A review of foint sealant standards and specifications for aircraft pavements

Road & Transport Research, Jun 2000 by White, G, Allman, M

MATERIAL PERFORMANCE REQUIREMENTS

The following requirements are considered to be an adequate set of performance characteristics for an aircraft pavement joint sealant material under Australian conditions:

Resistance to intrusions: A sealant's ability to resist a small, and possibly sharp, object being pushed into it by the force of a passing aircraft or maintenance vehicle wheel is essential. This can be measured by placing a small steel or aluminium piece on a cured sealant bead and dropping a weight onto the 'intrusion' to simulate a traversing aircraft wheel.

Performance after heat aging: Given the heat exposure that a joint sealant 'in a pavement undergoes, it is important that the material chosen is able to resist a reduction in performance resulting from heat aging. To assess this resistance, weight loss caused by heat aging is assessed, as weight loss relates directly to elasticity and, therefore, to sealant performance (Panek and Cook, 1991). A sample of sealant is baked in a 70 deg C oven for 14 days and its weigh loss over that period calculated.

Adhesion and cohesion: The ability of a sealant material to be able to adhere to the substrate and remain cohesive is essential. The Hockman cycle, as specified in ASTM C 920, which includes the casting of a sealant sample between two concrete blocks and repeatedly extending and compressing the sample over 20 hours and at various temperatures, adequately assesses the adhesive and cohesive performance of sealant materials. Consideration should be given to the requirement for a -26 deg C extension cycle as this very low temperature is not considered appropriate for Australian conditions.

Weatherability: It is essential that a pavement sealant material be stable under conditions of high moisture and exposure to UV radiation. Sealants should be able to withstand the Hockman cycle after one year of artificial or natural weathering, including exposure to UV and moisture, to be considered to adequately resist weathering.

Fuel resistance: Sealants used in aircraft refueling and parking areas are frequently exposed to aviation fuel and other cleaning solvents. The ability of a sealant material to maintain its performance characteristics after exposure to fuel is important for any aircraft pavement sealant. To be considered acceptably fuel resistant, a sealant should be able to pass the Hockman cycle after repeated exposure to aviation fuel.

Flame resistance: Because of exposure to flame sources such as jet blast, the sealant material's ability to resist flame is important. The exposure of a sealant to a 260 deg C flame for 2 minutes (as detailed in BS 5212:1990) and a visual inspection for flow, ignition, cracking, hardening, flaking and other effects is considered an appropriate assessment of the material's flame resistance.

MATERIAL DATA SHEETS

Product data sheets supplied by manufacturers and distributors to potential purchasers, display little (and non-uniform) performance information. A typical data sheet generally includes the following information relevant to material performance: