PSI - Issue 43

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

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3. Experimental Results and Discussion Loaded concrete sample was scanned by  CT tomography to analyze internal damage produced by cyclic load. The concrete sample was exposed to 2  10 6 load cycles. Additionally, to achieve this amount of load cycles, both specimens were tested with different load which produced different stress conditions in the specimen. The applied maximum load P max and consequent maximum applied stress in the middle of the span  max is shown in Table 3.

Table 3. Applied maximum load P max , stress  max at the mid-span and load cycles.

Maximum force P max (kN)

Maximum stress  max (MPa)

Load cycles N (cycle)

1.8

2.97

2  10 6

The maximum applied force P max and consequent maximum stress  max per load cycle is approx. 2.2 times lower than measured flexural strength. This is due to the aim of this study focusing on fatigue damage analysis in the high cycle fatigue region, which is for concrete higher than 1  10 4 load cycles. Thus, the load reduction was necessary to initiate the fatigue damage in the internal structure, while keeping the sample unbroken. The  CT tomography produce grayscale images, in which the black colour represent air, while the white colour corresponds to dense material. The grayscale is a result of random distribution of material density or phases. For concrete, the darkest phases correspond to pores, the brighter phases are coarse and fine aggregates Loeffler (2018). The hydration products are shown as grey material in between the aggregates Snoek et. al (2016). The obtained grayscale images are presented in Fig. 2 - Fig. 4 together with schematically drawn plane in which the grayscale image was taken.

(a)

(b)

Fig. 2. Location of the studied  CT plane X - Z plane (a) and (b) – the  CT tomography picture with the location of the crack.