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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. [ABSTRACT FROM AUTHOR]

The use of waste materials in concrete design draws the attention of researchers. Studies on the use of these materials both as binders and aggregates accelerate. In this study, ground granulated blast furnace slag (GGBFS) based geopolymer concrete was produced. 0, 25, 50, 75 and 100% recycled concrete aggregate (RCA) was used instead of river aggregate in the mixtures. These samples were exposed to temperatures at 100, 200, 400, 600 and 800 °C. The cooling process of these samples exposed to temperature was in 3 different forms: air, oven and water. Compressive strength, ultrasonic pulse velocity (UPV), weight loss, sorptivity and water absorption values of the samples were determined. At the same time, the changes in the microstructure of the samples under the elevated temperature were examined. Compressive strengths of the samples decreased with increasing RCA ratio in the mixture. Samples were severely affected due to elevated temperature, properties of the samples decreased. As the temperature degree increased, the weight loss and sorptivity values of the samples increased. As the temperatures to which the samples were exposed increased, there was a decrease in Ca/Si ratio and an increase in Si/Al ratio. The microstructure of the samples deteriorated at elevated temperatures. [ABSTRACT FROM AUTHOR]

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In this study, mechanical, visual, and microstructure changes of geopolymer concrete exposed to sulfate and salt effects were investigated. Elazığ ferrochrome slag (EFS) and blast furnace slag (BFS)‐based geopolymer concretes which completed curing time were immersed in 5% sodium sulfate (Na2SO4), magnesium sulfate (MgSO4), sodium chloride (NaCl), and magnesium chloride (MgCl2) solutions for 12 weeks. The compressive strength values, ultrasonic pulse velocities, visual inspections, weight, and length changes of the samples were determined in this investigation. In addition, scanning electron microscopy was performed for the microstructure analysis of the samples removed from the solutions. Sulfate solutions had a more negative effect on the samples than salt solutions. As the EFS ratio in the mixture increases, the loss rate in the strength of the samples exposed to sulfate and salt solutions decreased. While samples exposed to sodium chloride, sodium sulfate, and magnesium sulfate solutions occurred weight gain, samples exposed to magnesium chloride occurred weight loss. The samples in salt solutions shrank, while the samples in sulfate solutions expanded. No deterioration occurred on the surfaces of the samples exposed to the solutions for 12 weeks. [ABSTRACT FROM AUTHOR]

• The mechanical properties of the geopolymer concretes decreased somewhat with CR. • As the CR increased, the permeability of the geopolymer concrete decreased. • CR improved the F-T resistance of geopolymer concrete. • The strength of geopolymer concretes under the influence of sulfates increased. Today, due to the increasing demand in the building sector, the interest of researchers in sustainable building materials is increasing. Geopolymer concretes especially come to the forefront due to energy saving and recycling of waste materials. In this paper, slag based geopolymer concretes were produced by substituting crumb rubber (CR) in different proportions instead of fine aggregate. In the samples using 12 M potassium hydroxide (KOH) as alkali activator, river aggregate was used as aggregate. The 28-day compressive strengths of the samples were between 25.95 MPa and 38.17 MPa, between 9.8 MPa and 11.95 MPa at the end of 300F-T cycles, and between 40.65 MPa and 35.70 MPa in sulfate solutions at the end of 12 weeks. Sulfate (5% Na 2 SO 4 and 5% MgSO 4) and freeze–thaw (F-T) (100, 200 and 300 cycles) resistances of the samples cured in the laboratory were determined. As a result of durability tests, the compressive strength, weight changes, sorptivity, water absorption, visual and microstructure analysis of the samples were examined. While the compressive strength of the samples kept in sulfate solutions increased, the compressive strength of the samples exposed to F-T cycles decreased. Sodium sulfate solution caused more strength increase in the samples compared to magnesium sulfate solution. After 300F-T, the strength losses in the samples were over 60%. In general, although the CR slightly reduced the mechanical properties of the control samples, it reduced the permeability of the samples, which increased their durability. [ABSTRACT FROM AUTHOR]

• The effect of GP substitution on the high temperature resistance of geopolymer concrete was studied. • 5 groups of samples were subjected to 5 different temperatures. • GP improved the high temperature performance of geopolymer concretes. • Air cooling affected the samples less negatively than water cooling. Geopolymer concretes provide advantages in terms of recycling waste materials. Geopolymer concretes are advantageous in terms of both limiting the use of Portland cement and recycling waste materials. In this study, 5 different geopolymer concrete mixture groups were prepared by replacing slag with 0.5%, 10, 15 and 20% by weight glass powder (GP). Geopolymer concrete samples prepared by using 12 M sodium hydroxide solution as an alkali activator were cured in the laboratory environment. The samples, which completed their curing periods, were kept at 150, 300, 450, 600 and 750 °C temperatures for 1 h. Compressive strength, weight change and sorptivity values of these samples were determined. These results were interpreted together with the visual inspections and microstructure analyzes (SEM and EDS) of the samples. As the GP substitution rate increased, the mechanical properties of geopolymer concretes decreased. However, GP improved the performance of geopolymer concretes exposed to high temperatures. Cooling in air affected the samples less negatively than cooling in water. While the Ca/Si ratios of the samples decreased at 450 °C and above, the Si/Al ratio increased. [ABSTRACT FROM AUTHOR]