Influence of corrosion on the friction characteristics of the steel/concrete interface J. Cairns a, * , Y. Du b,1 , D. Law c,1 a Heriot-Watt University, School of the Built Environment, Edinburgh, EH14 4AS, UK b University of Birmingham, UK c Maunsell Australia Pty. Ltd., Melborne, Australia Received 6 September 2004; received in revised form 20 June 2005; accepted 30 June 2005 Available online 21 September 2005 Abstract This paper reports results of an experimental programme to measure changes in friction characteristics of the interface between rein- forcement and concrete as a result of the formation of corrosion products on the surface of the steel. The aim of the study was to deter- mine whether a weak corrosion layer contributes to reported reductions in residual bond capacity. Corrosion was carried out under accelerated conditions using three different conditioning regimes. Principal parameters included in the investigation are conditioning re- gime, the amount of corrosion, and the stiffness of the restraint to expansion of the corrosion products. Experimental results indicate that corrosion products do not impair friction characteristics of a bar/concrete interface when surface crack width does not exceed 1.0 mm. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Reinforced concrete; Corrosion; Bond 1. Introduction Corrosion of embedded reinforcement is the principal cause of deterioration of structural concrete. The effect of this deterioration on residual capacity is a matter of con- cern to those charged with ensuring safe operation of con- crete structures. Although a considerable amount of research has been conducted in recent years to develop models for the prediction of service life of concrete struc- tures, it has largely focussed on new construction and the initiation phase of service life up to the point at which cor- rosion of reinforcement initiates. Relatively little attention has been devoted to quantifying effects of corrosion dam- age on residual strength of existing structures in later stages of useful life once volumetric expansion of corrosion prod- ucts has led to longitudinal cracking of cover concrete. Although initiation of corrosion represents a useful defining point for Service Life design of a new structure, it is evident that many reinforced concrete structures con- tinue to function, with or without repair, once corrosion has become well established, and there is no widespread evidence of structural collapse to suggest that modest amounts of corrosion pose an appreciable threat to struc- tural stability. If engineers had available reliable means to assess residual strength of affected structures, then it might be acceptable to allow a structure to continue in ser- vice without repair until it had served out its required life- time, with consequent savings in lifetime costs. The direct effects of corrosion are loss of bar cross sec- tion, increase in bar diameter resulting from the volumetric expansion of the corrosion products, and a change in the mechanical characteristics of the bar/concrete interface on formation of corrosion products. Effects of corrosion on residual structural capacity are thus divided into those aspects which affect the reinforcement itself, those which affect the surrounding concrete, and those which affect 0950-0618/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2005.06.054 * Corresponding author. Tel.: +44 131 451 4411; fax: +44 131 451 6079. E-mail address: j.j.cairns@hw.ac.uk (J. Cairns). 1 Formerly Heriot-Watt University, Edinburgh, UK. www.elsevier.com/locate/conbuildmat Construction and Building Materials 21 (2007) 190–197 Construction and Building MATERIALS