Mechanical properties of SFRC using blended Recycled Tyre Steel Cords (RTSC) and Recycled Tyre Steel Fibres (RTSF)

Processed high-specification steel cords (RTSC) extracted from un-vulcanised rubber belt off-cuts have the potential to substitute (manufactured steel fibres) MSF in concrete, leading to enhanced structural performance and significant environmental benefits. The target of this research is to demonstrate that recycled-only fibre mixes could meet or exceed the performance of MSF-only mixes, at the same total fibre dosage. Direct tensile and single-fibre pull-out tests are carried out, to evaluate the tensile strength of RTSC and the interfacial bond behaviour between RTSC and concrete matrix, respectively. It is found that RTSC have a tensile strength greater than 2600 MPa and their critical embedded length is in the range of 25–40 mm. The flexural characteristics of 8 steel fibre reinforced concrete (SFRC) mixes at fibre dosages of 30 and 45 kg/m3are examined by using EN 14651:2005 3-point notched prism tests. RTSC with lengths of 60 mm are used on their own, or blended with post-processed steel fibres recovered from end-of-life tyres (RTSF) at varying dosages. The performance of two manufactured steel fibres (MSF)-only mixes and one RTSF-only mix is also examined. Comparisons in terms of flexural performance are made between MSF-only mixes versus recycled-fibre (RTSC on their own or blended with RTSF) mixes at the same total dosage. RTSC are found to be extremely well mobilised at larger crack widths and the post-cracking strength of recycled-fibre mixes is significantly higher (up to 103%) than MSF-only mixes at the same total fibre dosage. In addition, the flexural performance of concrete with recycled-fibre blends improves with increasing amounts of RTSC.