Mechanical Behavior and Ductility of Reinforcing Steel Under High-Temperature Exposure with Different Cooling Methods

The study of the behaviour of steel reinforcement in high temperatures is essential to understanding the performance of structural concrete after a fire. A special case is presented by steel reinforcements that are exposed to high temperatures after losing all or part of the nominal coating that protects them. In this work, detailed research has been carried out to understand the behaviour of two types of steel, B500SD (carbon) and EN 1.4301 (stainless), exposed to high temperatures. For this purpose, different heating temperatures (450, 800 and 1150 °C) and two types of cooling (rapid in water and slow at room temperature) were used. Mass loss and tensile strength were evaluated, and the ductility indices of these steels were analysed in detail, accompanied by a discussion with a statistical analysis and fractography. The results indicate that stainless steel performs better than carbon steel in a fire. The B500SD reinforcement exhibited a decrease in yield strength of up to 239 MPa (↓ 55%) compared to the reference specimen when heated to 1150 °C. Additionally, it has been observed that rapid cooling results in a more pronounced decrease in ductility in B500SD steel. However, slow cooling led to an increase in ductility in the three indices studied (Cosenza, Creazza and Ortega), with the presence of micro-void coalescence in the fractography corroborating the results. Thus, this research holds great practical interest in decision-making for the selection of structural materials, as it assesses the physical–mechanical behaviour of reinforced concrete after exposure to high temperatures.