Effects of 2 MGy gamma irradiation on the steel corrosion in cement-based composites

Abstract

A viable prediction of service life of reinforced concrete structures exposed to irradiation environment is necessary to support a license extension for currently operating nuclear power plants as well as to support concrete mix optimization for new builds. An experimental study was carried out to evaluate the corrosion performance of mild steel reinforcing bars under gamma irradiation at environmental conditions favoring accelerated carbonation. in elevated temperature. The electrochemical impedance spectroscopy and potentiodynamic electrochemical tests were performed to assess the corrosion rates on the rebar surfaces. Effects of irradiation were also examined in regard to capillary pore size distribution by mercury intrusion porosimetry and mesopore distribution based on nitrogen desorption data. Companion tests were performed to determine the compressive and flexural strength of mortar exposed to gamma irradiation. Relative effects of gamma irradiation are reported for mortar specimens containing fly ash or limestone powder used for partial replacement of Portland cement up to 40% by mass. Gamma irradiation dose up to 2 MGy was found to affect the properties of passive layer of steel in comparison to non-irradiated specimens. A decrease of corrosive potential and passivation potential was found. An increase of corrosion current density by an order of magnitude due to gamma irradiation was observed. Parameters of polarization curves of steel indicated unstable passive layer on steel reinforcement in irradiated mortars.