PSI - Issue 67

Jiří Němeček et al. / Procedia Structural Integrity 67 (2025) 17 – 22

21 5

J. Neˇmecˇek et al. / Structural Integrity Procedia 00 (2024) 000–000

3 . 0

50

b)

a)

Irradiated Control

Irradiated Control

2 . 5

40

2 . 0

30

1 . 5

20

1 . 0

Hardness (GPa)

10

Young’s modulus (GPa)

0 . 5

0 . 0

0

4% 11% 33% 43% 76% 100%

4% 11% 33% 43% 76% 100%

Relative humidity

Relative humidity

Fig. 3. Summary of micro-mechanical data of main hydrates measured with nanoindentation: (a) Young’s modulus; (b) Hardness.

Table 1. Observed changes in Young’s modulus and hardness between irradiated and control samples.

Category 1 (low RH)

Category 2 (medium RH)

Category 3 100%RH

4%RH

11%RH

33%RH

43%RH

76%RH

+ 24.6% + 15.5%

+ 24.8% + 34.7%

–25.5% –25.6%

∆ E ∆ H

+ 1.7% + 3.2%

+ 2.2% –4.6%

+ 6.9% –7.3%

in Khmurovska et al. (2021), but with an absorbed gamma dose approximately five times smaller. Nevertheless, similar findings of negligible changes of micro-mechanical properties were also observed. The third category was formed with samples stored in water (100% RH). In this category, a notable decrease was observed in both E (by 25.5%) and H (by 25.6%). The control samples exhibited a high E value of 34.4 GPa, whereas the irradiated sample had an E value of 25.6 GPa, indicating that the damage from irradiation significantly outweighed the sti ff ening e ff ects of hydration. This decline in mechanical properties was also accompanied by an approximate 10% loss of Portlandite, as shown by XRD measurements Neˇmecˇek et al. (2023).

4. Conclusions

This paper presents a nanomechanical analysis of gamma-irradiated cement pastes, with total absorbed dose of 2.88 MGy, exposed to a wide range of relative humidities from 4% to 100%. The e ff ects of irradiation were categorized into three groups based on the RH level. The following conclusions were drawn: • Irradiation at very low RHs (4% and 11%) led to significant increases in Young’s modulus (up to 25%) and hardness (up to 35%), likely due to water loss from the C–S–H gel interlayer caused by drying and water radiolysis. • Irradiation at medium RH levels (33%, 43%, and 76%) resulted in minimal changes in elastic modulus and hardness, indicating a negligible impact on micro-mechanical properties at the given gamma dose (2.88 MGy). • Irradiation of samples stored in water led to a significant reduction in both Young’s modulus (–25.5%) and hardness (–25.6%), with the damage from irradiation outweighing the sti ff ening e ff ects of hydration.