Q.: In new construction should we remove the rust from rebars to be sure we get good bond to the concrete?

A.: Laboratory tests have shown that a small amount of rust actually improves the bond because it increases the normal roughness of the surface. According to the Concrete Reinforcing Steel Institute (see their book Placing Reinforcing Bars), bars with rust are considered acceptable without cleaning or brushing, provided that the minimum dimensions, including height of deformations, and weight of a cleaned sample are within ASTM specification limits.