PSI - Issue 72

Yuriy Panchuk et al. / Procedia Structural Integrity 72 (2025) 216–221

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Table 1. Concrete Composition Type of concrete Cement, kg/m 3

Sand, kg/m 3

Crushed stone, kg/m 3

Water, l/m 3

Additive «Dofen», l/m 3

Cone draft, cm

FGC

400 340 416

1500

-

200 (W/C=0.5)

-

7…8 7…8 5…9

СGC -1 СGC -2

665 464

1150 1280

150 (W/C=0.44) - 180 (W/C=0.43) 24

The concrete prism samples had the following dimensions: 4x4x16 cm (FGC), 10x10x40 cm (SGC-1), and 15x15x60 cm (SGC-2), all made in horizontal molds. Concrete prisms from FGC and CGC-2 were compacted on a vibrating table in the laboratory, while the specimens from CGC-1 were compacted on a vibrating platform at the plant. The moulded specimens of FGC and SGC-2 were cured in metal molds covered with a damp cloth in the laboratory at an air temperature of 16 to 18°C and relative humidity of 53 to 71%. The specimens made from SGC-1 were cured in the plant’s steaming chamber. After curing, the samples of CGC -1 and CGC-2 were removed from the formwork and kept under laboratory conditions of temperature and humidity, while the factory samples were cured in a humid environment for 28 days before being stored in the laboratory. Concrete prisms measuring 4x4x16 cm made of FGC were tested for low-cycle compressive loads in a specially designed spring installation. Samples of concrete prisms measuring 10x10x40 cm from CGC-1 and 15x15x60 cm from CGC-2 were tested under cyclic loads using hydraulic equipment. Before testing, the prisms were centered at a load (0,15…0,20)fb, and efforts were made t o ensure that the longitudinal deformations measured on the faces of the prisms did not vary by more than ±10%. The specimens were loaded to the specified upper level with a constant stress rate of 0.6 ±0.2 MPa/s, with the load applied in increments equal to 10% of the anticipated destructive load. At each loading stage, the test lasted 4 to 5 minutes to permit the release of plastic deformations. Similarly, the samples were unloaded in increments to the lowest level, defined as zero. The number of cycles of load application to the concrete prism specimens during the tests was not limited; it was determined by the number of cycles that the specimen could endure before failure. To exclude the possible influence of the growth of concrete strength over time, the specimens were tested at a considerable age: 410 to 536 days (FGC); 143 to 178 days (SGC-1); and 350 to 371 and 601 days (SGC-2). For the set lower load level, which was considered zero, the upper level of low-cycle loading was defined as follows: for samples with FGC - (0.87…0.96)fb; for SGC -1 - (0.82…0.95)fb; and for SGC -2 - (0.78…0.88)fb. Two prisms made from SGC-2 were tested under low- cycle loads with a load level ranging (0…0.6)fb at ages of 598 and 601 days. Throughout the experimental studies, the following data were recorded: the value of the upper level of low cycle loading and the number of loading and unloading cycles until the sample's destruction. 3. Results and discussion The test results of the prisms made of FGC, SGC-1, and SGC-2, tested for low-cycle loads, are shown in Table 2. To describe the low-cycle fatigue formulas for the concrete used in the test prisms, a linear function was adopted in the form of a dependency “η cyc - n cyc ”: for FGC ηcyc = 1 – 0,094(ncyc – 1)/(ncyc + 2,499) ; 1) for СGC -1 ηcyc = 1 – 0,159(ncyc – 1)/(ncyc + 3,606) ; (2) for СGC -2 ηcyc = 1 – 0,253(ncyc – 1)/(ncyc + 11,490) . (3)