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17 3.1 Relevant Issues in Pavement Preservation The guidelines for developing PRS for pavement preservation treatments will differ from those for rehabilitation and reconstruction of flexible and rigid pavements for the following reasons: 1. Preservation treatment performance is greatly influenced by the pre-existing pavement con- ditions with respect to both structural capacity and functional condition. 2. Given that preservation treatments are non-structural fixes, different performance measures should be considered for their functional performance evaluations. For example, texture, raveling, flushing, bleeding and weathering are a few important indicators of performance for preservation treatments. 3. The construction materials used in preservation treatments can differ from conventional pavement materials. For example, most of the preservation treatments for flexible pavements use asphalt emulsions or polymer-modified asphalt emulsions as compared to conventional or modified asphalt binders used in pavement construction. 4. The construction processes used for preservation treatments differ from those for traditional pavement construction. For example, an important measure for chip seal success is the embed- ment depth of the aggregate whereas compaction density is a measure of quality for flexible pavement construction. Understanding the above differences highlights the complexities of developing PRS guide- lines for pavement preservation treatments. A literature review was conducted to examine the prevalent issues of pavement preservation. Given that a candidate PRS is based on pavement construction and material variables, the literature review also identified the types of acceptance quality assurance unique to pavement preservation used by highway agencies. An emphasis was placed on gathering the following information from past pavement preservation technical appraisals and other relevant literature: ⢠Types of widely used flexible and rigid pavement preservation treatments, ⢠Criteria used for preservation treatment selection, ⢠Specifications for preservation treatments, ⢠Measures used for quality assurance, ⢠Service life extensions expected of different treatments, and ⢠Types of distresses addressed by different preservation treatments. Current Practice C h a p t e r 3
18 performance-related Specifications for pavement preservation treatments 3.2 Commonly Used Preservation Treatments Preservation practices of several highway agencies (i.e., Alaska, California, Colorado, Georgia, Indiana, Michigan, Minnesota, New Mexico, North Carolina, Ohio, Oregon, Rhode Island, Texas, Washington, and Wisconsin) were evaluated based on information contained in the literature (Peshkin et al. 2011; Peshkin and Hoerner 2005; Kogler et al. 2008; Tenison and Hanson 2009; Tighe and Gransberg 2011). This evaluation showed that highway agencies generally use the same preservation treatments for flexible and rigid pavements (see Tables 3-1 and 3-2). The frequency of use of these preservation treatments was also examined to determine which treatments are suited for the development of PRS guidelines. A survey of 42 U.S. highway agencies and 7 Canadian agencies (Tighe and Gransberg 2011) indicated the use of preservation treatments for different pavement types shown in Table 3-3. This information indicates that the most commonly used treatments for flexible pavements are chip seals, HMA patches, and thin HMA overlays, and the most com- monly used rigid pavement preservation treatments are diamond grinding, joint sealing, and load- transfer restoration. Environmental conditions can influence preservation treatment effectiveness. For example, thin HMA overlays are susceptible to thermal cracking in cold regions. The use of preservation treatments in the different climate regions of the United States is documented in the literature (Peshkin et al. 2004, Peshkin and Hoerner 2005, Kogler et al. 2008, Tighe and Gransberg 2011). A study conducted by the Strategic Highway Research Program (SHRP) categorized the climate zones according to the freezing index (FI) as shown in Table 3-4 (Peshkin et al. 2011). The preservation treatments used in these climatic zones were determined from a survey of state DOTs (Peshkin et al. 2011) and the summaries are provided in Tables 3-5 and 3-6, for flexible and rigid pavements, respectively. The survey indicates some preference to certain treatments depending on climatic zones and road class. However, overall, the state of the prac- tice among different states shows that similar preservation treatments are used in the different climates and road classes. 3.3 Identification of AQCs and Performance Measures PRS are founded on relationships between materials and construction (M&C) characteristics (i.e., AQC) and expected performance measures. The M&C characteristics are parameters that are measures of quality and are either directly or indirectly related to expected pavement perfor- mance. As part of the literature review, several M&C characteristics related to pavement preser- vation construction were identified. These characteristics are also the candidate AQCs for use in preservation PRS. Tables 3-7 and 3-8 list the M&C characteristics for flexible and rigid pavement treatments, respectively. 3.4 Service Life Extensions The literature was also reviewed to determine the expected pavement service life extensions (SLEs) due to different types of preservation treatments. The expected SLEs for flexible pave- ment preservation treatments are well-documented (Peshkin et al. 2011, Eli Cuelho and Akin 2006). Typical ranges of pavement SLEs for rigid pavement preservation treatments are also available in the literature (Peshkin et al. 2011, Hiller and Buch 2004, Yildirim et al. 2010, Santero et al. 2009). Table 3-9 presents ranges of the SLEs for the most widely used preserva- tion treatments. The performance of the pavement depends not only on the treatment type but also on existing pavement conditions (Peshkin et al. 2004, Haider and Dwaikat 2012, Haider and Dwaikat 2011);
Current practice 19 Treatment Type/Climate Purpose Performance Measures AQCs Road Class Chip Seal (DF) Seal longitudinal, transverse and block cracking, inhibit and retard raveling/weathering, improve friction, improve ride quality, inhibit moisture infiltration Raveling, stripping bleeding flushing, cracking and rutting, friction loss, roughness, moisture infiltration Emulsion application rate Aggregate application rate Application temperature Asphalt and aggregate material type Texture depth Rural Crack Seal (DF, MF) Structural cracking early in development, prevent the intrusion of moisture through cracks Longitudinal, transverse, and reflective cracking, minor block cracking, wear HMA mix design Size, depth, type of cracks Adequate cleaning of cracks Types of crack sealant materials Seal existing layer adhesion Climate (moderate temperatures and dry pavement) Setting time and curing time Check for missed cracks Mixed Slurry Seal (MF, NF) Mostly functional, reduce tire pavement noise, not ideal for areas with severe cracking and high deflection Longitudinal and transverse reflective cracking, rutting, stripping, raveling, bleeding/flushing, weathering, loss of friction, roughness Binder content, fine aggregate and filler materials, asphalt cement content Aggregate gradation Application temperature Urban Thin HMA Overlay (DF, MF) Remove surface distresses including cracking and bleeding, improve ride, inhibit moisture infiltration Cracking, raveling, weathering, friction loss, bleeding, roughness, ride, moisture infiltration Layer thickness Mix design and aggregate gradation Asphalt content, density, air voids Rural Microsurfacing (MF) Hot In-place Recycling (MF) Cold In-place Recycling (DF, MF) Inhibit and retard raveling/weathering, retard asphalt aging and hardening, inhibit low and medium severity bleeding, improves friction, inhibit moisture infiltration, multiple courses can be used to correct minor rutting Remove low-severity longitudinal, block, and transverse cracking, remove raveling/weathering, improve friction, improve ride quality Remove low-severity longitudinal, block, and transverse cracking, remove raveling/weathering, improve friction, improve ride quality Longitudinal and transverse reflective cracking, raveling, bleeding/flushing, weathering, loss of friction, roughness Fatigue cracking, transverse and longitudinal cracking, block cracking, raveling, weathering, friction loss, bleeding, roughness, corrugation, rutting Longitudinal, transverse, and surface cracking, raveling, weathering, friction loss, bleeding, roughness, corrugation, rutting, bumps, sags Similar construction considerations as slurry seals Aggregate must be chemically compatible with emulsions Setting time, curing time Testing of recycled asphalt materials and virgin HMA if used Percentage of recycling agent in the recycled mix design Smoothness of finished surface, depth of scarification of existing surface course Setting time and placement of joint Testing of recycled asphalt materials and any additional aggregate added Testing of virgin HMA if used Size of pulverizing of existing surface course Percentage of recycling agent in the recycled mix design Smoothness, depth of planning of surface course, asphalt material application rate Mixed Urban Rural Table 3-1. Summary of preservation treatments for flexible pavements.
20 performance-related Specifications for pavement preservation treatments Climate Zone FI Range Location Deep freeze (DF) FI > 400 Northern states Moderate freeze (MF) 50 < FI ⤠400 Middle, central states No freeze (NF) FI ⤠50 Southern states and parts of coastlines Table 3-4. Climatic zone descriptions (Peshkin et al. 2011). Pavement Type Treatment Percent Flexible Chip seal 82.1 Hot patch 71.4 Thin overlay 71.4 Cold patch 67.9 Asphalt level-up 64.3 Crack seal 42.9 Fog seal 39.3 Slurry seal 39.3 Microsurfacing 35.7 Rigid Diamond grinding 92.6 Joint sealing 88.9 Dowel-bar retrofit 70.4 Crack seal 59.3 Mud jacking 51.9 Milling 29.6 Thin PCC overlay 29.6 Shot-blasting 22.2 Table 3-3. Percent of states using various preservation treatments (Tighe and Gransberg 2011). Treatment Type/Climate Purpose Performance Measures AQCs Road Class Diamond Grinding (MF, NF) Remove faulting, improve ride quality and surface friction Joint faulting, slab curling and warping, and friction loss (grinding); friction loss and splash and spray (grooving) Measures of or related to surface smoothness Ground area, bump heights, groove dimensions Spacing of saw blades, depth of cut Mixed Joint Seal/Crack Seal (DF, MF, NF) Reduce moisture infiltration and prevent intrusion of incompressible fines, reducing cracking, less effective on pavements with faulting Longitudinal cracking, transverse cracking, corner cracking - crack seal more effective when faulting, palling not present Material characteristics of sealant â shape factors, sealant bond, depth of sealant Mixed Load-Transfer Restoration (DF, NF) Improve load transfer, reduce or eliminate pumping, faulting, and corner breaks Joint faulting, pumping, corner breaks Placement of dowel bars, number and spacing Selection of patch material Compressive strength of patch material Slot cutting sizes Saw depth of slots, position (centered over joint or crack, parallel to roadway centerline) Mixed Partial-depth Repair (DF, MF, NF) Repair shallow spalling and improve ride quality, restore structural function of localized deterioration Joint spalling (non-material related), weak concrete that causes localized deterioration Patch area preparation, removal procedures for preparation, finishing procedures, texture, material selection Use of additional materials, i.e., bonding agents Depth of saw cut Mixed Table 3-2. Summary of preservation treatments for rigid pavements.
Road Climatic Region Crack Fill Crack Seal Slurry Seal Microsurfacing Single Chip Seal Multi- Chip Seal Thin HMA Overlay Cold Milling Hot IPR Cold IPR Rural Deep freeze E E L E E E L L E Moderate freeze E E M L L E E L E No freeze M M L M M M M L L Urban Deep freeze E E L M M M E L M Moderate freeze E E M M L E E M L No freeze E E M M E M M E M M M M E L M Note: IPR = In-place recycling, E = Extensive use (>66%), M = Moderate use (33% to 66%), L = Limited use (<33%) Table 3-5. Extent of use of flexible pavement preservation treatments (Peshkin et al. 2011). Note: E = Extensive use (>66%), M = Moderate use (33% to 66%), L = Limited use (<33%) Road Climatic Region PCC Joint Seal PCC Crack Seal Diamond Grinding Partial- depth Repair Dowel- Bar Retrofit Rural Deep freeze M M M E E Moderate freeze E E E E M No freeze E E E E M Urban Deep freeze E M M M M Moderate freeze E E E E M No freeze E E E E E Table 3-6. Extent of use of rigid pavement preservation treatments (Peshkin et al. 2011). Table 3-7. Performance measures and materials and construction characteristics for flexible pavement treatments (Peshkin et al. 2011). Treatment Types Performance Measures Materials and Construction Characteristics Chip seal Raveling, stripping bleeding flushing, cracking and rutting, friction loss, roughness, moisture infiltration Emulsion and aggregate application rate, application temperature Address existing surface conditions prior to placement, i.e., raised markers, cracked areas Spreader and distributor working in tandem Asphalt and aggregate material type Roller passes, curing time, brooming procedures Crack seal Longitudinal, transverse, and reflective cracking, minor block cracking, wear HMA mix design Size, depth, type of cracks Adequate cleaning of cracks Types of crack sealant materials Adhesion between seal and existing layer Climate (moderate temperatures and dry pavement) Setting time and curing time Check for missed cracks Slurry seal Longitudinal and transverse reflective cracking, rutting, stripping, raveling, bleeding/flushing, weathering, loss of friction, roughness Address existing conditions prior to placement, i.e., raised pavement markers, any areas requiring patching or crack sealing, clean surface Binder content, fine aggregate and filler materials, asphalt cement content Proper rolling procedures Aggregate gradation Climate conditions Application temperature (continued on next page)
22 performance-related Specifications for pavement preservation treatments Treatment Types Performance Measures Materials and Construction Characteristics Joint reseal Crack seal Longitudinal cracking, transverse cracking, corner cracking - crack seal more effective when faulting, palling not present Material characteristics of sealant â shape factors, sealant bond, depth of sealant Cleanliness of joint or crack Placement considerations based on material, experience, additional anticipated treatments Tack free sealants while setting Diamond grinding and grooving Joint faulting, slab curling and warping, and friction loss (grinding); friction loss and splash and spray (grooving) Surface smoothness, ground area, bump heights, groove dimensions Aggregate type and hardness Spacing of saw blades, depth of cut Address existing structural deficiencies Partial-depth repair Joint spalling (non-material related), weak concrete that causes localized deterioration Patch area preparation, removal procedures for preparation, finishing procedures, texture, material selection Use of additional materials, i.e., bonding agents Depth of saw cut Load-transfer restoration Joint faulting, pumping, corner breaks Placement of dowel bars, number and spacing Selection of patch material Compressive strength of patch material Slot cutting sizes Saw depth of slots, position (centered over joint or crack, parallel to roadway centerline) Compressible inserts to prevent patching material from entering the joint or crack Ensure placement procedures of patching material do not disturb dowel bar within slot Table 3-8. Performance measures and materials and construction characteristics for rigid pavement treatments (Peshkin et al. 2011). Treatment Types Performance Measures Materials and Construction Characteristics Thin HMA overlay Microsurfacing Hot in-place recycling Cold in-place recycling Cracking, raveling, weathering, friction loss, bleeding, roughness, ride, moisture infiltration Longitudinal and transverse reflective cracking, raveling, bleeding/flushing, weathering, loss of friction, roughness Fatigue cracking, transverse and longitudinal cracking, block cracking, raveling, weathering, friction loss, bleeding, roughness, corrugation, rutting Longitudinal, transverse, and surface cracking, raveling, weathering, friction loss, bleeding, roughness, corrugation, rutting, bumps, sags Layer thickness Mix design and aggregate gradation Asphalt content, density, air voids Pretreatment, i.e., milling, bump grinding, tack coat Cleanliness of pavement surface, setting time Similar construction considerations as slurry seals Aggregate must be chemically compatible with emulsions Climate, avoid rain and hot or freezing extremes Setting time, curing time Management of specialized equipment Address local structural problems if present Testing of recycled asphalt materials and virgin HMA if used Percentage of recycling agent in the recycled mix design Smoothness of finished surface, depth of scarification of existing surface course Setting time and placement of joint Management of specialized equipment Address local structural problems Testing of recycled asphalt materials and any additional aggregate added Testing of virgin HMA if used Size of pulverizing of existing surface course Percentage of recycling agent in the recycled mix design Smoothness, depth of planning of surface course, asphalt material application rate Table 3-7. (Continued).
Current practice 23 numerous studies have shown the typical ranges of SLEs for different preservation treatments. Variations in these may be attributed to the timings of treatment application. Appropriate pres- ervation treatment type selection and timing depends on how the existing pavement conditions are characterized. The survey of highway agencies has shown that different processes are used for selecting preservation treatment type and timing strategies (Peshkin and Hoerner 2005). Most agencies adopt simple methods for selecting treatment type and timing, including a combination of in-house guidelines (from historical records), engineering judgment, and estab- lished decision trees based on distress type and severity collected from pavement condition surveys (Peshkin and Hoerner 2005). However, the agencies recognize that the selected timing does not necessarily represent the âoptimal timingâ for applied treatments. 3.5 Identification of Preservation Treatments Based on the literature review, candidate preservation treatments were selected for develop- ing guidelines for performance-related specifications. These preservation treatments meet the following criteria: ⢠Commonly used treatment in preservation practices, ⢠Have AQCs that are objective and measurable during or after construction, and ⢠Have performance measures data over time. Tables 3-1 and 3-2 summarize the features of the most common pavement preservation treat- ments for flexible and rigid pavements, respectively. The tables also identify climates in which the treatments are used extensively and the road classes on which they are most commonly found (National Academies of Sciences, Engineering, and Medicine 2001). In addition, the tables outline the AQCs taken from the M&C properties of each treatment and the associated performance measures. The information summarized in these tables is used to identify AQCs of the different preservation treatments which relate to expected pavement performance and could be used in developing PRS guidelines. Pavement Type Treatment Type Typical Life Extension (Years) Flexible Crack seal 2 to 10 Single chip seal 7 to 12 Double chip seal 5 to 10 Microsurfacing 4 to 7 Fog seal 1 to 3 Slurry seal 3 to 8 Thin Overlay 3 to 23 Hot in-place recycling 3 to 8 Cold in-place recycling 4-17 Rigid Diamond grinding 8 to 15 Joint seal/crack seal 7 to 10 Dowel-bar retrofit 2 to 16 Partial-depth repair 5 to 15 Table 3-9. SLEs for preservation treatments (Peshkin et al. 2011, Eli Cuelho and Akin 2006, Wu et al. 2010).
