PSI - Issue 73

134 Loran Nermend et al. / Procedia Structural Integrity 73 (2025) 130–137 Author name / Structural Integrity Procedia 00 (2025) 000–000 5 the specimens. The test was performed using Vikasonic (Schleibinger, Germany) device coupled with 80 kHz transducers. The dynamic modulus of elasticity (E dyn ) was determined based on the velocity ( ) and density of prepared mixes, according to Eq. (1). = ρ ∙ 2 (1) To effectively evaluate the losses in compressive strength and dynamic elastic modulus, the results were expressed as relative values. These were calculated by dividing the measured value at a given temperature by the corresponding value obtained for the dried specimen (i.e., without high-temperature exposure). This is a standard method commonly used for comparing different specimens. The results of electrical resistivity are presented in Figure 4. A clear effect of the introduction of pristine particles on the reduction of electrical resistivity can be observed from the early stages of hydration. In contrast, the incorporation of silica-coated particles led to an increase in resistivity, which is consistent with findings reported in the literature. As reported by Saradar et al. (2024), presence of nanosilica particles increased the electrical resistivity of cementitious composites by up to 30% due to microstructural densification and reduced pore connectivity. Studies have shown that adding nanosilica to cement can increase electrical resistivity by a significant amount, depending on the nanosilica dosage and other factors. Similar observations were reported by Vipulanandan and Mohammed (2019), where 17% and 35% (for 0.5% and 1% nanosilica additions, respectively) increases in electrical resistivity was reported for cement-based composites. Therefore, it can be concluded that the synthesis of a silica shell on the surface of Bi 2 O 3 /Gd 2 O 3 particles exhibits potential to reduce the negative effects of particle presence with respect to the specimens’ electrical resistivity. 3. Results and Discussion 3.1. Electrical resistivity

Fig. 4. Electrical resistivity of cement mortars after 2, 7, 14, 28 and 90 days of curing in water

3.2. Elevated temperature performance Figure 5 (top row) presents the relative residual compressive strength after exposure to 450 °C and 600 °C , while Table 2 presents the specific values obtained from testing. It can be observed that printed specimens exhibit slightly greater losses in compressive strength compared to cast specimens. As reported by Rahul et al. (2019) and Cuevas et al. (2021), due to their layered structure, printed specimens exhibit anisotropic mechanical properties that vary depending on the loading direction. Consequently, debonding and interfacial failure between layers can occur during mechanical testing. Additionally, depending on the printing pattern, voids and defects may form, leading to a