Variation in steel-mortar bond strength and microstructure in cathodicallyprotected specimens after two-year exposure

Steel embedded in concrete passivates due to the formation of an oxide film that may be broken by exposure to aggressive environments. In such cases, reinforcing bars need to be cathodically protected. There are several criteria to select the adequate protection potential. In this paper it is proposed that steel could be polarised with three differen t potentials, -850, -1000 and -1250 mV, taken with respect to the saturated calomel electrode (SCE). Two electrolytes were employed: tap water and 3% sodium chloride solution. Mortar specimens were polarised for two years and , then, subjected to a pullout test in order to determine bond strength var iations at the steel-mortar interface. It was found that steel-mortar adhes ion diminished 10% when specimens were polarised at -1250 mV. These changes may be related to hydrogen evolution and to changes in the crystalline mic rostructure of the cement paste.