Cost and environmental effects of ocean-borne plastic flakes in cement mortar considering equivalent-strength mix design

The economic and environmental effects resulting from the use of ocean-borne plastic flakes applied to cement composite materials were quantitatively evaluated in terms of the equivalent-strength-based mix proportion. Waste plastic flakes were collected from ocean debris, and chemical properties were characterized to confirm the types of plastics. The plastic flakes were incorporated as fine aggregate to cement mortar mixtures at various mix proportions, and their effects on the workability and mechanical properties of the mortar were evaluated. A regression model of the compressive strength and mix proportion was established, and the effect of the use of flakes on the material cost and CO₂ footprint of the mixtures using this model was discussed. According to the concept of equivalent-strength mix proportion, the calculated social cost to utilize 1 kg of waste plastic from the ocean as fine aggregates for concrete was approximately 0.50 USD (0.30 USD for treatment and 0.17 USD for mix proportioning), which was approximately 80% higher than that of simple disposal. Moreover, an additional 1.1 kg of CO₂ emission related to strength compensation was yielded, which was also much higher than the CO₂-equivalent value for simple disposal, i.e., 0.255 kg.