# Effect of Fireproof Coatings on the Post-Fire Behavior of CFRP Composite Sheets
## 1 Introduction  
The growing demand for high-performance, reliable, cost-effective, and eco-friendly structural systems is driving increasing attention toward the utilization of novel materials in engineering practices. Among these materials, there is a notable emphasis on carbon fiber-reinforced polymer (CFRP) composites due to their exceptional performance [1; 2; 3]. CFRP composites are non-metallic materials composed of carbon fibers as the reinforcing material, synthetic resin as the matrix material, and the appropriate amount of auxiliary agents [4; 5]. [PERSON] and [PERSON] [6] prepared \"green\" recycled polyester based on PET and oleic acid, which could be used to prepare CFRP composites, making it very environmentally friendly. CFRP composites exhibit higher strength-to-weight ratios and exceptional durability in comparison to conventional steel reinforcements. Their high malleability allows them to be fabricated into various shapes and sizes, including profiles, sheets, plates, and bars, making them suitable for diverse engineering applications [7]. Significantly, CFRP composites find applications in two primary civil engineering fields: as structural reinforcement elements for existing structures and as elements to partially or entirely replace conventional steel bars in newly built structures [8; 9; 10; 11; 12]. However, given the potential exposure of infrastructures to fire hazards, it becomes essential to address the concerns related to their performance under fire conditions whenconsidering their implementation in structures. Notably, the first author, [PERSON] et al., undertook systematic investigations into the behavior and mechanical performance of high-strength steel S460, S690, and S960, both under fire conditions and after cooling down from fire [13; 14; 15]. These investigations utilized various methodologies, including controlled fire simulations and rigorous material testing procedures. The findings from these studies revealed significant degradation in material properties, including strength, modulus, and ductility. The methodology and findings of these studies provide key guidance for the design of the experiments in this paper, particularly with regard to fire simulation and the selection of experimental parameters. Based on the experience of these studies, it is possible to more accurately determine the material performance metrics that need to be evaluated. Under fire conditions, CFRP composites are directly exposed to heat flow and flame as structural reinforcement elements. While they serve as internal bars, they are not directly exposed. Despite the concrete cover insulating CFRP elements from heat flow, the concrete cover may fall off when the temperature exceeds a certain threshold, exposing CFRP elements to fire [8]. Additionally, high temperatures could lead to a decrease in the bonding strength between FRP composites and concrete [16]. Carbon fibers can withstand elevated temperatures exceeding 2000 \({}^{\circ}\)C [17]. However, when subjected to elevated temperatures, CFRP composites could experience significant degradation in their mechanical properties due to the resin's decomposition. This degradation becomes pronounced as the temperature surpasses the glass transition temperature (_Tg_), usually ranging between 50 \({}^{\circ}\)C and 120 \({}^{\circ}\)C [18; 19]. During this phase, a transition to a rubbery state occurs in the resin, leading to fiber-resin debonding as well as a rapid decline in strength. Subsequent cooling from this temperature range permits partial recovery of the mechanical performance of CFRP composites [20; 21]. It should be noted that surface temperatures in hot environments exposed to sunlight can also reach _Tg_. Once the temperature surpasses the decomposition temperature (_Td_), which generally falls between 300 and 400 \({}^{\circ}\)C, the resin matrix almost completely degrades, causing a substantial decrease in material properties.