PSI - Issue 68

Rami Hawileh et al. / Procedia Structural Integrity 68 (2025) 259–265 R. Hawileh et al./ Structural Integrity Procedia 00 (2025) 000–000

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members, as it becomes more vulnerable to spalling and strength deterioration under high temperatures. In contrast, HSC-ST+PP demonstrates significantly better performance, retaining 85% of its original strength at 600°, surpassing Eurocode 2’s strength reduction values by 40%. This distinctive behavior highlights the beneficial combination of steel and polypropylene fibers. The dense nature of the mix design, crack-bridging capabilities of steel fibers, and stress relief provided by the voids introduced by PP fibers all play a crucial role in preserving the concrete's structural integrity under high temperatures. This synergy enables HSC-ST+PP to outperform both NSC and HSC-ST in terms of strength retention and fire resistance.

(a)

(b) Fig. 1: Concrete samples after being exposed to 600°C: (a) Mix HSC-ST; (b) Mix HSC-ST+PP

100 120

y = -7E-05x 2 + 0,0205x + 89,535 R² = 0,9285

HSC-ST HSC-STPP Poly. (HSC-ST) Poly. (HSC-STPP)

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y = -0,0004x 2 + 0,1456x + 83,797 R² = 0,9297

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1000

Compressive Strength f'c (MPa)

Temperature (ºC)

Fig. 2: Compressive strength versus temperature for both mixes