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10 More than 100 documents were identified and compiled Table 2.1. Common Pavement for use in this study, either in electronic or hardcopy form. Preservation Treatments Each of the selected documents was catalogued and reviewed in greater detail. HMA-Surfaced Pavements PCC-Surfaced Pavements Appendix A contains an annotated bibliography of several Crack fill Joint resealing key documents. Key aspects of the literature review are included Crack seal Crack sealing in the summary provided later in this chapter. Cape seal Diamond grinding Fog seal Diamond grooving Survey of Practice Scrub seal Pavement patching The literature search was supplemented with an electronic Partial depth Slurry seal Full depth questionnaire distributed to SHAs, Canadian provinces, high- Rejuvenators Dowel bar retrofit way agencies of several large cities, international practitioners, Microsurfacing (i.e., load transfer restoration) and several industry representatives. The purpose of this Single course Thin PCC overlay survey was to identify pavement preservation practices on rural Multiple course and urban roadways, distinguished by surface type--HMA Chip seal Ultra-thin bonded wearing course or PCC--and high traffic levels (as defined by the reporting Single course agency). The survey focused on the following topics: Multiple course Thin HMA overlay (<1.5 in.) With polymer-modified binder Drainage preservation · Successful techniques for pavement preservation on high- Ultra-thin bonded wearing course traffic-volume roadways currently in use; Thin HMA overlay (<1.5 in.) · Potentially successful techniques for pavement preservation Cold milling and thin HMA overlay approaches that are not yet fully deployed; Ultra-thin HMA overlay (<0.75 in.) · Challenges and solutions to implementation on high-traffic- In-place HMA recycling volume roadways; and Hot (<1.95 in.) · Special considerations for quality control and quality assur- Cold (<4.0 in.) ance (QC/QA). Profile milling (diamond grinding) Ultra-thin whitetopping Recognizing that the definition of "high-traffic-volume roadways" is perhaps as much or more a matter of perception Drainage preservation as it is a matter of policy, the survey also asked the respondents Note: 1 in. = 25.4 mm to define what traffic volumes fell in that category for them. The questionnaire included the preservation treatments shown in Table 2.1. It called for respondents to link these Analysis and Summary treatments to roadways, differentiating by traffic volume and of Collected Information rural-versus-urban route, as well as matching closure time scenarios to treatment, indicating which pavement perfor- Literature Review mance issues are addressed by each treatment, and which This section provides a summary of the pertinent literature contracting mechanisms are used to ensure quality. Further- reviewed in the first phase of the study. The information more, it sought feedback concerning why certain treatments presented is intended to familiarize the reader with the key are not used by the responding agency (e.g., lack of experience, aspects regarding the use of preservation treatments on bias against, previous failures, cost, safety issues, and so on). high-traffic-volume roadways. The information was used To reduce the time required to fill out the 24-page question- in conjunction with information from additional pieces of naire, it was developed and administered using InstantSurvey, literature collected in the second phase of the study to aid the an online software tool that creates, distributes, manages, and development of the preservation guidelines featured in Guide- analyzes online surveys. The time period required for complet- lines for the Preservation of High-Traffic-Volume Roadways. ing the survey was approximately 8 weeks. The complete survey is provided in Appendix B, and a Pavement Preservation Overview detailed breakdown of the responses is provided in Appendix C. Key aspects of the survey results are included in the summary One definition of pavement preservation is that it is a planned provided later in this chapter. system of treating pavements at the optimum time to maximize
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11 Table 2.2. Classification of Pavement Activities by Purpose Purpose of Activity Restore Surface Improve or Restore Type of Activity Increase Capacity Increase Strength Slow Aging Characteristics Functionality New construction X X X X X Reconstruction X X X X X Major (heavy) rehabilitation X X X X Structural overlay X X X X Minor (light) rehabilitation X X X Preventive maintenance X X X Routine maintenance X Corrective (reactive) maintenance X Catastrophic maintenance X Source: Adapted from Geiger 2005. their useful life, thus enhancing pavement longevity at the to trigger major rehabilitation. Pavements at this condition lowest cost (Kuennen 2006b). It represents a proactive approach level receive minor rehabilitation treatments, such as thin to maintaining existing highway pavements that enables high- overlays or surface recycling, that restore functional qualities way agencies to reduce costly, time-consuming rehabilitation and, to a limited extent, structural integrity. The use of PM and reconstruction projects and the associated traffic disrup- treatments and minor rehabilitation techniques along with tions (Geiger 2005). routine maintenance are good options for a pavement that is Table 2.2 illustrates various pavement activities and their still in relatively good condition. primary purpose. The three shaded rows represent pavement If PM or minor rehabilitation is not used during the life of the preservation, indicating that it is composed of PM, some forms pavement, the pavement will deteriorate to the point that major of minor (nonstructural) rehabilitation, and some forms of rehabilitation (structural restoration, such as full-depth repairs routine maintenance (Geiger 2005). The darker shading or thick overlays, or even reconstruction) is necessary. When a indicates that PM is the primary component of pavement pavement develops significant levels of distress, pavement preservation. The general philosophy of pavement preserva- preservation activities are no longer viable treatment options. If tion is to apply preventive (actions intended to prevent, stop, PM or minor rehabilitation is used on a pavement that is highly or slow down deterioration), restorative (actions intended to deteriorated, the life of the chosen treatment can be greatly improve conditions or restore conditions to acceptable levels), reduced, especially on pavements with high traffic volumes. or limited corrective (actions intended to fix defects or reestab- lish structural integrity) treatments to pavements that are in Preventive relatively good condition and have little or no structural dete- Maintenance Preservation Good rioration. Application of the right treatment at the right time and in the right manner can help prolong the service life of the pavement. Incidentally, this is especially important for Reconstruction high-traffic-volume roadways where construction delays have Minor a large impact on users. Rehab Major One of the keys to an effective pavement preservation pro- Rehab gram on high-volume roadways is understanding pavement Rehabilitation performance. The typical life cycle of a pavement and the gen- Poor Routine/Corrective Maintenance eral categories of treatments that are appropriate at different times of the life of the pavement are presented in Figure 2.1. PM is used early in the life of the pavement, while the pavement Time (years) Source: Adapted from Peshkin et al. 2007. is still in good condition. When a pavement has deteriorated so that more extensive cracking and other distresses are present, Figure 2.1. Relationship between pavement condition the use of PM is no longer appropriate, but it could be too soon and different categories of pavement treatment.
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12 Preservation Treatments surface seals are most appropriate for pavements in good to very good condition, while preventive or restorative measures There is a broad range of treatments that may be used in the like thin HMA overlays, proprietary surfacings, and patching preservation of pavements. While many may focus on a specific are most appropriate for pavements in fair to good condition. treatment and its role in preservation, it is not the treatment More extensive restorative treatments like mill-and-HMA alone that defines preservation. Considering Table 2.2 and overlay, ultra-thin whitetopping, thin PCC overlays, and Figure 2.1, both the purpose and timing of the treatment help partial-depth recycling (i.e., hot in-place recycling [HIR] and define a preservation treatment. With that caveat, descriptions cold in-place recycling [CIR] confined to surface, intermediate, of treatments that are commonly used in pavement preservation or upper-base layers) are most appropriate for pavements in are provided in the Guidelines for the Preservation of High- fair condition. Traffic-Volume Roadways. The selection of appropriate preservation treatments is based In addition to the treatments listed in the Guidelines for not only upon the overall condition of the roadway, but also the Preservation of High-Traffic-Volume Roadways, drainage the specific visible distresses. For instance, if transverse crack- preservation is a treatment that can be carried out on both ing in an HMA-surfaced pavement is frequent but there is not HMA- and PCC-surfaced pavements. This activity consists of a high degree of edge deterioration, the pavement may be cleaning silt, debris, and vegetation at underdrain outlets and best treated with a surface treatment. If the cracks are low to replacing damaged or destroyed outlets. Although not directly moderate in frequency but have typically progressed to a point applied to the pavement structure, it is considered by many of high edge deterioration, then crack repair or patching may to be an essential tool in the preservation of the pavement, as be needed. In the case of pavements with transverse thermal or it helps to ensure adequate drainage of the structure. reflection cracks that are moderate in density and have little A few other types of preservation treatments were identified or no deterioration, the cracks can be treated effectively through and examined as part of the literature review. These treat- sealing operations. For pavements with a substantial amount of ments fall under one or another of the following categories: nonworking cracks (primarily longitudinal, but also transverse) (a) lengthy existence but limited overall use; (b) lengthy exis- with different size openings and relatively low levels of dete- tence but use limited to one or two agencies; (c) international rioration, an appropriate treatment is crack filling. use, with recent trials in the United States; or (d) new or inno- Thin HMA overlays are used on all types of roadways for vative, with recent trials in the United States. Known details functional improvements. The pavement to be restored using regarding each of these treatments are provided below. thin HMA overlays should be in good to fair condition. This Each preservation treatment has unique capabilities and type of treatment is particularly suitable for high-volume functions that enable them to accomplish the following: roads in urban areas where longer life and relatively low-noise surfaces are desired. Similarly, slurry seals do not usually per- · Prevent or delay the occurrence of new distresses or slow form well if the underlying pavement contains extensive cracks. the development of existing distresses; or According to the South Dakota DOT, slurry seals should not · Restore the integrity and functionality or serviceability of be used on deteriorated pavements. Chip seals, on the other the pavement or improve its surface characteristics. hand, can be applied during the majority of a pavement's life (Johnson 2000). However, the ideal benefits of chip sealing The primary means by which the treatments can achieve are achieved when the treatment is applied early. For instance, these goals are summarized in Tables 2.3 and 2.4. chip sealing can be used when the pavement has just begun to oxidize, and should not be applied to pavements with distress such as high-severity cracking, raveling, potholes, or rutting. Preservation Treatments and Existing Additionally, for the use of thin HMA overlays, cracking Pavement Condition should be of low to moderate severity and ideally should have The condition of a pavement has a significant impact on the been crack-sealed 6 to 12 months prior to the thin overlay ability of treatments to fulfill their respective goals, and so their application. Raveling should be of low to moderate severity, effectiveness is fairly variable. By the same token, a treatment with depressions caused by stripping of the surface no greater will not be very effective if the pavement condition is too good, than 0.25 in. (6 mm) deep. In addition, it is recommended to although that "problem" is rarely encountered. mill the surface before an overlay application when segregation, While it is difficult to establish optimal timings (in terms of raveling, or block cracking are present (Hein and Croteau 2004). the overall condition of the existing pavement) for the appli- If rutting is evident, the pavement can also receive a leveling cation of individual treatments, the timings of treatments course instead of milling. grouped according to similar goals and purposes are easier to Also identified in the literature search, ultra-thin bonded construct. Preventive treatments like joint or crack sealing and wearing course applications are typically used to seal the surface
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Table 2.3. Primary Capabilities and Functions of Preservation Treatments for HMA-Surfaced Pavements Prevention Restoration Improve Profile Seal/Waterproof Rejuvenate Surface/ Eliminate Eliminate Improve Texture (Lateral Surface Improve Texture Treatment Pavement Inhibit Oxidation Surface Defectsa Stable Ruts for Friction Drainage and Ride) for Noise Crack filling Crack sealing Cold milling Profile milling Rejuvenation Fog seal Scrub seal Slurry seal Microsurfacing Sand seal Chip seal (minor) Ultra-thin HMAOL Ultra-thin bonded wearing course Thin HMAOL Dense-graded Open-graded (OGFC)b Gap-graded (SMA) Mill and thin HMAOL Hot in-place recycling Surface recycling Remixing Repaving Cold in-place recycling Ultra-thin whitetopping Source: Modified from KYTC 2009. Note: HMAOL = Hot-mix asphalt overlay; OGFC = Open-graded friction course; SMA = Stone matrix asphalt. a Surface defects include weathering/raveling, bleeding, polishing, surface cracks, and so on. b Improves splash/spray. 13
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14 Table 2.4. Primary Capabilities and Functions of Preservation Treatments for PCC-Surfaced Pavements Prevention Restoration Prevent Improve Profile Seal/Waterproof Intrusion of Remove/Control Improve Texture (Lateral Surface Improve Texture Treatment Pavement Incompressibles Faulting for Friction Drainage and Ride) for Noise Crack sealing Joint resealing Diamond grinding Diamond grooving Partial-depth patching Full-depth patching a a Dowel bar retrofit Ultra-thin bonded wearing course Thin HMAOL Thin PCCOL Source: Modified from KYTC 2009. Note: HMAOL = Hot-mix asphalt overlay; PCCOL = Portland cement concrete overlay. a In conjunction with diamond grinding. to minimize weathering, raveling, and oxidation. Candidate associated with drainage improvement, dowel bar retrofitting, roads for this treatment usually should have ruts less than and undersealing. 0.5 in. deep, moderate to no cracking, and minor to no bleed- Regarding the use of diamond grinding on concrete pave- ing. In contrast, slurry seals are used to seal the surface of the ments, the pavement should not have corner breaks, spalling, existing asphalt pavement, retard surface raveling, seal small or popouts. The visible surface distress may include low- cracks, and improve surface friction. As with other surface severity cracking, faults not exceeding 0.25 in. (6 mm), and treatments, slurry seals should not be used where sealing the moderate to severe polishing. Pavements with moderate pavement would cause a stripping problem or where the under- to advanced material-related distresses, such as alkali-silica lying pavement is cracked (Wade et al. 2001). reaction (ASR) and D-cracking, are not good candidates for Other preventive treatments include fog seals, which can diamond grinding (Shuler 2006). be considered a candidate treatment to address raveling, and oxidation. However, a fog seal generally lasts only 1 to 2 years. Use of Preservation Treatments Microsurfacing is primarily used as a surface seal to address on High-Traffic-Volume Facilities rutting and loss of friction; this treatment also limits damage from water, oxidation, and ultraviolet (UV) rays, which cause While it is generally observed that the practice of pavement weathering, raveling, and surface cracking. preservation and the use of PM are growing among trans- A detailed analysis of the long-term pavement performance portation agencies, the majority of constructed preservation (LTPP) data from the four treatments used at SHRP Specific projects, in terms of treated lane miles, occur on lower-volume Pavement Study (SPS)-3 sites through 2001 indicated that thin roadways. One explanation for this is that typical PM treat- HMA overlays were most effective--followed by chip seals ments, such as chip seals and other thin surface treatments, and then slurry seals--in addressing roughness, rutting, and have historically been used on low-volume roads. However, fatigue cracking (Hall et al. 2002). Slurry seals showed no there are many indications that this is changing. effect on long-term roughness. The thin overlays, as expected, A 2004 survey conducted under the National Cooperative were the only treatment to affect long-term rutting. The study Highway Research Program (NCHRP) 20-07 revealed that concluded that, with respect to roughness, rutting, and crack- most agencies practice pavement preservation on all types ing on PCC pavements in the SPS-6 study, HMA overlay had of facilities (Peshkin and Hoerner 2005). This conclusion the best effect, followed by diamond grinding, full-depth was drawn from responses to the following question, "On repair, and joint and crack sealing. No added benefit was what facility types does your agency currently apply preven-
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15 Table 2.5. Summary of Facility Characteristics Associated with Projects Selected as Candidates for Pavement Preservation Projects Number of Respondents General ADT Range Associated with Using Preservation Different Roadway Classifications Roadway Classification (vehicles per day [vpd]) Rural Urban Freeway 30,000 and above 29 of 35 (83%) 26 of 35 (74%) Arterial 12,000 to 40,000 29 of 35 (83%) 27 of 35 (77%) Collector road 2,000 to 12,000 29 of 35 (83%) 27 of 35 (77%) Local road 2,000 24 of 35 (69%) 22 of 35 (63%) Source: Peshkin and Hoerner 2005. tive maintenance treatments?" The responses are shown in restricts their use to roads with AADT less than 1,200 vpd, and Table 2.5. Ohio limits their use to roads with less than 2,500 vpd AADT Results from this survey seemed to indicate that pavement (Galehouse 2004; Ohio DOT 2001). preservation is occurring as frequently, or even more frequently In other states, such as Utah, there was some concern in the case of rural roads, on higher-volume roadways as on about cost and relative performance of chip seals; following a lower-volume roadways. These results suggested that the more life-cycle study of chip seals, it was recommended that policies important distinction is between rural and urban roadways be modified to specify open-graded friction courses (OGFCs) for any traffic volume. for high-speed (greater than 55 mph [88 kph]), high-volume Although in general there may be a common association roads (AADT greater than 25,000 vpd), similar to practices in between typical preservation treatments and their use on low- Georgia, Nevada, and Oklahoma (Romero and Anderson 2005). volume roads, some departments of transportation (DOTs) OGFCs have also found success on high-volume roads in Florida are finding it effective to apply such treatments to high-volume (at 10 to 12 years) and Oregon (up to 8 years and 2.5 million roads. The DOTs identified in the literature as having per- equivalent single-axle loads [ESALs]) (Huddleston et al. 1993; formed preservation work on high-traffic-volume roadways Page 1993). At the same time, Connecticut and South Carolina (ADT 2,500 vpd) include Alabama, Arkansas, California, limit the use of OGFCs, and other states, including Illinois, Colorado, Florida, Georgia, Idaho, Montana, Oklahoma, Michigan, and Washington, have discontinued their use Oregon, Pennsylvania, South Dakota, Texas, Utah, Virginia, and because of poor performance. Washington State. International agencies proactive in the use Microsurfacing has been successful on high-volume roads of preservation treatments on high-volume roads include the in Texas, Kansas, Oklahoma, Pennsylvania, and Arkansas. United Kingdom, South Africa, Spain, France, and Australia. Oklahoma found that microsurfacing provides adequate While chip seals have seen the greatest use on low-volume performance for "at least 4 years under traffic volumes up to roadways (with a typical ADT less than 1,000 vpd), California 70,000 ADT" (Raza 1994). Virginia has applied microsurfacing allows them to be used on roads with average annual daily treatments to stretches of Interstate with AADTs ranging from traffic (AADT) up to 30,000 vpd (Romero and Anderson 2005). 14,000 up to 26,000 vpd, preserving "performance qualities The United Kingdom "commonly" uses chip seals on roads with for several years," whereas Michigan confirms this level of ADT greater than 20,000 vpd, as do Colorado and Montana performance, typically assuming service life for a single-course (Cuelho et al. 2006). In Washington State, chip seals were microsurfacing treatment of 3 to 5 years or up to 6 years for used on the Tacoma Narrows Bridge, which has an ADT of multiple courses (Morian et al. 2005; Peshkin and Hoerner 178,000 vpd (Kuennen 2006a). 2005). Indiana has determined that "severe climatic condi- Following the successes of other states, a study conducted tions," as opposed to traffic volume, have a greater effect on for the Utah DOT recommended that chip seal usage extend performance of microsurfacing treatments (Labi et al. 2007). to "certain roads with AADT up to 20,000 vehicles," while Cold in-place recycling (CIR), has found success in continuing the existing practice of using chip seals on high- Pennsylvania, where projects have outperformed their expected way sections with AADT less than 5,000 vpd (Romero and service life of 10 years by an average of 3 additional years Anderson 2005). On the other hand, while the Colorado DOT's (Morian et al. 2004). In Nevada, with regular crack sealing and maintenance superintendents believe chip seals "can be used judicious use of CIR, projects can achieve full life expectancy on high-volume roads (AADT up to 10,000 vpd)," one region of 15 to 20 years (Bemanian et al. 2006). In Quebec, Canada,
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16 Bergeron (2005) compared CIR practices with typical asphalt Specifically regarding high-volume roads, Gransberg resurfacing for highways with AADT of 20,000 vpd to deter- concluded: mine the difference in net present value and benefit-cost ratio. The additional performance of CIR compared with · Chip seals can be successfully used on high-volume roads if asphalt resurfacing resulted in higher benefit-cost ratios, even the agency's policy is to install it on roads before pavement though the net present values were higher for CIR. Bergeron distress becomes severe or the structural integrity of the also found that CIR net present values for national and underlying pavement is breached. regional roads (with an AADT of 12,000) were less and had · Both hot asphalt cement and emulsified asphalt binders even higher benefit-cost ratios. can be used successfully on high-volume roads. Binders Ultra-thin bonded wearing courses (also referred to as modified by polymers or crumb rubber seem to reinforce ultra-thin friction courses) are a relatively new preservation success. treatment but are generally considered appropriate for high- volume roads. The literature identifies performance studies Some other recommendations for applying chip seals to in two southern states, Alabama and Louisiana. Alabama has high-volume facilities include applying a "choke" aggregate had success using ultra-thin bonded wearing course on sev- to prevent dislodging larger aggregate chips or applying a fog eral high-volume roads including US 280 (13,000 ADT), or flush seal over the chip seal (Shuler 1998; Wade et al. 2001). AL 21 (7,500 ADT), I-65 (60,000 ADT), and I-29 (165,000 ADT) One region in Colorado applies fog seals within 2 to 10 days (Koch 2001). Missouri's first experiment using this treatment of placement on a "majority" of chip seals (Galehouse 2004). was damaged by freeze-thaw and snowplowing (MoDOT 1999). However, it should be noted that additional time may be This treatment has also been placed in several cold-weather required to allow emulsions to break (Wade et al. 2001). states, including Colorado, Michigan, New York, Ohio, Penn- Several additional considerations are recommended to sylvania, and Wisconsin (Koch 2001). Anecdotal reports are extend the applicability of chip seal treatments to higher- that it has been successful. traffic-volume roadways. These include the following (Beatty et al. 2002; Shuler 1998): SPECIAL CONSIDERATIONS FOR HIGH-TRAFFIC-VOLUME TREATMENTS A common concern regarding preservation treatment per- · Precoat aggregate to improve adhesion, an approach popu- formance on high-volume roads is the issue of treatment lar in South Africa and Australia. durability, or obtaining a cost-effective service life from the · Limit excess chips to 5% to 10%. preservation treatment, given the traffic level. As previously · Sweep excess chips prior to opening to traffic. asserted, effective preservation requires the appropriate treat- · Once opened to traffic, control speeds (via signage or a ment for a given pavement section, as well as proper timing pilot car) to reduce whip-off and to promote embedment. (Geoffroy 1996). For high-volume facilities, choosing the appropriate treatment may require additional considerations. In Canada, it has been confirmed that the structural integrity For example, as noted, chip seals see their most common of the seal is "dependent on the embedment of the aggregate application as wearing courses on low-volume roads, but they in the binder/substrate" because chip seals are leaner on high- have proven successful as surface treatments for high-volume volume roads to avoid bleeding (Croteau et al. 2005). roads. Using a chip seal on a high-volume road may require using a higher-quality aggregate or polymer-modified binder, PERFORMANCE OF TREATMENTS which has been effective for California and Washington State, ON HIGH-TRAFFIC-VOLUME FACILITIES with both reporting 5 to 7 years of serviceable life (Shuler 1998; Performance is varied for different preservation treatments on Geoffroy 1996). high-volume roadways. California reports "good performance" Gransberg's (2005) synthesis of chip sealing best practices from chip seals on facilities with up to 30,000 ADT, and found that all nine agencies (culled from 72 individual responses "good performance" from crack sealing, slurry sealing, and from 42 states and 12 cities and counties) reporting superior microsurfacing, as well as applying OGFCs and thin HMA results from chip sealing applications do the following: overlays for facilities with greater than 30,000 ADT. On the other hand, California does not recommend fog sealing on · Use polymer or crumb-rubber modified binders; facilities with greater than 5,000 ADT, and has typically expe- · Use pavement condition ratings as triggers, then select roads rienced "fair performance" with fog seals on facilities with less of moderate or less distress level with structural cross-section than 5,000 ADT (Shatnawi et al. 2006). rated fair or better; and Texas monitored performance of different PM treatments · Follow chip sealing applications with routine crack or fog on the SPS-3 sections (crack sealing, chip seals, slurry seals, sealing. and thin overlays), concluding that chip seals performed the
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17 best under a "wide range" of pavement conditions, as well as significantly from agency to agency, and there are gaps in the scoring the best on high- and low-volume sections. Consider- shared knowledge pool, especially regarding PM practices on ing initial cost, chip seal is a better choice on high-traffic roads, PCC roadways. Furthermore, "success" is a relative concept, especially where rutting is not a concern. If rutting is a major where what some agencies describe as successful is not con- problem, then a thin HMA overlay was determined to be the sidered as successful by others. Variations in traffic, climate, and most effective option (Chen et al. 2003). materials may account for some of these relative differences. Slurry seals have typical reported service lives of 3 to 5 years In any case, the full extent of each agency's PM program is on roads with "moderate to heavy traffic," effectively reducing difficult to gauge from the literature. In the next section, the crack development and raveling, as well as being "marginally review of the questionnaire responses illuminates state and effective" in preventing reflective cracking (Morian et al. 1997; provincial PM practices and can be viewed as a supplement Raza 1992). Flush seals are reported to survive "approximately to the information reported in the literature. 2 to 7 years" for traffic up to 5,000 ADT and up to 5 years for higher volumes (NCHRP 1997). Preservation Treatments and Climate Microsurfacing provided good rut resistance for 3 to 7 years in Kansas, Pennsylvania, Oklahoma, and Arkansas. Oklahoma Climate is commonly defined as the weather of a given region and Pennsylvania also note good surface friction for up to averaged over a long period of time (AMS 2008). It encom- 5.5 years of service (Raza 1994; Wade et al. 2001). However, in passes the statistics of temperature, humidity, atmospheric North Carolina, it was reported that once the microsurfaced pressure, wind, rainfall, and numerous other meteorological sections failed, they "deteriorated quickly" due to the pavement's elements, and is affected by latitude, terrain, altitude, ice or diminished structural integrity under heavy traffic loading snow cover, as well as nearby water bodies and their currents. (Morian et al. 2005). Climatic conditions impact preservation treatment usage OGFCs have reported service lives of 10 to 12 years on in at least two ways: determining construction timing, and Florida Interstates and up to 8 years in Oregon (Huddleston affecting treatment performance. Brief discussions of these et al. 1993; Page 1993). Reported average service lives for CIR impacts are provided in the following sections. treatments range from 5 to almost 13 years in Ohio and Pennsylvania (Hicks et al. 2000; Morian et al. 2004). Ultra-thin CLIMATIC EFFECTS ON CONSTRUCTION TIMING bonded wearing courses are generally reported to achieve Some treatments, especially those based on asphalt emulsions, service lives of between 7 and 12 years (Gilbert et al. 2004; are best applied under restricted temperature and humidity Peshkin and Hoerner 2005). conditions. Climate can directly affect curing time, which in Illinois reports successful service lives of 7 to 10 years using turn impacts treatment feasibility and opening to traffic. thin HMA overlays (1 to 1.5 in. [25 to 38 mm]) when correctly For example, crack sealing techniques are best applied when targeting specific pavement condition criteria, while one district temperatures are moderately cool (i.e., spring and fall in the in Indiana expects a 10- to 15-year pavement life extension northern half of the United States). Accordingly, the Ohio DOT using thin HMA overlays (Cuelho et al. 2006; Reed 1994). recommends that crack sealing, in contrast to most other PM Iowa DOT has also found best performance from thin HMA strategies, be performed in cooler weather when the pavement overlays compared to chip seals, fog seals, cape seals, slurry seals, has contracted, thus moderately expanding crack openings and even microsurfacing (Jahren et al. 2003). Washington State such that on very hot or cold days, the sealant will not bulge DOT most commonly uses thin HMA overlays for pavement excessively or risk pulling away (Cuelho et al. 2006). Because preservation, reserving chip seal applications for lower-traffic crack filling treats nonworking cracks that are not significantly areas (Li et al. 2008). affected by temperature fluctuations, crack filling can be applied In Colorado, it was noted that deicer compounds leave any time of the year when weather conditions are appropriate residue in pavement cracks, preventing adequate sidewall (i.e., no rain or snow). adhesion and, consequently, loss of crack sealant. Seasonal Fog seals, according to the South Dakota DOT, are not rec- limitations were recommended, including waiting "at least ommended for high-volume roadways because of the length two rainfall events" before commencing crack-filling operations of time required for slow setting emulsions to break, which (Galehouse 2004). In Utah, OGFCs have on average survived reduces the amount of surface friction immediately after 7 years, early failures being related to raveling, stripping, and application (Wade et al. 2001). potholing (Romero and Anderson 2005). The use of a slurry seal may not be appropriate for high- The literature gives some indication of how extensively volume roads where traffic must be allowed very soon after practitioners are making efforts to establish PM practices and application. In warm weather, slurry seals require at least policies for their high-traffic-volume roadways with varying 2 hours to cure, resulting in potential traffic delays. On the degrees of success. The performance of treatments varies other hand, microsurfacing cures and develops strength faster
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18 than conventional slurry seals and can be opened to rolling This product is more resistant to rutting, even with inferior traffic in about an hour; therefore it is more applicable for a aggregates, but due to its stiffer and more brittle nature, it can variety of environments. be susceptible to fatigue cracking and is less resistant to water In the case of chip seals, cold-applied seals must be placed damage and stripping than conventional asphalt. The tem- during the day and in warm temperatures, while hot-applied perature must be closely monitored during mixing to ensure chip seals can be placed at night and in cooler temperatures. the proper blend of asphalt and sulfur. The price and avail- Generally, the construction season runs from May to September ability of sulfur varies, making it difficult to predict prices and to take advantage of the warmest months for the northern feasibility. Its uses are similar to any other asphalt overlay, states (Gransberg 2005). Good performance related to favorable except that layer thickness may be decreased when rutting is climatic conditions during placement and also, importantly, the primary concern. Rut-resistant solutions are important in favorable climatic conditions during the weeks following the country's hot climate. placement. The major cause of pavement failure is weather India has included in its pavement preservation strategies related, such as when rain or extreme temperatures occur the use of stone matrix asphalt (SMA), microsurfacing, and cold shortly after construction (Croteau et al. 2005). in-place recycling. SMA is a type of HMA that uses a modi- Although thin HMA overlays can be placed successfully fied aggregate gradation. This gap-graded gradation creates a in a variety of climatic conditions, application in cooler tem- stable skeleton of top-size aggregate particles, whereas the fine peratures can impact the ability to achieve specified density. materials mix with the binder to create a stiff mastic to hold This is particular true for ultra-thin HMA overlays. the aggregate skeleton together. Fibers are sometimes included. This stone-on-stone contact makes a highly rut-resistant CLIMATIC EFFECTS ON TREATMENT PERFORMANCE material. Similar to the practices in Saudi Arabia, India has Whereas some preservation treatments, such as diamond placed important emphasis on the development of rut-resistant grinding on PCC pavements, may not be too affected by dif- asphalt mixes due to the hot climate. ferences in climate, most treatments do experience climate- France reports on an overall pavement strategy that is related performance effects. For example, the Indiana DOT focused on building strong and stiff underlying pavements has determined that severe climatic conditions, as opposed to and performing surface repaving every 10 to 15 years. As is traffic volume, have a greater effect on performance of certain common for many European countries, many of the roads treatments, such as microsurfacing (Labi et al. 2007). and maintenance contracts in France are privatized, so the Results of the SHRP SPS-3 study indicated that chip seals work may be performed and funded by private entities rather performed well across all climate zones and very well in wet than by the government. Seals and thin overlays are used for nonfreeze zones (Morian et al. 1998). Moreover, slurry seals improving skid resistance, reducing noise, and enhancing ride showed very good performance in nonfreeze climates, but smoothness between major repaving projects. Open-graded poor performance in freeze climates. Similarly, crack seals mixes are commonly used for noise reduction. In material showed good performance in nonfreeze climates, but signif- design, aggregate quality is emphasized, and both hot asphalt icantly reduced performance in freeze climates. mixes and emulsions are used for surface work. A new devel- opment, called a "bio-binder," which is asphalt cut back with vegetable oil to make a binder that is workable at normal tem- International Pavement Preservation Practices peratures, has been used on several projects, though full details In addition to information on preservation practices within of its performance are not known. the United States, some information was obtained about South Africa uses a variety of surface seals, especially chip international practices. The proper context for each treatment seals, even on high-volume roads. An important part of the strategy must be understood because the way in which each process is that the aggregate is precoated to reduce loss and country chooses its preservation strategy depends on its stan- stripping. Like France, South Africa emphasizes aggregate dard road design, climate, traffic patterns, and political and quality by limiting fines and securing quality aggregate regard- economic organization. Information collected from Saudi less of cost. Also, like France, it builds strong and thick pave- Arabia, India, France, South Africa, and Australia is provided ment sections, so that structural distresses are minimized and in the following descriptions. Note, however, that these are the use of chip seals address surface distresses only. Emulsions large, diverse countries and that what is reported may not be are used only for fog seals or rejuvenators; otherwise, hot representative of an entire country's practice. asphalt is used. Crumb rubber is used in both HMA and Saudi Arabia reported using sulfur asphalt, crack sealing, surface treatments. slurry seals, microsurfacing, and thin overlays as part of its Australia places a heavy emphasis on preservation, partic- preservation activities. Sulfur asphalt is a mixture of asphalt ularly keeping water away from the subgrade. Most roads binder and a sulfur compound that makes a stiffer product. have a very thick subbase, a strong unbonded base course,
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19 and an asphalt concrete wearing surface. An example of a Among the 28 agencies that responded to the experience PM process in Australia includes milling and placement of a question, one-half reported having more than 10 years of expe- stress-absorbing membrane, followed by an asphalt concrete rience and one-quarter reported having more than 20 years' overlay. Emphasis is placed on crack sealing with polymer- experience. modified binder to prevent water intrusion. Another PM technique is a tack coat that is followed by a geotextile and Treatment Selection Considerations then a chip seal. Most Australian states dedicate more fund- ing to PM than to reconstruction. For example, the state of In identifying the important considerations in selecting pre- Victoria dedicates 90% of its program to prevention and 10% servation treatments, respondents collectively reported the to reconstruction. following hierarchy: · High Priority Review of Survey Results 1. Safety concerns (76%) As shown in Table 2.6, 50 highway agencies responded to the 2. Treatment cost (74%) pavement preservation questionnaire; the FHWA's Central 3. Durability/expected life of treatment (64%) Federal Lands Highway Division (FHWA-CFLHD), National · Medium Priority Association of County Engineers (NACE), and National Asphalt 1. Availability of experienced contractor (60%) Pavement Association (NAPA) also provided responses. 2. Work zone considerations (59%) A review of the survey responses revealed that there was a 3. Tied: Risk associated with treatment failure; closure time wide range of experience in pavement preservation practices. (57%) · Low Priority 1. Availability of alternate route(s) (40%; however, one in four of all respondents considered this issue unimpor- Table 2.6. Summary of Survey Respondents tant) 2. Noise issues (39%) State Highway Agencies Canadian Provinces 3. Public perception (36%) Alaska Montana Alberta Arizona Nebraska British Columbia Traffic volume was considered of high priority by just over Arkansas Nevada Manitoba half of respondents and of medium priority by approximately California New Hampshire New Brunswick 40%. This implied that if pavement preservation is indeed practiced on high-traffic-volume roads, many agencies have Colorado New Mexico Ontario established standard practices using preservation treatments Connecticut New York Quebec for that application. Florida North Carolina Saskatchewan Responses regarding the most successful treatments indi- Georgia Ohio cated that they have low cost, good durability and long life expectancy, and fast application (important in getting work Hawaii Oklahoma Cities crews quickly out of harm's way and in minimizing impact Illinois Pennsylvania Phoenix, Ariz. on road users). These responses show the influence of the noted Indiana Rhode Island San Diego, Calif. priority factors on treatment selection. On the other hand, the Iowa South Carolina common complaints against the least successful preservation treatments that agencies have used were related to high cost Kansas South Dakota Toll Authorities and poor performance. Kentucky Tennessee Texas Turnpike Louisiana Texas Traffic Level and Treatment Use Maine Utah (3)a Michigan Virginia An important consideration affecting which preservation treatments are used on high-traffic-volume roadways is how Minnesota Washington the agency defines "high" traffic volumes. While some respon- a Mississippi (4) Wisconsin dents wanted the researchers to provide a definition for high Missouri Wyoming traffic volumes, it was recognized that different agencies use aAgencies that submitted multiple responses from various districts within markedly different definitions and that it would be better for the state have the number of responses indicated in parentheses. respondents themselves to provide this value. Accordingly, in
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20 order to better characterize the range of volumes considered, The high-traffic-volume criteria reported by agencies were the questionnaire asked respondents to provide their own initially analyzed for trends concerning the use of the preser- values for low (less than or equal to . . .), medium (a range), vation treatments. Some key findings from this initial analysis and high (greater than or equal to . . .) traffic volumes for are summarized in Tables 2.8 and 2.9, respectively. Each table both rural and urban roadways. In order to make further dis- lists the most-used treatments on HMA- and PCC-surfaced tinctions concerning treatment use on high-traffic-volume roadways, based on the three categories of high-traffic-volume roadways, the agency-defined criteria for high traffic volume criteria. were exclusively examined. These criteria were grouped into In addition to the information included in Tables 2.8 and 2.9, one of three categories for both rural and urban roadways-- the following specific details were noted from the responses "low" (ADT < 10,000 vpd), "medium" (ADT = 10,000 to regarding high-volume traffic: 19,999 vpd), and "high" (ADT 20,000 vpd). A summary of the high-traffic-volume criteria grouped according to these · Those agencies falling in the "high" criteria category reported three categories is provided in Table 2.7. not using the following treatments: cape seal, scrub seal, Table 2.7. Responding Agencies' High-Traffic-Volume Criteria and Criteria Categories High-Traffic-Volume Criteria Categories Low Criterion (ADT 20,000 vpd) Louisiana DOT (7,000) Alaska DOT (10,000) Connecticut DOT (30,000) Michigan DOT (3,400 est.) Hawaii DOT (10,000) Rhode Island DOT (30,000) Missouri DOT (1,000) Maine DOT (10,000) South Carolina DOT (20,000) Montana DOT (6,000) Minnesota DOT (10,000) British Columbia (100,000) New York DOT (4,000/lane) New Hampshire (10,000) Pennsylvania DOT (2,000) Oklahoma DOT (10,000) South Dakota DOT (1,500) Ontario (10,000) Washington DOT (5,000) Alberta (5,000) FHWA-CFLHD (4,000) For agencies that make a distinction between rural and urban traffic volume categorizations: Georgia DOT (5,000 rural/8,000 urban) Wyoming DOT (10,000 rural/15,000 urban) Virginia DOT (20,000 rural/40,000 urban) Iowa DOT (3,500 rural) Iowa DOT (11,500 urban) Florida DOT (10,000 rural) Florida DOT (40,000 urban) Kansas DOT (3,000 rural) Kansas DOT (20,000 urban) Kentucky DOT (5,000 rural) Kentucky DOT (10,000 urban) Mississippi DOT, Newton (3,0007,000 rural) Mississippi DOT, Newton (20,000 urban) Mississippi DOT, Batesville (2,000 rural) Mississippi DOT, Batesville (10,000 urban) Mississippi DOT, Tupelo (3,0007,000 rural) Mississippi DOT, Tupelo (20,000 urban) Nevada DOT (10,000 rural) Nevada DOT (100,000 urban) New Mexico DOT (5,000 rural) New Mexico DOT (15,000 urban) North Carolina DOT (5,000 rural) North Carolina DOT (10,000 urban) Tennessee DOT (5,000 rural) Tennessee DOT (10,000 urban) Texas DOT (1,000 rural) Texas DOT (10,000 urban) Manitoba (4,000 rural) Manitoba (10,000 urban) Quebec (8,000 rural) Quebec (20,000 urban)
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22 100 90 80 70 % of Agencies 60 50 40 30 20 10 0 ll al ng ng al er e y y y g g ng g n Fi rla rl a la rs in lin in tio Se Se m ci ci illi er cl pp ou ck yc ve ve va ly fa rf a M cy v ck p Po to C ra ec ur O O O er hi u e e ra te C g os os es C R R fil A A A th rin hi C M M M o r r e ce ce Pr i W ic ic Pr w rs ea H H H M M la la e ou al in in d in W -P -P ag e se Se i lle Th Th Th -C rs In In ed in ur M a- ou le a- p ra ot d nd co hi d- ng ltr ltr ol D -C H C ol Bo ti U U C Si ul le C M ng in Th Si Treatment Low (20,000) Figure 2.2. Treatment use on rural HMA-surfaced roadways, by category of high-traffic-volume criteria. least 60% (see Figure 2.3). Also shown in Figure 2.3, the com- using thin PCC overlays on urban roads. Nor did they bination treatment of cold milling and thin HMA overlay report using any "other" treatments on either rural or (<1.5 in.) is used on urban roads by at least 40% of report- urban roads. ing agencies. · For all agencies reporting "high" traffic volume designations, · For PCC pavements (Figures 2.4 and 2.5), those agen- joint seal, diamond grinding, and full-depth patching are cies with "high" traffic volume designations reported not used on PCC pavements by at least 80% of reporting agen- 100 90 80 70 % of Agencies 60 50 40 30 20 10 0 ll al ng ng al er e y y y g g ng g n Fi rla rla la rs in lin in tio Se Se m ci ci illi er cl pp ou ck yc ve ve va ly fa fa M cy v ck p Po to C ra ec r ur O O O er hi su e e ra te C g s es C R R fil A A A th ro ro rin hi C M M M o e ce ce Pr i W ic ic Pr w rs ea H H H M M la la e ou al in in d in W -P -P ag e e Se ille Th Th Th C rs rs In In ed in e- M a- ou ou a- p ra ot d nd l d- hi ng ltr ltr ol D -C tic H C ol Bo U U C Si ul le C M ng in Th Si Treatment Low (20,000) Figure 2.3. Treatment use on urban HMA-surfaced roadways, by category of high-traffic-volume criteria.
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23 100 90 80 70 % of Agencies 60 50 40 30 20 10 0 Joint Resealing Crack Seal Diamond Partial-Depth Full-Depth Dowel Bar Drainage Grinding Patching Patching Retrofit Preservation Treatment Low (20,000) Figure 2.4. Treatment use on rural PCC-surfaced roadways, by category of high-traffic-volume criteria. cies (see Figures 2.4 and 2.5). Crack seal is used on rural definition of high-traffic-volume ADT for rural and urban PCC roads by 100% of reporting agencies (see Figure 2.4). roadways. Using descriptive statistical analyses, histograms of ADT criterion levels for rural and urban roadways were created With some differences noted between the treatment usage (see Figures 2.6 and 2.7) and then analyzed to identify the trends for low-, medium-, and high-traffic-volume criteria ADT level at which at least 50% of reporting agencies are categories, an analysis was conducted to generate a numeric represented. From this analysis, it was determined that high 100 90 80 70 % of Agencies 60 50 40 30 20 10 0 Joint Resealing Crack Seal Diamond Partial-Depth Full-Depth Dowel Bar Drainage Grinding Patc hing Patc hing Retrofit Pres ervation Treatment Low (20,000) Figure 2.5. Treatment use on urban PCC-surfaced roadways, by category of high-traffic-volume criteria.
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24 14 100.00% 90.00% 12 80.00% 10 70.00% No. of Agencies 60.00% 8 50.00% 6 40.00% 4 30.00% 20.00% 2 10.00% 0 0.00% 20 to 99 30 to 99 40 to 99 50 to 99 60 to 99 70 to 99 80 to 99 90 to 99 00 to 99 00 o 1 9 00 1 9 00 o 1 9 00 o 1 9 00 o 1 9 00 1 9 00 o 2 9 00 o 4 9 99 9 00 9 + 11 0 t 999 12 0 to 099 13 0 t 199 14 0 t 299 15 0 t 399 20 0 to 499 3 0 0 t 9 99 50 0 t 999 to 9 1 0 99 00 00 o 9 00 19 00 29 00 3 9 00 49 00 59 00 69 00 79 10 00 89 0 99 10 0 t Rural ADT Levels Figure 2.6. Histogram and cumulative percentage of high-traffic-volume ADT on rural roadways. traffic volume should be defined as an ADT of at least 5,000 treatments described previously was revisited. Table 2.11 and and 10,000 vpd for rural and urban roadways, respectively. Figures 2.8 and 2.9 show the results of this analysis for HMA- Modifications were then made to Table 2.7 to reflect the surfaced roadways. responding agencies whose high-traffic-volume criteria meet Key findings from this analysis are summarized as follows: these new definitions. The results of this recategorization of agencies are shown in Table 2.10. However, it is recognized · As shown in Figures 2.8 and 2.9, crack fill and crack seal are that this categorization is still somewhat arbitrary, as for used by at least 75% of reporting agencies. Additionally, some the high value may be low and for others the high may on rural roads, drainage preservation and combined cold be too high. milling and thin HMA overlay are used by at least 70% and With the new high-volume traffic values serving as the basis 60% of agencies, respectively (see Figure 2.8). On urban for further treatment analysis, the evaluation of the "most used" roads, drainage preservation and combined cold milling 16 100.00% 14 90.00% 80.00% 12 70.00% No. of Agencies 10 60.00% 8 50.00% 6 40.00% 30.00% 4 20.00% 2 10.00% 0 0.00% 20 to 99 30 to 99 40 to 99 50 to 99 60 to 99 70 to 99 80 to 99 90 to 99 00 to 9 00 o 1 9 00 o 1 9 00 1 9 00 o 1 9 00 o 1 9 00 o 1 9 00 2 9 00 o 4 9 99 9 00 9 + 10 00 899 11 0 t 999 12 0 t 099 13 0 to 199 14 0 t 299 15 0 t 399 20 0 t 499 30 0 to 999 50 0 t 999 to 9 10 99 00 00 o 9 00 19 00 29 00 39 00 49 00 59 00 69 00 79 0 99 10 0 t Urban ADT Levels Figure 2.7. Histogram and cumulative percentage of high-traffic-volume ADT on urban roadways.
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25 Table 2.10. Recategorization of Agencies Based on New Definitions of Rural and Urban High-Traffic-Volume Levels New High-Traffic-Volume Criteria Categories Rural (ADT > 5,000 vpd) Urban (ADT > 10,000 vpd) Louisiana DOT (7,000) Alaska DOT (10,000) Washington DOT (5,000) Connecticut DOT (30,000) Alberta (5,000) Hawaii DOT (10,000) Maine DOT (10,000) Minnesota DOT (10,000) New Hampshire (10,000) Oklahoma DOT (10,000) Rhode Island DOT (30,000) South Carolina DOT (20,000) British Columbia (100,000) Ontario (10,000) For agencies that make a distinction between rural and urban traffic volume categorizations: Georgia DOT (5,000 rural) Wyoming DOT (10,000 rural) Wyoming DOT (15,000 urban) Virginia DOT (20,000 rural) Virginia DOT (40,000 urban) Iowa DOT (11,500 urban) Florida DOT (10,000 rural) Florida DOT (40,000 urban) Kansas DOT (20,000 urban) Kentucky DOT (5,000 rural) Kentucky DOT (10,000 urban) Mississippi DOT, Newton (3,0007,000 rural) Mississippi DOT, Newton (20,000 urban) Mississippi DOT, Batesville (10,000 urban) Mississippi DOT, Tupelo (3,0007,000 rural) Mississippi DOT, Tupelo (20,000 urban) Nevada DOT (10,000 rural) Nevada DOT (100,000 urban) New Mexico DOT (5,000 rural) New Mexico DOT (15,000 urban) North Carolina DOT (5,000 rural) North Carolina DOT (10,000 urban) Tennessee DOT (5,000 rural) Tennessee DOT (10,000 urban) Texas DOT (10,000 urban) Manitoba (10,000 urban) Quebec (8,000 rural) Quebec (20,000 urban) Categorizations by agencies not included in trend analysis: Organizations: NAPA (10,000); NACE (15,000 rural/60,000 urban). Other: Colorado DOT categorizes by ESALs. Caltrans categorizes by traffic index (TI): TI 18 rural and TI 15 urban, where TI = 9.0 × (ESAL ÷ 106)0.119. Utah DOT (Region 4) categorizes by Interstate or non-Interstate (25,000 ADT and 2,500 ADT, respectively). City of Phoenix, Ariz., categorizes by 20,000 ADT rural, 50,000 ADT urban.
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26 Table 2.11. Revised Analysis of Most-Used · A handful of agencies--Hawaii, Minnesota, Montana, Preservation Treatments for HMA-Surfaced and Alberta (Canada)--noted using "other" preservation High-Volume Roadways treatments. Hawaii reported only doing 1.5-in. (38-mm) HMA mill Commonly Used Preservation Treatments and fill as a preservation technique for rural and urban on HMA-Surfaced High-Volume Roadways roadways. Rural (ADT > 5,000 vpd) Urban (ADT > 10,000 vpd) Minnesota requires that all chip seal applications receive a fog seal. 60% SHAs and provinces report using: Montana applies thin HMA overlays (< 2.375 in. Crack fill Crack fill [< 60 mm]) on rural roadways. Crack seal Crack seal Alberta uses a combination of profile milling and thin Cold mill and thin HMA overlay Cold mill and thin HMA overlay overlay on rural roadways. Drainage preservation Drainage preservation Similar analyses were performed for treatments used on PCC pavements. The high-traffic-volume results were ana- 50% additionally report using: lyzed for trends concerning treatment use, as well as treat- Thin HMA overlay ment use in relation to pavement performance issues. The findings of this analysis are summarized in Table 2.12 and Figures 2.10 and 2.11. and thin HMA overlay are used by at least 60% and 70%, Key findings from the analysis of PCC treatments are respectively (see Figure 2.9). Also shown in Figure 2.9, single- summarized as follows: and multiple-course microsurfacing, ultra-thin bonded wearing course, and thin HMA overlays (<1.5 in. [<38 mm]) · As shown in Figures 2.10 and 2.11, for both rural and urban are used on urban roads by at least 40% of respondents. roadways, joint resealing, diamond grinding, and full-depth · Cape seal, scrub seal, and rejuvenator are not used by many patching are used by at least 70% of agencies. reporting agencies. In addition, on urban roads, fog seals and · Fewer than 40% of reporting agencies use diamond grooving, multiple-course chip seals are not used by many agencies. thin PCC overlays, or ultra-thin bonded wearing courses Therefore, they are not included in Figures 2.8 and 2.9. on both rural and urban roads. · Only one agency, Nevada DOT, reported using scrub seal on · Dowel bar retrofitting and drainage preservation are used rural or urban roadways with ADT 5,000 and 10,000 vpd, on urban roads by at least 50% of reporting agencies respectively. (see Figure 2.11). 100 90 80 70 % of Agencies 60 50 40 30 20 10 0 ll al ng ng al er e y y y g g ng g n Fi rla rla rla rs lin lin in tio Se Se m ci ci illi pp ou yc yc ck ve ve ve va ly rfa rfa M ck p Po to C ec ec ra O O O er hi su su ile ra te C g es C R R A A A ith rin ro ro hi of C M M M e ce ce Pr W ic ic Pr w rs ea H H H la la M M e ou al in in d in W -P -P ag ille e e Se Th Th Th -C rs rs In In ed in M a- a- le ou ou p ra ot d nd d- hi ng ltr ltr ol D -C tic H C Bo ol U U C Si ul le C M ng in Th Si Treatment Figure 2.8. Treatment use on rural HMA-surfaced roadways, based on revised definition of rural high traffic volume (ADT > 5,000 vpd).
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27 100 90 80 70 % of Agencies 60 50 40 30 20 10 0 ll al ng ng al er e y y y g g ng g n Fi rla rla rla rs lin lin in tio Se Se m ci ci illi pp ou yc yc ck ve ve ve va ly rfa rfa M ck p Po to C ec ec ra O O O er hi su su ile ra te C g es C R R A A A ith rin ro ro hi of C M M M e ce ce Pr W ic ic Pr w rs ea H H H la la M M e ou al in in d in W -P -P ag ille e e Se Th Th Th -C rs rs In In ed in M a- a- le ou ou p ra ot d nd d- hi ng ltr ltr ol D -C tic H C Bo ol U U C Si ul le C M ng in Th Si Treatment Figure 2.9. Treatment use on urban HMA-surfaced roadways, based on revised definition of urban high traffic volume (ADT > 10,000 vpd). · Only the Maine DOT reported using an "other" treatment of the majority reports using a different set of treatments for on PCC. Maine once applied an ultra-thin bonded wearing urban high-traffic-volume roadways from those for urban course on a PCC pavement, which has since been rubblized low-traffic-volume roadways. and paved with HMA. Of the treatments used on HMA-surfaced pavements, the majority (80%) of respondents indicated that chip seals In general, 60% of agencies report using a different set of are not considered applicable for rural or urban high-traffic- treatments for rural high-traffic-volume roadways than on volume roadways. Common issues were related to loose rock rural low-traffic-volume roads, while a slightly lower margin damage, flushing, dust, bleeding, raveling, noise concerns, and short life expectancy. However, when asked to rank the Table 2.12. Revised Analysis of Most-Used top three treatments used, approximately 40% of agencies Preservation Treatments for PCC-Surfaced included chip seals within the top three treatments used on High-Volume Roadways rural and urban high-traffic-volume roadways. Washington State, Wyoming, Alaska, Maine, Alberta (Canada), and British Commonly Used Preservation Treatments Columbia (Canada) report using chip seals on high-traffic- on PCC High-Volume Roadways volume rural roadways; Nevada, North Carolina, and Rhode Rural (ADT > 5,000 vpd) Urban (ADT > 10,000 vpd) Island report using chip seals on both rural and urban high- traffic-volume roads. Minnesota and New Hampshire report 70% SHAs and provinces report using: using chip seals with polymer-modified binders on high- Joint reseal Joint reseal traffic-volume urban roads. Diamond grinding Crack seal The most common and successful treatments used on high-traffic-volume roadways appear to be thin HMA Full-depth patching Diamond grinding overlays, cold milling and thin HMA overlay, and micro- Full-depth patching surfacing, with crack seal also being successful on high-traffic 50% additionally report using: rural roadways. As shown in Table 2.13, the least popular treatments are fog seal, scrub seal, and slurry seal, with just Crack seal Partial-depth patching over half of respondents indicating these treatments are not Partial-depth patching Dowel bar retrofit considered for use on high-traffic-volume rural and urban Dowel bar retrofit Drainage preservation roadways. Of the treatments used on PCC pavements, the majority Drainage preservation (approximately two-thirds) of respondents indicated ultra-thin
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28 100 90 80 % of Agencies 70 60 50 40 30 20 10 0 Joint Crack Seal Diamond Partial-Depth Full-Depth Dowel Bar Drainage Resealing Grinding Patching Patching Retrofit Preservation Treatment Figure 2.10. Treatment use on rural PCC-surfaced roadways, based on revised definition of rural high traffic volume (ADT > 5,000 vpd). bonded wearing courses and thin overlays (either HMA of respondents would be more likely to apply load-transfer or PCC) are not considered applicable for rural or urban restoration to such roads. (although by a lower margin) high-traffic-volume roadways, Based on responses, agencies appear to have well-established as shown in Table 2.14. policies regarding treatment use. Nearly 90% of respondents For the most part, truck traffic does not influence treat- indicated they are not considering using any other treatments ment use by reporting agencies. At most, nearly one-third of other than those they currently employ. Of the few agencies respondents report being less likely to use single-course chip considering alternate treatments, the majority do not have seal on roadways with high truck traffic, and just over a quarter the funding necessary to pursue such options. 100 90 80 70 % of Agencies 60 50 40 30 20 10 0 Joint Crack Seal Diamond Partial-Depth Full-Depth Dowel Bar Drainage Resealing Grinding Patching Patching Retrofit Preservation Treatment Figure 2.11. Treatment use on urban PCC-surfaced roadways, based on revised definition of urban high traffic volume (ADT > 10,000 vpd).
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29 Table 2.13. Summary of Preservation Treatments Table 2.14. Summary of Preservation Treatments Considered Not Applicable for HMA Rural Considered Not Applicable for PCC Rural and Urban Roadways and Urban Roadways Treatments for Hot-Mix Asphalt Not Applicable % Checked Treatments for Portland Cement Not Applicable % Checked (HMA)Surfaced Pavements Rural/Urban Concrete (PCC) Pavements Rural/Urban Fog seal 51/69 Thin PCC overlays 62/55 Scrub seal 54/72 Ultra-thin bonded wearing course 75/73 Slurry seal 51/62 Thin HMA overlays 62/55 (<1.5 in. [<38 mm]) Single-course chip seal 83/91 Multiple-course chip seal 80/88 Chip seals with polymer-modified 71/84 asphalt binder For PCC pavements, the top three pavement perfor- mance issues addressed are related to smoothness/ride quality Ultra-thin whitetopping 57/NA and surface distress, with some concern about noise issues. The most-used preservation treatments appear to address specific issues without as much overlap between treatments; Performance Issues Addressed that is, joint resealing targets light to moderate surface dis- by Preservation Treatments tresses (Figure 2.15), whereas full-depth patching targets The top three deficiencies addressed on rural HMA-surfaced moderate to high surface distresses (Figure 2.16), and diamond pavements are light and moderate surface distress, raveling, grinding targets smoothness, friction, and noise concerns and friction loss. On urban HMA-surfaced pavements, the (Figure 2.17). top three deficiencies are light surface distress, raveling, and friction loss. Work-Zone Requirements Considering the most-used treatments for HMA-surfaced pavements, the primary issues targeted are related to surface For most of the treatments listed, an overwhelming number deterioration. As shown in Figures 2.12 through 2.14, thin of respondents reported using overnight or single-shift closures HMA overlays are applied to target a wider range of perfor- for application. Ultra-thin whitetopping on HMA-surfaced mance issues, including raveling, bleeding, and friction pavements and thin PCC overlays on PCC pavements are concerns. exceptions, requiring longer closure times. On urban PCC 100% % of Agencies Using Treatment 80% 60% 40% Rural Urban 20% 0% g n g y n se s s s lit es es es in tio in tio oi ua el ed tr tr tr da ic N av is is is Q le Fr xi fD D D R B e O id rf rf ur Su Su /R tS th od vy gh oo ea M Li Sm H Figure 2.12. Percentage of agencies filling cracks on rural and urban high-traffic-volume HMA-surfaced roadways to address pavement distresses.
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30 % of Agencies Using Treatment 100% 80% 60% 40% Rural Urban 20% 0% g n g y n se s s s lit es es es in tio in tio oi ua el ed tr tr tr da ic N av is is is Q le Fr xi fD D D R B e O id rf rf ur Su Su /R tS th od vy gh oo ea M Li Sm H Figure 2.13. Percentage of agencies sealing cracks on rural and urban high-traffic-volume HMA-surfaced roadways to address pavement distresses. 100% % of Agencies Using Treatment 80% 60% 40% Rural 20% Urban 0% g n g y n se s s s lit es es es in tio in tio oi ua el ed tr tr tr da ic N av is is is Q le Fr xi fD D D R B e O id rf rf ur Su Su /R tS th od vy gh oo ea M Li Sm H Figure 2.14. Percentage of agencies applying thin HMA overlay on rural and urban high-traffic-volume HMA-surfaced roadways to address pavement distresses.
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31 100% % of Agencies Using Treatment 80% 60% 40% Rural Urban 20% 0% g n g y n se s s s lit es es es in tio in tio oi ua el ed tr tr tr da ic N av is is is Q le Fr xi fD D D R B e O id rf rf ur Su Su /R tS th od vy gh oo ea M Li Sm H Figure 2.15. Percentage of agencies resealing joints on rural and urban high-traffic-volume PCC roadways to address pavement distresses. 100% % of Agencies Using Treatment 80% 60% 40% Rural Urban 20% 0% g n g y n se s s s lit es es es in tio in tio oi ua el ed tr tr tr da ic N av is is is Q le Fr xi fD D D R B e O id rf rf ur Su Su /R tS th od vy gh oo ea M Li Sm H Figure 2.16. Percentage of agencies using full-depth patching on rural and urban high-traffic-volume PCC roadways to address pavement distresses.
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32 100% % of Agencies Using Treatment 80% 60% 40% Rural Urban 20% 0% g n g y n se s s s lit es es es in tio in tio oi ua el ed tr tr tr da ic N av is is is Q le Fr xi fD D D R B e O id rf rf ur Su Su /R tS th od vy gh oo ea M Li Sm H Figure 2.17. Percentage of agencies diamond grinding rural and urban high-traffic-volume PCC roadways to address pavement distresses. roadways, there is a distinct hierarchy amongst the scenarios, or for closure-time information. However, some guidance but the majority tends to use overnight or single-shift closures; was requested concerning the following: noticeably fewer note using longer closures, except for thin PCC overlays. · Other agency experience; · Typical noise associated with treatment; · Treatment production rate; Contracting Mechanisms · Treatment costs by region; Between 30% and 50% of the respondents reported using · Obtaining experienced contractors; contract maintenance for constructing preservation treatments · Material availability; and on high-traffic-volume HMA- and PCC-surfaced roadways. · Opening to traffic. Fewer than 25% reported using warranties for treatments applied to HMA-surface pavements, whereas less than 5% The areas where the most guidance is needed include the reported using warranties for treatments applied to PCC- following: surfaced pavements. Between 65% and 75% of the respondents indicated using · Durability and expected life of treatment; method-based specifications (with some level of QC/QA) for · Applicable traffic volume; and ensuring the quality and performance of treatments applied · Appropriate climatic conditions for treatment. to HMA-surfaced pavements, whereas between 50% and 75% used method-based specifications for treatments applied to Closing PCC-surfaced pavements. Between 25% and 50% indicated using performance specifications to ensure the quality and The survey of practice provided insight into agency practices performance of treatments applied to both surface types. regarding pavement preservation of high-traffic-volume The majority of those that do not currently practice QC/QA roadways. Although most agencies use a variety of preserva- for pavement preservation indicated they do not plan to imple- tion treatments on their respective networks, a more selective ment such practices or to require warranties. approach is required when considering such treatments for use on high-traffic-volume roadways. By analyzing treatment preference across the United States and Canada through this Preservation Guidance Needs survey, the more commonly used treatments were identified, In general, the respondents did not report that guidance is allowing the evaluation of best practices for a limited number needed for determining typical traffic control requirements of treatments.