Effect of silica fume and waste rubber on the performance of slag‐based geopolymer mortars under high temperatures

In this study, the fire resistance of slag‐based geopolymer mortars was investigated and the effect of silica fume (SF) and waste rubber (WR) on this resistance was determined. In slag‐based geopolymer mortars activated using 12M NaOH solution, 0%, 5%, and 10% by weight SF was substituted for slag; 0%, 5%, 10%, and 15% WR by volume were substituted for fine aggregate. The samples that completed the curing period were exposed to temperatures of 250°C, 500°C, and 750°C for 1 h, and the mechanical (compressive, flexural and splitting tensile strengths, and impact resistance), physical (weight change and sorptivity) and microstructure (scanning electron microscopy [SEM] and energy dispersive spectroscopy [EDS]) properties of these samples were examined. The compressive strengths of the samples without WR were between 48.10 and 60.97 MPa, and the samples without SF were between 28.52 and 48.10 MPa. Strength losses at 750°C were between 51.5% and 73.5%. As the SF substitution increased, the samples' mechanical and physical properties improved, whereas as the WR substitution increased, the samples' mechanical and physical properties declined. While the SF substitution had a positive effect on the fire resistance of the samples, the WR substitution had a negative effect. It is thought that the choice of geopolymer binder as a binder in the mortar and the use of waste tires as aggregate contribute to the literature in terms of both preventing environmental pollution and ensuring the recycling of these materials.