Design principle of tunnel fire retardant coating

A lot of work has been done in the research of tunnel fire retardant coatings at home and abroad. For example, domestic scholars put forward tunnel fire retardant coatings with silicate as the main base, aluminum hydroxide, expanded vermiculite and magnesium trisilicate as fillers, and sodium tetraborate as flame retardant additives; Aiming at the characteristics that tunnel masonry is not resistant to high temperature, a kind of fire retardant coating for hydraulic tunnel with inorganic cementing material as the main component is developed. The coating can be used for fire protection of both steel structure and concrete. A new type of physical intumescent flame retardant was developed, and a halogen-free, environmentally friendly and excellent flame retardant physical intumescent fire retardant coating was prepared with expandable graphite as the main component.

However, foreign scholars have developed inorganic fire retardant coatings for building surfaces, which are composed of hydraulic white cement, water glass, vermiculite, expanded perlite and inorganic glass fiber. This paper introduces a kind of fire retardant coating mainly composed of sepiolite, travertine, reinforced fiber, high alumina cement and amorphous silica. The coating has good thermal insulation and explosion-proof performance, and can be applied to building external walls, tunnels and the like. A fireproof coating for metal and concrete surfaces is composed of bentonite, aluminum silicate, wollastonite, magnesium silicate, glass beads and some porous fillers, and the binder is one or more of water glass, portland cement, gypsum and phosphate.

The tunnel fire retardant coatings reported above are all based on inorganic materials such as water glass, cement, white cement, high alumina cement and phosphate, with perlite, expanded vermiculite, microporous calcium silicate, diatomite, fly ash glass beads, sepiolite powder and talcum powder as fillers, glass fiber, steel fiber and polypropylene fiber as reinforcing materials, and oxides of aluminum, magnesium, boron and zinc containing crystal water as flame retardants. However, according to the patents of various fire retardant coatings at home and abroad, the coatings used to protect nonflammable building structures include organic intumescent thick slurry coatings and light inorganic fire retardant coatings. At the fire temperature, the carbon foam layer of organic intumescent fire retardant coating is easy to disappear gradually, which reduces the fire prevention and heat insulation effect. No matter how good the coating is, when the coating is increased to 4 mm, the fire resistance limit is only1h. Inorganic fire retardant coatings can meet the fire resistance requirements of 1 ~ 2h or even longer due to their light density, low thermal conductivity and good fire resistance. However, fire retardant coatings composed of pure inorganic substances are easy to be hard, brittle, cracked and peeled off. Therefore, in the study of tunnel fire retardant coatings, the research technical route of non-intumescent, pollution-free waterborne organic-inorganic composite coatings should generally be adopted.