Which characteristic affects the bond strength in concrete structures?

The surface roughness of the rebar is a crucial characteristic that significantly affects the bond strength in concrete structures. This is because the rougher the surface of the rebar, the more mechanical interlock can occur between the concrete and the rebar. A rough surface enhances the friction between the rebar and the surrounding concrete, leading to improved adhesion and ultimately stronger structural integrity.

When concrete cures around the rebar, this interlocking helps to effectively transfer loads between the concrete and the reinforcement. If the surface of the rebar is smooth, the bond strength will be reduced, which can lead to issues such as slippage under load or even structural failure over time.

The other characteristics listed, while they may have some influence on various aspects of concrete and rebar performance, do not play the same fundamental role in bond strength. For example, the brand of rebar generally refers to manufacturing quality rather than specific bond attributes, and the length of rebar is more related to how it is employed within a structure rather than its direct bonding characteristics. The color of concrete is mostly related to aesthetics and does not affect the bond strength between concrete and rebar.