Introduction

This specification has been prepared by WRc plc under the direction of the Sewers and Water Mains Committee in consultation with manufacturers, BRE, CIRIA and Water Industry.

The performance of sealants and changes after Iong term immersion in aqueous media have been investigated in detail to support the development of this specification (see refs. CIRIA/WRc reports). This foundation work was funded by the UK Water Industry, Department of the Environment and manufacturers. When sealants are exposed to aqueous media in the service environment a number of distinct phenomena may occur which can influence their performance, and may contribute to the failure of the sealant to perform the intended functions. The primary effects concerned are first, the absorption of water by the sealant, which may cause softening depending upon the chemical nature of the sealant, its cure mechanism and state of cure at the time it is first exposed to moisture. Secondly, the diffusion of liquid water to the sealant/primer/substrate interfaces may impair the adhesive bond of the sealant to the joint surfaces. The laboratory evaluation of these effects in this specification is based upon tensile testing in which the modulus and the extensibility of sealant test joints after varying durations of immersion in aqueous media are used as indices of performance. A system of performance evaluation based upon changes in these indices with immersion is defined. The requirements of this specification therefore address the need particularly for sealant materials to achieve their fully cured properties quickly and to maintain both their physical bulk and failure properties within specified limits after immersion.

This document specifies the primary performance and durability requirements for joint sealants for Water Industry use including tests for effect on water quality and the water resistance requirements for appropriate conditions of long term service. Appendix A defines the method of test for resistance to aqueous media and Appendix B defines a method for determining the acceptability of changes to sealants after this test providing a visual method of assessment.  Appendix A is equally relevant to joint sealants used in concrete structures retaining water as well as other aqueous media. Application of the test method is also relevant to joint sealants used in less arduous conditions such as overflow structures and structures exposed to the weather with appropriate amendment to the duration and conditions of immersion. As a guide, a test period of 12 months is specified to assess long term resistance to aqueous media.

The method of test for resistance to aqueous media included in this specification is relevant to sealants applied in a paste-like consistency to concrete surfaces using recommended primers. These sealants sub­sequently cure to generate elastomeric working properties under specified cure conditions.

Caveats

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