PSI - Issue 43

Vlastimil Bílek et al. / Procedia Structural Integrity 43 (2023) 107–112 Author name / Structural Integrity Procedia 00 (2022) 000 – 000

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exchanging water (humidity) with the environment. These specimens were also stored in the laboratory, at a temperature of (20 ± 2) ° C. The results obtained at the age of 28 days are presented in this paper. The specimens of prisms with the geometry of 40 × 40 × 160 mm were prepared for CT tomography and for bending and compressive strength testing. Another set of specimens of prisms with the geometry of 80 × 80 × 480 mm was made for the testing of fracture properties.

Table 1. Composition of concretes (1 m 3 ). Water to cement ratio

0.50 450 225

0.40 450 180

0.30 450 135

CEM I 42.5 R Hranice

Water

Superplasticizer

1.5

9

11

sand Tovacov 0/4 mm

990 700

1050

1110

crushed granite Litice 4/8 mm

740

780

2.2. Fracture-Mechanical Properties – Methods of Measurement The specimens of prisms with the geometry of 40×40×160 mm were prepared for testing the basic mechanical properties: bending and compressive strength. Firstly, the specimens were tested for bending strength, and the fragments were subsequently used to measure the compressive strength. The specimens of prisms with the geometry of 80 × 80 × 480 mm were made to test fracture properties. A notch up to one third of the height of the specimens (c. 27 mm depth) was cut into the beams 220 mm from one end of the beam at the age of 28 days. Fracture tests in accordance with the Karihaloo and Nallathambi model (1989) or Karihaloo (1995) were performed on the notched beam (span of 400 mm). The fracture toughness K IC ef is the main result of these tests. The modulus of elasticity in three-point bending on the notched beam E ef as well as the modulus of rupture f r (which is calculated as the flexural strength on the notched beam) are partial results of these tests. After the fracture test, a part of the broken beam, the length of which is approximately 260 mm, was used for the test of the bending strength f b (span of 220 mm).

Table 2. Parameters of the tomographic system settings and the resulting CT volume.

Operating voltage Power outputs Focal spot size Cu Filter, thickness

215 kV

88 W

X-ray source setting (Rotating reflection target)

C 30 mm

2 mm

Radiograph image exposure

1000 ms

Frame per one radiograph projections Flat detector Number of pixels Number of radiograph projection

2

Scan parameters

2000 × 2000

3300 31 µm

Cubic voxel size CT volume data type

8 bit (256 grey level) C 2 500 000 000 C 40 × 40 × 40 mm

3D CT Volume

Number of Voxels in CT Volume

CT volume size

2.3. Computed Tomography – CT The scanning of concrete specimens was performed in the XT H 225 ST tomographic system by Nikon Metrology. A fragment of the test specimen in its middle part was scanned by 3D micro-tomography using an X-ray cone beam. The input data for a CT volume recons truction was taken as a part of a 360° rotation of the specimen. Table 2 shows the parameters of the tomographic system settings and the resulting CT volume. The 3D CT Pro software from Nikon Metrology was used for CT volume reconstruction and visualization, and porosity analyses were performed in the VG Studio MAX v. 3.3.2 software from Volume Graphics GmbH.