Question
Does occurrence of rust have adverse collision to bond performance of bar reinforcement?

Answer
In fact, presence of rust in bars cannot have adverse impact to the bond performance and it depends on sorts of bar reinforcement in consideration.

In plain round bars, rust on bars improves bond presentation by formation of rough surfaces which enhances friction amid steel and concrete.

But, for deformed bars, same theory cannot concern. Presence of rust impairs bond strength since corrosion occurs at raised ribs and subsequently fills space between ribs, therefore evening out unique deformed shape. In essence, bond between concrete and deformed bars originates from mechanical lock among raised ribs and concrete. On contrary, bond between concrete and plain round bars obtains from adhesion and boundary friction. With such distinction in mechanism in bonding, behaviour of bond between deformed bars and plain round bars in occurrence of rust varies.