Mechanical and durability performance of concrete with recycled tire steel fibers

The increasing waste tire disposal and the related environmental pollution have led to the further exploration of utilizing recycled-tire steel fiber (RTSF) to replace industrial steel fiber (ISF) for better cost-effective concrete production. This study compares the workability, mechanical properties, and durability of RTSF-reinforced concrete (RSC) to those of commercial ISF-reinforced concrete (ISC). Plain concrete samples, ISC samples named IS05 and IS05R (with 0.5% of ISF by volume), and RSC samples named RS05, RS10, and RS15 with threevolume percentages of RTSF (0.5%, 1.0%, and 1.5%) were prepared accordingly. The results show that RSC has better flowability than ISC when adding the same volume percentage of fibers. In terms of mechanical properties, the addition of RTSF slightly increases the 28-day compressive strength. The splitting tensile strength is also increased by up to 15.4% with the added RTSF, which is very close to the ISF (16.9%). Regarding flexural performance, RS15 samples show a very close enhancing effect to IS05 samples with enlarged residual strength and fracture energy. The ultrasonic pulse velocity test results also indicate that both RTSF and ISF slightly increase the concrete modulus. In terms of durability, RS10 samples reduce drying shrinkage by up to 9.2%, which is better than IS05 samples (6.3%). RTSF also improves the freeze-thaw resistance by reducing the change percentage of relative dynamic modulus and increasing the durability factor by up to 4.6%. Overall, the RTSFs in concrete have a slightly lower mechanical reinforcement and better workability by comparing with one type of thin ISFs. These findings can facilitate the usage of RTSF in concrete mixes as mechanical reinforcements and provide another market for waste tire fiber recycling.