*Proceeding Paper* **Influence of Environmental Conditions on Steel Corrosion in Concrete Exposed to Gamma Radiation †**

**Mariusz D ˛abrowski 1,\* , Justyna Kuziak 2, Kinga Dziedzic <sup>1</sup> and Michał A. Glinicki <sup>1</sup>**


**Abstract:** This article examines the problem of the service life of reinforced concrete structures intended for nuclear power plants and radiation waste storage bunkers when exposed to radiation. This research focused on assessing the corrosion resistance of steel bars under conditions of simultaneous exposure to gamma radiation and various environmental conditions affecting the rate of carbonation. Electrochemical measurements of steel bars were carried out on samples in three environmental conditions: in a laboratory–dry; enclosed in a can at RH = 50%; and enclosed in a can at RH = 100%. The durability of the passivation layer of steel on non-irradiated and irradiated specimens after 8 months of exposure to gamma radiation was compared. A lower degradation effect of gamma radiation was visible in fully water-saturated specimens.

**Keywords:** corrosion of steel; relative humidity variability; carbonation condition; EIS; polarization curve

Izabela Hager

4.0/).

Published: 13 March 2023

**Citation:** D ˛abrowski, M.; Kuziak, J.; Dziedzic, K.; Glinicki, M.A. Influence of Environmental Conditions on Steel Corrosion in Concrete Exposed to Gamma Radiation. *Mater. Proc.* **2023**, *13*, 44. https://doi.org/10.3390/ materproc2023013044

Academic Editors: Katarzyna Mróz, Tomasz Tracz, Tomasz Zdeb and

**Copyright:** © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/

**1. Introduction**

The durability of nuclear power plant constructions, with a service life of 30 years or more, is a desirable feature affecting electricity prices [1]. The corrosion of steel in concrete structures exposed to irradiation is one of the important parameters determining the long term suitability of the structure for further operation [2]. The structural properties of existing and new nuclear power plant buildings should be well established in terms of the expected period of operation.

The irradiation-induced aging of concrete in nuclear power plants, occurring over a long period of time in nuclear environments, should be considered. Common knowledge concerning the influence of gamma radiation shows that a significant deterioration of mechanical properties of concrete occurs when the gamma dose exceeds the threshold of 1 × 108 Gy [3]. However, there are studies that report the deterioration of concrete properties resulting just from a few MGy of gamma radiation [4–6], especially in the early stage of hardening [7,8]. For the reinforced concrete structures of a nuclear power plant, the impact of CO2 from the atmosphere is very important. Researchers confirm that the main product of carbonation is the formation of calcite and vaterite [9–11] and have suggested an increase in the rate of the carbonation reaction. Normally, reinforcing bars surrounded by concrete exist in high pH (around 13 for Portland cement) conditions, and such an alkaline environment protects against steel corrosion and the further deterioration of the structure. The acceleration of carbonation lowers the pH of the concrete and consequently leads to steel depassivation [12,13]. In addition, gamma radiation causes the decomposition of the aqueous pore solution near the steel reinforcing bars and the formation of oxidizing and reducing compounds [14], which can affect the properties of the passivation layer on

*Mater. Proc.* **2023**, *13*, 44. https://doi.org/10.3390/materproc2023013044 https://www.mdpi.com/journal/materproc 359

the steel surface. Investigations into gamma radiation on corrosion of metals and alloys are generally measured in water solution systems, simulating cement matrix conditions. Studies [15,16] conducted on different types of steel and alloys (AISI 304, carbon steel) and gamma radiation doses (range from 75 kGy to 3 MGy) did not provide a consistent answer regarding the effect of irradiation on steel corrosion. In the case of real cementbased composite systems, the low dose (300 kGy) of gamma radiation [17] does not change the properties of the steel protective layer. A dose of up to 2 MGy, as seen in previous research [18], demonstrated the effect of gamma radiation on the reduction of the protective properties of the passive layer of steel in mortar, located in a sealed can with CO2 and medium relative humidity (RH = 50%). The effect has not been unequivocally confirmed, due to a lack of studies that have conducted measurements in strong radiation fields. A marginal number of papers (as reported in review paper [12]) consider the influence of humidity conditions on the passivation of steel in gamma radiation field. Humidity conditions are of key importance for the intensity of concrete carbonation [9] and, consequently, for the conditions of the reinforcement steel.

This research is a continuation of considerations concerning the effects of gamma radiation on steel corrosion in cement-based materials [18]. The main purpose of this research is to assess the effect of gamma radiation on reinforcing steel in humid conditions that favour concrete carbonation (approximately RH = 50%) and inhibit carbonation (RH = 100%). The potentiodynamic and electrochemical impedance spectroscopy measurements were used to assess the susceptibility of the steel to corrosion.
