*2.2. Specimen Conditioning and Gamma Radiation Exposure*

Cylindrical mortar specimens with central placed steel rod were divided into three groups after curing time: the first was to be irradiated and second and third to be stored in the laboratory without irradiation. The two groups of specimens were placed in steel cans, as shown in Figure 1a. The third group was conditioned without canning. Subsequently, each group of specimens was placed in a CTS climate-controlled chamber (65% RH and CO2 concentration of 1% in the air). Specimens were conditioned in open cans in the climate chamber for 24 h and then the cans were closed. The environmental conditions in the cans were designed for two RH—fully water-saturated condition and RH = 50 ± 5% (controlled by superabsorbent polymer). The third group of specimens, after 24 h of conditioning without a can, was cured under laboratory conditions (23 ± 1 ◦C and RH = 43 ± 5%).

**Figure 1.** Location of specimens in the cans, (**a**) the arrangement of sealed cans (**b**), and the view of the prismatic steel box (**c**) immersed in the reactor pool close to spent nuclear fuel rods.

The research reactor of National Centre for Nuclear Research was used for the gamma irradiation of specimens sealed in cans and set in a prismatic steel box (Figure 1) in a manner described in detail in [18]. The absorbed dose was determined as the average value of two dosimeters attached to the walls of the cans. The dose of gamma radiation absorbed by the samples was close to 1.8 MGy. The specimens in the nuclear reactor-spent fuel pool were irradiated for 8 months. The second group of canned specimens was stored in climatic chamber at 38 ◦C without irradiation for the same period. The temperature in the climatic chamber corresponds with the temperature of irradiation specimen conditions. The measurements of environmental conditions (temperature and humidity) in closed cans confirmed the correctness of the adopted conditions. The results of mortar carbonation are presented and discussed in the research of Józwiak-Nied ´ ´ zwiedzka et al. [23].
