Effect of design parameters on sulfate resistance in cement-based fibrous composites exposed to high temperatures

The main purpose of the study is to examine the changes in the basic engineering properties of cement-based fiber composites caused by sulfate attack together with high temperature. For this purpose; in a scenario where cement-based fiber composites containing steel and polypropylene fibers are exposed to fire and sulfate effects, compressive strength and UPV values were measured in order to examine the basic engineering properties and Scanning Electron Microscope (SEM) images of the samples were used to observe the changes in microstructural dimensions. Within the scope of the experiment, steel fibers with a length of 6 mm and a diameter of 0.16 and 0.35 mm and a polypropylene fiber with a diameter of 0.30 mm were used. The samples were kept at 600 °C for two hours at the end of the third day after production before being exposed to standard, 5% saturated sodium sulfate and 5% saturated potassium sulfate curing conditions to create 6 different mixture parameters. While the design parameters were being created, the water/cement ratio was selected as 0.35 in mixtures that did not contain fly ash, while the fly ash/binder ratio was determined as 0.30 in mixtures that contained fly ash. As a result of the experiments carried out, it was determined that fly ash p1rovided impermeability by reducing porosity in the concrete matrix, and although it slightly reduced the early age strength in the concrete, it created a more durable structure over time. It was determined that, among the steel fibers with different slenderness ratios, the steel fiber with a diameter value of 0.16 mm, which has a high slenderness ratio, positively contributed more to the compressive strength. In addition, it was determined by SEM images that the polypropylene fibers melted due to the high temperature applied before the sulfate attack created voids that were suitable for the development of ettringite.