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

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16 C H A P T E R 4 In this approach, test sections of preservation treatments or strategies are constructed and monitored, and the obtained data are analyzed in order to develop pavement response models and distress transfer functions associated with those treatments or strategies. The test sections consider a range of pavement and surface material types, a range of traffic loadings and climatic conditions, and different treatment types and strategies, and include pavements that receive no treatments after initial con- struction (until rehabilitation) to serve as controls. Process Description Several steps are required to develop response models that consider the effects of preservation on pavement performance. 1. Treatment and Strategy Selection: The various preservation treatments or strategies and the related performance objec- tives are identified. Since the MEPDG evaluates pavement condition in terms of ride, rutting, cracking, and faulting, preservation treatments that influence these parameters are considered. Table 6 lists examples of suggested pres- ervation treatments for addressing specific objectives and the affected performance measures (Peshkin et al. 2004). 2. Experimental Design Development: An experimental design is developed that includes the range of relevant variables (e.g., pavement type, treatment and strategy types, traffic, environment, treatment timings). The experimental design should take into consideration recently constructed pave- ments that have received no preservation treatments but on which preservation treatments will be applied at a later time and also should consider the following key elements (Peshkin et al. 2004): – Site selection: Pavement type, pavement design, exist- ing pavement condition, pavement age, traffic level, and climate condition. – Treatment types: Selected treatments to address different pavement preservation objectives. – Treatment timing: Varied treatment application timing to consider the effects of existing pavement condition on treatment performance (i.e., when to apply the first treatment and how often subsequent treatments are applied). – Site layout: Project length, section length, and replicate sections. – Experiment duration: Depending on the type of treat- ment (e.g., a few years for crack sealing or fog sealing or several years for thin overlay or diamond grinding). The experimental design could range from one test site representing a specific pavement design, climatic zone, and traffic level to multiple test sites encompassing different pavement designs subjected to different traffic levels and climates. One or more similar or different preservation treatments applied at similar or different times after con- struction (except for control sections that remain untreated) may be considered. 3. Test Section Construction: A combination of existing pave- ments and new test sections that meet the requirements of the experimental design are constructed according to specific requirements. 4. Performance Monitoring: Test sections (including con trol sections) are monitored on at least an annual basis using either manual or automated condition surveys (more fre- quent performance monitoring might be necessary for some treatments). The performance evaluation of HMA pavements should include block cracking, fatigue crack- ing, linear cracking, rutting, bleeding, raveling, weather ing (oxidation), polished aggregate, potholes, and patching, and the evaluation of PCC pavements should include corner breaks, linear cracking, joint seal damage, joint spalling, joint faulting, pumping, blowups, and patching (Peshkin et al. 2004). Measurement of surface friction, surface tex- ture, and tire-pavement noise performance may be con- sidered because preservation treatments are frequently applied to address these pavement surface characteristics. Developing Response Models for Considering the Effects of Preservation in the MEPDG Procedures

17 5. Performance Models Development: Performance prediction models are developed for the various pavement preserva- tion treatments or strategies using the data obtained from the preservation test sections to supplement the MEPDG models. The models should consider the effects of climate, traffic loading, material properties, and existing pavement condition. The NCHRP Project 1-37A Final Report (ARA, Inc. 2004) describes and illustrates the model forms and variables used to develop acceptable performance models. 6. Model Calibration and Validation: In this final step, the developed performance models are calibrated and validated using the procedures identified in the AASHTO Guide for the Local Calibration of the Mechanistic-Empirical Pave- ment Design Guide (herein referred to as the Local Cali- bration Guide) (AASHTO 2010). The calibration process should recognize that preservation treatments can affect the structural properties and thermal/moisture condi- tions of the existing pavement and the material properties of the top pavement layer; these will affect the computed stresses and strains. Preservation treatment thickness (or removal depth, in the case of milling/grinding) from design or as-built records, thermal/moisture profile data from instrumented pavements, and pavement structure material property data from non-destructive testing (NDT) may be used to adjust layer thicknesses, temperatures, water contents, or material properties to reflect treatment appli- cation. The calibration process will result in revised coef- ficients for either or both the load-response model and distress transfer function associated with a particular per- formance indicator. Feasibility Assessment Developing pavement preservation response models pro- vides a comprehensive framework for accounting for the effects of preservation treatments or strategies on pavement performance (both structural and functional) but requires an extensive experimental investigation and long-term data collection effort. The design analysis requires a modified Pavement ME Design software program that includes new models to supplement the current MEPDG models and new programming code and input screens for defining the pos- sible treatments or strategies and details (e.g., thicknesses and properties of treatments and the criteria for their appli- cation). Implementing this approach requires the develop- ment of a detailed experimental design, the identification of locations for test sections (including untreated control sections), the application of preservation treatments, and the collection of performance monitoring data over several years. Also, it requires the development of a database of relevant information (e.g., preservation treatments or strategies, traf- fic conditions, climate conditions, pavement performance measures) and a significant data analysis and modeling effort to develop performance prediction models. The approach can also be used to develop models for surface defects (e.g., ravel- ing and deformation distresses) and pavement surface char- acteristics (e.g., friction and noise) that are not considered in the MEPDG. Because of the requirement for long-term performance monitoring and data collection, this approach is likely to be implemented as part of a national research effort or a multi- agency cooperative research program. However, it can also be implemented under an agency-wide effort. An example illustrating the process of developing pavement preservation response models is presented in the following. Example of Implementation Process The Indiana Department of Transportation (INDOT) is one of a few agencies that have constructed MEPDG-designed pavements or pavements specifically intended for additional performance model calibration. INDOT has completed over 100 paving projects since 2009 using the MEPDG design anal- ysis procedure (Nantung 2010). The projects included both flexible and rigid designs located on roads throughout the state ranging from Interstates to moderately trafficked U.S. Table 6. Preservation treatment and performance objectives. Preventive Maintenance Objective Preservation Treatments Performance Measure/ Condition HMA Pavements PCC Pavements Improve Ride SlS, MS, thin HMAOL, UTBWC DG IRI Extend Pavement Life CrS, FS, ScS, ChS, SlS, MS, thin HMAOL, UTBWC CrS, JRS, DG Cracking, patching, rutting, raveling, faulting, pumping, spalling, potholes Reduce Moisture Infiltration CrS, FS, ScS, ChS, SlS, MS, thin HMAOL, UTBWC CrS, JRS Cracking, patching, rutting, raveling, faulting, pumping, spalling, potholes Notes: CrS = crack seal, FS = fog seal, SlS = slurry seal, ScS = scrub seal, ChS = chip seal, MS = microsurfacing, HMAOL = HMA overlay, UTBWC = ultrathin bonded wearing course, JRS = joint resealing, DG = diamond grinding, IRI = International Roughness Index.

18 and state routes to low-volume state routes. Data from these projects are used in a hypothetical example to illustrate the development of pavement preservation response models for conventional and full-depth HMA pavements treated with a single application of chip seals, microsurfacing, or thin HMA overlay. This follows the process described in this chapter and incorporates certain assumptions. Step 1: Preservation Treatment and Performance Model Selection The flexible pavements considered in this example were designed according to the MEPDG procedures. Preservation treatments, such as a single application of chip seals, micro- surfacing, or thin HMA overlay, are considered. Table 7 shows the key performance objectives for each treatment and the associated application criteria. Models for predicting rutting, transverse thermal cracking, alligator cracking, longitudi- nal cracking, International Roughness Index (IRI), raveling/ weathering, and friction will be considered. Step 2: Experimental Design Development Considering the two distinct climates available in Indiana: wet, hard freeze, and spring thaw (northern half of state) and wet, freeze-thaw cycling (southern half of state), the matrix shown in Table 8 has been proposed to serve as the experi- mental design. It includes six test sites, designated Test Sites 1 through 6, each of which will include 20 test sections (two replicates of each of the nine preservation sections and the untreated control section). The experimental design also iden- tifies the preservation treatments proposed for each site and their time of application. Step 3: Test Site Identification and Construction From the many flexible pavement projects that were designed and constructed in recent years using the MEPDG, several projects with sufficient length to accommodate the planned 20 test sections have been identified as candidates for Test Sites 1 through 5; no projects were identified for Test Site 6. However, a review of the design and construction/materials data for these projects revealed that candidate projects for Test Site 1 lacked the materials/construction data needed for analy- sis and model building. Therefore, Test Site 1 was eliminated from the experiment design, and the matrix was modified to include only four test sites (Test Sites 2 through 5). The four most appropriate projects were selected to serve as Test Sites 2 through 5. These projects were constructed in 2010 and 2011. The design and construction/materials data for these pavements were compiled. According to the sched- ule for preservation treatment application given in the exper- imental matrix, these treatments will be applied between 2014 and 2019 (first treatment will be applied in 2014 as a 4-year treatment for pavements built in 2010, and last treat- ment will be applied in 2019 as an 8-year treatment for pave- ments built in 2011). Table 9 shows the revised experimental design matrix. Test section limits were established within each site with consideration given to construction/materials data and other relevant items. The preservation treatments listed in Table 9 for the differ- ent test sections will be constructed between 2014 and 2019. Treatment design and construction/materials data (including weather conditions) will be collected, reviewed, and compiled for use in the performance model development. Treatment AADT1 Existing Pavement Distress Rutting, in. IRI, in./mi Friction Treatment? Surface Aging Crack Seal Any Low to moderately severe surface cracks N/A N/A No N/A Fog Seal <5,0002 Low-severity environmental surface cracks N/A N/A No3 Reduces aging and oxidation, arrests minor raveling Seal Coat (i.e., Chip Seal) <5,0002 Low-severity environmental surface cracks <0.254 N/A4 Yes Arrests aging, oxidation, and minor raveling Microsurfacing Any Low-severity surface cracks Any <130 Yes Arrests aging, oxidation, and minor raveling UBWC Any Low to moderately severe surface cracks <0.25 <140 Yes Arrests aging, oxidation, and moderate raveling HMA Inlay Any Low to moderately severe surface cracks Any <150 Yes Replaces aged, oxidized, or raveled surface HMA Overlay Any Low to moderately severe surface cracks Any <150 Yes Arrests aging, oxidation, and moderate raveling Notes: 1 For mainline pavement. 2 Unless traffic can be adequately controlled. 3 Treatment may reduce skid numbers. 4 Treatment does not address this. N/A = not applicable. AADT = average annual daily traffic. Table 7. INDOT HMA pavement preventive maintenance treatments (INDOT 2011).

Table 9. Revised experimental design matrix. Climate Zone Preservation Treatment Flexible Pavements Conventional HMA Full-Depth HMA Low-Volume State Routes Moderate Volume U.S. and State Routes Interstate and Freeway Routes 1 (Wet, Hard Freeze, and Spring Thaw) Site Description: Site 1—No project available Site 2—U.S. 24 Phase 2, Fort Wayne 2011 Site 3—Airport Expressway @ I-465, Indianapolis 2010 (0) Untreated control (1a) Chip seal @ Year 4 (1b) Chip seal @ Year 5 (1c) Chip seal @ Year 6 (2a) Microsurface @ Year 4 (2b) Microsurface @ Year 5 (2c) Microsurface @ Year 6 (3a) Thin HMA OL @ Year 4 (3b) Thin HMA OL @ Year 5 (3c) Thin HMA OL @ Year 6 2 (Wet, Freeze- Thaw Cycling) Site Description: Site 4—SR 66, Evansville 2010 Site 5—SR 641, Terre Haute 2010 Site 6—No project available (0) Untreated control (1a) Chip seal @ Year 4 (1b) Chip seal @ Year 6 (1c) Chip seal @ Year 8 (2a) Microsurface @ Year 4 (2b) Microsurface @ Year 6 (2c) Microsurface @ Year 8 (3a) Thin HMA OL @ Year 4 (3b) Thin HMA OL @ Year 6 (3c) Thin HMA OL @ Year 8 Notes: HMA OL = HMA overlay. Shaded cells indicate no test sections (suitable projects not available). Climate Zone Preservation Treatment Flexible Pavements Conventional HMA Full-Depth HMA Low-Volume State Routes Moderate Volume U.S. and State Routes Interstate and Freeway Routes 1 (Wet, Hard Freeze, and Spring Thaw) (0) Untreated control Site 1 Site 2 Site 3 (chip seals excluded)(1a) Chip seal @ Year 4 (1b) Chip seal @ Year 5 (1c) Chip seal @ Year 6 (2a) Microsurface @ Year 4 (2b) Microsurface @ Year 5 (2c) Microsurface @ Year 6 (3a) Thin HMA OL @ Year 4 (3b) Thin HMA OL @ Year 5 (3c) Thin HMA OL @ Year 6 2 (Wet, Freeze- Thaw Cycling) (0) Untreated control Site 4 Site 5 Site 6 (chip seals excluded)(1a) Chip seal @ Year 4 (1b) Chip seal @ Year 6 (1c) Chip seal @ Year 8 (2a) Microsurface @ Year 4 (2b) Microsurface @ Year 6 (2c) Microsurface @ Year 8 (3a) Thin HMA OL @ Year 4 (3b) Thin HMA OL @ Year 6 (3c) Thin HMA OL @ Year 8 Note: HMA OL = HMA overlay. Table 8. Proposed experimental design matrix.

20 Step 4: Performance Monitoring and Database Development A condition data collection protocol was developed to record annual measurements of rutting, transverse thermal crack- ing, alligator cracking, longitudinal cracking, IRI, raveling/ weathering, friction, and macrotexture (as a supplement to friction). Also, a falling weight deflectometer (FWD) testing plan to evaluate pavement structural response before and after the application of preservation treatments was also developed. The DOT will monitor test site conditions and collect the required data, according to the data collection protocol, for several years following the placement of the preservation treatments. These data, together with the data collected during construction, will be reviewed for completeness and accuracy and will be compiled into a database. Step 5: Develop Performance Models As sufficient time-series performance data become available from the test sections, performance prediction models and dis- tress transfer functions will be developed for both the untreated control pavements and the preservation-treated pavements. Also, raveling and friction models will be developed. The ravel- ing models will consider asphalt binder grade/viscosity and content, aggregate type, air voids in the HMA mixture, pave- ment age, axle load repetitions, thermal conductivity, surface shortwave absorptivity, and average annual freezing index. The friction models will consider variables such as aggregate type and polish susceptibility, aggregate gradation, asphalt binder grade/viscosity, effective asphalt binder content, pavement age, and axle load repetitions. Step 6: Model Calibration and Validation The procedures identified in the Local Calibration Guide (AASHTO 2010) will be used to calibrate and validate the models developed for each performance parameter. The orig- inal pavement structure data, treatment application thickness data, and before-and-after deflection data from FWD testing will be used to modify appropriate parts of the models (e.g., layer thicknesses, material properties, moisture contents, temperatures) to reflect the effects of preservation treatment application. For example, the HMA layer rut depth model is adjusted to reflect the post-treatment effect on HMA layer thickness, depth confinement factor, and mix layer tempera- ture. Similarly, the alligator and longitudinal cracking model is adjusted to reflect the post-treatment effect on HMA layer thickness and dynamic modulus. This process results in a unique set of calibration coefficients for each preservation treatment (in addition to the calibration coefficients for the control pavement).