Investigating the effects of polyethylene terephthalate (PET) plastic and fly ash on the mechnical properties of concrete

• Main Authors: Crisostomo, Rafael Elijah M., Cruz, Steven Rey S., Fernandez, Cris Angelo C., Imperial, Benedict A.
• Format: text
• Language: English
• Published: Animo Repository 2017
• Subjects: Fly ash; Polyethylene terephthalate; Concrete
• Online Access: https://animorepository.dlsu.edu.ph/etd_bachelors/7736
• Institution: De La Salle University

Polyethylene terephthalate or PET plastics and fly ash are one of the most abundant non-recycled waste materials in the country largely due to market demands and coal power plants. The study tested the use of varying amount PET plastics and 30% fly ash as partial substitutes for fine aggregates and cement, respectively, on concrete's mechanical properties. The compressive strength test results show that 5% to 10% PET plastic substitution increased the compressive strength of fly ash concrete. In addition, adding 30% fly ash substitution and 5% PET plastics substitution on concrete lead to an increase in flexural strength. However, further increase of PET plastics content was found to decrease concrete's flexural strength. The optimum percentage of PET plastic were found to be approximately 8% and 5% for maximum compressive strength and maximum flexural strength, respectively. Mathematical models which may be used to predict the anticipated compressive strength, separately, per percentage of PET plastics up to 15%. The models were verified using the Pearson-r correlation wherein the compressive strength model yielded an r-value of 0.923 and an r-value 0.944 for the flexural strength model. Both r-values suggested that the generated models may be used to accurately predict the strength of concrete. The study also provides information on its effect on unit weight and workability of concrete, in which alternative concrete samples were lighter and more workable compared to using concrete without partial substitution of any material. In addition, the strength-strain behavior of concrete was observed and tested. It was found that adding PET plastics does not significantly affect the stress-strain behavior and strength development of concrete samples. The study also provided an analysis on the bond of particles of the concrete through scanning electron microscopy with energy dispersive x-ray analysis (SEM-EDX). The results show that the bonding between the particles of the concrete constituents were adequate up to 10% PET plastic substitution. With these, it was proven that PET plastics and fly ash may be used as substitutes for concrete mixtures for structural elements which require increased compressive and flexural strength, decreased unit weight , and higher workability without adding admixtures.