Effect of recycled heterogeneous carbonaceous aggregate on fire performance of high strength concrete

Presently, significant attention is directed towards utilisation of recycled plastic waste as an environmentally sustainable substitute for natural aggregate in cementitious concrete materials. This is aimed to bolster the greening endeavours of local construction industry and address the pressing need to improve global plastic recycling rates. Despite extensive literature on different mechanisms underlying various fire responses and spalling behaviour of cementitious materials, it remains unclear if these propositions are applicable to the mechanisms behind the fire response of concrete materials incorporated with polymeric aggregate. Therefore, the key focus of this study is to examine the effect of recycled heterogeneous carbonaceous aggregate (RHCA), recovered from municipal solid waste streams, on fire performance of high strength concrete (HSC). A series of analytical and microscopic tests were carried out at 200, 400, 600 and 800 °C on six HSC mixes containing 0, 10, 20, 30, 40, and 50 % RHCA by volume of natural sand as replacement to address the knowledge gaps. The experimental data shows that incorporation of RHCA resulted in a higher mass loss and lower mechanical properties in residual state. It is revealed that thermal expansion of RHCA below its melting temperature was responsible for creation of interconnected crack network within the concrete system that has direct bearing on the residual physical and mechanical properties of the concrete specimens often subjected to fire conditions. Although explosive spalling is avoided under ISO 834 heating, thermochemical mechanisms based on radical reactions and the Bolland-Gee autoxidation scheme were applied to explain the occurrence of ignition at high RHCA content. Finally, fire load density of concrete mixes with varying amounts of RHCA is quantified and recommended for different occupancies under Eurocode 1 EN1991-1-2.