Which surface conditions may hinder the bonding of reinforcing bars to concrete?

The bonding of reinforcing bars to concrete is critically important for ensuring the structural integrity and performance of reinforced concrete elements. The presence of contaminants on the surface of reinforcing bars can significantly hinder proper bonding.

When reinforcing bars are coated with substances like mill scale, rust, oil, and mud, these materials create a barrier between the concrete and the steel, preventing the two from making effective contact. Mill scale, which is a flaky surface that forms on hot-rolled steel, can inhibit the bond, as can rust, which alters the surface texture and can introduce unevenness. Oils and mud also create a layer that disrupts the adhesion process of concrete to the steel. All these contaminants lead to a compromised bond, potentially affecting the load-bearing capacity of the structure.

In contrast, options presenting smooth and clean surfaces are more conducive to good bonding, as they provide a suitable texture for the concrete to grip the reinforcing bars. Similarly, conditions of high humidity and moderate temperatures, or excessive moisture and cold temperatures, may affect concrete curing or placement but do not directly interfere with the essential bond that needs to be established with the reinforcing bars.