Fiber-Reinforced High-Performance Concretes Exposed to High Temperature: Materials Behavior and Structural Implications

The many studies devoted in the last twenty years to high strength/high performance concrete (HSC/HPC) demonstrate its very interesting properties in terms of stiffness, strength and durability. These pluses, however, arepartly counterbalanced by a few minuses(such as greater brittleness at room temperature and greater heat sensitivity), that can be reduced – and even zeroed – by introducing fibers, which improve concrete toughnessat any temperature (steel fibers)and durability at hightemperature (mainly polymeric fibers). Since many are the parameters affecting concrete properties at high temperature,keeping constant the volumetric fraction of the cementitious matrix (as done in this research project) is a must whenever different fibrous mixes are to be compared. To have further information on the role of steel and polymeric fibers on HSC/HPC behavior at high temperature, seven mixes have been investigated in terms of thermal diffusivity, stress-strain curves in compression and elastic modulus (fc = 60 MPa; T = 20-750°C, hot and residual conditions).Among polypropylene fibers, fibrillated fibers have an edge over monofilament fibers in residual conditions, while steel fibers are the most effective in both hot and residual conditions. A structural application is presented as well, concerning two R/C columns (with/without steel fibers) subjected to standard fire, where the structural behavior at any fire duration is enhanced thanks to the extra ductility provided by the fibers.