Fire Behavior and Adhesion of Magnesium Phosphate Coatings for the Protection of Steel Structures

This paper presents the main properties of magnesium phosphate cements (MPCs) to be used as coatings for passive fire protection of steel structures. The influence of various additions, i.e., waste glass powder, fly ash, a styrene–acrylic dispersion, and expandable graphite, on the fire behavior and the adhesion to steel substrates of magnesium phosphate coatings is presented in this paper. The setting time of studied cements is extended when magnesia, the main component of MPCs, is partially replaced with fly ash or/and waste glass powder. The mineralogical composition of these cements, before and after thermal treatment at 1050 °C, was assessed by X-ray diffraction and could explain the changes in compressive strength, volume, and mass recorded for the thermally treated specimens. The studied magnesium phosphate coatings have a good adherence to the steel substrate (assessed by a pull-off test) both before and after direct contact with a flame (fire test) and decrease the temperature of the steel substrate by 30% with respect to the one recorded for the uncoated steel plate.