PSI - Issue 42

Stanislav Seitl et al. / Procedia Structural Integrity 42 (2022) 1512–1519 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Lee (1982), Hordijk (1993), Lee & Barr (2004), Seitl et al. (2018), Seitl et al. (2019a,b), Šimonová et al. (2021), Kachkouch et al. (2022), Miarka et al. (2022)) that bring a decrease in their performances with time. It has been shown, that fatigue load could be the reason for many structures’ deteriorations due to the microcracks formation in the cement matrix and its propagation within the material. The fatigue of a component is a phenomenon characterized by the descent that occurs due to the repetition of loads that individually cannot produce failure. The fatigue phenomenon is associated with the change of material properties through microcracks and can lead to failure. It is well known that the durability and compressive strength of concrete are closely related to the water to cement ratio ( w / c ). The exponential relationship between the w / c and compressive strength is the fundamental of concrete technology. Since water to cement ratio is a generic parameter for concrete strength development with age it is an appropriate parameter for normalization directly or indirectly through the strength, it can develop upon hardening. Further by normalization of the entire data by their corresponding compressive strength values at water to cement ratio of 0.5 ( generalize Abrams’ la w ( w / c is between 0.3 and 1.20) – see Nagaraj & Banu (1996)): 0.5 ⁄ = −0.2 + 0.6(1 ⁄ ( ⁄ )) for 0.5 > 30 MPa (1) and 0.5 = −0.73 + 0.865(1 ( ⁄ ) ⁄ ) ⁄ for 0.5  30 MPa , (2) where, f c is compressive strength, w / c is the water to cement ratio by volume. Some more details you can find in eg. Kostmaka et al. (2011), Oyedele et al. (2022). It was decided to test 3 different water to cement ratios (0.5, 0.4, 0.3) for the same maximum size of aggregates D max = 8 mm and one mixture with w / c = 0.3 and D max = 16 mm) and compare them based on their fatigue and fracture mechanical behavior. This contribution introduces and compares fatigue and fracture mechanical properties obtained from static and fatigue tests for four kinds of concrete, with similar volume of cement but various volume of water. The focus was set on the bulk density, flexural and compressive cube strength, fracture toughness and fatigue properties ( S−N − Wöhler curve). All of these tests are important for a practical application in the design of precast concrete structures.

Nomenclature  a

Stress amplitude

Maximum applied stress Minimum applied stress

 max  min

Young’s modulus

E

Frequency

f

Concrete compressive strength

f c

Concrete compressive strength for w / c = 0.5

f c0.5

Bending strength Fracture toughness

f b

K IC

Number of cycles in a test and/or loading

N N f

Number of cycles to failure

Stress ratio

R

Maximum applied stress level Minimum applied stress level

S max S min w / c VD

Water to cement ratio

Volume density Work of fracture

W F