Study On The Prescription Of Super-thin Intumescent Fire Retardant Coatings For Steel Structures

Steel structure is increasingly used in the construction industry at home and abroad, but it has difficulty in resisting fire. Its fireproof limit of steel for architecture is only 15min. The aim to protect steel structure from fire is to increase its fireproof limit, thus preventing distortion, even collapse resulting from the sharply increasing temperature. There will be more time for firemen to put down the fire and evacuate people. So lots of casualties and huge economical loss caused by the fire will be avoided or reduced.Among all the protection methods of steel structures, it's the most effective, economical, and practical to spread fire retardant coatings on them directly. A new type of super-thin intumescent fire retardant coatings with excellent fireproof performance and decoration was much developed in 1990s. It could be used widely. Preparation and fireproof mechanism of super-thin fire retardant coatings were studied in the paper.Monobasic ammonium phosphate(ADP) was selected as dehydrating agent, and melamine(MEL) as blister, pentaerythritol(PER) as carburetant during the experiments. The effect of the components on the performance of fire retardant coatings was studied. Firstly, three levels of three factors in the fire retardant system were determined based on a serial of preparatory experiments and the given literature. Secondly, the orthogonal experiments were carried out for fire retardant system through simple fireproof experimental setting. The fireproof time was evaluated in the orthogonal experiments. An analysis of the results through L₉(3⁴) orthogonal table indicated MEL had the greatest influence on fireproof performance of fire retardant coatings in the fire retardant system, next PER, last ADP. The optimal ratio of prescription was determined asADP:MEL:PER = 16.9%:21.2%:6.3%.Theoretically, every process and the possible reaction in super-thin intumescent fire retardant coatings were deduced. It was proposed that the strength and viscosity of inorganic charring layer were key factors to the fireproof time during the decomposing process of super-thin intumescent fire retardant coatings for steel structures. It was found that strength of charring layer was enhanced and physical properties of the coatings were improved when pigments and stuffings with appropriate amount were added. The optimal amount (quality per cent) of TiO₂ was 5.3%, and that of ZnO was 2.5%.