Influence of polyethylene terephthalate (PET) flakes coating on the microstructure and mechanical properties of alkali activated composites

The objective of this research is the improvement of the mechanical strengths of the alkali activated slag composites with polyethylene terephthalate (PET) flakes content. The main drawback when large PET flakes (2-9 mm) are used in these composites is reduced adhesion between plastic surface and binding matrix. Therefore, the PET flakes were coated with two types of adhesives – based on polyvinyl acetate or sodium silicate solution, and then covered with fly ash, waste glass or slag powders. The microstructure (assessed by scanning electron microscopy) of interfacial transition zone between the PET flakes coated with waste glass and slag powders is denser than for uncoated PET flakes; this explains the improvement of the compressive strength of these mortars especially after longer curing times (28 days). The flexural strengths of the mortars with PET flakes are higher than for reference mortar (with sand aggregate) and the apparent density of the alkali activated composites with PET flakes are in general smaller than for the reference mortar. Thus, the coating of PET flakes improves the mechanical behaviour of mortars, preserving also a low apparent density. These results can lead to a wider recycling of PET waste, slag and waste glass powder, promoting circular economy and reducing the CO 2 footprint without compromising the critical mechanical strength of mortars. • Recycling of PET flakes in alkali activated slag cement • Coating of PET flakes with SCMs to improve adhesion to the cement paste • Modification of interfacial transition zone and mechanical properties