High-performance hybrid-fibre concrete

Abstract

Although concrete is the most utilised building material nowdays, this material has a large shortcoming: it has a good resistance against compressive stresses, but a very low resistance against tensile stresses. Usual way to solve this problem is the application of steel reinforcement in concrete structures. Other possibility is the application of different types of fibres in concrete, for example steel or synthetic fibres: this material is then called "fibre concrete". In the past, many types of fibre concrete were developed. For many of them, the added value of fibres was rather low: almost no improvement of tensile strength could be achieved. In this research project, an innovative type of fibre concrete is developed, with improved both the tensile strength and the ductility: the Hybrid-Fibre Concrete (HFC). The expression "Hybrid" is here applied to point out to the hybridisation of fibres: short and long steel fibres were combined together in one concrete mixture. This is opposite to the conventional steel fibre concretes, which contain only one type of fibre. Within this research project, all important aspects needed for successful development and applications of Hybrid-Fibre Concrete have been considered. In total 15 mixtures, with different types and amounts of steel fibres were developed and tested in the fresh state (workability, with the self-compactability as a main goal) as well as in the hardened state (uniaxial tensile tests, flexural tests, pullout tests on single fibres and compressive tests). A new analytical model for bridging of cracks by fibres was developed and successfully implemented for tensile softening response of HFC. At the end, the utilisation of HFC in the engineering practice was discussed, including a case-study on light precast prestressed beams made of HFC, without conventional reinforcement. There many other possibilities for the applications of this material in building engineering, civil infrastructure, geotechnical and tunnelling engineering. It is also expected that the durability of the Hybrid-Fibre Concrete is better compared to conventional concrete, which could be its another big advantage.