Spalling behavior and performance of ultra-high-performance concrete subjected to elevated temperature: A review

Ultra-high-performance concrete (UHPC) surpasses normal strength concrete in engineering properties such as durability under extreme conditions, strength, and ductility characteristics. However, the dense structure, impermeable nature, and lack of capillary pores in ultra-high-performance concrete may diminish its resistance to spalling when subjected to intense heating conditions, unlike normal and high-strength concrete. The behavior of UHPC under such conditions has not been extensively researched, especially in the context of engineering properties and spalling behavior. Existing knowledge is primarily inferred from normal and high-strength concrete behavior under high temperatures, but this approach has sparked contention due to differing phenomena at play. Given ultra-high-performance concrete's distinct composition and excellent mechanical features, the principles applied to normal and high-strength concrete may not sufficiently explain its complex behavior during thermal exposure, particularly regarding spalling and engineering properties. Furthermore, enhancing its fire resistance becomes increasingly crucial as UHPC gains popularity in new and existing structures. To bridge this knowledge gap, this review paper presents various facets of UHPC during intense heat exposure, emphasizing engineering properties, fire-induced spalling, its factors, underlying mechanisms, microstructural analysis, performance, and preventative and remedial strategies. Future research recommendations are also offered to improve UHPC's performance under elevated temperatures, potentially leveraging current knowledge in the field.