Effects of elevated temperatures on the properties of ground granulated blast furnace slag (GGBFS) based geopolymer concretes containing recycled concrete aggregate

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.