Finding the right match for stadium joints

Neil Roberts, Product Manager at ARBO^®, discusses the specification considerations for sealing concrete joints in stadiums.

The specification requirements for sealants used for concrete joints vary depending on the structure and use of the building in question. For stadiums, which are increasingly complex buildings, the demands of choosing a sealant build-up that will meet the requirements of both the structure and occupants for an extended service life are similarly complex.

Manufacturers of specialist joint sealing and adhesive products are well-placed to offer guidance to specifiers and building designers. However, the reverse is also true, concerning guidance on the planned use, surroundings and environment into which sealant products will be applied in order to offer effective advice.

Considering context

Most of the joints requiring sealants in a stadium are situated in terraced areas where there will be regular footfall as people walk to and from their seats. Many stadiums will also host non-sports events, which means that specifiers also need to consider a wider demographic… and their footwear. While high heels may not be match-day attire, this type of point load could affect the integrity of the seal during music events.

It is not only what’s happening on the structure that makes the correct choice of sealant for the concrete joint important, but the type of accommodation below the stadium auditorium is also a potential risk factor. Stadiums are not just a place to go to support a team or be entertained, they are also businesses with staff based in offices that are often located below the terraces. Toilet facilities and refreshment stands may also be located here and there is an increasing move towards attracting additional facilities, such as primary care hubs and co-working spaces into stadium buildings to make the most of the building for the local community and bring in rental revenue.

The waterproofing performance of the sealant is vital for protecting both the accommodation and the occupiers below from water ingress throughout the structure’s service life. To prevent leaks, the joints need to be sealed with a material that will provide an effective barrier to water ingress, despite the wear and tear of footfall and natural movement of the structure, which will be exacerbated by the loading and circulation of large crowd volumes.

Perhaps even more vital is protection from fire. The open layout of a stadium can mean a lack of compartmentation, potentially allowing a rapid spread of fire. Where fire seal integrity is required, joints can be designed to incorporate a fire-resisting sealant to prevent the passage of fire to the terrace from below, or passing from the terraces to the accommodation below. Where fire seals are required, specification must focus on selecting a product that delivers an appropriate level of fire integrity and an effective seal against water penetration.

Working with the concrete structure

Specification of the joint sealant should always strongly consider the calculations for anticipated structural movement provided by the engineer; selecting a sealant with an appropriate movement accommodation factor.

 The amount of flex the sealant needs to provide to cope with movement is dependent on a range of factors. The concrete structure is subject to movement due to thermal changes and dynamic loading, for example, so any variable that could affect movement needs to be considered.

The size and capacity of the stadium are key, and with a number of supersized stadiums now being planned or progressed, the technical demands on sealants are greater than ever.

Ensuring performance

It is essential to ensure the correct installation processes are followed to achieve the required performance and service life.

The concrete must be fully cured, and the surface must be dry when the seal is formed to ensure high levels of adhesion. While the application temperature range for most sealants is as broad as 5–50°C, low temperatures can present a risk of moisture and with a porous substrate such as concrete, it is not as simple as wiping the surface dry. Residual moisture may still be present and could compromise the integrity of the sealant joint.

Assuming site preparation is meticulous, the performance of the sealant depends heavily on balancing the need for toughness with flexibility and fire safety properties. A sealant that can withstand the level of point loading and abrasion required for a stadium terrace is usually tougher but less flexible than a fire-resistant sealant, so a ‘dual seal’ approach is often recommended. In this way, if the anticipated movement compromises the robust sealant beyond the limits of its flexibility, the fire protection of the more flexible fire-resistant layer remains intact.

An optimised build-up can comprise primer, a joint backer of appropriately sized closed-cell, cross-linked polyethylene foam, and a dual seal, such as a lower fire seal and a tougher upper seal more capable of withstanding abrasion and traffic etc. Clearly, sufficient depth is required in the terrace structure to accommodate a dual seal joint system; and this needs to be considered at the design stage.

Once installed, the seal should be inspected every six months, so that remedial action can be taken should there be any physical damage to the seal due to vandalism, improper use of cleaning chemicals or other causes. It is important to note that the sealant is there to create a flexible joint between structural concrete elements and not to reinforce/protect the edge of the concrete or contribute structurally.

Small spec, large significance

The sealant system used in concrete joints in a stadium may cost less than 1% of the construction, but it punches way above its weight in terms of significance. And, if the joint should fail, remediation can be onerous and expensive, so a right-first-time approach is best.

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