The pulling out of steel bars from concrete is resisted by the gripping action of concrete known as bond and the resulting stress is called bond stress. The resistance offered to slipping of bars is due to three factors:
- The chemical adhesion between the two materials
- The friction due to natural roughness of bars
- The mechanical anchorage of the closely spaced rib-shaped deformation made on the bar surface.
The bond strength can be increased by:
- Providing rough surface of steel deformed bars
- By providing sufficient cover
- Providing rich mix concrete