RELATIONSHIPS BETWEEN MECHANICAL PROPERTIES (COMPRESSIVE STRENGTH) AND PHYSICAL PROPERTIES (POROSITY) AT HIGH TEMPERATURES

Introduction: This research is a part of a broader study on the evolution of concrete properties when exposed to high temperatures. It aims to analyze the behavior of ordinary concretes at elevated temperatures, incorporating either organic or synthetic fibers in the same dosage. Metods: Three concrete compositions were formulated: plain concrete without fibers (CO1), polypropylene fiber-reinforced concrete (CFP), and chicken feather fiber-reinforced concrete (CFC1), with both fiber-reinforced types containing an identical fiber dosage of 0.9 %. The prepared specimens were subjected to a heating-cooling cycle at 150 °C, 300 °C, 450 °C, and 600 °C, with a heating rate of 1 °C per minute. The residual physical and mechanical properties of the different concretes were then analyzed. Results: The concretes studied exhibited similar initial mechanical properties. However, the concrete reinforced with chicken feather fibers demonstrated superior residual physical and mechanical performance compared to the other concretes. Overall, the residual mechanical performance of the fiber-reinforced concretes was greater than that of the plain concrete, confirming the positive contribution of fibers to strength retention at temperatures up to 600 °C. Finally, a correlation between compressive strength and porosity was established for the three concrete types. This correlation provides a reliable method for estimating the compressive strength of concreted containing different types of fibers when exposed to high temperatures.