Development of a paste for passive fire protection mainly composed of granulated blast furnace slag

In this study, the behavior of granulated blast furnace slag as a component of passive fire protection materials is evaluated. To investigate the performance of blast furnace slag, different replacement levels from 0 to 80 wt% have been analyzed. Different properties, such as physical, mechanical, and insulating capacity and leaching, have been thoroughly analyzed. Pastes made of a combination of granulated blast furnace slag and gypsum can be potentially used as a component in construction materials for passive protection against fire. The results indicate that the mechanical properties diminish when the slag content increases. It was concluded that replacements lower than 60 wt% comply with all the mechanical demands. A slight reduction of the insulating capacity was observed when the slag content was increased. Additionally, no heavy metal leaching problems have been detected. Significance The current research presents the results of a study to reuse granulated blast furnace slag in fire‐resistant pastes with gypsum. Blast furnace slags decrease the thermal diffusivity of the paste at high temperatures, improving its insulating capacity. It facilitates its use in specific and high‐value applications with similar properties to commercial materials and increases the recycling rate with any heavy‐metal leaching problem.