Consideration of Preservation in Pavement Design and Analysis Procedures (2015)

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4C H A P T E R 2 This chapter summarizes the state of the practice of pave- ment preservation and the MEPDG design analysis process as gleaned from a literature review and interviews with SHA and industry personnel. The summary covers items of rele- vance to the development of approaches for considering the effects of preservation in the MEPDG procedures, includ- ing (1) preservation programs and practices, (2) pavement and preservation treatment performance analysis tech- niques, and (3) preservation consideration in the MEPDG procedures. Literature Review The literature review focused on (1) highway pavement preservation activities and their effects on pavement perfor- mance and (2) MEPDG performance prediction models and their refinements and local calibrations. The review was lim- ited to studies undertaken in the previous 5 to 7 years and tar- geted mostly domestic sources, including NCHRP and TRB, AASHTO, Federal Highway Administration (FHWA) and National Highway Institute, selected state departments of transportation (DOTs), national pavement research programs and centers (e.g., Innovative Pavement Research Foundation, Airfield Asphalt Pavement Technology Program, National Center for Asphalt Technology [NCAT], and National Con- crete Pavement Technology Center), pavement preservation organizations (e.g., Foundation for Pavement Preservation and National Center for Pavement Preservation [NCPP]), and industry associations (e.g., National Asphalt Pavement Asso- ciation [NAPA], American Concrete Pavement Association [ACPA], International Slurry Surfacing Association [ISSA], and Asphalt Emulsion Manufacturer’s Association [AEMA]). A bibliography of the identified documents is provided in Appendix A. Summaries of the effects of several HMA and PCC preservation treatments are provided in Appendices B and C, respectively. Two syntheses, one on pavement pres- ervation and the other on the MEPDG, are provided in Appendices D and E, respectively; key aspects are presented in this chapter. SHA and Industry Group Interviews The literature review was supplemented with interviews of SHAs and industry groups. The SHA interviews provided information regarding pavement preservation policies and practices, agency perspectives on the effects of preservation on pavement performance, current pavement design procedures, MEPDG implementation status and activities (past, current, and future), and procedures used to consider preservation in the pavement design/analysis process. The industry group interviews provided information on the industry’s involve- ment with pavement preservation and the MEPDG. SHA Interviews SHAs active in developing pavement preservation programs or evaluating or implementing the MEPDG were identified. These agencies were evaluated with consideration to (1) extent of preservation practice and level of agency experience with preservation; (2) extent of involvement in MEPDG evalua- tion, implementation, and use (particularly as it relates to local calibration and the incorporation of preservation into the MEPDG); and (3) likely availability of the data needed to evaluate the effects of preservation on pavement performance. Fourteen agencies (from Arizona, California, Indiana, Kansas, Maryland, Minnesota, Missouri, New Jersey, North Carolina, Ohio, Texas, Utah, Virginia, and Washington State) were then selected for interviews. Interview participants were identified through discussions with SHA staff; they represented the areas of maintenance/ State of the Practice

5 preservation, pavement design, pavement management, or research. The interviews addressed the following topics: • Background, nature, and status of the agency’s pavement preservation program. • Scope of the agency’s preservation program. • Extent of the agency’s tracking of the performance of pres- ervation treatments. • Agency’s current pavement design procedure (if not MEPDG). • Status of the agency’s MEPDG implementation effort. • Agency’s desire for enabling the MEPDG analysis proce- dure to consider the effects of preservation treatments on pavement performance. • Availability of performance data (with and without preser- vation) and other data (design, construction/materials, traf- fic, climate, etc.) that can be used in developing procedures for considering preservation in the MEPDG procedures. Interview questions and responses are provided in Appen- dix F; key findings from the interviews are discussed in this chapter. Industry Group Interviews Representatives from five industry groups (ACPA, NAPA, AEMA, ISSA, and NCPP) were interviewed to determine their organization’s (1) familiarity and involvement with pavement preservation practices, (2) level of involvement with SHAs in evaluating preservation treatment performance and developing preservation and practices, and (3) familiarity and involvement with the MEPDG. The questions and responses are provided in Appendix G; key findings from the interviews are discussed in this chapter. Pavement Preservation Programs and Practices This section describes SHA preservation programs and practices; specifically, the types of treatments and their rela- tive levels of use as well as the conditions for their use. Cuelho et al. (2006) conducted a survey of 34 SHAs and five Canadian provincial highway agencies (PHAs) to estab- lish the frequency of using each of 16 preventive mainte- nance treatments for flexible pavements. Participants were asked to rate on a scale of 1 to 5 how often they use each treatment (1 being “never” and 5 being “always”); the mean ratings and corresponding rankings are listed in Table 1. As noted, the most frequently used treatments were crack seal- ing, thin HMA overlay, chip seal, maintenance of drainage features, and microsurfacing. A survey of U.S. and Canadian highway agencies con- ducted in 2009 (Peshkin et al. 2011a; Peshkin et al. 2011b) provided updated information on pavement preservation programs and practices for all facility types and traffic levels (low, medium, and high) as defined by the agency. Treatment Count Percent1 Mean St. Dev. Don’t Know Never Heard of It Overall Rank Crack Seal 43 91.5 3.67 0.808 0 0 1 Fog Seal 43 91.5 1.77 0.718 0 0 11 Cape Seal 44 93.6 1.25 0.508 5 7 15 Chip Seal 44 93.6 3.20 1.286 0 0 3 Ultrathin Friction Coarse 43 91.5 1.92 0.784 2 3 9 Slurry Seal 44 93.6 1.74 0.621 1 0 12 Scrub Seal 43 91.5 1.24 0.435 1 9 16 Thin Overlay (with or without mill) 44 93.6 3.66 0.805 0 0 2 Microsurfacing 44 93.6 2.46 0.926 0 0 5 Hot In-Place Recycling 43 91.5 1.81 0.824 0 0 10 Cold In-Place Recycling 44 93.6 1.98 0.902 0 0 8 PCCP Diamond Grinding 44 93.6 2.38 1.011 2 0 6 PCCP Diamond Grooving 43 91.5 1.54 0.600 4 0 14 PCCP Undersealing 44 93.6 1.69 0.863 4 1 13 PCCP Dowel Retrofit 43 91.5 2.10 1.020 2 0 7 Maint. of Drainage Features 44 93.6 2.63 0.952 1 0 4 Note: 1 Out of 47 responses. Table 1. Frequency of use of preventive maintenance treatments for flexible pavements (Cuelho et al. 2006).

6The survey (Peshkin et al. 2011a) provided information about treatment usage by pavement type (asphalt-surfaced or concrete-surfaced pavements) and highway setting (urban versus rural). The most extensively used treatments (≥67% of responding agencies) for asphalt-surfaced pavements, considering all traffic ranges and both urban and rural set- tings, were crack filling, crack sealing, and drainage preser- vation, and the moderately used treatments (33% to 66% of respondents) were thin HMA overlays, with and without milling. For concrete-surfaced pavements, the most exten- sively used treatments were crack sealing, diamond grinding, and full-depth patching, and the moderately used treatments were joint resealing, partial-depth patching, dowel-bar retro- fit, and drainage preservation. This survey also indicated that some treatments, such as microsurfacing, chip seals, ultrathin whitetopping, and dowel-bar retrofit, were less commonly used on higher-trafficked roads due in part to expected dura- bility issues. Another survey (Peshkin et al. 2011b) indicated less use of some treatments, such as slurry seals, microsurfac- ing, thin and ultrathin HMA overlays, joint resealing, diamond grinding, and diamond grooving, in more severe climates (e.g., deep freeze). Considerations in selecting preservation treatments were safety concerns (76% of respondents), treatment cost (74%), and durability/expected life of treatment (64%) (Peshkin et al. 2011a). The primary asphalt-surfaced pavement deficiencies addressed by preservation were light and moderate surface dis- tress (e.g., surface cracks, raveling/weathering, and bleeding) and friction loss. For concrete pavements, the primary perfor- mance issues addressed by preservation were smoothness/ride quality, light surface distress, friction loss, and noise. The interviews revealed that most agencies equate preserva- tion with preventive maintenance, but some agencies classify preservation as including a broader set of activities, ranging from preventive maintenance to major rehabilitation and even reconstruction. In some cases, the definition of preservation is most closely linked to allowable treatments from a funding perspective rather than a program approach. A few agencies have an official preservation program, and one or more staff are designated as preservation engineers. The interviews also indicated that preservation treatments are applied to all types and classes of roads, usually guided by criteria that define the treatments that can be applied to a specific pavement type under specific conditions (e.g., traf- fic levels, existing pavement conditions). The use of preserva- tion treatments varies among agencies; some only use a few treatments, and others use many different treatments (various combinations of HMA mix types, HMA overlay thicknesses, milling depths, and recycling options). The most commonly used treatments for asphalt-surfaced pavements are crack sealing, chip seals, microsurfacing, and thin HMA overlays. For concrete-surfaced pavements, the most commonly used treatments are diamond grinding, partial-depth repair, and full-depth repair. Pavement and Preservation Treatment Performance Treatment performance is a major consideration in account- ing for the effects of future scheduled preservation in pavement design. This section presents findings from SHA studies to assess treatment performance and its effects on pavement con- dition over time and pavement life. Information is provided on the types of preservation that have been studied, the nature of the sources for the studies (i.e., experimental or test sections, in-service pavement management system [PMS] sections), the methods used to evaluate performance (i.e., performance of treatment versus treated pavement, performance measures used), and the experiences in developing performance trends or models that could be used in mechanistic-empirical pave- ment design procedures. Cuelho et al. (2006) reported on several preservation perfor- mance studies conducted throughout North America between 1989 and 2005. They described the applied treatments and their advantages/disadvantages and reported the expected performance lives of each treatment. Although some of the studies included monitoring of pavement performance (e.g., roughness, cracking, rutting, and raveling), performance was generally reported in terms of treatment service life (i.e., how long a treatment lasts) or, in a few cases, the pavement life or the extension in pavement life as a result of the treatment). In several pavement performance studies undertaken since 2005, condition data were collected and analyzed to assess performance and estimate pavement life extension (a sum- mary is provided in Appendix D). Many of these studies eval- uated in-service pavement sections on which preservation treatments were applied or included the design, construction, and performance monitoring of test sections. More recent studies have focused on in-service sections and less on experimental sections. Evaluations of in-service sec- tions are ongoing or recently completed in California, Illinois, Michigan, Louisiana, Indiana, and New England. Other recent in-service pavements are LTPP surface maintenance (Morian et al. 2011), Oklahoma pavement retexturing experiments (Gransberg et al. 2010), Minnesota DOT (MnDOT) flexible and rigid pavement preservation treatment test sections at the MnROAD test facility (MnDOT 2011), and the NCAT test site with 23 short sections of different flexible pavement preservation treatments (NCAT 2013). The most common methods for assessing treatment per- formance are treatment service life, pavement life extension, and performance benefit area. Treatment Service Life: Treatment service life refers to how long a treatment serves its function until a subsequent preser-

7 vation and rehabilitation (P&R) treatment will be needed to address one or more issues (e.g., raveling, rutting, smoothness, and friction) that have reached a specified condition threshold. Treatment service life can be estimated from analysis of historical P&R events or performance data. When consid- ering historical P&R event data, the years in which pres- ervation and other treatments were applied are identified, and the ages of the various applied treatments are com- puted, statistically analyzed, and presented in the form of (1) descriptive statistics (e.g., mean, standard deviation) of age at time of subsequent P&R, (2) frequency distribution plots that show the number of sections as a function of age (or traffic) that have failed (i.e., replaced with a P&R treat- ment), and (3) cumulative frequency distribution plots (i.e., failure curves or, alternatively, survival curves) that show the percentages of sections as a function of age (or cumula- tive traffic) that have failed. When considering historical performance of a specific treatment, post-treatment time-series (or traffic-series) per- formance data (e.g., individual distresses, smoothness, over- all condition ratings, composite condition indexes, friction, texture) are collected and statistically analyzed. Data may be presented in the form of plots of performance over time (or cumulative traffic) that show the time until a subse- quent P&R treatment was applied (Scenario 1A in Figure 2) or the time until a specified condition threshold (consid- ered unacceptable) is reached or is projected to be reached (Scenario 1B in Figure 2). Data may also be presented in the form of (1) descriptive statistics, (2) frequency distribution plots, or (3) cumulative frequency distribution plots. Pavement Life Extension: Pavement life extension is expressed in terms of the number of years of additional pavement life attributed to treatment application. The added life may be estimated based on structural or functional performance, as characterized by key surface distresses (e.g., cracking, rutting, faulting, punchouts, raveling, and spalling), or as characterized by key pavement surface characteristics (e.g., smoothness, friction, texture, and pavement-tire noise). Because pavement life extension is related to the perfor- mance of the pavement without a preservation treatment, pre-treatment pavement condition is required for deter- mining the life extension. Pavement life extension can be estimated from analysis of historical performance data of a specific treatment. Both pre- treatment and post-treatment time-series (or traffic-series) performance data (e.g., individual distresses, smoothness, over- all condition ratings, composite condition indexes, surface characteristics [e.g., friction, texture], and deflection proper- ties) are collected in the form of (1) plots of performance over time (or cumulative traffic) that show the time until the immediate pre-treatment condition level was reached or is projected to be reached (Scenario 2A in Figure 2), (2) plots of performance over time (or cumulative traffic) that show the time until the specified condition threshold level was reached Figure 2. Preservation treatment life and pavement life extension. Adapted from Peshkin et al. 2011a, Sousa and Way 2009a, and Rajagopal 2010. (2A) Pavement Life Extension based on immediate pre-treatment condition level (2B) Pavement Life Extension based on specified condition threshold level Unacceptable Condition Threshold Level (repair/rehab trigger) Pavement Condition Time, years Application of Preservation Treatment Immediate Pre-Treatment Condition Level Existing Pavement Structure Very Poor Very Good Subsequent Preservation or Rehab Treatment (1B) Treatment Life based on specified condition threshold level (1A) Treatment Life based on subsequent preservation or rehab treatment

8or is projected to be reached (Scenario 2B in Figure 2), and (3) descriptive statistics, frequency distribution plots, or cumu- lative distribution plots of pavement life extension. Performance Benefit Area: The benefit provided by a treat- ment may be measured by the area under the pavement age versus performance curve (based on structural or functional performance) contributed by the treatment (i.e., above that provided by the untreated pavement). The performance ben- efit area can only be obtained through an analysis of historical performance data for both pre-treatment and post-treatment time-series (or traffic-series) pavement performance data (e.g., individual distresses, smoothness, overall condition ratings, composite condition indexes, surface characteristics [e.g., friction, texture], and deflection properties) that are col- lected for a particular preservation treatment type. The data are then statistically analyzed and presented in the form of (1) plots of performance over time (or cumulative traffic) that show the area bounded by the performance curves of the treated and untreated pavements and a specified condition threshold level (Scenario 3 in Figure 3), and/or (2) descriptive statistics of the performance benefit areas. The responses indicated that pavement performance is monitored by most of the interviewed states, although some states have had problems either in tracking the locations of preservation treatment projects or reliability of the collected performance data. Experience in evaluating treatment per- formance data or developing treatment performance models varied among agencies. Treatment performance has generally been evaluated in terms of treatment life (based on experi- ence, time between applications, or time until surface con- dition has returned to the pre-treatment level) and not in terms of effect on pavement life. Performance models have been developed for use in pavement programming; details are provided in Appendix F. Preservation and the MEPDG Consideration of preservation in the MEPDG has been noted in only three of the reviewed reports. Banerjee et al. (2010) used data from 13 LTPP Specific Pavement Studies 3 (SPS-3) test sections to develop local calibration factors for the MEPDG HMA rutting model that account for the combined effects of preservation treatment and climate. In the local calibration of the MEPDG HMA performance models, Von Quintus and Moulthrop (2007) used data from 102 pavement sections to demonstrate the value of separate fatigue cracking model calibration factors for sections with and without pres- ervation treatments. California DOT (Caltrans) developed a tool to account for the effects of preservation in pavement design by (a) resetting distress and smoothness levels when a treatment is scheduled and (b) adjusting pavement structure moduli corresponding to scheduled preservation treatments (Ullidtz et al. 2010). Further details of these studies are pro- vided in Appendix E. Adapted from Peshkin et al. 2004. (3) Performance Benefit Area based on area bounded by treated and untreated pavement condition curves and specified condition threshold level Unacceptable Condition Threshold Level (repair/rehab trigger) Pavement Condition Time, years Application of Preservation Treatment Immediate Pre-Treatment Condition Level Existing Pavement Structure Very Poor Very Good Performance Benefit Area Figure 3. Preservation treatment effectiveness as indicated by the performance benefit area.

9 Most of the interviewed SHAs did not consider pavement preservation in the design procedure. However, Minnesota noted that preservation treatments probably have been applied to all pavement sections used in the development of perfor- mance models for the R-value and Mn/Pave design procedures. Some agencies suggested that preservation can be considered in rehabilitation design by adjusting the structural coefficient values of the existing pavement layers in the AASHTO design procedure. California’s CalME program allows consideration of the effects of preservation on pavement performance by resetting certain distresses to zero at the year of treatment application (e.g., a thin overlay applied at year 10 reduces rutting to zero at that year). The program’s incremental-recursive function also allows changes to asphalt material properties (e.g., dynamic modulus) to account for the effect of preservation treatments (e.g., a rejuvenator would soften the existing asphalt surface, and a seal coat would reduce the rate at which the existing asphalt surface hardens). Most SHAs reported issues or limitations with the data needed for developing models that consider the effects of pres- ervation in the design procedures. These limitations included compatibility between the agency PMS data and the MEPDG input data, pavement section location, availability of historical performance data, and availability of untreated sections for direct comparison with preservation-treated sections.