Effect of Activator Type on the Fire Resistance of Geopolymer Binders Incorporating Construction and Demolition Waste and Slag

Increasing circular economy trends have encouraged researchers to develop new binding materials such as geopolymers. In the context of waste material utilization, geopolymers are considered suitable alternative materials to cement. However, early geopolymer studies primarily focused on the development of fire-resistant materials. Parallel to the growing circular economy trend, the utilization of construction and demolition waste in binding materials has become increasingly popular. Previous studies have shown that construction and demolition waste-based geopolymers can achieve comparable performance to those produced with conventional precursors such as blast furnace slag and fly ash. This research aims to assess the fire resistance of geopolymers produced using construction and demolition waste and ground granulated blast furnace slag. Different Na₂SiO₃/NaOH ratios ranging from 0 to 1.00 were evaluated as the main experimental parameter. The results indicate that among the tested mixtures, the geopolymer activated solely with 10 M NaOH exhibited the highest fire resistance performance after exposure to 600°C, with flexural and compressive strength losses of 79.8% and 53.6%, respectively. The addition of Na₂SiO₃ reduced the fire durability of geopolymer mortars, increasing the flexural strength losses to approximately 84–88%. In addition, it is expected that these results may vary depending on the type and reactivity of the raw materials used.