HPC Subjected to High Temperature: A Study on Intrinsic and Mechanical Damage

Heat-exposed High-Performance Concrete (HPC) has been the subject of relatively few studies focused on the relationship between the chemo-physical processes occurring in concrete constituents (microscopic level) and concrete mechanical properties (macroscopic level). In order to investigate the correlation between the intrinsic damage and the mechanical damage induced by heat exposure, eleven concrete mixes have been investigated, differing for: compressive strength (fcm,cube ≥ 45, 70, 95 MPa), aggregate type, fiber type (polymeric and metallic) and fiber content. The microstructural and mechanical characterization was carried out on concrete specimens before and after being exposed to 105, 250, 500 and 750°C. The results show that using different experimental techniques at the microstructural level allows to monitor the development of microcracks, whose size is similar to that of macropores. This behavior at the nano-, micro-level is reflected by the post-peak branch of the stress-strain curve at the macro-level. This extensive investigation allows to understand concrete mechanical decay due to heating on the basis of microstructural observations, paving the way to mix optimization for high temperature and fire.