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Connections between precast concrete units can be formed using adhesives (such as epoxies) rather than cement-based mortars. The adhesives are significantly stronger that the surface layer of the concrete, which must be suitably prepared to remove loose material such as laitance. Adhesive joints should be designed so that they act primarily in shear or compression. The major advantage of adhesives is their rapid gain in strength. Suitably formulated epoxy adhesives gain their full strength in a matter of hours while cementitious materials will take several days or weeks.
The main use of adhesives in concrete bridges is in glued segmental construction. However, the epoxy mortar placed between the match-cast units is primarily to seal the joint and to provide a uniform bearing area. Adhesives have been used in a number of building applications to form the connections between precast units. For the roof of the Sydney Opera House adhesives were chosen in preference to conventional mortar because of the very thin, watertight bond lines that could be obtained and the improved rate of erection because of the rapid gain in strength. It was estimated that about 6 months of construction time was saved in all.
Adhesives are also very suitable for connecting concrete units to other materials, for example for attaching fixing brackets to precast concrete cladding panels.
Other references:Institution of Structural Engineers, ´Guide to the structural use of adhesives´, 1999.