Guide for Conducting Forensic Investigations of Highway Pavements (2013)

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136 A t t A c h m e n t Guide for Conducting Forensic Investigations of Highway Pavements: Background Research

137 138 1. Introduction 139 2. Review of Existing Practices 139 2.1 Literature Review 139 2.2 State Highway Agency Survey Questionnaire 140 3. Forensic Investigation Elements 140 3.1 Applications 142 3.2 Generic Issues 143 3.3 Project Specific Issues 146 4. Guide Development 146 4.1 Preliminary Guide 147 4.2 Assessment of Preliminary Guide 150 4.3 Revised Guide 150 5. Summary, Conclusions, and Recommendations 150 5.1 Summary 151 5.2 Conclusions 151 5.3 Recommendations c o n t e n t s

138 1. Introduction Hundreds of pavement forensic investigations have been performed in this country over the decades to address a num- ber of objectives. However, rarely are any two forensic inves- tigations carried out in the same manner primarily because: • Objectives of and the reasons for doing a forensic investi- gation vary from one project to another. • Budget, time, and manpower constraints limit the variety of available investigation techniques and procedures. • Recording and documentation of observations often vary. • Standard or widely accepted guidelines to promote consis- tency on a national scale do not exist. In essence, each pavement forensic investigation under- taken in the past has typically been a case study that pro- vided limited useful information for subsequent studies, and hence there was a need for developing a standardized guide for nation-wide use in conducting forensic investigations of highway pavements. NCHRP Project 01-49 was initiated to address this need. The objective of this study was to develop a Guide for Con- ducting Forensic Investigations of Highway Pavements that considers relevant factors, such as functional and structural performance, construction- and/or material-related distress, long-term effects of traffic and environment, pavement type, sampling and testing requirements, and sequence of activi- ties. Moreover, the guide needed to address the full spectrum of possible objectives to allow use throughout the pavements community. Achieving this objective will lead to other ben- efits, such as: • Maximizing the information collected from an investi- gation, • Conducting more cost-effective investigations, • Improving understanding of how and why pavements behave as they do, and • Providing valuable data in support of model development for use in pavement evaluation and design procedures and/or improved technologies. These benefits will be manifested as forensic investigations are performed in a more systematic fashion throughout the United States. In addition, it is important to use a standard format for storing and disseminating the findings and out- comes from completed investigations. Pavement forensic investigations are carried out for wide- ranging reasons, including: • Investigating why pavements fail, and more specifically, the underlying causes of premature pavement failures. • Understanding the factors contributing to exceptional pavement performance and longevity. • Collecting data to support development and/or calibration of performance prediction models. • Collecting data to support investigations into the long-term effects of traffic and environment on material properties. • Checking the functionality and calibration of pavement instrumentation. Because pavement forensic investigations can serve many objectives and they may be performed under widely varying conditions (pavement type, distresses, traffic, ambient condi- tions, etc.), the guide should address the numerous possible combinations of objectives and conditions. Moreover, when conducting forensic investigations, it is important to “expect the unexpected,” and allow flexibility in adapting to field con- ditions. In addition, multiple levels of assessment should be considered when performing such investigations, ranging from simple visual observations, to coring and trenching operations, to routine pavement performance and materials testing, and to the more sophisticated techniques such as chemical analyses and digital and scanning electron microscope studies. Accordingly, the guide developed under this project effort helps establish clear and concise objectives for carrying out a forensic investigation on a particular project (i.e., determine the purpose of the forensic investigation and identify how the investigation results will be used). In addition, the guide explains the level of investigation and activities at each level that are required to meet the objectives. Because there is not a single set of activities that applies to all possible objectives and project specific conditions (pave- ment type, environment, traffic, etc.), the implementation of the guide developed in this project will provide: • A step-by-step procedure that will guide highway agency personnel and other interested parties in tailoring foren- sic investigation plans to meet the desired objectives and project specific conditions. • Detailed information (the “what” and the “how”) and guid- ance to allow highway agency personnel and other inter- ested parties to develop and implement a well thought out and planned forensic investigation. • Suggestions for database architecture for storing the find- ings of forensic investigations to facilitate use by others. • Guidance on how best to use the forensic investigation results, including changes in practice to prevent recurrence of premature failures, means for disseminating results, and lessons learned. Ultimately, the approach to any given forensic investiga- tion will depend on the objective of the investigation, how the findings from the investigation will be used, and the available resources.

139 The approach for developing the guide consisted of the following activities: 1. Review the literature on forensic investigations. 2. Identify and evaluate forensic investigation elements. 3. Prepare a forensic investigation guide outline and devel- opment process. 4. Develop preliminary forensic investigation guide. 5. Prepare and execute a plan for assessing the preliminary guide in the field. 6. Revise the guide. This report documents the results and findings of this work, which were intended to establish the foundation (i.e., out- line and process) for and actual development, assessment, and finalization of the pavement forensic investigation guide. The information presented in this report is organized in five chapters. Chapter 1 provides an introduction that covers back- ground, project objective, and major research issues. Chapter 2 presents a review of existing practices, including general trends and major findings from the available information and from the survey of state highway agencies. Chapter 3 describes the forensic investigation elements, including the identification and evaluation of the applications and elements involved in conducting investigations of different pavement types and conditions. Chapter 4 discusses the process for guide develop- ment, and Chapter 5 provides a summary, conclusions, and recommendations for research. 2. Review of Existing Practices The objective of this review was to collect and assess infor- mation relevant to pavement forensic investigations to estab- lish a reasonable body of knowledge for use in the development of the guide. To accomplish this objective, the following two activities were pursued: (a) review of literature available from various sources and (b) a web-based survey questionnaire of state highway agencies. 2.1 Literature Review The purpose of the literature review was to identify, review, and synthesize information for use in the preparation of the guide. A large number of documents from various sources were identified and reviewed. Key information was extracted from the relevant documents, which are listed in the Bibliography. With regards to the types of pavements studied and the reasons for conducting the investigation, the majority of the investigations involved asphalt pavements or layers, the majority of which were concerned with poor performance or pavement failures. Investigations of concrete and composite pavement failures were also documented, as well as investiga- tions into exceptionally good performance and other reasons such as calibration of performance models and evaluating instrumentation and forensic equipment. The specific objectives of reported investigations, in descending order of frequency, were: • Evaluation of poor pavement performance. • Comparative evaluation of pavement performance. • Application of pavement testing equipment or method. • Forensic investigation approach. • Evaluation of good pavement performance. Regarding forensic investigation techniques, the most com- mon field activity was coring followed by distress surveys, deflection (e.g., falling weight deflectometer [FWD]) testing, dynamic cone penetrometer (DCP) testing, sampling, trench- ing, roughness surveys, and ground penetrating radar (GPR) measurements. The literature review provided valuable insight into the practice of forensic investigations that was used in preparing an outline for forensic investigation guide. The most com- mon forensic investigation elements in these references were analysis/interpretation and forensic techniques followed by planning/implementation, use in broader pavement appli- cations, recording/documenting/dissemination, and lessons learned. Most of the documents involved studies of new HMA pavements, but numerous investigations also involved new PCC pavements, overlays, and other pavement structures. Most investigations dealt with the cause of poor pavement performance or failure. Coring was the most common foren- sic investigation technique discussed, followed by routine laboratory testing, distress surveys, and deflection testing. 2.2 State Highway Agency Survey Questionnaire To gather additional information for development of the guide, a survey questionnaire was distributed to the state highway agencies. The survey questionnaire was also intended to identify agencies interested in conducting field assessments and provide input to finalize the guide. Of the 52 highway agencies (50 states, the District of Colum- bia, and Puerto Rico) contacted, 37 completed the question- naire. Table 1 summarizes the reasons reported by these agencies for conducting (or not conducting) forensic investi- gations. Other reported reasons include: • To support studies conducted as part of an accelerated pave- ment test facility. • To assist development of repair techniques (e.g., a forensic investigation was done during development of an experi- mental process to use precast concrete repair slabs).

140 • To evaluate new products. • To evaluate existing pavement conditions and properties for use in determining rehabilitation strategies. Among the reasons reported for not performing forensic investigations were the lack of an established investigation program, the unavailability of specialized manpower, or the fact that such investigations are performed by a state univer- sity or the FHWA when needed. The reasons for conducting forensic investigations stated in Table 1 are consistent with those identified from the litera- ture review, with pavement failures being the most common purpose of these investigations. Data collection to support development or calibration of performance models and inves- tigation into the long-term effects of traffic and the environ- ment on layer and material properties, exceptional pavement performance or longevity, and all other objectives were less common. Calibration of models and long-term effects are usually undertaken by universities or other research organi- zations on behalf of state highway agencies, therefore these options may have been underrepresented by the agency when completing the survey questionnaire. In summary, the results of the questionnaire revealed that forensic investigations are being conducted primarily to inves- tigate the underlying causes of pavement failures. Investiga- tions to understand pavement longevity, to collect data to support development or calibration of performance models, and/or investigate long-term effects of traffic and environment are conducted less frequently. The survey identified agencies interested in supporting a field assessment of the guide and expanding upon the purpose of forensic investigations. 3. Forensic Investigation Elements This chapter provides a framework for development of the guide using the applications and critical elements identified in Chapter 2. These elements are divided into generic agency issues and project specific issues. 3.1 Applications A critical element to a successful pavement forensic inves- tigation is having a clear understanding of the purpose of the investigation and how the results from that investiga- tion will be used. Potential pavement applications include the following: • Determining reasons for poor pavement performance/ premature pavement failures • Understanding exceptional pavement performance/ longevity • Collecting specific data for rehabilitation design • Validating pavement performance (actual vs. predicted) • Close-out investigations of experimental test sections • Collecting data to support development/calibration of pavement performance prediction models • Collecting data to understand/quantify long-term effects of traffic and environment on material properties • Collecting data to implement improved design and/or construction practices • Collecting data for support of pavement-related legal matters • Certifying warranties • Evaluating new products or techniques • A combination of two or more of the above Each of the above applications is generic in nature and can and should be made more specific (e.g., to investigate pre- mature rutting of HMA pavements on Interstate XYZ between mileposts X and Y). Although there may be many reasons for carrying out forensic investigations, they all address pavement perfor- mance. Therefore, successful achievement of any given foren- sic investigation requires a clear understanding of how pavements perform/behave and why they perform/behave as they do. Purpose of Investigation Response Percent 1. To investigate underlying causes of pavement failures 81% 2. To collect data to support development and/or calibration of performance models 43% 3. To collect data to support investigation into the long-term effects of traffic and the environment on layer and material (HMA, PCC, etc.) properties 35% 4. To understand factors contributing to exceptional pavement performance/longevity 24% 5. Agency does not perform forensic investigations 16% 6. Other 16% Table 1. Purpose for conducting forensic investigations.

141 There are four factors whose separate and combined effects define the performance of pavements. These are: • Pavement structure – Pavement type: new asphalt (with or without a cement treated base or CTB layer); new PCC (jointed plain, jointed reinforced, continuously reinforced, precast, etc.); asphalt overlay over existing asphalt; asphalt over- lay over existing concrete; concrete overlay over exist- ing concrete (bonded and unbonded); concrete overlay over existing asphalt; and others (integrated concrete pavers, whitetopping overlay, etc.). – Pavement layers: thicknesses, material types, material properties, drainage, shoulders, joints and steel rein- forcement in concrete pavements, quality of construc- tion and related issues, ambient conditions at time of construction, and others. • Subgrade soil: material types, material properties, stabili- zation, embankment, cut/fill, depth to bedrock, drainage, and others. • Traffic: traffic volumes (design versus actual), traffic loads/ load spectra (design versus actual), traffic growth (design versus actual), seasonal trends, load restrictions, and others. • Environmental conditions: air and surface temperatures, precipitation, wind, solar radiation, subsurface moisture, subsurface temperature, construction ambient conditions, unusual and/or catastrophic events, freeze/thaw cycles, freezing days, and others. Successful forensic investigations require the collection of information pertaining to pavement performance and the factors affecting that performance. Depending on the appli- cation, pavement performance measures may include one or more of the following elements: • Pavement distress data (using manual or automated dis- tress surveys): for asphalt surfaces this includes crack- ing, patching and potholes, surface deformation, surface defects, and miscellaneous distresses; for jointed plain concrete surfaces this includes cracking, joint deficiencies, surface defects, and miscellaneous distresses; for continu- ously reinforced concrete surfaces this includes cracking, surface defects, and miscellaneous distresses. • Pavement deflection data (using FWD or other devices): maximum deflection, deflection basin, deflection indices, layer moduli, overall structural capacity, load transfer and voids, other deflection parameters, longitudinal and trans- verse variability, etc. • Pavement roughness/elevation data (longitudinal and/or transverse): pavement roughness, International Roughness Index (IRI), rutting, elevation versus station, other rough- ness parameters, longitudinal and transverse roughness variability, etc. • Pavement surface friction data: surface macro-texture, sur- face micro-texture, skid resistance, other friction param- eters, other considerations, and longitudinal and transverse friction variability. • Tire pavement noise: surface macro-texture, surface micro- texture, faulting in PCC, pavement surface tining and grooving, clogging and/or raveling of open-graded friction courses, longitudinal and transverse noise variability, and other considerations. Similarly, information regarding the factors that influence pavement performance may include one or more of the fol- lowing elements: • Pavement structure and subgrade soil information available or obtained through one or more of the following methods: trenching, test pits and coring/boring, ground penetrating radar (GPR), dynamic cone penetrometer (DCP), drainage surveys (video or other means), field materials sampling and testing activities (e.g., tube suction and retain strength tests), laboratory materials testing, specialized testing (digi- tal and scanning electron microscope analysis, and chemi- cal tests), pachometer surveys of JPC and CRC, MIT scan (magnetic tomography technology) of portland cement concrete (PCC), and other destructive and non-destructive testing techniques. • Traffic information available or obtained through one or more of the following methods: automatic traffic recorder (ATR) or automatic vehicle classifier (AVC) counts, weigh- in-motion (WIM) measurements, average daily traffic (ADT) and estimated single-axle load (ESAL) estimates (if monitoring data is not available). • Environmental information available or obtained from one or more weather stations (e.g., National Climatic Data Center), from a road weather information system (RWIS), or through the use of surface and/or subsurface instrumentation. Unless it is already available, gathering the information on all of the pavement performance measures and all of the factors affecting pavement performance is unnecessary and generally beyond the available resources of most state high- way agencies. Forensic investigations may contain common elements amongst them, but the actual elements will ulti- mately depend on the forensic investigation application and relevant pavement factors. FWD testing, distress surveys, GPR surveys, and coring, for example, may be common to pavement failure/poor performance investigations but these techniques may not be necessary for pavement friction and/or

142 noise-related issues. Accordingly, another critical element in an investigation is achieving the best balance between require- ments, priorities, and available resources. Clearly setting and understanding the objectives of the investigation should aid in determining the appropriate data that should be collected. 3.2 Generic Issues A clear understanding of the reasons for conducting a forensic investigation and how the results will be used is impor- tant. However, there are three other elements that need to be addressed in advance of consideration of any forensic inves- tigation. They are: • Establishing a protocol for forensic investigations, • Identifying and appointing forensic investigation person- nel, and • Developing forensic investigation documentation pro- cedures. The activities associated with these elements are shown in Figure 1. To ensure that forensic investigations are performed in a consistent and systematic matter, it is important that an agency establish a forensic investigation protocol. This prac- tice will increase the chances of success and ensure consis- tent reporting of results throughout an agency; help justify changes to guidelines, manuals, specifications, and current practices; and eliminate the recurrence of problems. This pro- tocol should be communicated to individuals in the agency, and they should be encouraged to follow it. The protocol should include: • Reasons for having the protocol, • Agency approach to: – Assembling forensic investigation teams. – Requesting a forensic investigation. – Undertaking forensic investigations. • Procedures for documentation and dissemination of find- ings, and • Procedures for implementing findings and/or adopting recommendations. Three alternate approaches to the formation of the foren- sic investigation team were reported in the literature: (1) the team is established on a project-by-project basis and it typi- cally consists of both contractors and highway agency person- nel; (2) a project specific team approach, where the team is established based on the magnitude of the investigation and the controlling jurisdiction; and (3) a permanent team to han- dle all forensic investigations. There are advantages and disadvantages to each of these approaches. The establishment of a permanent team, for example, provides continuity, consistency and uniformity to forensic investigations within the state. This approach also provides for a group of individuals who are easy to identify and to contact to handle investigation requests, make go/no-go decisions, etc. However, establishing a permanent team that undertakes all investigations is often not feasible because of the range of expertise required to handle all potential applications. The formation of a virtual team of one or two key, perma- nent individuals from within the highway agency who select other team members depending on the issue being investi- gated has desirable features. This approach makes good use of the available resources by providing a permanent focus group (consistency and document management), but allows tailoring of the team (specific expertise) to address project specific conditions (e.g., asphalt vs. concrete), objectives, and level of investigation. Also of importance is the establishment of forensic inves- tigation documentation procedures within the highway agency. Specifically, a document management process and an auditable documentation trail of each investigation will help move away from the case study approach that has been Agency Forensic Investigation Policy and Procedures 1. Establish a protocol for forensic investigations 3. Develop forensic investigation documentation procedures + Investigation requests + Reporting formats + Database + Dissemination methods Undertake Project Specific Forensic Investigations 2. Identify and appoint forensic investigation personnel: + Investigation Coordinator + Investigation Director + Investigation Team Figure 1. Generic issues.

143 historically used by highway agencies towards the build-up of knowledge (lessons learned) and the consistent dissemi- nation of results throughout the agency. In this manner, the information provided by the document management process will enable highway agencies to justify changes to construc- tion practices and specifications, address problem issues to avoid recurrence, or improve performance. A key element of the documentation procedures is the establishment of an agency protocol for requesting an investi- gation, including a form for requesting an investigation and a communication channel to ensure that forms are directed to the forensic investigation team leader. Another key element is the establishment of a standard reporting format, including checklists, forms, records of decision, investigation reports, implementation of recommendations, etc. Yet another key element is the establishment of a means of dissemination such as a website, paper and web-enabled reports, a database, workshops and webinars, or an annual DVD. Because information on forensic investigation documen- tation procedures is not readily available, the establishment of such procedures was a critical element of the guide. Rec- ommendations for establishing the database architecture and critical elements are provided. 3.3 Project Specific Issues Once the generic agency issues have been addressed, proj- ect specific issues must be considered as part of a forensic investigation. These project specific issues are shown in Fig- ure 2 and listed in chronological order from the planning of the investigation to the close-out activities, as follows: • Preparing a forensic investigation request: a forensic inves- tigation begins with one or more individuals within or associated with the highway agency requesting an inves- tigation. Establishing the need for such an investigation should then be addressed; i.e., why should the investiga- tion be undertaken, what are the associated expectations, and how will the results be used. Therefore, the use of a standard “forensic investigation request form” is consid- ered an appropriate tool and hence was included in the guide. This form will provide basic information necessary for understanding why the investigation is necessary. • Initiating the forensic investigation: within the documen- tation procedures, it is necessary to acknowledge receipt of the forensic investigation request and to open a foren- sic investigation file for the project in question. To ensure consistency among investigations and to maximize the benefits from these investigations, the contents of the file should be specified. • Undertaking a background study: the purpose of this study is to determine whether or not the requested investigation is indeed necessary, the required level of investigation, and the objectives that need to be met. Activities under this element of the investigation typically include: – Determining whether the request is valid and the objec- tive is appropriate, and if so, establishing a preliminary hypothesis as to the probable reasons for the noted pave- ment observation/performance. – Collecting relevant information, including: 77 An interview with individuals requesting the inves- tigation, 77 Interviews with agency and industry personnel famil- iar with the road/project, and 77 Gathering relevant information (e.g., design and as- built/constructed information; pavement manage- ment system data; maintenance records; and climate, traffic, and other relevant information such as acci- dents and incidents). The outcome of this effort is a brief report that contains information about the request for the investigation, the summary of available information, justification for and expected benefits from undertaking the investigation, pri- orities and suggested level of investigation, preliminary estimate of resources, and record of decision (i.e., go or no-go decision). • Completing a standard “record of decision form,” “avail- able and missing data/information form,” “site visit form,” and “summary report” is important to the successful com- pletion of the activities to be carried out under this element of the forensic investigation. These forms as well as a sug- gested summary report template are included in the guide. • Preparing a detailed investigation plan: if the decision is made to proceed with the investigation, the next step is to prepare a detailed investigation plan. This plan will typi- cally include: – Selecting the forensic investigation team. Guidance must be provided as to the composition and expertise of the team as well as the roles and responsibilities of the indi- vidual team members based on the issues being inves- tigated. Ultimately, this team will develop the detailed investigation plan. – Preparing clear and concise objectives, including an understanding of how the results will be used. – Establishing the nature of the investigation: general investigation (e.g., premature failure on a highway) or investigation of a research test section. – Selecting an appropriate level of investigation to meet the objectives and to balance requirements and resources, and understanding the consequences of not under- taking the appropriate level of investigation. The level of investigation can range from simple visual assess- ments, to non-destructive testing, to coring, and/or to test pits and trenches. Selecting a higher than necessary

144 Figure 2. Project specific issues. level of investigation will result in a waste of time and resources. Conversely, selecting a less than necessary level of investigation will lead to an inadequate evalu- ation and possibly inadequately address the issue and require follow-up actions. – Performing a pre-investigation site visit to: (1) establish longitudinal and transverse limits of the forensic inves- tigation project either visually or with non-destructive testing; (2) visually assess the delineated forensic inves- tigation project section; (3) establish the surface condi- tion, longitudinal and transverse variability, and identify “good” and “bad” comparison sections; (4) identify locations for destructive testing if required; (5) assess safety, traffic control, logistical, and time requirements;

145 and (6) document the project site using photographs and/or videos. – Writing an investigation plan that addresses the activi- ties that need to be performed in order to meet the objectives. This plan must address the following: 77 Use of data available, 77 Logistical arrangements (e.g., road closures, notifica- tions, team and equipment availability, etc), 77 Schedule (including dates and times for each resource and activity), 77 General data requirements (e.g., traffic, weather, other environmental, etc.), 77 Visual assessment requirements (including on-road and adjacent to road such as drainage and slope stability), 77 Non-destructive testing requirements (including types of test, numbers of tests, test locations, and pro- tocols that should be followed such as FWD, GPR, profilometer, skid tester, and noise measurements), 77 Destructive testing requirements (types of test, num- bers of tests, test locations, test methods and test pro- tocols, and repairs after testing — e.g., coring [dry or wet], boring, trenches, test pits [dry saw cut or wet saw cut], DCP, etc.), 77 Sampling requirements (including location of sam- ples, conditions under which samples should be taken, quantity of samples, packaging and storing of samples, and location where samples should be delivered), 77 Routine and/or specialized laboratory testing require- ments (e.g., Atterberg limits, gradations, mix asphalt content/voids/specific gravity, SuperPave tests, PCC compressive strength, resilient/complex modulus, thermal coefficient of expansion, as well as chemical analyses, microscope analyses, and CT scans), includ- ing test methods and number of tests, 77 Data analysis requirements (including protocols), 77 Reporting requirements (including how the results should be interpreted and used to address the inves- tigation objective), 77 Investigation plan review and approval, and 77 Record of approval of plan. To ensure consistency and uniformity among investiga- tions, the use of flowcharts, checklists, templates, examples and forms is necessary; such forms have been included in the guide. Similarly, the use of matrices detailing typical activities associated with the different forensic investiga- tion applications and pavement types is important; such matrices have also been included in the guide. • Implementing the forensic investigation plan: this element of the investigation entails undertaking the actual inves- tigation and recognizes that a number of issues may not have been addressed as part of the detailed investigation plan. Issues that could potentially need to be addressed at this stage include: – Specific details concerning the investigation arrange- ments, which may not have been considered, – Specific details concerning visual assessments (e.g., “expecting the unexpected,” roadside activities such as the use of side drains for irrigation channels, blocked drains, filled-in drains and plough furrows perpendic- ular to the road, construction and/or road use irregu- larities, etc.), – Specific details concerning destructive testing (e.g., spe- cial coring procedures such as taking dry cores if mois- ture damage is being investigated, additional information on logging of cores and interpretation of observations, as well as timing of specific observations in relation to removal of the core), – Specific information on the excavation of test pits/ trenches and preparing the test pit faces, specific infor- mation on the logging of test pits/trenches as well as timing of specific observations in relation to opening of the test pit, or adjusting the sampling and laboratory testing plan based on observations, – Specific information on in-pit testing including density, DCP, and chemical tests (e.g., to assess carbonation of cemented layers, presence of deleterious materials, etc.). The guide covers specific issues not typically addressed in manuals and procedures, but does not cover the basics of cor- ing procedures, excavation of test pits/trenches, etc. In addition, this phase of the investigation must also address the following items: • Analyzing the collected data and testing the preliminary hypothesis proposed at the beginning of the investigation. • Preparation of the forensic investigation report using a standard format that covers, as a minimum, the follow- ing items: – Executive Summary, – Introduction, – Objectives and hypothesis, – Final investigation plan, – Observations and measurements, – Analysis and interpretation, – Findings and conclusions, – Recommendations, – Lessons learned, – Dissemination of findings, – Investigation costs and cost/benefit analysis (if appli- cable), and – Location of data files. • Turning the investigation results into actions and dissemi- nating the lessons learned. • Closing-out of the investigation, including sending notifi- cations, initiating actions, completing the documentation

146 process, closing the project file, and updating the forensic investigations database as appropriate. As was the case with the preparation of the detailed inves- tigation plan, the use of flowcharts, checklists, examples, matrices, and forms is necessary for implementation of the plan and ensuring consistency and uniformity among inves- tigations; they are also included in the guide. Recommenda- tions for developing a forensic investigations database have been provided in the guide. 4. Guide Development The process of developing and assessing the forensic inves- tigation guide is described in this chapter. 4.1 Preliminary Guide The preliminary guide was developed through the follow- ing means: • Use of information gathered during the literature review and from the state highway agency survey questionnaire responses. This information was particularly useful in addressing the project specific issues. • Communications with state highway agencies such as the California, Colorado, Illinois, and Texas DOTs, which already have forensic investigation guidelines in place and also with other agencies such as the Minnesota and Virginia DOTs, which have performed numerous foren- sic investigations. These communications helped address the generic issues because limited information was found in the literature. • Relevant forensic investigation experience of the project team. The initial version of the guide consisted of the following five parts: • Introduction: described what forensic investigations are, detailed the objectives and scope of the guide, provided an overview of the key forensic investigation elements, and summarized the organization of the guide. • Generic Agency Issues: provided a procedure to help the state highway agency establish a forensic investigation team and forensic investigation documentation procedures. Although these issues are applicable to all forensic inves- tigations, they must be periodically reviewed and updated to account for organization changes and technological advances. The formation of a virtual team in which one or two key individuals select other team members depending on the issue being investigated was recommended. This approach provides a permanent focus group, but allows tai- loring of each team to address project specific conditions, objectives, and level of investigation. Key elements of the documentation procedures include the establishment of (1) a policy for requesting an investigation, (2) a standard reporting format, and (3) dissemination options for use by the agency. • Project Specific Issues: provided a step-by-step procedure to help state highway agencies logically and sequentially conduct forensic investigations on a project-by-project basis. These steps included: – Preparing forensic investigation requests; – Initiating forensic investigations; – Undertaking background studies (determine if the request is valid and the objective appropriate, establish an initial hypothesis as to the probable cause of the pave- ment condition, collect relevant information, and make go or no-go decisions); – Preparing detailed investigation plans (select a foren- sic investigation team, prepare clear and concise objec- tives, establish the nature of the investigation, select an appropriate level of investigation to meet the objec- tives and to balance requirements and resources, pre- investigation site visit to plan the investigation, and write an investigation plan that addresses activities that need to be performed); and – Implementing forensic investigation plans (address spe- cific details concerning the investigation, such as how to analyze the data collected, prepare the forensic investi- gation report using a standard format, turn the results into actions, disseminate the lessons learned, and close- out the investigation). • References: provided lists of relevant reference material used in the development of the guide. • Appendices: provided sample checklists, forms, matrices, and example completed checklists and forms in support of the generic and project specific issues described in the guide. To develop a practical guide and to ensure consistency and uniformity among investigations, it was necessary to include flowcharts, checklists, examples, and forms, as well as matri- ces detailing typical activities associated with the different forensic investigation applications and pavement types. In progressing to finalizing the guide, it was concluded that the most rational approach for conducting a forensic investiga- tion would involve three phases: • Background Study — collecting available project informa- tion and determining if it is sufficient to answer the ques- tions posed in establishing the investigation.

147 • Preliminary Investigation — performing non-destructive data collection (e.g., FWD, longitudinal profile) and analy- sis, and once again determining if it is sufficient to answer the questions posed in establishing the investigation. • Final Investigation — following the plan developed based on all information collected to date, and performing des- tructive data collection (i.e., coring, test pit) and analysis. As with the first two parts, this also concludes with determining if it is sufficient to answer the questions posed in establish- ing the investigation. By performing investigations in these three phases, agency resources will be optimized. For example, if the background study clearly answers the questions associ- ated with the investigation, then the costs associated with non-destructive and destructive sampling, testing, and analysis would be saved for those investigations where a background study is insufficient. • Forensic investigation case studies are included as an appen- dix to the guide. These case studies were selected to cover representative examples and to demonstrate how the guide applies in each instance. The preliminary guide was used in conducting the field assessments detailed in the next section. 4.2 Assessment of Preliminary Guide 4.2.1 Field Assessment Plan The purpose of this effort was to prepare a plan for assess- ing the preliminary guide using in-service pavements. The plan provided specific information on the proposed sites, data collection effort, anticipated level of participation by the highway agency, and other relevant information. Thirteen state highway agencies expressed interest in supporting the field assessments, but only six state DOTs participated in the field assessments: California, Kentucky, Minnesota, Ohio, Oregon, and Virginia. These states cover three AASHTO Regions; attempts to include an agency within Region 1 were unsuccessful. Based on these responses, assess- ment of the preliminary guide was planned for six in-service pavements. These pavements address different pavement types and were strategically selected across the United States to provide representative geographical/climatic/geologic coverage. It was expected that multiple objectives could be assessed at each of the six sites, some of which are listed below: • Investigating the underlying causes of premature pave- ment failures. • Understanding the factors contributing to exceptional pavement performance and longevity. • Collecting data to support development and/or calibration of performance prediction models, including materials and pavement performance information. • Collecting data to support investigation into the long-term effects of traffic and the environment on layer and material (HMA, PCC, etc.) properties. The field assessment plan presented in Table 2 details geo- graphical location (state), pavement type, and purposes of the forensic investigations for the six field assessment sites. One site each was proposed for California, Kentucky, Min- nesota, Ohio, Oregon, and Virginia. Four of the sites were asphalt surfaced pavements and the other two sites were con- crete surfaced pavements. Two investigation objectives were planned for each site with the exception of California, where three were planned, resulting in a total of 13 investigations. Pavement Type Investigate Poor Performance/ Pavement Failure Understand Exceptional Performance Development/ Calibration of Performance Models Quantify Long- Term Traffic and Environment Effects New AC California (CA-1-1) California (CA-1-2) California (CA-1-3) New PCC Ohio (OH-1-1) Ohio (OH-1-2) AC Overlay on AC Oregon (OR-1-1) Virginia (VA-1-1) Oregon (OR-1-2) Virginia (VA-1-2) AC Overlay on PCC Kentucky (KY-1-1) Kentucky (KY-1-2) PCC Overlay on PCC Minnesota (MN-1-1) Minnesota (MN-1-2) Notes: First two letters in parentheses denote the state abbreviation, first number denotes the field assessment site within the state, and second number denotes the investigation within the agency. Table 2. Field assessment plan by highway agency.

148 To maximize the benefits to the state highway agencies as well as to the project, participating agencies were asked to assist with activities such as traffic control, coring/trenching, and pavement repairs. Each of the agencies was provided with a copy of the pre- liminary guide at least 1 month in advance of the actual field assessments. The preliminary guide described the activities associated with the field assessments, including the following: • Conducting an initial meeting with each agency to review and discuss generic agency issues and to plan the prelimi- nary investigation according to the guide. • Supporting agencies with completion of the prelimi- nary investigation. If the preliminary investigation fully answered the questions of the investigation, then the proj- ect team would support the agencies with completion of the investigation as detailed in the guide; no further work would be required. • Conducting a second meeting with each agency to review, discuss, and plan the non-destructive testing investigation detailed in the guide. • Supporting agencies with the actual conduct of the non- destructive testing investigation, which could include activ- ities such as distress surveys, GPR surveys, FWD testing, DCP testing, and roughness surveys. If the non-destructive testing investigation fully answered the questions of the investigation, then the project team would support the agencies with completion of the investigation as detailed in the guide; no further work would be required. • Conducting a third meeting with the agencies to review, discuss, and plan the destructive/laboratory testing inves- tigation detailed in the guide. • Supporting agencies with the actual conduct of the destructive/laboratory testing investigation, which could include activities such as coring, trenching, routine labo- ratory testing, and specialized laboratory testing. On com- pletion of the destructive/laboratory testing investigation, the project team would support the agencies with comple- tion of the investigation as detailed in the guide. In addition to the project team’s experiences and lessons learned from the field assessments, the agencies provided valuable input towards finalizing the guide, by means of comments on the preliminary guide and the field assess- ments. It was also anticipated that summaries of the field assessments would be included in the case studies appendix (Appendix B) of the guide. 4.2.2 Field Assessments The assessment process was led by agency personnel and not by team members to provide more relevant feedback. Field assessment activities began in the summer of 2011 and were completed in the spring of 2012. The conduct of the assessments varied from agency to agency, as described in the following sections. Details of these investigations are provided in Appendix B of the guide. 4.2.2.1 Virginia The project selected by the Virginia DOT (VDOT) for the field assessment was an AC section on Interstate 81 that was exhibiting exceptionally good performance. A previous inter- nal investigation had concluded that the observed performance was due to subsurface drainage improvements performed in a previous rehabilitation. During the initial assessment meeting, roles and respon- sibilities of the various participants were reviewed. VDOT chose to have the investigation effort be led by a district materials engineer, with support from others in VDOT and the Virginia Center for Transportation Innovation and Research (VCTIR). Also, a site visit was performed and the potential contributing factors to the pavement performance were discussed. As part of the preliminary investigation phase, VDOT pre- pared a report containing information on the construction history, soils, geology, traffic, climate, and performance data. The report concluded that another contributing factor to the observed performance was an over-estimation of traffic dur- ing the design. To confirm various report elements, VDOT decided to proceed with the non-destructive testing (NDT) phase. The three techniques selected were edge drain videos, GPR, and FWD. The edge drain videos indicated that the drainage had clogged in a few locations and that the under- drains were not in place for the full length of the test section, while the GPR results indicated the travel lane was about 2 in. thicker than the passing lane. The FWD data showed a uni- form, high structural capacity throughout the section. Based on the findings from the first two phases, VDOT concluded that the original hypothesis was incorrect and that the primary reason for the exceptional performance was the thicker than designed pavement together with actual traffic loading below the design loads. To confirm these conclu- sions, VDOT proceeded with a destructive phase. A test pit was excavated on the shoulder, immediately adjacent to the pavement travel lane to confirm the GPR-derived layer thick- nesses, especially the asphalt concrete layer, and to conclu- sively establish the presence or not of edge drains. The test pit confirmed the absence of edge drains and the accuracy of the GPR-derived layer thicknesses. 4.2.2.2 Ohio The Ohio DOT (OhDOT) field assessment focused on the exceptionally good performance of a number of PCC pave- ment sections that are part of the Specific Pavement Studies (SPS 2) experiment of the Long-Term Pavement Perfor- mance (LTPP) program. These sections, located on the north

149 end of the project, were outperforming those on the south end of the project. It was hypothesized that the water table level and construction timing was the reason for the better performance on the northern end. During the initial assessment meeting, roles and responsi- bilities of the various participants were reviewed. An OhDOT headquarters pavement engineer was charged with leading the investigation with assistance from Ohio University, as needed. A site visit, also carried out as part of the initial meet- ing, confirmed that the PCC sections were in excellent condi- tion with little cracking and no faulting. Some sections had received dowel bar retrofitting of transverse cracks. Because the pavement sections in question were part of the LTPP program, a significant amount of data were avail- able (including on-site WIM). As a result, the OhDOT field assessment was concluded during the preliminary investiga- tion phase without the need for NDT or destructive testing. The exceptionally good performance of the pavement sec- tions in question was attributed to less built-in curl resulting from lower air temperatures, lower placement temperatures, and use of concrete mixtures with low cement contents. 4.2.2.3 Minnesota The selected project was approximately 10 miles long and consisted of an 8.5 in. PCC overlay over a 9 in. PCC pavement (with a 1.5 to 3 in. bond breaker). The overlay was placed in 1998 and was performing exceptionally well. A significant amount of information had been compiled in advance of the initial assessment meeting, but no hypothesis had been estab- lished. A Minnesota DOT (MnDOT) intern was assigned to lead the assessment activities with support from MnRoad personnel (including a MnRoad forensic engineer). The preliminary report, which contained relevant infor- mation regarding the pavement structure, soils, traffic, cli- mate, and pavement performance, was provided along with a set of completed forms from the guide. The report attributed the exceptional performance to relatively low traffic volumes, good drainage, good materials in the base and subbase, and good pavement base structure. While the preliminary report concluded that there was no need to proceed to the NDT evaluation phase, selected NDT activities were recommended to strengthen the con- clusions. These included the collection and analysis of GPR data, FWD testing, and drainage videos. However, these NDT activities were not carried out due to weather and staff availability constraints. 4.2.2.4 Kentucky An engineer in training from the maintenance section of the Kentucky Transportation Cabinet (KYTC) Pavement Management Division was charged with conducting the assessment. The engineer reviewed a number of potential projects related to premature failure of AC overlays on PCC pavements and initially proposed a project that had received an overlay in 2009 that was exhibiting reflection cracking. As part of the preliminary report, the purpose of the inves- tigation was modified to comparing the performance of thick and thin AC overlays on PCC pavements. The report con- cluded that thin AC overlays do not perform as well as thick ones and that adequate overlay thickness must be provided to control reflective cracking. While considerable useful information was compiled as part of the preliminary investigation phase, FWD testing was recommended as part of the NDT phase to strengthen the conclusions, but such testing was not performed because of resource constraints. 4.2.2.5 Oregon The Oregon DOT (OrDOT) field assessment was led by a pavement specialist from the construction section. The pur- pose of the investigation was to determine the cause of pre- mature rutting at three intersections that were rehabilitated with mill-and-asphalt inlay. The binder grade originally used was changed after significant rutting within days of beginning paving. Within 1 year, the re-blended mix exhibited substan- tial rutting and shoving. However, projects paved the follow- ing construction season with the same binder grade did not have this issue. Following the initial assessment meeting, the preliminary data review included studying available materials data such as asphalt binder content, laboratory determined air voids, maximum specific gravity, bulk specific gravity, voids in the mineral aggregate (VMA), voids filled with asphalt (VFA), gradation, and field compaction. Mix design, quality control, and inspector’s data were also reviewed. The hypothesis was that a combination of material properties and construction practices caused the premature failure. Due to the rapid onset of the rutting, a decision was made not to pursue the NDT phase, but to move directly to devel- oping a plan for destructive and laboratory testing. Cores were taken from areas of rutting and from areas where no rutting was observed. Eight control samples from the original mix were also obtained. Tests for asphalt content, air voids, VMA, and VFA all showed indications of a rut-susceptible mix. In addition to the high asphalt content and low air void content, the VFA and aggregate gradation on one or more sieves did not meet OrDOT specifications. Review of the QC/ QA data for the replacement mix, which also exhibited rut- ting, albeit at a slower rate than the original mix, showed VFA above the specification for most specimens tested. Upon analyzing the information gathered, the cause for the premature rutting was attributed to a combination of factors. Primary among these was the high VFA, with the high asphalt binder content, low air voids, and a change made

150 during construction to use lighter rollers during compaction also contributing to the failure. 4.2.2.6 California The California Department of Transportation (Caltrans) project involved a premature failure (alligator cracking and potholes in the outer wheel path and shoulder) on a recent mill-and-overlay and widening project. The assessment was led by an engineer from the Office of Flexible Pavements in the Division of Pavement Management. The team included others from the same office and district staff involved in the project. The project started with a review of the original project investigation, the project design, and the construction records. This was followed by a preliminary site visit to gather addi- tional information, identify the limits of the investigation, and identify areas of good and poor performance within the project, with an attempt to isolate the cause of the poor per- formance. A lack of structural adequacy and/or possible base failure was observed. Because no conclusive evidence identifying the cause of the problem was found during the preliminary phase, the investigation proceeded to the NDT phase (GPR and FWD) in an attempt to identify additional potential causes of the problem, including variation in the structure, differences in overlay thickness, and the presence of moisture. Based on the information collected, it was determined that for safety reasons, an undocumented lateral shift was made during rehabilitation that resulted in a portion of the overlay being loaded on a significantly reduced pavement structure. 4.3 Revised Guide The experience gained from the field assessments and the comments provided by the participating agencies were used to revise the guide. The guide contains nine chapters. Chapter 1 provides background information and the objectives, scope, approach, and organization of the guide. Chapter 2 summa- rizes the philosophy behind forensic investigations and the approach followed in this guide. Chapter 3 addresses requests for and initiation of a forensic investigation, including con- duct of a preliminary investigation or background study. Chapter 4 covers the planning of the investigation, including selection of the investigation team, pre-investigation site visit, and NDT requirements. Chapter 5 discusses NDT, analysis of the data collected, the preparation of an interim report, and making a decision on the adequacy of the collected informa- tion to address the issues being investigated. Chapter 6 covers updating the investigation plan based on the NDT analysis. Chapter 7 discusses destructive field testing and laboratory testing of samples and specimens removed from the pave- ment. Data analysis and hypothesis testing, and preparation of the final report are covered in Chapter 8. Chapter 9 includes review of the investigation, actions resulting from the investi- gation, and close-out of the investigation. Chapters 3 through 9 offer a suggested approach and are written in a procedural style to improve readability. This approach can be modified to suit agency procedures and expertise. 5. Summary, Conclusions, and Recommendations NCHRP Project 01-49 developed a guide for conducting forensic investigations of highway pavements. The following sections provide an overview of the process, as well as major conclusions and recommendations resulting from the proj- ect effort. 5.1 Summary Following a thorough review of existing practices and input from state highway agencies, a comprehensive guide regarding the conduct of pavement forensic investigations was developed. This guide was designed to support a wide range of purposes and a varying degree of experience by the individuals performing the investigation. Responses received from 37 state highway agencies indi- cated that six of the 37 did not perform forensic investiga- tions, while the other 31 agencies performed investigations for the following reasons: • Investigate underlying causes of pavement failure (30 of 31) • Collect data to support development and/or calibration of performance models (16 of 31) • Collect data to support investigation into the long-term effects of traffic and the environment on layer and materials properties (13 of 31) • Understand factors contributing to exceptional pavement performance (9 of 31) • Other (6 of 31) A preliminary guide was developed and assessed through field investigations in six states. The guide was then revised based on the field investigation results. Key elements of the revised guide include: • A general investigation philosophy to help users better understand forensic investigations and, in turn, to ensure the successful implementation of the guide. The philoso- phy entails the following three fundamental aspects: – Understanding pavement performance and factors that affect it, – Recognizing pavement performance data and informa- tion needs, and

151 – Avoiding premature conclusions about pavement performance. • A phased approach to forensic investigations to optimize agency resources. The phases include: – A desktop study of available project information, – NDT and analysis, and – Destructive testing and analysis. • Consideration of generic agency issues not tied to a spe- cific investigation, but critical to the success of an agency’s forensic investigation program. Those issues include: – Establishing a protocol for forensic investigations, – Identifying and appointing forensic investigation per- sonnel, and – Developing forensic investigation documentation procedures. • Case studies selected to cover representative examples of forensic investigations and to demonstrate how the guide applies in each instance. • Examples of forms and checklists recommended for use in forensic investigations. 5.2 Conclusions Through the performance of this project, a number of rel- evant conclusions were drawn, including the following: • There is a need for a formal forensic investigation process in many state highway agencies. In some instances, this is due to staff turnover and in others it will be a mechanism for ensuring that problems are not repeated and specifica- tions, test methods, manuals, and guidance documenta- tion are changed to reflect the learning that occurs in a forensic investigation. The guide will be particularly help- ful to those with no or limited pavement forensic investi- gation experience. • When selecting the forensic investigation coordinator, it is important to have this individual sufficiently high in the organizational structure to facilitate any requisite data col- lection, testing, and analysis activities. • Following a phased approach will be beneficial to state highway agencies so that time, money, and resources can be saved, and because the need for destructive testing may be eliminated where it is not necessary. • Keeping an open mind is an important element for a success- ful investigation; focusing on a single factor as the sole basis for the performance of a given pavement should be avoided. • A decision tree approach does not lend itself well to foren- sic investigations—there are too many variables to consider and a prescriptive process might miss key contributing fac- tors and interactions. • Understanding exceptional performance can be more chal- lenging than determining the causes of poor performance. • There are significant issues related to documentation of forensic investigations and implementation of the findings. An investigation is not successful if the findings are only available to those who participated in the investigation. • Implementation of investigation findings is a necessary step to accrue the benefits of the investigation. Considering that many of the assessment investigations did not require the destructive testing phase, the phased approach appears to be most effective in using the least resources to address the issues being investigated, recog- nizing that more expensive sampling and testing activities should be performed only when absolutely necessary. These savings can be used for performing additional investigations or updating guidance documents, manuals, test methods, codes of practice, and specifications to incorporate what has been learned from the investigations. 5.3 Recommendations Highway agencies are expected to benefit from the guide prepared in this project to varying degrees, depending on the agency’s experience with forensic investigations, and particularly with the effort spent on the generic issues over- riding the entire forensic investigation process. However, to enhance these benefits, two elements in particular need to be considered: • Establishing a consistent process for staffing forensic inves- tigations. A virtual team for the conduct of investigations, from which specific members would be involved with any particular investigation based on the elements of the investigation, is highly desirable. This approach allows for maximum flexibility within available resources. Alternate approaches include establishing a permanent forensic team (likely an option only for large agencies) or a differ- ent investigation team for every project. • Developing documentation procedures that ensure an auditable documentation trail, facilitate the build-up of knowledge throughout the agency, and aid the implemen- tation of investigation findings. Creating a national repository for forensic investigations would also be extremely beneficial to the pavements com- munity. A National Highway Pavements Forensics Clearing- house would be a valuable online resource that could allow the sharing of information between agencies, and support consistent documentation of completed investigations.

Abbreviations and acronyms used without definitions in TRB publications: A4A Airlines for America AAAE American Association of Airport Executives AASHO American Association of State Highway Officials AASHTO American Association of State Highway and Transportation Officials ACI–NA Airports Council International–North America ACRP Airport Cooperative Research Program ADA Americans with Disabilities Act APTA American Public Transportation Association ASCE American Society of Civil Engineers ASME American Society of Mechanical Engineers ASTM American Society for Testing and Materials ATA American Trucking Associations CTAA Community Transportation Association of America CTBSSP Commercial Truck and Bus Safety Synthesis Program DHS Department of Homeland Security DOE Department of Energy EPA Environmental Protection Agency FAA Federal Aviation Administration FHWA Federal Highway Administration FMCSA Federal Motor Carrier Safety Administration FRA Federal Railroad Administration FTA Federal Transit Administration HMCRP Hazardous Materials Cooperative Research Program IEEE Institute of Electrical and Electronics Engineers ISTEA Intermodal Surface Transportation Efficiency Act of 1991 ITE Institute of Transportation Engineers MAP-21 Moving Ahead for Progress in the 21st Century Act (2012) NASA National Aeronautics and Space Administration NASAO National Association of State Aviation Officials NCFRP National Cooperative Freight Research Program NCHRP National Cooperative Highway Research Program NHTSA National Highway Traffic Safety Administration NTSB National Transportation Safety Board PHMSA Pipeline and Hazardous Materials Safety Administration RITA Research and Innovative Technology Administration SAE Society of Automotive Engineers SAFETEA-LU Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (2005) TCRP Transit Cooperative Research Program TEA-21 Transportation Equity Act for the 21st Century (1998) TRB Transportation Research Board TSA Transportation Security Administration U.S.DOT United States Department of Transportation