PSI - Issue 74

Petr Miarka et al. / Procedia Structural Integrity 74 (2025) 50–55 Petr Miarka / Structural Integrity Procedia 00 (2025) 000 – 000

51

2

Nomenclature δ

deflection

compressive strength flexural strength

f c f ct

fracture energy

G F

N load cycle 3PBT three-point bending test CMOD crack mouth opening displacement FPZ fracture process zone OPC ordinary Portland cement ULS ultimate limit state

1. Introduction Fatigue failure of concrete caused by cyclic loading is unexpected as it has form of cumulative damage, which is often unintentionally omitted, as the main engineering parameters used in the structural design are compressive or flexural strength of the material. In such case, the structural design considers the fatigue assessment Lee and Barr (2004) as a stress reduction in critical locations produced by the external load, with the structural life related to total number of load cycles N . This approach is directly related to ultimate limit state (ULS) and to stress reduction by percentage of measured static compressive or flexural strengths Korte (2014a), respectively. Relation of stress-load cycles is often referred to as S-N curve or as Wöhler’s curve Basquin (1910). The increasing demand for resilient, economical, and long-lasting civil engineering structures highlights the pressing need to advance our understanding of crack initiation and fracture propagation in concrete under cyclic loading Mena-Alonso (2024). Despite ongoing research, the reliable prediction and mitigation of these fatigue-driven damage mechanisms remain unresolved challenges in both scientific inquiry and engineering practice Korte (2014b). This experimental study set its focus on the understanding of fatigue damage initiation and presents wide range data for assessment of fracture and fatigue resistance of concrete. For this, three-point bending test (3PBT) with a notch is used for static fracture, low-cycle and high-cycle experimental tests. The static fracture tests provide information of fracture energy G F . The low-cycle fatigue tests are controlled crack mouth opening displacement (CMOD) providing the information about the damage progress of each load cycle. Lastly, the high-cycle fatigue tests with a runtime set to 2 × 10 6 are of main focus. These experiments provide information of S-N field, Paris’s law proposed by Paris and Erdogan (1963). 2. Experimental details 2.1. Material Within this study ordinary Portland cement (OPC) was selected as a binder. OPC was mixed with three fractions of natural aggregates: sand 0/4 mm, granite 4/8 mm and granite 8/22 mm. A constant dosage of polycarboxylate superplasticizer Glenium 300 (BASF, Germany) was added to the mixture to achieve good workability. The water to cement ration w/c was 0.3. The mixture composition per 1 m 3 is shown in Table 1.

Table 1. Mixture composition per 1m 3 .

CEM I 42.5R [kg]

Water [kg]

Superplasticizer [kg]

Sand 0/4 [kg]

Granite 4/8 [kg]

Granite 8/22 [kg]

450

135

9

866

290

740