PSI - Issue 81

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

362

2. Materials and Methods 2.1. Materials

Ordinary Portland cement CEM I 42.5R PJSC Ivano-Frankivsk Cement (Ukraine), according to EN 197-1 standard, was used in the investigations. Natural sand of Zhovkva quarry (MF = 1.9), granite crushed stone of 2/5 mm as fine aggregates and granite crushed stone of 5/20 mm as a coarse aggregate were used for concrete preparation. Three cement contents of 300, 350 and 400 kg per 1 m 3 of concrete were selected for this study, designed to minimize the consumption of Portland cement in high strength concrete. Silica fume was used as a supplementary cementitious material, and nanosilica (Aerosil-380) was used as a nanofine additive for HSC. The amount of additives was 5.0% by weight of cement for silica fume and 0.5% by weight of cement for Aerosil 380. A polycarboxylate superplasticizer GLENIUM ACE 430 (PCE) was used as a water-reducing admixture. The dosage of polycarboxylate superplasticizer was 1.5% by weight of cement. For reinforcement at the macro- and mesoscale levels and to increase the impact resistance of HSC, polypropylene fiber (12 mm in length, 18 μm in diameter) was used. Рolypropylene fiber was added in the amount of 1 and 2% to control cracking. Table 1 presents the mix design proportions for all the combinations. The amount of water used in each mixture was adjusted to control workability and ensure a slump value of 180 – 200 mm (slump class S4 according to EN 206-1:2000).

Table 1. Proportions of concrete mixtures, kg/m 3 . Component

Composition number 1 2 3

4

5

6

7

8

9

Cement

300 350 400 300 350 400 300 350 400

Silica fume Aerosil 380 Natural sand Aggregate 2/5 Aggregate 5/20

15

17.5 20

15

17.5 20

15

17.5 20

1.5 1.75 2.0 1.5 1.75 2.0 1.5 1.75 2.0 584 568 552 584 568 552 584 568 552 146 142 138 146 142 138 146 142 138 1180 1150 1120 1180 1150 1120 1180 1150 1120

Fiber PCE

-

-

-

3

3.5 4

6

7

8

4.5 5.25 6

4.5 5.25 6

4.5 5.25 6

2.2. Preparation of the specimens and testing Concrete mixtures were mixed in a laboratory mixer. The cement, silica fume and Aerosil 380 were first mixed in the dry state for one minute, then coarse and fine aggregates were added and mixed. Pre-prepared water-PCE solution was added to the dry mixture and mixed for 2 min to obtain a homogenous fresh concrete mixture. Finely the polypropylene fibers were added for preparing FRC. Mixing was continued for further five minutes to achieve uniform distribution of the fiber. Consistency of fresh concrete was determined by the slump test according to EN 12350-2. Cubes (100 mm) were prepared from each batch for the compressive strength test, prisms (100x100x400 mm) – for the flexural strength test and cubes (70.7 mm) – for the impact test. The samples were cured in normal conditions for the hardening of concrete (90- 100% RH at 20± 3 o C) during the test period. After 28 and 360 days, the samples were tested for compressive strength, flexural strength and impact resistance. The drop-weight impact test is a simple one that is conducted on small-sized specimens and requires no sophisticated measurement systems. The impact test was performed in accordance with the impact testing procedures recommended by ACI Committee 544. The scheme of the device for testing impact resistance is shown in Fig. 1. The test was carried out by dropping a hammer weighing 10 N from a height of 1000 mm repeatedly on a 30 mm diameter hardened steel ball, which is placed on the top of the center of a cubical specimen. From this test, impact resistance was estimated as the specific energy absorption capacity for the initial visible crack and final crack (impact failure energy) of each specimen.