Physical and Mechanical Properties of Cement Mortars with Recycled Polyethylene Terephthalate: Influence of Grain Size and Composition

Polyethylene terephthalate (PET) with different grain size after grinding (fine and coarse) was recycled and used as aggregate for non-conventional lightweight cement mortars. The physical and mechanical characteristics were compared to conventional sand-based composites. The workability in the fresh state was evaluated. Accordingly, the composites showed decreases in fluidity with increases in PET percentage weight. Higher thermal insulation and lower mechanical strengths were observed with the increase in plastic dosage due to a density decrease and porosity increase in the composites. Finer grain size PET samples were more resistant (~12–24 MPa) than the coarse-grain samples (~3–23 MPa) due to the higher density and specific surface area of the aggregate. Conversely, higher thermal insulation was obtained with coarse PET addition (~0.6–0.2 W/mK vs. ~0.7–0.35 W/mK). A ductile behavior with discrete cracks after failure was observed after plastic addition to the mixture. Low wettability was observed in PET samples which, although more porous than the sand specimens, showed a hydrophobic behavior which contributed to water repellency. The reported physical, mechanical, thermal, wettability and microstructural features suggest the potential of these composites for both inside and outside applications of non-structural objects.