Optimal Timing of Pavement Preventive Maintenance Treatment Applications (2004) / Chapter Skim
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From page 18... ...
Pavement Performance The computation of the benefit associated with an applied preventive maintenance treatment requires knowledge of the anticipated performance of the pavement. The effect of a treatment on performance is determined by the change in condition indicators, such as International Roughness Index (IRI)
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Using this definition, different types of benefit may be associated with an application of a given preventive maintenance treatment. For example, applying a chip seal could result in benefits in the form of improved friction, retarded oxidation, or reduced rutting.
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This approach is explained with the following example. Assume that a particular preventive maintenance treatment timing results in individual benefit values of 27 percent for rutting, 12 percent for cracking, and 47 percent for friction.
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The methodology does not include other common types of condition-sensitive user costs (e.g., vehicle operating costs, discomfort, and accident costs) because the difference in pavement condition for preventive maintenance candidates is expected to be relatively small.
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, outlines the steps for estimating work zone user delay costs. The process requires at least the following information: • General project inputs (e.g., project length, number of lanes)
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However, because work zones associated with most preventive maintenance treatments are of relatively short duration and short length, queues are less likely to form and the error associated with this item is reduced. Additional Routine Maintenance Costs Different pavement structures and surfacing approaches require different needs for routine maintenance.
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From page 24... ...
Selection of Application Ages The optimal time to apply a selected preventive maintenance treatment is estimated by conducting analysis for different timing scenarios in which the treatment is applied at different pavement ages. Step 2: Selection of Benefit Cutoff Values The concept of optimal timing stipulates that treatments applied too soon or too late do not necessarily provide added benefit.
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From page 25... ...
The important benefit-related areas are those below condition indicator curves that decrease over time and above condition indicator curves that increase over time. The final do-nothing condition area for a given condition indicator is determined by applying the following area boundary conditions: • Y-axis limits -- in the y direction, the pertinent area is bounded by the defined upper and lower benefit cutoff values.
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From page 26... ...
In the previous example, if a preventive maintenance treatment is applied at a pavement age of 10 years, the performance curves for friction, rutting, and roughness, as shown in Figure 6, reach their triggering benefit cutoff values at 20, 22, and 24 years, respectively. Therefore, the expected service life (and analysis period)
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From page 27... ...
As mentioned previously, the important benefit-related area is the area below condition indicator curves that decrease over time or above condition indicator curves that increase over time (as shown in Figure 7)
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From page 28... ...
Upper benefit cutoff value Lower benefit cutoff value Do-nothing curve intersects benefit cutoff value at 17 years 5 10 15 20 Age, years Age, years Do-nothing curve intersects benefit cutoff value at 14 years Do-nothing curve intersects benefit cutoff value at 15 years This 14-year life is is the shortest of all expected condition indicator lives. The expected service life of the do-nothing condition is, therefore, set to 14 years.
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From page 29... ...
Upper benefit cutoff value Lower benefit cutoff value Post-treatment curve intersects governing benefit cutoff value at 24 years This 20-year life is is the shortest of all expected condition indicator lives. The post-treatment condition analysis period is, therefore, set to 20 years.
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UBC = Upper benefit cutoff value associated with the condition indicator. LBC = Lower benefit cutoff value associated with the condition indicator.
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. Note: if the analysis period is greater than or equal to the age at which the current condition indicator curve intersects the benefit cutoff value, this area will be the total do-nothing area (i.e., AREADN(i)
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. The total overall benefit contribution is then computed as the sum of the values calculated for each individual condition indicator.
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pi = Analysis period associated with the ith timing scenario (time from construction until year at which the first included condition indicator performance curve reaches the benefit cutoff value [from step 5]
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From page 34... ...
For an analysis to investigate six timing scenarios for a treatment applied on an HMA pavement 1, 2, 3, 4, 5, and 6 years after construction, benefit, cost, and B/C ratios are computed for each scenario using the previously outlined procedures. The computed values for this example are presented in Table 20.
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When actual field data are used for this analysis, expected condition versus age relationships (before and after preventive maintenance treatment applications) must be defined by either selecting an equation type and entering known equation coefficients, or fitting a regression equation using condition versus age data points.
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From page 36... ...
. • Define all timing scenarios that will be investigated -- The methodology evaluates treatment timings that are specified by the user (i.e., all possible treatment timings Analysis Type Selection Selection and Definition of Condition Indicators Selection of Preventive Maintenance Treatment Simplified Definition of "DoNothing" Performance Curves Simplified Definition of Post PM Treatment Performance Relationships Definition of Costs Definition of Benefit Ranking Factors Conduct Analysis Detailed Definition of Post PM Treatment Performance Relationships Detailed Definition of "DoNothing" Performance Curves Simple Detailed Definition of Application Ages (Timing Scenarios)
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From page 37... ...
• Define post-preventive maintenance performance relationships -- In order to compute benefit for a given performance indicator, the user defines how the pavement will perform in the prediction mode (i.e., condition indicator versus time relationships) after a preventive maintenance treatment is applied.
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The lower benefit cutoff value was conservatively set to a value of 0% cracking. Post-Preventive Maintenance Performance Relationships A series of linear post-treatment performance curves for the selected roughness, friction, and cracking condition indicators are available (24, 25)
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• Condition Indicators -- Three condition indicators are used in this analysis: roughness, friction, and cracking. • Preventive Maintenance Treatment Selection -- A seal coat applied at 1, 4, 7, 10, and 13 years is investigated.
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These results show that of the five investigated appli0 2 4 6 8 10 12 0 5 10 15 20 25 Age N on lo ad -R el at ed C ra ck in g Do Nothing The Best Treatment Application Lower Benefit Cutoff Value Upper Benefit Cutoff Value Figure 20. Cracking versus age for the most appropriate application age of 13 years for Case Study 1 -- Arizona.
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From page 41... ...
0 20 40 60 80 100 120 0 5 10 15 20 25 Age Fr ic tio n Do Nothing The Best Treatment Application Lower Benefit Cutoff Value Upper Benefit Cutoff Value Figure 22. Friction versus age for the most appropriate application age of 13 years for Case Study 1 -- Arizona.
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From page 42... ...
The second step of the KDOT modeling procedure is to compute an expected design life of a selected paving action. Based on the results of a multiple linear regression process, the following equation is used to compute the expected design life for a given paving activity on a flexible pavement: (Eq.
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From page 43... ...
is the sole condition indicator for this treatment. Note that at the time of initial construction, or the time at which all cracks are routed and sealed, this EqTCR condition indicator is set or Equivalent Thickness of Last Paving Action Design Life Projection Limit, yrs < 38 mm (1.50 in.)
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From page 44... ...
equivalent asphalt thickness. The following inputs are used in equation 9 to compute the design life associated for the initial construction.
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From page 45... ...
Since the rout and seal activity is a non-structural action, these year 1 EqTCR values are computed using equation 11. As 45 indicated previously, the expected treatment design life is a function of four different variables: • EqTCRprior -- the computed values given in Table 27.
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From page 46... ...
AGE + 0.0653 10.3 13 EqTCR = 0.0555 * AGE + 0.0820 9.7 TABLE 29 Computed post-treatment EqTCR values associated with the different chosen application ages TABLE 30 Determined post-preventive maintenance performance relationships for Case Study 2 -- Kansas
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From page 47... ...
• Preventive Maintenance Treatment Selection -- A custom treatment, Rout and Seal Cracks, is used. Application ages of 1, 3, 5, 7, 9, 11, and 13 years are investigated.
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From page 48... ...
Cost, PW $ Total Present Worth, $ EUAC, $ 1 $2,941 n/a n/a n/a $2,941 $243 3 $2,827 n/a n/a n/a $2,827 $214 5 $2,717 n/a n/a n/a $2,717 $191 7 $2,612 n/a n/a n/a $2,612 $171 9 $2,510 n/a n/a n/a $2,510 $154 11 $2,413 n/a n/a n/a $2,413 $140 13 $2,319 n/a n/a n/a $2,319 $128 Effectiveness Summary Application Age, yrs Effectiveness Index Total Benefit EUAC, $ Expected Life, yrs Expected Extension of Life, yrs 1 41.38 0.81 $243 14.0 4.3 3 58.89 1.01 $214 15.5 5.7 5 75.45 1.15 $191 16.9 7.2 7 89.09 1.22 $171 18.4 8.7 9 97.77 1.21 $154 19.9 10.2 11 100.00 1.12 $140 21.3 11.6 13 99.24 1.02 $128 22.7 13.0 TABLE 31 Analysis results for Case Study 2 -- Kansas
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From page 49... ...
Application Timing 0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 0 2 4 6 8 10 12 14 Timing of First PM Application, years Ex te ns io n of L ife , ye ar s EUAC ($)
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From page 50... ...
chip seals 1999 17 1994 to 1995 Crack sealing of HMA surfaces 1999 12 1994 to 1995 Non-structural HMA overlays without milling 2000 13 1995 to 1997 Double chip seals 2001 14 1995 to 2000 TABLE 32 Summary of projects (for selected treatment types) included in a recent evaluation of MDOT's Capital Preventive Maintenance Program
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These data are used to determine performance equations for all observed application ages for conventional chip seals and crack sealing. Based on general observations of the time series performance data, engineering judgment is used to choose linear regression equations to fit the monitoring data associated with each application age.
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From page 52... ...
of Sections with Meaningful RSL Values Construction Years of Selected Projects Application Ages of Data Conventional (single) chip seals 17 1994 to 1995 10, 11, 12 Crack sealing of bituminous surfaces 12 1994 to 1995 3, 4, 5, 7, 8 TABLE 35 Construction history analysis for the preventive maintenance sections conventional chip seals and bituminous crack sealing are shown in Figures 27 and 28, respectively.
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From page 53... ...
Post-treatment performance trends for bituminous crack sealing applied at different ages. Output Data Pavement Surface Type: HMA Treatment Type: Chip seal Application Years: 10, 11, 12 Expected Do-Nothing Service Life (yrs)
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• Benefit Weighting Factors -- Since only one condition indicator is used in each analysis session, the benefit weighting factor associated with the DI is set to 100 percent. Analysis Results The analysis results for the chip seal and crack sealing treatments are presented separately.
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From page 55... ...
were used on the 10 projects as preventive maintenance treatments. Split Seal treatment was used on 8 projects and Triple Seal treatment was used on 2 projects.
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Post-Preventive Maintenance Performance Relationships Construction and maintenance history of the 10 sections is summarized in Table 40. It appears there is a definitive relationship between the timing of the first and second preventive maintenance treatments (see Figure 31)
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General trend between the life of the first preventive maintenance treatment and its application timing (time after initial construction)
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From page 58... ...
Cost, PW $ Total Present Worth, $ EUAC, $ 4 $14,531.67 n/a n/a n/a $14,531.67 $943.00 5 $13,972.76 n/a n/a n/a $13,972.76 $902.39 9 $11,943.97 n/a n/a n/a $11,943.97 $829.87 13 $10,209.76 n/a n/a n/a $10,209.76 $744.37 14 $9,817.08 n/a n/a n/a $9,817.08 $715.75 Results Application Age, yrs Effectiveness Index Total Benefit EUAC, $ Expected Life, yrs Expected Extension of Life, yrs 4 87.43 1.04 $943.00 24.4 6.3 5 68.04 0.77 $902.39 24.6 6.5 9 100.00 1.05 $829.87 21.9 3.7 13 64.84 0.61 $744.37 20.3 2.1 14 55.32 0.50 $715.75 20.3 2.1 58 60 65 70 75 80 85 90 95 100 105 0 2 4 6 8 10 12 14 16 18 20 22 Age After Treatment Application, yrs Pa ve m en t C o n di tio n R a tin g (P CR ) AppAge = 4 (regression)
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From page 59... ...
• Preventive Maintenance Treatment Selection -- A custom treatment named Asphalt Seal Coat applied at ages of 4, 5, 9, 13, and 14 years is investigated. • Performance Relationships -- The do-nothing performance curve shown in Figure 30 and the post-preventive maintenance performance relationships defined in Table 41 are used.
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From page 60... ...
For flexible pavements, the initial search of the database identified the following SPS-3 sections as meeting these criteria: • 80 sections with chip seal coats • 80 sections with slurry seal coats • 69 sections with crack sealing • 79 sections with (thin) overlays The following types of condition indicator data are available for each of these sections: • Nonload-related and load-related cracking • Average rut depth • IRI • Friction
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From page 61... ...
A holistic approach to identifying the optimal time of preventive maintenance application is needed. Such an approach should address project selection, treatment selection, pavement performance monitoring, and data analysis and reporting.
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