A review of foint sealant standards and specifications for aircraft pavements

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

Australian Standards

The Australian Standards index was reviewed and no standard was found to refer to the testing of concrete pavement joints, joint sealant materials or sealants and adhesives in general. Some standards discussed the test methods for bituminous products, others dealt with specific adhesives such as those for the construction of automobiles. It was determined that there were no national standards or specifications detailing requirements for sealants in Australia, or standard tests for assessing the performance of such materials. Other organisations such as the Roads and Traffic Authority were found to specify proprietary products or material types (i.e. silicones) for use as sealant materials rather than specifying performance. It is thought that this approach to material selection is adopted where the cost of testing materials to ensure compliance with the performance requirements is excessive when compared with more frequent replacement of possibly inferior materials. When coupled with the lack of an endorsed specification for measuring performance, it is little wonder that industry does not attempt to specify sealant performance.

British Standards

A search of the British Standards Institution (BSI) index revealed that there were some standards relating to joint sealants for highways and airfields. One document specifically dealt with one-part gun-- grade silicone sealants but was marked 'obsolete'. Standard BS 5212, titled 'Cold applied joint sealant systems for concrete pavements', was specifically noted as being applicable to concrete aircraft pavements as well as highways (BSI, 1990). It has three parts, part 1 is a specification for the performance of cold-applied sealant materials and part 3 is a collection of test procedures required for performance assessment under part 1. Part 2 is a technical code of practice for the installation of such joint sealants. In order for a sealant material to be deemed adequate for use in concrete pavement joints, the following criteria must be met under parts 1 and 3 of this standard:

Rheological properties: Materials are required to be able to resist flow along an open inclined channel and sag in a horizontal channel. This property is not considered important for the long-term performance of a sealant material.

Penetration and recovery: In order to determine intrusion resistance, penetration with a domed penetrometer and recovery after penetration is measured. The initial penetration must not exceed 2 mm, and a minimum of 75% recovery must be achieved between the initial recovery and when the penetrometer is removed. This method of determining intrusion resistance does not closely simulate a sharp object being pushed into the sealant by a passing aircraft or vehicle wheel.

Forces and adhesion and cohesion in tension and compression: Three cycles of extension at 15 deg C and compression at -20 deg C are performed on a sealant sample cast between two mortar blocks. This process is intended to simulate the opening and closing of joints caused by the thermal expansion and contraction of pavement segments. The criterion for passing this test is a combination of a minimum area of sample showing adhesion and cohesion failure and a range of maximum compressive and tensile forces in the sample during extension and compression. This test prescribes a set extension (100%) and compression (50%) of the sample width, which cannot easily be modified for lower performance requirements (most non-silicone products are advertised as having a 12.5% or 25% joint movement capability). This minimum and maximum force requirement is thought to measure the degree of tensile stress on the sealant during joint opening, and thus to determine the likelihood of the sealant failing in adhesion or cohesion. Depending on the sealant material's tensile strength, any given force exerted during a cyclic load may or may not cause damage or complete failure. Thus, the requirement for minimum and maximum forces during extension seems inconclusive, as a sealant's tensile strength and the substrate-sealant bond strength, as well as the forces induced for a given extension of the joint, will determine the performance of the sealant material during compression-tension cycles.