Preparation and properties of hydrotalcite-foamed magnesium phosphate cement for fire protection of steel structures

Abstract

Foamed magnesium phosphate cement (MPC) is prepared for the fire protection of steel structures based on the carbonate decomposition reaction of hydrotalcite in acidic MPC paste. Hydrotalcite decomposes in an acidic MPC slurry to generate CO2, and approximately 50% of the theoretical gas generation remains in the MPC slurry to form foamed MPC with an apparent density of < 650 kg/m3 and 1-d compressive strength of > 4.0 MPa. The actual gas production of hydrotalcite in the MPC slurry gradually increases as the hydrotalcite content increases and the M/P ratio decreases. The fine hydrotalcite particles refine the pores and obstruct the paths between them, resulting in closed and uniform pores. When the thickness of the foamed MPC coating on the steel plate surface is only 6.0 mm, the temperature on the steel plate back after being subjected a 60 min fire resistance test is about 400 °C, which is significantly lower than the critical temperature (538 °C) for the steel structure to remain stable after encountering fire. Foamed MPC exhibits excellent fireproofing performance owing to its high porosity, low thermal conductivity, the release of CO2 in the pores, and the dehydration of hydration products, which retards heat transfer in case of fire.