Pergamon Cement and Concrete Research, Vol. 27, No. 12, pp. 181 l-18 15. 1997 Copyright 0 1997 Elsevier Science Ltd Printed in the USA. All rights reserved COX-8846/97 $17.00 + .oO PI1 SOOOS-8846(97)00172-5 EFFECT OF CORROSION ON THE BOND BETWEEN CONCRETE AND STEEL REBAR X. Fu and D.D.L. Chung’ Composite Materials Research Laboratory, State University of New York at Buffalo, Buffalo, NY 14260-4400 (Communicated by D.M. Roy) (Received August 6, 1997; in final form September 4, 1997) ABSTRACT The effect of corrosion on the bond between concrete and steel rebar was studied by measuring both bond strength and contact electrical resistivity. Corrosion of steel rebar in concrete immersed in saturated Ca(OH), solution was found to cause the bond strength to increase, and the contact resistivity increased until 5 weeks of corrosion. Further corrosion caused the bond strength to decrease, while the contact resistivity continued to increase. 0 1997 Elsevier Science Ltd Introduction Corrosion is one of the main causes for the limited durability of steel-reinforced concrete. The corrosion product, rust, resides at the interface between steel rebar and concrete, thus degrading the bond between steel rebar and concrete. However, rust that is well adhered to the underlying steel helps the bond between steel and concrete (1,2). Moreover, surface treatment of the steel with water to form a coating, prior to incorporation of the steel in concrete, increases the bond strength (3,4). In addition, the contact electrical resistivity between steel rebar and concrete increases with bond strength, suggesting that the interfacial phase (rust or a phase akin to rust) helps the bond (4-6). To clarify the effect of corrosion on the bond between steel and concrete, we report here a systematic study of both bond strength and contact resistivity as a function of corrosion time of steel-reinforced concrete. The contact resistivity is a quantity that increases mono- tonically with an increasing amount of interfacial phase (rust), because the interfacial phase has a much higher volume electrical resistivity than steel and most likely a higher resistivity than concrete as well. Therefore, the contact resistivity provides a better indication of the extent of corrosion than does the corrosion time. The correlation of bond strength and contact resistivity provides a correlation of bond strength and the extent of corrosion. For the same corrosion time, different samples can be different in bond strength and contact resistivity, because different samples can have different degrees of cleanliness at the interface, even prior to corrosion. This problem of data scatter can be alleviated by measuring ‘To whom correspondence should be addressed. 1811