AIRPORT PAVEMENT MAINTENANCE AND REHABILITATION AT ARIZONA AIRPORTS WITH ASPHALT-RUBBER David A. Gilbertson, P.E. and W. R. Meier, Jr., Ph.D., P.E.

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1 AIRPORT PAVEMENT MAINTENANCE AND REHABILITATION AT ARIZONA AIRPORTS WITH ASPHALT-RUBBER David A. Gilbertson, P.E. and W. R. Meier, Jr., Ph.D., P.E. Due to the fact that asphalt-rubber had its origin in Arizona, it is not surprising that a significant amount of the early developmental work using this product occurred within that state. McDonald, Morris, Schnormeier, and other Arizonians are all familiar names in those early efforts that have led to the industry that exists today. Most of the early work using asphalt-rubber was applied to highway and street pavements, although Schnormeier was involved with applications at Phoenix's Sky Harbor airport. Arizona has, however, a large number of smaller, General Aviations airports where asphalt rubber products have been effectively used. Funding procedures and ages of many of these General Aviation facilities necessitated some unique and imaginative pavement design procedures for which asphalt-rubber was found to be extremely useful. The levels and manner of funding of General Aviation airports by Arizona Department of Transportation (ADOT) and the Federal Aviation Administration (FAA) has often resulted in a staged approach to construction. Consequently, a facility would be built in a series of projects that all too frequently did not provide for adequate maintenance of previously constructed pavement. A number of Arizona's General Aviation airports have original construction dating back to World War II. They were 407

2 constructed at that time to serve in the war effort with no particular plans for future utilization. The existence of these facilities resulted in their further expansion as demand for airports increased. Today, many of these World War II airfields, and other airports constructed shortly after that period, are the sole air facility for many small communities and surrounding areas. Uses vary from light, single-engine pleasure crafts and crop sprayers to large surplus military aircraft utilized by the U. S. Forest Service as "Slurry Bombers" to assist in suppression of forest fires. Pavement distress encountered at General Aviation airports where traffic is almost totally small single or twin-engine aircraft is oftentimes induced by the environmental conditions rather than traffic loads. The Arizona airports being considered here vary geographically from Window Rock, elevation 6,700 feet, located in the remote northeast portion of the state to scottsdale Municipal Airport, elevation 1,500 feet within densely populated Maricopa County. Environmental conditions vary from searing deserts where pavement temperatures reach and exceed 150F to temperate climates characterized by winter snows and frozen subsurface conditions. Six Arizona airports where the authors have utilized asphaltrubber for pavement maintenance or rehabi li tation during the past ten years were examined for this study. These ai rports were: 408

3 -' Winslow Municipal Airport, Winslow, Arizona Mohave County Airport, Kingman, Arizona Scottsdale Municipal Airport, Scottsdale, Arizona Window Rock Airport, Window Rock, Arizona Skyranch at Carefree, Carefree, Arizona Eloy Municipal Airport, Eloy, Arizona The work performed at each of these facilities and the current condition of that work have been examined and are presented. Winslow Municipal Airport Winslow Municipal Airport is a facility dating back to the early 1940's with little maintenance performed in the intervening years. Winslow, Arizona is in the north central portion of the state, near the Navajo Indian Reservation. It lies at 4,850 feet elevation and has a temperate, though relatively dry, climate. In 1978, Runway 4/22 received a chip seal with asphalt-rubber binder to serve as the initial stage of a runway strengthening project that would be completed with a 2+ inch asphalt concrete overlay. To date, this overlay had not been constructed and this Stress-Absorbing Membrane (SAM) has continued to provide a quality take-off and landing surface. 409

4 In 1984, Runway 11/29 was maintained by sealing approximately 50,000 linear feet of cracks using asphalt-rubber crack sealant. This work sealed shrinkage cracks and prevented the intrusion of moisture into the moisture sensitive pavement subgrade. Cracks were cleaned and routed to provide a reservoi r for the crack sealant prior to application of the crack sealer. In 1983 and 1984, taxiways parallel to Runways 4/22 and 11/29 were rehabilitated utilizing a cold, in-place recycling technique. Recycling of the aged, extensively cracked pavement was accomplished by crushing the asphalt concrete surface and mixing the resulting product and a portion the underlying aggregate base with portland cement as a cement treated base (CTB). The CTB then received an asphalt-rubber chip seal to serve as a Stress-Absorbing Membrane Interlayer (SAMI) and an asphalt concrete surface course. The SAMI successfully relieved the stress from the shrinkage cracks generated within the underlying CTB and prevented their appearance in the pavement surface. It is worthy to note that all the work performed at Winslow Municipal Airport for these projects was constructed on schedule, wi thin budget and with minimum interference to aircraft operation. 410

5 Mohave County Airport Mohave County Ai rport at Kingman, Arizona is in the northwestern part of the state and is at an elevation of 3325 feet. The environment is that of a high desert with a moderate temperate climate. Construction at that facility using asphaltrubber was performed in 1983 and consisted of apron reconstruction using a SAMI. The parking apron was reconstructed by recycling the asphalt concrete surface and a portion of the aggregate base as a 6-inch CTB. This base course received an asphalt-rubber SAMI and a 2-inch thick asphalt concrete overlay. An area of 24,000 square yards was reconstructed in this manner. To date this area has provided outstanding service and shows only a slight amount of cracking. Scottsdale Municipal Airport Scottsdale Municipal Airport is in a locality with a desert environment and at an elevation of approximately 1,500 feet. Air traffic is substantial and consists of single and twin propeller driven aircraft in addition to jet aircraft up to 60,000-pound gross load. As with most airport facilities, it has been constructed in several stages as funds were available and needs present. Asphalt-rubber has been used in maintenance and rehabilitation projects since

6 In 1984 a severely cracked portion of the airport parking apron was rehabilitated by use of a SAM chip seal. Prior to chip sealing, an asphalt emulsion slurry seal was applied to fill the existing cracks. The application of the SAM was followed by an asphalt emulsion flush coat to help hold chips and avoid damage to aircraft associated with loose chips. During 1986 and 1987 further apron maintenance using asphaltrubber crack sealant, a SAMI and an asphalt concrete overlay for strengthening was carried out. The SAMI successfully reduced reflection cracking from an extensively cracked existing asphalt concrete pavement. In total, the Scottsdale Municipal Airport work has included 120,000+ linear feet of crack sealing, 55,000 square yards of SAM chip seal and cape seal, and 25,000 square yards of overlay with a SAMI. The performance of the rehabilitated pavements has been excellent. Window Rock Airport Window Rock, Arizona is the capital of the Navajo Nations and is located on the Navajo Reservation in the northeastern corner of the state of Arizona. The area is characterized by beautiful red sandstone cliffs, moisture sensitive, swelling clay-shale soils, and a harsh winter environment. 412

7 1984 construction at the Window Rock Airport consisted of crack sealing with asphalt rubber along the outer portions of Runway 2/20. taxiways and aprons. In addition. the center 75 feet of Runway 2/20 was reconstructed by recycling the existing pavement as a CTB followed by placement of a SAMI. and eventually. an asphalt concrete overlay. The runway successfully functioned with the SAMI serving as the sole surface course until the asphalt concrete overlay could be constructed approximately one year later. The function of the SAMI both as a surface layer and its later use as an interlayer to reduce reflection cracking from the CTB have been very successful. Skyranch at Carefree Skyranch at Carefree. Arizona is a privately owned airport serving this community north of Scottsdale. Original pavement construction at this faci li ty was an asphalt concrete surface over a cement treated base. As frequently occurs with this design. shrinkage cracks within the CTB resulted in block cracking of the bituminous surface. To repair this condition. Runway 6/24. taxiways and aprons received asphalt-rubber crack sealing in The application of this maintenance material has extended the life of this pavement and has prevented damage from water entering the pavement structure through cracks. The pavement has shown no progressive distress from the existing cracks that were sealed in this manner. 413

8 Eloy Municipal Airport Eloy Municipal Airport at Eloy, Arizona is approximately 60 miles southeast of Phoenix and is at an elevation of 1565 feet. It lies within an agricultural area where cotton, winter wheat and pecans are grown by use of extensive irrigation. As a result, many crop sprayers use this facility as a base for their operations. other light aircraft for both pleasure and business uses also depart and land from this airport. During 1987 Runway 2/20 received surface rehabilitation in the form of application of a rejuvenating agent followed by crack maintenance with asphalt-rubber crack sealant. The rejuvenated and sealed pavement received a Type II slurry seal for the completed surface. Some crack reflection has occurred within the slurry seal; however, it is of very low severity and the underlying sealant has kept the cracks sealed. The treatment applied has performed very well and an excellent take-off and landing surface has been maintained. 414

9 Conclusion The use of asphalt-rubber in pavement maintenance at Arizona General Aviation airports has been very successful. Asphaltrubber offers the engineering community many options in the creative design of pavement maintenance projects. It has proven to not only be cost effective, but also to result in quality finished surfaces required for airfield pavements. 415

10 "Airport Pavement Maintenance & Rehabilitation at Ariz<;ma Airports With Aspahtl-Rubber", by David A. Gilbertson, P.E., Scottsdale & Dr. W.R. Meier, Jr., P.E. Senior Materials Engineeer, Western Technologies, Inc., Phoenix, Az. Question/John Corcoran: Did you have any problem at all with the cement treated base with any cracks propogating through the SAM, and was that placed directly on top of that base? Dr. Meier: It was placed directly on top of the base. In some cases it was used as a SAMI with overlay, and some cases it was placed as a SAM. After four or five years, there are a few cracks that have shown up, nothing that needs to be maintained at this point. Those that have the asphalt concrete overlay, the only cracking that I saw is what I would consider to be shrinkage cracking within the asphalt concrete itself because it has not been treated with any surface treatment so that the crack propogation was quite minor. Tom Kirk: On that same line, I believe on the last job, the SAM was applied, I believe it was cement-treated, recycled pavement. Is that correct? Dr. Meier: Tom Kirk: That is correct! Have the shrinkage cracks shown any indication of appearing? Are they there yet or otherwise? Dr. Meier: They have appeared but not to the extent that there had to be any maintenance on them. You can tell where the cracks are but they are more of a "ghost" crack than anything else. I feel that when you do have a working crack with the SAMs that there is some movement that occurs in there but the material is forgiving, it tends to reheal itself. That would be an indication of the presence of the crack and I will say that in some cases, the cracking near the edges, there was some vegetation coming up through there, and something that needed to be maintained shortly. 416