Experimental characterization of VHPC reinforced with short synthetic fibers

Very-High-Performance Concrete (VHPC) are defined as concrete capable of reaching compressive strength higher than 80 MPa. These performances can be reached thanks to its compact and extremely dense microstructure, as a result of a proper mix. Together with their great durability properties, these concretes may lead to reduce cross sections of structural elements and thus save material and built volumes. The addition of synthetic fibers allows to significantly increase the toughness and crack opening resistance, beyond the tensile strength. These benefits can easily be traduced in an improved durability of the VHPC concrete. the aim of this research activity is to enlarge the experimental database of high-performances concrete reinforced with synthetic fibers having different size. In fact, contrary to the case of steel fibers, few works are report ed in literature regarding the types of fibers investigated herein. In the present work three Very High-Performance Fiber Reinforced Concrete (VHPFRC) mixes have been studied and characterized in laboratory. The mixes were realized with the same VHPC concrete matrix and different types of synthetic fibers: 10 mm straight polyvinyl alcohol (PVA) fibers; 30 mm waved polypropylene (PP) fibers; 40 mm waved polypropylene (PP) fibers. The first mix was realized using PVA fibers only, the second with 30 mm PP fibers and the last one was obtained by mixing PVA fibers and 40 mm PP fibers. A further VHPC mix with no fibers has been also realized and tested as reference material. Compression tests on both cylindrical and cubic specimens and modulus of elasticity tests have been performed for each mix. The VHPFRC toughness have been determined by means of three-points bending tests according to EN 14651. The bending parameters obtained from the experimental test have been compared between all the mixes and an analysis of the fracture energy has been performed. Moreover, each mix has been tested at bending with four-points setup in order to verify the efficiency of this test type for VHPC reinforced with synthetic fiber. The results provided in the paper highlight the different effects, in terms of mechanical response, caused by fibers of different size at different cracking stages of the tested materials.