PSI - Issue 42

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

1396

6

some authors, e.g. Richard (1995), to be beneficial as it reduces porosity and decreases the tendency to crack formation. However, in a composite with a tested composition and consistency, the positive effect of pressure was not confirmed. Autoclaving can be pronounced very effective way how to treat the RPC materials in order to achieve high compressive and flexural strength at both low and high strain rates. The compressive strength of the RPC composite increases after hydrothermal treatment. The increase in compressive strength ranged from 20.8-51.6% depending on the production technology. The highest strength gain was achieved in the case of samples prepared under laboratory conditions without vacuum or additional pressure (51.6% increase in compressive strength). The lowest increment was achieved for samples mixed at reduced pressure. This sample had a relatively high compressive strength value even when cured in water, therefore the increase in strength due to hydrothermal treatment was not so pronounced. Higher mechanical properties are achieved when the higher temperature (190°C) and longer dwell time (40 hours) are adopted. By comparing the values of f c s and f c dyn , the tested material can be evaluated as strain rate sensitive. At high strain rate SHPB tests, the failure occurred rapidly and the specimen can in some conditions be considered not being able to respond in the direction perpendicular to the loading, which causes inertial confining stress on the central core of the sample resulting in increased strength (Costovos 2008). According to Davies and Hunter (1964), errors in the SHPB tests due to both longitudinal and radial inertia become negligible if specimen dimensions satisfy L/D = √3 /4 , where v is the Poisson’s ratio of the specimen. The optimum L/D in order to minimize the inertia effect thus ranges from 0.39 to 0.44. To avoid the inertia effect, the specimens with suitable dimensions (L/D ratio of 0.43) were selected in presented research. The results show that the peak strength is sensitive to the strain rates for all tested specimens. The degree of strength increment, expressed as DIF fc , was similar to all tested batches and ranged between 1.45-2.62. No dependence of strain rate sensitivity on the method of preparation or treatment was observed. The DIF fc of all sample batches was at a similar level.

Fig. 3 Summary graphical depiction of the dynamic compressive strength of samples prepared and cured in different regimes.

4. Conclusions Experimental research evaluating the effect of mixing technology and curing conditions on the high strain rate compressive behavior of Reactive Powder Concrete (RPC) was performed. The following conclusions can be drawn: -Vacuum mixing reduces the pore content in the composite, which is accompanied by a significant increase in peak stress values at both quasistatic and high strain rate loading in case of water cured samples (22 and 16% increase in the quasistatic and dynamic regime, respectively).