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Guide for Conducting Forensic Investigations of Highway Pavements (2013)

Chapter: Chapter 2 - General Investigation Philosophy

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Suggested Citation:"Chapter 2 - General Investigation Philosophy." National Academies of Sciences, Engineering, and Medicine. 2013. Guide for Conducting Forensic Investigations of Highway Pavements. Washington, DC: The National Academies Press. doi: 10.17226/22507.
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Suggested Citation:"Chapter 2 - General Investigation Philosophy." National Academies of Sciences, Engineering, and Medicine. 2013. Guide for Conducting Forensic Investigations of Highway Pavements. Washington, DC: The National Academies Press. doi: 10.17226/22507.
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Suggested Citation:"Chapter 2 - General Investigation Philosophy." National Academies of Sciences, Engineering, and Medicine. 2013. Guide for Conducting Forensic Investigations of Highway Pavements. Washington, DC: The National Academies Press. doi: 10.17226/22507.
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Suggested Citation:"Chapter 2 - General Investigation Philosophy." National Academies of Sciences, Engineering, and Medicine. 2013. Guide for Conducting Forensic Investigations of Highway Pavements. Washington, DC: The National Academies Press. doi: 10.17226/22507.
×
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Suggested Citation:"Chapter 2 - General Investigation Philosophy." National Academies of Sciences, Engineering, and Medicine. 2013. Guide for Conducting Forensic Investigations of Highway Pavements. Washington, DC: The National Academies Press. doi: 10.17226/22507.
×
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Suggested Citation:"Chapter 2 - General Investigation Philosophy." National Academies of Sciences, Engineering, and Medicine. 2013. Guide for Conducting Forensic Investigations of Highway Pavements. Washington, DC: The National Academies Press. doi: 10.17226/22507.
×
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Suggested Citation:"Chapter 2 - General Investigation Philosophy." National Academies of Sciences, Engineering, and Medicine. 2013. Guide for Conducting Forensic Investigations of Highway Pavements. Washington, DC: The National Academies Press. doi: 10.17226/22507.
×
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Suggested Citation:"Chapter 2 - General Investigation Philosophy." National Academies of Sciences, Engineering, and Medicine. 2013. Guide for Conducting Forensic Investigations of Highway Pavements. Washington, DC: The National Academies Press. doi: 10.17226/22507.
×
Page 12

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5 Developing a framework or flowchart that provides a step- by-step process to guide the investigator in identifying the most likely reasons for the observed performance (be it poor or excep- tional) would be highly desirable. However, such an approach can realistically be developed only for investigations in which one issue only contributed to the observed performance (e.g., poor compaction leading to early rutting). The combination of potential investigation objectives and the numerous factors associated with each investigation make it difficult if not impos- sible (and in some cases, counterproductive) to develop a prac- tical framework that covers all possibilities. Instead, a general philosophy is provided in this chapter to better use the infor- mation obtained from the investigation. The philosophy entails the following three fundamental aspects: • Understanding pavement performance and the factors that affect it, • Recognizing pavement performance data and information needs, and • Avoiding premature or unsupported conclusions about pavement performance. 2.1 Understanding Pavement Performance The success of a forensic investigation requires a clear understanding of how pavements perform and why they perform/behave as they do. Four factors, separately or in combination, define the performance of a pavement: • Pavement structure — includes pavement type (e.g., new or rehabilitated asphalt or concrete pavement) and pave- ment layers (thicknesses, material types and properties, drainage, shoulders, joints and steel reinforcement in con- crete pavements, construction procedures, quality of con- struction and related issues, ambient conditions at time of construction, and others). • Subgrade soil — includes material types, material proper- ties, stabilization, embankment, cut/fill, depth to bedrock, drainage, and others. • Traffic — includes traffic volumes, traffic loads/load spec- tra, traffic growth, seasonal trends, load restrictions, and others. • Environmental conditions — includes air and surface tem- peratures, precipitation, wind, solar radiation, subsurface moisture, subsurface temperature, construction ambient conditions, unusual and/or catastrophic events, freeze/ thaw cycles, freezing days, and others. Environmental conditions, for example, may affect the pavement material layer properties. High moisture contents in unbound pavement and subgrade materials will generally lead to weaker layers, especially when they approach satu- ration conditions (e.g., during spring-thaw conditions). Similarly, high or low air temperatures result in low or high stiffness in asphalt concrete layers, respectively, which could make the asphalt concrete layer more susceptible to rutting or to cracking, respectively. The extent of the dam- age caused by traffic depends on the applied traffic loadings and volumes and pavement and subgrade material proper- ties at that time. To fully understand the performance of a given pave- ment, whether good, poor, or as anticipated, it is essential that each of the four pavement performance-related factors and their interactions be understood. This understanding is often difficult given the number of possible considerations in each of the four factors. Table 2.1 provides example con- siderations for three of the four factors, which are based on two pavement failure case studies presented in Appen- dix B. This example is intended to illustrate the potential complexities of forensic investigations. Additional consid- erations, which look at pavement performance scenarios including distress types and their causes, are presented in Section 2.4. C h a p t e r 2 General Investigation Philosophy

2.2 Recognizing Data and Information Needs Understanding the performance of a given pavement requires that data and information about each of the factors affecting performance (discussed in Section 2.1) be collected and analyzed. Three potential sets of data should be pursued in addition to the performance measures (e.g., surface dis- tress or roughness) of interest: • As-designed data and information, • As-constructed data and information, and • Comparison data and information. Because performance expectations are generally estab- lished during the pavement design process, gathering infor- mation on the as-designed conditions is vitally important to any given forensic investigation as it helps establish the basis for performance expectations or, in essence, the forensic investigation datum. The data and information needs apply to the four pavement performance factors discussed in Sec- tion 2.1 (i.e., pavement structure, subgrade soil, traffic, and environmental conditions). Recognizing that the as-designed conditions are often not replicated during the construction process, it is also impor- tant that data and information on the four pavement perfor- mance factors for the as-constructed conditions are collected and compared to the as-designed conditions. Heavier or more voluminous traffic, worse than anticipated climatic conditions, weaker and/or thinner pavement layers than designed, for example, in combination or alone, could help explain why a pavement performed worse than expected. Comparing as-designed data and information to the as-constructed data can help establish the reasons for the observed performance. To the extent feasible, the use of comparison data in the investigation is highly encouraged. For example, comparing the construction procedures, as- constructed data, and related information to those from another similar nearby project can help identify the rea- sons for the differing performance of similar pavement structures. If the issues being pursued pertain to the surface layer, for example, then a comparison project having similar subgrade soil, environmental conditions and base/subbase layers would allow for the direct comparison of the surface layer. Comparisons are also useful for investigating situa- tions in which unexpected factors contribute to the observed performance. For example, poor spreading of cement in the construction of cement treated bases can lead to isolated areas of high cement contents that result in isolated areas of reflected shrinkage cracks. 6 Primary Factor Considerations Pavement Structure Asphalt concrete surface layer Poor surface preparation, inadequate mix strength/stability, inadequate mix gradation, low binder content, incorrect binder grade/viscosity, incorrect fines content, incorrect mix tenderness, mix segregation, low mix temperature during paving/compaction, loose material on surface of base prior to paving, poor prime coat application, incorrect rolling pattern leading to isolated area of high air-void content, temporary change in construction process, moisture/freeze-thaw damage related to isolated poor compaction, paver malfunction, removal of chunks with insufficient material replacement, temporary change in construction process, incorrect thickness design, incorrect/variable as-built thickness, crack reflected from base problem, excess moisture in mix, rapid aging binder Treated base layer Differential compaction caused by recycler tires, incorrect compaction procedure to correct differential compaction, incorrect roller choice, poor/inconsistent compaction/rolling pattern, compaction after stabilizer set up, incorrect overlap procedure on second recycler pass, poor distribution of cement/double cement content in overlap/cement windrow caused by recycler apron, poor distribution of asphalt emulsion/foamed asphalt/double application of binder in overlap, incorrect compaction water application, poor material mixing, poor mix design, incorrect fines content, asphalt emulsion incompatible with aggregate, incorrect asphalt binder content, incorrect cement content, incorrect compaction moisture content/uneven distribution of water (e.g., damaged spray bar), incorrect stabilizer selection, incorrect base thickness design, incorrect/variable as-built base thickness, material change due to historical lane addition with different materials, incorrect reclaiming width (deleterious materials incorporated into base), excessive recycling depth, excessive fines/plasticity in recycled material Environment Surface drainage problem, subsurface drainage problem, drought causing clay shrinkage on side of road, seasonal roadside activity, abnormal rainfall event/season, seismic activity Traffic Inappropriate trafficking on stabilized base prior to surfacing, higher than design traffic, overloading Table 2.1. Pavement performance-related factors and considerations.

Historical data on older projects is often difficult to recover, which can complicate the design, as-constructed, and comparative reviews. This is a problem when attempt- ing to understand why a particular pavement has performed better than expected. The tracking and completion of a data and information matrix is also encouraged. An example for a new asphalt con- crete pavement is provided in Table 2.2. These matrices enable forensic investigators to identify available data and information and those unavailable at any point during the investigation. They require regular updates throughout the investigation process. Depending on the application, pavement performance may be characterized by a form of distress, deflection, roughness, friction, or noise, individually or in combinations, such as: • Pavement distress data (using manual or automated dis- tress surveys). – Asphalt concrete surface. 77 Cracking: fatigue cracking, block cracking, edge cracking, longitudinal cracking, reflection cracking, and transverse cracking. 77 Surface deformation: rutting and shoving. 77 Patching and potholes: patch deterioration and potholes. 77 Surface defects: bleeding, polished aggregate, and raveling. 77 Other distresses: lane-to-shoulder drop-off, water bleeding and pumping. – Jointed plain concrete (JPC) surface. 77 Cracking: transverse cracking, longitudinal cracking, corner breaks, and durability cracking (“D” cracking). 77 Faulting of transverse joints and cracks. 77 Joint deficiencies: transverse joint seal damage, lon- gitudinal joint seal damage, spalling of longitudinal joints, and spalling of transverse joints. 77 Surface defects: map cracking, scaling, polished aggregate, and popouts. 77 Other distresses: blowups, lane-to-shoulder drop- off, lane-to-shoulder separation, patch deterioration, and pumping. – Continuously reinforced concrete (CRC) surface. 77 Cracking: transverse cracking, longitudinal cracking, and durability cracking (“D” cracking). 77 Punchouts. 77 Surface defects: map cracking, scaling, polished aggregate, and popouts. 77 Other distresses: blowups, transverse construction joint deterioration, lane-to-shoulder drop-off, lane- to-shoulder separation, patch deterioration, spalling of longitudinal joints, pumping, and longitudinal joint seal damage. • Pavement deflection data (using FWD or other devices): maximum deflection, deflection basin, deflection indices, layer moduli, overall structural capacity, load transfer and voids, longitudinal and transverse variability, other deflec- tion parameters, etc. • Pavement roughness/elevation data (longitudinal and/or transverse): pavement roughness, International Rough- ness Index (IRI), rutting, elevation versus station, other roughness parameters, longitudinal and transverse rough- ness variability, etc. • Pavement surface friction data: surface macro-texture, sur- face micro-texture, skid resistance, other friction param- eters, longitudinal and transverse friction variability, and other considerations. • Pavement surface noise: surface macro-texture, surface micro-texture, faulting in PCC, surface tining and groov- ing, clogging and/or raveling of open-graded friction courses, longitudinal and transverse noise variability, and other noise parameters and considerations. 7 Performance Factors As-Designed As- Constructed Comparison Pavement Structures Asphalt concrete surface thickness Asphalt concrete surface modulus Cement treated base thickness Cement treated base modulus Granular subbase thickness Granular subbase modulus Subgrade Soil Subgrade soil type Subgrade soil modulus Traffic Load spectra Volumes Environmental Conditions Precipitation data Ambient temperature data Subsurface moisture conditions Subsurface temperature conditions Table 2.2. Forensic investigation data and information needs.

8collection of unnecessary data and ensure a successful out- come. The first task in a forensic investigation is to understand the issues underlying the request for the investigation and then setting objectives to address these issues. Establishing these issues and objectives will help guide the investigation pro- cess and ensure that appropriate data and information are gathered and analyzed before any conclusions are drawn. Investigators are cautioned against focusing on a single fac- tor contributing to the performance in question, as several factors (some of which may be unexpected and/or unantici- pated) may have contributed to the observed performance. In those cases where a single factor can be clearly identified, it is likely that a comprehensive forensic investigation would not be necessary. The case studies (Appendix B) have shown many instances in which the apparent cause of a premature failure was not the sole or even the correct cause of poor performance. 2.4 Pavement Performance Investigation Scenarios Most forensic investigations are carried out to understand poor pavement performance, early distress, or premature failures. To a certain extent, these investigations are prob- ably easier to conduct because considerable information on such issues is readily available. Table 2.3, for example, shows typical asphalt concrete pavement distress types and their possible (common or occasional) causes (1). Table 2.4 lists possible data and information requirements to identify the most likely causes of these distresses (1). Table 2.5 provides similar information for investigations of portland cement con- crete pavements (2), and Table 2.6 summarizes key material related distresses (MRD) (3). The information contained in Table 2.3 through Table 2.6 addresses to a large extent the aspects of the investigation dis- cussed in this chapter, namely understanding pavement per- formance and the factors that affect it, recognizing data and information needs, and avoiding premature or unsupported conclusions. However, it is important to recognize that these tables do not address all types of pavement failures (e.g., pave- ment roughness and loss of friction) or the full range of pos- sible investigation objectives. The conduct of forensic investigations into exception- ally well performing pavements is generally a more complex process, because there is no clear “starting point” as is the case with poor performing or failed pavements, and because these investigations usually take place later in the life of the pavement when obtaining design and construction data is more difficult. For example, it is possible that a pavement is considered performing exceptionally simply because the pavement surface was constructed thicker than designed. On Similarly, the factors that, separately or combined, influ- ence pavement performance may be obtained from the fol- lowing sources: • Pavement structure and subgrade soil information avail- able or obtained through one or more of the following methods: trenching; test pits and coring/boring; GPR; Dynamic Cone Penetrometer (DCP); drainage surveys (video or other means); field materials sampling and test- ing activities (e.g., tube suction and retained strength tests); laboratory materials testing; specialized testing (dig- ital and scanning electron microscope analysis, and chemi- cal tests); pachometer surveys of jointed and continuously reinforced concrete pavement (CRCP); magnetic tomog- raphy technology (MTT) scan of PCC; and other destruc- tive and non-destructive testing techniques. • Construction records from the resident engineer’s and other staff logs. • 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) or through the use of surface and/or subsurface instrumentation. In addition to performance measures, the collection of as- designed and as-constructed data and information may help identify possible reasons for the observed pavement perfor- mance or its variation from that anticipated. Comparing data from good and poor performing sections within a project (or good and poor performing pavements of the same design in the same area) helps to isolate factors that led to the differ- ences in performance. 2.3 Avoiding Premature Conclusions Gathering data and information on every possible pave- ment performance measure and every factor potentially affecting pavement performance is unnecessary and often beyond the available resources of most agencies. Forensic investigations will contain common elements, but specific investigation elements will ultimately depend on the issues being investigated and the associated relevant pavement factors. Achieving a balance between requirements, priori- ties, and available resources is part of each investigation. Establishing and understanding the investigation objectives and using them as the basis for collecting and analyzing the appropriate data and information will help eliminate the

9 M at Pr ob le m s D et er io ra tio n D ef or m at io n C ra ck in g D is tr es s C at eg or y Bleeding Checking Segregation Pumping Polished Aggr Stripping Raveling Patching Potholes Delamination Overlay Bumps Depression Shoving Corrugation Rutting Edge Block Reflective Transverse Fatigue Longitudinal Lo w S tre ng th o r L ow S ta bi lit y M ix P oo r M ix G ra da tio n Lo w A sp ha lt C on te nt H ig h A sp ha lt C on te nt Lo w A ir V oi d C on te nt H ig h A ir V oi d C on te nt Im pr op er F in es C on te nt Te nd er M ix S eg re ga te d M ix P oo r S ur fa ce P re pa ra tio n E xc es s/ In su ffi ci en t P rim e/ Ta ck Im pr op er C ra ck S ea lin g Te ch ni qu es Im pr op er C om pa ct io n Te ch ni qu es E xc es s M oi st ur e in M ix Lo w H M A T hi ck ne ss Lo w B as e/ S ub ba se T hi ck ne ss P oo r S ub gr ad e C om pa ct io n P oo r B as e/ S ub as e C om pa ct io n P oo r B as e/ S ub as e G ra da tio n H ig h A sp ha lt B in de r V is co si ty Lo w A sp ha lt B in de r V is co si ty Te m p. S us ce pt ib le A sp ha lt B in de r R ap id A gi ng A sp ha lt B in de r M oi st ur e S en si tiv e M ix P oo r A gg re ga te D ur ab ili ty P oo r A gg re ga te S ou nd ne ss P oo r A gg re ga te C le an ne ss H ig h E xp os ur e to M oi st ur e C oo l/C ol d P re va ili ng T em pe ra tu re s H ot P re va ili ng T em pe ra tu re s Fr ee ze -T ha w C yc lin g La rg e D ai ly T em pe ra tu re C yc le s H ig h Tr af fic V ol um e H ig h E S A L Tr uc k V ol um e E xp os ur e to S tu dd ed T ire s/ C ha in s In ad eq ua te P av em en t S tru ct ur e P oo r M at er ia l S el ec tio n P oo r D ra in ag e N ar ro w o r N on -E xi st en t S ho ul de rs N ar ro w L an e W id th E xc es si ve H or iz on ta l G eo m et ry Common cause of distressLegend Distress Type Overall Problem Mix Design Construction Possible Causes of Distress Materials Climate Traffic StructuralDesign Geometric Design Occasional cause of distress Table 2.3. Example Hot-mix Asphalt (HMA) distress types and possible causes (1). the other hand, the observed performance may be due to one or more less-easily identifiable reasons such as adjustments made at the asphalt or concrete plant on a particular paving day, use of different sources of aggregates, substitution of construction equipment, or use of different curing proce- dures of stabilized materials. While the reasons for undertaking the investigation may differ, the aspects discussed in this chapter are applicable to all types of forensic investigation including those undertaken to collect data for the calibration of mechanistic-empirical performance models. These aspects include understand- ing the factors affecting performance, collecting the neces- sary data and information, avoiding reaching premature or unsupported conclusions, and recognizing that a combina- tion of factors contribute to the observed performance. 2.5 Investigation Phases The investigation approach presented in this guide con- sists of three phases: 1. Preliminary investigation, 2. Non-destructive testing, and 3. Destructive and/or laboratory testing. This phased approach is intended to eliminate the need for collecting data and information beyond what is required to address the objectives and issues in question. It is possible, for example, that the investigation be successfully completed (issues addressed and questions answered) by completing the preliminary phase if sufficient data and information are available at this stage to draw valid conclusions.

10 Excessive Horizontal Geometry Narrow Lane With Narrow or Non-Existent Shoulders Poor Drainage Poor Material Selection Inadequate Pavement Structure Exposure to Studded Tires/Chains High ESAL Truck Volume High Traffic Volume Large Daily Temperature Cycles Freeze-Thaw Cycling Hot Prevailing Temperatures Cool/Cold Prevailing Temperatures High Exposure to Moisture Poor Aggregate Cleanness Poor Aggregate Soundness Poor Aggregate Durability Moisture Sensitive Mix Rapid Aging Asphalt Binder Temp. Susceptible Asphalt Binder Low or High Binder Viscosity Poor Base/Subase Gradation Poor Base/Subase Compaction Poor Subgrade Compaction Low Base/Subbase Thickness Low HMA Thickness Excess Moisture in Mix Improper Compaction Techniques Improper Crack Sealing Techniques Surface Prep/Excess/Lack Prime/Tack Segregated Mix Tender Mix Improper Fines Content Low or High Air Void Content Low or High Asphalt Content Poor Mix Gradation Low Strength or Low Stability Mix Cl im at e M at er ia ls Co ns tru ct io n M ix D es ig n G eo m et ric De si gn St ru ct ur al De si gn Tr af fic De sig n Re po rts Pl an s an d Sp ec ific at io ns Q C/ Q A Re co rd s As B ui lt Dr aw in gs La b M at er ia l T es t R es ul ts Pa st Su rv ey s/ ND T/ Sa m pl in g M al nt en an ce /R ep ai r Hi st or ie s Tr af fic D at a En vir on m en ta l/C lim at e Re co rd s PM S Re po rts W in ds hi el d Su rv ey De ta ile d Di st re ss S ur ve y No nd es tru di ve T es tin g Ev al ua tio n of N DT Un ifo rm ity St ru ct .. Ca pa cit y Ev al . (C al tra ns ) St ru ct C ap ac ity E va L. (B ac kc al c. ) Co rln g Au ge r B as e, S ub ba se an d/ or S ub gr ad e Sh el by (P us h) T ub e Te st P it (T re nc h) Dy na m ic Co ne /S ta nd ar d Pe ne tro m et er So il C la ss ific at io n G ra da tio n M oi st ur e Co nt en t De ns ity De ns ity As ph al t C on te nt Ai r V oi d Co nt en t As ph al t B in de r V isc os ity As ph al t T em pe ra tu re Su sc ep tib ilit y Ag gr eg at e G ra da tio n Co ar se A gg re ga te Ab ra sio n Ag gr eg at e Du ra bi lity Ag gr eg at e So un dn es s M oi st ur e Se ns itiv ity R- Va lu e (U nb ou nd M at er ia ls In di re ct T en sil e (B ou nd M at er ia ls) Re sil ie nt M od ul us (F in e/ Co ar se M at 'ls ) M od ul us (A sp ha lt M ixt ur es ) Typical test or data requirement Occasional test or data requirement Legend Possible Causes of Distress Records Review StructuralEvaluation Distress Survey Field Sampling & Testing Methods Unbound Mat's Bound Materials (Strength Related) Laboratory Testing (General Material Characteristics) Table 2.4. Example data requirements to identify cause of HMA pavement distress (1).

11 Structural Distress Contributing Factors1 Pavement Design Load Water Temp. Pavement Materials Construct. Structural Distress Cracking2 Transverse Longitudinal Corner Intersecting P P C C P P P P N N C C C C C N C C N C P P N N Possible causes of cracking: Fatigue, joint spacing too long, shallow or late joint sawing, base or edge restraint, loss of support, freeze-thaw and moisture-related settlement/heave, dowel bar lock-up, curling, and warping. Joint/Crack Deterioration Spalling Pumping2 Blowups Joint Seal Damage2 C C C C C P N C N P N C C N P C P C C P C N N C Possible causes of joint/crack deterioration: Incompressibles in joint/crack, material durability problems, subbase pumping, dowel socketing or corrosion, keyway failure, metal or plastic inserts, rupture and corrosion of steel in JRCP, high reinforcing steel. Punchouts2 P P C N C N Possible causes of punchouts: Loss of support, low steel content, inadequate concrete slab thickness, poor construction procedures. Durability D-cracking Alkali-Silica Reactivity (ASR) Freeze-thaw damage N N N N N N P P P C C P P P P N N C Possible causes of durability distresses: Poor aggregate quality, poor concentrate mixture quality, water in the pavement structure. Functional Distress Roughness Faulting2 Heave/swell2 Settlement2 Patch deterioration P C C C P N C C P P C C C P N C C C N C N N C C Possible causes of roughness: Poor load transfer, loss of support, subbase pumping, backfill settlement, freeze-thaw, and moisture-related settlement/heave, curling and warping, and poor construction practices. Surface Polishing N C N N P N Possible causes of surface polishing: High volumes of traffic, poor surface texture, wide uniform tine spacing, wide joint reservoirs, and wheel path abrasion because of studded tires or chains. Noise P C N N C P Possible causes of noise: High volumes of traffic, poor surface texture, wide uniform tine spacing, wide joint reservoirs, and wheel path abrasion because of studded tires or chains. Surface Defects Scaling Popouts Crazing Plastic shrinkage cracks N N N N N N N N C C N N C C C C P P C C P C P P Possible causes of surface defects: Over-finishing the surface, poor concrete mixture, reactive aggregates, and poor curing practices. 1 P= Primary Factor C= Contributing Factor N= Negligible Factor 2 Loss of support is an intermediary phase between the contributing factors and these distresses. Loss of support is affected by load, water, and design factors. Table 2.5. Example PCC distress types and possible causes (2).

12 Type of MRD Surface Distress Manifestations and Locations Causes/ Mechanisms Materials Related Distress Due to Physical Mechanisms Freeze-Thaw Deterioration of Hardened Cement Paste Scaling, spalling, or map cracking, generally initiating near joints or cracks; possible internal disruption of concrete matrix. Deterioration of saturated cement paste due to repeated freeze-thaw cycles. Deicer Scaling/ Deterioration Scaling or crazing of the slab surface with possible alteration of the concrete pore system and/or the hydrated cement paste leading to staining at joints/cracks. Deicing chemicals can amplify freeze-thaw deterioration and may interact chemically with cement hydration products. Freeze-Thaw Deterioration of Aggregate Cracking parallel to joints and cracks and later spalling; may be accompanied by surface staining. Freezing and thawing of susceptible coarse aggregates results in fracturing and/or excessive dilation of aggregate. Materials Related Distress Due to Chemical Mechanisms Alkali-Silica Reactivity (ASR) Map cracking over entire slab area and accompanying expansion- related distresses (joint closure, spalling, and blowups). Reactions involving hydroxyl and alkali ions in pore solution and reactive silica in aggregate resulting in the build-up of expansive pressures within aggregate, until tensile strength of surrounding paste matrix is exceeded, resulting in cracks. Alkali-Carbonate Reactivity (ACR) Map cracking over entire slab area and accompanying pressure- related distresses (spalling, blowups). Expansive reaction involving hydroxyl and alkali ions in pore solution and certain dolomitic aggregates resulting in dedolomitization and brucite formation. External Sulfate Attack Fine cracking near joints and slab edges or map cracking over entire slab area, ultimately resulting in joint or surface deterioration. Expansive formation of ettringite that occurs when external sources of sulfate (e.g., groundwater, deicing chemicals) react with the calcium sulfoaluminates. Internal Sulfate Attack Fine cracking near joints and slab edges or map cracking over entire slab area. Formation of ettringite from internal sources of sulfate that results in expansive disruption in the paste phase or fills available air voids, reducing freeze-thaw resistance. Corrosion of Embedded Steel Spalling, cracking, and deterioration at areas above or surrounding embedded steel. Chloride ions penetrate concrete, resulting in corrosion of embedded steel, and formation of high-volume oxidation products and resultant expansion. Table 2.6. Summary of key Materials Related Distresses (MRD) in PCC pavements (3).

Next: Chapter 3 - Investigation Request and Preliminary Investigation »
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TRB’s National Cooperative Highway Research Program Report 747: Guide for Conducting Forensic Investigations of Highway Pavements explores a process for conducting forensic investigations of pavements that is designed to help understand the reasons behind premature failures or exceptionally good performance. The process also allows for the collection of data for use in developing or calibrating performance-prediction models.

The report includes example forms and checklists for use during the conduct of an investigation. These forms can be modified to suit the particular requirements and procedures for the agency. The example forms are included with the print version of the report in CD-ROM format.

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