Synergetic effects of hybrid steel and recycled tyre polymer fibres on workability, mechanical strengths and toughness of concrete

Recycled tyre polymer fibre (RTPF) has been considered an eco-friendly and promising alternative to traditional polymer fibres to enhance the engineering behaviours of concrete. This paper presents an experimental study to explore the synergetic effects of hybrid steel fibre (SF, 0.5-1.5 vol%) and RTPF (0.1-0.4 vol%) in tailoring the workability and mechanical properties of concrete, including slump, compressive and splitting tensile strengths, flexural toughness and load-deflection response. The results showed that the addition of either SF or RTPF lead to a decrease in the workability of concrete by 28.3%-81.2%. In contrast, the increasing content of SF from 0.5 vol % to 1.0 vol% and RTPF from 0.1 vol% to 0.2 vol% would enhance the average strengths and flexural toughness of concrete. In addition, the optimal content of SF and RTPF is 1.0 vol% and 0.2 vol%, respectively, which can promote the average compressive strength of plain concrete by up to 13.2 %. The microstructural analysis further revealed the synergetic effects of hybrid SF and RTPF in controlling the micro-cracks of concrete, which would contribute to the higher energy absorption capacity of concrete. The results suggested that hybrid SF and RTPF hold promise as sustainable alternatives to synthetic fibres in full-scale structural applications.