Concrete Incorporating Recycled Plastic Aggregates: Physical and Mechanical Properties and Predictive Models

This paper presents a pilot study on the characterization of the physical and mechanical properties of a novel green concrete with two different substituted recycled plastic aggregates. A reference mix with an average compressive strength of around 60 MPa is considered. Recycled polyethylene terephthalate (PET) powder and recycled mixed plastic [polypropylene (PP) and polyethylene (PE)] granules were adopted to substitute fine and coarse aggregates. Two different substitution strategies were employed. In the first one, the PET powder is used to substitute the fine sand by volume. In the second one, the PET powder is used to substitute the fine sand while the recycled mixed plastic granules are used to substitute the coarse sand and fine coarse aggregates by volume (50% for PET powder and 50% for recycled mixed plastic granules). Four total replacement levels (5%, 10%, 20%, and 30%) by volume were considered. The fresh concrete properties (slump and density), compressive and flexural behavior, toughness, and permeability are investigated. Finally, a microscale characterization of the plastic-paste interface is provided. An interpretation of the test results of this study by comparing them with the findings of previous studies is provided, along with the provision of two predictive equations for the compressive and flexural strength reduction factors. Results show reduced flowability for PET cases due to particle shape, slight compressive strength reduction at low substitutions, improved flexural strength at low levels, decreased permeability, and microscale enhancements. The comprehensive evaluation indicates promising physical and mechanical performance of the novel green concrete.