Understanding waterstops

May 8, 2023

Thermoplastic and rubber extrusions
To accommodate varying hydrostatic pressure and movement, most thermoplastic and rubber waterstops come in different extruded profiles, widths, and thicknesses. For years, the most widely used waterstops were those anchored by having a dumbbell shape at each end, which provided a ‘cork-in-the-bottle’ seal when the joint opens. However, American Concrete Institute (ACI) 504R, Guide to Joint Sealants for Concrete Structures, reports this seal is ineffective at small joint movements, and at wider movements the waterstop
is placed in considerable tension. To overcome these issues, waterstop manufacturers developed profiles with multiple raised ribs to provide improved anchoring and sealing performance.

Both ribbed and dumbbell waterstops are available with flat-web or bulbed centers. They typically are available in 15.2-m (50-ft) rolls, in widths of 102 to 305 mm (4 to 12 in.) and thicknesses of 5 to 13 mm (3/16 to ½ in.). Flat-web waterstops are recommended for use in construction and contraction joints where little or no movement is expected. Since the center bulb flexes to accommodate both shear and transverse movements, these waterstops can be used in expansion, contraction, or construction joints. The center bulbs come in various sizes to accommodate differing amounts of joint movement, with larger-diameter center bulbs suitable for greater joint movements.

Some ribbed waterstops have a center bulb with
a thin tear-web on one side that ruptures upon joint expansion. With the tear-web broken, the center bulb can open up to the extended width of the joint without stressing the embedded ribbed sections. The tear-web keeps concrete out of the center bulb during concrete placement. Manufacturers recommend using tear-web waterstops where large movement is expected. They should be installed so the tear-web side faces the direction of positive pressure.

While rubber thermoset waterstops have excellent mechanical properties (i.e. high tensile strength and good elongation), they are difficult to field-fabricate as the rubber is vulcanized, meaning it has already taken a ‘set’ (i.e. thermoset) and cannot be heat-welded together like thermoplastic materials.

Read more: Understanding waterstops





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