Transient behavior of pure bitumen forced burning under ambient air and oxygen-deprived atmospheres

In this study, a series of experimental tests was performed using an open controlled-atmosphere cone calorimeter (CACC) to evaluate the burning behavior and flame extinction characteristics of pure bitumen, a material widely used in applications such as pavement construction and in the encapsulation of nuclear wastes. Despite its broad usage, the fire behavior of bitumen remains poorly understood, particularly under oxygen-limited conditions. The work aimed to investigate the influence of oxygen-depleted environments on forced combustion behavior under varying external heat fluxes. Tests were conducted under both well-ventilated and nitrogen-diluted atmospheres at ambient pressure. The effects of different external heat fluxes and oxygen mass fractions on the thermal response of the condensed and gas phases were thoroughly analyzed. Key combustion parameters were determined along with other thermal properties of the bitumen samples. Temperature profiles within the condensed phase revealed a uniform temperature distribution across the sample in the decomposition process, consistent with a liquid state during the combustion process. Consistent repeatability was observed until the onset of overflow from the sample container and subsequent carbonization. At this stage, a sudden increase in viscosity was noted, accompanied by the formation of a solid char layer on top of the sample. This transition was associated with significant swelling, resulting in complex flame dynamics and a sharp peak in heat release rate. Analysis of the effect of oxygen concentration demonstrated a direct influence on the gas phase, leading to a proportional trend in the flaming tests.