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18 CHAPTER FOUR TECHNOLOGY OF PAVEMENT PRESERVATION TREATMENTS This chapter describes the technology of pavement M&R ments are used across the country. For example, 84% of air- treatments for AC and PCC pavements. It also describes the ports (that have AC pavements) reported that they routinely survey results concerning the use and performance of M&R use crack sealing with hot-poured sealant (Table 3). Simi- treatments reported by airport agencies. larly, 61% of agencies (that have PCC pavements) reported that they are routinely using, or have tried using, joint seal- ing with silicone sealant (Table 4). SURVEY RESULTS The use of some M&R treatments depends on the size and Survey results for AC and PCC pavements are summarized volume of traffic of the airport, such as the treatments aimed in Tables 3 and 4, respectively. The tables contain informa- at increasing pavement friction. Consequently, although about tion on the usage and performance of common M&R treat- ments as reported by 50 representatives of airport agencies. 39% of the responding airports reported using diamond grind- There were 19 M&R treatments included in the survey for ing (routinely or on a trial basis), the percentage for small air- AC pavements (Table 3) and 19 M&R treatments for PCC ports would probably be considerably lower, and for large pavements (Table 4). The treatments traditionally considered airports most likely considerably higher. to be preventive maintenance treatments are shown in Tables 3 and 4 in italic font. For AC pavements, the following six M&R treatments were used by less than 15% of agencies that had AC pave- Data presented in Tables 3 and 4 are the percentages of ments on at least one facility: spray patching, texturization usage or performance of M&R treatments reported by survey using fine milling, microsurfacing, hot and cold in-place respondents. For example, referring to the first row of data in recycling, and PCC overlay. Table 3, 84% of airports that responded to the survey routinely use crack sealing with hot-poured sealant and 11% of airports For PCC pavements, the following four M&R treatments have tried using this treatment. Consequently, 95% of the air- were used by less than 15% of the agencies: load transfer ports routinely use or have tried using this treatment and the restoration treatments using sub-sealing and slab stitching, remaining 5% have not. Continuing with the example data in full-depth repairs using precast panels, and microsurfacing. the first row, 19% of the airports that routinely use or have tried using crack sealing with hot-poured sealant reported very good Performance of Maintenance performance with this treatment, 71% of the airports reported and Rehabilitation Treatments good performance, and 10% of the airports reported poor per- formance. The number of reporting airports, corresponding to Survey results concerning the performance of M&R treat- the percentages of airports given in Tables 3 and 4, are pre- ments reported in Tables 3 and 4 are not reliable because of sented in Appendix A as part of the Survey Questionnaire. sample size limitations and the lack of objective guidelines for the evaluation of treatment performance. A very large Approximately 70% of the responding airports had both sample size would be needed to obtain a statistically signifi- AC and PCC pavements on at least some airfield facilities, cant number of performance reports for the M&R treatments and about 30% of airports had both AC and PCC pavements that are not frequently used, even if all survey responses were on runways (Figure 11). Approximately 50% of airports had grouped in one sample. However, the treatment performance only AC pavements on runways and 20% of airports had only may depend on the environmental zone (e.g., wet-freeze, PCC pavements on runways. Considering the distribution of dry-freeze, dry-no freeze, and wet-no freeze) and on the air- pavement types, a large segment of airports need to have staff port facility (runway, taxiway, and apron) further increasing familiar with the technology of both AC and PCC pavements. the sample size. Use of Maintenance and Rehabilitation Treatments To obtain an objective rating of the treatment perfor- mance shown in Tables 3 and 4 would also require the devel- Information on the use of M&R treatments obtained from the opment of performance evaluation guidelines for all M&R survey provides a good indication of what types of such treat- treatments and adherence to such guidelines by the respon-

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19 TABLE 3 PAVEMENT PRESERVATION TREATMENTS FOR ASPHALT CONCRETE PAVEMENTS Survey Result, % Usage Performance Treatment Type Routine Good Good Tried Have Total Very Poor hot-poured sealant 84 11 95 19 71 10 Crack sealing with cold-applied sealant 9 7 16 17 66 17 hot mix 52 16 68 42 58 0 Small area (pothole) cold mix 43 18 61 13 50 37 patching using proprietary mix 9 11 20 25 50 25 Spray patching (includes manual chip seal) 5 7 11 0 100 0 Machine patching with AC 27 14 41 39 55 6 Milling and machine patching with AC 34 18 52 39 61 0 fine milling 7 5 11 20 80 0 Texturization using controlled shot blasting 0 16 16 0 71 29 Rejuvenators, fog seals, etc. 30 23 52 23 59 18 Surface treatment 15 18 43 6 81 13 Slurry seal 23 25 48 10 75 15 Microsurfacing 2 9 11 25 75 0 Hot-mix overlay 45 23 68 48 48 4 Milling and hot-mix overlay 45 18 64 58 42 0 Hot in-place recycling 5 2 7 N/A N/A N/A Cold in-place recycling 2 0 2 N/A N/A N/A Whitetopping (PCC overlay) 7 7 14 60 20 20 Notes: Treatments traditionally considered preventive maintenance treatments are in italics. N/A: sample size is too small. dents. For example, evaluation guidelines would need to be routinely use or tried making shallow repairs of PCC slabs prepared to explain what conditions need be met to rank the using PCC material or AC material. It is generally recom- performance of an overlay as very good. Several respondents mended that PCC material be used to repair PCC slabs. This did not provide performance ranking for treatments that they recommendation is supported by the performance data given do not use routinely, and some respondents were reluctant to in Figure 12. As expected, the survey data show somewhat provide any ranking at all. Nevertheless, the performance better performance of PCC material. information obtained from the survey provides information on overall trends. Innovative and Additional Treatments Average performance data from the survey respondents In addition to the common M&R treatments listed in Tables 3 for both AC and PCC pavements are presented in Table 5. and 4, airport agencies reported the use, and in some cases There is only a very small, statistically insignificant differ- commented on the performance, of the following innovative ence between the average performance of M&R treatments M&R treatments: for AC pavements and those for PCC pavements. For exam- ple, on the average, the performance of approximately 60% Stress-relieving membranes to retard reflective crack- of M&R treatments for AC pavements was rated as good, ing in AC overlays. whereas the corresponding number of M&R treatments for Proprietary materials for AC overlays. PCC pavements was about 58%. On average, only about Portland cement with high proportions of fly ash and 11% of M&R treatments for AC pavements received a poor blast furnace slag. performance, whereas the corresponding percentage for PCC Rejuvenators (asphalt emulsions) to stabilize granular pavements was 12. shoulders. Over-band method of sealing cracks in AC pavements For frequently used treatments, it is possible to identify with sealing material containing fibers. some expected trends in the performance of M&R treat- Slurry seals containing thermoplastic coal-tar (fuel- ments. For example, approximately 50% of airport agencies resistant) emulsion.

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20 TABLE 4 PAVEMENT PRESERVATION TREATMENTS FOR PORTLAND CEMENT CONCRETE PAVEMENTS Survey Result, % Usage Performance Treatment Type Routine Good Good Tried Have Total Very Poor Joint/crack sealing bituminous sealant 29 15 44 13 80 7 with silicone sealant 39 22 61 29 71 0 neoprene seal 7 22 29 36 36 27 Load transfer restoration sub-sealing and slab 2 5 7 N/A N/A N/A jacking slab stitching 2 5 7 N/A N/A N/A dowel retrofit 12 5 17 60 40 0 Shallow patch repair PCC 34 15 49 28 67 6 using AC 29 20 49 18 65 18 proprietary mix 17 17 34 42 42 17 Full and partial depth PCC 46 15 61 47 47 6 repairs or slab AC 20 39 59 31 54 15 replacement using proprietary mix 7 17 24 30 50 20 precast panels 2 2 5 N/A N/A N/A Machine patching with AC 5 12 17 33 50 17 Diamond grinding 5 34 39 21 79 0 Controlled shot blasting 0 15 15 0 80 20 Microsurfacing 0 5 5 N/A N/A N/A AC overlay 10 27 37 36 64 0 Bonded PCC overlay (whitetopping) 7 7 15 40 40 20 Notes: Treatments traditionally considered preventive maintenance treatments are in italics. N/A: sample size is too small. Fuel-resistant AC containing resin-modified asphalt Only AC Only PCC AC & PCC 80 cement. Warm-mix AC (rather than the traditional hot mix). Percentage of respondents 60 Transverse grooving of AC pavement surfaces to improve pavement friction. Specific repairs of wide or deteriorated pavement cracks 40 in AC pavements. Various types of fog seals. 20 Crack filling AC mixes (mastic) for repairs of large cracks in AC pavements. 0 Proprietary AC and PCC mixes for patching repairs. All facilities Runways only Facility type All of these M&R treatments and materials require continu- FIGURE 11 Distribution of pavement types. ing evaluation to document cost-effectiveness. TABLE 5 AVERAGE PERFORMANCE OF M&R TREATMENTS FOR DIFFERENT PAVEMENT TYPES Average Performance for all Treatments No. No. and Airports (%) of of Pavement Type Airports Treatments Very Good Good Poor AC Pavements 44 19 30.2 59.1 10.7 PCC Pavements 41 19 29.6 58.1 12.3