There are various forces that can act alone or together to force water through concrete. These are hydrostatic pressure, capillary action, wind driven rain, a difference in a vapour pressure between the two sides of the concrete or some combination of these. Water finds its way most readily through porous concretes, cracks, structural defects, or through joints that have not been properly designed, built or sealed. Sealants are flexible or rigid materials used to seal various joints and gaps in concrete and elsewhere to prevent the ingress of moisture into structure.
In this capacity they perform three functions:
(a) Accommodate joint movement
(b) Prevent the infiltration of the joint and
(c) Prevent the ingress of water into the structure
Selection of a suitable sealant depends upon the movement, width, and depth of the joint. Selection of sealants should follow a three step
(a) First the anticipated joint movement is determined
(b) Then the most appropriate sealant is selected to meet expected joint moment and other service requirements.
(c) Finally the depth of the sealant and the type of back up material in the joint are specified.
The class of sealant is selected either by considering the type of joint in which it will be placed or the type of substrate. Once the minimum sealant class has been determined, matching of sealant substrates and geometry begins. In most joints, any sealant of the recommended class will probably be acceptable. Final product selection requires careful examination of product literature for information on recommended geometry and nature of primers that may be required for various substrates. Joint depth affects the stress in a sealant. The base of the sealant bed should be free to move. Therefore a bond breaker must be used to ensure that the sealant does not bond to the base. Of the many joint back up materials available, only closed cell, foamed, polyethylene rod can be used safely with all types of sealants
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