Investigation of mechanical properties of alkali activated composites containing fly ash and blast furnace slag against high temperature

In this study, alkali-activated composite samples were produced by using ground blast furnace slag and F class fly ash as alternatives to cement. NaOH and Na2SiO3 solutions were used as alkali activators. As a result of the preliminary experiments, the activator/binder ratio was determined as 0.40 in the mixture prepared with a concentration of 14 moles and the samples were subjected to an activation temperature of 90 °C. By weight 0% UK-100% YFC, 75% UK-25% YFC, 50% UK-50% YFC, 75% YFC-25% UK and 100% UK-0% YFC series were produced and samples were prepared. After the samples were kept in the laboratory for 7 and 28 days, their mechanical behavior at high temperatures of 20 °C (laboratory temperature), 200 °C, 400 °C, 600 °C and 800 °C were investigated. Workability, setting start and end time, compressive strength, bending strength, abrasion resistance, ultrasound transmission rate, capillarity and unit weight tests were carried out on the samples, respectively. Obtained results were compared with reference samples. In addition, SEM and XRD methods were used for the microstructure analysis of the samples before and after the high temperature. As a result, decreases were observed in the strength of the composite samples prepared depending on the temperature increase. The highest compressive strength, bending strength and abrasion resistance were obtained in the reference samples containing 50% UK-50% YFC and kept at 20 °C for 28 days. The lowest values were obtained in samples containing 75% YFC-25% UK and kept at 800 °C for 28 days.