Influenza degli additivi modificatori di viscosità sulla distribuzione delle fibre nei calcestruzzi fibrorinforzati

Relevant studies have been carried out in these last years about the replacement of conventional shear reinforcement with metallic fibres in reinforced concrete structural elements. The efficacy of this technology, and hence the possibility of reliably implementing it in the production processes of a pre-cast factory, clearly depends on the possibility of achieving a homogenous and uniform distribution of fibres, reducing the influence of castings and vibration. An unproper design and placement of the fresh mix may lead to segregation of larger particles and of fibres thus limiting the possibilities for a structural use of fibre reinforced concrete. This work presents the results of a research program aimed at evaluating the influence of viscosity enhancing admixtures (VEA) on the fibre distribution in Steel Fibre Reinforced Concrete (SFRC) elements. First of all their influence has been investigated with reference to fibre distribution along casting direction in cylinder specimens. As a further step of the investigation small-scale prototypes have been cast with the same mixes previously tested and the distribution of fibres, as influenced by the mix-design of concrete, has been evaluated along the thickness and the cross-section as well as along the longitudinal axis of the prototypes. Results are really promising in sight of structural applications. In this framework some full-scale prototypes have been cast with the “optimum” mix, as came out from previously said experiments, and the repeatibility of results previously obtained has been checked with reference to them.