Flexural strength at high temperatures of a high strength steel and polypropylene fibre concrete

Concrete is a widely used material in building construction. In case of fire concrete is subjected to high temperatures exhibiting thermal instability for certain temperatures. The phenomenon leads sometimes to degradation of the concrete compromising the safety of the structures. This paper reports the results of an experimental investigation for assessing the fracture energy at ambient and high temperatures of a high strength polypropylene and steel fibre concrete. The experimental program was designed to evaluate the influence of various parameters that may influence the fracture energy of the fibre concretes in study. Five concrete compositions were tested with different steel fibre dosages and types: one without steel fibres (reference composition), two with Dramix 3D steel fibres and two with Dramix 5D steel fibres (45 and 75?kg/m3). All compositions had 2?kg/m3 of polypropylene fibres that were used to avoid spalling on the specimens. The results indicated that the addition of steel fibres improving the fracture energy of the concrete increasing its ultimate flexural strength and ductility at ambient temperature. However, at high temperatures a deterioration in the fracture energy and ultimate flexural strength with the increasing of temperature was observed. Concrete compositions with Dramix 5D steel fibres lead to higher fracture energy and flexural strength comparing to compositions with Dramix 3D steel fibres. The same happens when using higher dosages of steel fibres in the concrete composition. (C) 2019 Elsevier Ltd. All rights reserved.