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Standard Definitions for Common Types of Pavement Cracking 62 C H A P T E R 7 Conclusions There is a lack of field proven cracking protocols for automated systems that can be embraced by SHAs for implementation, particularly in the era of high-performance computing, and proliferating and ubiquitous Artificial Intelligence based tools. Traditional definitions, such as those as defined in the ASTM PCI and the LTPP Distress Manual, continue to play important roles in pavement engineering. However, 1-mm and sub-mm 3D pavement data are widely collected today at highway speeds, and their potential in pavement engineering has yet to be fully exploited due to lack of implementable cracking definitions and compatible processing tools. Cracking information is increasingly used for pavement management, design, and fulfilling national reporting requirements. Facing the need to obtain repeatable, consistent, and accurate cracking data, the research team was tasked in 2017 by the National Cooperative Highway Research Program (NCHRP) to define a new generation of cracking protocols for fully automated processing. The outcome of this research effort includes proposed definitions at three levels to assess pavement cracking for intended engineering applications. Built on a comprehensive review of previous research, published literature, survey of SHAs, and feedback from the NCHRP panel, recommendations for standard cracking definitions have been developed. In particular, the following five tasks have been accomplished for the project: ï· A summary of existing cracking data collection practices, including how data are collected and classified by type, severity, quantity, extent, units, and other factors, through a comprehensive literature review and survey of SHAs (Chapter 2). ï· A summary of the role of cracking data in different levels of decision-making processes, including acceptable levels of precision and bias for collected data based upon the relative impact of cracking types (Chapter 3). ï· A summary of desired cracking data by the SHAs (Chapter 4). ï· An initial recommendation of the most appropriate standard cracking definition for automated systems based on the results from previous work (Chapter 5). ï· Testing of the proposed levels of cracking definitions based on repeating field data collection, with initial positive results for applicability on both asphalt and concrete pavements (Chapter 6). Based on the survey of SHAs and research tasks completed for the project, three levels of cracking definitions were proposed to address the needs of both network and project level pavement management, MEPDG, and various reporting processes. Level 3 addresses cracking
Standard Definitions for Common Types of Pavement Cracking 63 extent at the network level and is a macro-indicator of general cracking extent on a pavement section, or network. Level 3 data satisfies HPMS and MAP-21 reporting needs and provides overall cracking information, which can be used as the initial qualification and evaluation of potential technology suppliers. Level 2 contains cracking information with low, medium, and high severity levels for pavements. Cracking severity in each zone, including zones for each wheel paths (zone 2 and zone 4), is also computed. Information on Level 2 can assist various network level PMS activities and identify locations with specific distress problems. Level 1 classifies linear cracking into longitudinal and transverse cracking in non-wheel paths, wheel path crack from the wheel paths, and sealed cracks for asphalt pavement. Level 1 also includes the proposed definition for concrete pavement. The general approach of applying the proposed cracking definitions are accumulative. That is, cracking analysis always starts with Level 3, then to Level 2, and finally for the most detailed process to Level 1. Finally, the team conducted initial field testing of the proposed cracking definitions on 12 pavement sites. The limited field data testing shows that the results are highly repeatable. Expansion of the proposed definitions to other project sites would potentially improve the CV values and demonstrate methods to mitigate and improve repeatability and comparability. âGround-Truthâ cracking information has been a constant discussion among the pavement community for decades. Its definition and implementation are a subject of debate as well. Even though âGround-Truthâ cracking data were not obtained in the data tests in the project, developing its definition and associated application to evaluate precision and bias levels of the proposed cracking definition is highly recommended in a new implementation project. In addition, since the testing was conducted without the direct participation of any SHAs, data validation on Level 3, Level 2, and Level 1 cracking presented in the report are considered preliminary. Participations of multiple SHAs are critical for the validation and implementation of the newly defined three levels of cracking definitions. It is therefore proposed that a validation and implementation process through field trials at several SHAs be conducted with direct participation and input from the agencies. Subsequently, modifications and refinements will be validated and incorporated into a final set of protocols that have sufficient justifications for a new AASHTO standard to guide future implementation of the new cracking definitions. Potential activities for an implementation and validation study include: 1. Solicit participation of a minimum of three SHAs to conduct field implementation trials. 2. Design experiments for conducting data collection, define what âGround-Truthâ cracking is, and develop a process to obtain the âGround-Truthâ results. 3. Design and conduct data analysis based on the three levels of cracking definitions and the collected data, including fully automated results and âGround-Truthâ results. 4. Identify gaps and shortcomings in the complete workflow in terms of meeting the needs of PMS, pavement design, and reporting, and propose modifications and fine-tuning of the cracking protocols. 5. Demonstrate true and fully automated cracking processing based on Deep-Learning methodology for both cracking identification and classification, and applications of the proposed cracking definitions on the fully automated results, and the âGround-Truthâ results. 6. Develop draft AASHTO standard for consideration by the AASHTO Committee on Materials and Pavements.