Guide for Conducting Forensic Investigations of Highway Pavements (2013)

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43 This chapter covers destructive field testing and labora- tory testing of samples and specimens removed from the pavement being investigated. Investigation arrangements, detailed visual assessments, coring, test pits, and laboratory tests are discussed. 7.1 Investigation Arrangements Detailed investigations (e.g., detailed visual assessments, coring, test pits/trenches, collection of samples for labora- tory testing) will typically require a road closure. Logistical arrangements for forensic investigations are usually ade- quately covered in existing agency procedures. Key issues that need to be considered include, but are not limited to: • Special notifications to other agency departments and high- way law enforcement. • Closure protocols (e.g., FHWA Manual on Uniform Traffic Devices, Part 6: Temporary Traffic Control [11], or agency equivalent) and arrangements with law enforcement. Note that traffic volumes might dictate that the closure is at night and/or for a limited time period, which may influ- ence the volume and level of testing. • Crew and equipment arrangements. • Coordination with utility service providers to mark loca- tions within the section where destructive testing will take place. • Repair of destructive test locations and reinstatement of core holes and test pits. 7.2 Visual Assessments Visual assessments are usually made in a road closure, which allows closer assessment of distresses than the initial assessment discussed in Section 4.2. Although the investi- gation may focus on only one specific issue, a comprehen- sive visual assessment is usually undertaken to identify all possible contributing factors. Reassess roadside conditions and activity in light of the initial findings, especially if mois- ture or other environmental factors are being considered. Always look for abnormalities and be constantly aware of unexpected phenomena. 7.2.1 Activity Location The precise location of destructive and additional non- destructive testing (if required) within the investigation is usually determined during the visual assessment. Consider the following: • Destructive testing is usually carried out in both distressed areas and those areas with no distress to allow a compari- son and to aid in identifying the key contributing factors. Examples of core locations on asphalt concrete/asphalt surface treatment, JPC, and CRC pavements for various types of distress are provided in Figure 7.1, Figure 7.2, and Figure 7.3 respectively. • DCP tests are typically taken in the same locations through a core hole or drill hole (a dry drill hole is preferred since the DCP test results are influenced by soil moisture con- tent, which will increase through use of water to cool the core barrel). • Test pit/trench locations and associated tests (e.g., Shelby tube) are best identified from FWD and/or GPR measure- ments and, where feasible, include both “good” and “poor” performing areas for comparison. An example of a test pit layout with associated tests is provided in Figure 7.4. • Allocate a unique number to each activity location. • Mark precise core and drill locations and test pit boundar- ies each with their identifying number on the pavement with spray paint. – Record these locations on the Investigation Site Report (example Form #16 in Appendix C). C h a p t e r 7 Destructive and Laboratory Testing

44 For the safety of work crews and road users, always keep sufficient space between the core rig and the centerline when coring in the wheelpath closest to traffic. Do not take cores between the centerline/lane delineator and the wheelpath unless both lanes are in the closure. Figure 7.1. Examples of core locations for asphalt and surface treatment sections. Replicate cores, one over crack, one in un-cracked area within 20 in (500 mm) of crack core, for longitudinal, transverse, and corner cracks Transverse joint spall Shoulder Centerline Wheelpaths Core to check PCC thickness, base condition, bonding and/or base erosion Cores over dowel bar to check existence, location, depth, alignment, corrosion, grout condition, etc. Figure 7.2. Examples of core locations for jointed plain concrete sections.

45 – Follow agency practice and standards for location refer- ences in a linear reference system (chainage, post-mile, station). – In many locations, relatively inexpensive GPS devices can use multiple satellites to provide precise latitude and longitude coordinates for core locations and other data, which allow the use of mapping software to plot all data together. – The FWD, profilometer, and other field testing equip- ment often has an integrated GPS capability, but dis- tance measurements from fixed objects (landmarks, bridges) are useful as an independent cross-check on the linear reference and GPS location data. 7.3 Key Issues Concerning Destructive Testing 7.3.1 Coring 7.3.1.1 Reference Material The following reference standards are applicable to coring activities conducted in forensic investigations: • AASHTO R 13, Conducting geotechnical subsurface investigations • AASHTO T 24, Obtaining and testing drilled and sawed beams of concrete Replicate cores, one over crack, one in uncracked area within 20 in. (500 mm) of crack core, for longitudinal and transverse cracks Shoulder Centerline Wheelpaths Cores to check PCC thickness, base condition, bonding, base erosion, depth and spacing of steel, etc. Figure 7.3. Examples of core locations for continuously reinforced concrete sections. Traffic direction Shoulder Core location DCP location Density location Centerline Test pit Not to scale Wheelpaths Figure 7.4. Example test pit layout.

46 • AASHTO T 225, Diamond core drilling for site investi- gation • ASTM D2488, Description and identification of soils (visual- manual procedure) • ASTM D4083, Description of frozen soils (visual-manual procedure) • ASTM D4220, Preserving and transporting soil samples 7.3.1.2 Coring Procedures General information on coring procedures is not provided in this guide. However, the following key issues should be considered when coring in forensic investigations: • Keep a log of each core and core hole. The level of detail recorded will depend on the extent of the information needed. Core log forms typically include procedural details (e.g., cooling medium, difficulties encountered in coring); core measurements; and core and core hole observations (discussed under core logging). Example forms are pro- vided in Appendix C (example Forms #17a and #17b). • Use a diamond bit coring drill to remove cores. Mist- cooled equipment is typically used; however, if moisture damage is a potential cause of the failure being investi- gated, air-cooled coring equipment should be used to limit the influence of the coring activity on the assessment. • Take cores at an angle of 90° to the surface in a man- ner that ensures the recovery of straight, intact smooth- surfaced samples suitable for layer analysis and labora- tory testing. • Observe the core hole (a flashlight may be required) to identify problems that may be contributing to the issues being investigated (e.g., areas of stripping, debonding, seg- regation, etc.). If available, use a borescope (Figure 7.5) to photograph problem areas. Borescopes are also useful for identifying and observing voids under concrete slabs (examples in Figure 7.6). • If cores do not come out intact, take a measurement down the core hole as a cross-check to the core measure- ment to account for any discrepancies in core height/ layer thickness caused by stripped layers, broken pieces, debonding, etc. 7.3.1.3 Types of Core Log Core logging requirements depend on the issues being investigated; however, cores serve one or more of three gen- eral purposes in forensic investigations (i.e., for thickness, for cause of distress, and for laboratory testing). One core can serve all three purposes if required, but care will need to be taken to obtain all required measurements and photographs before testing. 7.3.1.4 Core Logging Procedure Cores are a key component of most forensic investigations on all pavement types and they need to be logged in a system- atic manner with all observations carefully noted to facilitate use of data in subsequent interpretation and analysis. Traffic closure time constraints may dictate that only critical mea- surements, observations, and tests are taken on-site with non- critical activities performed after the closure. 1. Locate core position 2. Setup 3. Drill core 4. Label, photograph & record Yes No Perform time-critical tests Is the closure time constrained? 1. Measure core 2. Log core 3. Observe/test core 1. Place sample in cylinder 2. Ship to laboratory Repair core hole Figure 7.5. Example use of flexible video borescope in core hole.

47 If there is a time constraint on the closure, consider the following: • Immediately number all cores and mark them in terms of orientation to traffic direction (typically an arrow marked on the surface of the core with a waterproof marker). Record the core numbers and precise position where it was taken on the core log form (example Forms #17a and #17b in Appendix C). • Photograph the core and record the photograph number on the core log. Photographs of the cores against a mea- sure (Figure 7.7) may be required if the investigation is part of a contractual dispute. The core photo/measure- ment platform (Figure 7.7) can also be used to assemble broken cores for photos and provides an approximate measurement for later reference when taking precise mea- surements in the laboratory. These photographs provide a record of the order of the layers and their condition for later assessment, which is particularly useful when pave- ment layers come out in pieces or have layers that are not intact due to stripping or other causes. • Immediately make observations, tests, or measurements that are time-critical, such as: – Checking for carbonation of cementitiously stabilized layers. For cement or lime stabilized layers, spray the layer with a phenolphthalein solution to determine whether any carbonation of the layer has occurred (Fig- ure 7.8). Spray those areas of stabilized materials that do not react with the phenolphthalein solution (i.e., do not turn a dark red color) with a dilute hydrochloric acid solution and record the degree of any reaction (fizzing). If available, check similar material that has not been sta- bilized for the acid reaction and whether the reaction is weaker or the same as the stabilized layer. This will indicate whether calcium carbonate occurs naturally in the material. Carbonated material is generally unbound and is unlikely to come out of a core hole intact. – Measurements and inspection of cores that are likely to disintegrate with handling or exposure to the elements. If there is any concern that the properties of a core may change in between the time that it is taken and the time that it is studied (e.g., cracks widen with removal of confinement [Figure 7.9]), a photograph can be taken on-site to allow for later off-site comparisons. Figure 7.6. Borescope views of void under concrete pavement. Figure 7.7. Core measurement platform. Special precautions for handling phenolphtha­ lein and hydrochloric acid should be taken and suitable protective clothing and equipment should be worn when handling the chemicals

48 – Document key observations on the form for later refer- ence when logging the cores off-site. – Pack the cores in an air tight plastic canister and place the canisters in a crate to prevent damage during transport. If there is no time constraint on roadway closure, or if the core logging is conducted after the closure, consider the following: • Start core logging as soon as possible after extraction. On- site, this should be within 15 minutes after removal from the pavement before the moisture content of the surface changes substantially. • Number and mark the core and record number and loca- tion on the core log. • Lightly brush the core with a stiff brush to remove dust and sludge accumulated during drilling. Complete the cleaning by wiping the core with a damp cloth. • Do a quick visual assessment of the core to identify any distinct distresses or abnormalities. Log any observations on the form. • Photograph the core, if required, with an appropriate scale (Figure 7.7). • When the core includes intermediate layers that are no longer bound together by asphalt or cement, or it is badly cracked, use a ruler to measure the depth from the surface to the bottom of the core. This will provide a reference measurement for the overall core height when assembling the pieces in the laboratory for detailed measurements. Phenolphthalein reaction on core Hydrochloric acid reaction on disintegrated core Figure 7.8. Phenolphthalein and hydrochloric acid reactions on core. Figure 7.9. Example of crack widening with loss of confinement.

49 • If required in the test plan, measure and record the total thickness of the core as well as the thickness of each layer on the core to the nearest ± ¹⁄¹0 in. (or 1.0 mm) at four even intervals around the core using a core measuring jig, cali- pers, or a tape measure. Highlight the thickest and thinnest measurements. • If required in the test plan, describe any observed dis- tress in each layer in accordance with the layer designa- tions provided on the preliminary data sheets. Examples of core observations are shown in Figure 7.10 and Fig- ure 7.11. Summaries of pertinent parameters for asphalt and portland cement concrete wearing courses, and stabi- lized (bound) and unbound layers are provided in Check- lists #1 through #4 in Appendix D (note that unbound layers are unlikely to be extracted intact with the core). These parameters are assessed in terms of the following Debonded layers Top-down cracking Cracks did not reflect through overlay Cracks reflected through overlay Reflected cracks in debonded layers Cracks do not reflect. End of reflected crack Start of crack Reflected crack - start Reflected crack Reflected crack Underlying DGAC Overlay Figure 7.10. Examples of observations on asphalt cores.

50 suggested criteria (additional/other criteria may be appro- priate depending on the issue being investigated). – Severity: where applicable, rated on a scale of 1 (low), 2 (moderate), or 3 (high). Severity descriptors are pro- vided in Checklists #5 through #8 in Appendix D. – Extent: describes the percentage area, number of and/ or length of the parameter being assessed. Extent descriptors are also listed in Checklists #5 through #8 in Appendix D. – Start: where applicable, the start point of the distress (e.g., top or bottom of the surface layer). – End: where applicable, the terminal point of the distress. – Layers affected: indicates which layers are influenced by the parameter being assessed, listed in order from start to its terminal point. – Description: describes the pertinent aspects of the param- eter being assessed. – Implications: where applicable, lists the implications and consequences of the parameter (e.g., vertical crack provides a path for the ingress of water and the egress of pumped fines) and links to other distresses/attributes. • Compare cores taken in the wheelpaths with those taken between the wheelpaths to establish traffic effects such as densification and surface rutting (note that it is unlikely that unbound material from the base, subbase, and sub- grade will be extruded in a core and, consequently, deter- mining precisely where rutting has occurred in the lower layers is not possible using cores alone). Examine the condition and shapes of the layer interfaces to determine if rutting is confined to the surface layers and where any other distresses originate. • Note and describe any evidence of debonding between lay- ers (e.g., AC to AC, AC to base, AC to PCC, and PCC to base) and any other distress related to the debonding (e.g., crack origin). Failure around dowel bar on pre-cast slab Failure around dowel bar on dowel bar retrofit Assessment of tie bar location (middle of PCC) and permeable cement treated base (right side of core) Dowel bar failure/corrosion seen in core hole Figure 7.11. Examples of observations on concrete cores. Extracted core

51 • Note and describe evidence of leveling or correction courses in asphalt concrete pavements and interlayers in concrete pavements and between concrete and the base. • Note and describe other distresses and/or observations and the potential implications such as material degradation or segregation, pumping of fines from lower layers, erosion of the surface of stabilized base layers due to pumping, and drainage deficiencies. Degradation of the material as a result of frost action can be observed in areas where ground freezing occurs beneath the pavement. If the core was sampled to a depth that is deeper than the normal frost depth, visual observations of the material above and below the frost line will reveal the depth of degradation. Other distress phenomena that should be sought and noted in the cut face of the surface layer include tensile crack formation at the bottom of asphalt concrete layers and D-cracking in concrete layers. • Take close-up pictures of specific distresses and associated consequences (e.g., mottling around cracks indicating water saturation). 7.3.2 Test Pits and Trenches 7.3.2.1 Reference Material The following reference standards are applicable to test pit excavation activities conducted in forensic investigations: • AASHTO R 13, Conducting geotechnical subsurface inves- tigations • AASHTO R 19, Operational guidelines on test pits for eval- uating pavement performance • AASHTO T 24, Obtaining and testing drilled and sawed beams of concrete • AASHTO T 310, In-place density and moisture content of soil and aggregate by nuclear methods (shallow depth) • ASTM D2488, Description and identification of soils (visual- manual procedure) • ASTM D4083, Description of frozen soils (visual-manual procedure) • ASTM D4220, Preserving and transporting soil samples • ASTM D5195, Test method for density of soil and rock in-place at depths below the surface by nuclear methods 7.3.2.2 Test Pit Excavation: Removing the Surface Layers The following key issues pertaining to test pit/trench exca- vation procedures should be considered: • Document all observations and measurements on an appropriate set of forms (example Forms #18 through #23 in Appendix C). • Saw the pavement to the full depth of the wearing course and bound layers to the specified overall dimensions and into smaller pieces as necessary for removal. – Minimize the use of cooling water during sawing to reduce water contamination of layers. Vacuum water from the sawcut and sampling area during sawing. – Use air-cooled equipment if a moisture-related failure is being investigated. – If saws of sufficient blade diameter to cut through to the base of the treated layers are not available, use pneu- matic spades and chisels, but with care to minimize damage to underlying untreated layers. – If material samples from the test pit are required, cut slabs of the wearing course to the appropriate dimen- sions to satisfy the testing requirements. • When taking slabs to investigate potential dowel problems of jointed plain concrete pavements, identify the length of the dowels (including any longitudinal misalignment) and cut the slab on both sides of joint behind the dowels. Drill Motorist and worker safety during test pit excavation, sampling, and testing are of major concern and appropriate measures need to be taken. Saw cutting for test pit Test pit slab removal

52 four holes on the slab, place eyebolts in them and epoxy the bolts into place. Once the epoxy has set, use a small hydraulic lift arm or other available equipment to lift the joint out of the pavement and onto a truck for transport to the laboratory. Similar procedures can be used for extract- ing sections from CRCP. • Mark wearing course samples on the top with an arrow to show the direction of traffic prior to removal from the pavement and a sample number. Log the number on the test pit evaluation form. The marking material should be waterproof to remain clearly visible. • Place the selected samples top down on a sheet of plywood and remove any excess water and loose material from the underlying layer. Do not put any excess pressure on the slab as this may cause it to crack. • Check the underside of the slab (Figure 7.12 and Fig- ure 7.13). On asphalt surfaces, a clean surface with no base material attached indicates the surface may have debonded (Figure 7.12c). The presence of salt crystals may indicate salt damage in the upper regions of the base or lower region of the surfacing. • Check all around the slab for any distress not related to the sawcut, specifically evidence linked to the issues being inves- tigated, such as moisture damage in asphalt (stripping). • If the surface material is required for laboratory testing, place it in a cloth or plastic bag and label the bag with the sample number. Log the sample on the sample inven- tory form. 7.3.2.3 Observation of Underlying Layers Before disturbing the surface of the underlying layers, check for any unusual conditions that may have had an influ- ence on the issues being investigated, such as: • A layer of fine material, which could be an indication of over-rolling/crushing during construction, disintegration under traffic, or pumping of fines from lower layers. a) Investigation of slab underside b) Layer assessment of slab c) Debonded layers Figure 7.12. Checking AC slabs after removing from the test pit.

53 • Mottling, which usually indicates fluctuating moisture contents. • A layer of loose material on top of a stabilized layer, which could indicate that carbonation of cemented layers has occurred, or inappropriate curing, re-mixing and/or final compaction techniques were followed on cementitious or asphalt stabilized layers. • A thin layer of inconsistent material on top of the base, which could indicate that a leveling course of potentially substandard material was used to bring the layer to grade. • The presence of salt crystals and other chemical substances, which may be encountered when using certain mine dump rock as base materials, or if the compaction water or ground water contain certain minerals. Log all observations on the assessment form (example Form #18 in Appendix C). Photographs should be taken and logged to record any key observations. 7.3.2.4 In-Pit Testing Once the visual assessment is complete, destructive in-pit testing can continue. The need for and type of in-pit testing on the layers underlying the surfacing layers will depend on the issues being investigated. Potential tests include: • Density and moisture content measured with a nuclear density gauge or similar device to determine whether base and subbase compaction influenced performance (note that moisture contents can be influenced by water from the sawing operation). • Layer thickness and shear strength determined with a DCP (note that DCP measurements can be influenced by water from the sawing operation, coarser aggregate, and the presence of stabilized layers). • Permeability measured with a permeameter to deter- mine the rate of ingress of water into the base for inves- tigating moisture-related problems and permeable base performance. Follow standard test procedures and log all results on an appropriate form (example Forms #22 and #23 in Appendix C for density/moisture content and DCP tests, respectively). 7.3.2.5 Test Pit Excavation: Base and Subgrade Layers Excavation of the test pit can continue once the surface visual assessment and in-pit testing are complete. The follow- ing considerations are relevant to the excavation of the base and subgrade layers: • Carefully remove the remaining base course layer to expose the subbase and/or subgrade layers, which may also be sam- pled if required. Continue excavation to a depth of at least 6 in. (150 mm) below the top of the subgrade or fill material. Separate the materials from each layer (Figure 7.14). Figure 7.13. Removing and checking PCC slabs. Density measurements in test pit

54 – Take a 10 lb (5.0 kg) sample for laboratory moisture determination from each layer stockpile. – If a backhoe bucket with teeth is used to excavate untreated layers, care must be exercised during the last 1 in. (2~3 cm) to avoid disturbing the underlying layer if specific testing is required on the layer. Hand excava- tion of the last part of each untreated layer is preferred. • Select the test pit face that will be assessed. • Scrape the face with a spade to get as smooth a surface as possible. Brush to remove dust, sludge and any excess water from sawing (Figure 7.15). Wipe the wearing course layers with a damp cloth to highlight any distresses (e.g., cracks are clearer when the test pit face is damp). • Demarcate each layer with string lines. This entails ham- mering nails at each side of the test pit face and at high and low points across the layer and connecting the nails with a string line, keeping it tight and level (i.e., no sag). – Use the string lines to provide a reference line for mea- surements, layer observation and description, and pho- tographs (Figure 7.16). – Be careful when identifying the different layers, espe- cially if the saw cut has gone into unbound materials. The smooth cut left by the saw blade can often be mis- taken for a bound layer. • Collect samples from the stockpiles of uncontaminated material of those layers identified as needing additional testing. Care must be exercised to avoid contamination of material from one layer with material from another layer. The sample size will depend on the identified testing. Log the sample on the material inventory sheet (example Form #21 in Appendix C). 7.3.2.6 Test Pit Logging Test pit logging involves a series of measurements and observations on the test pit face. Every assessment will be different and will depend on the purpose of the investi- gation, the distress that has developed (or would typically develop, but has not) over time, its causes and related con- sequences. Therefore, each pit will have to be closely exam- ined, measured, logged, and photographed in a systematic Hand-finished test pit face Close-up of brushed pit face Surfacing Base Subbase Figure 7.14. Separated layer samples from test pit excavation. Figure 7.15. Test pit after excavation and finishing.

55 manner and all observations carefully noted to ensure that data is useful for subsequent interpretation and analysis. Capture all relevant and potentially relevant information on a form, or series of forms (example Forms #20 through #23 in Appendix C). The following procedure is recommended for logging test pits: • Start logging the test pit within 15 minutes after comple- tion of excavation, before the moisture content of the face of the test pit changes significantly. For consistency, logging should be carried out on the “front” face of the test pit relative to traffic direction (Figure 7.17), but this can be changed to suit specific investigation requirements (e.g., location of distress) or because of the position of the sun. If appropriate to the investigation, simplify the assessment by dividing the test pit face into zones (Fig- ure 7.18), such as: – Zone 1: Edge of test pit (shoulder) to outside edge of outer wheelpath – Zone 2: Outer wheelpath – Zone 3: Outside edge of outer wheelpath to inside edge of inner wheelpath – Zone 4: Inner wheelpath – Zone 5: Outside edge of inner wheelpath to edge of test pit (inside lane edge) It must be remembered at all times that the purpose of a forensic investigation is not only to establish the cause of distress and/or failure (i.e., a post mortem investigation), but also to understand how the pavement behaved and to enable comparison with other similar pavements. Test pit assessors should look for and expect the unexpected, and try to relate what they see to material properties and construction practices, as well as traffic, and/or environmental influences. Figure 7.16. Test pit layer definition. Traffic direction ShoulderCenterline Test pit Wheelpaths Assessment face Figure 7.17. Plan view of test pit face to be logged.

56 or combine Zones 2, 3, and 4 into one zone and divide the test pit face into three zones as follows: – Zone 1: Edge of test pit (shoulder) to outside edge of outer wheelpath – Zone 2: Area under and between the wheelpaths – Zone 3: Outside edge of inner wheelpath to edge of test pit (inside lane edge) • If layer thickness is an issue to be investigated, accurate measurements will be required. Take measurements as follows: – Place a straight edge with marked 2.0 in. (50 mm) inter- vals on the top edge of the test pit. – Raise the low end of the straight edge until level so that crossfall can be measured. – Mark the edges of the wheelpaths on the straight edge. – Starting at the shoulder/outside edge of the lane and working towards the inside, take a series of measure- ments to the nearest 0.1 in. (or 1.0 mm) that will be used to record the thickness of each layer and the degree of rutting in each layer. Measure from the top of the straight edge to the: 77 Top of the surface 77 Top of each layer in the surface 77 Top of the base 77 Top of each subsequent layer below the base 77 Top of the subgrade • Record the layer profiles and measurements on the test pit profile form (example Form #18 in Appendix C). Also note the edges of the wheelpaths. Actual layer thick- nesses can be determined later using a spreadsheet (Fig- ure 7.19). Note deviations from the expected measurements together with the possible influence of this deviation on the overall performance of the pavement. Give special atten- tion to: – Rutting in underlying layers but not in the surface (Fig- ure 7.20a). ShoulderLane edge Wheelpaths Wearing course Base Subbase Subgrade Zone 4Zone 5 Zone 3 Zone 2 Zone 1 0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 0 10 0 20 0 30 0 40 0 50 0 60 0 70 0 80 0 90 0 10 00 11 00 12 00 13 00 14 00 15 00 Cross section (mm) D ep th ( m m ) Surface Base (257mm) Subgrade HMA (79mm) R-HMA-G (56mm) Subbase (116mm) Wheelpath Figure 7.18. Zoning of the test pit face. Figure 7.19. Example spreadsheet plot of layer thickness measurements.

57 – Obvious differences between the pavement design and as-built records (e.g., thicker or thinner layers [Fig- ure 7.20b]). – Thin layers that may have been added as a leveling course and become delaminated. – Describe each layer in accordance with the layer desig- nations provided on the preliminary data sheets using the parameters provided in Checklists #1 through #4 in Appendix D. These parameters are assessed in terms of the following suggested criteria (additional/other crite- ria may be appropriate depending on the issue being investigated): 77 Severity: where applicable, rated on a scale of 1 (low), 2 (moderate), or 3 (high). Severity descriptors are pro- vided in Checklists #5 through #8 in Appendix D. 77 Extent: describes the percentage area, number of and/ or length of the parameter being assessed. Extent descriptors are also listed in Checklists #5 through #8 in Appendix D. 77 Start: where applicable, the start point of the defect (e.g., surface or 1.0 in. [25 mm] below subbase/base interface in Zone 1). 77 End: where applicable, the terminal point of the defect. 77 Layers and zones affected: indicates which layers and zones are influenced by the parameter being assessed, listed in order from start to its terminal point. 77 Description: describes the pertinent aspects of the parameter being assessed. 77 Implications: where applicable, lists the implications and consequences of the parameter (e.g., vertical crack provides a path for the ingress of water and the egress of fines) and links to other distress/attributes. • Spray bound layers that have been stabilized with cement or lime with a phenolphthalein solution to determine if carbonation of the layer has occurred (Figure 7.21) or if the entire layer was correctly stabilized. – Well cemented layers will turn a dark red color, while carbonated areas will have little or no reaction, with severity usually increasing from top to bottom. The upper regions of carbonated layers are often also weak and relatively loosely bound and carbonated layers typi- cally have lower than expected strengths and stiffnesses when tested with FWD and DCP. a) Note rutting in underlying AC layer. b) Note variable thickness of all layers. Figure 7.20. Example observations from test pits. Strong cementation throughout layer Cement stabilization at top of layer only HCl reaction Phenolphthalein reaction Phenolphthalein reaction at top of base only Figure 7.21. Phenolphthalein and hydrochloric acid reactions in test pits.

58 – Spray areas of suspected carbonation with a dilute hydro- chloric acid (HCl) solution to check for the presence of cement and the degree of reaction (fizzing). Note that calcareous materials in the layer aggregate such as dolo- mite and limestone will react with the hydrochloric acid and this should be factored into the interpretation. If possible, check the acid reaction with similar material that has not been stabilized and determine whether the reaction is weaker or the same as the stabilized layer. This will indicate if calcium carbonate occurs naturally in the material. • Look for signs of reworking of cemented layers, typically indicated by weak cementation. • Examine the condition and shapes of the layer interfaces to determine where rutting and other distress originates. – Deep ruts at the surface not reflected at the base/subbase interface indicate that the rutting has taken place in the base course or asphalt concrete surfacing. Surface ruts that are mirrored at the base/subbase interface or the subbase/subgrade interface are generally a consequence of compaction or shear at a depth below the interface. – Shearing/movement within layers in the form of shiny shear planes (slickenslides) that is sometimes observed in specific layers may indicate problems within that layer. • Note and describe any other distress/behavior and its implications such as material degradation or segregation, stripping, cracking (e.g., tensile crack formation at the bottom of asphalt concrete layers, thermal cracks start- ing at the surface of asphalt layers, D-cracking in portland cement concrete layers, and shrinkage cracking or heaving of swelling subgrade soils), debonding, intrusion of sub- grade fines into the subbase and/or base, erosion of the surface of the base layer due to pumping, and drainage deficiencies. Trace cracks from start point to end point and determine cause of the crack (e.g., shrinkage, settle- ment, differential compaction, fatigue, reflection, ther- mal, etc.). – Degradation of the material due to frost action can be observed in areas where ground freezing occurs beneath the pavement. If the test pit is deeper than the normal frost depth, visual observations of the material above and below the frost line will reveal to what depth degra- dation has progressed. • Take good quality digital photographs of the test pit pro- file and key observations during the evaluation. The pho- tographs should be taken at and keyed to the locations described on the test pit log, and provide a total view of the test pit as well as close-up views of the pavement pro- files (Figure 7.22). All photographs should be taken with the sun behind the photographer whenever possible to avoid shadows. Close-up pictures should be taken of dis- tress and associated consequences (e.g., mottling around cracks indicating water saturation) within the pavement structure and cross-referenced to the assessment form. • Collect any additional samples from specific layers or spe- cific points in the layer for additional testing and/or obser- vation. Number each sample and record the sampling position and reason why it was taken (e.g., type of testing required) on the material inventory form. • On completion of all test pit activities, ensure that the pit is correctly backfilled and all excess materials are removed from the site before the road is reopened to traffic. 7.4 Key Issues Concerning Laboratory Testing The need for laboratory testing and the type and number of tests required will depend on the issues being investigated. Laboratory test methods and procedures are not discussed in this guide. Special precautions for handling phenolphtha­ lein and hydrochloric acid should be taken and suitable protective clothing and equipment should be worn when handling the chemicals. Total view of test pit Close-up view of distress (rut in underlying AC) Figure 7.22. Example general test pit photographs.

59 In addition to standard tests, specialists on the investiga- tion team may request/undertake specialized testing to fully understand the issues being investigated. Examples include: • X-ray diffraction and surface energy measurements to assess aggregate chemistry and its effects on bonding of asphalt and cement and hydration products of portland and other hydraulic cements. • Microscope and scanning electron microscope analyses (example in Figure 7.23) to observe bonding mechanisms, micro-cracking, and new cement crystal growth. • CT scans to assess void connectivity and aggregate orien- tation. • Petrographic analysis of aggregates (example in Fig- ure 7.24), for ASR and other aggregate-related problems. • Chloride contents of concrete to determine corrosion potential around reinforcing steel and dowels. • Phase analysis of reinforcing steel and other metallic materials to compare with specifications. • Chemical analysis of epoxy coatings and other anti- corrosion coatings. • Chemical analysis for the presence of solvents, softening agents, fuel spills, and other materials that may be in the asphalt from contamination during manufacturing, trans- portation or other construction processes, or have been spilled on the pavement during use. Development of calcite crystals associated with cracking during carbonation (x270) New calcite crystals developing on previously well cemented aggregation of particles (x1,100) 1 day 7 days Figure 7.23. Example scanning electron microscope images used in carbonation study. Figure 7.24. Example petrographic analysis of ASR in PCC pavement.