Waste glass recycling in magnesium phosphate coatings for the fire protection of steel structures

The paper focus on the valorization of soda lime silica waste glass powder in the manufacture of fire protective coatings, for steel structures, based on magnesium phosphate cements (MPCs); waste glass powder is used to substitute part of dead burned magnesia (one of the main components of MPC) or to obtain lightweight aggregate (Gt) by alkali activation with NaOH solution followed by thermal treatment at 900 °C for 1 h. Commercially available expanded perlite is also used in MPCs to replace dead-burned magnesia or as lightweight aggregate. The MPCs mineralogical composition (assessed by XRD), microstructure and adhesion to steel plate (assessed by SEM) as well as the changes which occurs during the thermal treatment (assessed by DTA-TG analyses) are used to explain the fire behaviour and insulation properties of these coatings. The studied MPC coatings adhered very well to the steel plate, even after two consecutive fire tests (direct contact with butane flame for 60 min) and effectively decreased the substrate temperature. The coating thickness plays an important role in decreasing the temperature of the steel substrate; for thinner coatings the rate of temperature increase, in the first 10 min, is 3–4 times higher (depending on the coating composition) as compared with thicker coatings. The presence of lightweight porous aggregates, such as expanded perlite or Gt, combined with the increase of water content of MPC coatings, contributes to the decrease of the steel plate temperature during the fire test.