Guide for Conducting Forensic Investigations of Highway Pavements (2013)

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17 Forensic investigations are often undertaken because of the unclear reasons for specific pavement performance. Given this uncertainty, deciding on the most appropriate level of investigation is often difficult. Therefore, a system- atic phased approach in which the results of early phases define the actions required in subsequent phases is desired (Figure 4.1, with relevant section numbers in the guide). This approach may take a little longer if all phases are ulti- mately required and, in some instances, may require more than one site visit and more than one closure, but it will limit unnecessary work, which is especially important if destructive testing is being considered. The phases typically include visual assessments, NDT, and if necessary, destruc- tive testing and laboratory testing. 4.1 Selecting a Project Investigation Team The forensic investigation coordinator selects a project investigation team with the expertise (and team size) needed to address the issues being investigated. The team, selected from the virtual team (discussed in Appendix A), depends on the specific issues being investigated and location of the project, but will typically include one or more of the follow- ing individuals: • The forensic investigation coordinator: – Manages the investigation. – Compiles the documentation (e.g., investigation plan, reports, approvals, records of decision, etc.). – Makes all logistical arrangements (e.g., notifies other departments, arranges for traffic closures, arranges NDT, etc.). – Obtains all necessary approvals. • The individual requesting the investigation, if appropriate: – Provides local input and project-related data. – Implements (or supports/directs the implementa- tion of) the actions identified on completion of the investigation. • The design engineer: – Participates in discussions about differences between the design and as-built records. • The area maintenance superintendent (or similar position): – Provides information on maintenance and highway performance/behavior trends in the area. – Provides input on maintenance activities undertaken on the project being investigated. – Provides information regarding existence and condi- tion of drainage features such as edge drains, permeable layers, and daylighting of drainage layers. – Makes all arrangements for the local work crew and equipment. C h a p t e r 4 Initial Forensic Investigation Plan Opening a pit or trench is often the first con- sideration in many forensic investigations, and although desirable for data collection and project completeness, a number of factors should be considered before carrying out such an extensive study. A phased approach will also require a phased investiga- tion plan. The initial investigation plan typically includes details on establishing the team, a pre-investigation site visit and deciding on NDT requirements. The findings from this first phase of the study are then used to determine whether sufficient data has been collected to address the issues being considered, or if additional information from a more inten- sive study, usually with non-destructive and possibly also destructive testing, will be required.

18 Complete non-destructive testing (NDT) Data analysis and NDT report Close out project Investigation issue(s) addressed? Complete additional NDT and/or destructive testing Revise investigation plan for additional (e.g., destructive) testing Investigation plan approved? Preliminary investigation and approved investigation plan Record of decision Yes Yes No No Data analysis Investigation issue(s) addressed? Yes No P ha se 1 P ha se 2 P ha se 3 Prepare report with recommendations/actions Record of decision Chapters 3 & 4 Section 5.3 Sections 5.1 – 5.2 Section 5.4 Section 8.2 Sections 7.1 - 7.4 Section 6.2 Section 6.1 Section 8.1 Sections 9.1 – 9.3 Section 8.3 Figure 4.1. Phased approach to forensic investigations.

19 • The district materials engineer (or similar position): – Relates the issues being investigated to performance/ behavior of other roads in the area. – Coordinates collection of specimens (e.g., cores), raw materials, etc. • An agency or university/research center “expert” on the particular issues being investigated (if appropriate): – Provides specialist expertise and testing services and assists with data analysis, interpretation, and prepara- tion of the report. • If appropriate, the contractor and/or material supplier (if the investigation will not lead to a claim or legal action): – Identifies deviations from standard practice. – Identifies any deviations in material sourcing or properties. Detailed forensic investigations will usually also require the following: • NDT equipment managers. • Laboratory to perform required routine and specialized testing. • A work crew. The investigation coordinator documents the team names, contact details, and responsibilities on an appropriate form and distributes it to the team (example Form #5 in Appendix C). 4.2 Pre-Investigation Site Visit A pre-investigation site visit is undertaken by all or by selected team members to: • Conduct an initial visual assessment. • Determine the initial limits of the forensic investigation. • Conduct a safety assessment. • Identify the need for NDT, and if required, types and potential test locations. The pre-investigation site visit is undertaken from a vehicle with observations and photographs from the shoulder and usually does not require a road closure. Photographs of the issues being investigated together with possible contributing factors are used to prepare test plans and inform members of the team who did not participate in the site visit. The forensic investigation coordinator documents the pre- investigation site visit on an appropriate form (example Form #6 and Form #7 in Appendix C). 4.2.1 Initial Visual Assessment An initial visual assessment allows the team to review the issues under investigation; observe any distress (or absence of distress) associated with the issues; identify any other distresses and/or performance, environmental, and traffic- related issues that may influence the investigation; determine the limits of the investigation; identify the tests that need to be considered; and identify potential safety and logistical problems associated with later assessments and testing. The assessment involves first driving the project in both directions for general familiarization with the site and identification of locations requiring closer observation, and then return- ing to those locations for a more detailed evaluation from the shoulder. State visual assessment guidelines (if available) and/or the Distress Identification Manual for the Long-term Pavement Performance Program (4) should be followed and observations documented on the appropriate forms (exam- ple Forms #8 and #9 in Appendix C). Consider the following: • Observe the distress under traffic and record any specific issues (e.g., pumping, increased noise levels, or driver reac- tion to the conditions). Consider the effect of different weather conditions on performance and look for evidence of this performance (e.g., discoloration of pavement from pumped fines or temporary flooding, rutting caused by higher than normal temperatures, rutting caused by studded tires/chains, damage caused by snow removal equipment). • Look for causes of problems that are restricted to a short section of the pavement (e.g., end-of-load segregation of materials, an accident that has caused mechanical dam- age, a spill that has affected the surfacing, a blocked drain, influence from road side activities, transition from cut to fill, utility cut reinstatements, etc.). • Look for evidence of construction activities that lead to cycli- cal types of distress (e.g., end-of-load segregation that can cause raveling, daily start or end of construction problems). • Check for widened sections of road that may have different structural sections or that place the wheelpath on the joint. • Take photographs of all observations. • Identify and record potential locations for destructive test- ing that may be required later in the study. This may include comparative sections (e.g., good and poor performance).

20 • Include an assessment of roadside conditions and activi- ties that may contribute to the issues being investigated. Investigators are encouraged to observe, investigate, and document all possible contributing factors, recognizing that poor performance is often attributed to a number of reasons. Examples include: – Side drains and culverts have been blocked by agricultural activity or new access roads (example of filled-in drains to facilitate equipment movements in Figure 4.2). – Side drains are used for moving irrigation water (example in Figure 4.3). FWD measurements will often differentiate areas where side drains are flooded for prolonged periods. – Plow furrows run perpendicular or at an angle to the road (example in Figure 4.4). – Irrigation water contacts the road (example in Figure 4.5 also common with vegetated medians in urban areas). – Water flows into the roadway from access roads and driveways (example in Figure 4.6). – Unstable slopes. – Dysfunctional slope drainage systems. Figure 4.2. Blocked side drain and culvert. Figure 4.3. Side drain used for irrigation water. Figure 4.4. Plow furrows perpendicular to road. Figure 4.5. Irrigation water sprays on the road. Figure 4.6. Access road drainage problems (note digout).

21 locations that should be avoided if possible, such as ramps, curves, intersections, and rises. – Work on underground services and utilities (i.e., dis- tress may be associated with utility failure/work). – Vegetation (especially large trees) in close proximity to the road. – Isolated areas receiving prolonged shade when the remainder of the road is in constant sunlight. – Transitions between cut and fill. – New developments that may have resulted in temporary large increases in construction traffic. 4.2.2 Initial Limits of the Forensic Investigation The initial limits of the forensic investigation (i.e., begin and end points) will depend on the investigation and the issues being considered. The extent of the sections being investigated may be limited to an isolated location, a single lane, or all lanes for the entire length of a construction proj- ect. The area within the limits should include the issues being investigated and to the extent possible, and, if applicable, a “control” section, where the issues being investigated are not apparent, to allow for comparisons. Examples of control sec- tions include (but are not limited to) the following: • The area between the wheelpaths if the issue being investi- gated appears to be limited to the wheelpaths. • A different day’s production if the issue being investigated appears to be limited to a specific day or batch of materials. • Conventional construction or materials if alternatives were experimented with over a short section (e.g., experi- mental sections, comparing HMA to warm-mix asphalt). • A section with no distress on a different part of the project or similar project. • A smooth section adjacent to one with poor ride quality. Depending on the issues being investigated, initial limits are typically set based on project information and/or the visual assessment and then refined using non-destructive tests. Generally, construction issues account for a majority of premature pavement failures. Hence, it is important to identify the extent of existing and potential failures. NDT on distressed and control sections (i.e., sections with no distress) is useful for identifying those areas that have not yet shown such distress but may exhibit similar performance at a later time. 4.2.3 Safety Assessment A safety assessment should be undertaken to identify potential safety hazards for the crew and road users in later investigations. This assessment will help determine the most appropriate time to undertake the investigation and identify This guide does not cover safety management for forensic investigations. Agency guidelines for road closures, NDT, and other related activities should be followed. 4.2.4 Initial NDT Requirements Although the issues being investigated are likely mani- fested on the surface of the road, the factors contributing to the issues will invariably be a result of something occur- ring within the pavement structure, and consequently “out of sight.” An appropriate form of NDT is often the most effective means of identifying and quantifying these fac- tors and determining the extent of their impact. The need for destructive testing and the precise location where it takes place will usually be decided based on the findings of these assessments. NDT is also used to identify additional problem areas that have not yet exhibited signs of distress, to delineate uniform sections, and to quantify variation along the project being investigated. Many agencies conduct routine NDT as part of their pavement management system activities. Pavement Management System (PMS) data for the section of road being investigated should be checked during the background study to deter- mine whether additional testing is required. 4.2.4.1. Introduction to Commonly Used NDT Equipment Ground Penetrating Radar (GPR), Falling Weight Deflec- tometer (FWD), friction testers, and profilometers are the most common types of NDT equipment used in forensic investigations. GPR equipment is typically used to provide a rapid assessment of layer thickness and to delineate cer- tain problem areas such as debonding, presence of moisture, voids under concrete slabs, and other issues that are nor- mally assessed through coring. FWD equipment is typically used to measure deflections to quantify structural issues. Friction testing and profile measuring equipment are used to assess frictional (skid) resistance and ride quality issues, respectively. On-board Sound Intensity (OBSI) equipment

22 thickness variation, stripping, and possibly debonding. They can be operated at highway speeds; however, data quality decreases with increasing speed and a closure may be required to obtain more accurate results. They can be adversely affected by other transmitters such as cellular telephone towers. Ground-coupled antennas (Figure 4.8) generally have better lateral resolution than air-coupled antennas and are either used in contact with the road or slightly above it (~0.75 in. [20 mm]). They are suited for assessing the entire structure (except for about 1.0 in. [25 mm] near the surface), including most surface issues discussed earlier, assessing the thickness of pavement layers and identifying voids under slabs. Ground- coupled antennas are more suited for slow speeds, which allow the collection of higher resolution data but typically require a road closure. They are less influenced by outside interference and can be used at highway speeds. Permeameter & Friction Testing for measuring noise is less common, but of growing interest. Other more labor intensive types of non-destructive testing equipment such as nuclear and non-nuclear density gauges (for measuring compaction), seismic pavement analyz- ers (SPA, for measuring site-specific stiffness), laser texture meters (for measuring texture), permeameters (for measur- ing permeability), and magnetic tomography technology (for determining dowel presence, location, and alignment) are typically used within a traffic closure in later stages of the investigation. Information on non-destructive testing equipment and on the specifics of set up and operation is available in the literature and not covered in this guide. Most agencies routinely perform deflection, friction, and profile measurements and further dis- cussion is not warranted. However, some key issues are high- lighted. GPR is a relatively new technology used in forensic investigations; some information is provided for guidance. The forensic investigation coordinator must ensure that the investigation team has adequate expertise with the operation of the equipment and associated data analysis. Ground Penetrating Radar (GPR) GPR is an electromag- netic sounding method in which a transducer (transmitter/ receiver) is passed over the surface of a pavement. Short- duration pulses of radio energy are transmitted into the pave- ment and reflections from within are detected by the receiver. Changes in the dielectric properties are used (in conjunction with positional [GPS] information) to assess layer thickness, presence of moisture, voids, and other anomalies. The tech- nology is maturing, but developments in the apparatus and the way in which the data is interpreted continue. Equipment configuration (i.e., antenna choice and frequency) and data interpretation is dependent on the nature of the investigation and requires specific expertise. Air-coupled antennas (Figure 4.7) are typically used to iden- tify and delineate wearing course problems such as overlay Figure 4.7. GPR with rear mounted air-coupled transducer. Figure 4.8. GPR pod containing MHz ground-coupled transducers.

23 Key issues to consider include: • Ensure that the equipment has a valid calibration certificate. • On rutted asphalt pavements, test in between the wheel- paths to ensure that the plate seats firmly on the surface. On cracked asphalt pavements, test in the area of least cracking (also typically between wheelpaths). Test any asphalt pave- ments when the surface temperature is above 60°F (15°C), especially for thick asphalt layers, otherwise the deflections will be very small and difficult to distinguish from general noise. Always use a non-recorded “seating” drop prior to recorded drops to ensure all geophones are in stable con- tact with the highway surface. • On concrete pavements, test location on the slab will depend on the issues being investigated. Load transfer efficiency is measured across the joints in the wheelpaths, stiffness is measured in the center of the slab, and curling is measured across the joint at the slab corners. Example test locations for jointed concrete pavements are shown in Figure 4.11. • Load transfer efficiency can only be evaluated when test- ing temperatures are low, preferably below 77°F (25°C). At higher temperatures, the slabs will often have expanded sufficiently for aggregate interlock to produce uniformly high load transfer measurements. • For stiffness testing on concrete, take measurements at cooler temperatures (i.e., at night or early in the morning) to ensure contact between the slab and underlying layers at the center of the slab. Testing at high temperatures (i.e., afternoon) can result in misleading backcalculated stiffnesses as the center of the slab may not be in contact with the underlying layers. Example reference materials for FWD testing include: • Long-Term Pavement Performance Program Manual for Falling Weight Deflectometer Measurements, Version 4.1, December 2006 (7). Low frequency transducers (200 to 600 MHz [Figure 4.9]) have good depth penetration, but relatively poor lateral/verti- cal resolution and are used for assessing subgrade and base lay- ers. Higher frequency transducers (>600 MHz) have relatively poor depth penetration, but good lateral/vertical resolution and are used with air-coupled antennas for assessing wearing course layers. Combinations of antennas type and frequency are possible and should be used where information on the full depth of the pavement and its foundation layers is required. The output from any GPR configuration is unlikely to be conclusive when used alone in forensic investigations. How- ever, when used in combination with other equipment such as FWD, GPR can be useful for identifying areas of the proj- ect that require additional investigation. Limited coring is generally required to calibrate GPR data. Example reference materials for GPR testing include: • NCHRP Synthesis of Highway Practice 255: Ground Pen- etrating Radar for Evaluating Subsurface Conditions for Transportation Facilities (5). • FCC 02-48, Revision of Part 15 of the Commission’s Rules Regarding Ultra-Wideband Transmission Systems (6). • ASTM D4748, Determining the Thickness of Bound Pave- ment Layers Using Short Pulse Radar. Falling Weight Deflectometer (FWD) FWD testing (Figure 4.10) generally requires a full closure, but rolling clo- sures can be used on lower traffic volume roads with good sight distance. A small number of cores will be required to confirm layer thickness. FWD measurements are highly influenced by the test location and temperature; these fac- tors must be considered when correlating test measurements to performance. Figure 4.9. Cart-based GPR with low frequency ground-coupled transducer. Figure 4.10. Falling Weight Deflectometer.

24 • ASTM D4694, Standard Test Method for Deflections with a Falling-Weight-Type Impulse Load Device. • ASTM D4695, Guide for General Pavement Deflection Measurements. Profilometer Profile is usually measured with lasers in customized vehicles (Figure 4.12) that collect a range of data for use in pavement management systems including longitu- dinal and transverse profile, micro- and macro-texture, crack pattern, photologs, and GPS coordinates. Stand-alone units that can be attached to any vehicle are also available. Profile can be measured at highway speeds without the need for a road closure, and therefore the entire project under investi- gation is typically measured. Data quality is usually sufficient to quantify smoothness/ride quality issues that would typi- cally be studied in a forensic investigation. However, detailed investigations of small areas may be required and can be undertaken with walking profilometers, if necessary, within a road closure. Equipment should be appropriately calibrated. Example reference materials for profiling include: • AASHTO PP 37, Standard Practice for Determination of International Roughness Index for Quantifying Rough- ness of Pavements. • AASHTO R36, Standard Practice for Evaluating Faulting of Concrete Pavements. • ASTM E867, Terminology Relating to Vehicle-Pavement Systems. • ASTM E950, Standard Test Method for Measuring the Longitudinal Profile of Traveled Surfaces with an Acceler- ometer Established Inertial Profiling Reference. • ASTM E1166, Guide for Network Level Pavement Man- agement. Friction Testers Frictional (or skid) resistance is mea- sured with a variety of equipment such as locked wheel fric- tion testers (Figure 4.13), dynamic friction testers, and pen- dulum testers. Locked wheel friction testers do not require a Figure 4.11. Example FWD test locations on jointed plain concrete pavements. Figure 4.12. Profilometer van.

25 4.2.4.2. Examples of the Use of NDT in Forensic Investigations Examples of how NDT is used in forensic investigations are provided in Table 4.1 for asphalt surfaced pavements and in Table 4.2 for concrete surfaced pavements. Additional examples cited in the literature are summarized in Appen- dix F. Concrete surfaced pavement includes jointed plain concrete pavement (JPCP), continuously reinforced concrete pavement (CRCP), and jointed reinforced concrete pave- ment (JRCP). If the pavement being investigated consists of an asphalt surface over concrete pavement, then information for both asphalt surfaced and concrete surfaced pavement should be considered depending on the distresses appearing on the pavement surface. Targeted coring is always required for determining actual pavement thickness for FWD tests and for calibrating GPR results for thickness estimation and layer type identifica- tion. Some cores are also needed to determine the theoreti- cal maximum density (TMD) of HMA, which can be used with nuclear or non-nuclear bulk density measurements to calculate air-void content. These cores can also be used to check for factors contributing to the issues being investigated (e.g., stripping, debonding, ASR, and aggregate degradation). Coring can often be done during the road closure for FWD testing to eliminate the need for additional road closures if no further field investigation is required. 4.2.4.3. Testing Frequency The amount of testing required depends on the issues being investigated; however, consideration should be given traffic closure and are more likely to be used in initial inves- tigations over a length of road to determine whether friction values are above or below agency norms and to identify spe- cific areas requiring additional investigation. Dynamic fric- tion testers and pendulum testers are typically used for more detailed examination of micro-texture and require a traffic closure. Skid resistance standards are set by state highway agencies and will depend on a number of factors including aggregate characteristics, climate, and traffic. Example reference materials for friction testers include: • ASTM E274, Standard test method for skid resistance of paved surfaces using a full-scale tire. • ASTM E2340, Standard test method for measuring the skid resistance of pavements and other trafficked surfaces using a continuous reading, fixed-slip technique. Noise Testers The most common method for measur- ing tire-pavement noise is the OBSI method (Figure 4.14), in which measurements are taken at highway speed. Data quality is sufficient to quantify pavement surface issues contributing to noise such as raveling, large aggregates, or clogging/over- compaction of open-graded friction courses that would typi- cally be studied in a forensic investigation. Results are usually used in conjunction with visual assessment data (e.g., areas of raveling, large stone size, crack sealing, or joint spalling), and/ or permeability measurements to assess clogging on open- graded mixes, and with texture measurements (such as mean profile depth [MPD] on asphalt concrete surfaced pavement or mean texture depth [MTD] on PCC surfaced pavement). Example reference materials for noise measurements include: • NCHRP Report 630: Measuring Tire-Pavement Noise at the Source (8). • AASHTO TP76, Standard Method of Test for Measure- ment of Tire/Pavement Noise Using the On-Board Sound Intensity (OBSI) Method. Figure 4.13. Locked wheel friction tester. Figure 4.14. On-board Sound Intensity Meter (OBSI).

26 Issue Possible Contributing Factors Type of Non-Destructive Testing Typical Testing Frequency Exceptional performance Design Construction Materials GPR, FWD GPR, FWD, nuclear gauge GPR, FWD - GPR: continuous (2 scans/yd [m]) - FWD: 75 ft (25 m) intervals, 3 to 15 ft (1 to 5 m) in defined problem areas, offset in adjacent lanes Rutting Asphalt densification Asphalt shearing Base, subbase or subgrade failure Stabilization failure Insufficient layer thickness Moisture damage Poor compaction Incorrect binder Inappropriate or not followed mix design Nuclear gauge1 Transverse profilometer/ straightedge FWD, drain inspection FWD GPR, FWD, nuclear gauge1 GPR, FWD, nuclear gauge1 GPR, nuclear gauge1 Not appropriate Not appropriate - GPR: continuous (2 scans/m) - FWD: 75 ft (25 m) intervals, 3 to 15 ft (1 to 5 m) in defined problem areas - Nuclear gauge: per state test method - Transverse profilometer/straightedge in defined problem areas Alligator cracking Base, subbase or subgrade failure Moisture damage Layer debonding Thickness, compaction Incorrect binder Excessive binder aging Inappropriate or not followed mix design FWD, drain inspection GPR, FWD GPR, FWD GPR, nuclear gauge1 Not appropriate Not appropriate Not appropriate - GPR: continuous (20 scans/yd [m]) - FWD: 75 ft (25 m) intervals, 3 to 15 ft (1 to 5 m) in defined problem areas - Nuclear gauge: per state test method Transverse cracking Compaction Incorrect binder Reflection cracking Shrinkage in stabilized base Frost/moisture damage in unbound layer Nuclear gauge1 Not appropriate Not appropriate (GPR in some situations)2 Not appropriate (GPR in some situations) Drain inspection - Nuclear gauge: per state test method Longitudinal cracking Base, subbase or subgrade failure Moisture damage Construction joint compaction Shoulder design and construction Excessive stabilizer in recycling overlaps Stabilization failure GPR, FWD, drain inspection GPR, FWD Nuclear gauge1 GPR, FWD GPR Not appropriate - GPR: continuous (2 scans/yd [m]) - FWD: 75 ft (25 m) intervals, 3 to 15 ft (1 to 5 m) in defined problem areas - Nuclear gauge: per state test method Block cracking Shrinkage in stabilized base Binder properties (burning or rapid aging) Not appropriate (GPR in some situations) Not appropriate Ride quality/roughness Constructed ride quality Cracks Potholes Large aggregates Raveling Profilometer3 Profilometer3 Profilometer3 Profilometer3 Not appropriate - Profilometer continuous (use measurement from between wheelpaths to determine initial IRI) 1 Take at least three cores of each material to determine TMD per ASTM D2041 or AASHTO equivalent. Take nuclear gauge measurements between the wheelpaths and in the wheelpath to determine construction compaction and extent of densification, minimum 10 in problem areas. 2 GPR may be used to identify the source of reflective or shrinkage cracks deep within a pavement structure. 3 Profilometer can potentially be run between the wheelpaths to estimate as-constructed ride quality. Surface failure/potholes Moisture damage Delamination Shoulder design and construction Poor cross slope GPR, FWD GPR, FWD GPR, FWD, drain inspection Survey or measure with level - GPR: continuous (20 scans/yd [m], multiple scans) - FWD: 75 ft (25 m) intervals, 3 to 15 ft (1 to 5 m) in defined problem areas - 15 ft (5 m) intervals in affected area Excessive noise Mix design Raveling Cracking Clogging of porous surface OBSI OBSI, longitudinal profilometer3, laser texture meter4 OBSI Permeameter - OBSI: continuous - Profilometer: continuous - Laser texture meter: affected area - Permeameter: In and between wheelpaths Frictional characteristics Polished aggregate Flushing/bleeding Friction tester, texture meter Friction tester - Friction tester: continuous - Texture meter: affected area 4 Mean profile depth can be measured using a high-speed longitudinal profilometer on a test vehicle requiring no closure or by a stationary laser texture meter in a traffic closure Table 4.1. Examples of NDT on asphalt surfaced pavements. Profile, friction, noise and some GPR testing can be done at highway speeds and consequently these tests do not require traffic closures. FWD testing is a stop-and-start activity, while project level GPR is undertaken at walking speeds, with both requiring a full or rolling closure, which needs to be taken into consideration when setting investigation limits. to assessing as much of a construction project as is fea- sible to: • Identify other areas where the issues being investigated have not yet manifested on the surface but may occur. • Check variability to determine if it is consistent with the issues being investigated. • Identify trends in performance/behavior that may corre- late with factors identified in the preliminary investiga- tion (e.g., weather events, changes in materials suppliers, breaks in production, equipment breakdowns, etc.).

27 Issue Possible Contributing Factors Type of Non-Destructive Testing Typical Testing Frequency Exceptional performance Design Construction Materials GPR1, FWD1 Profilometer, OBSI GPR, FWD - GPR: continuous (2 scans/yd [m]) - FWD: corners, mid-slab, mid-joint - Profilometer: continuous Corner cracking Voids Load transfer Temperature and shrinkage curl Concrete stiffness Dowel failure or absence of dowels GPR1 FWD3 Profilometer2 FWD4, SPA MTT scan - GPR: continuous (slow speed, 20 scans/m) - FWD: corners - FWD,SPA: slab center - Profilometer: continuous - MTT scan: affected area D-cracking Materials or moisture/frost damage Not appropriate Longitudinal cracking Base or subgrade failure/stabilization cracks Temperature and shrinkage curl Concrete stiffness FWD FWD3,4 FWD4, SPA - FWD: either side of crack - FWD: corners - FWD: slab center - SPA: slab center Transverse cracking Edge support Load transfer on tied shoulders Swelling soils/frost heave GPR1 FWD Not appropriate - GPR: continuous (20 scans/yd [m]) - FWD: both sides of joint Early age cracks Improper curing, late sawing Not appropriate Faulting Erosion/pumping Load transfer GPR1 FWD - GPR: continuous - FWD: corners and joints Spalling Construction/maintenance deficiencies Frost Not appropriate Not appropriate Joint failure/separation Design/construction/maintenance deficiencies Dowel bar failure/seizure from misalignment Not appropriate MTT scan - MTT scan: affected area Pumping Load transfer Base erosion FWD3 FWD - FWD: joints and corners - FWD: corners Punchouts Base failure and/or subbase erosion GPR1 - GPR: continuous (20 scans/yd [m]) Ride quality/roughness/ Settlement Construction deficiencies Faulting Moisture/frost Support (voids) Profilometer2 Profilometer2 GPR, FWD GPR - Profilometer: continuous - GPR: continuous (slow speed, 20 scans/yd [m], multiple profiles) - FWD: joints and corners Excessive noise Surface texture from construction, grinding, grooving, fines loss OBSI Texture meter - OBSI: continuous - Texture meter: affected area Poor skid resistance Polished aggregate Poor surface texture from construction, grinding, grooving Friction tester Friction tester, texture meter - Friction tester: continuous - Texture meter: affected area 1 GPR and FWD may not be appropriate on CRCP as steel reinforcement attenuates the signal. 2 A wide spot or bar laser is needed for effective road roughness measurements on tined or grooved concrete. Texture measurements with a standard laser profilometer are not effective, and a texture meter should be used if these lasers are not available. 3 FWD for estimating load transfer. 4 FWD for backcalculation of stiffness. Table 4.2. Examples of NDT on concrete surfaced pavements. Typical NDT intervals in forensic investigations are listed in Table 4.3. 4.2.4.4. Initial NDT Plan The investigation coordinator prepares an initial NDT plan based on the initial investigation observations and team member discussions. The plan should include the following (example Form #10 in Appendix C): • Type of NDT required and why it is required. • Start and end points of each test. • Lanes to be tested. • Sampling frequency. • Date that the testing is required. • Expected duration of testing. • Data requirements/format. • Specific requirements. • Closure requirements. • Core requirements (for GPR and FWD calibration and ini- tial investigation). • Data analysis/interpretation requirements. • Arrangements for the testing (e.g., contacting the testers, arranging for closures and crew, arranging for data inter- pretation expertise, etc.). 4.3 Preparing a Cost Estimate After collecting all relevant data for the plan, the investiga- tion coordinator prepares a cost estimate using a spreadsheet template that includes agency costs of the various components. 4.4 Writing an Initial Investigation Plan The forensic investigation coordinator prepares an initial investigation plan at this point in the investigation to document the formation of the investigation team, the findings of the

28 pre-investigation site visit, and to provide details of the NDT, the results of which will be used to finalize the investigation plan. The initial plan should include the following (example Form #11 in Appendix C): • Preliminary Investigation Report (example Form #4 in Appendix C). • Team members and each team members’ contact details and responsibilities (example Form #5 in Appendix C). • Initial visual assessment forms (example Forms #6 through #9 in Appendix C) with: – Summary of observations. – Investigation start and end points. – Safety assessment. • The initial NDT plan (example Form #10 in Appendix C). • Data analysis/interpretation requirements. • Reporting formats and due dates. • Logistical arrangements (e.g., road closures, notifications, team and equipment availability, etc.). • Schedule, including dates and times for each resource and activity. If the agency does not have access to GPR equipment and the issues being investigated are related to layer thick- ness, moisture damage, and/or layer debonding, destruc- tive testing will be required and the guide for preparing the final investigation plan discussed in Chapter 6 should be followed. 4.5 Approval of Initial Investigation Plan and Record of Decision The forensic investigation coordinator obtains approval (and if necessary, funding) for the initial investigation plan from the investigation director and adds a record of decision to proceed with NDT to the project file. Test Interval Test Duration/ Lane-mile1 Road Closure Required? GPR – General layer thickness/layer definition GPR – Asphalt densification GPR – Problem identification/delineation on AC GPR – Problem identification on PCC GPR – Void location Continuous (2 scans/m) Continuous Continuous (20 scans/m) Joint/joint area/crack Suspected area 2 minutes 2 minutes 90 minutes - - No2 No Yes Yes Yes FWD – Problem delineation on AC pavement FWD – Specific problem investigation on AC FWD – Problem delineation on PCC pavement FWD – Specific problem investigation on PCC 80 ft (25 m)3 30 ft (10 m) Not appropriate Joint/crack/slab center 90 minutes 225 minutes - 50 drops/hour Yes Yes - Yes Profilometer – Overall smoothness Friction tester – Skid resistance OBSI – Noise levels Continuous Continuous Continuous 2 minutes 2 minutes 2 minutes No No No 1 Test duration does not include closure set up and take down. 2 A limited number of cores are required for calibration. A road closure is required for coring. 3 Longer test intervals can be adopted if there are constraints such as traffic or limited closure schedules; however, this increases the risk of missing weaker sections. A second round of testing with closer intervals (e.g. 30 ft [10 m]) may be required to test specific problem areas. Table 4.3. Example NDT intervals.