PSI - Issue 43

Petr Miarka et al. / Procedia Structural Integrity 43 (2023) 124–129 Author name / Structural Integrity Procedia 00 (2022) 000 – 000

126

3

Fig. 1. 3PB configuration used in fatigue test together with sample’s dimensions.

The analysed specimen’s inner structure was examined using a GE phoenix V|tome| X standalone high-resolution micro-CT scanner. The scanner provides spatial resolution of 52  m/voxel using a specimen with cross-section geometry approximately of 80  40 mm 2 by 40-mm long with a total volume of 1239  1844  1648 voxels. The scans used in this study were produced by an acceleration voltage of 200 kV and 300  A tube current. The specimen was rotated during a scan by total of 360° and the projection images were then reconstructed by a commercial software utilizing the VGL 3.2 cone-beam reconstruction algorithm. Since the fatigue damage evolution is progressive in the concrete samples, micro-CT scans were done after exposure to certain number of load cycles to provide insight into the fatigue damage evolution in material’s inner structure. 2.2. Mixture composition The high-performance concrete (HPC) designed with ordinary Portland cement CEM I 42.5 R as a binder with water to cement ratio w / c of 0.5 (Nawy 2001). A commercial polycarboxylate based superplasticizer was used to achieve good workability of the mixture. The aggregates were sand 0/4 and crushed granite aggregates 4/8 mm. The mixture composition is presented in Table 1.

Table 1. Mixture composition per 1 m 3 .

CEM I 42.5 R (kg)

Effective water (kg)

Superplasticizer (kg)

Sand 0/4 mm (kg)

Crushed aggregates 4/8 mm (kg)

450

225

1.5

990

700

Concrete was in a laboratory mixer in a volume of 20 litters. After mixing, the concrete was placed into steel molds and they were covered in (PE) sheet to reduce water exchange with the environment. Because of the same reason, the samples were additionally covered in PE foil after demolding at the age of 1 day. At the age of 28 days, this mixture was tested to obtain mechanical properties according to European standards as well as to have basic information on fracture mechanical properties. These material’s pa rameters are presented in Table 2.

Table 2. Measured fracture and mechanical properties at the age of 28 days.

Volume density (kgm -3 )

Compressive strength (MPa)

Flexural strength (MPa)

Modulus of elasticity (GPa)

Fracture toughness (MPam 1/2 )

Work of fracture (Jm -2 )

2200  6

45.0  0.4

6.5  0.5

32.3  2.3

1.04  0.09

108  18

The measured mechanical properties as well as fracture mechanical properties have similar values as the previously studied mixtures, see (Miarka 2022).