A review of foint sealant standards and specifications for aircraft pavements

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

Given the importance of joint sealants for the purposes described above, it is essential that the most cost-effective material and sealing program possible be identified and implemented. One part of a cost-effective and successful joint sealing program is the selection of the most appropriate sealant material based on a value for money analysis.

MATERIALS FOR PAVEMENT JOINT SEALANTS

In the past, many different joint sealing materials have been used. In the early days of rigid pavement construction, bitumen and rubber products were used which were more joint fillers (fill without creating a seal) rather than sealants. Nowadays, most sealants are high performing, cold-applied, elastomeric polymers supplied by a number of manufacturers. There are three common types: polysulfides, polyurethanes, and silicones.

Polysulfides

These were the first real high-performance sealants developed with the ability to maintain their integrity for up to 20 years and to withstand joint movements of up to 25% (Panek and Cook, 1991). These sealants can be made resistant to fuel and other chemicals, but will deteriorate under excessive UV exposure. Their main failure mode is a combination of adhesion and cohesion loss, and they have been found to perform better in tension than in compression due to low recovery (Panek and Cook, 1991). They are also known to exhibit a decrease in performance at elevated temperatures and to have a poor resistance to abrasion (Sealant, Waterproofing and Restoration Institute, 1995). This family of polymers gives off a pungent and foul sulfurous odour during curing and installation.

Polyurethanes

This form of cold-poured elastomer is similar to the polysulfides, but exhibits better resilience in cyclic compression tests (Klosowski, 1989), as well as excellent adhesion to a variety of substrates including concrete (Sealant, Waterproofing and Restoration Institute, 1995). These materials are also able to withstand joint movements of up to 25%, but this can be reduced at higher temperatures as the modulus of elasticity changes significantly with temperature (Klosowski, 1989). Urethanes are also known to stiffen with age. While this is true of all chemically cured sealants, it is considered to be more pronounced with the polyurethanes (Klosowski, 1989). These products exhibit a decrease in performance at elevated temperatures and there is known to be a significant difference in performance between brands (Sealant, Waterproofing and Restoration Institute, 1995).

Silicones

The silicone sealants are considered the ultimate of all sealants (Sealant, Waterproofing and Restoration Institute, 1995). They show good characteristics with regard to aging, weathering, durability and intrusion resistance, and they can withstand joint movement up to 50% of joint width. Their properties change very little with changes in temperature (Klosowski, 1989). The drawback with these sealants is threefold. First, they are sometimes difficult to apply and suppliers usually specify careful joint preparation, with only a few companies endorsed by the silicone suppliers to install the sealant. These strict installation requirements make the silicone range of sealants relatively expensive. The second major drawback with silicone sealants is that they are not able to adhere to bitumen products so a bitumen-concrete joint cannot be sealed with them. Finally, once a silicone is installed, no polyurethane or polysulfide product can ever be used in that joint. This limits the choice of replacement sealants. Silicones are also known to absorb petroleum products such as aviation fuel (Spells, 1987). Although not necessarily detrimental to performance, this characteristic may cause silicones to be considered unacceptable under some standards.