# Effect of Fireproof Coatings on the Post-Fire Behavior of CFRP Composite Sheets
## 3 Experimental Results and Discussion
### Standard Fire Condition  
Under the standard fire condition, the temperature reached 841.8 \({}^{\circ}\)C, 902.3 \({}^{\circ}\)C, and 945.3 \({}^{\circ}\)C after 0.5 h, 0.75 h, and 1 h heating, respectively. Figure 9 depicts CFRP sheets after exposure to the standard fire (before and after coating removal). The fireproof coatings on the surface of CFRP sheets after 0.5 h and 0.75 h of standard fire heating exhibited an oxidation phenomenon, resulting in color darkening. However, after 1 h of heating, the fireproofing coatings also showed cracks. After removing the fireproof coatings on the surface, the morphology of CFRP sheets heated for 0.5 h and 0.75 h remained almost unchanged from that at ambient temperature. In contrast, the debonding of fibers and resin occurred in CFRP sheets after 1 h of heating. Figure 10 presents the typical failure modes of CFRP bending test specimens after exposure to the standard fire conducted at ambient temperature.  
Figure 9: CFRP sheets exposed after 0.5 h, 0.75 h, and 1 h standard fire: (**a**) before the removal of coatings; (**b**) after the removal of coatings.  
Figure 11 displays the load-deflection curves of CFRP specimens with different thicknesses after exposure to the standard fire. These load-deflection curves also demonstrated linear elastic properties. Upon reaching a specific load level, the specimen experienced sudden failure and brittle damage. Notably, the peak loads of CFRP sheets after 1 h of heating showed a significant reduction compared to those after 0.5 h and 0.75 h of heating.  
Figure 11: Load–deflection curves of CFRP sheets with various thicknesses after standard fire exposure: (**a**) 2 mm thickness; (**b**) 3 mm thickness.  
Figure 10: Failure modes of CFRP specimens are: (**a**) after 0.5 h standard fire; (**b**) after 0.75 h standard fire; and (**c**) after 1 h standard fire.  
The flexural properties of CFRP specimens after exposure to standard fire are shown in Table 4. The thickness of the fireproof coatings under standard fire conditions amounted to 35 mm, which played a dominant role in influencing the fire protection effectiveness of the coatings. Conversely, variations in coating types and sheet thicknesses exhibited minimal impact on the post-fire flexural performance. The reduction factors of flexural strength and flexural modulus of CFRP sheets coated with coatings of 35 mm, heated for 0.5 h and 0.75 h, were approximately 0.90, indicating that the fireproof coatings provide effective fire protection to the CFRP sheets during these periods. However, after 1 h heating, the flexural strength and modulus for CFRP sheets with coatings of 35 mm thickness exhibited a significant decrease to only 0.07 and 0.13 times those at ambient temperature, implying the reduced effectiveness of coatings in protecting CFRP sheets after relatively long exposure to elevated temperatures (i.e., beyond 900 \({}^{\circ}\)C under the standard fire condition), leading to significant degradation in the performance of CFRP composites. This failure can be related to the high-temperature resistance of the coating and the effectiveness of the fire barrier. The fracture deflection remains almost unchanged under standard fire conditions. Consequently, it can be concluded that CFRP sheets coated with Type C1 and C2 coatings of 35 mm thickness demonstrate a fire-resistance duration exceeding 0.75 h under standard fire conditions.  
According to the Chinese specification GB50016-2014 [38], under the standard fire condition, CFRP sheets coated with Type C1 and C2 coatings of 35 mm thickness meet the requirements of fire-resistance class IV (columns), class IV (beams), and class III (floor slabs), respectively.