Post-Fire Mechanical Degradation and Residual Capacity of Ultra-High Performance Concrete (UHPC): A Systematic Review of Analytical Models and Post-Fire Structural Assessment Methods

Abstract

Abstract

Ultra-high performance concrete (UHPC) is now specified in structural work where its high compressive strength, durability, and toughness justify the cost. The same dense, low-permeability microstructure that gives it this strength also makes it spall more readily in fire than ordinary concrete, and how it behaves during and after fire exposure is still not well settled. This review pulls together what is known about UHPC's response to elevated temperature and what is left of its strength once it cools. It works through the mechanisms behind spalling and property loss, what fibre type and hybridisation do to explosive spalling, and the residual compressive, tensile, and flexural strengths reported in studies that rarely agree on mix design, heating regime, or fibre system. From there it looks at the analytical and machine-learning models built to predict residual strength and spalling risk, at how beams, columns, and beam-column joints perform under and after fire loading, and at the non-destructive and destructive methods used to assess fire-damaged UHPC on site. What comes out of all this is a field with plenty of experimental data but not much agreement on mechanism, no shared test or cooling procedure, and prediction models trained on datasets too small to trust outside the study that built them. The review ends by setting out where that leaves future work, most notably that almost nothing has been published on UHPC under torsion, and that there is still no standard fire-test and cooling protocol for the material.