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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2. Materials and methods Portland cement CEM I 52.5 R Alborg, Silica fume RW-Füller Q1, fine sand 0-0.5 Bzenec quary, Quartz powder Microdorsilit 405 and 2500 with medium grain size 6 and 42 µm, respectively and superplasticizer Glenium were used to prepare the test specimens. All specimens had identical composition summarized in Table 1.

Table 1. Composition of the RPC.

Material

Sand 0-0,5 mm

CEM I 52.5 R

Silica Fume

Quartz powder 405

Quartz powder 2500

Superplasticizer

Water

Amount (kg/m3)

900

800

150

150

50

0.14

150

The individual batches of samples varied in their production process and subsequent curing regime. Three different production methods were tested: 1) mixing under ambient pressure+standard moulding without additional pressure (designation RPC); 2) vacuum mixing+standard moulding without additional pressure (designation RPC-V); 3) mixing under ambient pressure+ moulding with subsequent 5 MPa pressure during the setting time (designation RPC-P); Three curing conditions after demoulding were adopted: 1) curing in water at an ambient temperature; Hydrothermal treatment was performed in laboratory autoclave NR-150/3000 (see Fig. 1 left). For quasi-static compressive and flexural strength tests and bulk density determination, specimens with the dimension of 20x20x100 mm were prepared. The mechanical parameters were obtained using the universal strength testing machine TIRAtest 2710, R58/02, at a speed of 5 mm/min. Split Hopkinson pressure bar (SHPB) equipment was used to determine the composite behaviour at compression at strain rates around 2000 s-1 (the schematic of the test is outlined in Fig. 1). For the SHPB tests, the cylindrical specimens with a diameter of 15 mm and length of 6.5 mm were prepared by waterjet cutting. Considering the material composition, the selected size is sufficient to be fully representative. 2) curing under hydrothermal conditions at 190°C for 40 hours; 3) curing under hydrothermal conditions at 180°C for 8 hours.

Fig. 1 NR-150/300 autoclave (left), schematic of the SHPB test (middle) and test samples to be tested using SHPB device

The SHPB test is based on one-dimensional elastic wave propagation theory. During the measurement, the specimen is placed between the ends of two straight rods, incident rod and the transmitted rod. At the end of the incident rod, a stress wave is formed by the striker. The wave propagates through the rod towards the sample. After reaching the sample, the incident wave splits into the transmitted wave, which passes through the sample into the transmitted rod, causing the sample to be deformed. Part of the wave is reflected back to the incident rod. Deformation is measured by strain gauges placed on the rods. Assuming that the deformation in the sample is uniform, the stress and strain can be calculated from the amplitudes of the incident, transmitted and reflected waves.