Fireproof inorganic coatings based on sodium silicate solution with intumescent additions were prepared and tested to assess their ability to limit the negative effect of a fire. The intumescent materials were obtained by the alkali activation of waste glass powder (obtained by the grinding of recycled soda-lime culet) and slag (waste resulting from the metallurgical industry). The replacement of talc (used as filler in paint formulation) with the intumescent materials obtained by the alkaline activation of waste glass powder (WGP), determined an increase in the intumescence coefficient (up to 65%) and decreased the activation temperature of this process. To evaluate these coatings’ abilities to prevent or delay the temperature increase in metal structures, the paints were applied on steel plates and tested in direct contact with the flame of a butane burner for 60 min. The coatings prevented the increase in the steel substrate temperature over one considered critical (500°C) for steel mechanical properties; the combination of two coatings, with different intumescence activation temperatures, correlated with the increase in the coating’s thickness, sensibly reduced the rate of temperature increase (up to 75%) in the steel substrate.

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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.