6.8-Installation of compression seals
Compression seals require a uniform joint width along the whole length with straight, smooth, spall-free, properly cleaned joint faces to permit proper installation and to provide uniform contact. It is advantageous to remove sharp rises at the joint edge or to form or saw the joint with a slight rounded or V-edge.
A neoprene-based or other lubricant (which may have adhesive properties for most applications) is applied in a bead to the upper edge of each joint face to facilitate installation of the seal. The lubricant is fluid at normal temperatures and is usually applied by a hand-pressure applicator. Where machine installation of the sealant is used for pavement joints, this unit may also be designed to apply the lubricant, which then generally should be a thixotropic formulation. The lubricant must be applied immediately ahead of inserting the seal so that it does not prematurely dry out. For installation either by hand roller or with the machine, the seal is positioned vertically over the joint opening and then, by pressing down and forward, it is forced into the opening. The seal must not be twisted, folded over on itself or stretched during this operation. A small permissibly amount of stretching, up to 5 percent, may occur as the seal is forced in. The seal must not be willfully stretched (thus reducing its cross section) to make installation easier and the seal length go further. Near zero stretch can be achieved with both hand and automatic machine installation which may be desirable since the seal will not be under tension along its length nor reduced in effective width. It is important to install the seal at the specified depth. In highway pavements, this is usually slightly below the surface to keep it out of contact with traffic. The seal should be installed in as long a continuous piece as possible. If field splices cannot be avoided they should be made in the least critical location as far as maintaining a sealed joint is concerned. Usually the seal is spliced simply by butting it against the next length with some lubricant adhesive. However, more sophisticated means are available and may be warranted where it is important that a splice should not part. Where a compression seal is to be installed between precast units, it may be attached to the face of one and compressed as the adjacent unit is positioned.
The polybutylene impregnated foam type of compression seal is pre-compressed and inserted in the joint opening. To achieve a good bond, the joint faces may first require priming with an epoxy adhesive. Other cellular foams such as ethylene vinyl acetate are installed in a similar fashion.
Why Sealing is Needed
1.4 The introduction of joints creates openings which must usually be sealed in order to prevent passage of gases, liquids or other unwanted substances into or through the openings.
In buildings, to protect the occupants and the contents, it is important to prevent intrusion of wind and rain. In tanks, most canals, pipes and dams, joints must be sealed to prevent the contents from being lost.
Moreover, in most structures exposed to the weather the concrete itself must be protected against the possibility of damage from freezing and thawing, wetting and drying, leaching or erosion caused by any concentrated or excessive influx of water at joints. Foreign solid matter, including ice, must be prevented from collecting in open joints; otherwise, the joints cannot close freely later. Should this happen, high stresses may be generated and damage to the concrete may occur. In industrial floors the concrete at the edges of joints often
needs the protection of a filler or sealant between armored faces capable of preventing damage from impact of concentrated loads such as steel-wheeled traffic. In recent years, concern over the spread of flames, smoke and toxic fumes has made the fire resistance of joint sealing systems a consideration, especially in high-rise buildings.
The specific function of sealants is to prevent the intrusion of liquids (sometimes under pressure), solids or gases, and to protect the concrete against damage. In certain applications secondary functions are to improve thermal and acoustical installations, damp vibrations or prevent unwanted matter from collecting in crevices. Sealants must often perform their prime function, while subject to repeated contractions and expansions as the joint opens and closes and while exposed to heat, cold, moisture, sunlight, and sometimes, aggressive chemicals. As discussed in Chapters 2, 3 and 6, these conditions impose special requirements on the properties of the materials and the method of installation.