Concrete Fire Testing - A Review of the Thermal Boundary Conditions

Experimental studies of concrete in fire or at elevated temperature have traditionally given relatively little scientific attention to quantifying the severity, and to some extent reproducibility, of the thermal boundary conditions imposed on specimens during testing. This paper examines the heat transfer fundamentals of fire testing when controlling the time-history of temperature inside a furnace (or oven), versus controlling the time-history of incident radiant heat flux at a specimen’s exposed surface. The thermal boundary conditions of a concrete specimen during fire testing are fundamentally based on conservation of energy, and thus typically formulated in terms of heat fluxes. While from the standpoint of concrete fire behaviour the aim is typically only to gauge the distribution of temperatures inside concrete; this is rarely explicitly acknowledged or quantified during concrete fire testing. This shows that continued unexamined use of varied heating techniques presents a serious threat to harmonization of the thermal boundary conditions imposed during concrete testing. The current work proposes adopting test control by in-depth temperature distributions or net heat fluxes for a rigorous comparison of the thermal boundary conditions imposed on test specimens when using different heating techniques.