Simulation of fracture on PFRC specimens subjected to high temperature using a cohesive model

Abstract

Concrete has been traditionally reinforced with steel rebars that confer good tensile properties to this material. Nevertheless, concrete can also be reinforced with fibres, which have been traditionally made of steel, although in the last years new types of fibres have appeared, such as polypropylene fibres, glass fibres or polyolefin fibres. Their use widens the range of application of fibre-reinforced concrete (FRC) and has experienced an significant boost by national and international standards, which now include guidelines for their use in structures. More specifically, textured polyolefin macro-fibres have proved to provide very good tensile properties in concrete. The use of these fibres has significant advantages when compared with traditional steel fibres, since they reduce the tear and wear of devices involved in their production, avoid corrosion problems in concrete and have no influence on magnetic fields, which can be very important in some situations. Concrete properties, both in fresh and hardened states, have been extensively studied in the last years, proving to be a promising alternative to steel fibres. Fracture of FRC, and more specifically of PFRC, has been successfully reproduced using the finite element analysis by means of an embedded cohesive model with a trilinear softening function. On another note, concrete has a good behaviour when subjected to high temperatures and fire, especially when it is compared with other traditional construction materials, such as wood or steel. Nevertheless, concrete reinforcement is usually made of materials that are critically sensitive to these events and the behaviour of the composite material must be assessed to meet the requirements described in the structural standards. With regard to polyole fin-fibre reinforced concrete (PFRC), a recent study has analysed how the fracture properties of this material degrade when subjected to high-temperatures, ranging from 20°C to 200°C. As temperature increases, fibres modify their geometry and their mechanical properties, which leads to a reduction of their effectiveness. In this work, the fracture behaviour of PFRC specimens subjected to high temperatures is reproduced by using an embedded cohesive model that uses a trilinear softening function. The specific trilinear softening diagram that provides a good numerical simulation of fracture is obtained for each temperature increment. This helps to understand how the trilinear diagram must be adapted when PFRC is subjected to high temperatures and will allow the use of this model to a wider range of situations.