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23 TABLE 7 EXAMPLE LEVELS OF SERVICE FOR A MEDIUM-SIZE GENERAL AVIATION AIRPORT WITH AC PAVEMENTS Level of Service Minimum Acceptable Level of Average PCI for all Sections Service Facility Type Target or desirable Minimum acceptable PCI for Individual Sections Runway 80 65 55 Taxiway 70 60 45 Apron 70 60 40 of service can also be defined in terms of other pavement sur- ment M&R treatments is shown in Table 8. The relationship face defects such as rutting depth. shown in this table, developed for all key pavement dis- tresses, is called a maintenance policy in MicroPAVER. Trigger Levels IDENTIFICATION OF NEEDS In addition to using levels of service to estimate the need for pavement M&R, trigger levels provide timing guidance for Identification of needs on the network level consists of the pavement M&R treatments. An example of levels of service following four steps: and trigger values is provided in Figure 13. Trigger values may be general or treatment specific. 1. Identification of pavement sections that require M&R treatments because of the level-of-service require- General Trigger Levels General trigger levels provide ments or because of trigger levels. guidance on what types of M&R treatments are considered 2. Selection of M&R treatments for the sections identi- for a given pavement condition. For example, MicroPAVER fied in step 1. enables the user to specify the PCI levels that trigger a reha- 3. Estimation of the costs for the implementation of bilitation treatment. M&R treatments selected in step 2. 4. Prioritization of projects if the cost of the treatments, Treatment-Specific Trigger Levels These trigger levels are estimated in step 3, exceeds the available budget. The related to the need to apply a preservation treatment at the selection and prioritization of projects is done system- right time to be effective, before the pavement reaches a con- atically and objectively using the procedures described dition where a different, more expensive treatment would be in the next chapter. needed. For example, sealing of cracks in AC pavements is most effective when the pavement is still in very good con- Identification of needs is discussed separately for two dition. An example of a trigger level for crack sealing and for time horizons: an overlay is shown in Figure 13. · Short-term planning for time horizons of about 5 years Closely related to the concept of trigger levels is the link- or less. For simplicity, it is also assumed that the ana- age between specific pavement surface distresses and the rec- lytical procedures used for short-term planning do not ommended pavement M&R treatments. An example of the include the generation and evaluation of alternative treat- linkage between pavement cracking and recommended pave- ments in future years. · Long-term planning for time horizons of more than 5 years. In this case, analytical procedures can include the Performance curve 100 generation and evaluation of alternative treatments in future years. Pavement Condition Index, PCI Trigger level for crack sealing Target level of service for average network condition Short-Term Planning Trigger level for overlay (mill and fill) Many airports use short-term planning to identify and prior- Minimum acceptable level of itize pavement M&R needs. The typical procedure consists service for individual sections of the following steps: a) Updating Pavement Inventory--Pavement inventory, 0 including pavement condition, is updated. The update Pavement age, years includes results of all recent pavement-related projects FIGURE 13 Example of levels of service and trigger levels. and other changes to the pavement infrastructure.
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24 TABLE 8 EXAMPLE OF MAINTENANCE POLICY FOR CRACKING Recommended Maintenance Treatment Severity of Pavement Cracking AC pavements PCC pavements Low None--continue to monitor None--continue to monitor Medium Crack routing and sealing Crack sealing High Crack repairs Full-depth repairs b) Defining Scope of Work--Pavement preservation the M&R treatment. Figure 14 provides a summary of treatments that can be planned at least a year in advance survey responses regarding the methods used for the are included, whether corrective maintenance, preven- selection of M&R treatments. For example, about 85% tive maintenance, or rehabilitation treatments. The treat- of respondents use engineering judgment and 30% of ments may include, for example, sealing of cracks and the respondents use computer-based tools. Decision joints, AC overlays, full-depth repairs of PCC pave- trees were used by about 6% of the respondents. How- ments, and installation of subdrains. ever, engineering judgment often includes reasoning c) Reviewing Pavement Preservation Needs for Each Air- that has the structure of decision trees. port Pavement Section--One of the reasons for dividing The need for maintenance treatments, particularly a pavement network into sections is to create future preventive maintenance treatments, is determined using pavement repair units. Each section is considered in turn trigger values for individual pavement surface dis- to decide if the section is expected to require any M&R tresses. For example, using the PCI pavement distress work during the next 5 years, or during the given plan- evaluation terminology, the occurrence of joint seal ning horizon. Many sections may not require any treat- damage at the medium or high severity triggers the ment during the planning horizon, whereas other sec- need for joint sealing, and the occurrence of corner tions may require preventive maintenance or other types break at the medium or high severity levels triggers the of treatments. The decisions are based on the mandated need for full-depth patching with PCC. An example of levels of service (Table 7) and trigger values such as the network-level maintenance plan generated by those shown in Figure 13. The needs take into account MicroPAVER for the small airport shown in Figure 7 expected pavement deterioration during the planning is shown in Table 10. The exact extent of maintenance period. The identification of needs is documentation of work is determined on the project level. For example, the needs that are necessary on the basis of the levels of the existence of the 11 corner breaks was estimated by service. sampling (and not by an actual field count) and verified An example of pavement preservation needs for a by a detailed survey on the project level. Similarly, the small airport (shown in Figure 7) is given in Table 9. size of the full-depth patches to repair the cracks needs Table 9 was generated by MicroPAVER. In this exam- to be determined individually for each crack repair. ple, the costs of the major M&R treatments depend on For localized M&R treatments, MicroPAVER uses the PCI levels. The actual type of M&R treatments is maintenance polices that match the distresses with not defined. M&R treatments (Table 8). Major M&R treatments are d) Selecting Treatment Types--To refine the cost esti- identified as a function of the PCI level in terms of costs mates, airport pavement maintenance managers select only (Table 9). Other software packages identify generic TABLE 9 EXAMPLE OF 2009 5-YEAR MAJOR M&R PLAN FOR UNLIMITED BUDGET Plan Branch Section Section Major Year Name Number Area, ft2 Maintenance, $ M&R, $ Cost, $ 2009 A01 10 48,000 0 238,000 238,000 20 46,000 49,400 0 49,400 THEAST 10 17,800 0 97,100 97,000 RW1533 10 205,600 0 945,900 945,900 2010 No work identified 2010 No work identified etc. 5-year plan total 49,400 1,794,700 1,844,100 Source: Michigan Airports Division (2007).
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25 100 60 Percent of respondents Percent of respondents 75 40 50 20 0 25 Yes Budget No Have dedicated permitting preventive 0 maint. budget s Identification of preventive maintenance treatments am sts ns es t t t ie irs en en tre rit io xi gr f m gm io at e on ro ve on r rd er d p iti rp pa FIGURE 15 Systematic identification of preventive isi ju za id l nd na te ec ns g ha of in pu co tio maintenance needs. D co ge n er m he st ra er ne A Co or pe W th gi W O O En Selection of treatments · What will be the condition of the pavement network FIGURE 14 Methods used to select M&R treatments 10 years from now given the existing budget? on the network level. · What is the future funding to achieve a specified level of service? · How much additional funding will be needed in the treatment types; for example, an AC overlay, and the future to compensate for reduced funding now? corresponding cost of the generic treatment types. The · What would be the impact on the network condition of actual treatment design, including the design of pre- diverting funds to preventive maintenance or lower- overlay improvements, overlay thickness, and material cost treatments? properties, is done on the project level. · What would be the impact of constructing new runways e) Selection of Preventive Maintenance Treatments-- or taxiways on the pavement preservation budget? About 56% of airports systematically identify pave- ments that would benefit from preventive maintenance The accuracy of future funding requirements for airport and 35% of airports do so when budget permits (Figure pavement maintenance depends on the reliability of long- 14). For comparison purposes, Figure 15 also shows that term prediction of pavement performance and the generation 33% of airports have dedicated budgets for preventive of feasible alternatives. Long-term planning and prioritiza- maintenance. The existence of a dedicated budget for tion can consider, for each section, several treatment options preventive maintenance is considered to be one of the in each analysis year. This results in a large number of pos- prerequisites for timely, successful, and sustainable oper- sible combinations of program years and treatments for one ation of preventive pavement maintenance programs. section alone. Long-Term Planning The concept of generating alternative M&R treatments for different years is illustrated for one pavement section in Long-term planning for airport pavement maintenance needs Figure 16. For clarity, only two treatments (microsurfacing can improve engineering and economic decision making by and overlay) and two analysis years (now-plus-3 years and helping answer the following example questions: now-plus-9 years) are considered. Alternative 1 is microsur- TABLE 10 EXAMPLE MAINTENANCE PLAN Pavement Surface Distress Branch Section Name No. Type Severity Quantity Unit Maintenance Treatment Cost A01 20 Corner High 11 Slab Full-depth patching with PCC $9,500 break Linear Medium 150 Feet Crack sealing $400 cracking Joint seal High 460 Slab Joint sealing $34,000 damage Shattered High 4 Slab Full-depth patching with PCC $4,700 slab Corner High 12 Slab Partial-depth patching with $800 spalling PCC Total $49,400
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26 Micro-surfacing Overlay facing to be constructed 3 years from now. Alternative 2 is 100 an overlay to be constructed in year now plus 9 years, when 1 the existing pavement will reach the minimum acceptable Pavement Condition Index 2 level of service. Minimum acceptable service Sophisticated software generates and evaluates multiple level treatment options. For the example shown in Figure 16 it means generating the two alternative treatments (microsur- facing and overlay) at two different years, and estimating 0 their life spans. The life spans of the alternatives and their Now Now + 3 Now + 9 costs are used subsequently to select the most cost-effective Pavement age, years alternative. This type of analysis has been carried out by FIGURE 16 Pavement performance prediction for many highway agencies, but is not routinely done by airport multi-year identification of needs. agencies.