Bond strength to concrete of Galvanized reinforcing bars

 

The results of extensive programs of pull-out testing by a number of researchers reveal no significant difference in the bond strengths of black and galvanized steel deformed (ie, ribbed) reinforcing bars in concrete.

The tests also indicate no significant difference in the bond strengths of black and galvanized plain bars in concrete.

 

Bond strengths of galvanized unpassivated steel bars and black steel bars to concrete*

 

Bond strengths of galvanized plain bars at various levels of chromate additions to concrete*

 

Passivation and additives

The research into bond strengths also shows that there is little or no need for the current practice of chromate passivation of galvanized reinforcement by the galvanizer (other than to minimise the possibility of wet storage staining), or the alternative addition of chromium trioxide to the concrete mix. While the addition of chromates to the concrete mix in the ratio of 35-150 ppm by weight of cement increases the bond strength of galvanized plain bars significantly, there is no measurable improvement in the bond strength of galvanized deformed bars, as the mechanical interlock effect provides almost all of the bond.