appendix c pavement evaluation - juneau, · pdf filesubject: runway 8-26 pavement evaluation...

$: APPENDIX C PAVEMENT EVALUATION - Juneau, · PDF fileSubject: Runway 8-26 Pavement Evaluation and Alternatives Page 2 i:\1420300\reports\1420300 jnu pavement evaluation memo_te_ud.docx$
APPENDIX C

PAVEMENT EVALUATION

Technical Memorandum

I:\1420300\Reports\1420300 JNU Pavement Evaluation Memo_TE_UD.docx Form Revised: 11/2012

Date: October 7, 2013 W.O.#: 1420300

To: Ken Nichols, JNU Airport Engineer cc: Zane Shanklin, P.E.

From: Johnathan G. Limb, P.E.

Project: JNU Runway 8-26 Rehabilitation

Subject: Runway 8-26 Pavement Evaluation and Recommendations

INTRODUCTION

In 2011 the Federal Aviation Administration (FAA) inspected Juneau International Airport’s (JNU) runway (RW) and determined that the pavement was deteriorating and producing enough foreign object debris (FOD) that it posed a danger to public safety and needed to be repaired. The City and Borough of Juneau (CBJ) completed emergency repairs on the middle section of the runway in October 2012 and June 2013, which solved the FOD and safety issues, but the airport would like to rehabilitate the runway’s pavement since it is nearing the end of its 20‐year design life. CBJ contracted USKH Inc. (USKH) to evaluate the condition of the runway pavement and prepare construction documents for the permanent rehabilitation of the runway. Located on the mainland of Southeast Alaska, opposite Douglas Island, Juneau was built at the heart of the inside passage along the Gastineau Channel. It lies 900 air miles northwest of Seattle, Washington and 577 air miles southeast of Anchorage. Juneau has a mild maritime climate. Average summer temperatures range from 44° F to 65° F and winter temperatures range from 25° F to 35° F. It is in the mildest climate zone in Alaska. Annual precipitation averages 54 inches at the airport. Snowfall averages 101 inches each year. Juneau is only accessible by air and sea; the airport is located approximately 10 miles north of the city in the Mendenhall Valley, and serves scheduled jet flights, air taxis, medivacs, and helicopter flight‐seeing operations. The airport, owned by CBJ, provides a paved 8,857‐foot long by 150‐foot wide runway with a parallel taxiway and a seaplane base. Alaska Airlines operates a range of 737‐400s to 737‐900s into JNU for scheduled passenger and cargo service, which place the highest demand on the runway, but the airport is also utilized by U. S. Coast Guard C‐130 Hercules and U.S. Air Force C‐17 Globemasters on occasion. Part 135 air taxi operators utilize aircraft ranging from Cessna 206, 207, and 208s; Piper Navajo’s; to Dehavilland DHC‐2 Otters on amphibious floats. The bulk of the Part 135 operations are concentrated on the RW 8 end of the runway and almost exclusively use Taxiway C for access to the parking ramp. Medivac operators utilize Lear 35/36s and KingAir B200s. Additionally, a wide variety of unscheduled private business jets as large as Gulfstream G‐VIs and Bombardier Global Expresses land at JNU. The proposed project will rehabilitate RW 8‐26’s pavement by removing existing deteriorated pavement and placing new hot mix asphalt. This memo details documents reviewed in preparation for a pavement inspection by USKH, description of the existing pavement structure, and findings of the pavement inspection and subsequent geotechnical investigation efforts. Pavement rehabilitation alternatives are also provided based on the findings of the pavement evaluation.

Subject: Runway 8-26 Pavement Evaluation and Alternatives Page 2

i:\1420300\reports\1420300 jnu pavement evaluation memo_te_ud.docx Revised: 11/2012

PAVEMENT EVALUATION

USKH began evaluating RW 8‐26’s pavement by first reviewing the following available information:

1997 Runway Rehabilitation Project asbuilts and design memos

FAA compliance inspection reports

The 2012 Pavement Inspection Report prepared by the Alaska Department of Transportation (DOT&PF)

A pavement inspection was performed by USKH to determine size, type, and severity of existing pavement distresses as well as their location on the runway. This pavement inspection was used to determine locations of borings and cores to be taken for the geotechnical investigation. The newly constructed RW 26 extension pavement was not included in the inspection.

1997 Runway Rehabilitation Project

Based on design memo prepared by USKH for the 1996 runway rehabilitation project, the existing runway asphalt concrete (AC) thickness varies between 8 and 16 inches. The original portion of the runway (the western 5,000 feet) generally consists of 6 to 8 inches of AC over a layer of asphalt emulsion sand. The eastern portion generally consists of 10 to 12 inches of AC over the subbase. The upper layer of the entire runway was a porous friction course (PFC) approximately 3 inches thick constructed in 1982. Beneath the AC layers approximately 6 feet of sand embankment makes up the bulk of the runway structural section. The runway shoulders vary in thickness from 1.5 to 3 inches. A pavement evaluation completed as part of the memo found no structural in adequacies with the runway pavement.

As part of the 1997 project, approximately 2.75 inches was cold‐planed to remove the PFC layer, and it was replaced it with the same thickness of new AC pavement. Shoulders were removed during this project and replaced with 2.75 inches of AC. Before the new lift of AC was placed, existing transverse cracks were repaired and overlaid with a non‐woven geotextile centered over the cracks to minimize reflection through the new surface.

FAA Compliance Inspection Reports

The FAA’s November 14‐18, 2011 compliance inspection report mentioned alligator cracking and severe raveling near the centerline of the runway producing FOD in the form of loose aggregate. Observations from the inspection noted:

“Longitudinal and alligator cracking exist for the entire length of the active runway. Although JNU crack sealant repairs have taken place numerous times over the past 8 years, the temporary repairs to extend the longevity of pavement have not resolved the problems. As such, the constant flow of water source into the crack pavement of the active runway with freeze‐thaw conditions has only increased the degeneration of the pavement. Recommend a total rehabilitation‐pavement project to ensure the safety of Part 139 carriers are not jeopardized for future aircraft operations.”

David Whato, FAA Airport Certification Safety Inspector, visited JNU on April 16 – 17, 2012 and made observations of the runway condition, some of which included:

The asphalt is not oily or tightly compacted as it should appear



A significant assault by urea, ice, snow removal operations, UV rays, freeze/thawing and air carrier aircraft operations has pushed this asphalt surface to the end of its useful life

The RW 8/26 asphalt appears oxidized, crumbling, and deteriorating at an accelerated rate.

The asphalt binder is drying out and the surface is becoming “brittle” and prone to cracking.

The seams where the asphalt sections joins have been separating and now create surface variations that could impair directional control of air carrier aircraft.

The seams will no longer hold crack sealant and have become a conduit for water to drain, eroding the based and subbase.

The crack sealant is peeling up with sand, debris, and aggregate attached and must be removed by maintenance crews on a daily basis to reduce the chances of ingestion by aircraft engines.

Airport maintenance personnel broom and vacuum the surface daily based on the rate of deterioration to minimize the engine ingestion risk to aircraft.

At some locations I was able to remove individual pieces of aggregate and crack sealant with my fingers!

Raveling is visible everywhere due to loss of binder and this rough texture cause’s additional wear on tires.

Maintenance crews at Juneau have exhausted their efforts to crack seal and maintain these seams.

Efforts to reseal these locations were not helpful since snow removal equipment was removing it as fast as they could get the cracks sealed, and the airport was sweeping the runway daily to remove FOD as a result of the deteriorating asphalt. Based on David Whato’s observations, a full runway rehabilitation project was recommended by the FAA to correct the deficiencies.

2012 DOT&PF Pavement Condition Index (PCI) Report for JNU

The DOT&PF Pavement Inspection Report from July 2012 assigns the runway a PCI (Pavement Condition Index) of 61.23, which indicates corrective maintenance is recommended. The target PCI range for runways is 70 to 100. A closer look at the results of the individual sections showed that the entire center third of the runway has a PCI ranging from 40 to 54, requiring rehabilitation. The outer sections had PCIs ranging from 60 to 69, requiring corrective maintenance.

The report mentioned high severity raveling and medium severity alligator cracking within the center section of the runway consistent with the FAA’s compliance inspection observations. Additionally high severity longitudinal/traverse cracking was observed throughout all sections of the runway. Low severity raveling in some locations was observed on the outer sections as well as low severity alligator cracking and longitudinal cracking.

USKH Pavement Inspection

USKH visited JNU and performed a visual pavement inspection of RW 8‐26 on August 27 ‐28, 2013. Pavement distresses were mapped by hand and severity of distresses noted.

As previously mentioned, the airport repaired many of the distresses causing FOD and aircraft safety concerns with a pair of patching projects in October 2012 and June 2013, which span a total width of 50 feet. A 2‐foot‐wide swath of existing pavement remains down the center of the runway so the patching operation did not affect the runway centerline lights. The patches seem to have taken care of the immediate problem of high severity raveling and alligator cracking causing FOD danger to aircraft operation, and are holding up well; although, this pavement has not lasted through a winter season where it will see extensive freeze‐thaw action and be subjected to snow and ice removal operations.



The most prevalent distresses on runway are low to medium severity longitudinal cracks that run the entire length of the runway. These cracks appear to be along construction joints where the runway was paved in 1997 and are spaced approximately 17 feet apart. The widest of these cracks have been routed to 1‐1/2 to 2 inches wide and filled with crack sealant, which currently appears to be holding. The narrow cracks are untreated.

A second series of sporadic (discontinuous) low severity longitudinal cracks exist in some locations between the construction joint cracks. Some of these were thought to possibly be the result of the reflection of construction joint in a lower layer of asphalt. But, the spacing is too close, and another cause is not apparent so cores were taken at several of these locations. The pending geotechnical report may provide more insight. These cracks have been repaired near both runway thresholds, but reduce in severity toward the midpoint of the runway and are generally unsealed.

Sealed Construction Joints and Reflection Cracks

An area of pavement settlement “sink hole” near Taxiway F on the south edge of the runway was identified by JNU staff to the inspectors . This patched area is reported to move up and down with the seasons and the airport has repaired it multiple times. The distress is likely due to a subgrade issue and will be investigated as part of the geotechnical investigation. Currently, the cracks that bound this distress have been routed and crack sealed.



“Sink Hole” Near Taxiway F

As identified by the DOT&PF pavement Inspection report, medium severity traverse cracks were observed sporadically along the runway. The cracks do not appear to form on a predictable frequency as is typical with transverse cracks, but directly coincide with the locations of transverse cracks The crack formation appears to start at both edges of the runway pavement and connect at the center. Some of the observed cracks span across the full width of the runway, less that portion of the runway repaired by the center patch; others do not fully span the runway. One interesting observation is a number of these cracks appear to coincide with centerline lighting cans. Most of the cracks have been routed and sealed.

The highest concentration of distresses was observed between taxiways D and B, increasing in severity with proximity to the intersection of Taxiway C. This is due to the large traffic volume of aircraft that utilizes Taxiway C to access the Part 135 apron and the JNU terminal. Distresses observed were low severity alligator cracking, low to medium severity longitudinal cracking, and low severity raveling.



Alligator cracking and raveling near Taxiway C.

The area of the temporary threshold for the current Phase II Runway Safety Area (RSA) improvement project has multiple “craters” created by 737 turnaround movements. These are formed by pilots locking one of the jet’s main gear to pivot the aircraft around, reducing their turning radius when aligning the jet with the runway for takeoff. Additionally the binder appears to be losing its ability to hold aggregate in the asphalt matrix, which is contributing to FOD. The surface appears pock marked near the thresholds where this phenomenon is especially occurring. This is also pronounced where temporary runway markings have been hydro blasted, causing aggregate to easily be removed from the matrix.

Geotechnical Investigation

Geotechnical engineers from PN&D took cores of the runway asphalt and boreholes at a number of the pavement distresses identified by USKH’s pavement inspection. The field work took place on the nights of September 16‐19, 2013. Four cores and four boreholes were taken through distresses identified by the pavement evaluation inspections. Cores were also taken through the suspected reflection cracking to determine if they are a product of previous paving lane construction joints. Boreholes were taken through possible alligator crack locations as well as one within the center patch where suspected alligator cracking had occurred, to determine if subgrade repair would need to be considered to correct these deficiencies. Additionally, a borehole was drilled at the sink hole as identified by the pavement inspection.

Materials testing as part of this investigation is currently ongoing and has not yet been completed.



RUNWAY REHABILITATION ALTERNATIVES

Although the high severity longitudinal cracks still remain on the runway, it appears the center patches have alleviated the immediate danger to aircraft safety. But the runway surface pavement is at the end of its useful life based on the observations of the binder performance and the severity of cracks being repaired and maintained by JNU.

Rehabilitation of the runway pavement can be accomplished by several means; the most severe alternative being complete pavement reconstruction. This would require the entire pavement section be removed and new base course and AC layers constructed. This alternative is not recommended for consideration because the runway pavement shows very little sign of structural failure. The few areas of questionable structural distresses can be corrected by localized repairs. The distresses that occur are the result of environmental and construction factors, not structural deficiencies; therefore, complete pavement replacement is unnecessary. It is also extremely expensive and would be very consuming requiring the centerline lighting be completely replaced, which would add additional cost and construction time requirements.

There are two pavement rehabilitation alternatives that are much more appropriate. Both alternatives are similar in that the upper layers of deteriorating AC will be removed and 5‐inches of new AC will be placed. The two alternatives vary in the thickness of pavement that will be removed.

Alternative A – Cold-plane 5 inches and Replace 5 inches of AC

This alternative will remove 5inches of existing runway asphalt by cold‐planing and repave with the same amount. This will remove almost the full pavement depth of the existing pavement to help minimize reflection of existing pavement distresses into the new runway surface. Additionally, the runway shoulders will be removed and replaced.

After the runway is cold‐planed, it will be paved with 5 inches of AC, returning the runway to the original grade and cross slope. This alternative will minimize the need for additional grading at taxiway intersections. Shoulders will be paved with 2 inches of AC to match current average thickness and cross slope, eliminating the need for runway edge lighting adjustments.

The depth of cold‐planing will extend below the edge of the centerline light cans and expose the system. This will require the existing lighting system to be replaced before the runway is repaved. However, it would allow re‐spacing the centerline lighting to meet FAA standards.

The cold‐plane operation will produce a large amount of recycled asphalt product (RAP) that can be reused around the airport for fill or temporary surfacing material, but it will not be available in the short term for this rehabilitation project. This RAP will be useful for future airport rehabilitation projects, but storage on airport property will need to be considered as the airport has no identified immediate use for the RAP.

Alternative B – Cold-plane 2.75 inches and Replace with 5-inches of AC

This preferred alternative will remove approximately 2.75 inches of the existing runway and replace it with 5 inches of AC. This alternative will take advantage of using a portion of the existing asphalt to increase the thickness of the new asphalt layer at no additional cost while contributing to the overall strength of the pavement layer. The additional thickness of AC will also reduce reflective cracking. As with the previous alternative, the full thickness of the paved shoulders will be removed and replaced with new AC. To aid in



drainage, the shoulders may be steepened. Shoulder grades per AC 150/5300‐13A can be increased to as steep as 5%.

The additional 2.25‐inch thickness will raise the runway elevation, which will require some minor paving/regrading at the taxiway intersections to the new runway. The new grades may also translate into additional safety area regrading to maintain RSA grades within required tolerances; these can be established with a portion of the RAP recovered from the cold‐planing operation.

Since the cold‐planing will not penetrate below the bottom of the runway centerline lighting can grade rings, the centerline lighting can remain in place, reducing overall project cost and construction time requirements. Additionally, the alternative will produce less RAP than Alternative A, requiring less airport real estate for storage.

ADDITIONAL CONSIDERATIONS

Current paving practices for airport runways will help extend the life of the new runway pavement. Modified performance grade asphalt binder will be used in the new AC to help resist degradation by environmental factors. Also cold joints will be cut back and coated with joint adhesive to extend the life of the construction joints. These two practices will help the runway achieve its expected 20‐year life before requiring rehabilitation.

appendix c pavement evaluation - juneau, · pdf filesubject: runway 8-26 pavement evaluation...

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