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55 scenario choices suggests that the year 5 application is the far Case Study 4--North Carolina more cost-effective choice for applying crack sealing. Fig- ure 29 shows plots of EI, extension of life, and EUAC versus Introduction treatment application age for this analysis. While an age of 5 years is the suggested application age North Carolina Department of Transportation (NCDOT) based on the default analysis approach (i.e., analyzing bene- provided project data for 10 HMA sections, including pave- fit and cost simultaneously), this may not represent the phi- ment condition rating (PCR) history, treatment type, year of losophy of all agencies. For example, if the benefit differences treatment application, the (estimated) year of the previous in the crack sealing example were considered insignificant, an maintenance treatment, and pavement structure (from cor- application age of 8 years would become most appropriate as ing) for 5 of the 10 sections. Treatments organized by type it provides the lowest EUAC value. Therefore, it is always and DOT division were obtained from NCDOT's "2001 Road important for an agency to consider the analysis results in Oil Summary (28)." Cost information was obtained from conjunction with other established goals. NCDOT pavement management unit staff. Treatment Selection Effectiveness Index vs. Application Timing Two different asphalt seal coats (Triple Seal and Split 100 Effectiveness Index Seal) were used on the 10 projects as preventive maintenance 80 treatments. Split Seal treatment was used on 8 projects and 60 Triple Seal treatment was used on 2 projects. Construction 40 details described in Section 660 of North Carolina's State 20 Construction Handbook (29) are summarized. 0 0 2 4 6 8 10 Split Seal. A split seal consists of two applications of asphalt Timing of First PM Application, years binder and aggregate. Total binder and aggregate application rates are approximately 2.04 to 2.26 L/m2 (0.45 to 0.50 gal/yd2) and 16 to 19 kg/m2 (30 to 35 lb/yd2), respectively. In the Extension of Life vs. Application Timing first application, approximately 0.91 to 1.13 L/m2 (0.20 to 0.25 gal/yd2) of asphalt material is applied to the existing 8.0 surface, followed immediately by the application of approx- Extension of Life, 7.0 6.0 imately 11 to 12 kg/m2 (20 to 22 lb/yd2) of seal coat aggre- 5.0 years 4.0 gate spread uniformly over the treated surface. Immediately 3.0 after the first application of seal aggregate has been made 2.0 uniform, the remainder of the required amount of asphalt 1.0 0.0 material and seal coat aggregate are applied and the seal coat 0 2 4 6 8 10 is rolled; specific rolling instructions are provided in Section Timing of First PM Application, years 660 of the handbook (28). Triple Seal. To construct a triple seal, approximately 0.91 to EUAC ($) vs. Application Timing 1.13 L/m2 (0.20 to 0.25 gal/yd2) of liquid asphalt is applied to the existing surface followed immediately by the appli- $700 $600 cation of approximately 8 to 9 kg/m2 (15 to 17 lb/yd2) of $500 seal coat aggregate spread uniformly over the treated surface. EUAC ($) $400 The operation is performed three times; aggregate applied $300 in the final application is then rolled as described in the $200 $100 handbook (29). $ 0 2 4 6 8 10 Timing of First PM Application, years Treatment Costs Treatment costs are summarized in NCDOT's "2001 Road Figure 29. Summary charts of crack sealing Oil Summary (28)." Relevant details are provided in Table 39 for Case Study 3--Michigan. for both treatment types.

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56 TABLE 39 Summary of 2001 treatment cost data Range of Average Average Unit Cost Unit Costs Total Cost for Data Determined No. of Length of Area of of from All for Each Treatment Divisions Preservation Preservation Preservation Divisions, Division, Type with Data Projects, km Projects, m2 Projects, $ $/m2 $/m2 Split Seal 12 1,166 6,154,018 $2,346,429 $0.84 $0.75 to 1.05 Triple Seal 9 88 475,022 $643,093 $1.24 $0.97 to 1.65 2 2 Note: 1 mi = 1.61 km; 1 yd =0.84 m Condition Indicator through this time series data (through a value of 100 at time zero) as shown in Figure 30. To check the reasonableness Time series PCR data are provided for the 10 sections. The of this approach, the age at which the resulting regression pavement condition rating is a composite index that reflects equation (PCR = -1.6506 Age + 100) crosses the assumed the extent of surface distress, expressed on a 0 to 100 scale condition trigger level of 70 is determined. The expected age (a value of 100 represents a pavement with no distress). at this trigger value is 18.2 years, which is reasonable. Benefit Cutoff Values Post-Preventive Maintenance Performance Based on the pavement condition time-series data, a lower Relationships benefit cutoff value of 70 is selected, suggesting that when the condition falls below 70, a second asphalt seal coat is trig- Construction and maintenance history of the 10 sections is gered. The benefit calculations are not subjected to any limit summarized in Table 40. It appears there is a definitive rela- on the upper end (i.e., an upper benefit cutoff value of 100 is tionship between the timing of the first and second preventive used for the analysis). maintenance treatments (see Figure 31). The trend indicates that the life of the first preventive maintenance treatment is longer when applied sooner rather than later after initial Do-Nothing Performance Curves construction. As shown in Table 40, monitoring data associated with All analyzed preventive asphalt seal coats were placed on first treatment application ages of 4, 5, 8, 9, 11, 13, and 14 pavements that already had a Mat and Seal treatment applied. years are available (two sections with unknown construction To simplify the analysis, the performance of the existing Mat history were ignored). Three additional sections were elimi- and Seal layers is defined as the do-nothing performance. Thus nated from the analysis. One of these sections with an appli- the do-nothing performance curve is defined by the time series cation age of 8 years was eliminated because the monitoring performance data from the Mat and Seal layer application year data for the section did not appear to be representative; treat- (defined as year 0) to the application year of the first preven- ment condition deteriorated at a much more rapid rate than tive asphalt seal coat. A representative do-nothing curve is any other sections. Two other sections with application ages then assumed for the analysis by fitting a linear equation of 11 years were eliminated because the data showed com- 120 Pavement Condition 100 Rating (PCR) 80 60 40 PCR = -1.6506 * Age + 100 20 R2 = 0.2605 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Pavement Age, years Figure 30. Assumed representative do-nothing curve for the North Carolina projects.

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57 TABLE 40 Construction history analysis for the 10 asphalt seal coat sections Age at Time from Timing of First First Last First Treatment Assumed Preventive Preventive Preventive Application to Original Maintenance Maintenance Maintenance Last Treatment State Construction Treatment Treatment Treatment, Application, Route Year Year Year yrs yrs SR 1125 1984 1992 1999 8 7 SR 1226 1982 1986 2000 4 14 SR 2249 1980 1991 2000 11 9 SR 2018 1982 1993 2000 11 7 SR 2028 1980 1989 2000 9 11 SR 1828 1982 1996 2002 14 6 SR 1722 Unknown SR 1721 1983 1988 2002 5 14 SR 2245 1982 1995 2002 13 7 SR 1719 Unknown 16 Time from first PM application until second PM 14 12 application, years 10 8 6 4 2 0 0 2 4 6 8 10 12 14 16 Timing of First Asphalt Seal Coat (time since original construction) Figure 31. General trend between the life of the first preventive maintenance treatment and its application timing (time after initial construction). TABLE 41 Post-treatment performance relationships for Case Study 4--North Carolina Computed Life Until Equation Reaches Application Lower Benefit Cutoff Age Regression Equation Level (PCR = 70) 4 PCR = 100 0.007535 * AGE 2.747556 20.4 1.511787 5 PCR = 100 0.333097 * AGE 19.6 9 PCR = 100 5.618E-12 * AGE 11.474446 12.9 13 PCR = 100 0.000138 * AGE 6.191617 7.3 14 PCR = 100 0.020379 * AGE 3.969362 6.3

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58 105 100 AppAge = 4 (regression) Pavement Condition Rating 95 AppAge = 5 (regression) 90 AppAge = 9 (regression) AppAge = 13 (regression) 85 (PCR) AppAge = 14 (regression) 80 AppAge = 4 (raw data) 75 AppAge = 5 (raw data) AppAge = 9 (raw data) 70 AppAge = 13 (raw data) 65 Lower Benefit Cutoff Value App Age = 14 (raw data) 60 0 2 4 6 8 10 12 14 16 18 20 22 Age After Treatment Application, yrs Figure 32. Determined post-treatment performance relationships for Case Study 4-- North Carolina. TABLE 42 Analysis results for Case Study 4--North Carolina Output Data Pavement Surface Type: HMA Treatment Type: Asphalt Seal Coat Application Years: 4, 5, 9, 13, 14 Expected Do-Nothing Service Life (yrs): 18.18 Benefit Summary Individual Benefit Summary Benefit Ranking Factors => 100 Pavement Application Condition Age, yrs Total Benefit Rating 4 1.04 1.04 5 0.77 0.77 9 1.05 1.05 13 0.61 0.61 14 0.50 0.50 Cost Summary Other Application Treatment User Cost, PW Maintenance Rehab. Cost, Total Present Age, yrs Cost, PW $ $ Cost, PW $ PW $ 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 Expected Application Effectiveness Expected Life, Extension of Age, yrs Index Total Benefit EUAC, $ yrs 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

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59 pletely different rates of deterioration, without clarification. The analysis compares the expected post-preventive mainte- Effectiveness Index vs. Application Timing nance trends associated with assumed application ages of 4, 5, 9, 13, and 14 years after initial construction. 100 90 Effectiveness Index Based on general observations of the time series perfor- 80 mance data, engineering judgment was used to select an 70 exponential regression equation to fit the monitoring data for 60 each of the application ages. The exponential model type is 50 40 a good choice for a decreasing trend that has a known start- 30 ing condition value. In this case, the initial PCR is always 20 100; therefore, each of the individual post-preventive main- 10 tenance relationships must yield a value of 100 at an age of 0 0 5 10 15 zero. The equation form PCR = C - m (Age)P was selected; the specific regression equations are listed in Table 41 and Timing of First PM Application, years plotted (along with the reported data) in Figure 32. Extension of Life vs. Application Timing Analysis Setup 7.0 Extension of Life, years 6.0 The following inputs are used in the analysis: 5.0 4.0 Analysis Type--A detailed analysis type is selected 3.0 since actual data are being analyzed. 2.0 Condition Indicators--A custom condition indicator 1.0 is defined and labeled Pavement Condition Rating. Preventive Maintenance Treatment Selection--A cus- 0.0 0 5 10 15 tom treatment named Asphalt Seal Coat applied at ages of 4, 5, 9, 13, and 14 years is investigated. Timing of First PM Application, years Performance Relationships--The do-nothing perfor- mance curve shown in Figure 30 and the post-preventive EUAC ($) vs. Application Timing maintenance performance relationships defined in Table 41 are used. $1,000 Project Definition--A typical project size is defined to $900 be 15,290 m2 (20,000 yd2). $800 Cost Data--Only treatment costs are included in the $700 EUAC ($) $600 cost analysis (i.e., rehabilitation, user, and routine main- $500 tenance costs are excluded). Because data for three split $400 seal and two triple seal projects are used, a treatment $300 unit cost of $1.02/m2 ($0.85/yd2) is chosen for this analy- $200 $100 sis, because it is within the observed cost ranges for both $ treatment types. The selected project size and unit cost 0 5 10 15 would yield a total cost of $17,000 for each treatment Timing of First PM Application, years application; a discount rate of 4.0 percent was also cho- sen for the analysis. Benefit Weighting Factors--Because only one con- Figure 33. Summary charts for Case Study 4-- dition indicator is used in the analysis session, the ben- North Carolina. efit weighting factor associated with the PCR is set to 100 percent. ages, applying the treatment at age 9 is the most cost-effective choice as indicated by an EI of 100. At this application age 9, a life extension of 3.7 years is expected (i.e., the pavement Analysis Results will last 3.7 more years than the 18.2 years expected if no treat- ment is applied), with an EUAC of approximately $830. The Results of the analysis are summarized in Table 42. These largest expected extension of life (6.5 years) is with a treatment results indicate that out of the five investigated application applied at age 5 that provides the second highest EUAC and the