EK35^® Case Study

Case Study

Fines Preservation That Ecologically Manages Gravel Runway

Gravel Runway Fines Preservation for Ecological Management
The Alaska DOT and PF has nearly 300 remote gravel runway operations for commercial, charter and private air traffic. One of the DOTs’ needs in operating these runways is to minimize the gradual loss of vital fines. These fines are one of the sources of fugitive dust that impacts the health of neighboring populations (e.g., U.S. EPA PM10 and PM2.5 requirements) and aircraft operations.  Any approach taken in gravel runway fines preservation must minimize the environmental impact on the local ecology and leave aircraft surfaces undamaged. This must be accomplished with local gravel sources, local construction equipment, minimum manpower and severe winter weather.

Loose gravel, due to the effects of weather and aircraft loading, costs air carriers tens of thousands of dollars annually in engine and airframe damage. An additional objective for the DOTs is the development of gravel runway fines preservation methods that holds the gravel in place for consecutive years with minimal maintenance requirements.

Solutions for Gravel Runway Operations
Midwest has assisted the AKDOT and PF in developing gravel runway fines preservation methods for gravel runway rehabilitation and maintenance per DOT dust reduction, environmental and chemical requirements. These methods have been provided through local contractors who are trained by Midwest, experienced in the methodology and intimately supported by Midwest.

The gravel runway operation and rehabilitation methods have been documented and successfully used over a 5-year period on gravel runways in both Alaska and Canada (e.g. the Northwest Territories and Quebec). These methods use Midwest’s EK35®, a fluid-binder system, which is applied to the gravel to primarily bind the surface together and secondarily increase the bearing capacity (CBR).  EK35 is typically applied at a rate of one gallon for every 40 square feet (1/40). The improved strength is sustained for one to more than three years without maintenance through the binding effects of the fluid on the gravel surface.  Consequently, fines are preserved, the gravel stays in place and dust is controlled to minimal levels.

Maintenance, when it does occur, has involved the reapplication of EK35 at a typical rate of one gallon for every 120 square feet (1/120).  Preventative maintenance can be performed at the same one to three-plus year interval, depending on the type of gravel and the state of runway bearing capacity.  EK35 has been applied to 19 gravel runways operated by the AKDOT and PF since 2001.

Example of Effective Gravel Runway Fines Preservation
A good example of what is possible is illustrated by the EK35 application to the runway at Tanana, AK in the AKDOT and PF’s Northern Region during 2007 and 2008. The runway is 4,400 ft. long by 150 ft. wide, with the center 90 ft. (between landing lights) being used for air traffic. The runway is constructed of silty, sandy gravel. In 2007, the runway received a 1/40 EK35 topical application over its center 90 ft. In mid-2008, the runway received a 1/120 EK35 reapplication over its center 50 ft. when surface conditions were observed to be changing, but not significantly enough to affect dust levels or aircraft operations.

During the last few years, EK35 has been independently certified to reduce PM10 dust emissions by greater than 85% and PM2.5 emissions by 60% after a one year period after application and without maintenance. EK35 was also independently certified to be non-injurious to aircraft surfaces when used as a stabilizing agent and dust suppressant by the Boeing Company per their specification D6-17487, “Evaluation of Aircraft Maintenance Materials.“ In addition, EK35 was independently demonstrated to have negligible environmental impact in regard to meeting US EPA guidelines for bulk constituents, polynuclear aromatic hydrocarbons, TCLP regulatory levels for metals, volatiles, semi-volatiles, pesticides and herbicides and aquatic toxicity.

The AKDOT and PF and pilots using the runway deemed the gravel runway fines preservation performance in the time since the initial EK35 application to be excellent. This included dust reduction, FOD and environmental performance.  As an added value, the EK35 applications sustained sufficient structural integrity of runway surfaces to serve the aircraft using the runway, thereby assuring passenger and aircraft safety.

The entire width of the runway that is open to air traffic has sustained an average surface CBR of ~ 23 in the year since the original EK35 application. This exceeds the minimum surface CBR of 20 recommended by Hawker – Beech for the safe operation of its Model 1900 aircraft, a typical user of the Tanana runway and many other AKDOT and PF runways. With time, EK35 continues to be slowly absorbed into expansive soils and penetrate deeper into the runway surface. The effects of local weather do not promote the loss of EK35 from the gravel.  Consequently, scheduled reapplication of EK35 is needed to sustain gravel runway fines preservation and structural integrity at as-built levels. The recent reapplication of EK35 to the center of the runway surface increased the surface CBR to an average of ~ 52, enough to sustain performance for at least another year.  This is in contrast to the average surface CBR of ~ 15 for the portion of the runway that received no EK35. In the case of runways with sandy gravel, EK35 reapplication has not been necessary for more than 3 years (e.g., Chicken, AK). Figure 2 shows that the EK35 applications improved the structural uniformity of the runway surface which should also improve the surface’s capability to sustain efficient distribution for stress from air traffic. These CBR values are based on a comprehensive sampling of ~ 12,000 ft2 of the touchdown area using surface stiffness measurements per ASTM D5768 as an index of CBR.

The EK35 applications at Tanana appear sufficient to meet AKDOT and PF dust, environmental and chemical requirements while also providing the surface structural integrity to safely support gravel runway operations.

Questions for the ADOT and PF M and O can be posed to Clark Milne, Maintenance Engineer, Northern Region, Alaska DOT and PF 907-451-5285, clark.milne@alaska.gov.

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