Residual bond strength of corroded plain round bars

This paper reports results of an experimental programme to measure changes in bond characteristics of plain round reinforcement as a result of corrosion. Principal parameters included in the investigation are the amount of corrosion, the presence of confining reinforcement in the form of links, cover thickness and the initial condition of the reinforcement. In the absence of confining links, bond strength of bars cast near the bottom of a pour is found to reduce with increasing corrosion. However, although top-cast bars were initially weaker, small amounts of corrosion were sufficient to raise bond strength to that of bottom-cast bars. With increasing corrosion, strength reduced in a similar manner to bottom-cast bars. Confining reinforcement had little influence on bond strength prior to the onset of corrosion, but plays an important role in maintaining strength once corrosion becomes established. Results from these tests suggest that surface crack width may provide a better parameter than section loss or corrosion penetration through which to assess residual bond strength. The reasons for this are explained, and empirical relationships for residual strength are derived.