PSI - Issue 81

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

363

(a)

(b)

Fig. 1. (a) scheme of the impact test setup; (b) the testing machine.

3. Results and Discussions The results of the compressive strength test after 28 days showed that concretes without fiber (compositions 1-3) and FRC with 1% fiber (compositions 4-6) are characterized by a strength above 60 MPa, which corresponds to the strength for HSC (Fig. 2). It should be noted that the adding of fiber causes a decrease of the consistence of the fresh concrete, which requires the adding of a higher amount of water and leads to a decrease of compressive strength by 3-10%. An assessment of the efficiency of cement use shows that the specific consumption of Portland cement per unit of design strength varies within 3.9 – 4.4 kg/MPa. When 2% fiber is added, the strength decreases even more (by 14 – 17%), and the compressive strength of FRC with a Portland cement consumption of 300 kg/m 3 decreases to 52.1 MPa, which does not correspond to HSC. The intensive increase in strength of HSCs during 28 days does not prevent further increase during the year. As the test results showed, all samples of the concrete compositions have an increase in strength by 7.1 – 19.2% during hardening time. For example, the strength of concrete 1 increases from 68.3 MPa to 78.5 MPa, and fiber concrete 4 from 61.7 MPa to 73.1 MPa. The increase rate of compressive strength from 28 to 360 days for all concretes is almost the same, although there is a pattern - the higher the concrete strength after 28 days (the higher the consumption of Portland cement), the smaller the increase of strength after 360 days is observed, which is due to the creation of a dense structure in the initial period. Also, a greater increase of 9.6 – 19.2% is observed for fiber concretes with 2% fiber (compositions 7 – 9).

100 120

28 days 360 days

106.5

104,0

97,8

96,3

92,2

0 20 40 60 80

84,9

78,5

73,1

62,1

89,3 99,4

87,1 96,8

MPa

75,5 84,1

68,3

61,7

52,1

Compressive strength,

1

2

3

4

5

6

7

8

9

Composition

Fig. 2. Compressive strength of concretes.

The resistance to bending or flexural strength is a key component of durability strength testing. The increase in flexural strength contributes to the increase in crack resistance characteristics. Therefore, the flexural strength of the designed concretes after 28 and 360 days was investigated (Fig. 3). As can be seen from the test results, the flexural strength of concrete after 28 days increases when the amount of cement in the concrete increases. Thus, the flexural strength increases from 5.8 MPa to 7.8 MPa for concretes with a cement consumption of 300 and 400 kg/m 3 , respectively. The use of fiber also contributes to the increase of flexural strength. Thus, the strength of concrete with 1% fiber increases by 29.8 – 43.6% compared to concrete without fiber. It should be noted that the flexural strength of FRC increases with an increase in cement consumption. When increasing the fiber dosage to 2%, the flexural strength increases by 52 – 59%, unlike the compressive strength.