Today it is possible to bond any material, including concrete itself, firmly and permanently to a hardened concrete surface. Such bonding, using epoxy based "glues", becomes as strong, and frequently stronger, than can be achieved by any mechanical means of connection. These glues or bonding agents are made up of two liquids- a base resin and a curing agent (or hardener) which are mixed immediately prior to use.
Three factors will influence the end properties of a bonded joint: (1) correct choice of resin grade and hardener; (2) proper surface preparation; and (3) careful application. The epoxy based compounds will have high strength at a very early age and extreme chemical resistance, which measure that a bonded joint will remain unaffected by environmental contamination. The strength of a bonding joint if made properly will always far exceed that of even the best quality concrete. The flexural strength of concrete, for example, will lie in the 600 to 800 psi range; a typical cured resin, on the other hand, will show a cross-breaking strength around 5,800 psi, which means that any breakage will occur through the surrounding concrete rather than through the joint. It also means, however, that a contractor should not expect too much from a bonding agent-remember that if a resin with a tensile strength of 2,000 psi is used to join two concrete slabs each having a tensile strength of 300 psi, the effective strength of the bonded until is still only 300 psi. When dealing with epoxy bonding, however, keep in mind that is advantageous to consult the manufacturer's technical representatives before beginning a job.