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C H A P T E R 3 Development of Preservation Guidelines for High-Traffic-Volume Roadways The results of the literature review and the questionnaire sur- of the treatment selection process depicted in Figure 3.1. vey are an excellent starting point for identifying the state of In this process, the current and historical conditions of the the practice for preservation of high-traffic-volume facilities. existing pavement are first established through condition The information indicates the types of treatments that can be surveys or the agency's pavement management system (PMS) successfully used on pavements with high traffic volumes, and records or both. A preliminary list of preservation treatments it also reveals much about other key factors that can influence that best address the deficiencies of the existing pavement the selection of treatments at the project level. Specific insights is then developed. The candidate treatments are evaluated obtained relate to the following: according to their ability to satisfy the performance needs and construction constraints of the project. A final list of feasible Performance Attributes treatments is then generated and these treatments are analyzed · Effect of existing pavement condition (distress) and service- for cost-effectiveness and other considerations to arrive at ability (smoothness) on treatment performance. the preferred treatment. · Effect of traffic volume on treatment performance. · Effect of climate and environment on treatment performance: Preliminary Analysis of Direct climatic and environmental stresses; and Treatment Feasibility: Stresses associated with snowplowing and studded or Consideration of Existing chained tire use. Pavement Conditions · Effect of treatment on pavement condition, serviceability, safety (friction, surface drainage [splash/spray, cross slope]), Applying preservation treatments at the correct time is often and noise. cited as a key to cost-effectively extending pavement service- ability. If a treatment is applied too soon, funds are expended Constructability Issues on roads that do not require treatment or do not exhibit · Costs (agency and user). sufficient benefit to justify the costs. If a treatment is applied · Complexity of construction. too late, the road may have deteriorated to the point that the · Availability of skilled and experienced or qualified treatment is ineffective or does not add sufficient life to the contractors. pavement to justify the cost. Thus, the correct time represents · Need for specialized equipment or materials. a "window of opportunity" in terms of the condition or service- · Availability of quality materials. ability of the pavement. · Environmental constraints. Most practitioners agree that preservation treatments should · Traffic disruption. be applied during the period when the pavement remains in · Traffic control constraints. fair to good condition. A recent NCHRP survey on pavement · Restrictions on available time for lane closures to complete preservation revealed that more than two-thirds of the report- the work. ing agencies treat roads while they are still in fair to good condition, whereas less than 5% treat pavements in very This chapter draws upon the findings presented in Chap- poor condition (Peshkin and Hoerner 2005). This leads to ter 2 and incorporates additional information, concepts, and the conclusion that most state agencies try to restrict treat- ideas that convey the state of the practice within the backdrop ment to pavements in fair to good condition. Findings from 33
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34 Establish existing Determine Perform cost-effectiveness pavement project needs analysis and evaluate economic condition. and constraints. and noneconomic factors. Identify preliminary Identify final set Identify set of feasible of feasible preferred treatments. treatments. treatment. Figure 3.1. Process of selecting the preferred preservation treatment. the SHRP SPS-3 and SPS-4 studies of PM on both HMA before an expected rehabilitation is assigned to each treatment, and PCC support this, concluding that "treatments applied based either on the number of years remaining in the design to pavements in good condition had shown good results" life of the existing pavement structure or on the projected (Morian et al. 1997). performance trend (overall condition or smoothness curves Preservation treatments have often been applied according and corresponding terminal and threshold levels), as illustrated to a predetermined schedule based on a time (or a window in Figure 3.2. of time) since original construction or the last major reha- An example of RSL-based windows of opportunity is bilitation (e.g., crack seal at Year 5, apply a chip seal between featured in a report covering the development of a pave- Years 7 and 10). In some cases, recurring intervals were estab- ment PM program in Colorado (Galehouse 2004). The recom- lished (e.g., reseal joints every 7 years). This is also referred to by mended RSL criteria for various HMA- and PCC-surfaced some agencies as cyclic maintenance. The schedule was usually treatments are listed in Table 3.1. These criteria are used in established based on information obtained from maintenance conjunction with distress index scores (discussed later in this surveys or on agency experience with the types and rates of chapter), which provide the direct tie-in needed with pave- deterioration incurred by certain pavement types. However, ment condition. whereas a schedule-based approach has the advantage of ease of With the advancements in PMSs in recent years, the iden- budgeting and programming, it often results in poor treatment tification of candidate treatments can be more closely tied choices for existing problems (Shober and Friedrichs 1998) to the existing pavement conditions. Using historical data because pavement condition is only indirectly considered on overall condition (pavement condition index/rating [PCI/ through the proxy of time. PCR]), serviceability (present serviceability index/rating A variation of the schedule-based approach is remaining [PSI/PSR]), or roughness (international roughness index service life (RSL). In this approach, a minimum time period [IRI]), performance models can be developed for groups of Existing Pavement Minimum Condition Treatment Application Remaining Window Service Life (RSL) Terminal/Threshold Condition Level Time Projected Year of Major Rehabilitation Figure 3.2. Remaining service life approach to establishing treatment application windows.
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35 Table 3.1. Recommended RSL Criteria for PM Treatments in Colorado Flexible Pavements Rigid Pavements Minimum RSL Minimum RSL Treatment (years) Treatment (years) Crack filling 9 Crack sealing 10 Crack sealing 10 Joint resealing 10 Sand seals 9 Diamond grinding 8 Chip seals 8 Partial-depth spall repair 10 Microsurfacing (single course) 12 Dowel bar retrofit 10 Microsurfacing (multiple course) 8 Full-depth concrete repair 7 Ultra-thin bonded wearing course 8 Thin HMA overlay 6 Mill and thin HMA overlay 6 Source: Galehouse 2004. similar pavements (i.e., pavement families), which can then general guidelines for establishing condition-based windows be used to set condition-based windows of opportunity for of opportunity for preservation treatments on high-traffic- individual treatment types. As overall condition, serviceability, volume facilities. or roughness is tracked at the project level, feasible treatments Two important considerations in the identification of can be identified according to the established windows of treatments based on windows of opportunity are the rate opportunity (see Figure 3.3). of deterioration and the gap between when a treatment is Overall condition, serviceability, and roughness measures selected and when it formally gets constructed. Pavements do not indicate specific pavement deficiencies or problems; showing abnormally high reductions in condition (say more they can only provide a general indication of when specific than 4 to 5 PCI/PCR points per year or more than 7 to 8 in./mi treatments should be considered for use. Hence, it is criti- (0.11 to 0.13 mm/m) of IRI per year) are likely being affected cal that they be augmented with application criteria pertaining by structural or subsurface material issues that could greatly to individual pavement distresses. The next section presents limit the effectiveness of a preservation treatment. If the gap some examples in which overall pavement condition is eval- between treatment selection and construction is expected to be uated in conjunction with detailed distress data in order to 1 year or more, the conditions of the pavement will likely have identify candidate preservation treatments. It also presents changed enough to warrant the reevaluation of treatments. Overall Condition, Serviceability, or Roughness Condition/Serviceability Trendline Appropriate Condition/ Serviceability Range Condition-Based Windows of Opportunity Appropriate Roughness Range Roughness Trendline Time Figure 3.3. Windows of opportunity based on age and overall condition.
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36 This is particularly true if the condition data upon which Table 3.2. Ohio DOT Condition Criteria a treatment was selected did not fully reflect the conditions for PM Treatments at the time of selection (i.e., the condition survey data were collected or processed several months before the evaluation Pavement Condition Rating (PCR) Rangea or selection process). Flexible Composite PM Treatment Pavements Pavements Windows of Opportunity Crack sealing 75 to 95 75 to 95 Ohio, New York, and Alberta represent agencies that use Chip seal 75 to 90 75 to 90 overall pavement condition in conjunction with detailed Microsurfacing 75 to 90 75 to 90 distress data to identify candidate preservation treatments. As (single course) seen in Table 3.2, the Ohio DOT uses PCR ranges as criterion Microsurfacing 75 to 90 75 to 90 for identifying candidate PM treatments for HMA-surfaced (double course) pavements. The PCR ranges for five of the six treatments span PMAC overlay 75 to 90 75 to 90 the same condition range defined by ODOT as good (75 to 90), Thin HMA overlay 75 to 90 75 to 90 while the range for the sixth treatment, crack sealing, extends partly into the very good condition category (90 to 100). As dis- Source: ODOT 2001. Note: PMAC = Polymer-modified asphalt concrete. cussed later, additional criteria, including detailed distress data a Condition categories listed in ODOT Pavement Condition Rating Manual: and traffic levels, are also used by Ohio in identifying candidate 90100, very good; 7590, good; 6575, fair; 5565, fair to poor; 4055, poor; treatments. 040, very poor. The New York State DOT uses a 1-to-10 surface condi- tion rating along with pavement roughness (IRI) to identify candidate treatments (preventive and rehabilitation) for high- entail light to moderate forms of rehabilitation are candidates traffic-volume roads. The performance curve and windows of for pavements with (a) condition ratings between 5.5 and 6.5 opportunity shown in Figure 3.4 provide a general basis for and IRI 95 in./mi ( 1.5 mm/m) or (b) condition ratings the treatment selection matrix, which is shown in Figure 3.5. between 6.5 and 7.5 and 96 IRI 170 in./mi (1.51 IRI Generally speaking, non-paving-type PM (i.e., crack sealing) 2.7 mm/m). is prescribed for pavements with surface ratings between The Alberta Ministry of Transportation (MOT) uses pave- 7.5 and 8.5 and any level of roughness. Paving-type PM, such ment smoothness as the first level in the hierarchy of assessing as ultra-thin and thin HMA overlays, are candidates for pave- and selecting preservation treatments (Alberta MOT 2006). ments with condition ratings between 6.5 and 7.5 and with Rural highway pavements smoother than the following IRI IRI 95 in./mi ( 1.5 mm/m). Multicourse treatments that levels are analyzed according to individual distress types, Condition Rating Do Nothing Pavement Performance Curve and 10 Windows of Opportunity Nonpaving PM 9 PM Paving 8 Multicourse 7 Major Rehab/ Recon 6 5 Time Source: NYSDOT 2008. Figure 3.4. Condition rating windows of opportunity for various forms of pavement preservation for New York highways.
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37 9+ D D D D D D Flexible Overlay 1 Crack seal 8 CIPR (not used on high 8 1 1 1 1 1 1 volume) Surf 7 5 5A 9 9 11 11 3 Thin overlay 9 Mill and fill Rating 5 6.3 mm asphalt 11 Mill and fill 6 9 9 9 11 12 12 w/underlying pvt repairs 5A 6.3 mm asphalt 12 Major rehab: 2-course 5 9 9 11 12 12 13 mill and fill OL w/repairs 6 1.5 in. hot-mix overlay 13 Reconstruction: 3-course 60 6195 96135 136170 171220 >220 OL w/repairs Ride Quality (IRI, in./mi) D Defer treatment Pavement Surface Rating Based on Frequency and Severity Descriptions Severity Frequency Moderate Very Travel Is None Slight Minor Moderate Severe Impassable to Severe Severe Impaired No distress is present. A single None 10/9 - - - - - - - - random defect per 0.10 mi is allowed. Most of pavement is free of distress. One or two cracks or distresses are Infrequent - 8 8 8 7 7 - - - visible for the next 0.10 mi. Much of pavement is free of Infrequent cracking. Large blocks of distress- to - 8 7 7 7 6 6 - - free pavement are present. occasional Much (0.5) of the pavement is cracked. Uncracked or Occasional undistressed blocks of pavement - 7 7 6 6 5 5 - - to frequent range from 20 to 30 ft/lane to 12 ft/lane. Nearly all the pavement is cracked. Uncracked or undistressed blocks of Frequent - 7 6 6 5 4 3 2 1 pavement are 12 ft2 or less. Mostly cracked. Cracks or distress Very are continuous and spaced only a few - 6 6 5 5 4 3 2 1 frequent feet apart. Slight: Cracks are tight, single, and only a few feet long. Tight, single longitudinal joint cracks, partial or continuous, are included. Minor: Cracks are generally <0.125 in. wide, some with minor secondary cracks, no or very few connected cracks. May have a few small spalls (<1 ft2). Moderate: Cracks are generally >0.125 in. wide, secondary cracking is common, some cracks connected; may have some minor popouts or small (1 to 2 ft) to medium (3 to 4 ft) patching. Moderate to Severe: Distresses vary from "moderate" to "severe." Severe: Cracks are wide and/or have extensive interconnected secondary cracking; holes, loose material, and/or patching are common; patches may have patches. Very Severe: Cracks are very wide; holes and/or patching is extensive; patches extend across the full lane or extend several feet along the lane; patches on patches are common. Travel Is Impaired: Holes in pavement are large and/or pavement has so many layers of patches that the section can be traveled only at reduced speed. Impassible: Travel by ordinary car would risk damage to the vehicle. Source: NYSDOT 2008. Figure 3.5. Treatment selection matrix used for high-traffic-volume (AADT > 20,000 vpd) HMA-surfaced Interstates and highways in New York.
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38 severities, and extents to determine candidate preservation adequately designed and constructed pavement, there is a fairly treatments: consistent pattern to distress development and to the sequence of treatments intended to address the distresses at various AADT, vpd IRI Trigger, in./mi (mm/m) points in the deterioration cycle. The pattern is as follows: <400 190 (3.0) 400 to 1,500 165 (2.6) · Within the first few years of HMA construction, various environment-related distresses often begin to develop at the 1,501 to 6,000 145 (2.3) pavement surface, causing the overall condition to reduce 6,001 to 8,000 132.5 (2.1) slightly. Preventive treatments, like crack sealing and thin >8,000 120 (1.9) surface seals, are best applied at this time in order to slow or reduce the severity of these distresses. Pavements rougher than these levels are analyzed for struc- · As environment-related distresses continue to develop and tural capacity to determine treatment thickness requirements. other non-load-related distresses emerge, a further reduction Candidate treatments are then identified based on detailed in overall condition occurs and some roughness becomes assessments of individual distress types, severities, and extents. apparent. Consequently, more significant treatments, like Depending on the structural needs and specific deficiencies chip seals and thin overlays, become more suitable for use. to be addressed, the candidate treatments may range from low- · Further distress development (and possibly the initial onset cost preventive treatments to expensive major rehabilitation of some load-related distresses) reduces the overall condition activities. Figure 3.6 illustrates the process used by Alberta. and increases roughness even more, making restorative treat- ments, such as mill-and-overlay and in-place recycling, the Guidelines for Condition-Based more appropriate preservation treatment options. · As load-related distresses become more significant, mod- Windows of Opportunity erate to major forms of pavement rehabilitation become Although overall condition, serviceability, and roughness appropriate. indicators are not indicators of the specific forms of distress that are present, they can effectively serve as preliminary identifiers Using the information just presented and the following of candidate preservation treatments. This is because for an categories of PCI (USACE et al. 2004) and IRI (FHWA 2002), Segment smoother than IRI (ride level) Segment rougher than trigger value trigger value 20-year structural overlay requirement--OL (20 yr) OL (20 yr) > 40 mm OL (20 yr) < 40 mm 40 mm < OL (20 yr) < 70 mm 70 mm < OL (20 yr) < 90 mm OL (20 yr) 90 mm Preventive maintenance Preventive maintenance HIR OL (20 yr) Thin OL Thin OL Mill and inlay HIR HIR OL (10 yr) Mill and inlay Mill and inlay IL (20 yr) Two-lift OL OL (10 yr) IL (20 yr) Environmental/construction Traffic/load distresses distresses Potholes, dips, heaves, and Transverse Longitudinal Segregation Ravel local distortion cracks centerline cracks Rutting Longitudinal wheelpath Wheelpath fatigue cracks flushing/bleeding Source: Alberta MOT 2006. Figure 3.6. Alberta guidelines for assessing pavement preservation treatments and strategies.
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39 Table 3.3. Recommended PCI Windows of Opportunity for Pavement Preservation Treatments HMA-Surfaced Pavements PCC-Surfaced Pavements Treatment PCI Window Treatment PCI Window Crack fill 75 to 90 Concrete joint resealing 75 to 90 Crack seal 80 to 95 Concrete crack sealing 70 to 90 Slurry seal (Type III) 70 to 85 Diamond grinding 70 to 90 Microsurfacing, single 70 to 85 Diamond grooving 70 to 90 Microsurfacing, double 70 to 85 Partial-depth concrete patching 65 to 85 Chip seal, single Conventional 70 to 85 Full-depth concrete patching 65 to 85 Polymer modified 70 to 85 Chip seal, double Conventional 70 to 85 Dowel bar retrofitting 65 to 85 Polymer modified 70 to 85 Ultra-thin bonded wearing course 65 to 85 Ultra-thin bonded wearing course 70 to 90 Ultra-thin HMAOL 65 to 85 Thin HMA overlay 70 to 90 Thin HMAOL 60 to 80 Cold milling and thin HMAOL 60 to 75 Hot in-place recycling Surf recycle and HMAOL 70 to 85 Remixing and HMAOL 60 to 75 Repaving 60 to 75 Cold in-place recycling and HMAOL 60 to 75 Profile milling 80 to 90 Ultra-thin whitetopping 60 to 80 Note: HMAOL = Hot-mix asphalt overlay. some basic guidelines for condition-based windows of oppor- treatment selection. Agency practices and experiences will tunity have been developed and are presented in Table 3.3: generally dictate any adjustments or refinements that need to be made. Condition Description PCI Good 86 to 100 Detailed Assessment of Satisfactory 71 to 85 Treatments and Deficiencies Fair 56 to 70 Because preservation treatments address pavement deficien- IRI, in./mi (mm/m) Condition Description cies to varying degrees and no one treatment is best suited to <95 (<1.5) Good ride quality and all conditions, a detailed assessment is needed that matches good condition treatment capabilities with existing deficiencies. Ideally, this 95 to 119 (1.5 to 1.88) Acceptable ride quality, assessment should consider not only the specific distress types fair condition present and their causes but also the severity and extent of each 120 to 170 (1.9) Acceptable ride quality, observed distress. Moreover, it should consider important mediocre condition functional performance attributes, such as friction, splash- spray, and pavement-tire noise. The windows of opportunity listed in Table 3.3 can be Two approaches for identifying feasible preservation treat- considered as starting points or reference values for agencies ments based on existing pavement deficiencies are decision sup- that have not developed formal criteria for preservation port matrices and decision support trees. Both approaches rely
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40 Table 3.4. Example Decision Support Matrix for Identifying Flexible Pavement PM Strategies Seal Coat Slurry Seal Microsurfacing Rut Depth 1. Traffic Treatment 1 in. ADT < 2000 R R R 0.5 in. 2000 > ADT Microsurfacingc One course Scratch Rut box and Multiple < 5000 Ma Ma R course final surface placement ADT > 5000 NR NR R and final with rut 2. Bleeding R R R surface box 3. Rutting NR R R Slurry seald One course One course Microsurfacing See note e scratch course 4. Raveling R R R and final 5. Cracking surface Few tight cracks R R R Extensive cracking R NR NR 6. Improving friction Yes Yes Yesb 7. Snowplow Most Moderately Least damage susceptible susceptible Susceptible Source: Jahren et al. 2000. Courtesy of Center for Transportation Research and Education, Iowa State University. Note: R = Recommended; NR = Not recommended; M = Marginal. a There is a greater likelihood of success when used in lower-speed traffic. b Microsurfacing reportedly retains high friction for a longer period of time. c As recommended by International Slurry Seal Association. d Current practice in Iowa. e Sometimes successful (anecdotal evidence). on a set of rules and criteria to identify appropriate preservation · Difficult to develop matrix that can incorporate multiple treatments; the former uses a tabular structure like the one pavement distress types (i.e., do not always address the shown in Table 3.4 and the latter, a more systematic graphical actual distress conditions); approach like the one illustrated in Figure 3.7 (Peshkin and · Generally only designed to focus attention on one or two Hoerner 2005). treatments that have worked well in the past and tend to The benefits and limitations of these approaches were ignore or overlook new or improved treatments that may previously identified by Hicks et al. (2000) as follows: be more effective; · Do not include more comprehensive evaluation of various Benefits feasible alternatives and life-cycle cost analysis (LCCA) to · Make use of existing experience; determine the most cost-effective strategy; and · Work well for local conditions; · Not good for network evaluation. · Good as project-level tools; · Reflect decision processes normally used by an agency; The last two limitations listed are not relevant in the present · Flexible in modifying both the decision criteria and the study because the treatment selection framework and method- associated treatments; ology developed and presented in this report are intended for · Generate consistent treatment recommendations; and use at the project level and include a cost-effectiveness analysis · Explain and program selection process with relative ease. component. The rules and criteria behind decision support matrixes Limitations or trees are based on an understanding (from past experience · Not always transferrable from agency to agency; or historical performance data) of the ability of individual · May be more difficult to innovate or introduce new treatments to fix or mitigate specific distresses. As illustrated treatments; in Figure 3.8, a key step in developing rules and criteria is to · Hard to incorporate all important factors (e.g., competing evaluate the primary purposes and functions of treatments in projects, functional classification, remaining life); relation to the factors and causes of individual distresses, the
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41 Structural M&R Surface Wear Environmental Deterioration Fatigue Cracking Rutting M&R Treatment Severity Cracking Extent Extent Severity Treatment Crack Low Low Mill/Fill Seal 40 mm Surface Moderate Low Low Moderate Mill/Fill Treatment 50 mm Crack Seal and High High Mill/Fill 40-mm OL 75 mm Crack Low Low Mill 50 mm Seal 75-mm OL Crack Seal and Moderate Moderate No Yes Moderate Moderate Mill 75 mm 40-mm OL 100-mm OL Mill/Fill High High Mill 100 mm 50 mm 125-mm OL Mill/Fill Low Low Mill 100 mm 50 mm 150-mm OL Mill/Fill Moderate High High Moderate Rem HMA, Repl 50 mm Base, Repave Mill/Fill High High Total 50 mm Reconstruct Source: Hicks et al. 1999. Figure 3.7. Example decision support tree for identifying flexible pavement preservation and rehabilitation strategies. Treatment Purposes/Functions Treatment Prevent/delay Slow/reduce rate Restore integrity Types distress of distress and functionality of development development pavement Causes/Factors Causes/Factors Environmental effects Distresses Traffic loading effects (temp, moisture, UV) (frequency, intensity, type) Causes/Factors Causes/Factors Material deficiencies Structural (design/construction inadequacies related) (design related) Subgrade Figure 3.8. Matching of treatments with distress types through evaluation of treatment purposes/functions and distress causes/factors.