PSI - Issue 42

Martina Drdlová et al. / Procedia Structural Integrity 42 (2022) 1382–1390 Drdlova et al/ Structural Integrity Procedia 00 (2022) 000 – 000

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Table 2 Summary of physico-mechanical parameters of test samples

Designation/ Parameter Bulk density

HPFRC

HPFRC 3

PC

PC PU

PC 3

PC DR

PC MESH UHPFRC UHPFRC 3

2480 14.1

2489 28.9

2353

2310 9.76

2373 17.1

2479 10.7

2394 16.7

2583 36.5

2664 43.2

Flexural strength (MPa)

6.1

Fig. 2 Comparison of bending stress/deformation curves for all groups of specimens

Assessing the effect of material itself on the flexural strength in the quasistatic regime, The UHPFRC brings the best performance, as expected. The flexural strength of UHPFRC is more than six times higher than that of plain PC concrete. In terms of reinforcement and strengthening, the introduction of rebar reinforcement has the highest effect on the flexural strength and load bearing capacity, followed by reinforcing mesh (increase in flexural tensile strength by about 180% in both cases). The fibres also increase the flexural tensile strength quite effectively (by about 75% compared to the material without fibre reinforcement) and also increase the overall load carrying capacity. External reinforcement with polyurea increases the flexural strength at a level similar to the addition of fibres, but there is an immediate sharp drop in stress once the critical strength is reached. The results of the impact tests are summarized in Table 3. For each variant, a minimum of 3 determinations were carried out. The impact toughness was calculated according to equation (1). The comparison of the specimens without reinforcement shows the highest impact strength of the UHPFRC specimens (41.03 kJ/m 2 ). As expected, the PC material showed the lowest impact resistance (13.4 kJ/m 2 ). Unlike the UHPFRC and HPFRC variants, the PC material did not contain any fibre reinforcement. However, even the PC (PCDR) specimens reinforced with fibres exhibited lower impact toughness (16.5 kJ/m 2 ) compared to the high-value concrete variants UHPFRC and HPFRC. Comparison of the high value concrete variants shows higher impact resistance of the material with fine-grained aggregate and higher strength (UHPFRC). The difference is quite significant (20.5 kJ/m 2 for HPFRC vs. 41.03 for UHPFRC) and corresponds to the results of the quasi-static tests and results published by Luo (2001). Strong concrete matrix is beneficial for improving the impact resistance of the concrete. The pullout of steel fibres from the high strength matrix can absorb a large amount of energy generated by the impact process.