Design Of Super-Thin Fire Resistant Coating For Steel Structure And Study Of Its Characteristics Of Pyrolysis

Steel structure has been widely used in the domestic and overseas construction industry for its advantages such as high strength, low deadweight and wonderful ductility. Though incombustible, steel materials possess high heat conductivity and poor fire-resisting performances. Without fire precaution measures, their fireproofing limit is just a quarter of hour, far less than the fireproofing standard time specified by the national construction design specifications. Effective fire precaution means should be taken to strengthen the fire resistive ability of steel structure.Various fire precaution means have been utilized to protect steel structure and fire resistant coating is an ideal, effective, economical and practical one. A new type of fire precaution coatings has been developed in 1990s, with super thin-filmed fire resistivity for steel structure coating which possesses excellent performances both decorative and fire-resisting properties. In this paper, investigation on the formulation of the new kind of coating and the characteristics of thermal degradation of fire resistant coating, the components of fire retardant system, and fire retardant system have been presented, besides, the kinetics of fire retardant coating is also studied.Super thin-filmed fire resistant coating for steel structure consists of binders, flame-retardants and other components. Binders greatly influence the properties of the intumescent coating, ensuring its physicochemical properties under regular ambient and nonflammability and excellent intumescent effect in case of fire. The mixture of amino resin and acrylic resin has been selected based on the comparison of the charring layer characteristics from different resin systems. The ratio of the resins also has great influence on the physicochemical and fire-resisting properties of the coating and the optimum ratio and added amount of the resins have been decided.Fire-resisting performance of the coating is determined by the fire retardant system. Ammonium polyphosphate (APP), is selected as dehydrating agent, and melamine(MEL)as blister, pentaerythritol (PE) as carburetant. The effects of the components on theperformances of the coating have been studied and the formulation has been optimize.The ratio of the components also has effect on the general property of the coating. Effects of the consumption of the pigment and filling on the properties of the coating have been investigated and the optional consumption is determined by adjusting the ratio of the pigment and the binders. The coating has high solid content and great surface tension. Rheological agent and flow agent are added to improve the rheologic and leveling property, and storage stability and physicochemical properties are promoted simultaneously. The adhesive capacity of resins is too high to wet powdery materials,adding solution can reduce the skin free energy, and it help to grind and disperse. During the construction, the adding of solution can modify the adhesive capacity and leveling property, so it can ensure the excellent appearance and other physicochemical property.By advanced apparatus and analysis methods such as thermogravimetry (TG),differential thermal analysis (DTA), the thermal degradation behavior of both the components and the fire retardant system is studied. At the same time,the influence of different base resins, the content of base resins, the ratio of components of fire retardant system on the thermal degradation behaviors of fire retardant coating are presented. The results of the TG and DTG curves show that, in the whole intumescing process, APP, PER and MEL cooperate with each other and synergism is generated; The kind of base resin and its contents, the ratio of the component of fire retardant system and their contents all have great influence on the thermal degradation behaviors of fire retardant coating; The concentration of oxygen has no influence on the thermal degradation of fire retardant coating below 345℃, while the influence can not be neglected above 345℃, but compare with the factors mentioned previously, the influence is small.The kinetic method of thermal analysis is adopted to study the kinetic model of pyrolysis of fire resistant coating, it show that the courses of thermal degradation may be divided into five stages, the function mechanisms of every stage are not the same as well: the first stage can be described as one-dimensional diffuseness reaction Dl,the second, the third stage can be described as 1.5 order chemistry reaction RO(1.5),the fourth stage can bedescribed as second-order chemistry reaction RO(2), the last stage can be described as first-order chemistry reaction RO(1).At the same time, the pyrolysis parameters and equations of kinetics are solved out.