Influence of Recycled PET Fibres on Mechanical Properties of Concrete

Plastic wastes have destructive impact on the environment and the nature is on the verge of plastic waste crisis. The only things that will determine the future of the planet are the common actions of humans. All forms of plastics used in everyday routine disposed of at the end of service life which cannot be completely recycled instantly, and thus large quantities of non-biodegrable waste are disposed to landfills every year. Recycling method is accepted as one the most environmentally reliable methods of disposing plastic waste. Polyethylene terephthalate (PET) represents the greatest fraction among the plastic waste subsequent to polyethylene. PET is generally obtained in considerable amounts from the plastic bottles used as containers for water and other soft drinks. Due to its favourable properties such as low density, high durability, low cost and ease of fabrication, the consumption and thus the production of PET bottles has drastically increased in recent years. Therefore, the specific interest is growing currently in utilization of this waste in the form of aggregates or fibres as concrete constituents. North Cyprus is a country with no industrial demand of plastic bottles, utilization of recycled bottles in concrete applications thereby contributes towards a more environmentally sustainable mitigation method of this waste by reducing the amount of PET waste in the nature. This study aims to investigate the mechanical properties of recycled PET fibre reinforced concrete. The main properties examined during the present work were compressive strength, tensile strengths, plastic shrinkage resistance, impact resistance and pull-out resistance. Recycled PET fibre reinforced concrete (RPFRC)specimens were prepared and tested according to related standards. PET fibres with diameters of 0.45 mm, 0.65 mm and 1.00 mm, lengths of 20 mm and 30 mm and fibre volume fractions of 0.5%, 1.0%, 1.5% and 2.0% were used in the experiments. The results revealed that addition of fibres reduced the workability of concrete samples at fresh stage due to increasing surface area and inter particle friction. Compressive strength, tensile strength and flexural strength of RPFRC specimens were slightly higher than control specimen for several recycled PET fibre dimensions up to 1.5% volume fraction due to bridging effect of fibres. However, further increase in volume fraction has resulted in decrease according to formation of air voids due to entanglement. The addition of recycled were observed to improve plastic shrinkage resistance of RPFRC compared to control concrete. At some points, PET fibres were eliminated all cracks formed due to plastic shrinkage. Even though no apparent effect of PET fibres was observed on the impact resistance of concrete specimens, significant effect on the ultimate failure energies were observed. Pull-out resistance tests were carried out to find-out the bonding resistance of each fibre. However, the fibre with highest surface area achieved highest pull-out strength, individual pull-out strength of fibre does not reflect the performance when applied in larger volumetric ratios.