PSI - Issue 42

Stanislav Seitl et al. / Procedia Structural Integrity 42 (2022) 1512–1519 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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The modulus of elasticity of concrete with various w / c ratio and different D max are mentioned in Tab. 2. It can be concluded that E from 32 up to 44.6 GPa is significantly affected by w / c ratio and no significant influence of the maximum size of aggregate is observed (differences in the values are up to 3 GPa). The effective fracture toughness of concrete with various w / c ratio and different D max are mentioned in Tab. 2. It can be concluded that K IC is significantly affected by w / c ratio and no significant influence of the maximum size of aggregate is obvious. After 28 days, the K IC values practically stay constant for given w / c ratio. The fracture work of concrete with various w / c ratio and different D max are mentioned in Tab. 2 – last column of the table. It can be concluded that W F is affected by both w / c ratio and maximum size of aggregate. After 28 days the W F values for w / c = 0.5 increase regularly 108 (28 days), 116 (91 days) and 131 Jm -2 (365 days), but for another w / c = 0.4; 0.3, W F values singly oscillate, but are always larger than those of w / c = 0.5. There are only little date to assess the effect of the maximum size of aggregate on the W F values. 4.2. Fatigue properties of concrete with various water to cement ratio and D max The experimentally obtained pilot fatigue results ( S – N curve) for concrete with various water to cement ratio and D max are shown in Fig. 4-5, where the bending stress amplitude applied during the fatigue experiments is plotted against the logarithm of the number of cycles to failure or at 2  10 6 cycles, a limited number of cycles, for run-outs i.e. for unbroken specimens. Relationships between maximum stress level (   a (1)) and the number of cycles to runout (2×10 6 ) are investigated. Tab. 4 shows test results of the relationship between stress level and endurance fatigue life. Under decreasing w / c , fatigue life increases as the concrete compression stress increases, and then the fatigue resistance of w / c = 0.3 concrete seems to be 60 % for high-grade concrete in comparison to 50 % for w / c = 0.5 concrete. This study found that the maximum size of aggregates has not a significant effect on the fatigue properties, see Fig. 5, especially on the fatigue limit 2×10 6 cycles, this means that the weak point of the concrete is the pasta/composition.

Fig. 4. Fatigue results of concrete with various water to cement ratio for D max =8 mm and its Kohout- Věchet fit.