PSI - Issue 81

Nazar Sydor et al. / Procedia Structural Integrity 81 (2026) 360–366

364

10 12 14 16

28 days 360 days

13,5

12,2

11,5

10,7

9,5

8,6

0 2 4 6 8

8,1

7,6

12,4

6,3

11,2

10,5

9,8

8,6

7,8

7,4

6,9

5,7

Flexural strength, MPa

1

2

3

4

5

6

7

8

9

Composition

Fig. 3. Flexural strength of concretes.

The flexural strength of concretes after 360 days of hardening increases by 8 – 10% compared to the strength of concretes after 28 days and varies within 6.3 – 8.6 MPa for HSCs, and 8.1 – 13.5 MPa for high-strength FRCs. The results of impact resistance tests of concretes after 28 and 360 days of hardening are given in Fig. 4.

first visible crack impact failure energy

89

86.1

85.3

82.6

70.1

65.2

4.5 9.9

51.2

50.0

49.5

11.5

7.1 14.7

45.1

39.6

39.4

6.4

4.4 4.9 Impact resistance, J/cm3 after 28 days after 360 days 5.9 6.1

6.7 7.2

33.4

35.4

41.0

44.1

45.0

45.2

55.5

65.0

75.8

79.3

80.3

81.5

1

2

3

4

5

6

7

8

9

Composition

Fig. 4. Impact resistance of concretes.

It is shown that the impact strength of HSCs without fibers after 360 days increases by 1.9 – 2.1 times compared to the impact strength of concretes after 28 days. The consumption of Portland cement has a negligible effect on the change in impact resistance after 28 and 360 days. It is shown that polypropylene fibers helped to maintain a significant number of impacts before cracking. Thus, the impact energy increases from 9.9 J/cm 3 to 65.2 J/cm 3 for HSCs with a cement consumption of 300 kg/m 3 No. 1 and FRC 4, respectively. The impact strength of high strength fiber reinforced concretes, which characterizes the appearance of the first crack, after 360 days, increases by 1.1 – 1.2 times compared to the strength of FRCs after 28 days of hardening, and the impact strength, which characterizes complete failure, increases by 1.07 – 1.09 times. 4. Conclusions High-strength concrete demonstrates an increase in compressive strength by 7.1 – 19.2% compared to the strength after 28 days. Concretes with higher compressive strength after 28 days demonstrate less strength increase after 360 days. The impact strength of HSCs without fibers after 360 days increases by 1.9 – 2.1 times compared to the impact strength of concretes after 28 days. The impact strength of high-strength FRC increases by 1.07 – 1.09 times after 360 days compared to that of FRC after 28 days. The results demonstrate the long-term potential of improving the concrete properties, which are important for the long-term service of high-strength FRC structures.