Influence of steel and/or polypropylene fibres on the behaviour of concrete at high temperature: Spalling, transfer and mechanical properties

In this study different mixtures of high strength concretes (70 MPa) were prepared with different natures of aggregates, moisture content, length and dosage of polypropylene fibres (PPF) and steel fibres (SF) and subjected to the standard ISO 834 fire. Concretes with 60 kg/m3 of SF show spalling while plain concrete (without fibres) and concrete with 0.75 kg/m3 of PPF and 60 kg/m3 of SF did not spall. Microstructure, thermal, hydric and mechanical properties of concretes were investigated. PPF increase the porosity and permeability of concretes. Steel fibres control crack development which reduce the stress relaxation phenomenon and the size of new pores.