Behavior of ultra-high-performance concrete under elevated temperatures: A comprehensive review of mechanical, physical, thermal, and microstructural properties

Ultra-High-Performance Concrete (UHPC) is a cutting-edge material with exceptional mechanical strength, durability, and resilience. However, its behavior under elevated temperatures is not fully understood, which limits its broader application in fire-safe and high-temperature environments. Therefore, this article provides a detailed review of Ultra-High-Performance Concrete under thermal exposure, focusing on its mechanical behavior (e.g., compressive, tensile, and flexural strength), physical properties (e.g., porosity, ultrasonic pulse velocity), thermal characteristics (e.g., conductivity, expansion), and microstructural characteristics. The role of fiber reinforcement, including fiber type, dosage, and hybridization, in mitigating thermal degradation and enhancing spalling resistance is critically assessed. The findings synthesize experimental results, identifying key factors influencing the performance of Ultra-High Performance Fiber Reinforced Concrete (UHPFRC), such as heating rates, fiber-matrix interactions, and microstructural stability. The review highlights significant gaps in the literature, including limited studies on flexural strength, unit weight, and the combined effects of heating and cooling cycles. The review concludes with targeted recommendations for future research, emphasizing the need to explore underrepresented variables such as long-term thermal effects, advanced fiber systems, and sustainable production methods. This work serves as a comprehensive resource for advancing the development of UHPC for fire-safe and high-temperature applications.