Behavior of hybrid steel and recycled polymer fibres reinforced rubberized concrete under flexural fatigue loading

Recycled rubber granules (RRG) and recycled tyre polymer fibre (RTPF) as concrete reinforcement are promising for developing eco-friendly materials and tackling solid waste disposal problems. This paper experimentally investigates the multiscale synergistic effects of RTPF (0.05-0.2 vol%), RRG (0.05-0.2 vol%) and steel fibre (SF, 0.5-1.5 vol%) on the improvement of concrete flexural fatigue behavior. Results point that the additions of RTPF and RRG from 0.05 vol% to 0.1 vol% would increase the fatigue life by 2.56 %-9.96 %, while increasing the contents of SF from 0.5 vol% to 1.5 vol% would increase that by 18.97 %-39.35 %. The fatigue life of all mixtures obeyed a two-parameter Weibull distribution. The utilization of the developed double-logarithm fatigue equation in fatigue strength estimation was accurate at various failure probabilities (correlation coefficients in the range of 0.9237-0.9603). The fatigue failure evolution process for each mixture was subdivided into three stages, including rapid developing stage I, steady developing stage II and dramatical damage stage III. The fatigue failure modes and microstructural analysis revealed that the multiscale combination among SF, RTPF and RRG can control the crack formation and expansion and delay the fatigue damage. Considering the fatigue life and evolution of fatigue damage, the optimal dosage of SF, RTPF and RRG is 1.5 vol%, 0.1 vol% and 0.1 vol%, respectively.