What is the quantitative relationship between the expansion ratio of the carbon foam layer of intumescent fire retardant coating and its fire resistance performance?
Publish Time: 2025-10-23
In modern building safety systems, steel structures are widely used due to their high strength, lightweight, and easy construction. However, their fire resistance is poor and they tend to soften and destabilize rapidly at high temperatures, making them a key weakness in building fire protection design. To address this issue, intumescent fire retardant coatings for interior steel structures have emerged. Applied to the surface of steel structures, intumescent fire retardant coatings expand upon exposure to heat during a fire, forming a porous, dense carbon insulation layer that effectively isolates heat transfer and slows the temperature rise of the steel structure, thereby significantly improving its fire resistance. The coating's "expansion ratio," as a core performance indicator, has a close and quantifiable inherent relationship with its ultimate fire resistance performance.1. Definition and Mechanism of Expansion RatioThe expansion ratio refers to the degree to which a fire retardant coating expands in volume upon exposure to heat. This process depends on the coating's internal "expansion system," which primarily consists of three components: an acid source, a carbon source, and a gas source. When the temperature rises above 200°C, the acid source decomposes to produce acidic substances, which promote the dehydration and carbonization of the carbon source. Simultaneously, the gas source releases a large amount of non-combustible gas, driving the molten material to rapidly foam and expand, ultimately forming a honeycomb-shaped carbon insulation layer.2. Positive Correlation between Expansion Ratio and Thermal Insulation EfficiencyThe expansion ratio directly determines the thickness and pore structure of the carbon layer, which in turn affects its thermal insulation performance. Research has shown that within a certain range, a higher expansion ratio results in a thicker carbon layer, more and more uniformly distributed pores within it, and lower thermal conductivity. Experimental data shows that increasing the expansion ratio from 5 to 15 reduces the thermal conductivity of the carbon layer by over 30%, significantly slowing the transfer of heat to the steel substrate. This means that under the same fire conditions, coatings with high expansion ratios can prolong the time it takes for steel components to reach critical temperatures, thereby extending their fire resistance. For example, beams meeting a 1.5-hour fire resistance rating typically require a coating expansion ratio of 8-12, while a 2.5-hour fire resistance rating may require even higher expansion performance.3. Nonlinear Relationship and Performance BottlenecksAlthough the expansion ratio is positively correlated with fire resistance, this relationship is not linear and infinite. When the expansion ratio is too high, the char layer may become too loose and weak, making it prone to cracking and flaking under high-temperature airflow or fire water impact, thereby weakening its protective effect. Furthermore, excessive expansion can cause internal pores in the char layer to connect, forming "heat channels" and reducing overall insulation efficiency. Therefore, the ideal expansion ratio should be within an "optimal range" that ensures sufficient insulation thickness while maintaining the density and mechanical strength of the char layer. Currently, the expansion ratio of high-quality indoor intumescent fire retardant coatings is typically controlled between 8 and 15 times to achieve the optimal balance between fire resistance and structural stability.4. Comprehensive Factors Affecting Fire ResistanceIt is important to note that the expansion ratio is not the only factor determining fire resistance performance. The coating's original thickness, bond strength, durability, and construction quality are also crucial. For example, even with a high expansion ratio, if the coating lacks adhesion and peels off in the early stages of a fire, it will be ineffective. Furthermore, the cross-sectional modulus of different steel components also affects the heating rate. Therefore, in practical applications, the coating thickness and formulation performance must be comprehensively designed based on the component type and fire resistance rating requirements.The expansion ratio of the carbon foam layer of intumescent fire retardant coatings has a clear quantitative positive correlation with its fire resistance performance, making it a key parameter for evaluating coating effectiveness. Optimizing the formulation to achieve moderate and stable expansion is key to improving the fire resistance of steel structures.
