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50 Case Study 3--Michigan · Seal and retard the oxidation of an existing pavement surface, Introduction · Improve skid resistance, · Seal fine surface cracks in the pavement, thus reducing Michigan DOT has a well-documented preventive main- the intrusion of water into the pavement structure, and tenance program with many years of experience. Much of · Retard the raveling of aggregate from a weathered pave- MDOT's preventive maintenance is applied through a capi- ment surface. tal preventive maintenance (CPM) program aimed at pro- tecting the pavement structure, slowing the rate of pavement The existing pavement should exhibit a good cross section and deterioration, and correcting pavement surface deficiencies, a good base. The visible distress may include (1) slight ravel- mostly through the use of surface treatments. The CPM guide- ing and surface wear, (2) longitudinal and transverse cracks lines indicate that preventive maintenance projects should be with a minor amount of secondary cracking and a slight ravel- relatively simple and should focus on pavement structures ing along the crack face, (3) first signs of block cracking, or with more than 2 years of remaining service life. Severely (4) slight to moderate flushing or polishing and/or an occa- distressed pavement structures or pavements with a severely sional patch in good condition. MDOT reports an expected life distorted cross section are generally not candidate projects extension of 3 to 6 years from a chip seal application on a for the CPM program (11). flexible pavement. MDOT provided data for 56 preventive maintenance proj- ects of HMA pavements. Much of the data were from a report Crack Sealing of Bituminous Surfaces. MDOT specifies a documenting a 3-year evaluation of MDOT's Capital Pre- "cut and seal" technique to seal cracks on bituminous pave- ments. This method consists of cutting the desired reservoir ventive Maintenance Projects (26). Table 32 presents evalu- shape at the working crack in the existing bituminous sur- ation details of four treatment types that were initially con- face, cleaning the cut surfaces, and placing the specified sidered for use in this project. sealant into the cavity to prevent the intrusion of water and Specific types of data available for each project consist of incompressible material. the following: The existing bituminous surface should be a relatively newly placed surface on a good base with a good cross sec- · Project location data (route number, project number, tion. On a flexible base, the bituminous surface should be MDOT region, beginning and ending mileposts, project 2 to 4 years old, and 1 to 2 years old on a composite pave- length), ment. The visible surface distress may include fairly straight, · Construction history (pavement type, initial construc- open longitudinal and transverse cracks with slight secondary tion type and year, rehabilitation and treatment history), cracking and slight raveling at the crack face, and no patch- · Traffic information (1993/1994 and 1997 ADT), ing or very few patches in excellent condition. MDOT reports · Distress data, and an expected life extension of up to 3 years on a flexible pave- · Computed remaining service life (RSL). ment as a result of crack sealing. However, it is noted that in order to remain effective, this treatment should be followed Conventional chip seal and crack sealing data were selected by routine maintenance crack sealing operations when addi- for evaluation. Descriptions of these two activities (as pre- tional cracks develop. sented in MDOT's CPM Manual) are included below (11). Treatment Costs Conventional (Single) Chip Seals. A single chip seal is defined as an application of a polymer modified asphalt emul- Average cost data for the two chosen treatment types are sion with a cover aggregate. The purpose of a chip seal is to listed in Table 33 (26). TABLE 32 Summary of projects (for selected treatment types) included in a recent evaluation of MDOT's Capital Preventive Maintenance Program Number of Construction Year of Projects Years of Selected Treatment Evaluation Evaluated Projects Conventional (single) chip seals 1999 17 1994 to 1995 Crack sealing of HMA surfaces 1999 12 1994 to 1995 Non-structural HMA overlays 2000 13 1995 to 1997 without milling Double chip seals 2001 14 1995 to 2000
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51 TABLE 33 Average treatment cost data Average Cost, $/lane-km Year of Treatment Type ($/lane-mi) Cost Data Conventional (single) chip seals $7,603 ($12,240) 1998 Crack sealing of bituminous surfaces (bituminous crack treatment) $4,288 ($6,900) 1998 Condition Indicators analysis. However, the benefit calculations are not limited on the lower end (i.e., a lower benefit cutoff value of 0 is used MDOT performance data are expressed in terms of a dis- for the analysis). tress index (DI) and ride quality index (RQI). DI is a mea- sure of the extent of surface distress and is expressed on a 0 to 100 scale, where a value of 0 represents a pavement with Do-Nothing Performance Curves no distress. MDOT uses DI to determine the RSL of a pave- ment, that is, the number of years left to reach a threshold DI A linear do-nothing curve is assumed for this analysis value of 50 (27). because no data were available to support the use of an alter- RQI is an objective measure of ride quality computed from native. This relationship is defined by the line that passes the power spectral density (PSD) of the road surface profile. through DI = 0 at an age of zero, and DI = 50 (terminal DI Table 34 summarizes Michigan's RQI ranges and associated value) at an assumed age of 13 years (see Figure 26). Thus, subjective ride quality rating. the linear equation representing the do-nothing DI versus age For the projects included in this analysis, 1999 RSL val- relationship is as follows: ues are provided for the conventional chip seal and crack sealing projects and 2000 RSL values are provided for the DI = 3.8462 × Age (Eq. 14) non-structural overlay projects. RSL values are not available for the double chip seals, making it very difficult to deter- mine meaningful performance relationships without addi- Post-Preventive Maintenance Performance tional monitoring data. Relationships The RSL data are used to complete estimated linear perfor- mance trends by defining the pavement age at which the pave- Available data are listed in Table 35. These data are used ment is expected to reach a terminal DI value of 50. Because to determine performance equations for all observed appli- RSL is only a function of DI, RQI could not be used as a con- cation ages for conventional chip seals and crack sealing. dition indicator. RSL data were not available for some sections. Based on general observations of the time series perfor- MDOT has also investigated the practice of sealing cracks mance data, engineering judgment is used to choose linear prior to the placement of conventional chip seals on bituminous regression equations to fit the monitoring data associated surfaced pavements; the database includes sections both with with each application age. Since the initial DI rating is and without presealing. Because of the limited number of sec- always zero, the linear model equation will take the form tions for which data are available, the current conventional chip DI = m × (TAGE), where m is the slope of the line and TAGE seal data groups all projects together regardless of whether they is the age of the treatment (i.e., years since placement). The received presealing. determined regression equations are listed in Table 36. Charts showing the posttreatment performance trends for Benefit Cutoff Values To remain consistent with the DI threshold used for RSL, 80 an upper benefit cutoff value of 50 is chosen for use in the 70 Distress Index (DI) 60 DI = 3.8462 * Age 50 TABLE 34 RQI ranges and their 40 subjective ride quality ratings 30 20 Subjective Ride 10 RQI Range Quality 0 0 to 30 Excellent 0 1 2 3 4 5 6 7 8 9 10 11 12 13 31 to 54 Good Pavement Age, years 55 to 70 Fair Figure 26. Assumed distress index do-nothing curve > 70 Poor for Case Study 3--Michigan.
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52 TABLE 35 Construction history analysis for the preventive maintenance sections No. of Sections Construction with Meaningful Years of Selected Application Ages Treatment Type RSL Values Projects of Data Conventional (single) chip 17 1994 to 1995 10, 11, 12 seals Crack sealing of 12 1994 to 1995 3, 4, 5, 7, 8 bituminous surfaces TABLE 36 Treatment performance relationships Computed Treatment Life Application Until Equation Reaches Upper Treatment Age or Age Benefit Cutoff Level (DI = 50), Type Range Regression Equation years Conventional 10 DI = 10.05 × TAGE 5.0 (single) chip 11 DI = 7.4447 × TAGE 6.7 seals 12 DI = 8.26685 × TAGE 6.0 Crack sealing 3 DI = 4.825 × TAGE 10.4 of bituminous 4 DI = 3.3814 × TAGE 14.8 surfaces 5 DI = 3.2394 × TAGE 15.4 7 DI = 6.6536 × TAGE 7.5 8 DI = 5.0327 × TAGE 9.9 conventional chip seals and bituminous crack sealing are · Analysis Type--A detailed analysis type is selected for shown in Figures 27 and 28, respectively. both analyses since actual data are being analyzed. · Condition Indicators--A custom condition indicator Analysis Setup is defined and labeled Distress Index for both analysis sessions. Because two different treatments are considered, two sep- · Preventive Maintenance Treatment Selection--The arate analyses are conducted. Specifically, the analyses are treatments defined for the two different analyses are performed using the following inputs and assumptions: Chip Seals and Crack Sealing, respectively. 80 70 60 App Age = 10 yrs Distress Index, DI 50 App Age = 11 yrs App Age = 12 yrs 40 Linear (App Age = 10 yrs) Upper Benefit 30 Linear (App Age = 11 yrs) Cutoff Value Linear (App Age = 12 yrs) 20 10 0 0 5 10 15 20 Treatment Age, yrs Figure 27. Post-treatment performance trends for chip seals applied at different ages.
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53 80 Upper Benefit 70 Cutoff Value App Age = 3 yrs 60 App Age = 4 yrs App Age = 5 yrs Distress Index, DI 50 App Age = 7 yrs App Age = 8 yrs 40 Linear (App Age = 3 yrs) 30 Linear (App Age = 4 yrs) Linear (App Age = 5 yrs) 20 Linear (App Age = 7 yrs) Linear (App Age = 8 yrs) 10 0 0 5 10 15 20 Treatment Age, yrs Figure 28. Post-treatment performance trends for bituminous crack sealing applied at different ages. TABLE 37 Analysis results of chip seal for Case Study 3--Michigan Output Data Pavement Surface Type: HMA Treatment Type: Chip seal Application Years: 10, 11, 12 Expected Do-Nothing Service Life (yrs): 13.00 Benefit Summary Individual Benefit Summary Benefit Ranking Factors => 100 Application Distress Index Age, yrs Total Benefit (DI) 10 0.33 0.33 11 0.49 0.49 12 0.46 0.46 Cost Summary Other Application Treatment User Cost, PW Maintenance Rehab. Cost, Total Present Age, yrs Cost, PW $ $ Cost, PW $ PW $ Worth, $ EUAC, $ 10 $8,268.91 n/a n/a n/a $8,268.91 $744.62 11 $7,950.87 n/a n/a n/a $7,950.87 $634.99 12 $7,645.07 n/a n/a n/a $7,645.07 $602.80 Effectiveness Summary Expected Application Effectiveness Expected Life, Extension of Age, yrs Index Total Benefit EUAC, $ yrs Life, yrs 10 56.99 0.33 $744.62 15.0 2.0 11 100.00 0.49 $634.99 17.7 4.7 12 98.16 0.46 $602.80 18.0 5.0
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54 · Performance Relationships--For both analyses, the Chip Seal Example. The results of the chip seal analysis are do-nothing performance relationship shown in Figure 26 listed in Table 37. These results indicate that of the three and the respective post-treatment performance relation- investigated application ages, applying the treatment at age 11 ships defined in Table 36 are used. is the most cost-effective option as indicated by an EI of 100, · Project Definition--A typical project size is defined as although the application age of 12 produced a greater life 1.6 km (1 mi) long. extension (5.0 years) and a smaller EUAC ($603) than the · Cost Data--Only treatment costs are included in the year 11 timing option. Note that the EI for the year 12 timing cost analysis (i.e., rehabilitation, user, and routine main- scenario is 98.16, which is very close to 100. Therefore, for tenance costs are excluded). The unit costs per mile are all practical purposes, a chip seal applied at year 12 is likely listed in Table 33; a discount rate of 4.0 percent is used. to be as effective as a chip seal applied at year 11. · Benefit Weighting Factors--Since only one condi- tion indicator is used in each analysis session, the ben- Crack Sealing Example. The results of the crack sealing efit weighting factor associated with the DI is set to analysis are listed in Table 38. These results indicate that of the 100 percent. five investigated application ages, applying the treatment at age 5 is the most cost-effective option as indicated by an EI of 100. This timing scenario not only produces the largest total benefit Analysis Results value (0.81) and the largest extension of life (7.4 years), it also has the second lowest EUAC at $2,427. The second most effec- The analysis results for the chip seal and crack sealing tive timing scenario is the year 8 application with an EI of treatments are presented separately. 78.55. The large difference between the first and second timing TABLE 38 Analysis results of crack sealing for Case Study 3--Michigan Output Data Pavement Surface Type: HMA Treatment Type: Crack sealing Application Years: 3, 4, 5, 7, 8 Expected Do-Nothing Service Life (yrs): 13.00 Benefit Summary Individual Benefit Summary Benefit Ranking Factors => 100 Application Composite Age, yrs Total Benefit Index 3 0.21 0.21 4 0.66 0.66 5 0.81 0.81 7 0.37 0.37 8 0.62 0.62 Cost Summary Other Application Treatment User Cost, PW Maintenance Rehab. Cost, Total Present Age, yrs Cost, PW $ $ Cost, PW $ PW $ Worth, $ EUAC, $ 3 $6,134.08 n/a n/a n/a $6,134.08 $601.51 4 $5,898.15 n/a n/a n/a $5,898.15 $452.51 5 $5,671.30 n/a n/a n/a $5,671.30 $411.46 7 $5,243.43 n/a n/a n/a $5,243.43 $483.19 8 $5,041.76 n/a n/a n/a $5,041.76 $399.26 Effectiveness Summary Expected Application Effectiveness Expected Life, Extension of Age, yrs Index Total Benefit EUAC, $ yrs Life, yrs 3 17.38 0.21 $601.51 13.4 0.4 4 74.01 0.66 $452.51 18.8 5.8 5 100.00 0.81 $411.46 20.4 7.4 7 38.44 0.37 $483.19 14.5 1.5 8 78.55 0.62 $399.26 17.9 4.9