## 3 Research Results and Discussion  
Analysis of Degradation of Reinforced Concrete Structures Exposed to Gamma Radiation from the Standpoint of Reinforcement Corrosion  
1.1 Concrete Degradation Due to Exposure to Ionizing Radiation, Contributing to Corrosion of Reinforcement Bars  
The main effects of ionizing radiation on concrete shields for nuclear power plants and radioactive and nuclear waste storage facilities include [70]: (1) an increase in temperature (\"radiogenic heating\"); (2) activation of concrete components (moreover, according to [70], this type of effect matters solely for the decommissioning of buildings and structureswhere radioactive and nuclear materials were handled, and it is also characteristic of direct interaction with neutrons [70]); (3) higher expansion coefficients and swelling of the material; (4) changes in air and water permeability coefficients; (5) carbonization of the cement matrix (primarily due to gamma radiation) and accompanying changes in properties and structure (for example, lower porosity, shrinkage, and others); as well as (6) radiolysis of water. Radiation-Related Structural Changes in Concrete  
Currently, most studies on the degradation of concrete in facilities where nuclear and radioactive materials are handled focus on the effect of neutrons (or mixed neutron and gamma radiation fields, where neutron radiation plays a predominant role). This effect is greatest for the above-mentioned material [70; 71; 72; 73; 74; 75; 76; 77; 78; 79; 80; 81; 82; 83; 84; 85; 86; 87; 88; 89; 90; 91; 92; 93; 94; 95; 96; 97; 98; 99; 100; 101; 102; 103; 104; 105; 106; 107; 108; 109; 110; 111; 111; 112; 113; 114; 115; 116; 117]. However, despite the (1) dry storage of radioactive waste, (2) appropriate handling of radioactive materials, preventing neutron bombardment, and (3) gamma radiation being the main type of effect [118; 119; 120], destruction of concrete structures, such as waste storage packages, can still be premature [59]. In general, changes in the physico-mechanical properties of concrete composites are due to the presence and magnitude of radiation-triggered deformations of elements that comprise the composite of elements. They are different for the binder, rock, and minerals of aggregates. Experiments prove that it is the large fraction of concrete fillers that triggers its radiation-induced deformations. Fine filler does not have a significant effect on this process. Moreover, a relative increase in linear dimensions (\"radiation-induced swelling\") is caused mainly by neutron radiation, rather than gamma radiation [117; 121]. In turn, authors of [122] report that gamma radiation has little effect on the properties of the filler and that much greater changes should be expected in the cement dough. The threshold value at which mechanical properties of concrete deteriorate is an accumulated dose of gamma radiation exceeding \(10^{8}\) Gy [70; 72; 73; 74; 75; 30; 76; 77; 78; 79; 80; 81; 82; 83; 84; 85; 86; 87; 88; 89; 90; 91; 92; 93; 94; 95; 96; 97; 98; 99; 100; 101; 102; 103; 104; 105; 106; 107; 108; 109; 110; 111; 113; 114; 115; 116; 117; 118; 119; 120; 121; 122; 123; 124; 125]. If a dose exceeds \(10^{9}\) Gy, there is evidence of a 25-60% decrease in the compressive strength of concrete [73]. One study reports an extreme (50%) decrease in the strength of concrete at a dose above 1 GGy [59; 123]. However, a number of studies show that even at lower values of the accumulated dose (several MGy), gamma ray quanta are capable of affecting the properties of concrete [70; 76; 77; 78], in particular, at the early stage of the cement stone strength gain and hardening [53; 74; 122; 123; 124; 125]. Hence, the study [70] cites the work of [PERSON] et al. (2005) [78], which reports that even if the accumulated dose is \(5\cdot 10^{5}\) Gy, the strength of concrete decreases by 10%, according to an experimental study of specimens irradiated with gamma radiation for 90 days. The authors of a study [70] report the experiments conducted by [PERSON] and [PERSON] (2001).