N141-012 TITLE: Method for the Detection of Voids Underneath Aluminum Matting - 2 (AM-2)

TECHNOLOGY AREAS: Materials/Processes, Sensors, Electronics

ACQUISITION PROGRAM: PMA 251

OBJECTIVE: Develop a non-invasive void detection method technology with the capability to detect voids underneath aluminum airfield matting (AM-2).

DESCRIPTION: The Expeditionary Airfield (EAF) is a shorebased, mobile air base, which permits deployment of landing force aircraft within effective range of ground forces. EAFs rely heavily on fully supported Aluminum Matting - 2 (AM-2) for safe and efficient operations. One significant concern is the formation and presence of voids underneath the AM-2 which introduce challenges and the potential for damaging effects to aircraft and crew. Filled with water or air, voids occur naturally when water flows through soil, pushing the soil down and out from under the airfield surface. This factor, combined with the impact of an aircraft landing on the AM-2 surface, can compromise the mat’s ability to support normal airfield operations. If the foundation of the AM-2 is not fully supported, the mat can become damaged, potentially resulting in damage to the aircraft, equipment, and personnel. The current void detection technology used in the fleet uses a vehicle that is driven across the mat. Any mat movement as a result of the vehicle's weight is then measured for deflection and if the deflection is significant enough, the mat is removed and the subgrade is reworked. This technique can sometimes spot a void just under the mat; however, if the void is few feet below the mat’s surface this method can be inadequate. The detection of voids underneath AM-2 is critical to the life of the mat, the aircraft and the safety of the warfighter.

In order for a void detection method of this nature to effectively detect voids underneath AM-2, the properties and specifications of AM-2 should be considered. These properties present a unique challenge in detecting sub-grade voids. Radar, ultrasound, and thermal imaging have been investigated unsuccessfully in the past. Ground penetrating radar was found to be inefficient due to its inability to penetrate AM-2’s metallic structure. The AM-2 cellular structure results in a lot of deflection and "noise", making it difficult for the inspector to read and interpret the data.

A non-invasive, user-friendly void detection sensor is needed. The solution should be non-invasive to minimize airfield downtime and non-destructive as it should not disturb the sub grade. The void detection sensor must identify and locate voids six inches or greater in diameter and down to three feet below final grade. EAFs can have airfield runway dimensions of 96 feet wide by 4,000 feet long and greater, justifying the need for a method that can cover large swaths of airfield quickly and easily; if not remotely, without increasing operator workload. AM-2 is used in a wide variety of operational conditions, ranging from arctic zones, temperate zones, tropical and subtropical zones, semi-arid and arid zones warranting the need for a method that can be easily and effectively transported and operated in a plethora of climatic conditions. The technology would not only aid in ensuring the safety of the Warfighter, equipment, and aircraft, but it would also increase ease-of-use and provide cost reduction opportunities, as well as commercial applications. The ability to detect voids underneath metallic matting would also enable preventive maintenance, allowing problems to be addressed before they escalate and result in costly, damaging effects.

Made of 6061-T6 aluminum, AM-2 is cellular in structure with integral aluminum ribs. AM-2 features 13 cells, a top skin thickness of approximately 0.14 inches and a bottom skin thickness of approximately 0.125 inches, and AM-2 comes in two different sizes with overall dimensions measuring two feet by six feet by 1.5 inches and two feet by 12 feet by 1.5 inches. In addition, AM-2 is painted green and the top skin is covered with an epoxy-based nonskid material; a void detection method should take into account these properties as they could potentially affect the method’s capabilities.

The AM-2 expanse can serve a variety of functions (e.g. airfield runways, taxiways, parking areas, and Vertical Takeoff and Landing (VTOL) pads), and are painted and marked differently, depending on intended function. Yellow paint, white paint and glass beads are just a few marking materials that a void detection method must be able to penetrate. In addition, the ideal method should also be able to penetrate rubber/tire buildup, Petroleum, Oils, and Lubricants (POLs), deicing chemicals, and hydraulic fluid, as these materials can be present on AM-2. All of these different materials must be understood by the sensor and its data must be displayed in a clear and concise manner.

PHASE I: Develop a conceptual design for a void detection method that meets the requirements above. Prove the feasibility of such a device through analysis and/or lab demonstrations.

PHASE II: Finalize, build and demonstrate a prototype with the capability to detect voids underneath AM-2. Provide estimates for production cost.

PHASE III: Build production units for transition for EAF use. Provide logistics, including operational and maintenance manuals.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: In addition to benefits provided to the DoD, the application of a method that could detect voids underneath aluminum airfield mat would be particularly beneficial to the construction industry and municipal public works. A device of this nature would provide the ability to detect soil erosion underneath buildings, roads, or runways. By determining the condition of the infrastructure early on, maintenance work and preventive measures can be taken to ensure the integrity of the infrastructure; thereby reducing replacement costs and failure of the infrastructure.

REFERENCES:
1. Pre-Engineered Structures: Short Airfield for Tactical Support. Retrieved from www.globalsecurity.org/military/library/policy/navy/nrtc/14251_ch11.pdf

2. Garcia, Lyan. Development of Lightweight Airfield Matting Systems. US Army Corps of Engineers. Retrieved from http://www.usace-isc.org/presentation/Civil%20Engineering/Development%20of%20Lightweight%20Airfield%20Matting%20Systems_Garcia_Lyan.pdf

KEYWORDS: Expeditionary Airfield (Eaf); Mat; Void Detection; Void; method; AM-2

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