Evaluating the shear bond strength between old and new concrete through a new test method

The interface between new concrete (overlay) and old concrete (substrate) plays an important role in the overall success of any repair. A good bond ensures long-term durability and monolithic action (i.e. the overlay contributes to both the stiffness and load-carrying capacity). Research has shown that the substrate roughness, which is highly dependent on the surface preparation method, has an influence on the interface bond strength, though there is no consensus on the extent of this effect. Thus, through a new bond test, an experimental study was conducted to evaluate the effect of substrate roughness on bond strength, also considering the effect of overlay strength. In addition, the possible consequence of roughness on interface ductility was evaluated. The results indicate an increase in bond strength with an increase in surface roughness, although the resulting increase in ductility with surface roughness was more pronounced. The strength of the overlay was also found to be an important parameter for smooth substrates or substrates with low roughness.