National Academies Press: OpenBook

Common Airport Pavement Maintenance Practices (2011)

Chapter: Chapter Seven - Project Design and Implementation

« Previous: Chapter Six - Prioritization, Planning, and Budgeting
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Suggested Citation:"Chapter Seven - Project Design and Implementation." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Page 33
Suggested Citation:"Chapter Seven - Project Design and Implementation." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Page 34
Suggested Citation:"Chapter Seven - Project Design and Implementation." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Page 35
Suggested Citation:"Chapter Seven - Project Design and Implementation." National Academies of Sciences, Engineering, and Medicine. 2011. Common Airport Pavement Maintenance Practices. Washington, DC: The National Academies Press. doi: 10.17226/14500.
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Page 35

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33 The final treatment type and associated technical details and costs are determined at the project level. The project-level activities discussed in this chapter include project design, project implementation, and the monitoring of completed projects. The project design and implementation is an inte- gral part of the airport pavement management process (Haas et al. 1994). PROJECT DESIGN Project design determines the specific treatment type and design details for the construction of the project, such as layer types, material properties, and construction details. The selected M&R treatments address the primary cause of pave- ment deterioration and not just the distresses seen on the pave- ment surface during a PCI survey. Compared with the network- level identification of needs and prioritization, the project-level design requires additional data and data with greater detail. For large or complicated projects, the design process consists of a preliminary design stage and the final design stage. The preliminary design stage includes: (1) identification of alterna- tives, (2) design of alternatives, and (3) selection of a recom- mended alternative. The final design stage includes detailed design of the selected alternative. Identification of Alternative Maintenance and Rehabilitation Treatments Common M&R treatments for airfield pavements are listed in Tables 3 and 4 in chapter four, and are described in the Cata- log of Airport Pavement Preservation Treatments. Treat- ments can be used alone or in combination. For example, seal- ing of longitudinal and transverse cracks in AC pavements and machine patching with hot mix can be carried out together with a microsurfacing treatment or an AC overlay. The objec- tive of the identification of alternatives is to ensure that no viable alternative is overlooked. Alternatives that are not real- istic or practical need not be evaluated. There are also situa- tions where there are no alternatives and only one practical M&R treatment exists. The generation of M&R alternatives uses similar consid- erations as those used for the design of M&R treatments. For brevity, these considerations were combined and are listed here. • Facility type and the associated requirements for per- formance reliability of the M&R treatments. • Pavement surface quality in terms of surface friction, roughness, and the potential for FOD. • Existing pavement condition, surface distresses, and pavement performance history. • Construction history and previous experience with a particular treatment under similar circumstances. • Physical properties of the existing pavement structure. For the design of M&R treatments, this may require coring and boring of the existing pavement structure to obtain dimensions and material samples, and the use of a dynamic cone penetrometer. • Structural pavement strength. For the design of M&R treatments, the determination of pavement strength (struc- tural support) can be done with pavement deflection test- ing. A good reference is FAA Advisory Circular on Use of Nondestructive Testing Devices in the Evaluation of Airport Pavements (2004). • Anticipated traffic loads in terms of the number of oper- ations, particularly departures, and the type of aircraft. • Environmental exposure, such as pavement temperature extremes, number of freeze–thaw cycles, and exposure to fuel spills. • Life-cycle costs. • Benefits; for example, estimated life span of the treat- ment and frictional properties of the pavement surface. • Time of year available for construction. • Availability of funds, qualified or suitable contractors, agency staff, and availability of materials. • Facility downtime (for the current pavement M&R treat- ment and for subsequent treatments) and associated user costs. • Operational constraints and construction phasing requirements. Over time, many agencies have developed various techni- cal aides for the selection of pavement preservation treatments on the network and project levels. Some of the procedures used on the network level were discussed in chapter five. Good sources of information are comprehensive pavement mainte- nance guides developed by state highway agencies mentioned previously—California (2008), Michigan (1999), Minnesota (2001), and Ohio (2001). Other notable references include an FHWA report, Selecting a Preventive Maintenance Treatment for Flexible Pavements (Hicks et al. 2000; Wade et al. 2007b). CHAPTER SEVEN PROJECT DESIGN AND IMPLEMENTATION

Design of Alternative Maintenance and Rehabilitation Treatments The M&R treatment design enables the analyst to estimate the project-specific costs and benefits, and other attributes of the competing treatments. Design considerations were listed in the previous section. Basic information on the design of M&R treatments is given in the Catalog of Airport Pavement Preser- vation Treatments in Appendix B. Selection of the Recommended Maintenance and Rehabilitation Treatments Candidate M&R treatments are typically ranked by airport pavement maintenance managers according to their esti- mated benefits and costs. Estimation of benefits for mainte- nance treatments are in terms of the extension of pavement life of the original pavement. This concept is illustrated in Figure 24. Maintenance treatments, particularly preventive mainte- nance treatments, do not substantially increase the longevity of the existing pavement condition as shown in the top part of Figure 24. The main benefit of a maintenance treatment is the difference between the life span of the original pavement with and without the maintenance treatment. For example, full-depth repairs of PCC pavements may last 15 years or more, but may extend the life of a specific pavement section by only 12 years, because the section may fail owing to the presence and progression of other distresses. Treatment costs include life-cycle costs defined in the Glossary of Terms. Because construction costs depend on 34 location, time, quantities, and the capacity of the local indus- try, and other factors, project-specific construction costs are typically used in the evaluation of the M&R treatments. The methods used to select the recommended M&R alter- native include life-cycle cost analysis, cost-effectiveness evaluation, and ranking analysis. The ranking analysis method is the most comprehensive and is typically used for important projects. Life-Cycle Cost Analysis Life-cycle cost analysis (LCCA) facilitates the selection of the least expensive alternative. LCCA can incorporate the costs of not only the initial M&R treatments, but also the sub- sequent treatments. For example, the installation of retrofit- ted subdrains may have a beneficial effect on more than one rehabilitation cycle. Maintenance treatments, particularly preventive mainte- nance treatments, postpone more expensive rehabilitation treatments. However, the cost of maintenance treatments is paid much sooner than the cost of any future rehabilitation treatment. The need to pay now rather than later is explicitly recognized in the LCCA by discounting all costs to their present value. It is important that the analysis period, the period for which the costs are included in the analysis, be suf- ficiently long to take into account all relevant consequences of alternative treatments. The FHWA publication Life-Cycle Cost Analysis in Pavement Design (Walls and Smith 1998) provides a detailed description of the LCCA procedures. The LCCA methodology has been also used to recommend opti- 15 20 Beneficial life Benefits due to a maintenance treatment Pa ve m en t C on di tio n In de x 0 70 100 5 10 150 0 Beneficial life Extended pavement life due to a maintenance treatment Pavement performance curve Pavement age, years Pa ve m en t C on di tio n In de x 0 70 100 5 10 Target level of service Extended pavement life due to a rehabilitation treatment Benefits due to a rehabilitation treatment Target level of service FIGURE 24 Benefits for M&R treatments in terms of beneficial life.

35 mal timing of preventive maintenance treatments by Peshkin et al. (2004). A new LCCA guide and software package is also being developed under Airfield Asphalt Pavement Tech- nology Program Project 06-06. The methodology of LCCA consists of the following steps: • Inclusion of all viable and practical alternative M&R treatments. • Determination of agency costs for each alternative. The agency costs include the initial construction costs and subsequent M&R costs throughout the analysis period. • Determination of user costs. Many agencies do not include user costs in LCCA on the project level, because user costs are often similar for all alternatives and do not affect agency budget. However, when construction of M&R alternatives may have a different impact on airport operations and revenues, for example because of the differences in the length of construction, user costs are included. • Selection of economic parameters for LCCA in terms of the discount rate and analysis period. • Calculation of the net present value of agency costs and user costs. • Selection of the alternative. The alternative with the lowest agency and user costs is the best from the eco- nomical point of view. Cost-effectiveness Evaluation Cost-effectiveness is the ratio and effectiveness (benefits) to life-cycle costs. The effectiveness is calculated using a simi- lar procedure as that used on the network level described in the section on Prioritization for Long-term Planning, with the additional benefit of using more reliable project-specific data. On the network level, the effectiveness is calculated by multiplying the area under the PCI performance curve by the number of aircraft operations and the surface area of the sec- tion. The area under the performance curve, considered to be a measure of pavement serviceability, is illustrated in Fig- ure 18 in chapter six. On the project level, the number of air- craft operations and the surface area are the same for all alter- natives and need not be considered. The cost-effectiveness method provides an improvement over the LCCA method by taking into account differences in pavement serviceability provided by different alternatives. Ranking Evaluation Some of the attributes of M&R treatments, such as disruption of airport operations, previous agency experience with the treatment, sustainability, or improved pavement friction, can- not be readily quantified in monetary terms. M&R treatments may also create additional benefits in the form of improved pavement surface or impose operational constraints during con- struction. For this reason, in addition to the LCCA that takes into account monetary aspects of cost and benefits, a systematic assessment of other treatment attributes may also be carried out. For example, consider two alternative rehabilitation treat- ments for an AC pavement on a runway of a small airport: a traditional overlay and in-place recycling. In addition to the LCCA that may favor in-place recycling, it is advisable to also consider other attributes: • Effectiveness of the two alternatives. Effectiveness is defined as the area under the pavement performance curve (see Figure 18). • Agency experience with the performance of the alter- natives. • Availability of qualified contractors. • Reliability of cost estimates, particularly if local con- tractors are not available to carry out a specific alterna- tive M&R treatment. • Environmental and sustainability benefits owing to recycling of AC pavement material in-place. • Potential for future cost savings if a new, less expensive rehabilitation method becomes available. • Compatibility with phased or off-peak construction requirements. A step-by-step example of this approach is provided in Selecting a Preventive Maintenance Treatment for Flexible Pavements (Hicks et al. 2000). Briefly, the procedure con- sists of four steps: 1. Selection of relevant attributes that are important to the customer and the agency. The list of attributes given in the earlier example is only illustrative and does not include many other attributes that may be important for specific alternatives, such as pavement friction, sensitivity to weather during construction, and avail- ability of quality materials. 2. Assigning relative importance to the attributes using a rating factor. The total score of 100 is distributed to all relevant attributes. 3. Scoring each attribute in terms of its importance for the selection of the preferred treatment. This is accom- plished using scoring factors on a 5-point scale, 5 being very important, and 1 not important. 4. Calculating total scores for all alternative treatments by summing the product of rating and scoring factors obtained for all attributes. PROJECT IMPLEMENTATION AND MONITORING The application of M&R treatments currently considers the use of appropriate materials, construction methods, and qual- ity control and assurance procedures. Following the trends of the highway construction industry, many airports use end- result specifications for construction quality control. In addi- tion to quality control and quality assurance procedures, air- port operators also use construction warranties. Warranties

provide a catch-all provision to ensure basic construction quality. Warranties are particularly important for pavement maintenance treatments where the construction materials and procedures are difficult to specify and enforce. In addition to the periodic condition evaluation of the entire pavement network, discussed in chapter four, airports 36 evaluate periodically specific pavement M&R treatments, particularly treatments that are not routinely used. This enables the airport pavement manager to expand, modify, or discontinue specific treatments based on their documented field effectiveness. According to data presented in Figure 6 (in chapter two), only 45% of agencies reported using an APMS to determine the performance of the past M&R treatments.

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TRB’s Airport Cooperative Research Program (ACRP) Synthesis 22: Common Airport Pavement Maintenance Practices explores how airports implement a pavement maintenance management program, including inspecting and tracking pavement condition, scheduling maintenance, identifying necessary funds, and treating distresses in asphalt and concrete pavements.

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