A close look at fire-induced explosive spalling of ultra-high performance concrete: from materials to structures

The advent of ultra-high performance concrete (UHPC) represents a significant leap in concrete technology. Yet, the material’s vulnerability to fire-induced explosive spalling, characterized by concrete fragments being forcefully dislodged from the mass in fire scenarios, is the Achilles’ heel that could severely jeopardize UHPC’s integrity and hence structural safety. In response to this risk, there has been a growing interest in studying the explosive spalling of UHPC under fire exposure. This paper provides a critical review of the state-of-the-art research in this area. It looks into different experimental approaches for observing and demystifying fire-induced explosive spalling, then assesses how various factors (e.g., fiber type) affect UHPC’s propensity to such unfavorable events. Moving forward, the paper discusses numerical predictions of this phenomenon and, further, explains the consequences of explosive spalling on the fire resistance of UHPC components. Thus, the paper brings to light key insights from a large body of published literature. It also puts forward strategies to tackle this risk, with a focus on structural-level interventions, which have been largely overlooked in previous studies. The paper concludes by summarizing critical findings, highlighting ongoing challenges, pinpointing current knowledge gaps, and charting future research pathways.