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    Long-term properties of steel fiber reinforced silica fume based AAMs at ambient and high temperatures
    (Elsevier Ltd, 2024) Sarıdemir, Mustafa; Bulut, Metehan; Deniz, Suvat; Deneme, İbrahim Özgür
    In this study, the influences of Class C fly ash (FA), steel fiber (STF) and high temperature are researched on the mechanical and microstructural properties of STF reinforced silica fume (SF) based alkali activated mortars (AAMs) cured at the ambient (25 °C) temperature. The STF reinforced SF based AAMs are produced with 10%, 15%, 20% and 25% Class C FA by weight in place of SF, 0.5%, 1% and 1.5% STF by volume, liquid sodium silicate (Na2SiO3) and solid sodium hydroxide (NaOH). The apparent density (?a), ultrasonic pulse velocity (Upv), flexural strength (ffs) and compressive strength (fc) results of the STF reinforced control mortars (CMs) and SF based AAMs subjected to the ambient and elevated temperatures are investigated. The microstructural investigations are conducted with X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM)/energy dispersive X-ray (EDAX). Moreover, color changes, pores and interfacial transition zones (ITZs) in samples exposed to the ambient and high temperatures are examined by a stereoscopic microscope (SM). The results have shown that the high strengths can be obtained from STF reinforced SF based AAMs at ambient temperature (25 °C) and the optimum Class C FA and STF contents are 15% and 1%. Additionally, when STF reinforced SF based AAMs are exposed to high temperatures (especially 750 °C and 1000 °C), a serious decrease in the mechanical properties is observed due to the formation of a porous and spongy structure in the matrix and the STFs completely oxidizing and losing their properties.