What Does Bond Strength Mean?
Bond strength can be explained, in chemistry, as the strength with which a chemical bond holds two atoms together. This is conventionally measured in terms of the amount of energy, in kilocalories per mole, required to break the bond.
In engineering, it is amount of adhesion between bonded surfaces. It is measured by the stress needed to separate the bonded layers from each other. In engineering, the amount of adhesion between bonded surfaces is measured in terms of the stress required to separate a layer of material from the base to which it is bonded.
Bond strength is intimately linked to bond order and can be quantified by:
- Bond energy
- Bond-dissociation energy
Coating by galvanizing or by epoxy affects the bond strength. Bond strength increases with surface roughness.
Corrosionpedia Explains Bond Strength
In terms of corrosion, bond strength is most commonly used in reinforced concrete. It is a measure of the transfer of load between the concrete and reinforcement. Bond strength is influenced by:
- Bar geometries
- Concrete properties
- Amount of confinement around the bar
- Surface conditions of the bar
For reinforced concrete , it is necessary to create a suitable bond between steel bars and the surrounding concrete. The bond ensures that there is little or no slip of the steel bars relative to the concrete and the means by which stress is transferred across the steel-concrete. Bond resistance is made up of chemical adhesion, friction and mechanical interlock between the bar and surrounding concrete.
A loss of bond between the concrete and reinforcement could lead to failure of the structure. Research on the effect of environmental corrosion on the bond between steel bars and concrete, reports considerable loss of bond strength.
The bond strength of concrete is a function of compressive strength and is approximately proportional to the compressive strength up to 20 MPa. For higher strength, the increase of bond strength is progressively smaller. The bond strength of high-pressured steam-cured concrete is low. The strength of concrete as a whole depends upon the bond strength of the hydrated hardened cement paste.
For polluted and non-polluted steel bars, small bar sizes have greater bond strength than larger bar sizes if the embedded length is small.
The presence of rust on the surface of the steel, provided the rust is well connected to the underlying steel, improves the bond of plain bars and does not impair the bond of deformed reinforcement. The bond may also be beneficially affected by the shrinkage of concrete relative to the steel.