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146 Table 13-1. Comparison of multi-aircraft bed per- $9 formance: exit speeds for full arrest in 400-ft bed. $8 Cost to Establish ($M) $7 Aircraft Glass Foam Engineered Aggregate Aggregate Foam $6 $5 CRJ-200 70+ 70+ 70+ $4 B737-800 70+ 63 70+ $3 B747-400 46 39 56 Installation $2 Site Preparation $1 $- mance estimates are based on some test data, historical use of the materials, and engineering judgment. An exhaustive envi- ronmental test program has not been undertaken as part of this program. Life-cycle performance has been assumed to result from a combination of the core materials used and the protective measures taken to shield those materials from the elements. Figure 13-3. Relative estimated cost comparison From a materials standpoint, the glass foam and aggre- assuming survey costs (150 ft x 300 ft bed). gate foam concepts both use closed-cell glass foams that inherently resist water penetration. The engineered aggre- gate is composed of hard spherical pellets. All three of these In all three cases, the proposed designs offer life-cycle poten- materials appear to offer superior inherent resistance to gen- tial beyond the 10-year bed replacement interval that is eral handling and moisture/chemical exposure when com- assumed necessary for the current EMAS technology (29). pared to cellular cement. Of the three, the engineered aggregate is the most durable 13.4. Cost Comparison material because it is not a crushable low-density foam. How- ever, the arresting properties of engineered aggregate can be The relative costs for the current EMAS and the candi- affected by the dampness of the material in a manner that is date systems are compared in Figure 13-3 and Figure 13-4 unlikely to affect the glass and aggregate foams. using survey cost assumptions and estimates from FAA The glass and aggregate foam materials showed degrada- Order 5200.9, respectively. The general trends appear tion if subjected to fully immersed freezethaw cycling con- similar in either case, with the aggregate foam concept pro- ditions. Protection from standing water conditions would be viding the least expensive alternative, and the glass foam required in all three cases, which is feasible using the pro- posed protective measures. Where such measures are taken, the materials have demonstrated a long service life. $7 With regard to protective measures, methods for covering $6 and sealing the three candidate materials against moisture, Cost to Establish ($M) standing water, jet blast, and freezing conditions have been $5 examined (see respective chapters). For the aggregate foam $4 and engineered aggregate approaches, the use of geo-plastics $3 and geo-textiles could render the beds essentially isolated from water entrainment and freezethaw damage. The glass $2 Installation foam material could be packaged in a manner similar to that $1 Site Preparation of the current EMAS cellular cement or equipped with an alternative monolithic sealed top layer. $- Both the aggregate foam and engineered aggregate concepts propose using a turf layer atop the beds, which is novel for arrestor beds. While modeling predictions indicate that this is feasible, additional testing in wet and freezing conditions would be required to characterize that facet of environmental per- formance. Alternative cover layers are possible in the event of Figure 13-4. Relative estimated cost comparison adverse performance. assuming FAA Order 5200.9 costs (150 ft x 300 ft bed).