In-Plane Loaded Concrete Slabs Subjected to Fire: a Novel Test Set-up to Investigate Spalling

Despite the rather good knowledge on the mechanical behaviour of High-Performance Concrete at high temperature, further investigations are still needed, particularly as concerns spalling (to which High-Performance Concrete is very sensitive). Spalling is a complex issue, being the result of the interaction among concrete mechanical decay with temperature, pore pressure build-up due to water vaporization, and stress induced by thermal gradients and external loads. How these aspects influence each other, however, is not completely clear. Within this context, an experimental campaign has been launched at the Politecnico di Milano in collaboration with CTG-Italcementi Group (Bergamo, Italy), focusing on 4 concrete mixes (fcm ≈ 60 MPa; silico-calcareous aggregate), namely without or with one of 3 different fibre types (steel fibre and monofilament or fibrillated polypropylene fibres). The main goals of the study are: (a) to investigate the interaction between pore pressure and stress in triggering spalling, and (b) to understand the role played by fibre. To this aim, a novel test procedure has been designed, consisting on concrete slabs exposed to fire at the intrados and subjected to compressive load via hydraulic jacks.