PSI - Issue 83

Wijdane Kachach et al. / Procedia Structural Integrity 83 (2026) 154–161

156

Comparing several forms of FRP reveals that, although carbon fibers are more thermally stable than glass or basalt substitutes, all of them lose performance at high temperatures. Aramid FRP wrapping can counteract some impacts, according to (Xu et al., 2024), with mild heating at 200°C occasionally increasing compressive strength and decreasing weight loss. However, all systems—aramid, basalt, and carbon FRP—will eventually experience bond breakdown at higher temperature thresholds, which will reduce their ability to withstand extended fire exposure. After a fire, damage continues. According to (Xu et al., 2024), repeated salt exposure and fast freeze-thaw cycles are two more environmental stressors that worsen the deterioration of mechanical qualities. After the fire, CFRP once more shown somewhat superior retention than GFRP or BFRP, although residual compressive strength and stiffness gradually decreased. All fiber types showed notable modulus and strength decreases in spite of these relative variations, demonstrating that fire exposure hastens longer-term susceptibility to environmental degradation.

Tab. 1. Experimental results found in the literature (Yun et al., 2025)

Author

Type

Fiber type

Vf (%)

Tg (°C)

Td (°C)

Diameter (mm)

ft (MPa)

Ecfp (GPa)

Temperature range (°C)

(Yun et al., 2025b) (Zhou et al., 2019) (J. Xu et al., 2020) (Ashrafi et al., 2017) (Ashrafi et al., 2017) (Ashrafi et al., 2017) (Wu et al., 2023)

Rod

CFRP

60

80

300

6.4

2070

124

20–600

Tendon CFRP

65

126

350

8

2070

156

25–500

Tendon CFRP

N/A

220

300

5

2675

176.3

20–600

Rebar

CFRP

75

110

300

5

2100

150

25–450

Rebar

CFRP

85

110

300

5

1900

125

25–450

Rebar

CFRP

85

105

300

5

1700

117

25–450

Rebar

CFRP

60

95– 125

320– 350

7

2445

166

25–300

Design practice considers preventative measures essential due to these weaknesses. Since FRP materials cannot withstand fire on their own, they need to be protected by enough concrete cover or external fireproofing, as highlighted by (Yun et al., 2025). ACI 440.1R-15 and other international design recommendations state that enough cover thickness is necessary to postpone the exposure of FRP bars to critical temperatures and stop the quick loss of structural capacity in areas that are susceptible to fire. These issues are further supported by experimental results. (Protchenko, 2022) found that after two hours of fire exposure, beams reinforced with hybrid FRP (carbon/basalt) lost up to 70% of their load-carrying capability, whereas beams reinforced only with BFRP frequently failed before the test period was over. Given that basalt-based composites perform worse than hybrid or carbon fiber systems, our findings highlight the extent of temperature sensitivity in FRP reinforcement. When FRP-reinforced concrete members are subjected to fire, mechanical stiffness and elastic modulus decrease in tandem with strength, according to early analytical work by (Saafi, 2002). Tests have revealed axial and flexural stiffness losses of over 50%, with comparable deterioration patterns seen in the tangent modulus, a measure of post peak stiffness. These decreases often show either linear or exponential deterioration curves and are proportional to temperature and fire duration. The main flaw in FRP was found to be the resin component, which loses the majority of its mechanical qualities close to or above its glass transition temperature (Tg, usually 100–180 °C) and seriously impairs the reinforcement's ability to support loads. This is especially true when thermal post-curing is not applied. Furthermore, it was shown by (Saafi, 2002) that the deterioration process is cumulative over time, with flexural and shear strength decreasing as exposure time increases. As little as 40 minutes of fire exposure can seriously reduce the useable structural strength of GFRP-reinforced beams. Although massive concrete covers helped to postpone the deterioration, they were unable to stop it completely.