Study On The Optimisation Of Steel Fibre Reinforced Concrete

The first study on using steel fibre reinforced concrete (SFRC) as an alternative to traditional reinforcement concrete could date back to1960s. Since then, vast of significant researches were conducted to reach deeper understanding on this composite material. In the past decades, the industry has been demanding for the use of SFRC in structural applications, especially in the underground constructions. The application of SFRC in segmental linings of tunnels or shafts has many advantages, such as improving the mechanical behaviour, increasing toughness, fire resistance, fatigue resistance etc. Furthermore, the use of SFRC may lead to the total or a partial removal of traditional rebars.To design SFRC structural elements, two key issues are difficult to resolve. Firstly, to design a precast element according to the regulations and guidelines, tests are required, but these test results often display large scatter. Secondly there is little research into how the efficiency of the fibres changes with increasing fibre volume, and different concrete types.This dissertation proposes to answer these questions through the analysis of results produced from a large experimental campaign.3Point Bending, Multi Direction, Barcelona, Inductance and Compression tests were performed on two types of concrete, conventional steel fibre reinforced concrete (CSFRC) and steel fibre reinforced self-compacting concrete (SFRSCC) with3different fibre content of30,45and60kg/m3. A similar relationship between the amount of fibres and coefficient of variation was observed in each of the tensile tests. Furthermore, a correlation between efficiency of the fibres and fibre content could be seen; the results are significant, an increase in50and100%respectively, for CSFRC and SFRSCC, in fibre efficiency by using the ideal fibre volume.The reasons behind the varying efficiency of the material are complex; due to the fact that several tests were carried out, the reasons behind it could be identified as a confluence three independent factors; namely preferential fibre orientation, fibre balling and the viscosity of the concrete mixture.The implications of finding the optimum fibre efficiency are that for a Sabadell Tunnel segment, rebar could be eliminated from the design and the tunnel segment could be reduced in thickness. For CSFRC the reduction in thickness is12%and for SFRSCC the reduction is40%. This led to a significant financial advantage, in terms of the raw material cost, the optimised CSFRC tunnel segment is31.60%cheaper, and for the SFRSCC tunnel segments it is35.81%cheaper. This did not take into account the labour and manufacturing cost, which will make both segments more financially attractive, but SFRSCC especially so due to the lack of need for vibration.