Nondestructive Testing to Identify Delaminations Between HMA Layers, Volume 1 - Summary (2013)

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8The research team for this study was composed of experts in the fields of nondestructive testing (NDT) and hot-mix asphalt (HMA) from multiple organizations. The organi- zations were the National Center for Asphalt Technology (NCAT); Infrasense, Inc.; the U.S. Army Corps of Engineers Engineering Research and Development Center (ERDC); and the Center for Nondestructive Evaluation. In addition, Infrasense used two NDT consultants from the University of Florida and Northeastern University. This study was divided into two phases. Phase 1 was intended to identify potential NDT techniques and to prepare research programs for developing and evaluating these techniques. Phase 2 was intended to conduct the research programs and to refine the best candidate NDT technologies. Phase 1 In the first part of Phase 1, the research team identified and assessed new and existing NDT techniques that would be capable of determining the existence, extent, and depth of delaminations and discontinuities in HMA pavements. Some of those NDT techniques would not have the poten- tial to provide rapid results with near 100% continuous coverage of the pavement area. In addition to assessing the existing NDT methods found in the literature review, the research team also contacted manufacturers of NDT devices to discuss potential development of new or modification of existing NDT techniques for determining the delamination between HMA layers. Invitations were sent to 21 vendors based in the United States and other countries to attend an informational meeting with the research team. During the informational meeting, the research team (a) discussed the research plan and seed money that would be used to encourage the companies to develop or significantly mod- ify the equipment and (b) requested preliminary proposals from the vendors. The research team received six prelimi- nary proposals from the manufacturers. The research team evaluated each vendor’s preliminary proposal with a vendor evaluation form (Figure 2.1) in which the evaluation criteria were based on technical, economic, and practical conditions facing highway engineering practitioners. The most impor- tant evaluation criterion was the potential of the NDT tech- nique to identify delamination. After completing the literature review and the evaluation of the preliminary proposals, the research team met with the panel of experts (Table 2.1), who represented the expertise and diversity critical to assist the research team with the task of selecting the most promising NDT techniques for further evaluation. At the meeting, the research team first presented an overview of the SHRP 2 research objective and work plan, a summary of the technologies under consideration, and the criteria developed to evaluate the proposals from interested vendors. Then, the six NDT equipment vendors gave brief presentations on their proposals. After the vendors’ presenta- tions, the research team shared the team’s evaluation of the vendors’ proposals, presented recommendations on which vendor proposals to advance into Phase 2, and shared the outline for the Phase 2 effort. The expert panel provided valu- able comments to the research team. On the basis of results of Phase 1, including the meeting with the expert panel, the following six NDT technologies, consisting of three ground penetrating radars (GPR), two mechanical wave techniques, and two infrared (IR) thermog- raphy devices, were selected for further evaluation in Phase 2. • GPR from Geophysical Survey Systems, Inc. (GSSI), USA • GPR from MALA AB, Sweden • GPR from 3d-Radar AS, Norway • Mechanical wave from Geomedia Research and Develop- ment (Geomedia), USA • Mechanical wave from Olson Instruments, Inc. (Olson), USA • IR camera from Infrared Cameras, Inc. (ICI), USA • IR camera from Infrasense, manufactured by FLIR, Worldwide C h a P t e r 2 Research Approach

9 Vendor: Evaluator: Each Research Team Member ID Evaluation Factor Evaluation Level Comments Point Weight Key Indicators Description: na na A Potential for Identifying Delamination High (8–10 points) = high potential Medium (5–7 points) = low potential Low (<5 points) = not going to work 40% B Potential to Implement High (8–10 points)= can be implemented immediately Medium (5–7 points) = may be implemented if modified Low (<5 points) = cannot be implemented 5% Equipment C Equipment Availability High (8 to 10 points) = commercially available Medium (5 to 7 points) = modification needed Low (<5 points)= prototype being developed 10% D Current Application High (8 to 10 points)=– used for evaluating asphalt pavements Medium (5 to 7 points) = used for evaluating other pavement types Low (< 5 points) = used for other structures or have not been 5% used E Costs (Equipment + Operation) High (8 to10 points)=– < $50,000 Medium (5 to7 points) = $50,000 ~ $150,000 Low (< 5 points) = > $150,000 5% Measurement and Analysis F Speed of Data Collection High (8 to10 pts) = highway speed greater than 45 mph Medium (5 to7 points) = speed of 5 to 45 mph Low (< 5 points) = speed less than 5 mph, point testing 10% G Depth of Effective Applicability High (8 to10 points) = at least the top 5 in. Medium (5 to7 points) = top 3 in. Low (< 5 points) = top 1 in. 10% H Simplicity of Data Analysis High (8 to10 points) = automated with minimum training Medium (5 to7 points) = automated but requires expertise Low (< 5 points) = manual and requires expertise 10% Figure 2.1. Vendor evaluation form. (continued on next page)

10 I Results High (8 to10 points) = detailed location and severity (3-D mapping) Medium (5 to7 points) = detailed location, no severity ( basic map) Low (< 5 points) = general presence, no detail (tables) 5% Advantages and Limitations Advantages Description: na na Limitations Description: na na Possible Description: na na Modification Note: na = not applicable. Figure 2.1. Vendor evaluation form (continued). Table 2.1. Panel of Experts Name Affiliation Expertise Area Jim Musselman the Florida DOT Pavement material and construction Kim Willoughby the Washington State DOT Pavement material, research, and NDT Andrew Gisi the Kansas DOT Pavement design, geotechnical, and research Nadarajah Sivaneswaran Federal Highway Administration Pavement management, design, and research John Harvey University of California, Davis Pavement design, material, and NDT research Harold Von Quintus Applied Research Associates Pavement design, evaluation, and NDT Note: DOT = Department of Transportation. In addition, the expert panel recommended that the research include deflection measurement methods. Therefore, the fol- lowing two deflection measurement methods were selected for further evaluation in Phase 2. FWD with equipment from NCAT and LWD with equipment from ERDC. Phase 2 Phase 2 was divided into three primary tasks: controlled eval- uation, uncontrolled evaluation, and reporting findings. The first task in Phase 2 evaluated all eight NDT technology ven- dors and assessed which components of each system needed further development. Each NDT technique was evaluated under controlled laboratory conditions (except for the FWD) and controlled field conditions. The controlled testing was performed under both warm-dry and cold-wet environmen- tal conditions to observe the change (if any) in the NDT mea- surement. The controlled laboratory evaluation was carried out by using two slabs with built-in delaminated interfaces, and the controlled field evaluation was conducted with test sections built at the NCAT Pavement Test Track to simulate full-scale, real-world pavement conditions. The first round of controlled testing was conducted under warm and dry environmental conditions. The layout of the delaminated areas for both controlled laboratory and field evaluation sections was withheld from the equipment

11 technicians who conducted the testing and analyzed the data. There were no identifying marks on the test slabs or test sec- tions. After evaluating results of the first controlled evalua- tion, the research team shared the evaluation results with each NDT equipment manufacturer. The team discussed potential refinement of existing NDT hardware and software to improve the device’s ability to measure delamination between HMA layers. The second round of controlled evaluation was con- ducted under cool and wet pavement conditions. The proce- dure for evaluating each NDT technique was the same as that conducted in the first round of testing. However, the start- ing location for measurements was changed slightly to alter the location of the delamination during the test and water was injected into the delamination. Plastic standpipes were installed at several locations and filled with water to apply hydrostatic pressure into the delaminated layer interfaces. It was anticipated that the presence of water at the delaminated interfaces would change the GPR’s ability to detect the delamination. At the completion of the controlled evaluations, the research team assessed the controlled testing results and the proposed improvements of hardware and software from the manufac- turers to select the most promising NDT methods for further evaluation. The selection criteria were based on technical, economic, and practical conditions facing highway engineer- ing practitioners. The parameters evaluated included the ability to measure the extent and depth of the delaminated area, accuracy, repeatability, area of coverage, speed of data collection, and speed and sophistication of data analysis. The research team also met with the SHRP 2 staff and panel of experts to review the evaluation and selection results. Two NDT techniques, GPR from 3d-Radar and mechanical wave technique from Olson Instruments, Inc., were selected for further refinement and uncontrolled field evaluation later in the study. Seed money was distributed to the two NDT ven- dors to encourage them to refine the equipment and software. After the vendors had refined their equipment and analy- sis software, the uncontrolled field evaluation was conducted to measure the effectiveness of the NDT technologies under field conditions. Each evaluation site included uncontrolled pavement sections that had been identified as having delami- nation problems. Validation sites were selected in Florida, Kansas, Maine, and Washington State. Cores were extracted from areas identified as delamination by NDT techniques to verify the NDT results. At the conclusion of Phase 2, all testing results were ana- lyzed and summarized, and two reports were prepared to document the study. This volume summarizes the study and highlights the findings. Volumes 2 through 5 provide more detailed information for readers with specific interests. See Appendix D for a list of the topics in these volumes.