PSI - Issue 42

Martina Drdlová et al. / Procedia Structural Integrity 42 (2022) 1391–1397 Drdlova et al/ Structural Integrity Procedia 00 (2022) 000 – 000

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During the experiment, stress – strain relationship curves were captured; the peak stress was recorded as the dynamic compressive strength f cdyn . The measurement theory and methodology are described in detail in authors´previous work (Drdlova, et al. 2016 and Drdlova at al. 2018). The measured values of static and dynamic compressive strengths were used in the calculation of DIF fc (dynamic increase factor) according to the following equation, where f c dyn and f c s are the dynamic and static compressive strengths: = (1) 3. Results and discussion The mechanical parameters obtained by quasi-static loading and bulk density of the RPC samples are summarized in Table 2. The results from Split Hopkinson Pressure Bar compression experiments are presented in Table 3. Table 3 summarizes the evaluated critical peak stress (referred as dynamic compressive strength f cd yn ) of each specimen and calculated DIF fc . At least four samples for each batch were tested. Fig. 2 shows an example of captured stress strain diagram for two different specimens (RPC and RPC_V). Fig. 3 is the summary graphical depiction of the dynamic compressive strength of samples prepared and cured in different regimes.

Table 2. Physico-mechanical parameters of RPC samples prepared and cured under various conditions.

Parameter

Compressive strength (MPa)

Flexural strength (MPa)

Bulk density (kg/m 3 )

Curing regime/designation Water curing, 21°C, 28 days Hydrothermal curing, 180°C, 8 h. Hydrothermal curing, 190°C, 40h.

RPC

RPC-P

RPC-V RPC

RPC-P

RPC-V RPC

RPC-P

RPC-V

122 167 185

134.8 178.6

149 164 180

18.3 26.0 30.2

19.9 27.8 26.7

22.3 33.9 33.9

2322 2264 2280

2310 2268 2278

2401 2383 2337

181

Fig. 2 Example of the stress-strain diagrams at high strain rate loading of RPC (left) and RPC_V (right)

Analysing the test results presented in Table 2 and 3, it can be concluded that application of vacuum during the mixing process decreases the porosity of the specimens, which is manifested by increased bulk density. The increase in bulk density as the result of the introduction of vacuum into the mixing process was observed for all samples at a similar level, with increase between 2.5-5.2%. The effectiveness of vacuum mixing of UHPC/RPC in porosity reduction was also confirmed by Zdeb (2019) or Vojtisek (2021), who reported the reduction of porosity up to 60% for RPC materials cured in water and up to 80% for autoclaved materials mixed under reduced pressure. Regarding the mechanical parameters, in terms of strength increase, the effect of vacuummixing is particularly evident in the case of water cured specimens, where a significant increase in compressive and flexural tensile strength under quasi-static loading was observed, as well as an increase in dynamic compressive strength (in all cases about 20% increase). On the other hand, vacuum mixing does not bring substantial benefits in case the samples are further