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134 Table 11-9. Estimated costs to establish 11.6.4. Replacement and Overhaul aggregate foam arrestor, 150 x 300 ft, assuming Order 5200.9 costs for current FAA Order 5200.9 plans a full replacement for an EMAS EMAS, units of millions USD. after 10 years. Following this schedule for replacement may be required for the drainage version of the concept, but this Cost Category Aggregate Foam Current would probably not be required for the sealed watertight System EMAS bed. Given the minimal cost increase, adding the watertight Lower Upper membrane around the foam aggregate would likely afford Bound Bound considerable long-term savings. Eliminating the 10-year Site Preparation $ 0.34 $ 0.68 $ 0.68 replacement could effectively trim about $3.5M of present- Installation $ 2.16 $ 2.16 $ 3.83 value life-cycle costs, based on the replacement cost esti- Cost to Establish $ 2.50 $ 2.84 $ 4.50 mates of the survey. Percent of EMAS 56% 63% Rather than a scheduled replacement, periodic bed material sampling could be undertaken, perhaps in 3- to 5-year inter- In addition to the tables in this section, longer-term life- vals. Small areas of the cover layer could be removed, and a cycle issues could also be considered. FAA Order 5200.9 sample of the aggregate foam could be extracted and tested. includes a standard 10-year replacement interval for an The removal area would then require refilling and repair of EMAS, which translates into present-value life-cycle costs. the top layer. These periodic small-scale tests would provide Such a replacement could arguably be unnecessary for this assurance that the bed has not degraded and still meets per- arrestor concept (Section 11.6.4). Eliminating the assumed formance specifications. 10-year replacement could effectively trim about $2.6M of present-value life-cycle costs (based on the EMAS replace- ment cost estimates of the survey). 11.6.5. Repair After an overrun event, the rut areas would require repair. 11.6.3. Maintenance The foam aggregate remaining in the ruts would require removal and replacement. The damaged cover layer would also Maintenance for the aggregate foam concept would be rel- require removal from the rut areas and subsequent replace- atively simple, and should be limited to standard grounds- ment. Geo-textile and geo-plastic layers would also require keeping measures for the protective turf layer. Drainage of repair and fusing with the existing material to ensure contin- the area to prevent standing water is required, and periodic ued waterproofing, as applicable. inspections would be advisable to ensure that no issues arise due to seasonal weather changes. Due to the lack of joints and blocks, many protective measures used in current EMAS con- 11.7. Transition to a Fielded System struction would not be necessary. In order to transition the aggregate foam concept to a The aggregate foam material is expected to have a superior fielded system, the following additional development steps durability when compared with cellular cement. Aggregate may be advisable. foam does not exhibit the tendency to crumble during han- dling as occurs with cellular cement, nor does it exhibit overt sensitivity to moisture due to its closed cell microstructure. 11.7.1. Material Density and Many industrial applications of glass foam materials indicate Compaction Calibration long service life is possible with little degradation, as long as mild protective measures are taken. As shown in the example arrestor beds of Table 11-6 and However, the aggregate foam carries some maintenance Table 11-7, the compressive strengths for optimal designs issues not present for solid foam block material. The loose ranged from 59% to 103% of the tested material. To estimate aggregate could settle over time, or the aggregate pieces could the needed strength in the arrestment predictions, the meta- eventually break down into smaller pieces, changing the model data was simply scaled, which was an appropriate gradation of the material. These are both issues to address simplification. through inspections. Plate-shaped dimensional markers However, in migrating to a fielded system, several standard could be inserted below the turf layer and checked periodi- densities and gradations would probably be selected to pro- cally using surveying equipment for changes in height, and vide flexibility during the design of actual arrestors. For each aggregate samples could be tested periodically (discussed fur- density and gradation, some testing would be required to ther in the next section). generate calibration data.