The basic components of thick coated fire retardant coatings for steel structures are cementing materials (Portland cement, magnesium oxychloride or inorganic high temperature binder), aggregates (expanded vermiculite, expanded perlite, aluminium silicate fiber, mineral wool, rock wool, etc.), chemical additives (modifiers, hardeners, waterproofing agents, etc.) and water. Portland cement, magnesium oxychloride cement and inorganic binder are the basic materials of fire retardant coatings for steel structures. The commonly used inorganic binders include alkali metal silicates and phosphate materials. Liaoning magnesia-chrome brick

But free alkali metal ions often exist in alkali metal silicates, and acid gases and CO2 in the air will react with them. If alkali metal silicate is used as the base material of coatings alone, the film will not be water-resistant, moisture-resistant and weatherproof, and the coating is prone to cracking, dedusting and other undesirable phenomena. Therefore, if alkali metal silicate is used as the base material of fire retardant coatings for steel structures, the key problem to be solved first is to modify it, that is, to solve the problem of restraining free alkali metal ions.

Phosphate binders are also commonly used inorganic binders. When used as the base material of fire retardant coatings, the reaction between alkaline oxides and acid gases in the air is avoided, thus improving the physical and chemical properties of coatings such as weatherability and water resistance. However, the molar ratio of M/P in phosphate binders (M refers to metal, P refers to phosphorus) has a direct impact on the storage stability, water resistance and adhesion between coatings and steel substrates. Therefore, it is very important to control the molar ratio of base material in the development of fire retardant coatings for steel structures based on phosphate.

Because of the thick coating and large amount of fire retardant coatings for thick steel structures, the weight of buildings is increased. Therefore, attention should be paid to the addition of some lightweight materials and high-efficiency thermal insulation aggregates to reduce the density of the paint. The most used lightweight thermal insulation aggregates are expanded vermiculite and expanded perlite.

Vermiculite is a kind of aluminosilicate mineral containing iron and magnesium. It has layered structure and crystalline water between layers. When it is heated and expanded, it will squirm like a leech, so it is called vermiculite. After drying, crushing and screening, vermiculite is calcined at 850-1000 temperature, and the particles will expand more than 20 times, forming expanded vermiculite. Its density is 80-200 kg/m3, thermal conductivity is 0.17-0.25 W/(m.K), fire resistance is strong, sound absorption, sound insulation is good, non-toxic and tasteless, it is an important blend of fire retardant coatings.

Perlite is a glassy rock. It can be expanded to about 20 times after breaking, sieving, preheating and instant roasting, forming an expanded perlite with honeycomb like structure. Expanded perlite is extremely light in weight, with a bulk density of 80-250kg/m3 and thermal conductivity of 0.042-0.076W/(m.K). It has the characteristics of heat preservation, heat insulation, non-flammability, non-toxicity and good chemical stability. It is also an important filler in fire retardant coatings.