Study on lightweight design and fire insulation performance of brucite-based magnesium phosphate fire retardant coating

Magnesium phosphate cement has high strength, high temperature resistance and good bonding properties, but its high density limits its application in insulation and heat preservation as well as in fire protection of steel structures. In this study, natural water mica and dihydrogen phosphate ammonium were used as the main raw materials, and expanded perlite was introduced to prepare water mica-based magnesium phosphate (BMPC) fireproof coatings. The influence of expanded perlite on the physical and mechanical properties and fire resistance and insulation performance of the material was investigated, and the changes in the microstructure of the material before and after fire resistance were analyzed by XCT, XRD, TG-DTA and SEM. The results showed that the water absorption treatment of expanded perlite had a relatively small impact on the mechanical properties of BMPC; when the content was 20 wt%, the material had the best comprehensive performance, with a density reduced to 647 kg/m3, a 28d compressive strength of 7.2 MPa, a bonding strength with steel plate of 0.51 MPa, and a thermal conductivity reduced by 49.3%, and a fire resistance limit increased to 206 min. The material also exhibited almost no shrinkage. The modified expanded perlite BMPC has the advantages of light weight, high strength and excellent fire resistance and insulation performance, and can be used as a potential material for inorganic fireproof coatings for steel structures.