ORIGINAL ARTICLE Impact of crack width on bond: confined and unconfined rebar David W. Law • Denglei Tang • Thomas K. C. Molyneaux • Rebecca Gravina Received: 14 January 2010 / Accepted: 14 December 2010 / Published online: 23 December 2010 Ó RILEM 2010 Abstract This paper reports the results of a research project comparing the effect of surface crack width and degree of corrosion on the bond strength of confined and unconfined deformed 12 and 16 mm mild steel reinforcing bars. The corrosion was induced by chloride contamination of the concrete and an applied DC current. The principal parameters investigated were confinement of the reinforcement, the cover depth, bar diameter, degree of corrosion and the surface crack width. The results indicated that potential relationship between the crack width and the bond strength. The results also showed an increase in bond strength at the point where initial surface cracking was observed for bars with confining stirrups. No such increase was observed with unconfined specimens. Keywords Bond  Corrosion  Rebar  Cover  Crack width  Concrete 1 Introduction The corrosion of steel reinforcement is a major cause of the deterioration of reinforced concrete structures throughout the world. In uncorroded structures the bond between the steel reinforcement and the concrete ensures that reinforced concrete acts in a composite manner. However, when corrosion of the steel occurs this composite performance is adversely affected. This is due to the formation of corrosion products on the steel surface, which affect the bond between the steel and the concrete. The deterioration of reinforced concrete is charac- terized by a general or localized loss of section on the reinforcing bars and the formation of expansive corro- sion products. This deterioration can affect structures in a number of ways; the production of expansive products creates tensile stresses within the concrete, which can result in cracking and spalling of the concrete cover. This cracking can lead to accelerated ingress of the aggressive agents causing further corrosion. It can also result in a loss of strength and stiffness of the concrete cover. The corrosion products can also affect the bond strength between the concrete and the reinforcing steel. Finally the corrosion reduces the cross section of the reinforcing steel, which can affect the ductility of the steel and the load bearing capacity, which can ultimately impact upon the serviceability of the structure and the structural capacity [12, 25]. Previous research has investigated the impact of corrosion on bond [2–5, 7, 12, 20, 23–25, 27, 29], D. W. Law (&) School of the Built Environment, Heriot Watt University, Edinburgh EH14 4AS, UK e-mail: D.W.Law@hw.ac.uk D. Tang VicRoads, Melbourne, VIC, Australia T. K. C. Molyneaux  R. Gravina School of Civil, Environmental and Chemical Engineering, RMIT University, Melbourne, VIC 3000, Australia Materials and Structures (2011) 44:1287–1296 DOI 10.1617/s11527-010-9700-y