Experimental study on engineering properties of concrete reinforced with hybrid recycled tyre steel and polypropylene fibres

Recycled tyre steel fibre (RTSF) is considered as a potential and sustainable alternative to manufactured steel fibre (MSF), while RTSF resulted in lower energy absorption capacity and more serious corrosion problem in concrete compared to MSF. This paper presents an experimental study on engineering properties of concrete reinforced with hybrid RTSF (0.5%–0.9% Vf) and polypropylene fibre (PPF, 0.1%–0.5% Vf). Results show that combining RTSF with PPF could compensate the serious workability loss caused by RTSF and the workability was improved by 38.9%–66.7%. However, the compressive, splitting tensile and flexural strengths were weakened significantly when PPF was over 0.3% Vf in hybrid fibre reinforcement (total content of 1.0% Vf). The strain field shown in digital image correlation images suggests that hybrid RTSF and PPF can create a synergistic effect in restraining the crack growth and the post-cracking behaviour of concrete especially toughness that was enhanced with the presence of PPF. RTSF was more effective in restraining shrinkage of concrete than PPF. With the increase of PPF content in hybrid fibre reinforcement, the chloride migration coefficient of concrete was reduced by 4.9%–6.8% as compared with the mixture reinforced with only RTSF.