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33 CHAPTER SEVEN PROJECT DESIGN AND IMPLEMENTATION The final treatment type and associated technical details and · Facility type and the associated requirements for per- costs are determined at the project level. The project-level formance reliability of the M&R treatments. activities discussed in this chapter include project design, · Pavement surface quality in terms of surface friction, project implementation, and the monitoring of completed roughness, and the potential for FOD. projects. The project design and implementation is an inte- · Existing pavement condition, surface distresses, and gral part of the airport pavement management process (Haas pavement performance history. et al. 1994). · Construction history and previous experience with a particular treatment under similar circumstances. · Physical properties of the existing pavement structure. PROJECT DESIGN For the design of M&R treatments, this may require coring and boring of the existing pavement structure to Project design determines the specific treatment type and obtain dimensions and material samples, and the use of design details for the construction of the project, such as layer a dynamic cone penetrometer. types, material properties, and construction details. The · Structural pavement strength. For the design of M&R selected M&R treatments address the primary cause of pave- treatments, the determination of pavement strength (struc- ment deterioration and not just the distresses seen on the pave- tural support) can be done with pavement deflection test- ment surface during a PCI survey. Compared with the network- ing. A good reference is FAA Advisory Circular on Use level identification of needs and prioritization, the project-level of Nondestructive Testing Devices in the Evaluation of design requires additional data and data with greater detail. Airport Pavements (2004). For large or complicated projects, the design process consists · Anticipated traffic loads in terms of the number of oper- of a preliminary design stage and the final design stage. The ations, particularly departures, and the type of aircraft. preliminary design stage includes: (1) identification of alterna- · Environmental exposure, such as pavement temperature tives, (2) design of alternatives, and (3) selection of a recom- extremes, number of freezethaw cycles, and exposure mended alternative. The final design stage includes detailed to fuel spills. design of the selected alternative. · Life-cycle costs. · Benefits; for example, estimated life span of the treat- ment and frictional properties of the pavement surface. Identification of Alternative Maintenance and Rehabilitation Treatments · Time of year available for construction. · Availability of funds, qualified or suitable contractors, Common M&R treatments for airfield pavements are listed in agency staff, and availability of materials. Tables 3 and 4 in chapter four, and are described in the Cata- · Facility downtime (for the current pavement M&R treat- log of Airport Pavement Preservation Treatments. Treat- ment and for subsequent treatments) and associated user ments can be used alone or in combination. For example, seal- costs. ing of longitudinal and transverse cracks in AC pavements · Operational constraints and construction phasing and machine patching with hot mix can be carried out together requirements. with a microsurfacing treatment or an AC overlay. The objec- tive of the identification of alternatives is to ensure that no Over time, many agencies have developed various techni- viable alternative is overlooked. Alternatives that are not real- cal aides for the selection of pavement preservation treatments istic or practical need not be evaluated. There are also situa- on the network and project levels. Some of the procedures used tions where there are no alternatives and only one practical on the network level were discussed in chapter five. Good M&R treatment exists. sources of information are comprehensive pavement mainte- nance guides developed by state highway agencies mentioned The generation of M&R alternatives uses similar consid- previously--California (2008), Michigan (1999), Minnesota erations as those used for the design of M&R treatments. For (2001), and Ohio (2001). Other notable references include an brevity, these considerations were combined and are listed FHWA report, Selecting a Preventive Maintenance Treatment here. for Flexible Pavements (Hicks et al. 2000; Wade et al. 2007b).
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34 Design of Alternative Maintenance location, time, quantities, and the capacity of the local indus- and Rehabilitation Treatments try, and other factors, project-specific construction costs are typically used in the evaluation of the M&R treatments. The M&R treatment design enables the analyst to estimate the project-specific costs and benefits, and other attributes of the The methods used to select the recommended M&R alter- competing treatments. Design considerations were listed in native include life-cycle cost analysis, cost-effectiveness the previous section. Basic information on the design of M&R evaluation, and ranking analysis. The ranking analysis method treatments is given in the Catalog of Airport Pavement Preser- is the most comprehensive and is typically used for important vation Treatments in Appendix B. projects. Selection of the Recommended Maintenance and Rehabilitation Treatments Life-Cycle Cost Analysis Candidate M&R treatments are typically ranked by airport Life-cycle cost analysis (LCCA) facilitates the selection of pavement maintenance managers according to their esti- the least expensive alternative. LCCA can incorporate the mated benefits and costs. Estimation of benefits for mainte- costs of not only the initial M&R treatments, but also the sub- nance treatments are in terms of the extension of pavement sequent treatments. For example, the installation of retrofit- life of the original pavement. This concept is illustrated in ted subdrains may have a beneficial effect on more than one Figure 24. rehabilitation cycle. Maintenance treatments, particularly preventive mainte- Maintenance treatments, particularly preventive mainte- nance treatments, do not substantially increase the longevity nance treatments, postpone more expensive rehabilitation of the existing pavement condition as shown in the top part treatments. However, the cost of maintenance treatments is of Figure 24. The main benefit of a maintenance treatment is paid much sooner than the cost of any future rehabilitation the difference between the life span of the original pavement treatment. The need to pay now rather than later is explicitly with and without the maintenance treatment. For example, recognized in the LCCA by discounting all costs to their full-depth repairs of PCC pavements may last 15 years or present value. It is important that the analysis period, the more, but may extend the life of a specific pavement section period for which the costs are included in the analysis, be suf- by only 12 years, because the section may fail owing to the ficiently long to take into account all relevant consequences presence and progression of other distresses. of alternative treatments. The FHWA publication Life-Cycle Cost Analysis in Pavement Design (Walls and Smith 1998) Treatment costs include life-cycle costs defined in the provides a detailed description of the LCCA procedures. The Glossary of Terms. Because construction costs depend on LCCA methodology has been also used to recommend opti- Benefits due to a maintenance treatment 100 Pavement Condition Index Pavement performance curve 70 Target level of service Beneficial life Extended pavement life due to a maintenance treatment 0 0 5 10 15 Benefits due to a rehabilitation treatment 100 Pavement Condition Index Target level of service 70 Beneficial life Extended pavement life due to a rehabilitation treatment 0 0 5 10 15 20 Pavement age, years FIGURE 24 Benefits for M&R treatments in terms of beneficial life.