question: How complicated is the data analysis? Response: Both technologies require an understanding of the measurement principles associated with the NDT theory so that the testing is done under appropriate conditions to obtain good data. The analysis will require both manual manipulation of the data and analysis software that screens the data for signal changes. Analyses software will continue to evolve as user demand grows. 12

CHAPTER 4 Summary and Conclusions Phase 3 of this SHRP 2 study prepared user guidelines for using GPR and SASW/IE NDT technologies to detect delamination in asphalt pavements. The research team solicited input from NDT equipment vendors so the guidelines would accurately reflect the capability of each technology. The target users are highway agency pavement design and pavement management engineers and consultants who provide the same services. The research team prepared separate guidelines for GPR and SASW/IE. Each guideline is a concise overview of the NDT technology that includes general theory on the NDT principles, equipment specifications, output and display requirements, equipment calibration, testing conditions and settings, output data analysis, and reporting formats. The guidelines are not intended to be technician equipment operation or engineer data analysis training documents. There are five appendices to this report. Appendix A1 and Appendix A2 are a summary of the NDT vendor input for the guidelines. Appendix B1 is the GPR user guidelines. Appendix B2 contains a technical brief from each GPR vendor. Appendix C1 is the SASW/IE user guidelines. Appendix C2 contains a technical brief from each SASW/IE vendor. The vendor technical briefs were solicited from all known vendors, but not all vendors chose to submit a document. Both types of NDT technologies have functioning hardware and data collection systems. Data analysis is the challenging aspect of the technology, and software to support the analysis is advancing. Skilled technicians and engineers are needed to operate the equipment and analyze the data to identify pavement condition. The cost-effectiveness of each NDT device is dependent on the level of intended use and the diversity of applications it is applied to. Specific for this SHRP 2 study, both devices are suitable for pavement forensic studies and field investigations for pavement rehabilitation projects. GPR can be used for network-level pavement assessment, but to manage the volume of data and analysis will require further software development. Both devices can be used for field measurements to assess other roadway features, like bridge decks and culverts. The research team and key vendors held workshops in Alabama and Minnesota. In addition to the host state highway agency, neighboring agencies were invited to attend. A total of seven states participated in the workshops and gained a better understanding of the potential of GPR and SASW/IE technologies for asphalt pavement condition assessment. The execution of this study established and confirmed that NDT technologies have the ability to be important tools in the assessment of pavement condition and identification of pavement distress. The companies developing the equipment and software will continue to improve the capability of their systems if there is a reasonable potential for a profitable market. Improvements in the technologies will progress as demand for the technology expands. 13