The term bond refers to the adhesion between concrete and steel which resist the slipping of steel bar from the concrete. It is this bond which is responsible for transfer to stresses from steel to concrete and thereby providing composite action of steel and concrete in R.C.C. The bond develops due to setting of concrete on drying which results in gripping of the steel bars.
The bond resistance in reinforced concrete is obtained by following mechanisms:
- Chemical adhesion: It is due to gum like property of the substances, formed after setting of concrete.
- Frictional resistance: It is due to friction between steel and concrete.
- Gripping action: It is due to gripping of steel by the concrete on drying.
- Mechanical Interlock: It is provided by the corrugations or ribs present on the surface of the deformed bars.
The bond is assumed to be perfect in the design of reinforced concrete the bond between steel and concrete can be increased by the following methods:
- Using deformed or twisted bar.
- Using rich mix of concrete.
- Adequate compaction and curing of concrete for proper setting.
- Providing hooks at the end of the reinforcing bars.