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

Abstract

Steel embedded in concrete passivates due to the for mation 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 protec tion potential. In this paper it is proposed that steel could be polarised with three different 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 variations at the steel-mortar interface. It was found that steel-mortar adhesion diminished 10% when specimens were polarised at -1250 InV. These changes may be related to hydrogen evolution and to changes in the crystalline microstructure of the cement paste.